Dielectric layer created using ALD to deposit multiple components
A dielectric layer is created for use with non-volatile memory and/or other devices. The dielectric layer is created using atomic layer deposition to deposit multiple components whose mole fractions change as a function of depth in the dielectric layer in order to create a rounded bottom of a conduction band profile for the dielectric layer.
Semiconductor memory devices have become more popular for use in various electronic devices. For example, non-volatile semiconductor memory is used in cellular telephones, digital cameras, personal digital assistants, mobile computing devices, non-mobile computing devices, and other devices. Electrical Erasable Programmable Read Only Memory (EEPROM) and flash memory are among the most popular non-volatile semiconductor memories.
Typical EEPROMs and flash memories utilize a memory cell with a floating gate that is provided above a channel region in a semiconductor substrate. The floating gate is separated from the channel region by a dielectric layer. For example, the channel region is positioned in a p-well between source and drain regions. A control gate is provided over and separated from the floating gate. The threshold voltage of the memory cell is controlled by the amount of excess charge that is retained on the floating gate. That is, the level of charge on the floating gate determines the minimum amount of voltage that must be applied to the control gate before the memory cell is turned on to permit conduction between its source and drain.
Some EEPROM and flash memory devices have a floating gate that is used to store two ranges of charges and, therefore, the memory cell can be programmed/erased between two states (e.g. a binary memory cell). A multi-bit or multi-state flash memory cell is implemented by identifying multiple, distinct threshold voltage ranges within a device. Each distinct threshold voltage range corresponds to predetermined values for the set of data bits. The specific relationship between the data programmed into the memory cell and the threshold voltage levels of the cell depends upon the data encoding scheme adopted for the cells. For example, U.S. Pat. No. 6,222,762 and U.S. patent application Ser. No. 10/461,244, “Tracking Cells For A Memory System,” filed on Jun. 13, 2003, both of which are incorporated herein by reference in their entirety, describe various data encoding schemes for multi-state flash memory cells. To achieve proper data storage for a multi-state cell, the multiple ranges of threshold voltage levels should be separated from each other by sufficient margin so that the level of the memory cell can be read, programmed or erased in an unambiguous manner.
When programming typical prior art EEPROM or flash memory devices, a program voltage is applied to the control gate and the bit line is grounded. Electrons from the channel are injected into the floating gate. When electrons accumulate in the floating gate, the floating gate becomes negatively charged and the threshold voltage of the memory cell as seen from the control gate is raised.
Typically, the program voltage (e.g., 12-20 volts) applied to the control gate is applied as a series of pulses. The magnitude of the pulses is increased with each successive pulse by a predetermined step size (e.g. 0.2 v). In the periods between the pulses, verify operations are carried out. That is, the programming level of each cell of a group of cells being programmed in parallel is read between each programming pulse to determine whether it is equal to or greater than each individual cell's targeted verify level to which it is being programmed. One means of verifying the programming is to test conduction at a specific compare point. The cells that are verified to be sufficiently programmed are locked out, for example, by raising the bit line voltage from 0 to Vdd just before the application of a programming pulse on those bit lines whose corresponding cells are to be inhibited from further programming in order to stop the programming process for those cells. The above described programming technique, and others, can be used in combination with various self boosting techniques, for example, as described in U.S. patent application Ser. No. 10/379,608, titled “Self Boosting Technique,” filed on Mar. 5, 2003, incorporated herein by reference in its entirety. Additionally, an efficient verify technique can be used, such as described in U.S. patent application Ser. No. 10/314,055, “Smart Verify for Multi-State Memories,” filed Dec. 5, 2002, incorporated herein by reference in its entirety.
Typical prior art memory cells are erased by raising the p-well to an erase voltage (e.g. 20 volts) and grounding the control gate. The source and drain are floating. Electrons are transferred from the floating gate to the p-well region and the threshold voltage is lowered.
Typically, the program and erase process described above is accomplished using electric field induced tunneling, also known as Fowler-Nordheim tunneling. While Fowler-Nordheim tunneling has worked well, and continues to work well, there is a desire to increase the speed of the program and erase processes, and to lower the voltages used to program and erase. However, it is preferable that an improvement in speed or magnitude of voltage is not made at an unreasonable loss of data retention time.
In “Resonant Fowler-Nordheim Tunneling through Layered Tunnel Barriers and its Possible Applications,” Alexander Korotkov and Konstantin Likharev, 1999 IEEE, 0-7803-5413-3/99 (hereinafter “Likharev I”); “Riding the Crest of a New Wave in Memory, NOVORAM: A new Concept for Fast, Bit-Addressable Nonvolatile Memory Based on Crested Barriers,” Konstantin and Likharev, Circuits and Devices, July 2000, p. 17 (hereinafter “Likharev II”); and U.S. Pat. No. 6,121,654, Sep. 19, 2000 “Memory device having a crested tunnel barrier” (hereinafter “the '654 Patent”), it is suggested that charge injection may be sped up by using profiled (“crested”) tunnel barriers with a potential maximum in the middle. Likharev I and Likharev II specifically suggest using a tunnel barrier dielectric layer with a triangular shaped bottom of a conduction band profile. However, such a proposal is not optimal. For example, at the peak of the apex, there is a sudden transition which may set up for trapping. Furthermore, an author of Likharev I and Likharev II specifically suggests that such a triangular barrier may have fabrication issues. Similarly, the '654 patent proposes a tunnel barrier dielectric layer with a round shaped bottom of a conduction band profile; however, the '654 patent admits that such a barrier may be difficult to manufacture.
SUMMARY OF THE INVENTIONA dielectric layer is disclosed that is created using atomic layer deposition to deposit multiple components whose mole fractions change as a function of depth in the dielectric layer in order to create a rounded bottom of a conduction band profile for the dielectric layer.
One embodiment includes creating said dielectric layer using atomic layer deposition to add a first component and a second component so that said dielectric layer gradually transitions from said first component to said second component and back to said first component.
One embodiment includes creating a first edge region using atomic layer deposition to add one or more layers of a first component and one or more layers of a second component, where the first edge region has a first conduction band bottom level. A center region is created using atomic layer deposition to add one or more layers of the first component and one or more layers of the second component. The center region has a second conduction band bottom level. A second edge region is created using atomic layer deposition to add one or more layers of the first component and one or more layers of the second component. The center region is between the first edge region and the second edge region. The second edge region has a third conduction band bottom level. The second conduction band bottom level is greater than the first conduction band bottom level and the third conduction band bottom level.
The processes described herein can be used to create a dielectric layer comprising a first type of component added by atomic layer deposition and a second first type of component added by atomic layer deposition. The first type of component and the second first type of component have varying mole fractions as a function of depth in the dielectric layer in order to create a rounded bottom of a conduction band profile for the dielectric layer.
