JP2012178377A - METHOD FOR MANUFACTURING GaN-BASED SEMICONDUCTOR SUBSTRATE - Google Patents

Abstract

A method of manufacturing a GaN-based semiconductor substrate capable of significantly reducing the time required for surface processing and improving productivity.
In surface processing of a GaN-based semiconductor substrate, the surface of the GaN-based semiconductor substrate is mechanically polished (grinding process, lapping process), and then a chemical vapor phase is applied to the surface of the GaN-based semiconductor substrate. Etching is performed (CVE process).
Since the work-affected layer remaining on the surface of the GaN-based semiconductor substrate after the lapping process is efficiently removed by the CVE process, the time required for the surface processing of the GaN-based semiconductor substrate can be greatly shortened.
[Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a GaN-based semiconductor substrate, and particularly to a surface processing technique for a GaN-based semiconductor substrate.

Conventionally, a semiconductor device (for example, an electronic device or an optical device) obtained by epitaxially growing a nitride compound semiconductor such as GaN (hereinafter referred to as a GaN-based semiconductor) on a substrate is known. In this semiconductor device, for example, a GaN thick film is grown by hydride vapor phase epitaxy (HVPE) on an NdGaO ₃ substrate (hereinafter, NGO substrate) whose pseudo lattice constant is close to that of a GaN-based semiconductor. A GaN free-standing substrate (a substrate made of only GaN, hereinafter referred to as a GaN substrate) is used.

  In general, the GaN substrate obtained by the HVPE method is subjected to the surface processing shown in FIG. That is, the GaN substrate is subjected to a mechanical polishing process (a grinding process (step S21), a lapping process (step S22)), and a chemical mechanical polishing (CMP) process (step S23) to be used for manufacturing a semiconductor device. Is done.

Here, in the grinding process of step S21, the dimension (for example, substrate thickness) of the GaN substrate is controlled to be within a predetermined range by mechanical polishing (rough polishing) using a grindstone. At this time, since mechanical energy is applied to the GaN substrate, crystal lattice distortion called a work-affected layer occurs near the surface of the substrate.
In the lapping process of step S22, the surface roughness of the GaN substrate is improved by mechanical polishing (intermediate polishing) using finely-grained abrasive grains in stages. In the lapping process, the work-affected layer generated in the grinding process is removed, while mechanical energy is applied to the GaN substrate, so that a new work-affected layer is formed. That is, a work-affected layer with small damage remains even after the lapping process.
In the CMP process of step S23, the work-affected layer remaining after the lapping process is removed by chemical mechanical polishing (finish polishing) using ultrafine abrasive grains, and the surface roughness of the GaN substrate is further improved. In the CMP process, the mechanical polishing effect is increased by the chemical action of the ultrafine abrasive grains, so that the work-affected layer is hardly formed.

By the way, as a technique regarding the surface processing of the GaN-based semiconductor substrate, for example, there are Patent Documents 1 to 5. Patent Documents 1 and 2 disclose that a dry etching process is performed instead of or in addition to the CMP process. Patent Document 3 discloses that a dry etching process is performed between the lapping process and the CMP process. Patent Documents 4 and 5 disclose performing a dry etching process after the CMP process.
Here, the types of dry etching include a method in which a GaN substrate is exposed to a reactive gas (vapor phase etching) and a method in which gas is ionized and etched by plasma (reactive ion etching). Patent Documents 6 and 7 disclose that a reactive gas (for example, chlorine gas or hydrogen chloride gas) made of hydrogen or halogen can be applied to vapor phase etching of a GaN-based semiconductor material.

International Publication No. WO2008 / 047627 International Publication No. WO2009 / 107567 Japanese Patent No. 3252702 JP 2008-181953 A International Publication No. WO2005 / 041283 Japanese translation of PCT publication No. 2003-504835 Special table 2004-538652 gazette

However, since GaN is chemically very unstable, the effect of removing the work-affected layer due to the chemical action in the CMP process becomes very small. That is, in the conventional surface processing shown in FIG. 2, since the polishing rate in the CMP step (step S23) is slow, it takes a long time to completely remove the work-affected layer, resulting in a decrease in productivity. End up.
In addition, the techniques described in Patent Documents 1 to 7 do not introduce a vapor phase etching process for the purpose of shortening the time required for the surface processing of the GaN-based semiconductor substrate, but disclose the vapor phase disclosed therein. The etching conditions are not in line with the purpose of shortening the surface processing time.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method for manufacturing a GaN-based semiconductor substrate that can significantly reduce the time required for surface processing and improve productivity.

