Semiconductor substrate and method for manufacturing the same

Abstract

To provide a semiconductor substrate with an antireflection coating.SOLUTION: A semiconductor substrate is provided with an antireflection coating. The semiconductor substrate is transparent to visible light. The antireflection coating is disposed on the back surface of the semiconductor substrate and includes a first coating containing metal. The antireflection coating includes a second coating disposed on the surface of the first coating. The second film does not contain metal and has a barrier property against diffusion of metal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The technology disclosed in this specification relates to a semiconductor substrate and a method for manufacturing the semiconductor substrate.

[0002] Patent Document 1 discloses a photolithography technique using a transparent compound semiconductor substrate. In this technique, a metal-containing film is formed on the back surface of the substrate as an anti-reflection film. This suppresses the reflection of sensor light and exposure light from the back surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2002-280297 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the technique of Patent Document 1, there is a risk that the wafer stage or chuck within the device may be contaminated with metal due to the metal contained in the anti-reflective film on the back surface of the substrate during the semiconductor manufacturing process. [Means for solving the problem]

[0005] The semiconductor substrate disclosed in this specification is a semiconductor substrate provided with an anti-reflective film. The semiconductor substrate is transparent to visible light. The anti-reflective film is disposed on the rear surface of the semiconductor substrate and includes a first film containing a metal. The anti-reflective film includes a second film disposed on the surface of the first film. The second film does not contain a metal and has a barrier property against diffusion of the metal.

[0006] In the above semiconductor substrate, the back surface of the semiconductor substrate can be protected by the second film having a barrier property against metal diffusion, which prevents the metal contained in the first film from diffusing during the semiconductor manufacturing process and causing metal contamination inside the device. [Brief description of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view of a semiconductor substrate 1 having an anti-reflection film 2 according to a first embodiment. [Diagram 2] 3 is a diagram illustrating the film thickness d of the intermediate film 11. FIG. [Diagram 3] 1 is a cross-sectional view of a semiconductor substrate 1 having an anti-reflection film 2a according to a second embodiment. [Figure 4] FIG. 11 is a cross-sectional view of a semiconductor substrate 1 having an antireflection film 2b according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The technical elements disclosed in this specification are listed below. Note that each of the technical elements below is useful independently.

[0009] In one example of the semiconductor substrate disclosed herein, the melting points of the first film and the second film may be 1100° C. or higher.

[0010] This configuration makes it possible to prevent the first film and the second film from being damaged during a semiconductor manufacturing process using the semiconductor substrate.

[0011] In the example semiconductor substrate disclosed in this specification, the first film may have an extinction coefficient of 2.0 or more.

[0012] According to this configuration, the light incident from the surface of the semiconductor substrate can be absorbed with high efficiency by the first film, making it possible to suppress reflection of the incident light.

[0013] In the example semiconductor substrate disclosed in the present specification, the semiconductor substrate may have a band gap energy of 4.5 eV or more. The first film may have a laminated structure of a film that absorbs visible light and a film that absorbs ultraviolet light.

[0014] A semiconductor substrate having a band gap energy of 4.5 eV or more is transparent to ultraviolet light as well. With this configuration, a film that absorbs visible light and a film that absorbs ultraviolet light are separately provided, making it possible to suppress reflection of both visible light and ultraviolet light.

[0015] In the semiconductor substrate of the example disclosed herein, the anti-reflective coating may further include a third film disposed between the rear surface of the semiconductor substrate and the first film. The third film may be free of metal and have a barrier property against diffusion of metal.

[0016] According to this configuration, the third film having a barrier property against metal diffusion can suppress the diffusion of metal contained in the first film into the semiconductor substrate, and an anti-reflection effect can be obtained at the interface between the third film and the semiconductor substrate.

[0017] In one example of the semiconductor substrate disclosed herein, the third film may be SiC. The first film may be W.

[0018] In one example of the semiconductor substrate disclosed herein, the third film may be AlN, and the first film may be Ta.