In one embodiment, after deposition of one or more precursors and a purge step, the atomic layer deposition cycle includes a nitridation step that is followed by or overlapped by an oxidation step. One example implementation includes introducing a first set of one or more precursors into a chamber, introducing one or more nitriding agents into the chamber after introducing the first precursor, and introducing one or more oxidizing agents into the chamber. The nitriding agents are introduced during a first time period. The oxidizing agents are introduced during a second time period. The second time period is shorter than the first time period, starts after the first time period starts and/or includes a lower concentration than during the first time period.
The dielectric layer described above can be used with various types of flash memory devices, other types of non-volatile memory or other electronic devices.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 13A-F depict the non-volatile memory device of
FIGS. 19A-C are graphs that illustrate co-injection processes.
The invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to an or one embodiment in this disclosure are not necessarily the same embodiment, and such references mean at least one.
In the following description, various aspects of the present invention will be described. However, it will be apparent to those skilled in the art that the present invention may be practiced with only some or all of the aspects of the present disclosure. For purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without all of the specific details. In other instances, well known features are omitted or simplified in order not to obscure the present invention.
Various embodiments will be described as multiple discreet steps in turn, in a manner that is most helpful in understanding the present invention. However, the order of this description should not be construed as to imply that these operations are necessarily order dependent.
When an electric field is applied to a device according to
It would be desirable that the application of the electric field lower the height of the bottom of the conduction band. Thus, it is proposed to use a rounded bottom of a conduction band profile for a dielectric layer. This can be accomplished by using two or more components to create the dielectric layer.
An electric field causes the bottom of the conduction band and top of the valance band to be altered as depicted in
Atomic Layer Deposition (ALD) can be employed to deposit mixed multiple dielectrics to achieve such a rounded (or otherwise crested) bottom of a conduction band profile for the dielectric layer. Example of sets of dielectric materials that can be deposited using ALD include HfO2 (hafnium oxide) and Al2O3 (aluminum oxide), hafnium oxide with silicon oxide, hafnium oxide with silicon dioxide, aluminum oxide with silicon oxide, as well as other sets of two or more materials.
ALD is a self-limiting chemisorption reaction. The basic sequence of ALD processing is composed of four steps. First, there is chemisorption of a first precursor on a substrate surface within an ALD chamber. Second, excess materials are purged out of the chamber using a purge gas, which leaves a monolayer of precursor absorbed on the substrate surface. Third, a second precursor is introduced into the chamber, which reacts with the adsorbate to form a monolayer. Fourth, un-reactive material or byproduct is purged out of the chamber by the purge gas. The cycle is then repeated to lay down additional layers. An example of a purge gas can be an inert gas. In some embodiments, the substrate (e.g., Si substrate) is first cleaned in a cleaning solution (e.g., 4% HF solution) to remove native oxide layers and blown free of particles before loading into the ALD chamber.
The two dielectric materials being deposited by ALD are added such that the mole fractions of each of the two materials varies as a function of depth in the dielectric layer in order to create the crested (e.g. rounded) bottom of the conduction band profile for that dielectric layer. For example, assume that within each region of the dielectric layer, the multiple dielectrics are added as (HfO2)X(Al2O3)1-X, where the mole fraction of HfO2 is X and the mole fraction of Al2O3 is 1-X. Alternatively, the multiple dielectrics can be added as (HfO2)1-X(Al2O3)X, where the mole fraction of HfO2 is 1-X and the mole fraction of Al2O3 is X. In either case X can be a number greater than or equal to zero. The variable X will gradually change with depth in the dielectric layer. The switching of chemistry of the ALD deposited dielectrics every single cycle or every few cycles can create the gradual change in mole fraction to create the rounded barrier. An annealing process of proper duration and temperature may further smooth the changing of the of the mole fraction.
In one embodiment, the dielectric is divided into regions. Within each region, the dielectric components added using ALD (two or more components) will have particular mole fractions such that the mole fractions vary from region to region. That is, in one region, the components will have a first set of mole fractions while in another region, the components will have a second set of mole fractions. In other embodiments, however, the mole fraction can vary within the region. Other embodiments will not employ the use of regions.
In step 172, the process includes preparing the regions of the dielectric that are between the edge region and the center region of the dielectric layer. These regions created in step 172 are the transition regions. Each of these regions will be created using ALD as a composite of Al2O3 and HfO2. Each region will have different mole fractions for the two components so that the mole fractions change as the regions get closer to the center of the dielectric in order for the bottom of the connection band to increase such that the profile is rounded.
In step 174, the center region of the dielectric layer is prepared using ALD according to a set of mole fractions for the center of the barrier. The center region has the highest Ec. In one embodiment, the center region is created as a composite of Al2O3 and HfO2 using ALD according to mole fractions for the edge of the barrier. In another embodiment, the center region is created as pure Al2O3.
In step 176, the regions of the dielectric that are transitioning between the center region and the edge region closest to the polysilicon floating gate are added. Each of these transition regions are created as a composite of Al2O3 and HfO2 using ALD according to various mole fractions for transitioning between the center of the barrier with the highest EC and the edge of the barrier with the lowest Ec.
In step 178, the edge region of the dielectric closest to the polysilicon floating gate is created using ALD according to mole fractions for the edge of the barrier with the lowest EC. In one embodiment, the edge region is created as a composite of Al2O3 and HfO2 using ALD according to mole fractions for the edge of the barrier. In another embodiment, the edge region is created as pure HfO2.
In step 180, an annealing process is performed. As noted above, the annealing process can be performed at other times in addition to or instead of when depicted in
In one embodiment, each region of the dielectric will be composed of eight layers of dielectric material. That is, eight iterations of one or more ALD processes will be used to create eight layers, which will comprise one region of the dielectric layer. In one example implementation, there may be seven such regions; therefore, the dielectric layer will include 56 layers. In other embodiments, more or less than eight layers can be used within each region, and more or less than seven regions can be used.
Steps 200 and 212 include preparing a dielectric as a [7,1] composite of HfO2 and Al2O3. There are various different configurations for adding seven layers of HfO2 and one layer of Al2O3. The flowchart of
Steps 202 and 210 of
Step 204 and Step 208 include creating a [5,3] composite.
Step 206 of
In one embodiment of a process for using ALD to add multiple layers of two or more components having varying mole fractions as a function of depth to form a dielectric layer, the mole fractions at the edges and/or center of one of the components can be zero. The resulting dielectric would then be composed of a first material at the two edges and a second material at the center, with a composition that gradually changes from the first material to the second material moving from either dielectric edge towards the center of the dielectric. For example, looking at
The dielectric layer described above can be used in various devices, components, etc. In one example, the dielectric layer is used as a tunnel dielectric for a flash memory cell.