The invention according to claim 1 is a first step of performing mechanical polishing on the surface of the GaN-based semiconductor substrate;
And a second step of performing chemical vapor etching on the surface of the GaN-based semiconductor substrate after the first step.

  According to a second aspect of the present invention, in the method for manufacturing a GaN-based semiconductor substrate according to the first aspect, a third step of performing chemical mechanical polishing on the surface of the GaN-based semiconductor substrate after the second step is performed. It is characterized by providing.

  According to a third aspect of the present invention, in the method for manufacturing a GaN-based semiconductor substrate according to the first or second aspect, the second step is performed with an etching gas containing one or more of halogen, hydrogen, or a compound thereof. It is characterized by being.

  Invention of Claim 4 is a manufacturing method of the GaN-type semiconductor substrate as described in any one of Claim 1 to 3, The etching amount in the said 2nd process is 0.1-20 micrometers. And

  Invention of Claim 5 is a manufacturing method of the GaN-type semiconductor substrate as described in any one of Claim 1 to 4, The etching temperature in the said 2nd process is 500-1000 degreeC, It is characterized by the above-mentioned. To do.

  The invention according to claim 6 is the method for producing a GaN-based semiconductor substrate according to any one of claims 1 to 5, wherein the etching time in the second step is 1 to 600 minutes. To do.

  According to the present invention, the work-affected layer remaining after the mechanical polishing process can be efficiently removed by a chemical vapor etching (CVE) process, so that the surface processing of the GaN-based semiconductor substrate can be performed. The required time is greatly shortened. Accordingly, the productivity of the GaN-based semiconductor substrate is significantly improved.

It is a figure which shows the surface processing process which concerns on embodiment. It is a figure which shows an example of the conventional surface processing. It is a figure which shows the relationship between the etching amount and the deterioration amount of surface roughness. It is a figure which shows the relationship between etching temperature and an etching rate. It is a figure which shows the schematic of a CVE apparatus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, as an example of a GaN-based semiconductor substrate, surface processing of a GaN substrate obtained by growing a GaN thick film on an NGO substrate by HVPE will be described.

FIG. 1 is a diagram showing surface processing according to the present embodiment.
As shown in FIG. 1, first, in the grinding step (step S11), mechanical polishing (rough polishing) using a grindstone is performed on the front and back surfaces of the GaN substrate. In this grinding process, the dimensions of the GaN substrate (for example, the thickness of the GaN substrate) are controlled to be within a predetermined range. At this time, since mechanical energy is applied to the GaN substrate, a work-affected layer is formed thick in the vicinity of the substrate surface layer.

  Next, in the lapping process (step S12) after the grinding process, mechanical polishing (intermediate polishing) is performed on the GaN substrate surface using fine abrasive grains having a particle diameter smaller than that of the grindstone used in the grinding process. In this lapping process, the surface roughness of the GaN substrate is improved by mechanical polishing using fine grains of abrasive grains in stages. In the lapping process, the work-affected layer generated in the grinding process is removed, while mechanical energy is applied to the GaN substrate, so that a new work-affected layer is formed.

  Next, in the CVE process (step S13) after the mechanical polishing process, chemical vapor etching is performed on the surface of the GaN substrate. By this CVE process, the work-affected layer remaining after the lapping process can be efficiently removed. Conventionally, since the work-affected layer remaining after the lapping process is removed by the CMP process, a long time is required. However, the equivalent work-affected layer can be completely removed in a short time in the CVE process.

  Here, the chemical vapor etching is a method of chemically etching the GaN substrate surface with a reactive etching gas (for example, chlorine gas, hydrogen chloride gas) made of halogen, hydrogen, or a compound thereof. The CVE process can be performed using an apparatus (for example, an HVPE apparatus) having a configuration capable of introducing an etching gas in a state where a GaN substrate is disposed in the reaction tube.

