JPS58175845A - Structure of isolation diffusion region in semiconductor device - Google Patents

Abstract

PURPOSE:To improve an effective area ratio by a method wherein an impurity of a small diffusion constant is diffused from the element forming surface side of a semiconductor substrate, an impurity of a large diffusion constant is diffused from the reverse side, and both diffusion regions are connected in the substrate and used as the isolation diffusion region. CONSTITUTION:Both surfaces of the substrate 1 are coated selectively with oxide film 2, and a diffusion impurity layer 3 containing boron is deposited onto the surface, to which an element is formed, and a diffusion impurity layer 5 containing aluminum onto the reverse side. Both impurities are diffused through heat treatment, and connected in the substrate, and the isolation diffusion region is formed. A junction point of both diffusion regions 4, 6 is brought close to the surface, which intends to be formed, because aluminum has a diffusion constant approximately sextuple as large as that of boron in silicon. The size W1 of a utilizable semiconductor surface is made large with the approach of the junction point.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the form of isolation diffusion regions formed in a semiconductor substrate during the manufacture of a semiconductor device.

Conventionally, when two or more independent element formation heads are formed in a semiconductor substrate, adjacent element formations** are electrically insulated from each other. Semiconductor substrate KI area! A method of forming the Ill [K through it is widely used (this is called an isolation diffusion region).If the semiconductor substrate is a p-type, phosphorus is used as an isolation diffusion impurity; if the semiconductor substrate is an n-type, phosphorus is used as an isolation diffusion impurity. In some cases, boron or aluminum is used as a separated and diffused impurity.And, except for special cases, n-type semiconductor substrates are used for power system devices.
An explanation will be given of a mutually separated and expanded region formed on a conventional n-type half-quad substrate.

Figures 1 (a) to (C) are cross-sectional views showing the state at each process stage when only boron is used as the conventional p-type impurity. First, as shown in Figure 1 (a), , semiconductor substrate (
(hereinafter simply referred to as the substrate) [11] Impurity diffusion of nona oxide @ (2) is performed. The part corresponding to the frame was selectively removed by photolithography, and then the image shown in Figure 1 (
t+) All surfaces on both sides including the removed part as shown
Attached to the tic table 1 (hereinafter referred to as ``debojishi'') 5
to form a diffused impurity layer (1), and further heated to a high temperature (1200℃).
The substrate (1) is heat-treated at a temperature of 1° C. or above) to form a predetermined isolation diffusion region (4) as shown in FIG.

When boron is used as the p-type impurity, the process is relatively simple as described above, but the diffusion coefficient of boron to silicon is small and the practical diffusion depth is 100 to 120 μm.
Since the thickness of the substrate 11 must be less than 0.0 m, the thickness of the substrate 11 must be less than 0.0 m, and the substrate 11 is easily broken during the process, making it impossible to use a large substrate.

#! Figures 2 (&) to (1) are cross-sectional views showing the state a at each process step when only aluminum is used as the conventional p-type impurity. First, as shown in Figure 2 (SL) K, Vζ,
As in the case of FIG. 1, the oxide film (2) on the surface of the substrate (1)
) is selectively removed, and then, as shown in FIG. 2(b), [12Ii! i! The entire surface of both sides, including the removed parts, is made of aluminum and is made of alumonium. Diffusion impurity (5) such as silicon is made by II and tree method, etc., and as shown in Fig. 42(o)K, the diffusion impurity (6) other than the part corresponding to the region to be diffused is selected by photolithography. If necessary, chemical treatment such as anodic oxidation is performed, and then the substrate (111c t%i temperature (1200'C
A heat treatment is performed in the above steps to form desired separation and diffusion regions (6) as shown in Figure 2 (d).

As mentioned above, when ram' is used for aluminum as a p-type impurity, the process becomes complicated and the cost becomes low, but on the other hand, the diffusion coefficient of aluminum for silicon is about 6 times that of boron. It has a high degree of redness, it is possible to make the diffusion radius 200 μm or more, and the substrate [11
The thickness of the substrate 1110 can be increased, and therefore the size of the substrate 1110 can be increased.

However, the horizontal diffusion method is 9kK for the vertical expansion of 1kK.
It is known that R is 0.9 times radical, and separation and diffusion R
When δ becomes deeper, the isolation diffusion region (@
) is narrowed (indicated by width W in the figure), and when forming a predetermined cord from this surface, it becomes necessary to increase the size of the substrate.

As described above, conventional methods using a single p-type impurity have drawbacks, both when boron is used and when aluminum is used.

