JPH06216028A - Epitaxial wafer and manufacture thereof - Google Patents

Abstract

PURPOSE:To restrain an epitaxial layer from changing in resistivity by a method wherein an impurity layer which contains impurities of opposite type conductivity to that of a semiconductor substrate and is lower in concentration than the substrate is formed at a boundary surface between the semiconductor substrate and the epitaxial layer. CONSTITUTION:An impurity layer 14 containing P-type impurities is formed on the surface of a semiconductor substrate 11. At this point, P-type impurities contained in the impurity layer 14 are set in concentration so as not to exceed N-type impurities contained in the semiconductor substrate 11. Then, an N-type low concentration epitaxial layer 12 which is as thick as 6 to 100mum, prescribed in resistance, and used for the formation of a CCD image sensing element is made to grow on a semiconductor substrate 11 to form an epitaxial well 13. Thereafter, the CCD image sensing element is formed on the epitaxial layer 12. By this setup, an epitaxial layer can be restrained from changing in resistivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epitaxial wafer in which an epitaxial layer having the same conductivity type as that of the semiconductor substrate and a relatively low impurity concentration is provided on the semiconductor substrate having a relatively high impurity concentration, and an epitaxial wafer having the same. The present invention relates to a manufacturing method.

[0002]

2. Description of the Related Art In a CCD image pickup device having a vertical overflow drain structure using an n-type semiconductor substrate, a voltage is applied to the back surface of the semiconductor substrate having a p-well formed on the front surface side to thereby prevent an overflow barrier. There is an electronic shutter function of lowering the potential of the p-well, which has become a problem, and discharging excess charges accumulated in the photosensitive portion to the semiconductor substrate.

However, with the recent reduction in the size of pixels, the shutter voltage increases and the power consumption tends to increase. On the other hand, about 10 from the surface of the semiconductor substrate
If the high-concentration n-type layer is formed in advance in a region deeper than about μm, the p-well is susceptible to the shutter voltage modulation, so that the shutter voltage can be lowered.

Therefore, conventionally, as shown in FIG.
A high-concentration n-type semiconductor substrate 11 prepared by the CZ method is prepared, and as shown in FIG. A semiconductor substrate 1 having a low-concentration n-type epitaxial layer 12
With the epitaxial wafer 13 grown on 1,
The above structure was obtained.

[0005]

However, as shown in FIG. 3C, the high concentration semiconductor substrate is formed by the heat treatment for growing the epitaxial layer 12 and the heat treatment for forming the CCD image pickup device thereafter. Impurities diffuse from 11 to the low-concentration epitaxial layer 12. As a result, the resistivity of the epitaxial layer 12 changed, the potentials of the photosensitive portion and the charge transfer portion were not stable, and good characteristics could not be obtained.

If the thickness of the epitaxial layer 12 is made sufficiently thick, the semiconductor substrate 11 is changed to the epitaxial layer 1 from the semiconductor substrate 11.
It is possible to reduce the influence of the impurities diffused in 2.
However, if the film thickness of the epitaxial wafer 13 is increased, the manufacturing cost of the epitaxial wafer 13 increases,
The shutter voltage also becomes high.

[0007]

In an epitaxial wafer 13 according to a first aspect of the present invention, an epitaxial layer 12 having the same conductivity type as that of the semiconductor substrate 11 and a relatively low impurity concentration is formed on the semiconductor substrate 11 having a relatively high impurity concentration. In the epitaxial wafer 13 provided with the semiconductor substrate 11 and the epitaxial layer 12, an impurity layer 14 containing an impurity of a conductivity type opposite to that of the semiconductor substrate 11 at a concentration lower than that of the semiconductor substrate 11 is formed. Is formed at the boundary part of.

In the epitaxial wafer 13 of claim 2, the impurity layer 14 is formed on the semiconductor substrate 11 in the epitaxial wafer 13 of claim 1.

A third aspect of the present invention is the epitaxial wafer 13 according to the first aspect, wherein the impurity layer 14 is formed on the epitaxial layer 12.

In the method of manufacturing the epitaxial wafer 13 of claim 4, the impurity is introduced into the semiconductor substrate 11 when manufacturing the epitaxial wafer 13 of claim 2.

According to the method of manufacturing the epitaxial wafer 13 of claim 5, in manufacturing the epitaxial wafer 13 of claim 3, the impurities are added to the source gas for growing the epitaxial layer 12 at the beginning of the step of growing the epitaxial layer 12. Is added to form the impurity layer 14.

In the method for manufacturing the epitaxial wafer 13 according to claim 6, in the manufacturing of the epitaxial wafer 13 according to claim 1, after the epitaxial layer 12 is grown, the impurities are ionized from above the epitaxial layer 12 to the boundary portion. By implanting the impurity layer 14
To form.

[0013]

In the epitaxial wafer 13 and the method of manufacturing the same according to the present invention, the semiconductor substrate 11 having a relatively high impurity concentration during the heat treatment for growing the epitaxial layer 12 and subsequently forming the semiconductor device.
Even if impurities are diffused into the epitaxial layer 12 at a relatively low temperature, the diffused impurities are compensated by the impurities of the conductivity type opposite to that of the semiconductor substrate 11 included in the impurity layer 14.