FIG. 3 shows the relationship between the etching amount by the CVE process and the deterioration amount of the surface roughness of the GaN substrate. Here, the deterioration amount of the surface roughness of the GaN substrate is
(Surface roughness after CVE)-(Surface roughness before CVE)
Is the meaning. As shown in FIG. 3, when the etching amount in the CVE process exceeds 20 μm, the deterioration amount of the surface roughness of the GaN substrate becomes 140 nm or more and greatly deteriorates. Therefore, it takes a long time to improve the surface roughness in the CMP process. You can see that it is necessary. On the other hand, if the etching amount in the CVE process is less than 0.1 μm, there are often places where the work-affected layer remaining after the lapping process cannot be removed. As a result, the time required for the CMP process is significantly increased. Therefore, the etching amount in the CVE process is desirably 0.1 to 20 μm.
Further, in order to suppress the surface roughness, a small amount of Ga halide gas may be added in addition to the etching gas in CVE.
In order to shorten the time required for the CMP process, the surface roughness after the CVE process is desirably 100 nm or less.

  FIG. 4 shows the relationship between the etching temperature and the etching rate in the CVE process. As shown in FIG. 4, when the etching temperature in the CVE process is less than 500 ° C., the etching rate is remarkably slow, so that the time required for the CVE process becomes long. On the other hand, when the etching temperature is higher than 1000 ° C., the etching rate exceeds 400 μm / h, and the etching rate is remarkably increased, so that it is difficult to properly control the etching amount in the CVE process. Therefore, the etching temperature in the CVE process is desirably 500 to 1000 ° C.

  On the other hand, if the etching time in the CVE process is less than 1 minute, the effect of etching does not appear and the processing time in the subsequent process cannot be shortened, so that the entire processing time becomes longer. On the other hand, when the etching time exceeds 600 minutes, a thermally deteriorated layer may be formed. Since the dissociation pressure of nitrogen is extremely high in the GaN substrate, the dissociative evaporation of nitrogen occurs on the surface layer when exposed for a long time exceeding 600 minutes even in an atmosphere of about 0.1 MPa and 500 ° C., and the surface of the GaN substrate In some cases, a defect called a heat-affected layer is formed. When the heat-affected layer is formed, the surface roughness on the substrate surface increases, and the CMP time in the subsequent process increases, which not only does not meet the purpose of shortening the time required for processing, Due to the imbalance of the equimetry, the performance of the electronic device manufactured using the GaN substrate is deteriorated. Therefore, in the CVE process, it is desirable that the etching time in the CVE process is 1 to 600 minutes in order to appropriately control the etching amount within a range where productivity is not impaired.

  Next, in the CMP process (step S14) after the CVE process, chemical mechanical polishing using ultrafine abrasive grains having a finer grain size than the abrasive grains used in the lapping process (step S12) is performed on the surface of the GaN substrate (step S12). Finish polishing). In this CMP step, the mechanical polishing effect is increased by the chemical action of the ultrafine abrasive grains, so that the surface roughness is further improved without forming a work-affected layer. In addition, since the work-affected layer is almost removed in the CVE process, the CMP process may be performed to a desired surface roughness. Therefore, the time required for the CMP process is significantly shortened compared to the conventional method.

Thus, in the embodiment, mechanical polishing (the grinding process in step S11 and the lapping process in step S12) is performed on the surface of the GaN substrate, and then chemical vapor etching (CVE process) is performed on the GaN substrate. I do.
According to this method, since the work-affected layer remaining after the lapping process can be efficiently removed by the CVE process, the time required for the surface processing of the GaN substrate is greatly shortened. Therefore, the productivity of the GaN substrate is significantly improved.

  In the embodiment, since the CMP process is performed after the CVE process, the surface roughness of the GaN substrate can be further improved. Even if the surface state of the GaN substrate deteriorates after the CVE step, the desired surface state is realized by performing the CMP step.