[0019] One example of a method for manufacturing a semiconductor substrate disclosed in the present specification is a method for manufacturing a semiconductor substrate having an anti-reflection film. The method includes a step of preparing a semiconductor substrate that is transparent to visible light. The method includes a first film formation step of forming a first film containing a metal on a rear surface of the semiconductor substrate. The method includes a second film formation step of forming a second film not containing a metal and having a barrier property against metal diffusion on a surface of the first film.

[0020] According to this manufacturing method, the back surface of the semiconductor substrate can be protected by the second film, which has a barrier property against metal diffusion, and thus it is possible to prevent the metal contained in the first film from diffusing during the semiconductor manufacturing process, thereby preventing metal contamination inside the device.

[0021] The method for manufacturing a semiconductor substrate as an example disclosed in the present specification may further include a third film forming step of forming a metal-free third film having a barrier property against metal diffusion on the rear surface of the semiconductor substrate before the first film forming step. In the first film forming step, the first film may be formed on the rear surface of the semiconductor substrate via the third film.

[0022] According to this manufacturing method, the third film having a barrier property against metal diffusion can suppress the diffusion of metal contained in the first film into the semiconductor substrate, and an anti-reflection effect can be obtained at the interface between the third film and the semiconductor substrate. EXAMPLES

[0023] (Structure of semiconductor substrate 1 and anti-reflection film 2) 1 shows a cross-sectional view of a semiconductor substrate 1 provided with an anti-reflection film 2. The semiconductor substrate 1 is a substrate that is transparent to visible light. Examples of such semiconductor substrates include substrates made of wide-gap semiconductors (e.g., SiC, GaN, Ga2O3). In this embodiment, the material of the semiconductor substrate 1 is GaN.

[0024] The anti-reflection film 2 is disposed over the entire back surface 1r of the semiconductor substrate 1. The anti-reflection film 2 includes an intermediate film 11, an absorbing film 12, and a protective film 13. The intermediate film 11 is disposed on the back surface 1r of the semiconductor substrate 1. In other words, the intermediate film 11 is a film disposed between the back surface 1r and the absorbing film 12. The intermediate film 11 is a film that does not contain metal and has a barrier property against metal diffusion. The absorbing film 12 is disposed on the surface of the intermediate film 11 and is a film that contains metal. The term "film that contains metal" is a concept that includes a single metal film, an alloy film, a metal nitride film, and the like. The absorbing film 12 is a film with an extinction coefficient of 2.0 or more. The protective film 13 is disposed on the surface of the absorbing film 12. The protective film 13 is a film that does not contain metal and has a barrier property against metal diffusion.

[0025] An interface IF1 is formed between the semiconductor substrate 1 and the intermediate film 11. An interface IF2 is formed between the intermediate film 11 and the absorbing film 12. An interface IF3 is formed between the absorbing film 12 and the protective film 13.

[0026] The intermediate film 11, the absorbing film 12, and the protective film 13 preferably have melting points of 1100° C. or higher. During the semiconductor manufacturing process using the semiconductor substrate 1, activation annealing of GaN is performed. This activation annealing needs to be performed at 1100° C. or higher. Therefore, by setting the melting points of the intermediate film 11, the absorbing film 12, and the protective film 13 to 1100° C. or higher, these films can be prevented from being damaged during the manufacturing process.

[0027] (Function of Interlayer 11) The intermediate film 11 has a function of suppressing reflection at the interfaces IF1 and IF2 of light incident from the surface 1s of the semiconductor substrate 1. In addition, the intermediate film 11 has a function of suppressing diffusion of metal contained in the absorbing film 12 into the semiconductor substrate 1. This will be described in detail.

