Method for determining suitability of silicon substrate for epitaxy

Abstract

A method is disclosed for determining the suitability of silicon substrates for epitaxy and / or slip resistance during epitaxy and post-epitaxy thermal treatments. The method evaluates different substrates of epitaxial wafers by imaging the wafers with infrared depolarization. Infrared depolarization parameters are generated for each epitaxial wafer. By comparing the parameters, it is possible to determine which substrates are suitable for epitaxy and / or post-epitaxy thermal treatments.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 213,457, filed June 22, 2021, which is incorporated by reference in its entirety. [Technical field]

[0002] The field of the disclosure relates to methods for determining the suitability of silicon substrates for epitaxy, and in particular, to methods for determining slip resistance during epitaxy and post-epitaxy thermal treatments. [Background technology]

[0003] Slip frequently occurs during epitaxial wafer fabrication and during post-epitaxy thermal cycling. Slip resistance has become an increasingly important performance in advanced integrated circuit manufacturing technologies. Traditional methods for detecting slip resistance are processes that destroy the wafer, and the wafer cannot be preserved for use. For example, the wafer may be stressed in an annealing furnace and the wafer bow may be measured as an indicator of wafer strength. Furthermore, traditional processes do not allow the evaluation of slip resistance for different epitaxial substrates under different epitaxial and post-epitaxy treatments.

[0004] There is a need for a reliable, non-destructive process that can quantitatively evaluate and compare the slip resistance of different substrates under different epitaxial processes and thermal treatments.

[0005] This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and / or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. As such, it should be understood that these statements are to be read in this light, and not as admissions of prior art. Summary of the Invention

[0006] One aspect of the present disclosure is directed to a method of determining suitability of a silicon substrate for epitaxy. A first silicon substrate is placed on a susceptor disposed within a processing reactor. A front side of the first silicon substrate is contacted with a silicon-containing gas. The silicon-containing gas decomposes to form an epitaxial silicon layer on the first silicon substrate to form a first epitaxial wafer. The first epitaxial wafer is imaged by infrared depolarization and a first infrared depolarization parameter is determined. A second silicon substrate is placed on a susceptor disposed within a processing reactor. The second silicon substrate has a different composition than the first silicon substrate. A front side of the second silicon substrate is contacted with a silicon-containing gas. The silicon-containing gas decomposes to form an epitaxial silicon layer on the second silicon substrate to form a second epitaxial wafer. The second epitaxial wafer is imaged by infrared depolarization and a second infrared depolarization parameter is determined. The suitability of the first and second substrates for epitaxy is determined based on the first and second infrared depolarization parameters.

[0007] Yet another aspect of the present disclosure is directed to a method of determining suitability of a silicon substrate for epitaxy. The silicon substrate is placed on a susceptor disposed within a processing reactor. The front side of the silicon substrate is contacted with a silicon-containing gas. The silicon-containing gas decomposes to form an epitaxial silicon layer on the silicon substrate to form an epitaxial wafer. Only an annular edge region of the epitaxial wafer is imaged by infrared depolarization and an infrared depolarization parameter is determined.

[0008] Various refinements exist in the features described in relation to the above-mentioned aspects of the present disclosure. Further features may also be incorporated into the above-mentioned aspects of the present disclosure. These refinements and additional features may exist individually or in any combination. For example, the various features described below in relation to any of the illustrated embodiments of the present disclosure may be incorporated alone or in any combination into any of the above-mentioned aspects of the present disclosure. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of a semiconductor substrate for manufacturing an epitaxial wafer. [Diagram 2] FIG. 2 is a cross-sectional view of an epitaxial wafer. [Diagram 3] FIG. 3 is a flow chart of one embodiment of a method for determining the suitability of a silicon substrate for epitaxy. [Figure 4] FIG. 4 is a flow chart of another embodiment of a method for determining the suitability of a silicon substrate for epitaxy. [Diagram 5] FIG. 5 is a perspective view of a processing reactor for depositing epitaxial layers on a substrate with the reactor cover removed. [Figure 6] FIG. 6 is a schematic diagram of an apparatus for imaging an epitaxial wafer by infrared depolarization. [Figure 7] FIG. 7 is a top view of an epitaxial wafer showing the annular edge ring imaged with infrared depolarization. [Figure 8] FIG. 8 is a variation plot showing the depolarization of various epitaxial wafers during imaging.

