JP3173106B2 - Method of forming epitaxial wafer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an epitaxial wafer for forming a semiconductor device.

[0002]

2. Description of the Related Art An epitaxial wafer for forming a device sensitive to a crystal defect such as a CCD device is subjected to a gettering process on a semiconductor substrate in advance, and thereafter, an epitaxial layer is deposited on the semiconductor substrate. I do. In the epitaxial wafer thus formed, crystal defects generated during epitaxial growth and heavy metals taken in during epitaxial growth are taken into gettering sites during epitaxial growth. For this reason, since the crystal of the epitaxial layer has a high quality, a device can be formed on the epitaxial layer.

As the gettering process, for example, intrinsic gettering has been proposed. In intrinsic gettering, for example, a silicon substrate for a CCD element generated by the Czochralski method is heat-treated to precipitate oxygen in the silicon substrate. Then, a crystal defect is generated in the silicon substrate, and the generated crystal defect, precipitate, or the like is used as a gettering site to perform gettering. Or extrinsic gettering has been proposed. Extrinsic gettering is performed by forming a highly stressed film such as polycrystalline silicon on the back surface of the substrate, causing a strain field generated at the interface between the film and the substrate, and a transition or crystal generated by a subsequent annealing process. In this method, gettering is performed using a defect or the like as a gettering site.

[0004]

However, in the epitaxial wafer subjected to the intrinsic gettering or the extrinsic gettering, it is not possible to sufficiently remove the transition and the crystal defect in the epitaxial layer in which the device is formed. For this reason, for example, when a highly sensitive CCD element is formed in the epitaxial layer,
Image defects occur due to crystal defects or dislocations remaining in the epitaxial layer due to insufficient gettering. Therefore, it has been difficult to form a highly sensitive CCD device.

An object of the present invention is to provide a method for forming an epitaxial wafer having excellent crystallinity.

[0006]

SUMMARY OF THE INVENTION The present invention is a method for forming an epitaxial wafer which has been made to achieve the above object. That is, in the first step, after cleaning the semiconductor substrate, an impurity contamination preventing film is formed on the surface of the semiconductor substrate. Subsequently, in a second step, a getter layer made of a high-concentration impurity diffusion layer is formed on the surface layer on the back surface side of the semiconductor substrate. Next, in a third step, the impurity contamination preventing film is removed. Thereafter, in a fourth step, after cleaning the semiconductor substrate, an epitaxial layer is deposited on the surface of the semiconductor substrate. Alternatively, in the above forming method, after performing the first step and the second step, as a third step, a protective film is formed on the back surface side of the processed semiconductor substrate. Next, as a fourth step, the impurity contamination preventing film is removed. Then, as a fifth step,
After cleaning the semiconductor substrate, an epitaxial layer is deposited on the surface of the semiconductor substrate.

[0007]

According to the above method, since the getter layer is formed on the surface layer on the back surface side of the semiconductor substrate before the epitaxial growth is performed, the semiconductor substrate is gettered at the time of the epitaxial growth and at the beginning of the device process. Further, since the getter layer is formed of the high concentration impurity diffusion layer, gettering is performed strongly. For this reason, during the epitaxial growth, crystal defects or transitions occurring in the epitaxial layer, or heavy metals taken in the epitaxial layer are taken in the getter layer. After further forming a getter layer,
By forming the protective film on the back side of the semiconductor substrate, impurities of the getter layer are not diffused to the front side of the semiconductor substrate.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to a manufacturing process diagram shown in FIG. The first step shown in FIG. 1A is performed. In this step, first, the semiconductor substrate 11 is cleaned. As the semiconductor substrate 11, a single crystal silicon substrate having a flat mirror surface is used. In addition, the above-described cleaning is performed, for example, using R
Performed by CA cleaning. Next, an impurity contamination prevention film 12 is formed on the surface of the semiconductor substrate 11 by, for example, a normal chemical vapor deposition method. As the impurity contamination prevention film 12, any film may be formed as long as it can prevent the surface of the semiconductor substrate 11 from being contaminated by impurities due to the thermal diffusion process. For example, the impurity contamination prevention film 12 can be formed of a silicon oxide film. In this case, the impurity contamination prevention film 12 is formed to have a thickness of, for example, several hundred nm.