To program the memory cell, electrons tunnel through dielectric layer 306 into floating gate 308. To erase the memory cell of
Between N+ diffusion regions 324 is the channel 316. Above channel 316 is dielectric layer 330. Above dielectric area 330 is floating gate 332. Above floating gate 332 is dielectric layer 334. Dielectric layer 334 is made according to the processes described above. That is, dielectric layer 334 is made of two or more components (e.g., HfO2 and Al2O3), where both those components are added using ALD with varying mole fractions as a function of depth in the dielectric layer in order to create a rounded (or otherwise crested) bottom for a conduction band profile for the dielectric layer 334. (See
Above dielectric area 334 is a poly-silicon layer of control gate 336. Above poly-silicon layer 336 is a conductive barrier layer 338 made of Tungsten Nitride (WN). Above barrier layer 338 is a low resistivity metal gate layer 340 made of Tungtsen. WN layer 338 is used to reduce the inter-diffusion of Tungsten into the poly-silicon layer of control gate 336, and also of silicon into Tungsten layer 340. Note that, in one embodiment, control gate 336 consists of layers 336, 338, and 340 as they combine to form one electrode. In other embodiments, a single metal layer, or multiple metal layers without using a poly control gate sub-layer 336 can be used. Dielectric 330, floating gate 332, dielectric 334, poly-silicon layer of control gate 336, WN layer 338 of control gate, and Tungsten metal layer 340 of control gate comprise a stack. An array of memory cells will have many such stacks.
Various sizes and materials can be used when implementing the memory cell of
Use of high-K dielectric materials between the crystalline silicon channel, and a poly gate typically creates two interfacial layers above and below the high-K material itself. These interfacial layers are composed of SiO2, or Silicon Oxy-nitride (SiON), with some fraction of metal atoms that may have diffused from the high-K material itself. These interfacial layers are usually formed naturally and not intentionally, and in many applications these interfacial layers are undesirable, as their dielectric constant tends to be substantially lower than the dielectric constant of the high-K material. In this embodiment, because the high-K dielectric is substantially thicker than that used for gate dielectrics of advanced MOS logic transistors, an interfacial layer that is 1 nm thick or even thicker may not only be tolerable, but also a welcome feature. This will especially be the case if the lower K interfacial layer provides higher mobility for channel electrons, and/or higher immunity to leakage currents because of the higher energy barrier (bottom of the conduction band offset) that the interfacial layer may offer. Higher energy barriers reduce the possibility of electron injection into the high-K dielectric by both direct tunneling, and Fowler-Nordheim (FN) tunneling. Silicon nitride or other inter-diffusion barrier insulators and oxygen diffusion barrier insulators may also be deposited or grown at the interface of silicon and high-K material in order to impede inter-diffusion of various atoms across material boundaries and/or impede further growth of interfacial silicon oxide layers. Toward these ends, in some embodiments, layers of silicon oxide and/or silicon nitride may be intentionally grown and/or deposited to form part of the interfacial layers above and/or below the high-K dielectric(s).
Floating gate 332 is 20 nm and is typically made from poly-silicon that is degenerately doped with n-type dopants; however, other conducting materials, such as metals, can also be used. Dielectric 334 is 10 nm and is made of SiO2; however, other dielectric materials can also be used. Control gate sub layer 336 is 20 nm and is made from poly-silicon; however, other materials can also be used. The WN conducting diffusion barrier layer 338 is 4 nm thick. Tungsten metal control gate layer 340 is 40 nm thick. Other sizes for the above described components can also be implemented. Additionally, other suitable materials, such as replacing W/WN with Cobalt Silicide, can also be used. The floating gate and the control gate can also be composed of one or more layers of poly-silicon, Tungsten, Titanium, or other metals or semiconductors.
As mentioned above, dielectric 330 includes a high-K material. A “high-K material” is a dielectric material with a dielectric constant K greater than the dielectric constant of silicon dioxide. The dielectric constant K of silicon dioxide is in the range 3.9 to 4.2. For the same actual thickness, a high-K material will provide more capacitance per unit area than silicon dioxide (used for typical dielectric regions). In the background discussion above, it was stated that as channel size becomes smaller, the thickness of the dielectric region between the channel and the floating gate should be reduced. What is learned is that it is the effective thickness that must be reduced because it is the effective thickness that determines the control of the floating gate over the channel. Effective thickness is determined as follows:
where Actual Thickness is the physical thickness of the dielectric region, actualK is the dielectric constant for the material used in the dielectric region and SiliconDioxideK is the dielectric constant for SiO2.
A high-K material will have an effective thickness that is lower than its actual thickness. Therefore, a high-K material can be used with a smaller channel size. The smaller effective thickness accommodates the smaller channel size, allowing the gate to maintain the appropriate influence over the channel. The larger actual thickness of a high-K material helps prevent the leakage discussed above.
In one embodiment, the programming and erasing is performed by transferring charge (e.g., tunneling) between floating gate 332 and control gate 336, across dielectric 334. This is advantageous because the programming mechanism (e.g. tunneling) is now not so burdened with strong coupling. Rather, the strong steering function is placed between the floating gate and the channel, matching the strong channel coupling dictate for scaled channels. Thus, the memory cell of
Some advantages which may be realized with some embodiments of the above described memory cell includes the ability to properly scale the device; wear associated with program/erase can be confined to the inter-gate region (away from the channel), which can increase endurance; lower program/erase voltages and/or higher reliability by using thicker dielectrics; and the elimination of the need to aggressively scale tunnel oxide of traditional NAND (or flash memories with other architectures such as NOR). A designer of a memory cell according to the present invention should be mindful of GIDL and a lower control gate coupling ratio (less Qfg, stronger magnification of channel noise and larger manifestations of cell-to-cell variations).
In one embodiment, the memory cell of
The memory cells described in
In the present devices the substrate is tightly coupled to the floating gate via the high dielectric constant material and the control gate is relatively weakly coupled to the floating gate so that reversing the polarity of the definition of erase and program is convenient. That is, when the substrate is raised to a high potential, the floating gate is also raised to a relatively high potential, and many electrons are transferred to the floating gate by tunneling from a grounded control gate, resulting in the collection of cells having a high threshold as viewed from the control gate. Programming, or setting a variable threshold to represent the data state, is accomplished by selectively removing some electrons by raising the control gate in a controlled fashion and terminating the electron removal on a cell by cell basis. This results in selectively reducing the threshold voltage as seen from the control gate, in direct contrast to the prior art devices. This will be described more completely below in conjunction with
In one example, the drain and the p-well will receive 0 volts while the control gate receives a set of programming pulses with increasing magnitudes. In one embodiment, the magnitudes of the pulses range from 7 volts to 15 volts. In other embodiments, the range of pulses can be different. During programming of a memory cell, verify operations are carried out in the periods between the pulses. That is, the programming level of each cell of a group of cells being programmed in parallel is read between each programming pulse to determine whether it is equal to or greater than a verify level to which it is being programmed.
