JPH09237792A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor device whose breakdown strength is not lowered and which can prevent a change with the passage of time in a current amplification factor by a method wherein the upper part of the base-collector junction of a transistor is covered with a silicon nitride film and the action of an oxygen baking operation is performed only to its emitter-base junction. SOLUTION: A semiconductor device has a planar structure in which a base- collector junction 16 and a base-emitter junction 17 are terminated on the surface of a substrate 11. In the semiconductor device, an Si nitride film 18 is deposited, by a CVD method, on an Si film 14 on the surface of the substrate 11, the upper part of the base-collector junction 16 is covered by a hot etching operation, and the upper part of the base-emitter junction is patterned so as not to be covered. After that, the Si oxide film 14 on a base region 12 and on an emitter region 13 is opened so as to form contact holes, Al is deposited so as to be patterned, and Al electrodes 15 as a base and an emitter are formed. Then, the Al electrodes 15 are annealed, and a wafer is baked and treated in an oxygen atmosphere.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to improvement of reliability in a semiconductor device such as a transistor.

[0002]

2. Description of the Related Art In semiconductor devices such as NPN transistors and PNP transistors, a baking process in an oxygen atmosphere is performed near the final step in order to prevent the current amplification factor (hFE) from deteriorating with time, and the silicon substrate and the surface are subjected to a baking process. The interface state with the silicon oxide film is increased to prevent the fluctuation of hFE.

FIG. 2 is a sectional view showing a conventional semiconductor device. In the figure, 1 is a collector layer, an N type semiconductor substrate having a high concentration layer on the back surface, 2 is a P type base region, 3 is an N + type emitter region, 4 is a silicon oxide film,
Reference numeral 5 is an aluminum electrode. Base region 2 and emitter region 3
Is formed by selective diffusion from the surface of the substrate 1, and therefore the PN junction 6 is exposed on the surface of the substrate 1 and the surface is covered with the silicon oxide film 4 to provide a planar semiconductor device.

After the formation of the aluminum electrode 5 is completed, the entire substrate 1 is heat treated at 800 ° C. in an oxygen atmosphere for 1 hour.
By performing the operation for about 100 minutes, the fluctuation of hFE is prevented.

[0005]

However, baking in an oxygen atmosphere acts on the base-emitter junction.
Although it has the effect of preventing hFE deterioration, it has the drawback that when it acts on the base-collector junction, it suppresses the expansion of the depletion layer at the base-collector junction, which causes the side-effect of lowering the collector-base breakdown voltage of the transistor. .

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. The upper part of the base / collector junction of a transistor is covered with a silicon nitride film, and oxygen baking is applied only to the emitter / base junction. As a result, the present invention provides a method for manufacturing a semiconductor device, in which the breakdown voltage does not decrease and the current amplification factor can be prevented from changing over time.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional view showing a semiconductor device of the present invention. In the figure, 11 is a collector layer, an N-type silicon semiconductor substrate having a high concentration layer on the back surface, 12 is a P-type base region, 13 is an N + -type emitter region, 14 is a silicon oxide film, and 15 is aluminum. It is an electrode.

The base region 12 and the emitter region 13 are formed by selectively diffusing the silicon oxide film formed on the surface of the substrate 11 by a normal photoetching technique and using the oxide film as a selective mask. When base diffusion and emitter diffusion are performed in this way, the base-collector junction 1
6, and the base-emitter junction 17 has a planar structure terminating at the surface of the substrate 11.

Next, the silicon oxide film 1 on the surface of the substrate 11
4, a silicon nitride film 18 having a film thickness of about 1000 Å is deposited by the CVD method, and is patterned by photoetching so as to cover the upper portion of the base-collector junction 16 and not the upper portion of the base-emitter junction. The silicon nitride film 18 is at least the base-collector junction 17
It suffices that the upper part of the collector be covered, and it is not always necessary to cover the entire region that becomes the collector.

Thereafter, the silicon oxide film 14 on the base region 12 and the emitter region 13 is opened to form a contact hole, and aluminum or aluminum-silicon alloy is deposited by sputtering or vapor deposition method, and this is patterned by photoetching. By doing so, the base and emitter electrodes 15 are formed. Electrode pads for external connection are also formed in this step.

After the aluminum electrode 15 is annealed (alloying growth), as a final step, the wafer is baked in an oxygen atmosphere at 700 to 800 ° C. for about 100 minutes. In this step, the interface state is increased at the silicon / oxide film interface near the base / emitter junction 16. This interface level has the function of trapping and stabilizing ionic charges due to external factors, and increasing the level stabilizes the surface state, preventing the current amplification factor hFE from deteriorating over time. it can. On the other hand, base-collector junction 17
Since the silicon nitride film 18 blocks oxygen at the nearby silicon / oxide film interface, the interface level does not increase. The interface level near the base-collector junction 17 acts to suppress the expansion of the depletion layer that occurs in the base-collector junction near the interface. Therefore, by suppressing the increase in the interface level, Inter-collector breakdown voltage Vcbo
Can be prevented.

[0012]

As described above, according to the present invention,
Since oxygen baking is performed only on the base-emitter junction 16, it is possible to manufacture a transistor in which the current amplification factor hFE is not deteriorated with time and the breakdown voltage is not deteriorated by baking. Furthermore, since the silicon nitride film 18 prevents mobile ions from entering after being manufactured, the reliability of the product can be improved.

[Brief description of drawings]

FIG. 1 is a step view for explaining the present invention.

FIG. 2 is a step view for explaining a conventional example.

Claims (1)

[Claims] 1. A reverse-conductivity-type base region is formed on the surface of a single-conductivity-type semiconductor layer to be a collector, and a single-conductivity-type emitter region is formed on the surface of the base region. In the method of manufacturing a semiconductor device, the upper part of the PN junction between the collector and the base region is covered with a silicon nitride film, and the upper part of the PN junction between the base region and the emitter region is covered with the silicon nitride film. A method of manufacturing a semiconductor device, wherein the baking process is performed in a state where the semiconductor device is not covered with.