CN108133955B - NMOS transistor structure and forming method thereof - Google Patents
NMOS transistor structure and forming method thereof Download PDFInfo
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- CN108133955B CN108133955B CN201810017844.5A CN201810017844A CN108133955B CN 108133955 B CN108133955 B CN 108133955B CN 201810017844 A CN201810017844 A CN 201810017844A CN 108133955 B CN108133955 B CN 108133955B
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- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/76—Unipolar devices, e.g. field effect transistors
- H01L29/772—Field effect transistors
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Abstract
The invention discloses an NMOS transistor structure and a forming method thereof, and relates to the technical field of basic electronic components. The transistor comprises a substrate, a grid structure, a channel region, a source region and a drain region, the semiconductor structure further comprises a spherical blocking device and a carbon-containing material layer located at the interface of the substrate and the channel region and the interface of the substrate and the source region and the drain region, wherein the spherical blocking device is arranged in the substrate and located below the source region, the drain region and the channel region, the spherical blocking device is a cavity or is filled with an insulating medium, and the carbon-containing material layer located below the channel region has a carbon-silicon atom weight ratio of 1: (0.7-2.4), the leakage current of the formed semiconductor structure is obviously reduced, the electrical performance is obviously improved, and the method for forming the semiconductor structure has the advantages of simple process, low cost and less introduced impurities, and can further improve the performance of the semiconductor structure.
Description
Technical Field
The present application relates to the field of semiconductors, and more particularly, to a semiconductor structure and a method of forming the same, and an NMOS transistor and a method of forming the same.
Background
In the existing semiconductor structure, with the continuous reduction of the characteristic size of the MOS device, the length of a channel is shortened, and the width is also reduced in the same proportion, so that a serious short channel effect is caused. This is because when a high voltage is applied to the drain, the source is simultaneously affected by the electric field of the drain due to the short gate, and under the influence of the electric field, the barrier of the source junction is lowered, and the depletion layer of the drain expands and even connects to the depletion region of the source junction, so that the device cannot be turned off, resulting in a large leakage current. As the channel length is further shortened, short channel effects become more pronounced, severely degrading the threshold voltage of the transistor device.
In order to solve the above technical problems, the present invention provides a structure of a MOS transistor and a method for forming the structure, and particularly, a spherical blocking device is formed in a semiconductor substrate and located below a source region, a drain region, and a channel region, so that a coupling capacitance between the source region and the drain region can be weakened, and current leakage near the spherical blocking device can be reduced, thereby achieving effective turn-off of a transistor device. When the MOS transistor device with the spherical blocking device is formed, the position of the spherical blocking device is skillfully arranged, and the etching process at each stage is selected, so that the etching accuracy can be ensured, the additional etching damage is avoided, the process is simple, the injection cost is lower, and the device performance is improved.
Disclosure of Invention
The present invention provides a semiconductor structure comprising: the semiconductor structure comprises a substrate 101, a gate structure 108, a channel region 106, and source and drain regions 107, and is characterized in that the semiconductor structure further comprises a spherical blocking device 105 and a carbon-containing material layer located at an interface between the substrate and the channel region and at an interface between the substrate and the source and drain regions, wherein the spherical blocking device is disposed in the substrate and located below the source and drain regions and the channel region, the spherical blocking device is a cavity or is filled with an insulating medium, and the carbon-containing material layer located below the channel region has a carbon-silicon atomic weight ratio of 1: (0.7-2.4).
Preferably, the insulating medium is argon, nitrogen, carbon dioxide or sulfur hexafluoride gas.
Preferably, the spherical blocking means are isolated from each other and spaced from each other by 2-15nm, and the diameter of the spherical blocking means is 5-10 nm.
Preferably, the thickness of the carbon-containing material layer is 3-15 nm.
