Doped Poly-Silicon for PolyCMP Planarity Improvement
A method includes forming a polysilicon layer with an uneven upper surface over a first region and a second region of a substrate, doping a top portion of the polysilicon layer to change its removal rate, thereby forming a doped layer, and removing the doped layer in the first region to expose the polysilicon layer in the first region and leaving at least a portion of the doped layer in the second region. The method also includes removing the exposed polysilicon layer in the first region at a first removal rate and the doped layer in the second region at a second removal rate, the polysilicon layer in the second region being exposed after the doped layer in the second region is removed, and removing the polysilicon layer in the first region and the second region at a third removal rate and a fourth removal rate, respectively.
The semiconductor integrated circuit (IC) industry has experienced rapid growth. Over the course of this growth, functional density of the devices has generally increased while the device feature size or geometry has decreased. This scaling down process generally provides benefits by increasing production efficiency, lowering costs, and/or improving performance. Such scaling down has also increased the complexities of processing and manufacturing ICs and, for these advances to be realized similar developments in IC fabrication are needed.
Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.
Semiconductor ICs include devices such as transistors, capacitors, resistors, and inductors that are formed in or on the substrate of an IC using lithography and patterning techniques. These semiconductor devices are inter-connected according to the design of the IC to implement different functions. In a typical IC, the silicon area is divided into many regions for different functions. Due to the nature of different designs entailed by the different functions, some functional regions have a higher pattern density than other regions. For example, a region of the IC used for static random access memory (SRAM) may have a higher pattern density than a region for a logic function. The difference in pattern density may cause an undesirable “loading effect.” For example, a polysilicon layer formed on the substrate may be thicker in regions with high pattern density than regions with low pattern density. The unevenness, or topography, of the polysilicon layer may adversely affect the IC manufacturing process.
For illustration purposes, the present disclosure is described using a Fin Field-Effect Transistor (FinFET) device as an example. However, methods disclosed in the present disclosure are generic and are not limited to FinFET devices. One skilled in the art will appreciate from the descriptions below that methods in the present disclosure are applicable to planar devices as well. The use of FinFET device in the discussion below should not limit the scope of the current disclosure. In addition, processing steps described hereafter are for illustration purpose only and should not unduly limit the scope of the current disclosure. It is to be understood that the described processing steps may be modified, the order of processing steps may be altered, some processing steps may be deleted, and more processing steps may be added. These and other modifications are fully intended to be included in the scope of the current disclosure.
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In accordance with some embodiments, region 100 has a higher pattern density than region 200. Region 100 might correspond to a SRAM region in the IC, and region 200 might correspond to a logic region, a peripheral region, a standard-cell region, or other region with lower pattern density in the IC than region 100. Regions 300 and 400 may correspond to regions without a fin structure, thus having even lower pattern densities than region 200, for example. In addition, fins 104 in region 100 may have a height different from that of fins 104 in region 200, possibly due to different amount of etching when forming fins 104 in different regions. Despite the different fin heights, the top surfaces 104T of all fins 104 (see
In accordance with some embodiments, semiconductor device 700 is provided during fabrication and gate structure 160 is a sacrificial gate structure such as formed in a replacement gate process used to form a metal gate structure. In an embodiment, gate structure 160 includes polysilicon. In another embodiment, gate structure 160 includes a metal gate structure.
Semiconductor device 700 may include other layers and/or features not specifically illustrated including additional source/drain regions, interlayer dielectric (ILD) layers, contacts, interconnects, and/or other suitable features.
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Substrate 102 may be a silicon substrate. Alternatively, substrate 102 may comprise another elementary semiconductor, such as germanium; a compound semiconductor including silicon carbide, gallium arsenic, gallium phosphide, indium phosphide, indium arsenide, and/or indium antimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof. In some embodiments, substrate 102 is a semiconductor on insulator (SOI) substrate.