[0010] Corresponding reference characters indicate corresponding parts throughout the drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Provisions of the present disclosure relate to methods for determining suitability of silicon substrates for epitaxy, such as by measuring the slip resistance of the substrate during deposition of epitaxial layers and / or post-epitaxy thermal treatment. In some embodiments, the composition of the substrate material is varied and the resulting epitaxial wafers are imaged by infrared depolarization. The imaging results in one or more infrared depolarization parameters for each imaged wafer. The parameters can be used to determine the suitability of the silicon substrate for epitaxy (e.g., slip resistance).

[0012] Referring now to FIG. 1, there is shown a substrate 1 used in making an epitaxial wafer 20 (FIG. 2). The substrate 1 may be a monocrystalline silicon wafer, such as a wafer produced by the so-called Czochralski process. The substrate 1 has a front side 3 and a back side 9. The substrate 1, which is tested for suitability for use in epitaxial wafers and post-epitaxy processing (e.g., slip resistance), may have variable impurity concentrations (e.g., nitrogen or oxygen) and / or variable dopant concentrations (e.g., boron), as described further below.

[0013] Once a wafer 1 is selected (e.g., first step 100 (FIG. 3)), the wafer 1 is processed (e.g., sliced ​​from an ingot, followed by various steps of smoothing and / or reducing surface roughness). In a second step 200, an epitaxial layer 25 is deposited on the front side 3 (FIG. 1) of the substrate 1 by contacting the front side 3 with a silicon-containing gas that decomposes to form an epitaxial silicon layer 25 on the substrate 1. In general, unless otherwise stated, any method available to one skilled in the art for depositing a silicon epitaxial layer on a silicon substrate can be used. For example, the epitaxial layer 25 can be deposited in an exemplary processing reactor 110 shown in FIG. 5. The reactor 110 includes a processing chamber 102 in which a single semiconductor is etched. A gas manifold 140 is used to direct incoming gases into the processing chamber 102. The incoming process gases flow through the gas manifold 140 into the processing chamber 102 and are exhausted through a gas exhaust port. The reactor 110 includes a susceptor 120 disposed within the process chamber 102 to support the substrate 1. A preheat ring 126 surrounds the susceptor 120 and raises the temperature of the process gases before contacting the substrate 1. The substrate 1 is rotated and an epitaxial layer is uniformly deposited on the substrate 1.

[0014] Silicon may be deposited by epitaxy to any suitable thickness depending on the device application. For example, silicon may be deposited using metalorganic chemical vapor deposition (MOCVD), physical vapor deposition (PVD), chemical vapor deposition (CVD), low pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD), atmospheric pressure chemical vapor deposition (APCVD), reduced pressure chemical vapor deposition (RPCVD), or molecular beam epitaxy (MBE). Silicon precursors (i.e., silicon-containing gases) for LPCVD or PECVD include methylsilane, silicon tetrahydride (silane), trisilane, disilane, pentasilane, neopentasilane, tetrasilane, dichlorosilane (SiH 2 Cl 2 ), trichlorosilane (SiHCl 3 ), silicon tetrachloride (SiCl 4), etc. For example, silane (SiH 4 Silicon can be deposited by pyrolyzing SiO 2 ) at a temperature range of about 550° C. to about 690° C., such as about 580° C. to about 650° C. The chamber pressure is in the range of about 70 to about 400 mTorr.

[0015] In some embodiments, a boron-containing gas is introduced into the reactor 110 to dope the epitaxial layer with boron. 2 H 6 can be added to the deposition gas. B in the atmosphere used to obtain the desired properties (e.g., resistivity) 2 H 6 The mole fraction of depends on several factors, such as the amount of boron efflux from a particular substrate during epitaxial deposition, the amount of p-type and n-type dopants present as contaminants in the reactor and substrate, and the pressure and temperature of the reactor.

[0016] Once epitaxial layer 25 is deposited, epitaxial wafer 20 (sometimes referred to herein as the "first" epitaxial wafer) may be imaged by infrared depolarization to determine infrared depolarization parameters of wafer 20 (step 300 shown in FIG. 3). Epitaxial wafer 20 may be imaged directly after deposition of the layers, or one or more post-epitaxial processes (e.g., cleaning) may be performed. Infrared depolarization imaging may be performed with a commercially available inspection tool, such as a Scanning Infrared Depolarization (SIRD) system available from PVA TePla America, Inc. (Corona, Calif.) or a PSI system available from Semilab Semiconductor Physics Laboratory Co. (Ltd.) (Budapest, Hungary).