A method of forming a semiconductor structure, comprising: providing a substrate, depositing a first hard mask on the upper surface of the substrate, forming a plurality of first etching windows by adopting a photoetching process, and etching the substrate through the first etching windows to form a plurality of first deep grooves;
partially filling a silicon nitride material in the first deep groove; filling the unfilled part of the first deep groove by a first in-situ epitaxy process; carrying out planarization, and removing the first hard mask on the upper surface of the substrate to expose the upper surface of the substrate; depositing a second hard mask on the upper surface of the substrate, forming a plurality of second etching windows by adopting a photoetching process, and etching the first deep grooves filled by the first in-situ epitaxial process through the second etching windows to form a plurality of second deep grooves, wherein the width of each second deep groove is smaller than that of each first deep groove; removing the silicon nitride material; filling the second deep groove by adopting a second in-situ epitaxial process; carrying out planarization, and removing the second hard mask on the upper surface of the substrate to expose the upper surface of the substrate; depositing a third hard mask on the upper surface of the substrate, forming a third window by adopting a photoetching process, and carrying out carbon doping on the substrate through the third window; etching the channel injection region subjected to carbon doping to form a third groove, reserving a carbon doping region with a specific thickness at the bottom of the channel region in the step, and adopting a third in-situ epitaxial process to form the channel region again; annealing treatment is carried out, carbon atoms in the carbon doping region are activated, and the carbon atoms are diffused transversely and are diffused to the bottoms of the source region and the drain region to be formed; and forming a gate structure above the channel region, and forming a source region and a drain region in the substrate at two sides of the channel region.
Preferably, the specific thickness is 3 to 15 nm.
Preferably, after removing the silicon nitride material, spherical blocking means are formed, separated from each other by a distance of 2-15nm, said spherical blocking means having a diameter of 5-10 nm.
Preferably, the spherical blocking device is a cavity or is filled with an insulating medium, and the insulating medium is argon, nitrogen, carbon dioxide or sulfur hexafluoride gas.
Preferably, after the annealing process, the carbon-silicon atomic weight ratio in the carbon-doped region at the bottom of the channel region is 1: (0.7-2.4).
Preferably, the process for removing the silicon nitride material includes isotropic etching, and the process for etching the first deep trench, the second deep trench and the third deep trench is anisotropic etching.
The spherical blocking device is introduced into the semiconductor structure, so that the coupling capacitance between a source and a drain can be effectively weakened, the current leakage near the spherical blocking device is reduced, and the transistor device is effectively turned off; the carbon-containing material layer is formed at the source region, the drain region and the interface of the channel region and the substrate, so that the stress in the MOS transistor and the diffusion of the doped ions can be improved, the doped ions are prevented from being gathered at the interface of the source region, the drain region and the substrate, the conduction current of the device can be improved, and the tunneling leakage current between the channel region and the substrate is effectively reduced; by adjusting the factors such as implantation energy, implantation time and the like of carbon ion implantation, the weight ratio of carbon to silicon atoms in the carbon-containing material layer below the channel region in the finally formed device is 1: (0.7-2.4), optimization of transistor device performance can be achieved. And when the semiconductor structure is formed, a specific etching process is adopted to form a specific groove, so that the controllability of the process result is strong, and the yield is high.
Drawings
Figure 1 schematically illustrates an NMOS transistor structure of the present invention.
Fig. 2a to 2i schematically show cross-sectional views corresponding to steps of the method for manufacturing an NMOS transistor according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more clearly understood, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
This invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It will be understood that when an element such as a layer, region or substrate is referred to as being "formed on" or "disposed on" another element, it can be directly on the other element or intervening elements may also be present.
As shown in fig. 1, the NMOS transistor structure of the present invention includes: the transistor device comprises a substrate 101, a spherical blocking device 105 located in the substrate, wherein the spherical blocking device can effectively weaken the coupling capacitance between a source and a drain, reduce the current leakage near the spherical blocking device and realize effective turn-off of the transistor device, the source region 107 and the drain region 107 are located above the spherical blocking device, a channel region 106 located between the source region 107 and the drain region 107, a carbon doped layer is formed on the interface where the source region 107 and the drain region 107 are in contact with the substrate 101 and can block diffusion of source region doping ions and drain region doping ions of the NMOS device, and the carbon doped layer is also located at the interface between the channel region 106 and the substrate 101 and is located on a gate structure 108 located above the channel region 106. To further reduce the leakage current of the transistor device, a lightly doped source/drain structure (not shown) may also be provided.