[0028] When no film is disposed on the rear surface 1r of the semiconductor substrate 1 and the rear surface 1r is open to the atmosphere, light incident from the front surface 1s is reflected by the rear surface 1r. The reflectance at this time is calculated from the Fresnel equation to be 16.7%, which is a high value. On the other hand, when the intermediate film 11 is disposed on the rear surface 1r, an optical interference effect is obtained due to the refractive index difference between the semiconductor substrate 1 and the intermediate film 11. As a result, it is possible to reduce the reflectance at the interface IF1 between the semiconductor substrate 1 and the intermediate film 11 to, for example, 3% or less.

[0029] In addition, by appropriately adjusting the thickness d of the intermediate film 11, it is possible to cancel the reflected light from the interface IF2 between the intermediate film 11 and the absorbing film 12. This will be explained with reference to FIG. 2. If the refractive index of the semiconductor substrate 1 is n G , the refractive index of the intermediate film 11 is n 11 , the refractive index of the absorbing film 12 is n 12The angle of incident light passing through the semiconductor substrate 1 is denoted as θ, and the angle of the light in the intermediate film 11 is denoted as θ'. The light reflected at the interface IF1 between the semiconductor substrate 1 and the intermediate film 11 is denoted as A, and the light reflected at the interface IF2 between the intermediate film 11 and the absorbing film 12 is denoted as B. The general expressions for the optical paths L1 to L3 for an arbitrary angle θ are expressed by the following expressions (1) to (3). L1=d / cosθ'...Equation (1) L2=2×L1sinθ'...Equation (2) L3=L2×sinθ...Equation (3) Therefore, the optical path difference OD between light A and B is expressed by the following equation (4). Optical path difference OD=2×L1×n 11 -L3×n G ...Equation (4)

[0030] When the incident light is perpendicular, the angle of the incident light can be considered as 0°. In this case, the optical path difference OD is 2n 11 When the optical path difference OD satisfies the following formula (5), the lights A and B weaken each other. 2n 11 d=λ / 2×(2m+1)...Equation (5) Here, λ is the wavelength of the incident light, and m is an arbitrary number. Therefore, by adjusting the film thickness d of the intermediate film 11 so as to satisfy the formula (5), it is possible to further reduce the reflectance.

[0031] (Function of the absorption membrane 12) The absorbing film 12 is a film having an extinction coefficient of 2.0 or more. Therefore, the absorbing film 12 can efficiently absorb the incident light from the surface 1s of the semiconductor substrate 1. In addition, since the extinction coefficient is 2.0 or more, the thickness of the absorbing film 12 can be thin. In this embodiment, the thickness can be made thin to several tens of nm.

[0032] (Function of protective film 13) The protective film 13 has the function of preventing metal contained in the absorbing film 12 from contaminating the wafer stage and chuck of the semiconductor manufacturing equipment. In addition, since the absorbing film 12 contains metal, it is easily oxidized during the semiconductor manufacturing process, and the surface roughness is likely to increase. Therefore, by protecting the surface of the absorbing film 12 with the protective film 13, it is possible to prevent the surface roughness of the absorbing film 12. The flatness of the anti-reflection film 2 can be maintained. Since defocus during exposure can be suppressed, it is possible to precisely process fine patterns.

[0033] (Specific examples of intermediate film 11, absorbing film 12, and protective film 13) The following are examples of film types that can be used as the intermediate film 11. Here, n is the refractive index at a wavelength of 633 nm. AlN (n: 2.165, melting point: 2200°C), SiN (n: 2.023, melting point: 1900°C), SiC (n: 2.635, melting point: 2730°C), AlON (n: 1.791, melting point: 2150°C), SiON (n: 2.023, melting point: 1702°C), Ta2O5 (n: 2.165, melting point: 1872°C), TiN (n: 1.351, melting point: 2930°C), TiO2 (n: 2.493, melting point: 1843°C), Al2O3 (n: 1.77, melting point: 2072°C), ZrO2 (n: 2.208, melting point: 2715°C), HfO2 (n: 1.910, melting point: 2758°C).