In some embodiments, fins 104 may be formed in substrate 102 by etching trenches in substrate 102. The etching may be any suitable etch process, such as a reactive ion etch (RIE), neutral beam etch (NBE), the like, or a combination thereof. The etching may be anisotropic. The amount of etching may be different for fins 104 of FinFET device 500 and fins 104 of FinFET device 600, such that fins 104 in region 100 and region 200 have different heights, e.g., an upper surface 102a of substrate 102 is not level with an upper surface 102b of substrate 102.
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The pattern density difference between different regions of semiconductor device 700 (e.g., regions 100, 200, 300 and 400) causes a loading effect. As illustrated in
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In an exemplary embodiment of the current disclosure, the formation of the top layer 110 includes implanting carbon in the top portion of polysilicon layer 108 with a doping concentration, or dosage, from about 1E14/cm2 to about 1E17/cm2. A doping energy of about 1 Key may be used for the implantation of carbon. In another embodiment, the formation of the top layer 110 includes implanting boron in the top portion of polysilicon layer 108 with a dosage between about 1E14/cm2 to about 1E15/cm2. A doping energy between about 0.5 Key to about 100 Key, e.g., about 1 Key, may be used for the implantation of boron. Ion implantation devices, such as devices manufactured by Varian Company, Palo Alto, Calif., and Applied Materials, Inc. may be used.
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Since the lower portions of doped layer 110 protect underlying portions of polysilicon layer 108 from the CMP process, polysilicon layer 108 in the low pattern density regions (e.g., regions 300 and 400) are removed at a slower removal rate than polysilicon layer 108 in the high pattern density regions (e.g., regions 100 and 200) in the processing of
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Polysilicon gate structures 116 may also include a work function layer (not shown) tuned to have a proper work function for enhanced performance of FinFET devices 500 and 600. In some embodiments, polysilicon gate structures 116 comprises a work function layer over a gate dielectric layer, and a polysilicon layer (e.g., polysilicon layer 108) over the work function layer, such that the work function layer is disposed between the polysilicon layer and the gate dielectric layer. The work function layer may include, e.g., Ta, TiAl, TiAlN, TaCN, combination thereof, or multiplayers thereof, for n-type field effect transistors; or TiN, TaN, combination thereof, or multilayers thereof, for p-type field effect transistors.
It should be noted that the number of polysilicon stacks 116 is not limited by that shown in
In accordance with some embodiments of the present disclosure, gate spacers (not shown) are formed over sidewalls of polysilicon stacks 116 to define source/drain regions 120 on fins 104. The gate spacers are typically formed by blanket depositing a spacer layer (not shown) on the previously formed semiconductor structure 700. In an embodiment, the gate spacers may include a spacer liner (not shown) comprising SiN, SiC, SiGe, oxynitride, oxide, combinations thereof, or the like. The spacer layer may comprise SiN, oxynitride, SiC, SiON, oxide, combinations thereof, or the like and may be formed by methods utilized to form such a layer, such as CVD, plasma enhanced CVD, sputter, and other methods known in the art. The gate spacers are then patterned, for example, by anisotropically etching to remove the spacer layer from the horizontal surfaces of semiconductor structure 700.
After gate spacers are formed, source/drain regions 120 are formed in fins 104. In some embodiments, source/drain regions 120 may be doped by performing an implanting process to implant appropriate dopants to complement the dopants in fin 104. In other embodiments, an epitaxy (epi) process is performed to form source/drain regions 120 within fins 104. The source/drain regions 120 may be implemented by performing an etching process to form recess regions in fins 104 and then performing an epitaxy (epi) process to deposit a semiconductor material in the recess regions. The etching process may be a plasma dry etching processing. The epitaxy process may include CVD deposition techniques (e.g., vapor-phase epitaxy (VPE) and/or ultra-high vacuum CVD (UHV-CVD)), molecular beam epitaxy, and/or other suitable processes. The epitaxy process may use gaseous and/or liquid precursors, which interact with the composition (e.g., silicon) of the substrate. The semiconductor material may include Si, SiP, SiC, SiCP, a combination thereof, or any other suitable semiconductor material.
