JP2001077024A - Semiconductor substrate and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent leak current or poor breakdown-strength caused by bad crystallinity which takes place in a defective crystal region by comprising an insulating film for filling a recessed defect contained in a semiconductor wafer as well as a semiconductor device formed on the surface of semiconductor wafer. SOLUTION: By a CVD method, a silicon oxide film 23, for example, is grown to the thickness equal to, or larger than, the radius of a micro pipe 22. Here, the micro pipe 22 (hole part) is filled with the silicon oxide film 23 (b). Then the silicon oxide film 23 is etched and removed from the surface side of a substrate 21, with the etching stopped when reaching the substrate 21. Thus, only the micro pipe 22 is filled with the silicon oxide film 24 (c). Ion-implanting is performed with p-type impurity before thermal-treatment annealing to form a p-type layer 25 (d). Lastly an electrode 26 is formed to provide a semiconductor element where a large joint diode is formed (d).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor substrate and a method for manufacturing the same.

[0002]

2. Description of the Related Art In the field of industrial power, high-efficiency, large-capacity energy conversion elements are required for energy saving, and power conversion devices such as inverters made of Si-based semiconductors have been used.

[0003] Recently, it has been expected to realize a conversion device using, for example, a SiC semiconductor, which can be expected to operate with higher efficiency. However, several tens to several hundreds of crystal defects called micropipes exist in a wafer. As a result, it was not possible to manufacture a large-area device on a wafer size level required as a power device.

As described above, in order to realize a high-power power converter, a wafer-sized diode is required. Here, the SiC semiconductor is expected to realize a diode with low on-resistance due to its physical characteristics such as a wide band gap.

FIG. 2 is a perspective view of a conventional general SiC semiconductor wafer.

As shown in FIG. 1, on the surface of the SiC substrate 1, there are several tens to several hundreds of through-hole-shaped defects called micropipes 2 having a diameter of several microns to ten microns and extending inwardly of the substrate 1. Exists.

Here, using such a SiC substrate, p
The problem when fabricating an n-junction diode will be described with reference to FIG.

As shown in FIG. 3, an n-type substrate 11 is ion-implanted with Mg or the like and annealed to form a p-type layer 12, and then an upper electrode 13 is formed.

Here, for example, an arrow 1 indicating the position of a defect
At the locations indicated by 4 and 16, in the ion implantation step, ions flying from above the wafer pass through the through-holes to the substrate 11.
Injection layer 15 is formed at a deep position. Even if the p-type layer is formed by diffusion, it is obvious that the impurity diffuses through the through-hole and the same problem occurs, and the pn junction diode having such an abnormal projection in the depth direction has a large current. Normal characteristics cannot be expected, such as the occurrence of leakage and no diode breakdown voltage.

Further, for example, as shown in a position indicated by an arrow 16, the electrode material falls into a hole which is a larger defect to form a recessed portion 17, which may be attached to the pn junction. At this time, the pn junction is short-circuited and does not exhibit diode characteristics.

When a pn junction type diode is formed using the SiC substrate 1, there are the following problems.

(1) First, as shown in FIG. 4A, an n-type epi layer 18 is formed on an n-type substrate 11 including a micropipe by an epitaxial growth method. At this time, a defective crystal region 19 having various crystal orientations and containing many crystal defects is formed near the micropipe. This is because the epitaxial growth depending on the crystal orientation of the side surface of the hole of the micropipe occurs, and when the epitaxial growth spreads in the lateral direction, the epitaxial growth is caused by the growth layer that epitaxially grows from the original substrate 11 surface. It is considered one.

(2) Next, as shown in FIG.
g and the like are ion-implanted and annealed to form a p-type layer 20.

Here, in the annealing step after the ion implantation, the impurities implanted in the defective crystal region 19 diffuse abnormally deeply through crystal grain boundaries and crystal defects which are present in a large amount, and are shown in FIG. Such a jagged (not flat) joint surface is formed. A diode having such an uneven junction surface causes defects such as an increase in leakage current and a low withstand voltage.

Further, as shown in FIG. 4A, even if a metal is deposited on the semiconductor to form a Schottky diode, the poor crystallinity is caused at the position of the defective crystal region 19. Leakage current and defective breakdown voltage occur, and good diode characteristics cannot be obtained.

[0016]

As described above,
When trying to fabricate a large-area diode using a substrate with a micropipe, abnormalities in bonding, drop in electrode material, etc. occur at the hole of the micropipe, and poor crystallinity occurs at the position of the defective crystal region. Due to the resulting leakage current and defective breakdown voltage, there is a problem that a diode having normal characteristics cannot be realized.

