JP2003347304A - Silicon substrate and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for inactivating a defect with a high improvement effect of diffusion length of a polycrystalline silicon substrate. <P>SOLUTION: A second conductive layer is formed on the surface of a silicon substrate. Then the second conductive layer is removed. Then the surface of the silicon substrate where the second conductive layer is removed is irradiated with hydrogen. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing a silicon substrate and a silicon substrate manufactured by the method.

[0002]

2. Description of the Related Art In order to improve the quality of a polycrystalline silicon substrate, attempts have been made to introduce hydrogen from the surface of the polycrystalline silicon substrate to terminate a defective portion in the polycrystalline silicon substrate with hydrogen. Several methods for introducing hydrogen into silicon are known.

As a method for introducing hydrogen into silicon via a gas phase using a vacuum process, the following is known. JP-A-59-136926 discloses a method of directly irradiating a polycrystalline silicon substrate with hydrogen using hydrogen plasma. JP-A-58-23487 and JP-A-58-64035 describe a method of introducing hydrogen into a silicon crystal by accelerating hydrogen ions extracted from hydrogen plasma. JP-A-3-283471 discloses a method in which the surface is covered with an oxide film in order to avoid damage to the substrate due to ions, and the oxide film is removed after hydrogen plasma treatment.

[0004]

In the above prior art, the combined mode of hydrogen and silicon is monohydric,
There is no concept of controlling such as die hydride and trihydride. Therefore, the effect of inactivating defects is small depending on the substrate. For example, JP-A-58-23487,
In JP-A-58-64035, hydrogen ions extracted from hydrogen plasma are intentionally accelerated and introduced into a silicon crystal. In these methods, hydrogen termination is performed by accelerated ions having energy of several tens of eV or more, so that the bonding state between hydrogen and silicon (the binding energy is several eV) cannot be controlled. In JP-A-59-136926, a polycrystalline silicon substrate is directly exposed to hydrogen plasma to inactivate defects with atomic hydrogen. Although this patent mentions an increase in the number of Si-H modes as an interpretation of the defect inactivation phenomenon, it does not present data for mode identification and remains at the inference stage. In fact, since various types of defects are present on the surface of the polycrystalline silicon substrate, two types of coupling modes are increased by the hydrogen treatment. And, when the two coupling modes are increased by the hydrogen treatment, the diffusion length improvement is small. As described above, Japanese Patent Application Laid-Open No. 59-136926 intends to explain the phenomenon using the coupling mode of hydrogen and silicon, but says that the coupling mode is actually identified and controlled based on the data. hard. In JP-A-3-283471, the surface is previously covered with an oxide film and the oxide film is removed after the hydrogen plasma treatment. However, in this case, the defect passivation layer applied to the surface layer is also peeled off at the same time. This changes the hydrogen-silicon bonding mode formed on the substrate surface.

The present invention realizes a method for inactivating a defect in a polycrystalline silicon substrate having a higher effect of improving the diffusion length as compared with the prior art by controlling the coupling mode between hydrogen and silicon.

[0006]

According to the present invention, a step of forming a second conductive layer on the surface of a silicon substrate, a step of removing the second conductive layer, and a step of removing hydrogen from the surface of the silicon substrate from which the second conductive layer has been removed. There is provided a method for manufacturing a silicon substrate, comprising a step of irradiating.

Here, the second conductive layer forming step is characterized by using thermal diffusion or ion implantation.
The hydrogen irradiation step is desirably a catalytic CVD method or a hydrogen plasma processing method.

Further, there is provided a silicon substrate which has been subjected to a substrate treatment using the above method.

[0009]

DETAILED DESCRIPTION OF THE INVENTION It is known that atomic hydrogen terminates silicon dangling bonds on a silicon substrate to inactivate defects. The present inventor has further advanced this idea and found that there is a difference in the diffusion length improvement by controlling the coupling mode between hydrogen and silicon.This difference in the coupling mode is the difference in the silicon substrate pretreatment prior to hydrogen termination. It is clear that it depends. Conversely, it was shown that if this principle is used, the silicon substrate treatment prior to the hydrogen treatment can increase the effect of improving the substrate quality by the subsequent hydrogen-silicon bonding mode and hydrogen treatment.

