Method for treating a semiconductor film to reduce evaporation and degradation

Abstract

A method for protecting a semiconductor film composed of one or more layers during processing. The method includes directly contacting the surface of the semiconductor film with the surface of a protective cover (such as a separate substrate piece), the protective cover forming an airtight or hermetic seal with the surface of the semiconductor film in order to reduce material degradation and evaporation in the semiconductor film. The method includes processing the semiconductor film under some conditions such as thermal annealing and / or controlled environment, the conditions that may cause evaporation or degradation of the semiconductor film in the absence of the protective cover.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of the following co-pending and co-assigned applications under 35 USC § 119(e):

[0003] U.S. Provisional Application Serial No. 62 / 796,340, filed on Jan. 24, 2019, by Christian J. Zollner, Michael Iza, James S. Speck, Shuji Nakamura, and Steven P. Denbaars, entitled "METHOD FOR THERMAL TREATMENT OF SEMICONDUCTOR LAYERS WITH REDUCED EVAPORATION", Attorney Docket No. G&C30794.0663USP2 (UC 2018-252-2);

[0004] This application is incorporated herein by reference. BACKGROUND OF THE INVENTION 1. Field of the Invention

[0006] The present invention relates to a method for processing semiconductor film samples by covering the samples with a separate protective cover to prevent evaporation or degradation of the semiconductor film.

[0007] 2. Description of the Related Art

[0008] The use of gallium nitride (GaN) and its ternary and quaternary compounds containing aluminum and indium (AlGaN, InGaN, AlInGaN) has been well established for the fabrication of visible and ultraviolet optoelectronic devices and high-power electronic devices. These devices typically use growth techniques including molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), and hydride vapor phase epitaxy (HVPE) for epitaxial growth.

[0009] In addition, the development of AlGaN for short-wavelength devices has enabled nitride-based light-emitting diodes (LEDs) and laser diodes (LDs) to outperform many other research efforts. Thus, AlGaN-based materials and devices have become the primary material system for ultraviolet semiconductor applications.

[0010] However, the growth of high-quality AlN and AlGaN with high aluminum content remains a challenge. These materials, as well as all other group III nitride semiconductor materials, can be improved by various processing techniques, but there is typically a risk of film evaporation or degradation during these processing steps. By using a separate protective cover to protect the film, film evaporation or degradation can be reduced. Summary of the Invention

[0011] The present invention discloses a method for treating a semiconductor film to reduce evaporation or degradation. The method includes: providing a protective cover on or above the surface of the semiconductor film to prevent the semiconductor film from evaporating or degrading during processing; and processing the semiconductor film and the protective cover under one or more conditions that would cause the semiconductor film to evaporate or degrade in the absence of the protective cover, wherein the semiconductor film is processed to improve or change the material or device characteristics of the semiconductor film; and wherein the protective cover is a chemically inert material under the conditions for processing the semiconductor film.

[0012] The semiconductor film is grown on a substrate and includes one or more nitride base layers, wherein the nitride base layer includes (Al, Ga, In, B)N semiconductors, and the nitride base layer is grown on a polar plane, a non-polar plane, or a semi-polar plane.

[0013] The protective cover has an epitaxial-ready surface that forms an airtight or sealed contact with the surface of the semiconductor film, wherein the protective cover forms a direct contact with the semiconductor film. Preferably, the thickness of the protective cover is at least 10 micrometers. The protective cover is removed after processing the semiconductor film without any rinsing, cleaning, or chemical or physical etching procedures.

[0014] The conditions for processing the semiconductor film and the protective cover may include high-temperature thermal annealing of heating the semiconductor film and the protective cover to a high temperature of at least about 1000 °C (e.g., about 1000 °C to 2500 °C). The conditions for processing the semiconductor film and the protective cover may also include exposing the semiconductor film and the protective cover to a controlled environment of a semiconductor processing gas, wherein the semiconductor processing gas includes nitrogen, argon, ammonia, hydrogen, oxygen, or a synthesis gas. The semiconductor film and the protective cover may be exposed to the semiconductor processing gas at a pressure of less than about 100 atmospheres, e.g., less than about 1 atmosphere.

[0015] Finally, the protective cover includes silicon carbide (SiC), sapphire (Al2O3), aluminum nitride (AlN), gallium nitride (GaN), or spinel (MgAl2O4). Brief Description of the Drawings

[0016] Reference is now made to the drawings, where like reference numerals throughout represent corresponding parts:

[0017] Figure 1 is a flow chart of the process steps used in an embodiment of the present invention.