[0017] An example of an apparatus 200 for imaging an epitaxial wafer 20 is shown in Figure 6. A laser 230 transmits light through a polarizer 240. Linearly polarized light (e.g., wavelength approximately 1.3 μm) is transmitted approximately perpendicular to the surface of the wafer 20. The apparatus 200 shown directs light through the backside of the wafer 20, although in other embodiments, the apparatus 200 directs light through the frontside. The wafer 20 rotates as it is scanned.

[0018] The analyzer 250 measures the linear state of the light passing through the wafer 20. The analyzer 250 measures the power of the parallel (P||) and perpendicular (P⊥) electromagnetic field components by means of diodes 255, 257. Without being bound to a particular theory, it is believed that the stress field residing in the wafer 20 changes the polarization state through stress-induced birefringence. The depolarization is believed to be linearly correlated with the local stress in the volume through which the laser light passes.

[0019] Depolarization can be measured as follows: TIFF2024523480000002.tif783Depolarization (D) is a dimensionless value that ranges from 0 to 2. As Depolarization (D) approaches zero, little birefringence is observed, indicating no stress in the imaged wafer region. As Depolarization (D) approaches 1, circular polarization is present. As Depolarization (D) approaches 2, it indicates half plate (full shift in polarization). Depolarization (D) can be expressed in Depolarization Units (DU), where DU=10-6*D. In some embodiments, global stress defined by Depolarization Contrast (DC) may be used: TIFF2024523480000003.tif983 In some embodiments, the equivalent shear stress (G) can be determined (see pages 33-39 of the PVA TePla SIRD User Manual (2007) - the User Manual is incorporated herein by reference for all relevant consistent purposes).

[0020] Depolarization can be measured in "tracks" of the scanned surface, with each track having a number of "track points" within the track where depolarization is measured (see PVA TePla SIRD User Manual (2007), p. 32, incorporated herein by reference). An average can be established for each track, and the percentage of track points that deviate from the average (i.e., "failure rate") can be recorded. The failure rate of a track point may be based on a minimum deviation from the average depolarization of the track (±20% of the mean, or ±30%, ±40%, or ±50% of the mean). Resolution can be adjusted by changing the number of track points measured within a track, and by the spacing of the tracks.

[0021] 7, in some embodiments of the present disclosure, only the annular edge region 302 of the epitaxial wafer 20 is imaged by infrared depolarization to determine infrared depolarization parameters. For example, the annular edge region 302 may extend from at least about 85% of the radius R of the epitaxial wafer 20 toward the periphery 315. In other embodiments, the annular edge region 302 may extend from at least about 90% or at least about 95% of the radius R of the epitaxial wafer toward the periphery 315. The annular edge region 302 may terminate short of the periphery 315 or edge 315. For example, the annular edge region may extend to 99.5% of the radius R or to 99.9% of the radius R. In other embodiments, rather than imaging the wafer 20 only at the annular edge region, the entire wafer is imaged (optionally without imaging the edge exclusion region).

[0022] The infrared depolarization parameter of the wafer 20 can generally be any parameter based on the characterization of the imaging of the wafer (step 400 of FIG. 4). For example, the infrared depolarization parameter can be a wafer map (e.g., an image of the wafer showing defects, stress points, failure rate track points, or other characteristics of the scan). Alternatively or additionally, the parameter can be related to the "failure rate" of the track points (e.g., failure rate variation chart, failure rate average, or failure rate total). Or, alternatively or additionally, the parameter can be related to the depolarization value (e.g., depolarization value average or depolarization value total), depolarization contrast, or shear stress equivalent value.

[0023] Once the infrared depolarization parameter has been determined, the suitability of the substrate for use in epitaxy can be determined, e.g., the parameter can be compared to a threshold parameter and / or it can be determined whether the parameter is within a threshold range.

