JPH08115878A - Two-step epitaxially growing method - Google Patents

Abstract

PURPOSE: To further suppress the auto-doping by keeping a substrate at a lower temp. than the epitaxial reaction temp. of a first single crystal layer in an epitaxial growth interrupted step. CONSTITUTION: After a wafer 30 is mounted on a susceptor of an apparatus, its temp. is risen to pretreat the wafer 30. A mixed gas of H2 , SiH4 and PH3 is fed into a chamber to form a first Si single crystal layer 32 on the wafer 30 set at about 1065 deg.C. The mixed gas is stopped, only H2 gas is fed into the chamber at the same flow rate and the wafer 30 is set to a temp. lower 50-100 deg.C than the epitaxial growth temp. of the single crystal 32. Then, the wafer's temp. is risen to about 1065 deg.C, the foregoing mixed gas is fed into the chamber to form a second P-doped Si single crystal layer 34 on that layer 32.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for epitaxially growing a single crystal layer on a substrate containing a high concentration of impurities in two steps. More specifically, the diffusion of impurities from the substrate to the single crystal layer is performed. The present invention relates to a suppressed two-step epitaxial growth method.

[0002]

2. Description of the Related Art When epitaxially growing a single crystal layer on a Si wafer which is heavily doped with impurities such as As, one problem is to suppress the automatic doping of As into the single crystal layer. Autodoping is a phenomenon in which impurities contained in a substrate are evaporated by heating the substrate and taken into the growing epitaxial layer. A two-step epitaxial growth method has been implemented as one of means for suppressing autodoping. The two-step epitaxial growth method is a method of epitaxially growing a single crystal layer on a substrate containing a high concentration of impurities. After the substrate surface is thinly covered with the epitaxial single crystal layer at the initial stage of the epitaxial growth reaction, the single crystal epitaxial growth reaction is performed once. This is a method in which the gas containing impurities in the process chamber is replaced with an appropriate replacement gas and discharged, and the single crystal is epitaxially grown again when the impurity concentration in the gas phase becomes sufficiently low.

For example, when a P-doped Si single crystal is epitaxially grown on a Si wafer to which As is added at a high concentration, the conventional two-step epitaxial growth method is shown in FIG.
It is implemented based on the temperature profile with respect to the elapsed time as shown in. The reaction temperature on the vertical axis is exactly S
The temperature of the susceptor on which the i wafer is placed can be approximately regarded as the temperature of the Si wafer. In FIG. 4, and, respectively, the period of the film forming process of the first layer Si single crystal, the period of the film forming process of the second layer P-doped Si single crystal, and the period of the epitaxial growth interruption process, which will be described below, are shown.

In the conventional two-step epitaxial growth method, a hydrogen gas (H ₂ ) is first introduced into a process chamber by using an atmospheric pressure CVD apparatus, and a wafer 11
The wafer is pretreated by heating it to about 00 ° C. Then
The temperature was lowered to about 1065 ° C, and silane gas (Si
The reaction gas mixed with H ₄ ) was introduced into the process chamber, and the reaction time of about 30 seconds was short, and the first film with a film thickness of 0.1 μm
A layer of Si single crystal is formed on a Si wafer. Then the first
The Si reaction is interrupted while the wafer is maintained at about the same temperature as during the epitaxial growth of the Si single crystal layer, and only hydrogen gas is introduced, and the process chamber is purged and evacuated, and then diffused from the wafer. The impurities that have been removed are discharged. Subsequently, a second P-doped Si single crystal layer having a predetermined thickness is formed on the first Si single crystal layer.

[0005]

However, in the conventional two-step epitaxial growth method, it is difficult to suppress the autodoping to a satisfactory degree, and therefore the breakdown voltage of the semiconductor device is lowered and the characteristics of the semiconductor device are deteriorated. Therefore, the product yield is lowered.

Therefore, an object of the present invention is to improve the conventional method so that autodoping can be further suppressed.
A stepwise epitaxial growth method is provided.

