NONVOLATILE CHARGE TRAP MEMORY DEVICE HAVING A HIGH DIELECTRIC CONSTANT BLOCKING REGION
A nonvolatile charge trap memory device is described. The device includes a substrate having a channel region and a pair of source and drain regions. A gate stack is above the substrate over the channel region and between the pair of source and drain regions. The gate stack includes a high dielectric constant blocking region.
This application claims the benefit of U.S. Provisional Application No. 61/007,566, filed Dec. 12, 2007, the entire contents of which are hereby incorporated by reference herein.
TECHNICAL FIELDThe invention is in the field of Semiconductor Devices.
BACKGROUNDFor the past several decades, the scaling of features in integrated circuits has been a driving force behind an ever-growing semiconductor industry. Scaling to smaller and smaller features enables increased densities of functional units on the limited real estate of semiconductor chips. For example, shrinking transistor size allows for the incorporation of an increased number of memory devices on a chip, lending to the fabrication of products with increased capacity. The drive for ever-more capacity, however, is not without issue. The necessity to optimize the performance of each device becomes increasingly significant.
Non-volatile semiconductor memories typically use stacked floating gate type field-effect-transistors. In such transistors, electrons are injected into a floating gate of a memory cell to be programmed by biasing a control gate and grounding a body region of a substrate on which the memory cell is formed. An oxide-nitride-oxide (ONO) stack is used as either a charge storing layer, as in a semiconductor-oxide-nitride-oxide-semiconductor (SONOS) transistor, or as an isolation layer between the floating gate and control gate, as in a split gate flash transistor.
Referring to
One problem with conventional SONOS transistors is the limited program and erase window achievable with a conventional blocking layer 106C, inhibiting optimization of semiconductor device 100. For example,
A nonvolatile charge trap memory device and a method to form the same is described herein. In the following description, numerous specific details are set forth, such as specific dimensions, in order to provide a thorough understanding of the present invention. It will be apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known processing steps, such as patterning steps or wet chemical cleans, are not described in detail in order to not unnecessarily obscure the present invention. Furthermore, it is to be understood that the various embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale.
Disclosed herein is a nonvolatile charge trap memory device. The device may include a substrate having a channel region and a pair of source and drain regions. A gate stack may be formed above the substrate over the channel region and between the pair of source and drain regions. In an embodiment, the gate stack includes a high dielectric constant blocking region. In one embodiment, the high dielectric constant blocking region is a bi-layer blocking dielectric region having a first dielectric layer disposed directly above a charge-trapping layer and a second dielectric layer disposed directly above the first dielectric layer and directly below a gate layer. The dielectric constant of the first dielectric layer is lower than the dielectric constant of the second dielectric layer. In another embodiment, the high dielectric constant blocking region is a graded blocking dielectric layer disposed directly above a charge-trapping layer and directly below a gate layer. The dielectric constant of the graded blocking dielectric layer has a low-to-high gradient in the direction from the charge-trapping layer to the gate layer.
A nonvolatile charge trap memory device including a high dielectric constant blocking region may exhibit a relatively large program and erase window, enabling improved performance of such a device. For example, in accordance with an embodiment of the present invention,
The ability to achieve a deep erase in a nonvolatile charge trap memory device including a high dielectric constant blocking region may result from the ability of the high dielectric constant blocking region to mitigate back-streaming of electrons. Such back-streaming otherwise proceeds into a charge-trapping layer that is subject to an erase-mode voltage application. For example, in accordance with an embodiment of the present invention,
A nonvolatile charge trap memory device may include a multi-layer blocking dielectric region.
Referring to
Semiconductor device 500 may be any nonvolatile charge trap memory device. In one embodiment, semiconductor device 500 is a Flash-type device wherein the charge-trapping layer is a conductor layer or a semiconductor layer. In accordance with another embodiment of the present invention, semiconductor device 500 is a SONOS-type device wherein the charge-trapping layer is an insulator layer. By convention, SONOS stands for “Semiconductor-Oxide-Nitride-Oxide-Semiconductor,” where the first “Semiconductor” refers to the channel region material, the first “Oxide” refers to the tunnel dielectric layer, “Nitride” refers to the charge-trapping dielectric layer, the second “Oxide” refers to the blocking dielectric layer and the second “Semiconductor” refers to the gate layer. A SONOS-type device, however, is not limited to these specific materials, as described below.