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After ESL 130 is formed, ILD 140 may be deposited over ESL 130 and fills the space between polysilicon stacks 116. In some embodiments, ILD 140 comprises a dielectric material, such as silicon oxide, silicon nitride, silicon oxynitride, TEOS formed oxide, phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), low-k dielectric material, other suitable dielectric material, and/or combinations thereof. ILD 140 may be formed by CVD, ALD, PECVD, subatmospheric CVD (SACVD), flowable CVD, a high density plasma (HDP), a spin-on-dielectric process, the like, or a combination thereof.
In accordance with some embodiments, gate dielectric material 150 may include silicon oxide, silicon nitride, silicon oxy-nitride, or high-k dielectrics. Examples of gate dielectric material 150 and the formation methods of gate dielectric material 150 are similar to those of the dummy gate dielectric material discussed above, thus not repeated here.
In embodiments of the present disclosure, the gate electrode layer may comprise a single-layer or multilayer structure. In embodiments, the gate electrode layer comprises poly-silicon. Further, the gate electrode layer may be doped poly-silicon with the uniform or non-uniform doping. In other embodiments, the gate electrode layer comprises a metal selected from a group of W, Cu, Ti, Ag, Al, TiAl, TiAlN, TaC, TaCN, TaSiN, Mn, and Zr. In other embodiments, the gate electrode layer comprises a metal selected from a group of TiN, WN, TaN, and Ru. The gate electrode layer may be formed by a suitable process such as ALD, CVD, PVD, plating, or combinations thereof.
It should be noted that
The present disclosure has many advantages. By providing a planar upper surface for polysilicon layer 108 after the CMP process, equal gate heights can be achieved across all regions of the IC chip regardless of pattern densities. Equal gate heights are beneficial for IC chip performance, by making it easier to provide uniform RC delay and uniform accessing speed across all gates. During IC manufacturing process, multiple layers may be formed on top of polysilicon layer 108, which multiple layers may need to have uniform thickness and planar surface. A polysilicon layer 108 with a planar upper surface provides a flat base for forming other layers on top of it, which enables further processing such as CMP to achieve the desired uniform thickness and planar surface for the other layers. Lithography techniques are frequently used in IC manufacturing. Planar surfaces for layers above polysilicon layer 108, enabled by the current disclosure, are crucial for achieving desired accuracy in lithography. In a gate-last process, the sacrificial polysilicon stacks are removed and replaced by metal gate stacks. Equal polysilicon gate heights help to ensure the success of the gate replacement procedure. For example, when a planarization process is used to remove ESL and expose a top surface of the sacrificial polysilicon stacks, un-equal polysilicon gate heights may cause the planarization process to stop after removing ESL of a higher polysilicon stack and leaving residues of ESL on top of a lower polysilicon stack. The residual ESL may cause failure of the gate replacement procedure for the lower polysilicon stack. In contrast, an equal gate height will ensure that ESL on top of all the sacrificial polysilicon stacks are sufficiently removed, so the subsequent polysilicon stacks removal and replacement procedure can finish properly.
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In accordance with an embodiment, a method of manufacturing a semiconductor device includes forming a polysilicon layer over a first region and a second region of a substrate, the first region having a higher pattern density than the second region, the polysilicon layer having an uneven upper surface. The method also includes doping a top portion of the polysilicon layer, the doping changing the removal rate of the top portion, the top portion forming a doped layer after the doping. The method further includes removing the doped layer in the first region and leaving at least a portion of the doped layer in the second region. The removing the doped layer in the first region exposes the polysilicon layer in the first region. The method further includes removing the exposed polysilicon layer in the first region at a first removal rate and the doped layer in the second region at a second removal rate. The polysilicon layer in the second region is exposed after the doped layer in the second region is removed. The method further includes removing the polysilicon layer in the first region and the second region at a third removal rate and a fourth removal rate, respectively.