[0034] Examples of film types that can be used as the absorbing film 12 include the following, where k is the extinction coefficient at a wavelength of 633 nm: W (n: 3.637, melting point: 3407°C, k: 2.917), Ta (n: 1.724, melting point: 2985°C, k: 2.075), Mo (n: 3.7, melting point: 3548°C, k: 3.548), TiN (n: 1.351, melting point: 2930°C, k: 2.76), Cr (n: 3.136, melting point: 1907°C, k: 3.312), Nb (n: 2.827, melting point: 2477°C, k: 2.861).

[0035] Examples of the types of films that can be used as the protective film 13 include the following. SiN (melting point: 1900°C), SiON (melting point: 1702°C), SiC (melting point: 2730°C).

[0036] The intermediate film 11, absorbing film 12, and protective film 13 listed above can be freely combined. In this embodiment, as a first combination example, "intermediate film 11: SiC, absorbing film 12: W, protective film 13: SiC" was used. In this case, the reflectance from the rear surface 1r of the semiconductor substrate 1 was 3% or less. As a second combination example, "intermediate film 11: AlN, absorbing film 12: Ta, protective film 13: SiC" was used. In this case, the reflectance from the rear surface 1r was 2% or less.

[0037] (Method of manufacturing semiconductor devices) The following describes a method for manufacturing a semiconductor device using the semiconductor substrate 1. In step S1, the semiconductor substrate 1 is prepared.

[0038] In step S2, an anti-reflection film 2 is formed on the rear surface 1r of the semiconductor substrate 1. Specifically, an intermediate film 11 is formed on the rear surface 1r of the semiconductor substrate 1. An absorbing film 12 is formed on the surface of the intermediate film 11. A protective film 13 is formed on the surface of the absorbing film 12. The intermediate film 11, the absorbing film 12, and the protective film 13 can be formed using various methods such as a PVD method or a CVD method. The anti-reflection film 2 can be formed in advance on the front surface 1s side of the semiconductor substrate 1 before a device structure is manufactured.

[0039] In step S3, a device is formed on the front surface 1s side using a known semiconductor manufacturing process. In step S4, the rear surface 1r of the semiconductor substrate 1 is ground and polished. This removes the anti-reflection film 2 and thins the semiconductor substrate 1. In step S5, a rear surface electrode is formed. This completes the semiconductor device.

[0040] (effect) During exposure when forming a pattern on the front surface 1s of the semiconductor substrate 1 using photolithography technology, sensor light from a focus sensor or the like and exposure light are incident on the front surface 1s. By forming an anti-reflection film 2 on the rear surface 1r of the semiconductor substrate 1, it is possible to suppress reflection of the sensor light and exposure light from the rear surface 1r. It is possible to suppress erroneous measurement of focus and deformation of the photoresist shape during exposure caused by reflected light. EXAMPLES

[0041] (Structure of anti-reflection film 2a) The antireflection film 2a (FIG. 3) according to Example 2 differs from the antireflection film 2 (FIG. 1) of Example 1 in that it does not have an intermediate film 11. The same reference numerals are used to designate parts common to Example 1, and description thereof will be omitted.

[0042] The absorbing film 12 is disposed on the rear surface 1r of the semiconductor substrate 1. The protective film 13 is disposed on the surface of the absorbing film 12. An interface IF2a is formed between the semiconductor substrate 1 and the absorbing film 12. An interface IF3 is formed between the absorbing film 12 and the protective film 13.

[0043] The metal contained in the absorption film 12 is a metal that does not easily diffuse into the semiconductor substrate 1. Specifically, the type of metal may be selected so that the distance the metal diffuses from the interface IF2a into the semiconductor substrate 1 during the semiconductor manufacturing process is smaller than the film thickness removed by the back grinding in the above-mentioned step S4. This prevents the metal from remaining in a device completed using the semiconductor substrate 1, and therefore prevents the device characteristics from deteriorating.

[0044] When the semiconductor substrate 1 is made of GaN, for example, a metal that is less likely to diffuse into GaN than Mg may be selected as the metal contained in the absorbing film 12.