Here, the silicon substrate pre-treatment means a process of forming a second conductive layer on the surface of the silicon substrate and removing the second conductive layer. More specifically, this is a step of subjecting a P-type silicon wafer to phosphorus diffusion using POCl _{3 and} removing the diffusion layer by mixed acid infiltration. However, the means for forming the second conductive layer by phosphorus diffusion is not limited to the thermal diffusion treatment, and other means such as ion implantation may be used. As a result of this processing, it is considered that the bonding mode of silicon and hydrogen by the subsequent hydrogen processing can be controlled to a single bonding mode of any one of monohydride, die hydride, and trihydride bonding.

The present invention can obtain a particularly advantageous effect in the case of polycrystalline silicon. Phosphorus is desirable for the formation of the second conductive layer, but other impurities for forming the second conductive layer such as arsenic and antimony can be used. The removal of the second conductive layer is preferably performed by completely removing the second conductive layer. However, even if a part of the second conductive layer remains, the second conductive layer is also entirely removed, and the P-type silicon substrate is further removed. Some may be removed.
In this experiment, mixed acid infiltration was used as a removing method, but other methods such as dry etching using fluorine-based gas and mechanical polishing may be used. In this experiment, N was added to the P-type silicon substrate.
Although an impurity for generating a mold is introduced, an impurity for generating a P-type, such as boron or aluminum, may be introduced into an N-type silicon substrate.

Here, the hydrogen treatment means a step of irradiating a polycrystalline silicon substrate with atomic hydrogen. Catalytic CVD (contacting a tungsten wire heated to 1600 ° C. or higher with hydrogen gas to generate atomic hydrogen), plasma C
The VD method (high-energy electrons in plasma collide with hydrogen molecules to generate atomic hydrogen) and the like are common,
It is not limited to these. The present invention can be realized by means for supplying atomic hydrogen.

FIG. 1 shows the results of a hydrogen treatment experiment using a P-type polycrystalline silicon wafer. The horizontal axis is the diffusion length before hydrogen treatment, and the vertical axis is the diffusion length after hydrogen treatment. The black circles indicate a substrate (hereinafter referred to as A) from which a polycrystalline silicon wafer was subjected to a phosphorus diffusion treatment using POCl ₃ and a diffusion layer was removed by a mixed acid treatment.
White substrate is a polycrystalline silicon substrate (hereinafter referred to as a B-type substrate) that has not been subjected to the phosphorus diffusion process and the phosphorus diffusion layer removal process. The initial value of the diffusion length of the A-type substrate is 70 to 130.
μm, that of the B-type substrate is between 100 and 160 μm. 1
Both are overlapped between 00 and 130 μm, but the diffusion length after hydrogen treatment is clearly larger for the A-type substrate. The substrate from which the phosphorus diffusion treatment was performed and the diffusion layer was removed by the mixed acid treatment means that the improvement in the diffusion length was increased. It has been found that a larger improvement in the diffusion length can be obtained by performing the hydrogen treatment after performing the second conductive layer formation and the second conductive layer removal treatment on the polycrystalline silicon substrate.