[0007]

As a result of researching the autodoping mechanism in the conventional two-step epitaxial growth method, the present inventor has found that the temperature of the substrate during the interruption of the epitaxial reaction is the epitaxial growth of the single crystal layer of the first layer. It was found that autodoping proceeded because it was maintained at the same temperature as the time. That is, first, since the substrate temperature is high even during this period, the impurities in the substrate are evaporated from the back surface, the side surface, etc. of the substrate and thermally diffused into the process chamber. Therefore, the impurities are not completely discharged from the process chamber of the epitaxial growth apparatus, and the impurities enter the second single crystal layer during the epitaxial growth of the second single crystal layer, whereby the autodoping proceeds. Second, since the substrate temperature is high during the interruption period, impurities are thermally diffused from the substrate to the first single crystal layer near the interface between the substrate and the first single crystal layer. As a result, impurities of the substrate are present in the single crystal layer.

Based on the above findings, in order to achieve the above object, the two-step epitaxial growth method according to the present invention introduces a reaction gas into the process chamber of an epitaxial growth apparatus and deposits it on a substrate containing a high concentration of impurities. A step of epitaxially growing the first-layer single crystal layer, a step of forming the first-layer single crystal layer, and then interrupting the epitaxial growth and flowing a replacement gas into the process chamber, and then a second-layer single crystal layer. A two-stage epitaxial growth method comprising the step of epitaxially growing a layer,
50 ° from the epitaxial reaction temperature of the single crystal layer of the first layer
It is characterized by maintaining the temperature of the substrate at a temperature lower than C by 100 ° C.

In the present invention, when the single crystal layer is epitaxially grown, it is possible to dope the single crystal layer with impurities by mixing the reaction gas with the impurity gas.

The substitution gas used in the present invention is not particularly limited as long as it does not affect the characteristics of the substrate and the single crystal layer of the first layer. For example, an inert gas, hydrogen gas or the like can be used. In the present invention, by lowering the substrate temperature during the epitaxial growth interruption step below the epitaxial reaction temperature of the first-layer single crystal layer, the diffusion rate of impurities in the substrate into the process chamber and the diffusion into the first-layer single crystal layer. The operating speed can be significantly reduced. Thereby, autodoping can be significantly suppressed as compared with the conventional two-step epitaxial growth method. In the present invention,
The temperature during the step of interrupting the epitaxial growth is 50 ° C to 100 ° C from the epitaxial reaction temperature of the single crystal layer of the first layer.
C lower temperature means that the effect of the present invention is small if the temperature difference is less than 50 ° C, and conversely 100 ° C.
This is because a larger temperature difference may cause deformation such as strain in the substrate or the single crystal layer.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing the structure of an epitaxial growth apparatus (hereinafter simply referred to as an apparatus) 10 for carrying out a two-step epitaxial growth method according to the present invention. As shown in FIG. 1, the apparatus 10 basically has a chamber 14 surrounded by a bell jar 12, a gas nozzle 16 which stands substantially upright in the center of the chamber 14, a wafer W placed on the upper surface thereof, and rotates around the gas nozzle 16. It includes a susceptor 18 and a high frequency coil 20.

The gas nozzle 16 supplies nitrogen gas, hydrogen gas, silicon source gas and impurity gas to the chamber 14 according to the composition of the single crystal layer to be epitaxially grown. The chamber 14 is suctioned by an external gas suction device (not shown) through the exhaust hole 22 and maintained at a predetermined pressure. The high frequency coil 20 heats the wafer W via the susceptor 18 by a high frequency induction heating method. The heating condition is determined by setting the high frequency output on a program previously input to the high frequency oscillator. The high frequency output can be set in at least three stages for each work (one batch). For example, in the first output setting of the first stage, conditions for preheating the wafer are set, and in the second output setting, the reaction temperature for epitaxial growth of the first and second single-crystal layers is set. Conditions are set, and in the output setting of the third stage, conditions are set such that the temperature of the epitaxial growth interruption process is reached.