[0018] Figure 2Shows an X-ray diffraction data graph of a semiconductor layer including an aluminum nitride (AlN) layer, the semiconductor layer being epitaxially deposited on a substrate including 6H-polytype silicon carbide (6H-SiC), having a protective cover separating the SiC substrate wafer to prevent material evaporation.

[0019] Figure 3(a) And 3(b) Are optical images of two samples at high temperature, showing the difference between the protected (non-evaporated) sample and the unprotected (fully evaporated) sample. Detailed Description

[0020] In the following description of the preferred embodiments, reference is made to the drawings that form a part of the embodiments, and in which specific embodiments in which the invention may be practiced are shown by way of illustration. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention.

[0021] Overview

[0022] The present invention describes a method for protecting a sample including a semiconductor film, the protection being carried out by directly contacting (i.e., covering) the film with a protective cover (such as a separated substrate wafer) during a sample processing step. The sample processing step refers to processing the semiconductor film under some conditions, such as high-temperature thermal annealing and / or exposure to some semiconductor processing gases and / or a controlled environment of low-pressure atmosphere, etc., which may cause the film to evaporate or degrade without the protective cover, with the aim of improving or changing the material or device characteristics of the film.

[0023] Protecting the semiconductor film by covering the film with a protective cover provides a method for preventing the film from evaporating or degrading by forming an airtight or sealed state between the two atomically flat surfaces of the film and the protective cover during the sample processing step. This protection provides greater flexibility for exposing the sample to conditions or processes that may typically cause evaporation or degradation of the film.

[0024] The sample processing step may include heating the semiconductor film and the protective cover to a high temperature greater than about 1000 °C, more preferably about 1000 °C to 2500 °C. Temperatures above 2500 °C can be used, but typically require specialized equipment and processes and are thus impractical for most applications.

[0025] The sample processing step may further include exposing the semiconductor film and the protective cover to one or more semiconductor processing gases, such as nitrogen, argon, ammonia, hydrogen, oxygen, synthesis gas, or some other processing gas, and / or exposing to a low-pressure atmosphere of less than about 100 atmospheres, more preferably about 1 atmosphere or less. In addition, the sample processing step may include other harsh conditions, such as corrosive chemicals including hydrogen.

[0026] In one embodiment, the semiconductor film includes one or more nitride base layers grown on a substrate. The term "nitride base layer" or "Group III nitride" or "nitride" refers to any alloy composition of (Al, Ga, In, B)N semiconductors having the chemical formula Al w Ga x In y B z N, where:

[0027] 0 ≤ w ≤ 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and w + x + y + z = 1.

[0028] The nitride base layer may include multiple layers with different or gradient compositions, one or more layers with similar (Al, Ga, In, B)N compositions, or one or more layers with dissimilar (Al, Ga, In, B)N compositions. These layers may also be doped with elements such as silicon, germanium, magnesium, boron, iron, oxygen, and zinc.

[0029] The nitride base layer can be grown using deposition methods including: conventional chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), sputtering, atomic layer deposition (ALD), evaporation in a vacuum or controlled environment, ion beam deposition (IBD), hydride vapor phase epitaxy (HVPE), metalorganic chemical vapor deposition (MOCVD), or molecular beam epitaxy (MBE).

[0030] The nitride base layer can be grown in any crystal direction, such as on the polar c-plane or on non-polar planes such as the a-plane or m-plane, or on semi-polar planes such as the {20-21}, {11-22}, and {10-11} planes.

[0031] The nitride base layer can form a radiation-emitting layer sequence. The radiation-emitting layer sequence can include LEDs and LDs.

[0032] When processed using the method of the present invention, the nitride base layer can have improved or altered material or device characteristics.

[0033] A protective cover (such as a separate substrate sheet) may include silicon carbide (SiC), sapphire (Al2O3), aluminum nitride (AlN), gallium nitride (GaN), spinel ((MgAl)2O4), or any other commonly used substrate material. Preferably, the protective cover is inert under the conditions of the sample processing steps, which is in contrast to techniques that only reduce decomposition under short-term, relatively "mild" conditions (without harsh chemicals or low pressure), for example, it does not completely stop decomposition but only slows down the rate.

[0034] Regardless of the material type of the film or protective cover, the growth method, or the processing or storage conditions, the mechanism of semiconductor film protection should apply. However, the degree of protection and the reduction of material loss or degradation will vary depending on the material, growth method, and processing or storage conditions.