[Example 1]
In Example 1, a GaN thick film was grown on the NGO substrate by the HVPE method, and surface processing was performed using the GaN substrate obtained by removing the NGO substrate.

First, the front and back surfaces of the GaN substrate were ground by surface grinding so that the substrate thickness was about 500 μm (grinding process).
Next, two-stage lapping was performed using fine abrasive grains having a particle diameter smaller than that of the grindstone used in the grinding process (first lapping process and second lapping process). Details of the first lapping process and the second lapping process are as follows.

(First lapping process)
Polishing equipment: LP-50 made by Logitec
Abrasive: SiC slurry Abrasive grain (SiC) average particle size: 8 μm
Plate rotation speed: 60rpm
Processing pressure: 300 g / cm ²
Abrasive flow rate: 7ml / min
Polishing time: 2 hours Polishing amount: 20 μm

(Second wrapping process)
Polishing equipment: LP-50 made by Logitec
Abrasive: Polycrystalline diamond slurry Abrasive grains (polycrystalline diamond) Average particle diameter: 1 μm
Plate rotation speed: 60rpm
Processing pressure: 300 g / cm ²
Abrasive flow rate: 4ml / min
Polishing time: 4 hours Polishing amount: 9 μm

  In the first lapping step, the GaN substrate was polished by 20 μm, and the substrate thickness became 480 μm. In the second lapping step, the GaN substrate was polished by 9 μm, and the substrate thickness was 471 μm.

Next, chemical vapor etching was performed on the surface of the GaN substrate (CVE process). A schematic diagram of the CVE apparatus is shown in FIG. Inside the cylindrical heat-resistant reaction tube 2 provided with a heater 1 for heating on the outer periphery, a susceptor 5 for placing the substrate 3 is provided, and two from one end (right side in the figure) of the reaction tube 2. The gas supply nozzle 4 is extended toward the center of the reaction tube so that the reaction gas can flow from the gas supply nozzle 4 to the substrate surface on the susceptor 5.
Details of the CVE process are as follows. In the CVE process, the etching time was adjusted so that the work-affected layer was completely removed, that is, in the case of Example 1, the GaN substrate was etched by 4 μm and the substrate thickness was 467 μm.

(CVE process)
Reaction tube: Quartz, φ94mm
Gas flow rate: hydrogen chloride 100sccm, hydrogen 1000sccm
Etching temperature: 700 ° C
Etching time: 60 minutes

  Next, chemical mechanical polishing was performed to make the surface roughness generated in the CVE process a desired surface roughness (CMP process). In general, the amount of polishing by CMP increases as the amount of etching by CVE increases. Details of the CMP process in Example 1 are as follows.

(CMP process)
Polishing equipment: LP-50 made by Logitec
Polishing pad: SUBA600 manufactured by Nitta Haas
Abrasive: Colloidal silica slurry Abrasive grains (colloidal silica) Average particle diameter: 40 nm
Plate rotation speed: 60rpm
Processing pressure: 300g / cm2
Abrasive flow rate: 30ml / min
Polishing time: 6 hours Polishing amount: 1 μm
In the surface processing (lapping process, CVE process, CMP process) in the above-described embodiment, the total polishing amount (including the etching amount) was 34 μm, and the processing time was 13 hours.

[Example 2]
In the same process as in Example 1, only the CVE process was performed under the following conditions.
(CVE process)
Gas flow rate: chlorine 100sccm, hydrogen 1000sccm
Etching temperature: 850 ° C
Etching time: 60 minutes

[Example 3]
In the same process as in Example 1, only the CVE process was performed under the following conditions.
(CVE process)
Gas flow rate: hydrogen bromide 100sccm, hydrogen 1000sccm
Etching temperature: 700 ° C
Etching time: 90 minutes

[Example 4]
In the same process as in Example 1, only the CVE process and the CMP process were performed under the following conditions.
(CVE process)
Gas flow rate: hydrogen chloride 100 sccm, hydrogen 1000 sccm, gallium chloride 1 sccm
Etching temperature: 700 ° C
Etching time: 60 minutes (CMP process)
Polishing equipment: LP-50 made by Logitec
Polishing pad: SUBA600 manufactured by Nitta Haas
Abrasive: Colloidal silica slurry Abrasive grains (colloidal silica) Average particle diameter: 40 nm
Plate rotation speed: 60rpm
Processing pressure: 300g / cm2
Abrasive flow rate: 30ml / min
Polishing time: 4 hours Polishing amount: less than 1 μm In Example 4, the surface roughness in CVE is suppressed by adding a small amount of gallium chloride gas, and the time in the CMP process for the purpose of subsequent planarization is described in Example 1. It was possible to shorten it to ~ 3.