Next, a second step shown in FIG. 1B is performed. As shown in the figure, the semiconductor substrate 1 is
An impurity is introduced into the back surface of the semiconductor substrate 11 to form a getter layer 13 made of a high-concentration impurity diffusion layer on the surface layer on the back surface of the semiconductor substrate 11. The diffusion process is performed by, for example, a thermal diffusion process. When the semiconductor substrate 11 is formed of single crystal silicon, for example, phosphorus (P), boron (B), carbon (C), or the like is used as an impurity to be diffused into the semiconductor substrate 11. When the semiconductor substrate 11 is made of a compound semiconductor such as gallium arsenide (GaAs), for example, indium (In) or phosphorus (P) is used as an impurity. In this diffusion process, the semiconductor substrate 1
Since the surface side of the semiconductor substrate 11 is covered with the impurity contamination prevention film 12, the surface side of the semiconductor substrate 11 is not contaminated by the impurities used for the diffusion process.

Thereafter, a third step is performed as shown in FIG. In this step, the impurity contamination preventing film 12 (portion indicated by a chain line) formed on the semiconductor substrate 11 is removed. Then, the surface of the semiconductor substrate 11 is exposed. For example, in the case where the semiconductor substrate 11 whose surface is mirror-polished is used, the impurity contamination preventing film is removed by a removing method that does not impair the mirror state of the surface of the semiconductor substrate 11 after the impurity contamination preventing film 12 is removed. 12 is removed. Examples of such a removing method include dry etching and wet etching. When the surface of the semiconductor substrate 11 is formed as an etched surface, the removal of the impurity contamination preventing film 12 is performed by mirror polishing. As the mirror polishing method, there is, for example, mechanochemical polishing.

Thereafter, as shown in FIG. 1D, a fourth step is performed. In this step, first, the semiconductor substrate 11 is cleaned. This cleaning is performed by, for example, RCA cleaning. Subsequently, an epitaxial layer 14 is deposited on the surface of the semiconductor substrate 11 by a normal epitaxial growth method. This epitaxial layer 14 is made of, for example, a silicon epitaxial layer. At this time, crystal defects or transitions generated in the epitaxial layer 14 or the epitaxial layer 1
The heavy metals and the like taken in 4 move in the direction shown by the dashed arrow and are taken into the getter layer 13. As described above, the epitaxial wafer 10 is completed.

In the method of forming the epitaxial wafer 10, the getter layer 13 is formed on the back side of the semiconductor substrate 11 before the epitaxial growth is performed.
1 is gettering from the beginning of the device process. Also, since the getter layer 13 is formed of a high concentration impurity diffusion layer, gettering is performed strongly. Therefore, it is possible to form the epitaxial layer 14 having almost no crystal defects and no transition and containing no heavy metal.

In the above method, when phosphorus is used as an impurity in the diffusion process for forming the getter layer 13, the phosphorus is out-diffused during epitaxial growth and the surface of the semiconductor substrate 11 is contaminated with phosphorus. Therefore, in order to prevent outdiffusion of impurities in the getter layer 13, a protective film is formed on the back surface side of the semiconductor substrate 11.

Next, as a second embodiment, a method of manufacturing an epitaxial wafer when a protective film is formed will be described with reference to FIG. As shown in FIG. 2A, after the first step and the second step described in FIG. 1 are performed to form an impurity contamination preventing film 12 on the front surface side of the semiconductor substrate 11, the semiconductor The getter layer 13 is formed on the surface layer on the back side of the substrate 11.

Then, as shown in FIG. 2 (2), as a third step, a protective film 15 is formed on the entire surface of the semiconductor substrate 11 on which the above-mentioned processing has been performed, for example, by a chemical vapor deposition method. It is formed to a thickness. This protective film 15 is formed of a film capable of preventing impurities in the getter layer 13 from being out-diffused. Examples of such a film include silicon oxide (SiO ₂ ) and silicon nitride (SiN).