[0035] Process steps

[0036] Figure 1 is a flowchart of the process steps used in an embodiment of the present invention.

[0037] Block 100 represents the step of growing at least one semiconductor film on a substrate using, for example, a conventional method. In one embodiment, the semiconductor film includes one or more nitride base layers.

[0038] Block 102 represents the step of providing a protective cover on or above the surface of the semiconductor film to prevent the semiconductor film from evaporating or degrading during processing. In one embodiment, the protective cover is a chemically inert material under the conditions of processing the semiconductor film; the epitaxial-ready surface of the protective cover forms an airtight or sealed connection with the surface of the semiconductor film; the protective cover forms direct contact with the semiconductor film; and the thickness of the protective cover is at least 10 micrometers.

[0039] Block 104 represents the step of processing the substrate, semiconductor film, and protective cover under one or more conditions that would cause the semiconductor film without the protective cover to evaporate or degrade. The conditions may include high-temperature thermal annealing and / or a controlled environment. High-temperature thermal annealing heats the substrate, semiconductor film, and protective cover to at least about 1000 °C, for example, a high temperature of about 1000 °C to 2500 °C. The controlled environment exposes the substrate, semiconductor film, and protective cover to a semiconductor processing gas, where the semiconductor processing gas includes nitrogen, argon, ammonia, hydrogen, oxygen, or a synthesis gas. The substrate, semiconductor film, and protective cover may be exposed to the semiconductor processing gas at a pressure less than about 100 atmospheres, for example, about 1 atmosphere or lower.

[0040] Block 106 represents the step of removing the protective cover from the semiconductor film after processing without any rinsing, cleaning, or chemical or physical etching procedures.

[0041] Block 108 represents steps for continuing the further growth, processing, encapsulation, etc. of the semiconductor film.

[0042] Block 110 represents the final result of the method, i.e., the processed semiconductor film, which can be part of a semiconductor film stack composed of multiple films or layers. In one embodiment, the processed semiconductor film has improved or altered material or device characteristics compared to a semiconductor film not so processed.

[0043] Finally, note that steps 100 - 108 do not need to be performed in the exact order shown. For example, the steps can be performed in other orders and / or individual steps can be omitted without departing from the scope of the present invention.

[0044] Experimental results

[0045] Figure 2 A graph showing X-ray diffraction data of a semiconductor film including an aluminum nitride (AlN) layer, the data including the relationship between the full width at half maximum (FWHM) of the (102) X-ray rocking curve (ω) and the annealing conditions, where the semiconductor film is epitaxially deposited on a substrate comprising 6H polytype silicon carbide (6H-SiC). A protective cover including separated SiC substrate wafers is placed on the semiconductor layer, and then the entire sample including the AlN layer, the 6H-SiC substrate, and the separated SiC substrate wafers is annealed at various temperatures, 1600 °C for 4 hours, 1700 °C for 1 hour in an argon (Ar) environment, 1800 °C for 1 hour in an argon environment, and 1800 °C for 4 hours in an argon environment.

[0046] Known X-ray diffraction data is a quality factor for crystal quality to track the threading dislocation density. For example, a value of FWHM = 500 corresponds to 5E9 cm -2 , whereas a value of FWHM = 190 corresponds to 4E8 cm -2 , as confirmed by unpublished TEM (transmission electron microscopy) data.

[0047] As shown, when high-temperature annealing treatment is employed, the crystal quality of the AlN layer grown on 6H-SiC and protected by separated SiC substrate wafers to prevent material evaporation is significantly improved. Specifically, the covered samples show material improvement, while the uncovered samples are completely evaporated regardless of the processing conditions.

[0048] Figure 3(a) and 3(b)Is an optical image of two identical AlN / SiC wafers processed at 1650 °C for 4 hours in an argon (Ar) environment at 0.6 atmospheres, showing the difference between the protected (unevaporated) AlN / SiC sample in Fig. 3(a) and the unprotected (fully evaporated) AlN / SiC sample in Fig. 3(b), from the same epitaxial wafers through the same annealing treatment.

[0049] Specifically, for comparison, Fig. 3(a) shows the surface of an AlN epitaxial layer under annealing conditions with a protective SiC cover. Fig. 3(b) shows the surface of an AlN epitaxial layer subjected to the same annealing conditions without a protective SiC cover. The protected AlN epitaxial layer in Fig. 3(a) shows reduced material degradation and evaporation due to protection by the separated substrate piece, while the unprotected AlN epitaxial layer in Fig. 3(b) has completely evaporated. Specifically, the sample in Fig. 3(a) is protected with a protective SiC cover and almost all of the film remains (the thickness measured using optical reflectivity shows little change), while the sample in Fig. 3(b) is annealed under the same conditions without a protective SiC cover and the film has significantly evaporated (no X-ray peak of AlN was found for this sample).

