JPH0241168B2 - - 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 heat treatment process in a gold diffusion process for improving the switching speed of a bipolar transistor.

Generally, when bipolar transistors are manufactured on a semiconductor substrate, heavy metals such as gold, copper, and iron are diffused as carrier lifetime killers in order to improve the switching characteristics of the transistors.

FIG. 1 is a cross-sectional view of a general bipolar transistor. 1 is a semiconductor substrate, and 2 has N on its surface.
A type collector region 2, a P type base region 3, and an N type emitter region 4 are formed within the base region. 5 is a collector contact part, 6 is a buried layer,
7 is an element isolation section.

In the conventional gold diffusion process, after each region as described above is formed (diffused), a gold layer is deposited on the back surface of the substrate, and then heat treatment (1000-1100°C) is performed in an oxygen gas atmosphere. Gold was diffused into the substrate. To obtain sufficient life time killer, it is necessary to implant enough gold into the substrate. To do this, increase the temperature during heat treatment,
It is necessary to increase the solid solubility between gold and silicon of the substrate. However, when the temperature is raised to increase the solid solubility, diffusion of the emitter region formed by N-type impurities such as phosphorus (P) also progresses, causing the problem that a sufficient breakdown voltage of the transistor cannot be obtained. come. In other words, the breakdown voltage characteristic, which is one of the important characteristics of a transistor along with the switching speed, depends in part on the depth Xj of the emitter region 4, and in order to obtain a predetermined breakdown voltage, the depth of the diffusion of the emitter region 4 must be adjusted. need to be controlled.

Therefore, in the past, the temperature during heat treatment could not be raised much due to the problem of diffusion in the emitter region, and as a result, sufficient gold diffusion could not be achieved.

Therefore, an object of the present invention is to be able to control the diffusion of the emitter region using a parameter different from the temperature that controls gold diffusion, and to ensure sufficient gold diffusion that the emitter region does not diffuse even if the temperature is raised. The objective is to provide a manufacturing method that can suppress the

The present invention is characterized by a step in which a base region of an opposite conductivity type is provided on the surface of a substrate of one conductivity type, an emitter region of one conductivity type is provided in the base region, and a layer of heavy metal is grown on the back surface of the substrate. and heat-treating the substrate in a mixed gas atmosphere of oxygen gas and inert gas while controlling the mixing ratio of the mixed gas to diffuse the heavy metal into the substrate and to heat the emitter region with the mixed gas. and a step of diffusing the mixture to a depth determined by the mixing ratio.

An embodiment of the present invention will be described in detail below with reference to the drawings.

In this example, after a gold layer is deposited on the back surface of the substrate, the substrate is heat-treated in a mixed gas atmosphere of oxygen gas and nitrogen gas. FIG. 2 is a graph showing the relationship between the volume concentration of oxygen gas in the mixed gas and the depth of diffusion in the emitter region during heat treatment. The various conditions are that the diffusion substrate is a P-type silicon substrate, the surface crystal plane is a <111> plane, the sheet resistance is 1Ωcm, and the diffusion source is phosphorus (P).
The concentration was 25Ω/□, the temperature was 1050℃, and the processing time was 60 minutes. The oxygen concentration was as shown in the figure.

Although the principle is unknown, as is clear from this graph, the diffusion depth Xj of the emitter region becomes shallower by reducing the amount of oxygen gas in the mixed gas. In other words, the depth of diffusion in the emitter region can be suppressed by mixing an inert gas such as nitrogen gas into the atmosphere, which was conventionally done in an oxygen gas atmosphere.

Therefore, in the gold diffusion process, if the processing temperature is increased and the amount of inert gas in the atmosphere is controlled, sufficient gold diffusion can be achieved.
Moreover, the diffusion depth Xj of the emitter region can be suppressed and controlled to a desired depth. In particular, as shown in FIG. 2, by reducing the oxygen concentration to 10% or less, the diffusion depth of the emitter region can be sufficiently suppressed.

As explained above, according to the present invention, in the gold diffusion process, sufficient gold can be injected into the substrate by high temperature treatment so as to have a sufficient life time killer and increase the switching speed. Optimal breakdown voltage characteristics can be obtained by controlling the diffusion depth of the emitter region to a desired value while suppressing it.

Incidentally, as the inert gas, the same effect can be obtained by using Ar or the like in addition to nitrogen.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a general bipolar transistor, and FIG. 2 is a graph diagram for explaining the present invention. In the figure, 1: semiconductor substrate, 2: collector region,
3: base region, 4: emitter region, 8: heavy metal layer.

Claims (1)

[Claims] 1. A step of providing a base region of an opposite conductivity type on the surface of a substrate of one conductivity type, an emitter region of one conductivity type within the base region, a step of growing a layer of heavy metal on the back surface of the substrate, and a step of growing an oxygen gas layer. The substrate is heat-treated in a mixed gas atmosphere of and an inert gas while controlling the mixing ratio of the mixed gas to diffuse the heavy metal into the substrate and to form the emitter region according to the mixing ratio of the mixed gas. 1. A method of manufacturing a semiconductor device, comprising the step of diffusing to a predetermined depth.