The memory cells of
It should be noted that in flash memory chips, the convention has been to use the same floating gate oxide that is used between the floating gate and the channel for the gate oxide of low, and some medium voltage transistors in order to save extra process steps. Therefore the conventional tunnel oxide with a thickness that is usually greater than 8 nm has been limiting the performance, sub-threshold slope, and on-current drive of the low and some medium voltage transistors. This has resulted in slower program, and read characteristics. One advantage of the present invention is to provide a peripheral transistor gate oxide that is electrically and effectively much thinner than the conventional tunnel oxide, and is physically thicker than the conventional tunnel oxide. In other words, the peripheral circuitry will benefit from replacing the conventional tunnel oxide gate with high-K material(s) in alignment with the general trend of the semiconductor industry towards high-K materials.
Step 402 of
In step 406, the floating gate is deposited over dielectric layer 330 using CVD, PVD, ALD or another suitable method. The result of step 406 is depicted in
Step 408 of
In step 418, the inter-poly tunnel dielectric 334 is deposited using ALD. Dielectric layer 334 is made according to the processes described above. That is, dielectric layer 334 is made of two or more components (e.g., HfO2 and Al2O3), where both those components are added using ALD with varying mole fractions as a function of depth in the dielectric layer in order to create a rounded (or otherwise crested) bottom for a conduction band profile for the dielectric layer 334 (See
In step 440 of
On top of the Tungsten layer, a hard mask of Si3N4 is deposited using, for example, CVD in step 446. In step 448, photolithography is used to create patterns of perpendicular strips to the NAND chain, in order to etch the multi-gate stack and form word lines (i.e. control gates) that are isolated from one another. In step 450, etching is performed using plasma etching, ion milling, ion etching that is purely physical etching, or another suitable process to etch the various layers and form the individual word lines. In one embodiment, the etching is performed until the high-k material is reached. The process attempts to leave as much high-K material as possible, but tries to etch completely through the floating gate material. In another embodiment, the process will etch all the way to the substrate.
In step 452, sidewall oxidation, sidewall oxide deposition, or a combination of the two is performed. For side wall oxidation, the device is placed in a furnace at a high temperature and some fractional percentage of ambient oxygen gas, so that the exposed surfaces oxidize, which provides a protection layer. Sidewall oxidation can also be used to round the edges of the floating gate and the control gate. An alternative to high temperature (e.g. over 1000 degrees Celsius) oxide growth is low temperature (e.g. 400 degrees Celsius) oxide growth in high density Krypton plasma. More information about sidewall oxidation can be found in “New Paradigm of Silicon Technology,” Ohmi, Kotani, Hirayama and Morimoto, Proceedings of the IEEE, Vol. 89, No. 3, March 2001; ”Low-Tempetrature Growth of High Silicon Oxide Films by Oxygen Radical Generated in High Density Krypton Plasma,” Hirayama, Sekine, Saito and Ohmi, Dept. of Electronic Engineering, Tohoku University, Japan, 1999 IEEE; and “Highly Reliable Ultrathin Silicon Oxide Film Formation at Low Temperature by Oxygen Radical Generated in High-Density Krypton Plasma,” Sekine, Saito, Hirayama and Ohmi, Tohoku University, Japan, 2001 IEEE; all three of which are incorporated herein by reference in their entirety. Another way to deposit low temperature tunnel oxide may be by using Krypton Plasma, in conjunction with atomic layer deposition of Silicon Oxide or silicon Oxi-Nitride.
To achieve uniform tunneling a processing step may be employed in order to make the inter-gate tunnel dielectric thicker at the edges where the field lines may be more concentrated than near the middle. Oxidation may be a suitable way of achieving this end.
In step 454, an implant process is performed to create the N+ source/drain regions by Arsenic implantation. In one embodiment, a halo implant is also used. In step 456, an anneal process is performed. In one embodiment, a low temperature anneal process is performed to prevent damage to the high-K material. In some embodiments, a high-K material can be used that has a high thermal budget (e.g., able to endure high temperatures without degrading). In step 458, the process includes isotropically depositing and aniotropically etching sidewall material to form sidewall spacers.
In another embodiment, the methods and technologies described above can be applied to fabricate gradually changing barriers that are of the crested-K type as opposed to crested energy type as described earlier. A crested-K type tunnel barrier consists of a barrier where the dielectric constant or K of the barrier is maximized near the center point of the barrier thickness and the K value is made to diminish at points closer to the tunnel dielectric interfaces. Typically, a reduction in K is concomitant with an increase in barrier height, in terms of both the bottom of the conduction band barrier for electron tunneling and the top of valence band barrier for hole tunneling. Such a crested-K barrier is described in the article titled “Engineering of Conduction Band—Crested Barriers or Dielectric Constant—Crested Barriers in view of their application to floating-gate non-volatile memory devices” by J. Buckley, et. al., and published in IEEE 2004 Silicon Nanoelectronics workshop, incorporated herein by reference in its entirety. The article titled “VARIOT: A Novel Multilayer Tunnel Barrier Concept for Low-Voltage Nonvolatile Memory Devices” by B. Govoreanu, et. al., and published in IEEE ELECTRON DEVICE LETTERS, VOL. 24, NO. 2, FEBRUARY 2003 also addresses a Crested-K tunnel barrier and is incorporated herein by reference in its entirety.
The crested-K tunnel barrier has the advantage of placing the higher quality silicon oxide, which suffers from the least amount of trapping and surface states, adjacent the channel in conventional floating gate memory embodiments where the tunnel oxide resides between the channel and the floating gate. This higher quality interface layer improves mobility, and reduces RTS noise and VT fluctuations. The disadvantage of the K-crested tunnel barrier is that a potential well is formed by the tunnel dielectric as a result of the change in composition. This potential well can lead to enhanced trapping by trap sites within deeper portions of the dielectric. The potential well can persist under the application of high tunneling electric fields. The longer time constants associated with trapping and de-trapping of these deeper trap sites can lead to greater levels of noise and charge relaxation issues that are discussed in more detail in U.S. Pat. No. 6,850,441 Titled “Noise reduction technique for transistors and small devices utilizing an episodic agitation”, incorporated herein by reference in its entirety.
