JPS5986234A - Quality evaluation of diffused wafer - Google Patents

Abstract

PURPOSE:To obtain an improving method for discriminating the propriety of the bonding property when a P-N junction is formed by diffusing an impurity in the following steps by measuring the reverse leakage current of the P-N junction formed between layers by a heat treatment of specific conditions. CONSTITUTION:A P-N junction is formed by heat treating a silicon wafer formed by laminating two layers of P type having different densities at temperatures of 430-500 deg.C for the period required to invert only the low density side to N type, a reverse leakage current is measured for the junction, thereby evaluating the quality of the wafer and particularly evaluating the junction characteristics. For example, a diffused wafer 11 which becomes an N type layer 11a from the low density side P type layer is formed by heat treating it at 470 deg. for 13hr in nitrogen atmosphere. After a masking is executed by oxidation resistance wax, a mesa groove 12 is formed by mesa etching in depth isolated in N type layers from each other for approx. 2min with etchant having fluoric acid:acetic acid:nitric acid=1:1:2, and the wax is removed by Trichlene. Then, wirings of diode curve tracer 5 are connected to measure the reverse leakage current of the P-N junction.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to a method for evaluating the quality of diffusion wafers, especially for the production of pNP transistors, diodes, etc. has a higher concentration of P than the substrate.
The present invention relates to a method for evaluating the quality of a diffused wafer 1 in which mold impurities are diffused.

[゛Technical background of the invention]

Conventionally, to manufacture mainly PNP transistors, a silicon wafer (1a) whose conductivity type is P type as shown in FIG. 1) is used. This diffusion wafer is P
Type silicon wafer (hereinafter silicon wafer is abbreviated as wafer) is B! 0. After being immersed in an isopropyl alcohol solution, diffusion is performed at high temperature for a long time using a so-called deposition and slumping method, and then the diffusion layer on one main surface side is removed by #1000 lapping and mirror lapping. Normally, diffusion in this case is carried out in a diffusion furnace at 12
Since the heat treatment is carried out at a high temperature of 50' to 1300°C and for a long time of 150 to 200 hours, contamination from this diffusion furnace occurs. Therefore, in a later process, N-type impurities are diffused into the P-type first layer. When a PN junction is formed by applying this process, the reverse leakage current may become abnormally large and the attractive characteristics of the product may not be satisfied, so it is necessary to evaluate and guarantee its quality before proceeding to the subsequent process. .

Conventionally, as a means of guaranteeing the quality of wafers, samples were taken from the base lot of wafers to be evaluated as shown in Fig.
The quality was evaluated by the steps shown in FIGS. 1al to 1dl. In other words, CVD is applied to the failed wafer (1).
(Figure 1al)
Then, phosphorus (P) was diffused at 1100-1250°C to form a PN junction (Figure (b)), and mesa etching was performed to form mesas S+41, 141, etc. (Figure 1cl). The diode curve tracer 15) is wired to perform the measurement (Fig. 1d)).

[Problems with background technology] - According to the above-mentioned conventional technology, it takes N to evaluate a diffusion wafer.
Since this is done by forming a type diffusion layer, 11
Requires high-temperature heat treatment of 00 to 1250°C. This heat treatment has the drawback of causing new contamination from the diffusion furnace and induction of new crystal defects, which prevents accurate evaluation. However, there are drawbacks such as the need for a high-temperature diffusion furnace for forming an N-type diffusion layer and a special diffusion layer, which is expensive.

[Purpose of the invention]

In view of the above-mentioned conventional drawbacks, this invention aims to improve the quality of a wafer having a structure in which a P-type impurity is diffused on one main surface of a P-type silicon substrate at a higher concentration than that of the substrate. Provided is an improved method for determining the quality of the bonding characteristics when a PN junction is formed.

[Summary of the invention]

It is known that oxygen present in silicon generates donors when it is subjected to heat treatment at temperatures close to 450°C.

Taking advantage of this property, a silicon wafer in which two P-type layers with different concentrations are stacked is heat-treated at a temperature of 430 to 500°C for the time required for only the low concentration side to be inverted to N-type to form a PN junction. This is a method for evaluating the quality of this wafer, especially the bonding characteristics, by forming a wafer and measuring the reverse leakage current of this bond.