[Comparative example]
The comparative example is different from the example in that the CVE process is not performed in the surface processing of the GaN substrate. That is, as in the example, a GaN thick film was grown on the NGO substrate by the HVPE method, and the GaN substrate obtained by removing the NGO substrate was used to perform a grinding process and a lapping process. The substrate thickness after the grinding process was about 500 μm, and the substrate thickness after the lapping process was 471 μm.

Next, chemical mechanical polishing was performed on the surface of the GaN substrate (CMP process). The details of the CMP process are almost the same as in the embodiment. In the comparative example, the polishing time was 40 hours so that the work-affected layer was completely removed, that is, the GaN substrate was polished by 4 μm and the substrate thickness was 467 μm. That is, in the comparative example, the time required for the CMP process is 6 times or more that of the example.
In the surface processing treatment (lapping step, CMP step) in the comparative example described above, the total polishing amount was 33 μm, and the processing time was 46 hours.

Table 1 shows surface processing conditions and characteristics of the GaN substrate in Examples and Comparative Examples. The XRD full width at half maximum shown in Table 1 is a relative value with reference to the XRD full width at half maximum of the GaN substrate after the lapping process, and the surface roughness Ra is a measured value at an arbitrary point in the substrate plane.
As shown in Table 1, in the example and the comparative example, the processing amount in the surface processing, the crystallinity of the obtained GaN substrate, and the surface roughness are substantially equal. That is, in the example, the processing time can be greatly shortened in realizing the same properties as the GaN substrate obtained by the surface processing according to the comparative example.

As mentioned above, although the invention made by this inventor was concretely demonstrated based on embodiment, this invention is not limited to the said embodiment, It can change in the range which does not deviate from the summary.
For example, in the embodiment, the surface processing of the GaN substrate has been described, but the present invention can also be applied to the surface processing of a GaN-based semiconductor substrate other than GaN. Here, the GaN-based semiconductor other than GaN is a compound semiconductor represented by In _x Ga _y Al _1-xy N (0 ≦ x + y ≦ 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1). InGaN, AlGaN, InGaAlN, and the like.

In the embodiment, the CMP process is performed after the CVE process. However, when the surface state of the GaN substrate after the CVE process is in a desired state, the CMP process is omitted in the surface processing. Also good.
In the embodiment, the work-affected layer is completely removed by the CVE process, but a part of the work-affected layer is removed by the CMP process (that is, after the CVE process, the work is equivalent to the polishing amount in the CMP process). The altered layer may be left). Thereby, the time required for the surface processing can be further shortened.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Claims (6)

A first step of mechanically polishing the surface of the GaN-based semiconductor substrate;
A method of manufacturing a GaN-based semiconductor substrate, comprising: a second step of performing chemical vapor etching on the surface of the GaN-based semiconductor substrate after the first step.   The method for manufacturing a GaN-based semiconductor substrate according to claim 1, further comprising a third step of performing chemical mechanical polishing on the surface of the GaN-based semiconductor substrate after the second step.   3. The method of manufacturing a GaN-based semiconductor substrate according to claim 1, wherein the second step is performed by an etching gas containing one or more of halogen, hydrogen, or a compound thereof.   The method for manufacturing a GaN-based semiconductor substrate according to any one of claims 1 to 3, wherein an etching amount in the second step is 0.1 to 20 µm.   The method for producing a GaN-based semiconductor substrate according to any one of claims 1 to 4, wherein an etching temperature in the second step is 500 to 1000 ° C.   6. The method for producing a GaN-based semiconductor substrate according to claim 1, wherein the etching time in the second step is 1 to 600 minutes.

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