When an electric field is applied to a device according to
When an electric field is applied to a device according to
The energy band diagrams illustrate that electrons with energies within a few kT's of the Fermi level in the cathode can tunnel through a thin (1 nm to 3 nm), low-K, high band gap interface layer at the cathode, by direct tunneling into available energy states above the bottom of the conduction band of the high-K, low band gap layer. The electric field in the low-K interface layer is higher than the electric field in the high-K layer. The ratio of these two electric fields is proportional to the ratio of the two K's: Electric field in low-K interface layer is equal to electric field in the high-K material times the K of the high-K material and divided by the K of the low-K interface layer: E1n=(K2n/K1n)E2n. This is because the normal component of the electric flux density is conserved across a boundary interface that does not hold a sheet of charge (D1n=D2n), and electric flux density is the product of K of each material multiplied by the permittivity of free space multiplied by electric field: D=K ε0 E. The high electric field in the low-K interface layer increases the band bending in the low-K interface layer, and this makes the conditions more favorable for tunneling across the interface layer. The lower EC value of the high-K material as compared to that of the low-K interface layer provides available energy states for electrons coming from the cathode to elastically tunnel into these energy states of the high-K region.
The technology described herein provides for smoothly transitioning from a low-K interface layer into a high-K layer without having to subject the dielectric stack to high temperature annealing processes that may also deleteriously result in deeper transistor p-n junction, stronger short channel effects, and poly-crystallization of the high-K materials. In one embodiment the transition from low-K to high-K material is affected from the onset of the deposition of the low-K interface layer. In another embodiment, this transition is affected after some finite depth of the low-K material has already been deposited. The enhanced tunneling through a low-K/high-K barrier is maximized at a certain thickness of the low-K interface layer. Thinner or thicker interface layers typically result in less tunneling current. If the interface layer is too thin, then the band bending in the interface layer is not substantial enough to allow elastic tunneling as described earlier. If the interface layer is too thick, then the tunneling resistance of a thicker, high barrier interface layer diminishes the tunneling current. The optimal thickness of the interface layer depends on the dielectric constants of the two dielectrics, and the bottom of the conduction band values of the two dielectrics. This situation becomes somewhat more complicated to analyze with a smoothly transitioning crested-K barrier.
Yet another embodiment consists of a tunnel dielectric that is designed for tunneling in one direction only. In such a system, the tunnel dielectric may be designed only for tunneling during, for example, programming operations only. Erase may be performed by hot hole injection or by tunneling erase through a separate dielectric. In such a system. Instead of having a tri-layer system to create a crested-K barrier, only a bi-layer system is sufficient. The bi-layer system will simply consist of a low-K, high barrier interface layer adjacent the cathode, followed by a high-K, low barrier dielectric. The advantage of this system is that no potential well is formed, as it would be in a tri-layer dielectric system. Electrons tunneling into the high-K material experience only a down hill slide all the way into the anode, without encountering another high energy barrier which could lead to reflection of impinging electrons and their subsequent trapping into the high-K dielectric.
The technology described above also applies to dielectrics comprising more than 2 materials, where X is the mole fraction of the first material, Y is the mole fraction of the second material, and (1-X-Y) is the mole fraction of the third material. An example of the third material is nitrogen. The technology described herein also applies to dielectrics comprising more than 3 materials. A realistic example would be HfSiON (3 materials plus oxygen), or HfAlSiON (4 materials plus oxygen), or HfAlTaSiON (5 materials plus oxygen). In general, the technology described herein also applies to dielectrics comprising N different types of atoms, the mole fraction of any number of them being a function of depth
The data stored in the memory cells are read out by the column control circuit 504 and are output to external I/O lines via data input/output buffer 512. Program data to be stored in the memory cells are input to the data input/output buffer 512 via the external I/O lines, and transferred to the column control circuit 504. The external I/O lines are connected to controller 518.
Command data for controlling the flash memory device is input to controller 518. The command data informs the flash memory of what operation is requested. The input command is transferred to state machine 516, which controls column control circuit 504, row control circuit 506, c-source control 510, p-well control circuit 508 and data input/output buffer 512. State machine 516 can also output status data of the flash memory such as READY/BUSY or PASS/FAIL.
Controller 518 is connected or connectable with a host system such as a personal computer, a digital camera, personal digital assistant, etc. Controller 518 communicates with the host in order to receive commands from the host, receive data from the host, provide data to the host and provide status information to the host. Controller 518 converts commands from the host into command signals that can be interpreted and executed by command circuits 514, which is in communication with state machine 516. Controller 518 typically contains buffer memory for the user data being written to or read from the memory array.
One exemplar memory system comprises one integrated circuit that includes controller 518, and one or more integrated circuit chips that each contain a memory array and associated control, input/output and state machine circuits. The trend is to integrate the memory arrays and controller circuits of a system together on one or more integrated circuit chips. The memory system may be embedded as part of the host system, or may be included in a memory card (or other package) that is removably inserted into the host systems. Such a removable card may include the entire memory system (e.g. including the controller) or just the memory chip(s) and associated peripheral circuits (with the Controller being embedded in the host). Thus, the controller can be embedded in the host or included within a removable memory system.
In some implementations, some of the components of
In one embodiment of the present invention, NAND type flash memory cells are used. The NAND cells are arranged with multiple transistors in series between two select gates. The transistors in series and the select gates are referred to as a NAND string. The discussion herein is not limited to any particular number of memory cells in a NAND string or NAND chain. Furthermore, the present invention is not limited to NAND flash memory cells. In other embodiments flash memory cells other than NAND cells (e.g. NOR cells or other cells) can be used to implement the present invention. In yet other embodiments, non-volatile memory cells other than flash memory cells can be used to implement the present invention.
During read and programming operations, 4,256 memory cells are simultaneously selected. The memory cells selected have the same word line and the same kind of bit line (e.g. even bit lines or odd bit lines). Therefore, 532 bytes of data can be read or programmed simultaneously. In one embodiment, these 532 bytes of data that are simultaneously read or programmed form a logical page. Therefore, one block can store at least eight logical pages (four word lines, each with odd and even pages). When each memory cell stores two bits of data (e.g. a multi-level cell), one block stores 16 logical pages. Other sized blocks and pages can also be used with the present invention. Additionally, architectures other than that of
Another embodiment for creating the dielectric region of two or more materials with mole fractions varying as a function of depth is to co-inject the two materials during the ALD process. For example, the article “Ozone-Based Atomic Layer Depoistion of HfO2 and HfxSi1-xO2 and Film Characterization,” Senzaki, Park, Tweet, Conley and Onon, Mat. Res. Soc. Symp. Proc. Vol. 811, 2004 describes co-injecting two precursors during an ALD process.