Therefore, even if the thickness of the epitaxial layer 12 is thin, it is possible to reduce the influence of the diffusion of impurities from the semiconductor substrate 11 to the epitaxial layer 12 and suppress the change in the resistivity of the epitaxial layer 12. it can. Moreover, the semiconductor substrate 1 contained in the impurity layer 14
Since the impurity concentration of the conductivity type opposite to that of 1 is lower than that of the semiconductor substrate 11, the conductivity type of the semiconductor substrate 11 is not reversed by the impurities of the impurity layer 14.

[0015]

EXAMPLE An example of the present invention applied to an epitaxial wafer for forming a CCD image pickup device will be described below.
A description will be given with reference to FIGS. The components corresponding to those of the conventional example shown in FIG. 3 are designated by the same reference numerals.

Also in this embodiment, as shown in FIG.
A high-concentration n-type semiconductor substrate 11 created by the Z method is prepared. However, in this embodiment, the epitaxial layer 12 is immediately formed on the semiconductor substrate 11 as in the conventional example shown in FIG.
2) by thermal diffusion, or by ion implantation and subsequent heat treatment for recovering the crystallinity of the semiconductor substrate 11, as shown in FIG. First, an impurity layer 14 containing a type impurity is formed.

FIG. 1A shows the impurity concentration profile of the semiconductor substrate 11 in this state. As is clear from FIG. 1A, the concentration of the p-type impurity in the impurity layer 14 is set to a value not exceeding the impurity concentration of the n-type semiconductor substrate 11. Therefore, the conductivity type of the impurity layer 14 is also the same as that of the semiconductor substrate 11.

Next, as shown in FIG. 2C, a low-concentration n-type epitaxial layer 12 having a film thickness of about 6 to 10 μm and a predetermined resistivity necessary for forming a CCD image pickup device.
Are grown on the semiconductor substrate 11 to complete the epitaxial wafer 13. The CCD image sensor is then formed on the epitaxial layer 12.

FIG. 1B shows an impurity concentration profile of the semiconductor substrate 11 and the epitaxial layer 12 in this state. As is clear from FIG. 1 (b),
The n-type impurities diffuse from the high-concentration semiconductor substrate 11 to the low-concentration epitaxial layer 12 in the growth process of the epitaxial layer 12 and the heat treatment process for forming the CCD image sensor. At the same time, the impurities of the semiconductor substrate 11 are diffused. P-type impurities also diffuse from the layer 14 to the epitaxial layer 12.

Therefore, the n-type impurities and the p-type impurities diffused in the epitaxial layer 12 compensate each other, and the change in the resistivity of the epitaxial layer 12 is suppressed. Therefore, even if the epitaxial layer 12 is thin,
It is possible to form a CCD image pickup device in which the shutter voltage is reduced without changing the potentials of the photosensitive section and the charge transfer section.

Although the impurity layer 14 is formed in the semiconductor substrate 11 by introducing impurities into the semiconductor substrate 11 in the above embodiments, for example, the epitaxial layer 12 is used.
The impurity layer 14 may be formed in the epitaxial layer 12 by adding a p-type impurity to the source gas for growing the epitaxial layer 12 in the initial stage of the growth step. Alternatively, the impurity layer 14 may be formed by growing the epitaxial layer 12 and then ion-implanting a p-type impurity from above the epitaxial layer 12 to the boundary between the semiconductor substrate 11 and the epitaxial layer 12.

[0022]

In the epitaxial wafer and the method for manufacturing the same according to the present invention, even if the thickness of the epitaxial layer is small, the impurity is diffused from the semiconductor substrate to the epitaxial layer without inverting the conductivity type of the semiconductor substrate. The influence can be reduced and the change in the resistivity of the epitaxial layer can be suppressed. Therefore, it is possible to provide an epitaxial wafer capable of forming a semiconductor device having excellent characteristics at a low cost.

[Brief description of drawings]

FIG. 1 is a graph showing an impurity concentration profile before growth of an epitaxial layer and after formation of a CCD image sensor according to an embodiment of the present invention.

FIG. 2 is a side sectional view showing an embodiment in order of steps.

FIG. 3 is a side sectional view showing a conventional example of the invention of the present application in the order of steps.

[Explanation of symbols]

 11 semiconductor substrate 12 epitaxial layer 13 epitaxial wafer 14 impurity layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location H01L 27/14

Claims (6)

[Claims] 1. An epitaxial wafer in which an epitaxial layer having the same conductivity type as that of the semiconductor substrate and having a relatively low impurity concentration is provided on the semiconductor substrate having a relatively high impurity concentration, the conductivity being opposite to that of the semiconductor substrate. An epitaxial wafer, wherein an impurity layer containing a type impurity at a concentration lower than that of the semiconductor substrate is formed at a boundary between the semiconductor substrate and the epitaxial layer. 2. The epitaxial wafer according to claim 1, wherein the impurity layer is formed on the semiconductor substrate. 3. The epitaxial wafer according to claim 1, wherein the impurity layer is formed on the epitaxial layer. 4. The method of manufacturing an epitaxial wafer according to claim 2, wherein the impurity layer is formed by introducing the impurities into the semiconductor substrate. 5. The epitaxial wafer according to claim 3, wherein the impurity layer is formed by adding the impurities to a raw material gas for growing the epitaxial layer at an early stage of the epitaxial layer growth step. Manufacturing method. 6. The epitaxial wafer according to claim 1, wherein after the epitaxial layer is grown, the impurity layer is formed by ion-implanting the impurity from above the epitaxial layer to the boundary portion. Production method.