[0024] In some embodiments of the present disclosure, two or more epitaxial wafers are imaged by infrared depolarization and their respective infrared depolarization parameters are compared to determine the suitability of the epitaxial wafers (and in particular their substrates) for epitaxy (e.g., strength and / or slip resistance, and optionally after downstream thermal processing). For example, a first and a second epitaxial wafer can be imaged and their infrared depolarization parameters compared to determine which substrate is suitable for epitaxy. A first silicon substrate is placed on a susceptor 120 (FIG. 5) disposed within a processing reactor 110. A silicon-containing gas is contacted on the front side of the first silicon substrate, which decomposes to form an epitaxial silicon layer on the first silicon substrate, forming a first epitaxial wafer. The first epitaxial wafer is imaged by infrared depolarization and a first infrared depolarization parameter is determined.

[0025] A second silicon substrate is placed on a susceptor 120 (FIG. 5) also disposed within the process reactor 110. The second silicon substrate has a different composition than the first silicon substrate. A silicon-containing gas is contacted to the front side of the second silicon substrate, and the silicon-containing gas decomposes to form an epitaxial silicon layer on the second silicon substrate to form a second epitaxial wafer. The second epitaxial wafer is imaged by infrared depolarization and a second infrared depolarization parameter is determined.

[0026] According to an embodiment of the present disclosure, the suitability of the first and second substrates for epitaxy may be determined based on the first and second infrared depolarization parameters. For example, the first and second infrared depolarization parameters may be compared to determine whether the first and / or second silicon substrates are suitable for epitaxy. Alternatively or additionally, the first and second infrared depolarization parameters may be compared to a threshold parameter (e.g., a parameter for which the slip resistance of the substrate is known to be acceptable). Such a threshold parameter may be determined by determining an infrared depolarization parameter of a substrate known or found to have acceptable slip resistance in epitaxy. According to an embodiment of the present disclosure, the first and second infrared depolarization parameters are the same parameter.

[0027] As mentioned above, the substrates of the first and second epitaxial wafers may have different compositions (e.g., slip resistance) to determine the type of substrate suitable for epitaxy. For example, the first and second silicon substrates may have different impurity or dopant concentrations. For example, the first and second silicon substrates may have different concentrations of oxygen, oxygen precipitates, nitrogen, carbon, boron, or other dopants. The desired concentration of oxygen, oxygen precipitates, nitrogen, carbon, and / or boron or other dopants may be varied by controlling the Czochralski process, which pulls the ingot from which the substrates are sliced, from the silicon melt.

[0028] In some embodiments, three, four, five or more epitaxial wafers are imaged by infrared depolarization with each substrate having a different composition. The infrared depolarization parameters of the wafers are compared to determine which substrate is suitable for epitaxy (e.g., slip resistance). In embodiments where two or more epitaxial wafers are imaged, epitaxial silicon layers can be formed on each silicon substrate at the same process conditions (e.g., process time and temperature). Using the same or similar process conditions reduces the effect of process conditions on slip performance when comparing wafers.

[0029] 4, in some embodiments, after the epitaxial layers are deposited in step 200, the wafer may undergo a thermal treatment step 250 before imaging 300 (e.g., if multiple wafers are being imaged, both wafers are thermally treated to the same conditions). The thermal treatment step 250 may mimic a thermal treatment used during downstream device fabrication. For example, the thermal treatment may be to 1150° C. for 6 hours or more.

[0030] Compared to conventional methods of determining the suitability of silicon substrates for epitaxy, the disclosed method has several advantages. The method allows for quantitative evaluation and comparison of slip performance in different epitaxy processes and post-epitaxy thermal treatments when evaluating various types of substrates. The characterization process is consistent for each wafer tested. Because the method is non-destructive, the inspected wafers can be used commercially after imaging and characterization. In embodiments where only the edge region of the semiconductor structure is imaged, the epitaxial wafer can be scanned relatively quickly and / or a sharper resolution can be used without increasing the imaging time. The imaging of the edge region is representative of the wafer strength, since it has been found that the high temperature epitaxy process thermally shocks the internal stress field that is primarily present at the wafer edge. Infrared depolarization is characterized by its ability to detect internal stresses unlike other methods (e.g., surface scanning and XRT) and its higher sensitivity than other methods. Conventional methods (e.g., XRT) can only produce wafer maps, which are not quantitative.

