JPH0691145B2 - Semiconductor wafer sorting method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for selecting a semiconductor wafer, and more particularly to a method for selecting a semiconductor wafer in a buried diffusion step in a semiconductor device manufacturing process.

(Prior Art) In a method of manufacturing a semiconductor device, particularly when an N ⁺ type buried layer is formed on a P type semiconductor substrate, there are many subsequent heat treatment steps, and therefore, impurities such as antimony or arsenic having a small diffusion constant are used. After selectively forming an N ⁺ type buried layer on the P type semiconductor substrate with a compound and a chloride, an N type epitaxial layer is formed on the P type semiconductor substrate and the N ⁺ type buried layer. An isolation layer, a base layer and an emitter layer are formed in the N type epitaxial layer by diffusion.

However, when the element is formed by the diffusion process and the electrode is formed and then the characteristics thereof are inspected, as shown in FIG. 2, in the case of a good semiconductor element, as shown as a waveform a, The breakdown voltage between the collector layer and the P-type semiconductor substrate is high, and in the case of a defective semiconductor element, the breakdown voltage between the collector layer and the P-type semiconductor substrate is low, as indicated by the waveform b.

A mechanism showing such characteristics will be described with reference to FIGS. 3 and 4.

As shown in FIG. 3 (a), the thermal oxide film 2 on the P-type semiconductor substrate 1 is partially etched, and a window is opened in a portion where buried diffusion is performed. In this case, it is assumed that there is a foreign substance 3 on the thermal oxide film 2, which becomes a nucleus of the devitrification phenomenon of the thermal oxide film, which will be described later.

Next, as shown in FIG. 3B, embedded diffusion of antimony or arsenic is performed to form an embedded diffusion layer 5 in the P-type semiconductor substrate 1. On the other hand, the devitrification portion 4 is formed in the thermal oxide film 2 with the foreign matter 3 as a nucleus, and the N ⁺ type diffusion layer 6 is diffused to a region other than the designated portion of the P-type semiconductor substrate 1 through the crack of the devitrification portion. .

That is, it is well known that if there is any foreign matter on the thermal oxide film, the devitrification phenomenon occurs in the thermal oxide film with the foreign matter as a nucleus when the diffusion temperature is appropriate, and antimony or arsenic is passed through the devitrification portion. Are diffused, and N ⁺ type impurities are diffused outside the designated region.

Next, as shown in FIG. 3C, the oxide film 2 is entirely removed.

Next, as shown in FIG. 3D, epitaxial growth is performed on the P-type semiconductor substrate 1 to form an epitaxial growth layer 7.

Thereafter, as shown in FIG. 3 (e), the isolation layer 8 is formed by diffusion. Then, for example, after diffusion of the isolation layer, the N ⁺ -type diffusion layer 6 outside the designated region is formed.
And the isolation layer 8 collide. When this part A is enlarged, it becomes as shown in FIG. At this time, the impurity concentration of the diffusion layer 6 formed of antimony or arsenic outside the designated region is much higher than the impurity concentration of the epitaxial layer 7. Therefore, the reverse breakdown voltage of the defective junction 10 is lower than the reverse breakdown voltage of the good junction 9.

(To be Solved by the Invention Problems) However, the front removed N ⁺ -type buried layer formed prior to the oxide film as a way of impurities in the outside of the defined area when the N ⁺ -type buried layer forming checks whether diffused However, there is a method of examining a trace of diffusion (generally called rosette) on the P ⁺ type semiconductor substrate. However, the rosette that can be discovered by this method has a severe devitrification phenomenon, and only the oxide film with the oxide film burned on the P ⁺ type semiconductor substrate is discovered.

When the P ⁺ type semiconductor substrate is processed by Sirtl Etch or the like, impurity diffusion other than the designated region is found other than the place where the rosette is recognized by this method. This means that if the devitrification phenomenon is not so severe, the oxide film
Only the impurities pass through the cracks in the part where the devitrification phenomenon occurs, without advancing to the place where it is burned onto the P ⁺ type semiconductor substrate,
It indicates that the data is diffused outside the specified area. From this, the destructive inspection of the P-type semiconductor substrate has been the only way to detect the diffusion outside all the designated regions. Therefore, whether or not antimony or arsenic has diffused out of the designated region and has an influence cannot be determined without conducting a characteristic inspection through the steps up to electrode formation. Therefore, in the step of forming the N ⁺ type buried layer, even the electrodes are formed on the already defective semiconductor substrate, and the cost spent for this is wasted.

It is an object of the present invention to eliminate the above-mentioned problems, and to provide a method for selecting semiconductor wafers that is non-destructive immediately after the formation of an N ⁺ type buried layer and can accurately select good products and defective products.

(Means for Solving Problems) The present invention relates to a method for selecting a semiconductor wafer, wherein an N ⁺ buried layer is formed by using an antimony or arsenic compound as a substance for crystallizing an oxide film on a P-type semiconductor substrate. When selectively forming by diffusion, the oxide film on the P-type semiconductor substrate is partially removed immediately after the diffusion, and the traces of devitrification on the oxide film that appear are inspected to determine whether the semiconductor wafer is good or defective. The judgment is made.

(Operation) According to the present invention, in the method for selecting semiconductor wafers, the P
Oxide film on the P-type semiconductor substrate immediately after the diffusion when the N ⁺ buried layer is selectively diffused by a compound of antimony or arsenic as a substance for crystallizing the oxide film on the P-type semiconductor substrate Of the semiconductor wafer, by inspecting traces of devitrification on the oxide film that appeared,
Since the defect is determined, it is possible to determine the defect at the stage of forming the N ⁺ buried layer, and it is possible to eliminate waste of cost such as forming an electrode of a defective semiconductor wafer as in the conventional case. .