In another embodiment, a method of forming a Fin Field-Effect Transistor (FinFET) includes forming a first fin and a second fin in a first region and a second region of a substrate, respectively, forming isolation structures on opposing sides of each of the first and the second fins, and depositing a polysilicon layer over the substrate, the first and second fins, and the isolation structures, the polysilicon layer having an uneven upper surface. The method also includes treating a top portion of the polysilicon layer to form a reverse layer, the reverse layer having a removal rate slower than that of the polysilicon layer, and performing a planarization process. The planarization process includes removing a first region of the reverse layer to expose a first portion of the polysilicon layer while leaving a second region of the reverse layer covering a second portion of the polysilicon layer, removing the second region of the reverse layer at a first removal rate, and the exposed first portion of the polysilicon layer at a second removal rate, and after the second region of the reverse layer is removed and the second portion of the polysilicon layer is exposed, removing the first and the second portions of the polysilicon layer at a third removal rate and a fourth removal rate, respectively.
In yet another embodiment, a method of forming a semiconductor device includes providing a substrate with a first pattern density in a first region of the substrate and a second pattern density in a second region of the substrate, the second pattern density being different from the first pattern density, forming a polysilicon layer over the substrate, the polysilicon layer having an uneven upper surface, and implanting carbon in a top portion of the polysilicon layer to reduce the removal rate of the top portion, thereby forming a doped layer. The method also includes performing a planarization process. The planarization process includes breaking-through a first portion of the doped layer to expose a first portion of the polysilicon layer and leaving a second portion of the polysilicon layer covered by a second portion of the doped layer, removing the first portion of the polysilicon layer at a first removal rate, and the second portion of the doped layer at a second removal rate smaller than the first removal rate, until the second portion of the polysilicon layer is exposed, and removing the first portion of the polysilicon layer at a third removal rate, and the second portion of the polysilicon layer at a fourth removal rate larger than the third removal rate. The method further includes stopping the planarization process once the first and the second portions of the polysilicon layer have a coplanar upper surface.
While the invention has been described by way of example and in terms of the embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
Claims
1. A method of manufacturing a semiconductor device, the method comprising:
- forming a polysilicon layer over a first region and a second region of a substrate, the first region having a higher pattern density than the second region, the polysilicon layer having an uneven upper surface;
- doping a top portion of the polysilicon layer, the doping changing a removal rate of the top portion, the top portion forming a doped layer after the doping;
- removing the doped layer in the first region and leaving at least a portion of the doped layer in the second region, wherein the removing the doped layer in the first region exposes the polysilicon layer in the first region;
- removing the exposed polysilicon layer in the first region at a first removal rate and the doped layer in the second region at a second removal rate, wherein the polysilicon layer in the second region is exposed after the doped layer in the second region is removed; and
- removing the polysilicon layer in the first region and the second region at a third removal rate and a fourth removal rate, respectively.
2. The method of claim 1, wherein the doping reduces the removal rate of the top portion of the polysilicon layer.
3. The method of claim 1, wherein the doping is performed using carbon or boron as a dopant.
4. The method of claim 3, wherein the dopant is carbon with a doping concentration from about 1E14/cm2 to about 1E17/cm2.
5. The method of claim 3, wherein the dopant is boron with a doping concentration from about 1E14/cm2 to about 1E15/cm2.
6. The method of claim 3, wherein a thickness of the doped layer is in a range from about 50 Angstrom (Å) to about 200 Å.
7. The method of claim 1, wherein the first removal rate is greater than the second removal rate.
8. The method of claim 1, wherein the third removal rate is less than the fourth removal rate.
9. The method of claim 1 further comprising:
- stopping the removing the polysilicon layer in the first region and the second region upon detecting that upper surfaces of the polysilicon layer in the first and the second regions are substantially level with each other.
10. The method of claim 9 further comprising:
- after the stopping, patterning the polysilicon layer to form a first gate structure in the first region and a second gate structure in the second region, the first gate structure and the second gate structure having substantially equal gate heights.