Some high-k dielectrics can suffer from increased trapping, and poly-crystallization at lower temperatures. It has been found that film quality can be increased through introduction of nitrogen in high-K materials such as hafnium oxide, hafnium silicate, zirconium oxide, hafnium tantalum oxide, etc. Sufficient quantities of nitrogen can be more easily incorporated into these films by in-situ nitridation and/or by forming nitrides in-situ and then oxidizing these nitrides in-situ to form oxy-nitrides. Ammonia gas, nitrogen gas in presence of plasma, and/or in-situ or remotely generated radical nitrogen can be used for the nitridation of metal species. Any of these species (or others) can be referred to as nitriding agent. Water, ozone, in-situ or remotely generated radical oxygen can be used for oxidation. Any of these species or others) can be referred to as oxidizing agent. Both oxidizing or nitriding agents can be delivered in lower concentrations by mixing them with inert gases such as molecular nitrogen, or inert gases such as He, Ne, Ar, Kr, Xe, Rn. The hydrogen in any of these agents, such as ammonia or water can be replaced with the hydrogen isotope, deuterium.
A new complex ALD cycle is proposed here where after the deposition of the metal(s) precursors, and the purge of metal precursor(s), a nitridation step is performed followed by, or concurrently with, an oxidation step. For example, the nitridation and oxidation step can include first exposing the substrate surface to the nitriding agent, then purging this agent, and subsequently exposing the wafer to oxidizing agent and then purging the oxidizing agent. Alternatively, both the nitriding, and oxidizing agents can be simultaneously released into the chamber at appropriate ratios, and later purged. Another alternative is to first release the nitriding agent, shortly thereafter release the oxidizing agent, and finally purge the mixture. Yet another sequence is to first release the nitriding agent, followed by release of the oxidizing agent, and then followed by another release of the nitriding agent, all followed by a single purge. If multiple nitriding or oxidizing pulses are applied, the chemistries of each pulse can be different from the next pulse. The above processes can be performed within a single ALD cycle and across multiple ALD cycles. As the dielectric is being created at a rate one or sub-one atomic layer per cycle, the chemistries and exposure times and sequences can be varied to create a varying nitrogen and oxygen concentration as a function of depth.
There are various options for co-injecting the nitriding agent(s) and the oxidizing agent(s) (step 626). Three suitable options are depicted in
The process of
In one example of depositing a uniform hafnium silicon oxy-nitride film, each ALD cycle will start with the co-injection of the metal precursors TEMMAHf (tetrakis-ethylmethylamino hafnium) and TEMMASi (tetrakis-ethylmethylamino Silicon) at proper ratios to produce the desired concentrations of Hf and Si in the film. This is followed by purge of these precursor gases. Then a nitridation step using ammonia is employed, and this is followed by an oxidation step by releasing ozone in the ALD chamber. The ammonia and ozone gas are then purged in a single purge operation. The amounts of gas, the durations of exposure to each gas, and the delay between the release of ammonia and the subsequent release of ozone have to be tuned to achieve the desired incorporation levels of nitrogen/oxygen in the dielectric film.
It is known that the bonding energy of oxygen to most metals and to most semiconductors is greater than the bonding energy of nitrogen to the same. Therefore, in order to incorporate sufficient concentrations of nitrogen into high-K dielectric films, it may be beneficial to oxidize an already nitrided film rather than to nitride and already oxidized film. Oxidation of a nitrided film may create a film with fewer metal-to-metal or metal-to-silicon bonds, and/or fewer dangling bonds.
Another approach can include N cycles of HfSiN deposition followed by exposure to oxidizing agent, where N is an integer number greater than or equal to 1. This would allow the oxidation of HfSiN before the film becomes too thick for the underlying layers to be oxidized by reasonable exposure times and temperatures to oxidizing agent(s).
Silicon oxy-nitride with higher nitrogen concentrations can be ALD deposited by using the above method of first nitriding silicon and then oxidizing the silicon nitride. Another example of a suitable material is HfSiTaON.
When performing an ALD process, oxygen radicals may react more readily with a metal during the oxidation stage than regular oxygen. The reason for this is that for the case of radical oxygen no initial energy barrier associated with breaking the bond between the oxygen and whatever atom(s) it is bound to (for example another oxygen atom it may be bound to) needs to be surmounted. This means that radical oxygen will react more readily with metal or semi-conductor atoms and the energy released will be larger, translating into faster reaction rates and oxidation of more metal or semiconductor atoms. The quality of dielectric film depends on minimizing metal/semiconductor to metal/semiconductor bonds by making sure that all metal/semiconductor atoms are bonding to oxygen or nitrogen, and not to another metal atom. Metal/semiconductor to metal/semiconductor bonds can result in current leakage paths in dielectric materials. Examples of metal/semiconductor to metal/semiconductor bonds include Hf to Si bonds, Hf to Hf bonds, and Si to Si bonds. Radical oxygen with its stronger reactivity to metals can reduce the number of metal to metal bonds in dielectrics. Thus, in one embodiment, a high-density plasma is used to form oxygen radicals that serve as the oxidizing agent for ALD. Oxygen radicals and inert gas ions can be formed by first introducing an oxygen containing feed gas (radical generating feed gas) and an inert gas containing feed gas (ion generating feed gas) into a plasma chamber. The gases can be excited by a microwave source, for example, to produce oxygen radicals and other gas ions (Note: ions are not inert). After the radicals and ions are produced, they can be introduced to the deposition chamber to react with the first precursor at the substrate surface to form the desired oxide or oxynitride material.
In one embodiment, krypton is used as the ion generating feed gas. The meta-stable states of krypton have greater capability to selectively dissociate oxygen into oxygen radicals. Krypton shows greater efficiency in dissociating oxygen into highly reactive oxygen radicals rather than less reactive oxygen ions when compared with other inert gases.
In one embodiment, chuck 704 is coupled to a voltage bias that can electrostatically hold substrate wafer 708 to the chuck. Other means for maintaining the wafer in position can be used in various embodiments. Container 712 holds the first precursor which can be delivered uniformly over substrate wafer 708 through showerhead 714. In some embodiments, container 712 can include multiple containers to store multiple first precursors. A second container 738 can be provided to hold a second first precursor if so desired for a particular implementation.
Between precursor pulses and/or after introduction of inert gas into the chamber, excess reactant and by-products can be removed from the chamber through one or more valves 716 utilizing some pump(s) that are not shown in
System 700 further includes a plasma source chamber 720 for the generation of radicals that can serve as the second precursor (reactant) in the deposition process. A first feed gas such as Ar, Xe, Kr, He, N2 etc. can be delivered into chamber 720 from container 722 while a second feed gas such as H2O, H2, O2, or O3 can be delivered from container 724.