[0050] Advantages and improvements

[0051] The present invention provides a protective cover for a semiconductor film to ensure prevention of material evaporation or degradation during processing, such as through high-temperature thermal annealing and / or exposure to a controlled environment of semiconductor processing gases and / or low-pressure atmosphere. The present invention provides an airtight or sealed direct contact between the semiconductor film and the protective cover. The main advantage of such protection is that the semiconductor layer can be processed using, for example, high-temperature thermal annealing and / or a controlled environment, which improves the material or device characteristics of the film while preventing evaporation or degradation of the film.

[0052] Conclusion

[0053] The foregoing is a description of the preferred embodiments of the present invention. The foregoing description of one or more embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teachings. The scope of the invention is not intended to be limited by this detailed description, but rather by the appended claims.

Claims

1. A method, comprising: (a) growing a semiconductor film on or above a silicon carbide (SiC) substrate, the semiconductor film comprising an aluminum-containing nitride base layer; (b) placing a protective cover on the surface of the semiconductor film, the protective cover comprising a separated piece of the SiC substrate, wherein the surface of the protective cover forms a seal with the surface of the semiconductor film to prevent evaporation or degradation of the semiconductor film during processing; and (c) processing the SiC substrate, the semiconductor film, and the protective cover under one or more conditions that would cause the semiconductor film to evaporate or degrade in the absence of the protective cover; (d) wherein the semiconductor film is processed under the one or more conditions to change the material or properties of the semiconductor film; and (e) wherein the protective cover is a chemically inert material under the conditions for processing the semiconductor film.

2. The method according to claim 1, wherein, The nitride base layer is grown on a polar plane, a non-polar plane, or a semi-polar plane.

3. The method according to claim 1, wherein The epitaxy-ready surface of the surface of the protective cover forms a seal with the surface of the semiconductor film.

4. The method according to claim 1, wherein The protective cover forms direct contact with the semiconductor film.

5. The method according to claim 1, wherein The protective cover has a thickness of at least 10 micrometers.

6. The method according to claim 1, wherein The protective cover is removed after the processing without any chemical or physical etching procedures.

7. The method according to claim 1, wherein The protective cover is removed after the processing without any rinsing or cleaning procedures.

8. The method according to claim 1, wherein the conditions include high-temperature thermal annealing that heats the semiconductor film and the protective cover to a high temperature of at least 1000 °C.

9. The method according to claim 8, wherein, The high temperature is from 1000 °C to 2500 °C.

10. The method according to claim 1, wherein The conditions include exposing the semiconductor film and the protective cover to a controlled environment of a semiconductor processing gas.

11. The method according to claim 10, wherein, The semiconductor processing gas includes nitrogen, argon, ammonia, hydrogen, oxygen, or a synthesis gas.

12. The method according to claim 10, wherein, The semiconductor film and the protective cover are exposed to the semiconductor processing gas at a pressure of less than 100 atmospheres.

13. The method according to claim 12, wherein, The pressure is less than 1 atmosphere.

14. The method according to claim 1, wherein, The surface of the protective cover that forms the seal with the surface of the semiconductor film is atomically flat.

15. The method according to any one of claims 1 to 14, wherein, The seal is an airtight seal.

16. A semiconductor film processed by the method of claim 1.

17. A structure, comprising: (a) a semiconductor film, comprising an aluminum-containing nitride base layer, grown on or above a silicon carbide (SiC) substrate; (b) a protective cover, comprising a separated piece of the SiC substrate, placed on the surface of the semiconductor film to prevent evaporation or degradation of the semiconductor film during processing; (c) wherein the surface of the protective cover forms a seal with the surface of the semiconductor film; (d) wherein the protective cover is a chemically inert material under the conditions for processing the semiconductor film.

18. The structure according to claim 17, wherein, The epitaxy-ready surface of the surface of the protective cover forms the seal with the surface of the semiconductor film.

19. The structure according to claim 17, wherein, The surface of the protective cover that forms the seal with the surface of the semiconductor film is atomically flat.

20. The structure according to any one of claims 17 to 19, wherein, The seal is an airtight seal.

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