The present invention was made in view of the above points, and it is possible to effectively form elements by diffusing impurities with a small diffusion coefficient from the tag-forming front side of the substrate and diffusing impurities with a large diffusion coefficient from the back side. It is an object of the present invention to provide a configuration of an isolation diffusion region that allows the use of a sufficiently thick substrate while maintaining a large area ratio.

3vA(a) to (d) are cross-sectional views showing the state at the main stages of formation for explaining one embodiment of the present invention. First, as shown in Figure #I3<&), To,
Required portions of the oxide film (2) on both surfaces of the substrate (1) are selectively removed, and the oxide film (2) is then removed as shown in Figure 3 of the IC.
) is coated on the entire surface including the removed portion of boron.
Deposit the expanding ridge impurity (3), then evaporate aluminum and silicon on the entire back surface to form the second diffusion impurity MA1111.
Form m t5J. Next, Figure 3(c) K
As shown, the second diffusion impurity m (5
Of 7, the part corresponding to the diffusion-t chain acid is left and the other part is removed by photolithography, and then the substrate 111K is removed.
After high-temperature heat treatment, as shown in Figure 8 ((1) K,
An expanded fL area (4) is formed on the front side of the substrate tl+, and an aluminum expanded fL area (6) is formed on the back side of the substrate tl+ to form a desired separation/diffusion area. Finally, the second diffusion impurity layer (5), which is no longer needed, is chemically removed.

In the above embodiment, not only aluminum but also silicon is vapor-deposited on the back side in order to uniformize the diffusion depth of aluminum and the diffusion depth.

The purpose of removing the diffused impurity layer other than the portion corresponding to the 8 m diffusion area is to prevent aluminum and the oxide film (2) from reacting during heat treatment and causing the oxide film (2) to lose its masking function. In the inventors' experience, the separation of public discipline and amnesty is 14##
In the case of a heat treatment temperature of 15,150"C1ζ, the diffusion time of about 140 hours results in the diffusion of borax on the surface (4
) is 100 μm deep, and the aluminum diffusion region (
6) No. 1! lI! A thickness of 240 μm can be stably obtained.

Therefore, the thickness of the substrate [11] can be 30'0 μm. Moreover, since the diffusion number M of boron is small on the surface side, the effective area for forming the element (indicated by the width W in the figure) can be increased.

Incidentally, both the front and back diffusion regions may be formed at the same time or may be formed separately.

As explained above, in the present invention, the first impurity having a small diffusion coefficient is diffused from the surface of the semiconductor substrate on the element formation side to form a shallow first diffusion region, and #I2 having a large diffusion coefficient is diffused from the back surface. The impurity is diffused to form a deep second diffusion region, and these first and second diffusion regions are connected to form a separation diffusion region. Since the diffusion thickness of the isolation diffusion region can be increased while maintaining the thickness, a thick substrate can be used, and the risk of damage to the substrate is significantly reduced.

[Brief explanation of drawings]

#1lE (a) to (0) are cross-sectional views showing the main stages of four separate diffusion region formation processes using only boron as the conventional p-type impurity; Figures 2 (a) to (d) ) shows the state at the main stage of formation of a separated diffusion region in the case of using only aluminum as the p-type impurity,
Figures 3 (5L) to (d) illustrate an example of the weaving of this invention.
FIG. 3 is a cross-sectional view of the main stage of the formation process. In the figure, (1) is a semiconductor substrate, (4) is a boron diffusion chain acid (first diffusion region), and (6) is an aluminum diffusion #
4 region (second diffusion region). Note that the same reference numerals in the figures indicate the same or corresponding parts. Agent Ge Shu Di - (1 other person) Figure 1 Figure 21'dJ '7Wl-,. Figure 3

Claims (1)

[Scope of Claims] (A second semiconductor substrate formed to penetrate the semiconductor substrate in its thickness direction by selectively diffusing impurities from both the front and back principal directions of a semiconductor substrate of the conduction type 11). In the structure of the isolation diffusion region which has a conductive type and electrically isolates the semiconductor substrate into at least two parts, a first region having a small diffusion coefficient is separated from the surface of the semiconductor substrate on the side where the semiconductor system is preformed.
A shallow first diffusion region is formed by diffusing an impurity, and a second impurity having a large diffusion coefficient is diffused from the back surface of the semiconductor substrate to form a deep #I2 diffusion region.
1. A separation diffusion-castle structure in a semiconductor device, characterized in that diffusion regions No. 11 and II2 are connected. (2) The isolation diffusion region in the semiconductor device according to claim 1, wherein the semiconductor substrate is an n-type substrate, boron is used as the first impurity, and aluminum is used as the second impurity. structure.