The substrate 101 may be a silicon substrate, a silicon germanium substrate, a silicon carbide substrate, a silicon-on-insulator substrate, a germanium-on-insulator substrate, a glass substrate, or
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A group compound substrate, etc.; the spherical blocking means located in the substrate may be a spherical cavity filled with argon, nitrogen, carbon dioxide or sulphur hexafluoride gas. The spherical blocking devices are arranged below the channel region, the number of the spherical blocking devices is more than or equal to two, the spherical blocking devices are mutually isolated, the interval between the spherical blocking devices is 2-15nm, the diameter of the spherical blocking devices is preferably 5-10nm, and therefore on the premise that the strength of the substrate is guaranteed, the coupling capacitance between a source and a drain can be weakened to the greatest extent possible, current leakage near the spherical blocking devices is reduced, and effective turn-off of a transistor device is achieved. The source region and the drain region can be formed by carrying out an ion implantation process on the substrate, or can be formed by forming a semiconductor layer containing silicon and/or silicon germanium materials by an in-situ epitaxial process; in one embodiment, when the source region and the drain region are formed by an epitaxial process, raised source and drain region structures can be formed, which is beneficial to improving the stress of the device. A carbon-containing material layer (such as a silicon carbide or silicon germanium carbide layer) is formed at the source region, the drain region and the interface between the channel region and the substrate, and on one hand, the carbon-containing material layer at the bottom of the source region and the drain region can improve the stress in the N-type MOS transistor and the diffusion of doped ions, so that the doped ions are prevented from being accumulated at the interface between the source region, the drain region and the substrate, and the on-state current of the device can be improved; on the other hand, the carbon-containing material layer positioned below the channel region can effectively reduce the tunneling leakage current between the channel region and the substrate. The thickness of the carbon-containing material layer is preferably 3-15nm, the weight ratio of carbon to silicon atoms in the carbon-containing material layer below the channel region is 1: 0.7-1: 2.4, and researches show that the weight ratio of carbon to silicon atoms is regulated to be in the range, so that the leakage current of the device can be further reduced, and the current-carrying current during conduction is enhancedThe mobility is preferably 107 parts by mass of carbon atoms when the mass of silicon atoms is 100 parts by mass, which enables optimization of the device performance. The measurement of the carbon to silicon atomic weight ratio was determined by X-ray diffraction (XRD) testing of the carbonaceous material layer of the device. In addition, the gate structure further comprises a side wall, a gate insulating layer, a gate cover layer and a gate electrode positioned between the gate cover layer and the gate insulating layer, wherein the gate electrode material can comprise polycrystalline silicon and/or a metal material, and is specifically arranged into a single-layer or laminated structure of the polycrystalline silicon layer and/or the metal layer; the gate insulating layer comprises a single-layer or laminated structure of silicon oxide and/or silicon nitride, in one embodiment, the gate insulating layer comprises a laminated layer of a silicon oxide layer and a silicon nitride layer which are sequentially formed on the surface of the channel region, the silicon oxide layer is in direct contact with the surface of the channel region, so that the interface characteristic can be improved, the carrier mobility of the device during conduction can be further improved, and the subsequently formed silicon nitride layer can assist the gate insulating layer to have excellent insulating characteristics. The gate sidewall and the gate cap layer may be formed simultaneously, or may be formed of two different material layers, which may be formed by selecting dielectric materials such as silicon oxide, silicon nitride, etc. known in the art.
The method of manufacturing the NMOS transistor of the present invention is described below with reference to fig. 2a to 2 i.
First, a substrate 101 is provided, which may be silicon, silicon germanium, silicon carbide, silicon-on-insulator, germanium-on-insulator, glass, or
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Group compounds, etc.; a first hard mask M1, which may be a nitride and/or oxide of silicon, is deposited on the upper surface of the substrate 101, the first hard mask M1 is patterned using a photolithography etching process to form a plurality of first etching windows, and the substrate 101 is etched using the first etching windows as a mask, which is preferably an anisotropic etching process to etch substantially perpendicular to the sidewalls of the upper surface of the substrate 101 to form the first deep trenches 102. Using anisotropyThe first deep trench 102 formed by the etching method has substantially vertical sidewalls, and the etching process is selected to precisely control the position and shape of the deep trench, so that the performance of the finally formed device is within a predictable range.
Subsequently, the first deep trench 102 is filled with a silicon nitride material 103 with a certain thickness approximately equal to the diameter of the subsequently formed ball stop device 105. After filling silicon nitride material 103, the remaining portion of first deep trench 102 is filled using an in-situ epitaxial process, which forms a material that may be silicon, silicon germanium, or silicon carbide. After filling the first deep trenches 102, removing the first hard mask M1 and other impurities on the surface of the substrate 102 to expose the upper surface of the substrate 101, depositing a second hard mask layer M2 on the upper surface of the substrate 101, the material being silicon nitride and/or silicon oxide, patterning the second hard mask M2 by a photolithography etching process to form a plurality of second etching windows, the width of the second etching windows being smaller than the width of the first etching windows, anisotropically etching the substrate 101 using the second etching windows as a mask to form a plurality of second deep trenches 104 having substantially vertical sidewalls, the second deep trenches 104 being located in the region of the first deep trenches 102, in a preferred embodiment, the central axis of the second deep trenches 104 perpendicular to the upper surface of the substrate is collinear with the central axis of the first deep trenches 102 perpendicular to the upper surface of the substrate, and thereafter, while etching the silicon nitride material 103, the shape of the formed spherical blocking device can be controlled, and the parasitic resistance and the leakage current between the source region and the drain region can be favorably regulated and controlled.