Substrate 502 and, hence, channel region 512, may be composed of any material suitable for semiconductor device fabrication. In one embodiment, substrate 502 is a bulk substrate composed of a single crystal of a material which may include, but is not limited to, silicon, germanium, silicon-germanium or a III-V compound semiconductor material. In another embodiment, substrate 502 includes a bulk layer with a top epitaxial layer. In a specific embodiment, the bulk layer is composed of a single crystal of a material which may include, but is not limited to, silicon, germanium, silicon-germanium, a III-V compound semiconductor material and quartz, while the top epitaxial layer is composed of a single crystal layer which may include, but is not limited to, silicon, germanium, silicon-germanium and a III-V compound semiconductor material. In another embodiment, substrate 502 includes a top epitaxial layer on a middle insulator layer which is above a lower bulk layer. The top epitaxial layer is composed of a single crystal layer which may include, but is not limited to, silicon (i.e. to form a silicon-on-insulator (SOI) semiconductor substrate), germanium, silicon-germanium and a III-V compound semiconductor material. The insulator layer is composed of a material which may include, but is not limited to, silicon dioxide, silicon nitride and silicon oxy-nitride. The lower bulk layer is composed of a single crystal which may include, but is not limited to, silicon, germanium, silicon-germanium, a III-V compound semiconductor material and quartz. Substrate 502 and, hence, channel region 512, may include dopant impurity atoms. In a specific embodiment, channel region 512 is doped P-type and, in an alternative embodiment, channel region 512 is doped N-type.
Source and drain regions 510 in substrate 502 may be any regions having opposite conductivity to channel region 512. For example, in accordance with an embodiment of the present invention, source and drain regions 510 are N-type doped regions while channel region 512 is a P-type doped region. In one embodiment, substrate 502 and, hence, channel region 512, is composed of boron-doped single-crystal silicon having a boron concentration in the range of 1×1015-1×1019 atoms/cm3. Source and drain regions 510 are composed of phosphorous- or arsenic-doped regions having a concentration of N-type dopants in the range of 5×1016-5×1019 atoms/cm3. In a specific embodiment, source and drain regions 510 have a depth in substrate 502 in the range of 80-200 nanometers. In accordance with an alternative embodiment of the present invention, source and drain regions 510 are P-type doped regions while channel region 512 is an N-type doped region.
Tunnel dielectric layer 504A may be any material and have any thickness suitable to allow charge carriers to tunnel into the charge-trapping layer under an applied gate bias while maintaining a suitable barrier to leakage when the device is unbiased. In one embodiment, tunnel dielectric layer 504A is formed by a thermal oxidation process and is composed of silicon dioxide or silicon oxy-nitride, or a combination thereof. In another embodiment, tunnel dielectric layer 504A is formed by chemical vapor deposition or atomic layer deposition and is composed of a dielectric layer which may include, but is not limited to, silicon nitride, aluminum oxide, hafnium oxide, zirconium oxide, hafnium silicate, zirconium silicate, hafnium oxy-nitride, hafnium zirconium oxide and lanthanum oxide. In another embodiment, tunnel dielectric layer 504A is a bi-layer dielectric region including a bottom layer of a material such as, but not limited to, silicon dioxide or silicon oxy-nitride and a top layer of a material which may include, but is not limited to, silicon nitride, aluminum oxide, hafnium oxide, zirconium oxide, hafnium silicate, zirconium silicate, hafnium oxy-nitride, hafnium zirconium oxide and lanthanum oxide. Thus, in one embodiment, tunnel dielectric layer 504A includes a high-K dielectric portion. In a specific embodiment, tunnel dielectric layer 504A has a thickness in the range of 1-10 nanometers.
