JPH06216234A - Method of forming impurity diffusion region for isolation - Google Patents

Abstract

PURPOSE:To make it possible to provide isolation between a predetermined element forming region and other regions of the outside of the element forming region at a low cost without using an epitaxial semiconductor substrate and remarkably reducing the element forming region. CONSTITUTION:When an impurity diffusion region 8 for isolation between a predetermined element forming region A of a semiconductor substrate 1 and other regions B of the outside of the element forming region A is formed, the semiconductor substrate 1 in which a groove 5 is previously formed in the rear of the element forming region A is used as the semiconductor substrate, and conductive type impurity is diffused so as to extend across the front surface of the semiconductor substrate 1 and the bottom of the groove 5, and thus the impurity diffusion region 8 for isolation is formed.

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 impurity diffusion region for junction separation.

[0002]

2. Description of the Related Art Conventionally, in the case of a bipolar transistor, it is necessary to electrically isolate a predetermined element formation region and another region outside thereof. For this separation, what is called an impurity diffusion region is formed between the element formation region and another region outside the element formation region by diffusing impurities of opposite conductivity type in the thickness direction to form a junction separation between the element formation region and the other region. A junction separation method is used.

Furthermore, in recent years, bipolar devices and CMOS
In many cases, heterogeneous elements such as a BiCMOS transistor in which a control circuit and a smart power IC in which a control circuit and a power element are integrated into one chip are mixed.
The junction separation method is applied. However, when the junction isolation method is applied, conventionally, as shown in FIG. 9, it is necessary to use an epitaxial semiconductor substrate formed by depositing an n-type silicon layer 52 on a p-type silicon substrate 51 by an epitaxial method as shown in FIG. There is. In this case, p-type impurities for the buried layer are preliminarily introduced into the surface of the p-type silicon substrate 51 before the deposition by the epitaxial method, and the p-type impurities are introduced from the surface of the n-type silicon layer 52 after the deposition.
The diffusion of the pre-introduced p-type impurity into the n-type silicon layer 52 is also used to suppress the lateral diffusion of the p-type impurity as much as possible to reduce the decrease in the element formation region, so that the p ⁺ -type for junction separation is formed. The impurity diffusion region 53 is formed.

However, in the conventional method for forming the impurity diffusion region for junction separation, the epitaxial semiconductor substrate to be used is originally expensive and it is necessary to preliminarily introduce the impurities for the buried layer, which makes the cost very high. There is a problem of becoming. Of course, without using an epitaxial semiconductor substrate, it is conceivable to diffuse impurities of opposite conductivity type into a semiconductor substrate of the same conductivity type so as to reach from the substrate surface to the back surface, and perform junction separation. However, the required diffusion distance of impurities of opposite conductivity type is too long to be realized.

[0005]

In view of the above circumstances, the present invention eliminates the need for using an epitaxial semiconductor substrate and, at the same time, provides a predetermined element formation region and other parts outside it without significantly reducing the element formation region. It is an object of the present invention to provide a method capable of performing junction separation at low cost between regions.

[0006]

In order to solve the above-mentioned problems, in the method of forming an impurity diffusion region for junction isolation of the present invention, a predetermined element forming region of a semiconductor substrate and another region outside thereof are provided with an opposite structure. In a method of forming an impurity diffusion region that joins and separates the element formation region and another region by diffusing conductivity type impurities in the thickness direction of the substrate, the semiconductor substrate has a groove on the back side of the element formation region. Forming an impurity diffusion region for junction separation by diffusing the impurity of the opposite conductivity type so as to extend between the front surface of the semiconductor substrate and the bottom surface of the groove using a preformed semiconductor substrate. Is characterized by.

In the case of the present invention, the diffusion of impurities of opposite conductivity type for junction separation is performed so that the diffusion regions of both impurities are connected from both the front surface of the semiconductor substrate and the bottom surface of the groove. It can be said that this is a preferable mode because it has a large effect of suppressing the decrease of
Impurities of opposite conductivity type may be diffused only from one of the front surface of the semiconductor substrate and the bottom surface of the groove.

[0008]

In the method according to the present invention, since the impurities of opposite conductivity type are diffused so as to extend between the front surface of the semiconductor substrate and the bottom surface of the groove, the diffusion distance in the thickness direction is shortened by the depth of the groove. Even if an expensive epitaxial semiconductor substrate in which semiconductor layers having different conductivity types are stacked is not used as a semiconductor substrate, a semiconductor substrate having the same conductivity type as a whole can be used for separating a junction while suppressing a reduction in a necessary element formation region. Impurity diffusion regions can be formed.

In addition, in the method of the present invention, when the impurities of opposite conductivity type for junction separation are diffused from both the front surface of the semiconductor substrate and the bottom surface of the groove, the impurities are diffused from only one side. It is only half that in the case, and the lateral diffusion of impurities of the opposite conductivity type becomes shorter, so the effect of suppressing the reduction of the element formation region is great. Further, in the conventional case of adopting the method of preliminarily introducing the impurities for the buried layer, the limitation of the impurity concentration of the impurity diffusion region is relatively strict, but in the case of the present invention, since the normal impurity diffusion method is adopted, There is also an advantage that the restriction on the impurity concentration in the diffusion region is relaxed.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. It goes without saying that the present invention is not limited to the following embodiments. As shown in FIG. 2, both sides of the semiconductor substrate 1 made of only n-type silicon were thermally oxidized to a thickness of 5
000 Å thermal oxide films 2 and 3 are formed. 2 to 7, the back side of the substrate is shown as an upper side.