After the second deep trench 104 is formed, the silicon nitride material 103 is etched by using the second etching window as a mask by using an anisotropic etching process, and then the silicon nitride material 103 is completely removed by using an isotropic etching process to form a spherical cavity. In the embodiment, the anisotropic etching is firstly adopted to etch the groove with the same width as the second deep groove in the silicon nitride material 103, the efficiency is higher than that of removing the silicon nitride material 103 by adopting single anisotropic etching, the process time and the cost can be saved, in a better embodiment, the diameter of the spherical cavity is 5-10nm, and the interval between the spherical cavity and the silicon nitride material is 2-15 nm.
And then, in an argon atmosphere, filling the second deep groove by adopting an in-situ epitaxial growth process, wherein argon is remained in the spherical cavity at the moment, and forming the blocking device 105. In further embodiments, nitrogen, carbon dioxide or sulfur hexafluoride gas may also be used. In the embodiment, an additional cavity filling process is not needed, so that a good blocking effect can be realized, the process is simplified, the method is suitable for large-scale manufacturing of transistor devices, and the method is simplified and cleaned compared with the process of filling the solid insulating material in the cavity in the prior art.
Then, the surface of the substrate 101 is planarized again, and the second hard mask M2 and other impurities are removed to expose the upper surface of the substrate 101. In various embodiments of the present invention, the planarization process may be a chemical mechanical polishing process or a physical lapping polishing process, which are well known to those skilled in the art. In a preferred embodiment, during physical polishing, the number of grinding wheels is preferably selected within the range of 350-550, so that the roughness of the substrate surface after planarization is within the range of 8-20nm, and when source and drain regions are formed subsequently by means of ion implantation, the defect density of the surface of the source and drain regions can be reduced, thereby suppressing the contact resistance of the source and drain regions and further optimizing the performance of the transistor device.
Depositing a third hard mask M3, which may be a nitride and/or an oxide of silicon, on the upper surface of the substrate 101, patterning the third hard mask M3 by a photolithography process to form a plurality of third windows, and implanting carbon ions into the substrate 101 using the third windows as a mask to form a heavily doped region of carbon ions in the channel formation region. When the carbon ion implantation process is carried out, the implantation energy is 2 to 15kev, and the implantation time is 5 to 50 min.
Planarizing the surface of the substrate 101, removing the third hard mask M3 and other impurities to expose the upper surface of the substrate 101, depositing a fourth hard mask M4 (not shown) with a uniform thickness of 10-15nm, patterning the fourth hard mask M4 to form a fourth window, exposing the carbon doped region, etching the carbon doped region through the fourth window to form a third trench, and epitaxially filling the third trench with the same material as the substrate 101 in situ to form a channel region 106. In one embodiment, when the third trench having substantially vertical sidewalls is formed using an anisotropic etch, a carbon doped region remains at the bottom of the third trench with a thickness of 3-15 nm. In another preferred embodiment, carbon doped regions with a thickness of 3-15nm remain on the bottom and sidewalls of the third trench.
The surface of the substrate 101 is planarized to remove the fourth hard mask M4 and other impurities, thereby exposing the upper surface of the substrate 101. Thereafter, the substrate 101 is annealed, which may be rapid thermal annealing, spike annealing, or laser annealing, among other techniques well known in the art. In one embodiment, the rapid thermal annealing temperature is controlled at 900-1200 ℃ for 5-90 s. And after annealing treatment, activating carbon ions in the carbon doping region, and performing transverse diffusion on the carbon ions to the bottom of the source region and the drain region to be formed. In the invention, carbon ions exist at the interfaces of the source region, the drain region and the substrate and the interface of the channel region and the substrate, so that the diffusion of doped ions of the source region and the drain region to the substrate can be avoided, the leakage current of a device can be reduced, the lattice defect in the transistor can be reduced, and the carrier mobility in a conducting state can be improved. In one embodiment, after the annealing process, the weight ratio of carbon to silicon atoms in the carbon-doped region below the channel region is 1: 0.7-1: 2.4, and it is found through research that by defining the weight ratio of carbon to silicon atoms in the above range, the leakage current of the device can be further reduced, and the carrier mobility at the time of conduction can be enhanced, and preferably, when the mass of silicon atoms is 100 parts by mass, and the mass of carbon atoms is 107 parts by mass, the performance of the device can be optimized.