The present invention has been made to solve the above-mentioned problems, and it has been found that abnormalities in bonding, dropping of electrode material, etc. occur at positions of micropipe holes in a semiconductor substrate, and poor crystallinity occurs at positions of defective crystal regions. It is an object of the present invention to provide a semiconductor substrate and a method for manufacturing the same, which can prevent the occurrence of a leak current and a failure in breakdown voltage caused by the above.

[0018]

According to the present invention, in order to achieve the above object, there is provided a semiconductor substrate for forming a semiconductor device using a semiconductor wafer having a concave defect. And a semiconductor device formed on a surface of the semiconductor wafer.

[2] In the semiconductor substrate according to the above [1], the semiconductor device is a large-sized diode.

[3] The semiconductor substrate according to the above [1], wherein the semiconductor wafer is silicon, and the insulating film is a silicon oxide film.

[4] The semiconductor substrate according to the above [1], wherein the semiconductor wafer is SiC and the insulating film is a silicon nitride film.

[5] In a method of manufacturing a semiconductor substrate using a semiconductor wafer having a concave defect, a method of manufacturing a semiconductor substrate, comprising the steps of: forming an insulating film having a thickness enough to embed the concave defect in the semiconductor wafer having the concave defect; Forming a semiconductor device on the surface of the semiconductor wafer; forming an insulating film on the surface of the semiconductor wafer; and forming a semiconductor device on the surface of the semiconductor wafer.

[6] In a semiconductor substrate forming a semiconductor device for epitaxial growth on a semiconductor wafer containing a concave defect, an insulating film for embedding the concave defect of the semiconductor wafer containing the concave defect, and an epitaxial film on the surface of the semiconductor wafer. A semiconductor device having a layer is provided.

[7] In a method of manufacturing a semiconductor substrate for manufacturing a semiconductor device to be epitaxially grown by using a semiconductor wafer having a concave defect, an insulating film having a thickness enough to bury the concave defect in the semiconductor wafer having the concave defect. A step of forming a film, a step of removing an insulating film on the surface of the semiconductor wafer, and a step of forming a semiconductor device to be epitaxially grown on the surface of the semiconductor wafer.

[8] The method of manufacturing a semiconductor substrate according to the above [7], wherein the epitaxial growth is performed without exposing a side surface of the concave defect.

[0026]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view of a semiconductor device according to a first embodiment of the present invention, which shows a manufacturing process. In this embodiment, a large junction type diode is manufactured.

(1) First, as shown in FIG. 1A, a micropipe 22 exists in an n-type substrate 21 to be used.

(2) Then, as shown in FIG.
CVD (chemical vapor deposition)
For example, a silicon oxide film 23 is grown to a thickness equal to or larger than the radius of the micropipe 22 by an ition method. At this time, the micropipe 22 (hole) has a structure buried with the silicon oxide film 23.

(3) Next, as shown in FIG. 1C, the silicon oxide film 23 is etched from the surface side of the substrate 21 and removed, and when the silicon oxide film 23 reaches the substrate 21, the etching is stopped. Then, a structure in which only the micropipe 22 (hole) is buried with the silicon oxide film 24 is obtained.

(4) Next, as shown in FIG.
After ion implantation of the type impurity, the p-type layer 25 is formed by heat treatment annealing.

(5) Finally, as shown in FIG.
The electrode 26 is formed to obtain a semiconductor element on which a large junction diode is formed.

Thus, according to this embodiment, FIG.
As shown in (c), a defective portion (micropipe) 22 of the wafer is buried with an insulating silicon oxide film 23 (24). Therefore, in such a situation, FIG.
Even if the ion implantation is performed as shown in FIG. 3D, ions flying to the micropipe 22 (hole) are blocked by the silicon oxide film 24 filling the hole, and You cannot enter.

As a result, p formed inside the substrate 21
The bottom surface (joint) of the mold layer 25 becomes flat without being affected by the micropipe 22. Here, the silicon oxide film 24 filling the hole is thermally stable, and even if impurity ions are implanted therein, the impurities are diffused by the substrate 2.
It is very rare to reach within 1.

Here, for example, when the substrate 21 is made of SiC, it is preferable to use a silicon nitride film instead of the silicon oxide film used above. The reason is that since the densities of the SiC and the silicon nitride film are substantially the same, the implantation depth of the impurities is also substantially the same, and the bottom surface of the p-type layer 25 is flat.