To clarify the cause, the bonding state between hydrogen and silicon was examined by thermal desorption gas analysis. FIG. 2 shows the results. The horizontal axis indicates temperature, and the vertical axis indicates the amount of hydrogen gas. (A) shows the result for the A-type substrate, and (b) shows the result for the B-type substrate. The solid line is the result of the thermal desorption analysis of the substrate before the hydrogen treatment, and the dotted line is the result of the thermal desorption gas analysis before the hydrogen treatment. Therefore, the difference between the solid line and the dotted line means hydrogen added by the hydrogen treatment. 300-5
In the thermal desorption gas analysis at 00 ° C, it is considered that hydrogen mainly desorbs from the silicon surface including the crystal grain boundaries,
This result is considered to be mainly information obtained from silicon crystal grain boundaries. In thermal desorption gas analysis, the temperature at which hydrogen gas comes out differs depending on the mode of hydrogen-silicon bonding that exists. 400 for A-type substrates
The desorption of hydrogen at ℃ 500 ° C. is increasing, indicating that a single hydrogen-silicon bonding mode is generated by the hydrogen treatment. On the other hand, in the case of the B-type substrate, although gas release is observed at 400 to 500 ° C., hydrogen desorption increases at a temperature of 500 ° C. or higher, indicating that two hydrogen silicon bonding modes are generated by the hydrogen treatment. . As described above, it has been found that by performing the silicon substrate pretreatment, the hydrogen-silicon bonding mode at the grain boundary generated in the subsequent hydrogen treatment step is unified.

The above phenomenon is related to a reduction in silicon arrangement disorder at silicon crystal grain boundaries where a large number of defects exist. Impurities create strain in the silicon network. When impurities are located near the grain boundaries where many defects exist,
The strain generated by the impurities disturbs the arrangement of silicon at the grain boundaries. When the impurities contained in the silicon are removed by the phosphorus diffusion treatment and the diffusion layer removal treatment (see *), the disorder of the silicon arrangement due to the impurities is also removed. Without the phosphorus diffusion treatment, the disorder of the silicon arrangement at the grain boundaries due to impurities has caused a plurality of hydrogen-silicon bonding modes observed after the hydrogen treatment. Impurities were removed by phosphorus diffusion, and disorder of the silicon arrangement at grain boundaries was removed, so that the coupling mode between hydrogen and silicon was unified.

* The impurities include alkali metals such as Na, Li and K, and heavy metals such as Fe, Cu, Au and Cr. It is known that all of these impurities have a high diffusion rate in Si and penetrate at a considerably low temperature. Therefore, a getter sink was created at the lattice mismatched part of the wafer,
After the impurity is adsorbed to this portion by heat treatment during the process, the impurity is removed by etching, whereby the impurity concentration in silicon can be reduced. Lattice distortion in the crystal is often used as a getter sink. In order to introduce lattice distortion into silicon, the wafer is irradiated with an atmosphere of POCl ₃ , P ₂ O _5, or the like, and phosphorus is diffused at a high concentration to create a misfit transition inside the silicon (IEEE Transactions O).
n Electron Devices 37 (199
0) 382. )and so on.

From the above findings, it is possible to unify the hydrogen-silicon bonding mode generated by the subsequent hydrogen treatment by performing the phosphorus diffusion treatment on the base substrate in the hydrogen treatment. The effect of improving the diffusion length by hydrogen treatment can be increased by unifying the hydrogen-silicon bonding mode. It became clear.

When the polycrystalline silicon substrate produced in the present invention is used for a solar cell substrate, for example, the conversion efficiency can be improved. (Embodiment) FIG. 3 shows a schematic diagram of a phosphorus diffusion process for a P-type polycrystalline silicon substrate. About 350μm thickness, resistivity 1
Ω. A P-type polycrystalline silicon substrate 1 of about cm is washed by RCA method, and an N-type silicon layer 2 having a thickness of about 1.0 μm and an impurity concentration of 1.2 × 10 ²⁰ cm ⁻³ is formed by phosphorus diffusion.
At this time, the temperature of the silicon substrate and the temperature of the diffusion furnace were set to 950.
C. and the diffusion time was set to 1 hour. Next, the N-type diffusion layer 2 was removed using a mixed acid. After a dipping time of 40 seconds, about 10 μm is removed from the surface. Reference numeral 3 denotes a portion removed by the mixed acid treatment.