[Embodiments of the invention]

Next, one embodiment of the present invention will be explained in detail with reference to FIG. The wafer used for evaluation had a diameter of 76 mm and a thickness of 5 mm.
00μm, resistivity 16~'1QtJ side P-type silicon base is B, 0. After being immersed in an isopropyl alcohol solution of
A boron diffusion layer is formed at 102°/6-, and after removing the diffusion layer on one side, mirror polishing is performed on one side to a thickness of 230 μm to obtain the diffusion layer 1 shown in FIG. This diffusion wafer has 40 different lofts for its deposition and slumping, ie.

Evaluation was performed on A lot, B lot, C lot, and D lot.

That is, two sheets were extracted from each loft out of about 90 sheets, and quality evaluation was performed according to the steps shown in FIG. 3 1al to 1cl. First, in a nitrogen atmosphere, 470
℃ for 13 hours (Figure (a)).

As a result, a diffusion unihari is formed in which the P layer on the low key degree side becomes the N layer (lla). Next, add acid-resistant wax to J:
4 After masking the RI angle at a 5 ays pitch, oxycarboxylic acid (CH, C0OH): nitric acid ()
Mesa etching is performed to a depth where the N layers are separated from each other using an etching solution of INO, )=1:1:2 for about 2 minutes to form a mesa groove, and then the wax is removed using trichane. (Figure (h)). Next, wire the diode curve tracer (5) and measure the reverse leakage current of the PN junction (Figure (C)). If the result shows soft breakdown, it is a defective product. Lofts with hard breakdown are judged to be good quality lofts.

As described above, the leakage current in the reverse direction was determined at ten points on the wafer using a diode curve tracer, and the results are shown in FIG. As is clear from this figure, lot A was determined to be a defective product, and lots BD were both determined to be good products.

〔Effect of the invention〕

According to this invention, when evaluating the quality of a diffusion wafer, especially the bonding characteristics, it is only necessary to perform low-temperature heat treatment without requiring diffusion of N-type impurities by high-temperature heat treatment. This has the following advantages.

(11N for forming PN junction and evaluating quality)
Since the mold layer is formed by donor generation through low-temperature heat treatment at 430 to 500° C., the effects of high-anchor heat treatment such as contamination and induction of crystal defects can be ignored and accurate evaluation is possible.

To confirm this, two more sheets were taken from each of the diffusion sea urchins/'% of lots A to D mentioned in the Bankosho example.
Looking at Figure 4, which shows the results of measuring the reverse leakage current of a PN junction formed using the conventional method, it is clearly seen that there is a defect in the A-lot (excessive leakage current), but there is also leakage at the B-D opening. The current was somewhat large, making it difficult to distinguish between good and defective products, but this is probably due to the influence of contamination during the heat treatment during the formation of the N-type layer. On the other hand,
In Figure 5, which shows the leakage current according to the method of this invention, the A lot is defective and the R-D lot is good. I did ■. 1. It also matches well with FIG. 6, which shows the distribution of o (base-collector current) values for each loft.

(2) In the conventional method, a diffusion source of an N-type impurity such as phosphorus and associated equipment power I are necessary, but this is not necessary in the present invention.

(31 In the conventional method, one diffusion furnace is used to form the N-type layer.
A high-temperature device of about 100 to 1250'C was required, but in the present invention, a low temperature of about 430 to 500'C is required, so it is economical and has the advantage of being effective against deformation of the board, etc. .

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the wafer to be evaluated, and Figure 2 is a sectional view of the wafer to be evaluated.
dl is a cross-sectional view for explaining a conventional diffusion wafer quality evaluation method, FIG. 3 is a cross-sectional view for explaining a method of an embodiment of the present invention, and FIG. FIG. 5 is a diagram showing the measurement results of the reverse leakage current of a PN junction according to the conventional method; FIG.
The figure is a diagram showing the results of measuring the reverse leakage current (Icno) for the product. la P-type silicon substrate 5 Diode curve tracery
Diffusion wafer) 11a NN of diffusion wafer 12 Mesa groove agent Patent attorney Inoue - Male 1st figure 2nd figure 3rd figure 4th row/r → hbc. Figure 5 Figure 6

Claims (1)

[Claims] P-type impurity concentration is 3 x 10” to 4 x 10+6/-
The first layer is P-type and higher than the first NjI. A silicon wafer consisting of a second layer diffused to an N impurity concentration of 1 x 1 ()IT ~ 5 x 1o''/- was heated at 430°.
Heat treatment is performed at ~500° C. for 4 to 50 hours to reverse the N-type number of the first layer and form a PN junction with the second layer;
A method for evaluating the quality of a diffused wafer, characterized in that the quality of the silicon wafer is evaluated by determining the reverse leakage current of the PN junction.