[0031] [Example] The processes of the present disclosure are further illustrated by the following examples, which should not be construed in a limiting sense. Example 1: Infrared Depolarized Wafer Imaging to Determine Slip Resistance

[0032] Epitaxial wafers (300 mm) were imaged with infrared depolarized light (~1.3 μm) on a SIRD instrument (PVA TePla America, Inc., Corona, CA). The substrate of each epitaxial wafer was doped with boron. An annular edge region of each wafer was scanned from 144 mm to 149 mm (0.96% to 99.3% of the radius).

[0033] Epitaxial wafer C is p + The doping level is boron doped, and the other wafer is p - The doping levels were boron doped. Wafers A, B, and D were not nitrogen doped, and wafers E through I were nitrogen doped.

[0034] The wafer variation chart (40DU) showing the depolarization values ​​is shown in Figure 8. As shown in Figure 8, Wafer C had the least variation and the lowest average depolarization.

[0035] These results can be confirmed from the raw data in Table 1 (40 DU for all samples on wafers A-I): TIFF2024523480000004.tif88134 Table 1: Infrared depolarized imaging characteristics of different epitaxial wafers

[0036] As used herein, the terms "about," "substantially," "essentially," and "approximately," when used in conjunction with a range of dimensions, concentrations, temperatures, or other physical or chemical properties or characteristics, are meant to encompass the variation that may exist at the upper and / or lower limits of the range of the property or characteristic, including the variation due to, for example, rounding, measurement method, or other statistical variation.

[0037] When introducing elements of the disclosure or embodiments thereof, the articles "an," "the," and "said" are intended to mean that there are one or more elements. The terms "comprising," "including," "containing," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. The use of specific directional terms (e.g., "top," "bottom," "side," etc.) is for convenience of description and does not require a specific orientation of the items described.

[0038] Because various changes may be made in the above structures and methods without departing from the scope of the disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

Claims

1. A method for determining the compatibility of a silicon substrate with respect to epitaxy, comprising: placing a first silicon substrate on a susceptor disposed in a processing reactor; contacting a silicon-containing gas with the front surface of the first silicon substrate, decomposing the silicon-containing gas to form an epitaxial silicon layer on the first silicon substrate, and forming a first epitaxial wafer; imaging the first epitaxial wafer by infrared depolarization to determine a first infrared depolarization parameter; placing a second silicon substrate on the susceptor disposed in the processing reactor, the second silicon substrate having a composition different from that of the first silicon substrate; contacting a silicon-containing gas with the front surface of the second silicon substrate, decomposing the silicon-containing gas to form an epitaxial silicon layer on the second silicon substrate, and forming a second epitaxial wafer; imaging the second epitaxial wafer by infrared depolarization to determine a second infrared depolarization parameter; and determining the compatibility of the first silicon substrate and the second silicon substrate based on the first and second infrared depolarization parameters. A method.

2. Determining the compatibility of the first silicon substrate and the second silicon substrate with respect to epitaxy includes comparing the first infrared depolarization parameter and the second infrared depolarization parameter. The method according to claim 1.

3. The first infrared depolarization parameter and the second infrared depolarization parameter are the same parameter. The method according to claim 2.

4. Determining the compatibility of the first silicon substrate and the second silicon substrate with respect to epitaxy includes determining the slip resistance of the substrate. The method according to claim 1.

5. The first infrared depolarization parameter and the second infrared depolarization parameter are each selected from a wafer map, a defect rate variation chart, an average defect rate, a total defect rate, an average depolarization value, a total depolarization value, a depolarization contrast, and a shear stress equivalent value. The method according to claim 1.

6. The first infrared depolarization parameter and the second infrared depolarization parameter are related to the depolarization value. The method according to claim 1.

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13. The first silicon substrate and the second silicon substrate have different impurity or dopant concentrations. The method according to claim 1.

8. The first silicon substrate and the second silicon substrate have different concentrations of oxygen, nitrogen, carbon, or boron. The method according to claim 1.

9. Heat-treating the first epitaxial wafer before imaging the first epitaxial wafer, and further comprising heat-treating the second epitaxial wafer before imaging the second epitaxial wafer. The method according to claim 1.

10. Forming the epitaxial silicon layer on the first silicon substrate to form the first epitaxial wafer under the same process conditions as forming the epitaxial silicon layer on the second silicon substrate to form the second epitaxial wafer. The method according to claim 1.

11. Only the annular edge regions of the first and second epitaxial wafers are imaged. The method according to claim 1.

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