One or more microwave energy sources 726 or other suitable energy source (e.g., a radio frequency energy source) provide energy to the chamber through a horn antenna, waveguide, or other mechanism 728 to excite the feed gases and generate the high-density plasma. A dielectric barrier 730 that is impermeable to gases but permeable to microwaves (or RF waves if such an energy source is used) is provided between the energy source and gas mixture. In one embodiment, dielectric barrier 730 is quartz. In one embodiment, dielectric barrier 730 is preferably a material that will not oxidize or nitridize, etc. in the presence of oxygen or nitrogen radicals. Microwave energy source 726 excites the feed gases, forming a high-density mixed plasma in chamber 720. A mixture of an inert feed gas and an oxygen, hydrogen, nitrogen, or other desired reactant carrying second feed gas (e.g., molecular oxygen, O2) can be provided into the plasma source chamber. Microwave energy source 726 can excite the inert gas and second feed gas to form radicals that can serve as the second reactant in the deposition process. For example, an inert gas and oxygen bearing gas can be provided to the chamber and excited to generate oxygen radicals (O1D). Ions will also be generated from the first feed gas. These ions can impact the substrate along with the generated radicals to drive surface reactions between the first precursor and radicals (second precursor or reactant).
A plurality of valves 736 are provided in a separation layer 740 between the two chambers. The valves can be opened to deliver the radicals and ions to the substrate at the appropriate time during the deposition process. Any number of means for selectively delivering the radicals and ions from the plasma source chamber to the deposition chamber can be used in accordance with various embodiments. The valves as illustrated in
Note that
Purge operations can be done by employing vacuum pumps to remove gases from chambers (negative pressure), by injecting chemically inert purge gases into the chamber (positive pressure) that would remove the existing gases through orifices located at opposite side of the chamber, or by employing both positive pressure from injecting inert gas and simultaneous negative pressure by utilizing vacuum pumps.
In one embodiment, showerhead 714 is formed of a mesh material that allows materials delivered from plasma source chamber 720 to reach the substrate surface. In other embodiments, showerhead 714 can be moveable such that is placed above the substrate to introduce the first precursor and then moved out of the way to allow the second precursor to be delivered from plasma source chamber 702.
In one embodiment, krypton (Kr) is preferably used as an inert gas for the generation of oxygen and/or nitrogen radicals in a high-density mixed plasma to deposit one or more oxide, nitride, or oxynitride containing layers. A dielectric, e.g. aluminum oxide, silicon oxide, or hafnium oxide, hafnium silicate, or hafnium silicon oxynitride can be deposited with very high density using a Kr and oxygen carrying feed gas (e.g., O2) mixture, thus resulting in a robust, high quality oxide. For example, silicon oxides deposited from a Kr/O2 plasma can maintain a good O/Si mixture and have a low interface trap density that is comparable to or less than thermally grown silicon oxide.
Kr shows improved benefits over other inert gases for the production of oxygen radicals in a high-density mixed plasma.
The first metastable state of Kr is second closest to the dissociation energy of molecular oxygen into oxygen radicals and can be used to generate oxygen radicals from molecular oxygen. The second or higher metastable states of Kr, unlike Ar, are unable to excite molecular oxygen ions. Therefore, oxygen radicals can be selectively generated in Kr high-density plasma to produce a large concentration of oxygen radicals without also providing a large number of oxygen ions. This results in the deposition of oxide films having very good properties and deposition times. The resulting oxides should have low leakage currents, good breakdown field intensity, good charge to breakdown distribution, good stress-induced leakage current, low interface trap charge, and low bulk charge.
Inert gases such as Kr can also be used to deposit very high quality oxynitride films having similar benefits to those set forth above. For example, microwave excited high density Kr/O2/NH3 plasma can be used to deposit a silicon oxynitride film. By using Kr, the improvements over other inert gases as discussed above can be achieved in various embodiments. Nitride films can also be deposited using Kr or other inert gases.
Improved high-K dielectrics can be deposit by utilizing plasma generated oxygen and/or nitrogen radicals to improve the quality of the high-K dielectric through suppression of defect and trap sites. This is achieved by a more complete oxidation and/or nitridation process which is provided by the stronger reactivity of free radicals. Another benefit or sometimes a side effect of employing radicals is to grow thicker interface layers which are typically of lower K. For example, as HfSiON is being deposited on the top surface of a substrate, some free radical of oxygen and/or nitrogen will more readily diffuse through the high-K HfSiON layers and the existing interfacial layer and react with the silicon surface residing below the dielectrics to form silicon oxide, or silicon oxynitride. The interface layer will not be pure oxide or oxynitride, but will also contain some amounts of Hf. The quality of this grown lower-K, but higher band gap interface layer will be very good with low trap sites. This reduces the density of interface traps and shallow oxide traps, and provides a benefit ion terms of higher electron/hole mobility and lower noise and hysteresis. However, the low-K interface layer can increase leakage currents due to increased tunneling through the lower K interface layer when the electrode adjacent the interface layer is the cathode for electron injection. There is a higher field in the low-K interface layer since the K is lower in this layer. This can be an undesirable effect unless it is intentionally taken advantage of in devices where the objective is to increase the tunneling current.
In accordance with various embodiments, one or more techniques can be used to increase the radical concentration delivered to the substrate surface in order to increase the efficiency and quality of a deposited material such as an oxide from oxygen radicals.
The process of
Because the concentration of oxygen radicals (relative to molecular oxygen ions and molecular oxygen) affects the quality, efficiency, and rate of deposition of an oxide material it is desirable to increase the concentration of oxygen radicals relative to these other materials. The higher reactivity of free radicals may afford shorter pulse widths for the precursor 2. This can have a positive impact on the over all deposition rate. Accordingly, at step 788, one or more techniques are employed to increase the concentration of radicals relative to other materials that are delivered to the deposition chamber and ultimately the wafer from plasma source chamber 720. For example, an additional energy source can be included in the plasma source chamber to aid in the dissociation of molecular oxygen and oxygen ions into oxygen radicals. Additionally or alternatively, a bias can be applied in the deposition chamber to attract oxygen radicals to the wafer and/or to repel other less desirable materials from the wafer. In one embodiment, step 710 includes applying a bias in the plasma source chamber to attract less desirable charged ions such as oxygen ions away from the deposition chamber. Still yet in other embodiments, a selectively permeable membrane can be included in deposition system 700 to filter less desirable components and thereby increase the radical concentration. Additionally, step 788 can also include increasing the radical concentration in the plasma generated in plasma source chamber 720 and/or increasing the radical concentration after a mixture of radicals, ions, and less desirable components are introduced into the deposition chamber. Accordingly, in one embodiment step 788 is followed by the introduction of radicals and ions into deposition chamber 702 by opening valves 716. In other embodiments, step 788 is preceded by the introduction of radicals and ions into deposition chamber 702.