Next, atomic hydrogen irradiation was performed using the catalytic CVD apparatus shown in FIG. The polycrystalline silicon substrate 4 pre-processed as described above is mounted inside the processing chamber 5. The pressure inside the processing chamber is reduced to about 10 ⁻⁵ Pa. Then, 100 SCCM of H ₂ is introduced as a gas from the gas introduction hole 6, and the gas exhaust amount from the gas exhaust hole 7 is adjusted to a pressure of 0.4 Pa. The substrate temperature is set to be 500 ° C. A DC current of 11 A is passed through the catalyzer 8 made of a 0.4 mm diameter tungsten wire so that the wire temperature becomes 1650 ° C. The hydrogen gas in contact with the wire is decomposed into atomic hydrogen, and the substrate is irradiated. The hydrogen radical irradiation is performed for 30 minutes. The substrate was taken out of the catalytic CVD apparatus, and the diffusion length was measured using the SPV method.

Further, the hydrogen-treated P
Phosphorus is diffused into the polycrystalline silicon substrate and the thickness is about 1.0μ.
An n-type silicon layer having an impurity concentration of 1.2 × 10 ²⁰ cm ⁻³ was formed to produce a solar cell wafer. Comparative Example A comparative example is a method for inactivating defects by a method based on the prior art disclosed in Japanese Patent Application Laid-Open No. Sho 59-136926. About 350 μm thickness, resistivity 1Ω. The P-type polycrystalline substrate of about cm is cleaned by RCA method, and the catalytic CVD shown in FIG.
Atomic hydrogen irradiation was performed using an apparatus. The polycrystalline silicon substrate 4 is mounted inside the processing chamber 5. 10 inside the processing chamber
^{Reduce the} pressure to about ^-5 Pa. And, as a gas, H ₂ 10
0 SCCM is introduced from the gas introduction hole 6, and the gas exhaust amount from the gas exhaust hole 7 is adjusted to a pressure of 0.4 Pa. The substrate temperature is set to be 500 ° C. 0.4mm
A direct current of 11 A is applied to the catalyzer 8 made of tungsten wire having a diameter of 1650 ° C. so that the wire temperature becomes 1650 ° C. The hydrogen gas in contact with the wire is decomposed into atomic hydrogen, and the substrate is irradiated. Hydrogen radical irradiation 3
Perform for 0 minutes. The substrate is taken out from the catalytic CVD device and SPV
The diffusion length was measured using the method.

Table 1 shows changes in the diffusion length of the polycrystalline silicon substrates treated in the examples and the comparative examples. Although the diffusion length initial values in the example and the comparative example are almost the same, expansion of the diffusion length in the example is comparative example 1
It can be seen that it is larger by about 40 μm. This means
This shows that by performing the phosphorus diffusion treatment on the substrate in advance, the improvement rate of the diffusion length by the subsequent hydrogen treatment increases. As described above, the effect of the present invention was shown.

[0022]

[Table 1]

[Brief description of the drawings]

FIG. 1 shows the results of a hydrogen treatment experiment using a polycrystalline silicon substrate.

FIGS. 2A and 2B show the results of thermal desorption gas analysis, wherein FIG. 2A shows the results for an A-type substrate and FIG. 2B shows the results for a B-type substrate.

FIG. 3 is a schematic view illustrating a step of pretreatment of a silicon substrate.

FIG. 4 shows a catalytic CVD apparatus.

[Description of Signs] 1 P-type polycrystalline substrate 2 N layer formed by phosphorus diffusion 3 Portion removed by mixed acid infiltration 4 Polycrystalline silicon substrate 5 Processing chamber 6 H ₂ gas introduction hole 7 Gas exhaust hole 8 Catalyzer

Claims (4)

[Claims] 1. A method comprising: forming a second conductive layer on a surface of a silicon substrate; removing the second conductive layer; and irradiating hydrogen to the surface of the silicon substrate from which the second conductive layer has been removed. Manufacturing method of a silicon substrate. 2. The method according to claim 1, wherein the second conductive layer forming step uses thermal diffusion or ion implantation. 3. The step of irradiating with hydrogen is carried out by catalytic CVD.
2. The method for manufacturing a silicon substrate according to claim 1, wherein the method is a hydrogen plasma processing method. 4. A silicon substrate that has been subjected to substrate processing using the method according to claim 1.