Example A two-step epitaxial growth method according to the present invention was carried out using the apparatus 10 described above. 2A and 2B are cross-sectional views of the wafer for each step of the present epitaxial growth method. First, a wafer 30 having a high concentration of As added thereto is placed on the susceptor 18 of the apparatus 10, an external suction device is activated to replace the chamber 14 with H ₂ gas, and then the wafer 30 is moved by the high frequency coil 20. About 1100 °
The temperature was raised to C and the wafer 30 was subjected to pretreatment. The pretreatment is, for example, removing the natural oxide film on the surface. Next, the temperature of the wafer 30 is lowered to about 1065 ° C., and a mixed gas of H ₂ gas, SiH ₄ gas and PH ₃ is added to the chamber 1.
Then, the first single-layer Si single crystal 32 having a film thickness of about 0.1 μm was formed on the wafer 30 (see FIG. 2A). This required time was about 30 seconds. Next, the introduction of the mixed gas is stopped, and only the H ₂ gas having the same flow rate is supplied to the chamber 1.
4 was introduced, the temperature of the wafer 30 was lowered to about 995 ° C., and the wafer 30 was allowed to stand for about 20 minutes under these conditions. Then, the temperature of the wafer 30 is raised to about 1065 ° C. and a mixed gas of H ₂ gas, SiH ₄ gas and PH ₃ is introduced into the chamber 14 to introduce a P-doped Si single crystal of a second layer having a predetermined film thickness. 34 first
A layer was deposited on the Si single crystal 32.

The temperature profile with respect to the elapsed time in this embodiment is a curve as shown in FIG. In Figure 3,
Further, and indicate the period of the film forming process of the first layer Si single crystal 32, the period of the film forming process of the second layer P-doped Si single crystal 34, and the period of the epitaxial growth interruption process, respectively.
The reaction temperature on the vertical axis is, to be exact, the temperature of the susceptor on which the Si wafer is placed, but can be approximately regarded as the temperature of the Si wafer. In the P-doped Si single crystal 34 epitaxially grown in this example, the As auto-doping was suppressed, and an Si single crystal in which P was doped at a predetermined concentration could be obtained.

[0015]

According to the present invention, in the two-step epitaxial growth method, during the step of interrupting the epitaxial growth, the epitaxial reaction temperature of the single crystal layer of the first layer is 50 ° C. higher than the epitaxial reaction temperature.
By maintaining the temperature of the substrate at a temperature lower by 1 to 100 ° C., the rate of diffusion of impurities in the substrate into the process chamber and the rate of diffusion into the first single crystal layer can be significantly reduced. Therefore, the method of the present invention can significantly suppress autodoping as compared with the conventional two-step epitaxial growth method. By applying the method of the present invention,
Since a predetermined single crystal layer can be formed by epitaxial growth, the breakdown voltage becomes high, and as a result, the characteristics of the semiconductor device and the product yield are improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of an epitaxial growth apparatus for carrying out a two-step epitaxial growth method according to the present invention.

2A and 2B are cross-sectional views of a wafer for each step of the present epitaxial growth method.

FIG. 3 is a temperature profile with respect to elapsed time in an example according to the method of the present invention.

FIG. 4 is a temperature profile with respect to elapsed time in a conventional two-step epitaxial growth method.

[Explanation of symbols]

 10 Epitaxial growth apparatus for carrying out the method of the present invention 12 Bell jar 14 Chamber 16 Gas nozzle 18 Susceptor 20 High frequency coil 22 Exhaust hole 30 Wafer 32 First layer Si single crystal 34 Second layer P-doped Si single crystal

Claims (2)

[Claims] 1. A step of introducing a reaction gas into a process chamber of an epitaxial growth apparatus to epitaxially grow a single crystal layer of a first layer on a substrate containing a high concentration of impurities, and forming a single crystal layer of the first layer. Then, in the two-step epitaxial growth method including the epitaxial growth interrupting step of interrupting the epitaxial growth and flowing a replacement gas into the process chamber, and the step of epitaxially growing the second single-crystal layer. An epitaxial growth method, characterized in that the temperature of the substrate is maintained at a temperature 50 ° C. to 100 ° C. lower than the epitaxial reaction temperature of the single crystal layer of the layer. 2. The epitaxial growth method according to claim 1, wherein the reaction gas is mixed with an impurity gas so that the single crystal of the second layer is doped with the impurity.