Charge-trapping layer may be any material and have any thickness suitable to store charge and, hence, raise the threshold voltage of gate stack 504. In accordance with an embodiment of the present invention, charge-trapping layer 504B is formed by a chemical vapor deposition process and is composed of a dielectric material which may include, but is not limited to, stoichiometric silicon nitride, silicon-rich silicon nitride and silicon oxy-nitride. In one embodiment, charge-trapping layer 504B is composed of a bi-layer silicon oxy-nitride region. For example, in a specific embodiment, charge-trapping layer 504B includes an oxygen-rich portion and a silicon-rich portion and is formed by depositing an oxygen-rich oxy-nitride film by a first composition of gases and, subsequently, depositing a silicon-rich oxy-nitride film by a second composition of gases. In a particular embodiment, charge-trapping layer 504B is formed by modifying the flow rate of ammonia (NH3) gas, and introducing nitrous oxide (N2O) and dichlorosilane (SiH2Cl2) to provide the desired gas ratios to yield first an oxygen-rich oxy-nitride film and then a silicon-rich oxy-nitride film. In one embodiment, charge-trapping layer 504B has a thickness in the range of 5-10 nanometers. In accordance with an alternative embodiment of the present invention, charge-trapping layer 504B has a graded composition.
Multi-layer blocking dielectric region 504C may be composed of any material and have any thickness suitable to maintain a barrier to charge leakage without significantly decreasing the capacitance of gate stack 504. In accordance with an embodiment of the present invention, multi-layer blocking dielectric region 504C is a bi-layer blocking dielectric region having a first dielectric layer 506 disposed directly above charge-trapping layer 504B and having a second dielectric layer 508 disposed directly above first dielectric layer 506 and directly below gate layer 504D. In an embodiment, first dielectric layer 506 has a large barrier height while second dielectric layer 508 has a high dielectric constant. In one embodiment, the barrier height of first dielectric layer 506 is at least approximately 2 electron Volts (eV). In a specific embodiment, the barrier height of first dielectric layer 506 is at least approximately 3 eV. In an embodiment, the dielectric constant of first dielectric layer 506 is lower than the dielectric constant of second dielectric layer 508. In one embodiment, first dielectric layer 506 of bi-layer blocking dielectric region 504C is composed of silicon dioxide and second dielectric layer 508 is composed of silicon nitride. In another embodiment, first dielectric layer 506 of bi-layer blocking dielectric region 504C is composed of silicon dioxide and second dielectric layer 508 is composed of a material such as, but not limited to, aluminum oxide, hafnium oxide, zirconium oxide, hafnium silicate, zirconium silicate, hafnium oxy-nitride, hafnium zirconium oxide or lanthanum oxide. In a specific embodiment, first dielectric layer 506 of bi-layer blocking dielectric region 504C is composed of a material having a dielectric constant approximately in the range of 3.5-4.5 and second dielectric layer 508 is composed of a material having a dielectric constant above approximately 7. In accordance with an embodiment of the present invention, multi-layer blocking dielectric region 504C is formed in part by a chemical vapor deposition process. In one embodiment, multi-layer blocking dielectric region 504C is formed from at least two different materials. In a specific embodiment, forming multi-layer blocking dielectric region 504C from at least two different materials includes oxidizing a top portion of charge-trapping layer 504B and, subsequently, depositing a dielectric layer above the oxidized portion of charge-trapping layer 504B. In another specific embodiment, forming graded blocking dielectric layer 504C from at least two different materials includes depositing a first dielectric layer having a first dielectric constant and, subsequently, depositing a second dielectric layer having a second dielectric constant, wherein the second dielectric constant is greater than the first dielectric constant. In a particular embodiment, the first dielectric layer has a thickness approximately in the range of 0.5-3 nanometers, the second dielectric layer has a thickness approximately in the range of 2-5 nanometers, and the first and second dielectric layers are not inter-mixed. Thus, in accordance with an embodiment of the present invention, multi-layer blocking dielectric region 504C has an abrupt interface between first dielectric layer 506 and second dielectric layer 508, as depicted in
Gate layer 504D may be composed of any conductor or semiconductor material suitable for accommodating a bias during operation of a SONOS-type transistor. In accordance with an embodiment of the present invention, gate layer 504D is formed by a chemical vapor deposition process and is composed of doped poly-crystalline silicon. In another embodiment, gate layer 504D is formed by physical vapor deposition and is composed of a metal-containing material which may include, but is not limited to, metal nitrides, metal carbides, metal silicides, hafnium, zirconium, titanium, tantalum, aluminum, ruthenium, palladium, platinum, cobalt and nickel. In one embodiment, gate layer 504D is a high work-function gate layer.