(Example) Hereinafter, the Example of this invention is described in detail, referring drawings.

FIG. 1 is an explanatory view of a semiconductor wafer selection method according to the present invention.

First, in FIG. 1 (a), an N ⁺ type buried layer should be formed.
A thermal oxide film 12 is formed on the entire surface of the P ⁻ type semiconductor substrate 11, and N ⁺
The thermal oxide film 12 on the region where the mold burying layer is formed is selectively etched to expose a partial surface of the P ⁻ type semiconductor wafer 11. Here, it is assumed that the foreign matter 13 serving as the nucleus of devitrification exists on the thermal oxide film 12.

Next, as shown in FIG. 1 (b), antimony or arsenic is diffused into a designated region of its oxide or chloride by a coating method or a gas diffusion method to form an N ⁺ type buried layer 14. On the other hand, a devitrification portion is formed in the thermal oxide film 12 with the foreign substance 13 as a nucleus, and the N ⁺ -type diffusion layer 16 is diffused to a region other than the designated portion of the P-type semiconductor substrate 11 through a crack in the devitrification portion.

Next, after the completion of the diffusion, as shown in FIG. 1C, about 20 to 50% of the film thickness of the thermal oxide film 12 of all the wafers is removed and the surface thereof is inspected. In this case, the thermal oxide film in the portion where devitrification has occurred is denatured to form cracks. This can hardly be observed on the surface where the oxide film after diffusion is not removed. But as in this step,
If the oxide film is removed a little, the trace 15 of the devitrified portion can be clearly observed. FIG. 5 is an enlarged plan view with a microscope, and as is clear from this figure, the trace 15 of the devitrified portion is clearly observed. The traces that can be observed in this state cannot be found on the P ⁻ type semiconductor substrate after the oxide film is completely removed, but the N ⁺ type diffusion occurs in the P ⁻ type semiconductor substrate in the form of diffusion outside the designated region. This includes all the parts where the object layers are formed.

Further, as shown in FIG. 6, there is a correlation between the number of traces per unit area and the final non-defective product rate, and a P-type semiconductor wafer with many traces becomes a defective product. Then, assuming that the P-type semiconductor wafer having almost no trace has no influence of diffusion of N ⁺ -type impurities to the outside of the designated region, the subsequent steps are performed. That is, after removing all the remaining thermal oxide film of the P ⁻ type semiconductor wafer on which the N ⁺ type buried layer 14 is formed, the epitaxial layer 17 is formed as shown in FIG. 1D. After that, a thermal oxide film 18 is formed on the upper surface of the epitaxial layer 17, and the thermal oxide film 18 on the region where the isolation layer is to be formed is selectively etched to expose the surface of the epitaxial layer 17 in a ring shape. Next, P-type impurities are diffused from the exposed surface of the epitaxial layer 17 to form an isolation layer 19 as shown in FIG. 1 (e). After that, a desired element is formed in the N-type epitaxial layer surrounded by the isolation layer 19, and electrodes and wirings are formed.

INDUSTRIAL APPLICABILITY The present invention can be applied to general semiconductor devices that diffuse an antimony or arsenic oxide or chloride to form a buried layer.

The present invention is not limited to the above embodiment,
Various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

(Effects of the Invention) As described above in detail, according to the present invention, after the N ⁺ buried layer is formed on the P-type semiconductor wafer, the oxide film is removed halfway and traces of devitrification of the oxide film are obtained. By inspecting, it is possible to accurately select good and defective semiconductor wafers.

Therefore, it is possible to quickly select semiconductor wafers that are already defective at the stage of forming the N ⁺ buried layer as in the prior art, and to eliminate waste in the subsequent steps in the case of defective products.

[Brief description of drawings]

FIG. 1 is an explanatory view of a method for selecting semiconductor wafers according to the present invention, FIG. 2 is a withstand voltage characteristic view of a semiconductor element, FIG. 3 is an explanatory view of problems of a conventional semiconductor wafer, and FIG. FIG. 5 is an enlarged view of a portion, FIG. 5 is a partially enlarged plan view of FIG. 1, and FIG. 11 …… P ^- type semiconductor substrate, 12 …… thermal oxide film, 13 …… foreign matter,
14 …… N ⁺ type buried layer, 15 …… Mark of devitrification part, 16 …… N ⁺ type diffusion layer (outside the designated area), 17 …… Epitaxial layer, 18…
… Thermal oxide film, 19… Isolation layer.

Claims (3)

[Claims] 1. A step of (a) forming an N-type buried layer on a P-type semiconductor wafer using a diffusion source made of a substance capable of crystallizing an oxide film, and (b) the semiconductor after completion of drive-in. Providing a step of partially removing the film thickness of the oxide film on the wafer, (c) inspecting whether there is a trace of devitrification on the oxide film, and (d) outside the designated region of the semiconductor wafer. A method of selecting semiconductor wafers, comprising determining whether or not there is diffusion by the diffusion source. 2. The method for selecting a semiconductor wafer according to claim 1, wherein an oxide of antimony or arsenic is used as the substance in (a). 3. The method for selecting a semiconductor wafer according to claim 1, wherein a chloride of antimony or arsenic is used as the substance in (a).