After the thermal oxide films 2 and 3 are formed, as shown in FIG. 3, the thermal oxide film 2 on the element formation region of the semiconductor substrate 1 is partially removed by a photolithography process and an RIE process. The window 2a is opened and anisotropic etching is performed using the remaining thermal oxide film 2 as a mask. For example, if anisotropic etching is performed by immersing in a KOH aqueous solution at about 80 ° C., a groove 5 having an edge inclined at an angle of 54.5 ° can be formed at the window 2a on the back side of the element formation region. become. The groove 5 is formed so as to cover the portion where impurities of opposite conductivity type for junction separation are introduced.

After forming the groove, as shown in FIG. 4, the surface on the back side of the semiconductor substrate 1 is entirely covered with the thermal oxide film 6 including the inner surface of the groove 5 by thermal oxidation again. As can be seen, the window 6a is opened along the position between the element formation region in the thermal oxide film 6 at the bottom of the groove 5 and the other region outside thereof.
After forming the window 6a, as shown in FIG. 6, boron, which is a p-type impurity, has an energy of 50 keV and an implantation amount of 5E1.
As shown in FIG. 7, the p-type diffusion region 11 is formed by ion-implanting the ions in step 5 and then performing a heat treatment to form an oxide film in the window 6a and pre-diffuse boron.

Next, as shown in FIG. 8, a window 3a is opened along the position between the element forming region of the front thermal oxide film 3 of the semiconductor substrate 1 and the other region outside the region, and a p-type impurity is used. Energy of certain boron: 50 keV, injection amount: 5E1
Ion implantation is performed at 5. In this case, the window 3a is opened at a position facing the window 6a shown in FIG. 5, and boron, which is a p-type impurity, is implanted at a position facing the p-type diffusion region 11.

After the boron ion implantation, the semiconductor substrate 1 is placed in a diffusion treatment furnace, and a diffusion treatment is performed so that the diffusion regions made of boron implanted from both the front side and the back side are connected.
As a result, as shown in FIG. 1, a p-type impurity diffusion region 8 extending from the front side to the back side of the semiconductor substrate 1 is formed at a position between the element formation region and the region outside the semiconductor substrate 1, and the p-type impurity diffusion region 8 is formed. The element forming region A inside the diffusion region 8 and the other region B outside thereof are in a state of being electrically separated by the pn junction. That is, the p-type impurity diffusion region 8 is an impurity diffusion region for junction isolation.

As described above, in the case of the embodiment, p-type impurities for junction separation are diffused from both the front side and the bottom of the groove, and the diffusion is omitted for the depth of the groove 5. Therefore, the diffusion distance in the substrate thickness direction becomes short, and as a result, p
The type impurity diffusion region 8 does not extend so much in the lateral direction (of the substrate), and the element formation region does not become too narrow due to the formation of the p type impurity diffusion region 8. As described above, the predetermined element formation region can be junction-separated without using the epitaxial semiconductor substrate and without significantly reducing the element formation region.

[0016]

According to the method of forming the impurity diffusion region for junction separation of the present invention, an expensive epitaxial semiconductor substrate is used because the diffusion distance of impurities of opposite conductivity type in the substrate thickness direction is shortened by the depth of the groove. Even if an inexpensive semiconductor substrate having the same conductivity type is used as a whole, an impurity diffusion region for junction separation can be formed while suppressing a reduction in a necessary element formation region.

In addition, in the method of the present invention, when the opposite conductivity type impurities for junction separation are diffused from both the front surface of the semiconductor substrate and the bottom surface of the groove, the impurities are diffused from only one side. It is only half as compared with, and the lateral diffusion of impurities of opposite conductivity type becomes shorter, so that the effect of suppressing the reduction of the element formation region is great.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a semiconductor substrate that has undergone junction separation in an example.

FIG. 2 is an explanatory diagram of a thermal oxide film forming step in the example.

FIG. 3 is an explanatory diagram of a groove forming step in the example.

FIG. 4 is an explanatory diagram of a thermal oxide film forming step in the example.

FIG. 5 is an explanatory diagram of a window opening process in the thermal oxide film on the back side of the substrate in the example.

FIG. 6 is an explanatory diagram of an ion implantation step on the back side of the substrate in the example.

FIG. 7 is an explanatory diagram of a pre-diffusion process of implanted impurities in the example.

FIG. 8 is an explanatory diagram of a window opening / ion implantation process on the front side of the substrate in the example.

FIG. 9 is an explanatory view of a conventional semiconductor substrate after junction separation.

[Explanation of symbols]

 1 semiconductor substrate 2 thermal oxide film 3 thermal oxide film 5 groove 6 thermal oxide film 8 p-type impurity diffusion region (for junction separation) A element formation region B other region

Claims (2)

[Claims] 1. An element formation region and another region are bonded and separated by diffusing impurities of opposite conductivity type between a predetermined element formation region of a semiconductor substrate and another region outside thereof in the thickness direction of the substrate. In the method of forming an impurity diffusion region, a semiconductor substrate having a groove formed in advance on the back side of the element forming region is used as the semiconductor substrate, and the impurities of the opposite conductivity type are used on the front surface of the semiconductor substrate and the semiconductor substrate. A method for forming an impurity diffusion region for junction isolation, which comprises forming an impurity diffusion region for junction isolation by diffusing so as to extend between the bottoms of the grooves. 2. The junction isolation junction according to claim 1, wherein diffusion of impurities of opposite conductivity type for junction isolation is performed such that both impurity diffusion regions are connected from both the front surface of the semiconductor substrate and the bottom surface of the groove. Method of forming impurity diffusion region.