Also, as shown in FIG. 1E, the electrode 26 does not fall into the micropipe, so that there is no danger of short-circuiting the pn junction.

As described above, according to the first embodiment of the present invention, a large-sized diode can be manufactured even on a wafer having a concave defect such as a micropipe.

Further, in the embodiment of the present invention, SiC
A method of fabricating a large-sized diode by embedding micropipe defects peculiar to the substrate with an insulating film to avoid abnormal junction formation and electrode dropping has been described. However, the present invention enables formation of a conductive layer and formation of an electrode irrespective of the presence of a defective portion. Therefore, it is apparent that the embodiment of the present invention can be applied even when there is a factor that hinders formation of a uniform junction and formation of a normal electrode.
Further, in this embodiment, a large junction diode of a wafer size level has been described, but it is apparent that the present invention can be applied to a field effect transistor and a bipolar transistor.

Next, a second embodiment of the present invention will be described.

FIG. 5 is a sectional view showing a semiconductor device manufacturing process according to a second embodiment of the present invention.

In this embodiment, an example of manufacturing a large junction type diode will be described.

(1) First, as shown in FIG. 5A, a micropipe 32, which is a concave defect, is present in an n-type substrate 31 to be used.

(2) Then, as shown in FIG.
CVD (chemical vapor deposition)
For example, a silicon oxide film 33 is grown to a thickness equal to or larger than the radius of the micropipe 32 by an ition method. At this time, the micropipe 32 has a structure embedded with the silicon oxide film 33.

(3) Next, as shown in FIG. 5C, the silicon oxide film 33 is removed by etching from the front surface side of the substrate 31, and the etching is stopped when the silicon oxide film 33 reaches the substrate 31. Then, a structure in which only the hole of the micropipe 32 is buried with the silicon oxide film 34 is obtained.

(4) Next, as shown in FIG.
BE (Molecular Beam Epitax)
y) method or MOCVD (metal organic c
chemical vapor deposition
An n-type epi layer 35 is formed by the n) method. At this time, the silicon oxide film 3 located at the position of the micropipe 32
6, a region 35A where epi growth is not performed and epi growth is not performed is formed as shown in the enlarged view of FIG. 6, and is formed above the epi-layer silicon oxide film 34 that has grown laterally from the peripheral SiC surface. Will be combined. That is, the epi layer 3
The thickness of 5 is set to a thickness larger than the thickness at which the epi layer 35 is bonded above the silicon oxide film 34.

(5) Next, as shown in FIG.
A p-type conductive layer 36 is formed by ion implantation of p-type impurities and p-type epi growth, and finally an electrode 37 is formed to obtain a large junction diode.

As described above, according to the second embodiment of the present invention, as shown in FIG. 5D, since the defective portion (micropipe) of the wafer is buried with the insulating film, the epitaxial growth is performed. In addition, due to the lateral growth of epi from a region other than the insulating film, a defective portion of the wafer is also covered with the epi layer.

That is, according to the present embodiment, even for a wafer containing a concave defect that is fatal to bonding or an electrode, it is possible to form an epi layer that does not include a defect caused by the defect.

As a result, it is possible to realize a large-sized diode having no defective electric characteristics due to crystal defects.

Next, a third embodiment of the present invention will be described.

In the step shown in FIG. 5C, if the silicon oxide film 33 is excessively removed by etching, the surface of the silicon oxide film 34 may be slightly dented than the substrate 31. This is because when the etching rate of the silicon oxide film 33 is higher than the etching rate of the substrate 31 in the etching method of the silicon oxide film 33 (for example, in the etching of the silicon oxide film 33, a general plasma etching method using Freon gas is used. ) Easily occur. FIG. 7 shows this part.

That is, when the side exposed portion 31A is generated,
A crystal orientation different from the surface of the substrate 31 will appear, and epi-growth with a crystal orientation different from the surface of the substrate 31 will occur, causing crystal defects.

Therefore, a method in which the side surface of the above described concave defect is not exposed will be described with reference to FIG.

(1) First, as shown in FIG. 8A, similarly to FIG. 5C of the second embodiment, a concave defect of the substrate 41 is buried with a silicon oxide film. At this time, as shown in FIG. 7, the silicon oxide film is excessively etched, and the surface of the silicon oxide film 42 is lower than the surface of the substrate 41.

(2) Then, as shown in FIG.
The substrate 41 is selectively etched until its surface is lower than the surface of the silicon oxide film 42. At this time, the substrate 41
Is SiC, for example, if dry etching is performed using chlorine gas or the like, the above-described situation can be realized because the etching rate of SiC is higher than that of a silicon oxide film.