[0045] (effect) It is possible to suppress reflected light by the two-layer structure of the absorbing film 12 and the protective film 13. Since the structure of the anti-reflection film 2a can be simplified, it is possible to reduce the number of processes. EXAMPLES

[0046] (Structure of anti-reflection film 2b) The antireflection film 2b (FIG. 4) according to Example 3 is different from the antireflection film 2 (FIG. 1) according to Example 1 in that the absorbing film 12 has a laminated structure. The same reference numerals are used to designate parts common to Example 1, and description thereof will be omitted.

[0047] The semiconductor substrate 1 is formed of a material having a band gap energy of 4.5 eV or more. In this embodiment, the semiconductor substrate 1 is Ga2O3, and the band gap is 4.5 to 4.9 eV. The absorption film 12 includes a first absorption film 12U and a second absorption film 12L. The first absorption film 12U is a film capable of absorbing visible light having a wavelength of 400 to 750 nm. The second absorption film 12L is a film capable of absorbing ultraviolet light having a wavelength of 100 to 400 nm.

[0048] (effect) When the semiconductor substrate 1 is a semiconductor (e.g., Ga2O3) having a band gap energy of 4.5 eV or more, the semiconductor substrate 1 becomes transparent to ultraviolet exposure light (e.g., i-line (365 nm)). In this case, the absorption film 12 needs to absorb both visible light (sensor light) and ultraviolet light (exposure light). The absorption film 12 of the third embodiment is provided with a first absorption film 12U capable of absorbing visible light and a second absorption film 12L capable of absorbing ultraviolet light, separately. Therefore, it is possible to suppress reflection of both visible light (sensor light) and ultraviolet light (exposure light).

[0049] Although the embodiments have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or drawings achieves multiple objectives simultaneously, and achieving one of the objectives itself has technical utility.

[0050] The absorbing film 12 is an example of a first film. The protective film 13 is an example of a second film. The intermediate film 11 is an example of a third film. [Explanation of symbols]

[0051] 1: Semiconductor substrate 1s: Front surface 1r: Back surface 2, 2a, 2b: Anti-reflection film 11: Intermediate film 12: Absorption film 13: Protective film IF1 to IF3: Interface

Claims

1. A semiconductor substrate provided with an anti-reflective coating, The semiconductor substrate has a band gap energy of 4.5 eV or more, the semiconductor substrate is transparent to visible light; The anti-reflection film is a first film disposed on a rear surface of the semiconductor substrate and including a metal; a second film disposed on a surface of the first film, the second film having a barrier property against metal diffusion; It is equipped with The first film has a laminated structure of a film that absorbs visible light and a film that absorbs ultraviolet light.

2. A semiconductor substrate provided with an anti-reflective coating, the semiconductor substrate is transparent to visible light; The anti-reflection film is a first film disposed on a rear surface of the semiconductor substrate and including a metal; a second film disposed on a surface of the first film, the second film having a barrier property against metal diffusion; a third film disposed between a rear surface of the semiconductor substrate and the first film, the third film having a barrier property against diffusion of a metal; A semiconductor substrate comprising:

3. the third film is SiC; The semiconductor substrate of claim 2 , wherein the first film is W.

4. the third film is AlN; The semiconductor substrate of claim 2 , wherein the first film is Ta.

5. 5. The semiconductor substrate according to claim 1, wherein the melting points of the first film and the second film are 1100° C. or higher.

6. The semiconductor substrate according to claim 1 , wherein the first film has an extinction coefficient of 2.0 or more.

7. A method for manufacturing a semiconductor substrate having an anti-reflective coating comprising a first film, a second film, and a third film, comprising: providing a semiconductor substrate transparent to visible light; a third film formation step of forming the third film having a barrier property against metal diffusion on a rear surface of the semiconductor substrate; a first film formation step of forming the first film containing a metal on the rear surface of the semiconductor substrate via the third film; a second film formation step of forming the second film having a barrier property against metal diffusion on a surface of the first film; A method for manufacturing a semiconductor substrate comprising the steps of:

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