Forming a gate structure 108 on the upper surface of the channel region 106, where the gate structure 108 includes a gate insulating layer, a gate electrode, a gate cap layer and a gate sidewall, which are sequentially formed, and the gate electrode material may include polysilicon and/or a metal material, and is specifically set to be a single-layer or stacked structure of the polysilicon layer and/or the metal layer; the gate insulating layer comprises a single-layer or laminated structure of silicon oxide and/or silicon nitride, in one embodiment, the gate insulating layer comprises a laminated layer of a silicon oxide layer and a silicon nitride layer which are sequentially formed on the surface of the channel region, the silicon oxide layer is in direct contact with the surface of the channel region, so that the interface characteristic can be improved, the carrier mobility of the device during conduction can be further improved, and the subsequently formed silicon nitride layer can assist the gate insulating layer to have excellent insulating characteristics.
And finally, carrying out N-type ion doping on the substrate 101 at two sides of the grid structure by adopting an ion implantation method and taking the grid side wall as an implantation mask to form a source region and a drain region, and simultaneously carrying out carbon doping in the process of carrying out N-type ion doping so as to improve the stress of the device. In another embodiment, the substrate 101 may be further etched by using the gate sidewall spacers as a mask to form a fourth trench, and a source region and a drain region are epitaxially formed in the fourth trench in situ to form a complete transistor device. In another preferred embodiment, an atomic layer deposition method may be further used in the fourth trench to directly deposit the source and drain regions containing carbon atoms, so as to improve the formation quality of the source and drain regions.
Although the technical solutions disclosed in the present invention are as described above, the present invention is not limited thereto. Various changes and modifications may be effected by one skilled in the art without departing from the scope of the invention as defined in the claims.
Claims (6)
1. A method for forming an NMOS transistor structure comprises the following steps:
providing a substrate, depositing a first hard mask on the upper surface of the substrate, forming a plurality of first etching windows by adopting a photoetching process, and etching the substrate through the first etching windows to form a plurality of first deep grooves;
partially filling a silicon nitride material in the first deep groove;
filling the unfilled part of the first deep groove by a first in-situ epitaxy process;
carrying out planarization, and removing the first hard mask on the upper surface of the substrate to expose the upper surface of the substrate;
depositing a second hard mask on the upper surface of the substrate, forming a plurality of second etching windows by adopting a photoetching process, and etching the first deep grooves filled by the first in-situ epitaxial process through the second etching windows to form a plurality of second deep grooves, wherein the width of each second deep groove is smaller than that of each first deep groove;
removing the silicon nitride material to form a spherical cavity;
filling the second deep groove by adopting a second in-situ epitaxial growth process to form a spherical blocking device;
carrying out planarization, and removing the second hard mask on the upper surface of the substrate to expose the upper surface of the substrate;
depositing a third hard mask on the upper surface of the substrate, forming a third window by adopting a photoetching process, and carrying out carbon doping on the substrate through the third window;
etching the channel region subjected to carbon doping to form a third deep groove, reserving a carbon doping region with a specific thickness at the bottom of the channel region in the step, and adopting a third in-situ epitaxial process to form the channel region again;
annealing treatment is carried out, carbon atoms in the carbon doping region are activated, and the carbon atoms are diffused transversely and are diffused to the bottoms of the source region and the drain region to be formed;
and forming a gate structure above the channel region, and forming a source region and a drain region in the substrate at two sides of the channel region.
2. The method of forming an NMOS transistor structure of claim 1, wherein the specified thickness is 3-15 nm.
3. The method of claim 1 wherein the removal of the silicon nitride material forms spherical blocking devices separated from each other by a distance of 2-15nm, the spherical blocking devices having a diameter of 5-10 nm.
4. The method for forming the NMOS transistor structure of claim 3, wherein the spherical blocking device is a cavity or filled with an insulating medium, and the insulating medium is argon, nitrogen, carbon dioxide or sulfur hexafluoride gas.
5. The method for forming an NMOS transistor structure according to claim 1, wherein after the annealing process, the carbon-silicon atomic weight ratio in the carbon-doped region at the bottom of the channel region is 1: 0.7-1: 2.4.
6. The method of claim 1, wherein the process of removing the silicon nitride material comprises an isotropic etch, and the process of etching the first deep trench, the second deep trench, and the third deep trench is an anisotropic etch.
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