(3) Next, as shown in FIG. 8 (c), when epitaxial growth is performed, the growth follows only the crystal orientation of the surface of the substrate 41, and the single crystal layer 43 without crystal defects is formed.
Is obtained.

As described above, according to the third embodiment of the present invention, as shown in FIG. 8A, even when the surface of the insulating film is slightly dented from the substrate surface during etching,
By etching and lowering the substrate 41 side, a single crystal plane can be exposed on the substrate 41, and as a result, an epitaxial growth layer without defects can be realized over the entire substrate.

That is, according to the present embodiment, a method is provided which can reliably perform the step of embedding the insulating film in the defective portion, which is difficult to perform strictly. A large-sized diode having good characteristics can be manufactured because no epitaxial layer can be formed.

It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0060]

As described above, according to the present invention, the following effects can be obtained.

(1) A large semiconductor device, for example, a diode can be manufactured even on a wafer including a concave defect such as a micropipe.

(2) Even for a wafer containing a concave defect which is fatal to a junction or an electrode, it is possible to form an epilayer free from defects caused by the defect.

(3) Even if the surface of the insulating film is slightly dented from the substrate surface during etching, a single crystal plane can be exposed on the substrate by etching the substrate side to lower it. As a result, a defect-free epitaxial growth layer can be realized over the entire surface of the substrate.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a manufacturing process of a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a perspective view of a conventional general SiC semiconductor wafer.

FIG. 3 is an explanatory diagram of a problem when a pn junction type diode is manufactured using a conventional SiC substrate.

FIG. 4 is an explanatory diagram of another conventional problem.

FIG. 5 is a cross-sectional view illustrating a manufacturing process of a semiconductor device according to a second embodiment of the present invention.

FIG. 6 is an enlarged sectional view of a portion A in the step of FIG. 5 (d).

FIG. 7 is a diagram showing a problem in the step of FIG. 5 (c).

FIG. 8 is a cross-sectional view illustrating a manufacturing process of a semiconductor device according to a third embodiment of the present invention.

[Explanation of symbols]

 21, 31, 41 Substrate showing n-type conductivity 22, 32 Micropipe 23, 33, 42 Silicon oxide film 24, 34 Silicon oxide film filling holes 25 p-type layer 26, 37 Electrode 31A Side exposed portion 35 n-type epi layer 35A region where epi growth is not performed 36 p-type conductive layer 43 single-crystal layer

Claims (8)

[Claims] 1. A semiconductor substrate on which a semiconductor device is formed using a semiconductor wafer having a concave defect, wherein (a) an insulating film for embedding the concave defect of the semiconductor wafer including the concave defect, and (b) the semiconductor film. A semiconductor substrate comprising a semiconductor device formed on a surface of a wafer. 2. The semiconductor substrate according to claim 1, wherein said semiconductor device is a large-sized diode. 3. The semiconductor substrate according to claim 1, wherein said semiconductor wafer is silicon, and said insulating film is a silicon oxide film. 4. The semiconductor substrate according to claim 1, wherein said semiconductor wafer is made of SiC, and said insulating film is made of a silicon nitride film. 5. A semiconductor substrate manufacturing method for manufacturing a semiconductor device using a semiconductor wafer including a concave defect,
(A) forming an insulating film having a thickness enough to embed the concave defects in a semiconductor wafer including the concave defects;
A method for manufacturing a semiconductor substrate, comprising: (b) removing an insulating film from a surface of the semiconductor wafer; and (c) forming a semiconductor device on the surface of the semiconductor wafer. 6. A semiconductor substrate for forming a semiconductor device epitaxially grown on a semiconductor wafer including a concave defect, wherein (a) an insulating film for filling the concave defect of the semiconductor wafer including the concave defect, and (b) the semiconductor film. A semiconductor substrate comprising a semiconductor device having an epitaxial layer on a surface of a wafer. 7. A method for manufacturing a semiconductor substrate for manufacturing a semiconductor device for epitaxially growing using a semiconductor wafer including a concave defect, wherein (a) a film thickness sufficient to embed the concave defect in the semiconductor wafer including the concave defect. Forming an insulating film, (b) removing the insulating film from the surface of the semiconductor wafer, and (c) forming a semiconductor device to be epitaxially grown on the surface of the semiconductor wafer. Of manufacturing a semiconductor substrate. 8. The method of manufacturing a semiconductor substrate according to claim 7, wherein the epitaxial growth is performed so as not to expose a side surface of the concave defect.