11. The method of claim 10 further comprising replacing the first and the second gate structures with replacement gates in a gate-last process.
12. The method of claim 11, wherein the gate-last process comprises:
- forming an etch stop layer (ESL) and an inter-layer dielectric (ILD) layer over the substrate, the first gate structure, and the second gate structure;
- exposing top surfaces of the first gate structure and the second gate structure;
- removing the first gate structure and the second gate structure to form trenches; and
- forming a gate dielectric layer and a gate electrode layer in the respective trenches.
13.-20. (canceled)
21. A method of manufacturing a semiconductor device, the method comprising:
- depositing a polysilicon layer over a substrate, the substrate having a first region with a first pattern density that is larger than a second pattern density of a second region of the substrate, the polysilicon layer having an uneven upper surface;
- doping a top portion of the polysilicon layer to form a doped polysilicon layer over an undoped polysilicon layer, the doped polysilicon layer having a removal rate slower than that of the undoped polysilicon layer below the doped polysilicon layer;
- removing a first region of the doped polysilicon layer to expose a first portion of the undoped polysilicon layer while leaving a second region of the doped polysilicon layer covering a second portion of the undoped polysilicon layer;
- removing the exposed first portion of the undoped polysilicon layer at a first removal rate and the second region of the doped polysilicon layer at a second removal rate until the second portion of the undoped polysilicon layer is exposed; and
- removing the first and the second portions of the undoped polysilicon layer at a third removal rate and a fourth removal rate, respectively.
22. The method of claim 21, wherein the first removal rate is larger than the second removal rate.
23. The method of claim 22, wherein the third removal rate is smaller than the fourth removal rate.
24. The method of claim 21, further comprising stopping the removing the first and the second portions of the undoped polysilicon layer upon detecting that the first and the second portions of the undoped polysilicon layer have a coplanar upper surface.
25. The method of claim 21, further comprising, before depositing the polysilicon layer:
- forming a first plurality of fins and a second plurality of fins in the first region and the second region of the substrate, respectively; and
- forming isolation structures on opposing sides of the first plurality of fins and on opposing sides of the second plurality of fins, wherein the polysilicon layer is deposited over the first plurality of fins and over the second plurality of fins.
26. The method of claim 21, wherein the doping comprises doping the top portion of the polysilicon layer with carbon or boron.
27. The method of claim 21, further comprising monitoring a torque of a chemical mechanical planarization tool used for removal of the polysilicon layer to detect an end point for the removal of the polysilicon layer.
28. A method of manufacturing a semiconductor device, the method comprising:
- forming a polysilicon layer over a substrate, the polysilicon layer having an uneven upper surface, the substrate has a first pattern density in a first region of the substrate and a second pattern density in a second region of the substrate, the second pattern density being smaller than the first pattern density;
- doping the polysilicon layer with carbon or boron to form a first polysilicon layer over a second polysilicon layer, the first polysilicon layer having a higher dopant concentration of carbon or boron than the second polysilicon layer;
- removing a first portion of the first polysilicon layer to expose a first portion of the second polysilicon layer and leaving a second portion of the second polysilicon layer covered by a second portion of the first polysilicon layer;
- removing the first portion of the second polysilicon layer at a first removal rate and the second portion of the first polysilicon layer at a second removal rate smaller than the first removal rate until the second portion of the second polysilicon layer is exposed; and
- removing the first portion of the second polysilicon layer at a third removal rate and the second portion of the second polysilicon layer at a fourth removal rate larger than the third removal rate; and
- stopping removal of the second polysilicon layer once the first and the second portions of the second polysilicon layer have a coplanar upper surface.
Type: Application
Filed: Jul 1, 2016
Publication Date: Jan 4, 2018
Inventors: William Weilun Hong (Hsin-Chu), Po-Chin Nien (Taipei City), Ying-Tsung Chen (Hsin-Chu)
Application Number: 15/200,966