Next, as shown in FIG. 2C, a portion of the protective film 15 formed on the front surface side of the semiconductor substrate 11 is removed by a two-dot chain line. Further, as a fourth step, 1
The impurity contamination prevention film 12 indicated by the dashed line is removed. Then, the surface of the semiconductor substrate 11 is exposed. The above protective film 1
As a method for removing the impurity film 5 and the impurity contamination preventing film 12, for example, when a semiconductor substrate 11 whose surface is mirror-polished is used, the semiconductor substrate after removing the protective film 15 and the impurity contamination preventing film 12 is used. The protective film 15 and the impurity contamination prevention film 12 on the front surface side of the semiconductor substrate 11 are removed by a removing method that does not impair the mirror state of the surface of the semiconductor substrate 11. Examples of such a removing method include dry etching and wet etching. In addition, the semiconductor substrate 1
When the surface of the semiconductor substrate 11 is formed as an etched surface, the removal of the protective film 15 and the impurity contamination prevention film 12 on the surface side of the semiconductor substrate 11 is performed by mirror polishing. As the mirror polishing method, there is, for example, mechanochemical polishing.

Thereafter, a fifth step shown in FIG. 2D is performed. This step is performed in the same manner as the fourth step described with reference to FIG. Then, the epitaxial wafer 10 is completed by forming the epitaxial layer 14 on the front surface side of the semiconductor substrate 11. At this time, crystal defects and dislocations generated in the epitaxial layer 14 or heavy metals and the like taken in the epitaxial layer 14 are taken into the getter layer 13. Further, the impurity of the getter layer 13 is not out-diffused by the protective film 15. The manufacturing method described in the second embodiment is not limited to the case where the getter layer 13 is formed of an impurity diffusion layer into which phosphorus is introduced. It is also possible to adopt the case where the getter layer 13 is formed by introducing other impurities.

In the method for forming the epitaxial wafer 10 on which the protective film 15 is formed as described above, gettering is performed on the semiconductor substrate 11 from the beginning of the device process, as described in the first embodiment. Further, the epitaxial layer 14 has almost no crystal defects or dislocations and does not contain heavy metals. In addition, since the impurity of the getter layer 13 is not outdiffused by forming the protective film 15, the surface side of the semiconductor substrate 11 and the epitaxial layer 14 are not contaminated by the impurity in the getter layer 13.

[0019]

As described above, according to the present invention,
Since the getter layer is formed of the high concentration impurity diffusion layer, gettering is performed strongly. Therefore, during epitaxial growth, crystal defects and transitions occurring in the epitaxial layer,
Alternatively, the heavy metal taken into the epitaxial layer is almost taken into the gettering layer. Therefore, the formed epitaxial layer is free from crystal defects, dislocations, and heavy metals that adversely affect the device. Therefore, the quality of the epitaxial wafer is improved. Further, by forming the protective film, the surface side of the semiconductor substrate and the epitaxial layer are not contaminated by impurities of the getter layer. Therefore, the quality of the epitaxial wafer is further improved.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of a first embodiment.

FIG. 2 is a manufacturing process diagram of a second embodiment.

[Description of Reference Numerals] 10 epitaxial wafer 11 semiconductor substrate 12 impurity contamination prevention film 13 getter layer 14 epitaxial layer 15 protective film

Claims (2)

(57) [Claims] A first step of forming an impurity contamination preventing film on a surface of the semiconductor substrate after cleaning the semiconductor substrate; and introducing a high-concentration impurity by introducing an impurity into a surface layer on the back side of the semiconductor substrate. A second step of forming a getter layer made of a layer, a third step of removing the impurity contamination preventing film, and a fourth step of depositing an epitaxial layer on the surface of the semiconductor substrate after cleaning the semiconductor substrate. And a method for forming an epitaxial wafer. A first step of forming an impurity contamination preventing film on the surface of the semiconductor substrate after cleaning the semiconductor substrate; and introducing a high-concentration impurity by introducing an impurity into a surface layer on the back side of the semiconductor substrate. A second step of forming a getter layer made of a layer, a third step of forming a protective film on the back surface of the semiconductor substrate subjected to the processing, a fourth step of removing the impurity contamination preventing film, A fifth step of, after cleaning the semiconductor substrate, depositing an epitaxial layer on the surface of the semiconductor substrate.