JPS6159532B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and more particularly to an improvement in a method for selectively diffusing aluminum into a silicon substrate.

Since aluminum has a high diffusion rate in a silicon substrate, it is a very effective dopant for forming deep diffusion layers. BACKGROUND ART Conventionally, as a method for selectively diffusing aluminum into a silicon substrate, a method is known in which a predetermined pattern of aluminum is formed on the surface of a silicon substrate by vapor deposition or the like, and then the substrate is heated and diffused. In particular, when the area of the pattern of the aluminum vapor deposition film is large, the aluminum alloy becomes particulate due to surface tension when heated, causing unevenness on the bonding surface of the diffusion, and the aluminum may move on the surface of the silicon substrate due to gravity during heat treatment. It has drawbacks such as drooping and the pattern is greatly distorted.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a method for manufacturing a semiconductor device using an accurate aluminum selective diffusion method.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a sectional view of a silicon substrate showing a process diagram of selective aluminum diffusion.

a indicates the silicon substrate 11; Silicon substrate 1
1 has n-type conductivity, resistivity of 90 to 110 Ω-cm, no dislocation, (111) plane, diameter of 50 mm, and thickness of 450 mm. b
is an aluminum layer 12 on the surface of a silicon substrate 11.
This shows what was formed. The aluminum layer 12 is vacuum-deposited by electron beam heating at a deposition rate of 0.005 μm/s at a silicon substrate temperature of 250° C. and a pressure of 3×10 ⁻⁶ Torr or less using an aluminum wire with a purity of 99.9995% as a source. be. The thickness of the aluminum layer 12 was examined in the range of 0.1 to 8 μm. c shows a part of the aluminum layer 12 in which a pattern 12a is formed by ordinary photolithography. The aluminum pattern 12a has a width of 10,
20, 50, 100, 200, 500, 1000μm line shape,
Dot shape with a diameter of 10 to 1000 μm and a diameter of 4 mm
It has a ring shape of 10 to 1000 μm. However, if the aluminum layer 12 is thick, it is difficult to photo-etch a minute pattern, so this was excluded. A mixed solution of phosphoric acid, acetic acid, and nitric acid was used as the etching solution, and after the photoresist was removed, the aluminum-deposited surface was rinsed with a 10% aqueous potassium hydroxide solution and hydrochloric acid. d shows a cross-sectional view of the shape after heat-treating the silicon substrate and selectively diffusing aluminum. Diffusion is at a temperature of 1250
°C, time 24 h, and the atmosphere is a mixed flow of nitrogen and oxygen.

FIG. 2 shows the relationship between the thickness of the aluminum pattern 12a and the depth of diffusion.

The depth of the diffusion bond is approximately 12 mm
It can be seen that the variation varies depending on the thickness of the aluminum pattern 12a, and that the thinner the aluminum pattern 12a, the greater the variation in the diffusion layer, and the thicker the aluminum, the greater the variation.

FIG. 3 shows the uniformity of diffusion bonding and the quality of pattern accuracy in the relationship between the thickness of the aluminum pattern 12a and the size of the pattern in the above selective aluminum diffusion.

In the figure, the mark ◎ indicates bonding uniformity within ±3% and pattern accuracy within ±5%. The ○ mark indicates that any of the line, dot, and ring shapes is outside the above accuracy range, and the x mark indicates that all of them are outside the range.

If the pattern size is large and a thick aluminum pattern is used, aluminum will drip down the surface of the silicon substrate during the diffusion process, deteriorating pattern accuracy. On the other hand, when the pattern size is small, aluminum is oxidized and becomes lumpy due to surface tension during the diffusion process, impairing the uniformity of diffusion bonding. From the above results, it was found that the range shown by diagonal lines in FIG. 3 is appropriate for diffusion from the aluminum pattern 12a into the silicon substrate. In addition, the diffusion temperature is 1100℃
Experiments were also conducted for the case where the results were similar.

The reason that the depth of diffusion and pattern accuracy do not depend on the diffusion temperature is that aluminum drips down the surface of the silicon substrate and becomes lumpy due to surface tension in the early stage of heating (heating rate of 100℃). /
This seems to be because it occurs at

The above results were applied to the formation of an isolation layer (throughput diffusion layer) for manufacturing a planar thyristor.

FIG. 4 shows a cross-sectional view of the planar thyristor pellet 20. After forming isolation regions 21 by selectively diffusing aluminum from both main surfaces of the silicon substrate 11, ordinary semiconductor device manufacturing techniques are used to form an oxide film 22, photolithography, a boron emitter diffusion layer 23, and a base. Implement the diffusion layer 24, phosphorus emitter diffusion layer 25, etc.
Forms a pn junction. After a moat is formed by etching, a glass passivation 26 is applied to the bond exposed on the inner surface, and electrodes 27 to 29 are formed by vapor deposition, the moat is cut at the center of the isolation region 21 to form individual thyristor pellets. It is separated into 20 parts. At this time, when forming the isolation region 21 by selective aluminum diffusion, it is advantageous to use a thick aluminum pattern as shown in FIG. 2, since the isolation region can be formed in a short time.