The ion generating feed gas and radical generating feed gas need not be pulsed into the plasma chamber. In one embodiment, they can be continuously co-injected into the plasma chamber at the same rate as these gases leave the plasma chamber so as to maintain the plasma chamber average pressure over time scales spanning multiple cycles. In one embodiment, the sequence in which these gases are fed into the plasma chamber is not of much consequence so long as the proper partial pressures are maintained over long period of time. The sequence of release of various gases into the ALD chamber, however, has direct bearing on the type, quality, and deposition rate of the ALD films to be deposited. In some embodiment, steps from 782 to 788 can take place concurrently, or in another order. In some embodiments, it is not a serial step-by-step process.
Although embodiments are discussed above that use a high-density plasma to form oxygen radicals that serve as the oxidizing agent for ALD, other more traditional ALD processes can also be used.
In some embodiments, if exposure to oxidizing agent replaces the exiting nitrogen in the dielectric with oxygen, then it may become necessary to follow several cycles of pure nitridation of metal precursor with one control and possibly limited exposure cycle of oxidation in order to achieve the proper levels of nitridation in the films, as the nitrogen in the underlying layers may be more securely bonded to the metal atoms by virtue of having one or more atomic layers of the deposited materials over it. This may provide an undesired cyclic variation in the nitrogen and oxygen mole fraction as a function of depth. However an anneal operation with a proper temperature and duration may help to homogenize this variation on the scale of a few atomic layers without obliterating the desired concentration gradients that may be intended over larger length scales along the depth of the dielectric.
The foregoing detailed description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. The described embodiments were chosen in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.
Claims
1. A dielectric layer, comprising:
- a first type of component added by atomic layer deposition; and
- a second type of component added by atomic layer deposition, said first type of component and said second type of component have varying mole fractions as a function of depth in said dielectric layer in order to create a crested bottom of a conduction band profile for said dielectric layer.
2. A dielectric layer according to claim 1, further comprising:
- a third type of component, said third type of component have a varying mole fraction as a function of depth in said dielectric layer.
3. A dielectric layer according to claim 1, wherein:
- said first type of component and said second type of component have been annealed.
4. A dielectric layer according to claim 1, wherein:
- said dielectric layer includes multiple regions; and
- each of said multiple regions includes said first component and said second component with varying mole fractions for said first component and said second component as a function of depth in said dielectric layer.
5. A dielectric layer according to claim 4, wherein:
- said multiple regions include a first edge region having a first conduction band bottom level, a middle region having a second conduction band bottom level and a second edge region having a third conduction band bottom level, said second conduction band bottom level is greater than said first conduction band bottom level and said third conduction band bottom level.
6. A dielectric layer according to claim 5, wherein:
- a first region of said multiple regions includes seven layers of said first component and one layer of said second component;
- a second region of said multiple regions includes six layers of said first component and two layers of said second component;
- a third region of said multiple regions includes five layers of said first component and three layers of said second component;
- a fourth region of said multiple regions includes four layers of said first component and four layers of said second component;
- a fifth region of said multiple regions includes five layers of said first component and three layers of said second component;
- a sixth region of said multiple regions includes six layers of said first component and two layers of said second component; and
- a seventh region of said multiple regions includes seven layers of said first component and one layer of said second component.
7. A dielectric layer according to claim 6, wherein:
- said crested bottom of a conduction band profile for said dielectric layer is a rounded bottom of a conduction band profile for said dielectric layer.
8. A dielectric layer according to claim 1, wherein:
- said crested bottom of a conduction band profile for said dielectric layer is a rounded bottom of a conduction band profile for said dielectric layer.
9. A dielectric layer according to claim 1, wherein:
- said first component is a first dielectric; and
- said second component is a second dielectric.
10. A dielectric layer according to claim 1, wherein:
- said first component is Al2O3; and
- said second component is HfO2.
11. A dielectric layer according to claim 1, wherein:
- said second component has a mole fraction of zero at an edge of said dielectric layer.
12. A dielectric layer according to claim 1, wherein:
- said first component is at two edges of said dielectric layer and said second component is at a center of said dielectric layer, with a composition that gradually changes from the first component to said second component moving from either edge towards said center of said dielectric layer.
13. A non-volatile storage device, comprising:
- source/drain regions;
- a channel region between said source/drain regions;
- a floating gate;
- a control gate;
- a first dielectric region between said channel region and said floating gate, said first dielectric region includes a high-K material; and
- a second dielectric region between said floating gate and said control gate, said second dielectric region includes a first component added by atomic layer deposition and a second component added by atomic layer deposition, said first component and said second component have varying mole fractions as a function of depth in said second dielectric region in order to create a rounded bottom of a conduction band profile for said second dielectric region,
- wherein charge is transferred between said floating gate and said control gate via said second dielectric region.
14. A non-volatile storage device according to claim 13, wherein:
- said first type of component and said second type of component have been annealed.
15. A non-volatile storage device according to claim 13, wherein:
- said second dielectric region includes multiple regions;
- each of said multiple regions includes said first component and said second component with varying mole fractions for said first component and said second component; and
- said multiple regions include a first edge region having a first conduction band bottom level, a middle region having a second conduction band bottom level and a second edge region having a third conduction band bottom level, said second conduction band bottom level is greater than said first conduction band bottom level and said third conduction band bottom level.
16. A non-volatile storage device according to claim 13, wherein:
- said first component is a first dielectric; and
- said second component is a second dielectric.
17. A non-volatile storage device, comprising:
- source/drain regions;
- a channel region between said source/drain regions;
- a floating gate;
- a control gate; and
- a dielectric layer between said floating gate and said control gate, said dielectric layer includes a two or more components added by atomic layer deposition, said two or more components having varying mole fractions as a function of depth in said dielectric layer.
18. A non-volatile storage device according to claim 17, wherein:
- said two or more components have been annealed.
19. A non-volatile storage device according to claim 17, wherein:
- said dielectric layer includes multiple regions; and
- each of said multiple regions includes a first component and a second component with varying mole fractions for said first component and said second component as a function of depth in said dielectric layer.
20. A non-volatile storage device according to claim 16, wherein:
- said dielectric layer includes a first material and a second material;
- said first material is at two edges of said dielectric layer and said second material is at a center of said dielectric layer;
- between said edges and said center, said dielectric layer includes a composition that gradually changes from said first material to said second material moving from either edge towards said center of said dielectric layer.
21. A non-volatile storage device according to claim 17, wherein:
- said dielectric layer includes a first material and a second material; and
- said second material has a mole fraction of zero at an edge of said dielectric layer.
22. A non-volatile storage device according to claim 17, wherein:
- said dielectric layer includes three components added by atomic layer deposition that have varying mole fractions as a function of depth in said dielectric layer.
Type: Application
Filed: Sep 12, 2005
Publication Date: Feb 9, 2006
Inventor: Nima Mokhlesi (Los Gatos, CA)
Application Number: 11/224,599
International Classification: H01L 29/94 (20060101); H01L 29/788 (20060101);