JPS5915184B2 - Manufacturing method of semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device that provides a lower base resistance.

At present, the base external resistance rB has become a serious problem in integrated circuits.

When considering a diffused transistor, the base resistance rB is the resistance of the diffusion layer from the emitter 7 to the base contact portion 2a, as shown in FIG. In this figure, 1
is a semiconductor substrate with a collector and rope, 2 is a base, and 3 is Si
An insulating film made of O2, 4 a polysilicon film, 5 an emitter electrode, and 6 a base electrode. If the base resistance is large, there are disadvantages such as limiting high-speed operation of the transistor, so it is desirable to reduce this resistance. base resistance r
In order to reduce B, it is possible to increase the impurity concentration in the base and increase the cross-sectional area of the base, but if the impurity concentration is increased to the active base region directly under the emitter T, the emitter injection efficiency will decrease. , if the thickness is increased, the base width becomes larger, which impedes high-speed operation. The base 2 may be composed of a plurality of diffusion regions, but this will complicate the 10 steps and reduce the degree of integration, and if mask alignment errors occur, the effect of lowering the base resistance rB will be diminished. Therefore, the present invention uses self-alignment to increase the cross-sectional area of the base other than the active base region, that is, the connecting conductor between the portion sandwiched between the emitter T and collector 1 and serving as the base 15 and the base contact portion 2a. The aim is to make the base resistance rB smaller by deepening the portion A that plays a role. The method for manufacturing a semiconductor device of the present invention is to perform base diffusion of P-type boron on a semiconductor substrate, deposit an insulating film on the surface of the substrate 20, pattern it to form an emitter window, and then use polysilicon to form an emitter window. The method is characterized in that a film is grown, and then the polysilicon film is oxidized to bulge the bottom of the base layer portion where the film contacts the substrate, and then emitter diffusion is performed through the emitter window. , which will now be explained in detail with reference to examples. As shown in FIG. 2, in the present invention, an N-type silicon semiconductor substrate 1 is used, a base window is opened in a thermally oxidized SiO2 film 3 formed on its surface, and a base is diffused using boron B as a P-type 30 impurity. Form layer 2.

Next, a SiO2 film 11 is grown by CVD on the entire surface and patterned to form an emitter window Ila and a base contact window 11b. Furthermore, a polysilicon film 12 is grown 35 over the entire surface, but this polysilicon is not doped with impurities. Next, the polysilicon film 12 is oxidized in an oxidizing atmosphere at about 1000°C.

As a result, the film 12 is oxidized to SiO2 from the surface side, and in this process, impurity boron in the substrate portion or the base layer portion with which the polysilicon film 12 comes into contact is attracted to the polysilicon film side. A small amount of boron is also absorbed into the SiO2 films 3 and 11, but this effect of absorbing boron is remarkable during the process in which silicon is oxidized to become SiO2, whereas when oxidation does not progress, boron is absorbed into the SiO2 film. There is a big difference between the two since the amount of absorption is small.

Through this heat treatment for oxidation, the boron in the base layer 2 is diffused deep into the substrate, and the base layer expands, but the emitter window 11
Base layer 2 below the base contact window 11b
In this case, the spreading speed becomes extremely slow due to the v effect of absorption of boron into the polysilicon film, and the lower part of the base layer becomes uneven as shown in the figure. When the insulating film 11 for forming the emitter window and the base contact window is deposited by the CVD method, since this method allows low-temperature processing, the insulating film 11 is diffused into the base layer 2 in the process shown in FIG. This is effective in preventing the diffusion of impurities into the substrate and increasing the impurity concentration in the base layer 2 having the shape shown in FIG.

Furthermore, if the polysilicon film 12 is oxidized until the entire surface is oxidized, there will be too much difference, so it is better to stop halfway, and the remaining polysilicon film 12 can be used to prevent base short circuits.

That is, as is known, the aluminum of the electrode tends to form a eutectic alloy with the silicon of the substrate, which leads to base short circuits, but this can be prevented by interposing polysilicon. Next, the SiO2 film 13 is removed by etching, a PSG film containing N-type impurities is grown on the entire surface, and this is patterned to leave the part of the emitter window 11a and remove at least that of the base contact window 11b. Then, the N-type impurity is diffused from the PSG film into the base layer 2 through the emitter window by heat treatment in a still state, thereby forming the N-type emitter layer 14 as shown in FIG.

Thereafter, the PSG film is removed by etching, and an electrode material, usually aluminum, is deposited on the entire surface and patterned to form an emitter electrode 5 and a base electrode 6. The polysilicon film 12 is also removed by etching except for the portion between these electrodes and the substrate. Incidentally, if a collector contact diffusion layer is required, it can be formed simultaneously with the formation of the emitter layer 14 in exactly the same manner. As is clear from FIG. 4, the effective base layer portion 2a between the emitter layer 14 and the substrate collector portion 1a on which the embankment The base layer between the base layer (contact + diffusion is performed to form a P-type base contact portion below this base electrode) has a large cross-sectional area, and therefore the base resistance RB is low.

Moreover, since the impurity concentration in the effective base layer portion 2a is low as is clear from the above explanation, the carrier injection efficiency of the emitter does not decrease. Furthermore, if a highly concentrated base contact diffusion region is formed in advance under the base electrode 6, impurities will be diffused from the base contact diffusion region into the polysilicon film above it during heat treatment for emitter diffusion, resulting in a low -C resistivity. Good contact can be obtained. By the way, part of the surface of the semiconductor substrate with boron diffused was covered with a CVDSiO2 film, the other part was covered with a polysilicon film, and the polysilicon film was oxidized by heat treatment in a cold state. The impurity (boron) concentration of the lower semiconductor substrate is SiO
A difference of 10 to 30% was observed in the depth of the P-type region due to lower b1 boron, which is approximately half that of the lower part of the two films.

As described above in detail, according to the present invention, the base resistance RB can be set to an independent low value that does not depend on the emitter.

This is because in the past, there was a limit to the reduction of the base resistance RB because the emitter was formed to have a predetermined base width and pouring efficiency, but in the present invention, the base region is deformed as shown in the figure, so the unevenness can be reduced. By changing the degree, one can be freed from certain constraints.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a base resistor, and FIGS. 2 to 4 are process diagrams illustrating the manufacturing method of the present invention.

Claims (1)

[Claims] 1 Base diffusion is performed on a semiconductor substrate using boron as a P-type impurity, an insulating film is deposited on the surface of the substrate, and an emitter window is formed by patterning this, and then a polysilicon film is grown. . A method of manufacturing a semiconductor device, comprising: oxidizing the polysilicon film to bulge the bottom of the base layer portion where the film contacts the substrate; and then performing emitter diffusion through the emitter window. 2 SiO_2 grown by CVD method as an insulating film
2. The method of manufacturing a semiconductor device according to claim 1, wherein a PSC film doped with impurities is used for emitter diffusion.