FIG. 5a shows a portion of the aluminum pattern for isolation region 21. FIG. Width of aluminum pattern d: 100 μm, D: pitch 6.5 mm, orthogonal lattice shape, radius of curvature R of intersection corner is 500 μm, thickness of aluminum pattern 30
It is 0.3 μm. The size of the pattern in the isolation region is determined by the element design, and the thickness of the aluminum pattern 30 is selected from optimal conditions from FIGS. 2 and 3.

However, it has been found that in a lattice pattern, the line shape is different from the dot shape, and aluminum drips at the intersections of the lattice, deteriorating the pattern accuracy.

Figure 5b shows a schematic diagram of aluminum dripping at grid intersections.

This is thought to be because the amount of aluminum effectively increases at the intersections of the grid, causing dripping. As a countermeasure to this problem, reducing the thickness of the aluminum pattern may be considered, but this is disadvantageous because it requires a long time for isolation diffusion.

In contrast, the inventors have found that this problem can be solved without prolonging the diffusion time by using an improved pattern with aluminum defects at the intersections in the grid pattern.

FIG. 6 shows an example of an improved pattern.

In a, the effective amount of aluminum at the intersections is made equal to that at the edge portions 32 by providing an aluminum missing portion 31 in the center of the intersection region of the lattice of the aluminum pattern 30.

In b, the aluminum pattern 30 for each isolation region is formed into a ring shape of equal thickness, thereby providing a cutout in the center and eliminating intersections. This pattern is also extremely effective in cutting thick silicon substrates. That is, in a planar type thyristor, a plurality of semiconductor elements are formed on a silicon substrate and then cut at the center of the isolation region to separate them into individual pellets. Cutting can be done mechanically using a wire saw or diamond scriber, or thermally using a laser scriber.

When a thick silicon substrate is used, a long period of diffusion is required to form the isolation region, so that a strong alumina film with an oxidized aluminum pattern is formed on the surface of the isolation region. If a thick and strong alumina film is formed, there are disadvantages such as cracks in the pellet during cutting and poor directionality of the cutting grooves.

In the ring-shaped isolation region pattern, the aluminum pattern is removed from the cut grooves in advance, so the above-mentioned drawbacks can be prevented.

The aluminum pattern in the isolation region c is formed by a combination of dots 33 with a diameter of 50 .mu.m and lines 34 with a width of 50 .mu.m.

From FIGS. 2 and 3, dots and lines of 50 .mu.m can form isolation regions with the shortest diffusion time due to the relationship between pattern accuracy and aluminum pattern thickness. At this time, aluminum diffusion occurs not only in the depth direction of the silicon substrate, but also in the depth direction of the silicon substrate.
Each dot 33 and line 3 to spread horizontally
The diffusion layer below 4 is continuous.

All of the three methods described above were able to form isolation regions with good diffusion bonding uniformity and pattern accuracy. The improved aluminum patterning of the present invention does not require any special steps and can be formed by aluminum photolithography. This aluminum pattern can be used as alignment marks for subsequent photolithography of the base, emitter diffusion layer, etc.

According to the present invention, dripping of aluminum can be prevented and selective diffusion of aluminum can be performed with high precision.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing the process of selectively diffusing aluminum into a silicon substrate, Figure 2 is a characteristic diagram showing the relationship between aluminum pattern thickness and diffusion bonding depth in selective aluminum diffusion, and Figure 3 is a diagram showing the relationship between aluminum selective diffusion. A characteristic diagram showing the applicable range of the size of the diffusion pattern and the thickness of the aluminum pattern in diffusion. Figure 4 is a cross-sectional view of a planar thyristor pellet. Figures 5 a and b are isolation diagrams of a conventional planar thyristor. A plan view of an aluminum pattern for forming a region and a schematic view of a state in which aluminum drips down. FIGS. 6a, b, and c are plan views of an aluminum pattern for forming a planar thyristor according to the present invention. DESCRIPTION OF SYMBOLS 11... Silicon base, 12... Aluminum vapor deposition film, 30... Isolation pattern, 31... Defect part.

Claims (1)

[Claims] 1. After forming a grid-like aluminum pattern on at least one main surface of a silicon substrate, the silicon substrate is heated to diffuse aluminum into the silicon substrate, and the silicon substrate is separated by an isolation region. In a method for manufacturing a semiconductor device that includes a step of separating into a plurality of surrounded semiconductor devices,
A method for manufacturing a semiconductor device, characterized in that aluminum is diffused into a silicon substrate by providing a defective portion of aluminum within an intersection portion of the aluminum pattern. 2. A method for manufacturing a silicon semiconductor device according to claim 1, characterized in that a defect is provided in the center of the aluminum pattern. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the aluminum pattern has a defective portion formed by an arrangement of minute dots or narrow lines.