In another aspect of the present invention, a nonvolatile charge trap memory device may include a graded blocking dielectric layer.
Referring to
Semiconductor device 600 may be any semiconductor device described in association with semiconductor device 500 from
However, in contrast to semiconductor device 500, semiconductor device 600 includes a graded blocking dielectric layer 604C, as depicted in
A nonvolatile charge trap memory device may be fabricated to include a multi-layer blocking dielectric region.
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In another embodiment, a nonvolatile charge trap memory device is fabricated to include a graded blocking dielectric layer.
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Thus, nonvolatile charge trap memory devices have been disclosed. The devices each include a substrate having a channel region and a pair of source and drain regions. A gate stack is above the substrate over the channel region and between the pair of source and drain regions. In accordance with an embodiment of the present invention, the gate stack includes a high dielectric constant blocking region. In one embodiment, the high dielectric constant blocking region is a bi-layer blocking dielectric region. In another embodiment, the high dielectric constant blocking region is a graded blocking dielectric layer.
Claims
1. A nonvolatile charge trap memory device, comprising:
- a substrate having a channel region, a source region and a drain region; and
- a gate stack disposed above the substrate over the channel region and between the source region and the drain region, wherein the gate stack comprises a multi-layer blocking dielectric region.
2. The nonvolatile charge trap memory device of claim 1, wherein the nonvolatile charge trap memory device is a SONOS-type device, the gate stack further comprising:
- a tunnel dielectric layer disposed above the channel region;
- a charge-trapping layer disposed above the tunnel dielectric layer and below the multi-layer blocking dielectric region; and
- a gate layer disposed above the multi-layer blocking dielectric region.
3. The nonvolatile charge trap memory device of claim 2, wherein the multi-layer blocking dielectric region is a bi-layer blocking dielectric region having a first dielectric layer disposed directly above the charge-trapping layer and a second dielectric layer disposed directly above the first dielectric layer and directly below the gate layer, and wherein the dielectric constant of the first dielectric layer is lower than the dielectric constant of the second dielectric layer.
4. The nonvolatile charge trap memory device of claim 2, wherein the multi-layer blocking dielectric region is a bi-layer blocking dielectric region having a first dielectric layer disposed directly above the charge-trapping layer and a second dielectric layer disposed directly above the first dielectric layer and directly below the gate layer, wherein the first dielectric layer has a large barrier height, and wherein the second dielectric layer has a high dielectric constant.
5. The nonvolatile charge trap memory device of claim 3, wherein the first dielectric layer of the bi-layer blocking dielectric region comprises silicon dioxide, and wherein the second dielectric layer of the bi-layer blocking dielectric region comprises a material selected from the group consisting of silicon nitride, aluminum oxide, hafnium oxide, zirconium oxide, hafnium silicate, zirconium silicate, hafnium oxy-nitride, hafnium zirconium oxide and lanthanum oxide.
6. The nonvolatile charge trap memory device of claim 3, wherein the first dielectric layer of the bi-layer blocking dielectric region comprises a material having a dielectric constant approximately in the range of 3.5-4.5, and wherein the second dielectric layer of the bi-layer blocking dielectric region comprises a material having a dielectric constant above approximately 7.
7. The nonvolatile charge trap memory device of claim 2, wherein the tunnel dielectric layer comprises a high-K dielectric portion, wherein the charge-trapping layer comprises a bi-layer silicon oxy-nitride region, and wherein the gate layer is a high work-function gate layer.
8. A nonvolatile charge trap memory device, comprising:
- a substrate having a channel region, a source region and a drain region; and
- a gate stack disposed above the substrate over the channel region and between the source region and the drain region, wherein the gate stack comprises a graded blocking dielectric layer.
9. The nonvolatile charge trap memory device of claim 8, wherein the nonvolatile charge trap memory device is a SONOS-type device, the gate stack further comprising;
- a tunnel dielectric layer disposed above the channel region;
- a charge-trapping layer disposed above the tunnel dielectric layer and below the graded blocking dielectric layer; and
- a gate layer disposed above the graded blocking dielectric layer.
10. The nonvolatile charge trap memory device of claim 9, wherein the graded blocking dielectric layer is disposed directly above the charge-trapping layer and directly below the gate layer, and wherein the dielectric constant of the graded blocking dielectric layer has a low-to-high gradient in the direction from the charge-trapping layer to the gate layer.
11. The nonvolatile charge trap memory device of claim 10, wherein the portion of the graded blocking dielectric layer directly adjacent to the charge-trapping layer consists essentially of silicon dioxide, and wherein the portion of the graded blocking dielectric layer directly adjacent to the gate layer consists essentially of silicon nitride.
12. The nonvolatile charge trap memory device of claim 10, wherein the portion of the graded blocking dielectric layer directly adjacent to the charge-trapping layer consists essentially of silicon dioxide, and wherein the portion of the graded blocking dielectric layer directly adjacent to the gate layer consists essentially of a material selected from the group consisting of aluminum oxide, hafnium oxide, zirconium oxide, hafnium silicate, zirconium silicate, hafnium oxy-nitride, hafnium zirconium oxide and lanthanum oxide.
13. The nonvolatile charge trap memory device of claim 10, wherein the portion of the graded blocking dielectric layer directly adjacent to the charge-trapping layer consists essentially of a material having a dielectric constant approximately in the range of 3.5-4.5, and wherein the portion of the graded blocking dielectric layer directly adjacent to the gate layer consists essentially of a material having a dielectric constant above approximately 7.
14. The nonvolatile charge trap memory device of claim 9, wherein the tunnel dielectric layer comprises a high-K dielectric portion, wherein the charge-trapping layer comprises a bi-layer silicon oxy-nitride region, and wherein the gate layer is a high work-function gate layer.
15. A method of fabricating a nonvolatile charge trap memory device, comprising:
- providing a substrate;
- forming a gate stack above the substrate, wherein forming the gate stack comprises: forming a tunnel dielectric layer above the substrate; forming a charge-trapping layer above the tunnel dielectric layer; forming a blocking dielectric region above the charge-trapping layer, wherein the blocking dielectric region is formed from at least two different materials; forming a gate layer above the blocking dielectric region; and patterning the tunnel dielectric layer, the charge-trapping layer, the blocking dielectric region, and the gate layer; and
- forming a source region and a drain region in the substrate and on other side of the gate stack to provide a channel region in the substrate and below the gate stack.
16. The method of claim 15, wherein forming the blocking dielectric region from at least two different materials comprises oxidizing a top portion of the charge-trapping layer and, subsequently, depositing a dielectric layer above the oxidized portion of the charge-trapping layer.
17. The method of claim 15, wherein forming the blocking dielectric region from at least two different materials comprises depositing a first dielectric layer having a first dielectric constant and, subsequently, depositing a second dielectric layer having a second dielectric constant.
18. The method of claim 17, wherein the second dielectric constant is greater than the first dielectric constant.
19. The method of claim 15, wherein the blocking dielectric region is a bi-layer blocking dielectric region having a first dielectric layer disposed directly above the charge-trapping layer and a second dielectric layer disposed directly above the first dielectric layer and directly below the gate layer, and wherein the dielectric constant of the first dielectric layer is lower than the dielectric constant of the second dielectric layer.
20. The method of claim 15, wherein the blocking dielectric region is a graded blocking dielectric layer disposed directly above the charge-trapping layer and directly below the gate layer, and wherein the dielectric constant of the graded blocking dielectric layer has a low-to-high gradient in the direction from the charge-trapping layer to the gate layer.
Type: Application
Filed: Feb 13, 2008
Publication Date: Jun 18, 2009
Inventors: Igor Polishchuk (Fremont, CA), Sagy Levy (Zichron)
Application Number: 12/030,644
International Classification: H01L 29/792 (20060101); H01L 21/336 (20060101);