JPH07101676B2 - Method for manufacturing semiconductor device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a semiconductor element, and more particularly to a method for manufacturing a semiconductor element characterized by an impurity diffusion method.

(B) Conventional Technology Conventionally, when impurity diffusion is performed on a semiconductor substrate from both front and back surfaces of the substrate to obtain an isolation layer, an oxide film (SiO ₂ ) is used as an impurity mask and high temperature diffusion is performed. The process will be described with reference to FIGS. 5 (a) to 5 (b). First, oxide films 2 and 3 are formed on both surfaces of a semiconductor substrate 1 made of silicon (Si) [FIG. 5 (a)]. Next, the oxide films 2 and 3 in the region 4 to be diffused are removed by using a photolithography technique or the like (FIG. 5B), and further boron or the like is deposited on the upper surfaces of the oxide films 2 and 3 and the oxide film removing portion 4. Apply impurities 5 and 6 [Fifth
(Fig. (C)], at a high temperature of 1270 ° C for a long time, the diffusion region 7
The diffusion process is performed until the lower diffusion region 8 and the lower diffusion region 8 communicate with each other. Normally, the oxide film is about 5000 ~ 8000Å, but since it is a high temperature process here and a long time process, it is 15000 ~ 20000
After the diffusion is completed, the entire surface is etched, that is, the oxide film on the surface is partially removed and the boron-rich layer is removed.

(C) Problems to be Solved by the Invention In the conventional high temperature diffusion described above, since the treatment continues at high temperature for a long time, the oxide film reacts with impurities (boron), and many pinholes are generated in the oxide film ( (See FIG. 4), however, there is a problem that the withstand voltage of the oxide film deteriorates due to this pinhole, and the yield due to a short circuit or the like decreases.

The present invention has been made in view of the above problems, and provides a method for manufacturing a semiconductor device which prevents a reaction between an oxide film and impurities in high temperature diffusion, reduces the occurrence of pinholes, and has a high yield. The purpose is to do.

(D) Means and Actions for Solving the Problems A method for manufacturing a semiconductor device according to the present invention is to form an oxide film on a semiconductor substrate and then remove the oxide film in a region to be diffused.
After that, impurities are applied to the oxide film and the upper surface of the oxide film removal portion of the semiconductor substrate, the first impurity diffusion is performed by heating at a temperature of 1000 ° C. to 1300 ° C., and then the impurity layer on the oxide film is removed. And then for 100 hours to 2 at a temperature of 1000 ° C to 1300 ° C.
The second impurity diffusion is performed by heating for 00 hours to form a diffusion region in the semiconductor substrate.

In this semiconductor element manufacturing method, after the first impurity diffusion, which has a relatively short processing time of several tens of minutes, the impurity layer on the oxide film is removed, and the second impurity diffusion is performed at a high temperature for a long time. Since the impurities on the oxide film have already been removed, the reaction between the oxide film and the impurities is reduced even if the diffusion of the impurities at a high temperature for a long time is started, and the occurrence of pinholes in the oxide film is reduced.

(E) Examples Hereinafter, the present invention will be described in detail with reference to Examples.

1 (a) to 1 (f) are cross-sectional views of a semiconductor substrate showing an embodiment of the present invention and showing a diffusion process for forming an isolation layer for SCR on the semiconductor substrate. .

Forming oxide films 2 and 3 on both surfaces of a semiconductor substrate 1 made of silicon (Si) [FIG. 1 (a)], and removing oxide films 2 and 3 in a region 4 to be diffused [FIG. 1 (b)]. )], And applying impurities 5 and 6 such as boron to the upper surfaces of the oxide films 2 and 3 and the oxide film removing portion 4 [FIG. 1 (b)] are shown in FIGS. 5 (a) and 5 (b). ), The same as the conventional method shown in FIG. Here, as the boron source, PBF
(Polyboron film), BN, BCl ₃ etc. are used.

The feature of this embodiment is that the impurity diffusion is carried out for a relatively short time of about 30 to 60 minutes without changing to the high temperature and long time diffusion treatment, and the semiconductor substrate wafer 1 is removed from the oxide film removing portion 4 of the semiconductor substrate 1. Then, the growth of the diffusion regions 7 and 8 is started [Fig. 1 (d)]. An example of the temperature process in this process is as shown in FIG. The semiconductor substrate 1 is put in a heating furnace, and the semiconductor substrate (wafer) 1 is taken out of the heating furnace at a temperature of 1270 ° C. for 30 to 60 minutes. Next, the oxide film removing portion 4 is masked to remove the oxide film 2, 3 is photolithographically etched to remove the boron source on the oxide films 2 and 3 [FIG. 1 (e)]. On the contrary, in this photolithographic etching, the oxide film removing portion 4 is masked, so that the boron layer in this portion is not etched and the boron layer is not reduced, which is effective for the subsequent boron indentation. Next, the semiconductor substrate 1 is put into the heating furnace again, the impurity diffusion process shown in FIG. 2 is performed, and boron is pushed in. An example of the temperature process in this treatment is shown in FIG. 2B, and heating is performed at a high temperature of 1270 ° C. for a long time of 170 hours to 190 hours. As a result, x = 10 as a boron diffusion region.
It is possible to press 0 μ to 120 μ, and the diffusion region 7 from the upper surface of the semiconductor substrate 1 and the diffusion region 8 from the lower surface are connected,
The isolation layer 9 is formed [FIG. 1 (f)].

Here, prior to the second impurity diffusion for a long time at high temperature,
The reason for performing the impurity diffusion of is described. As described above, when the impurity diffusion is continuously performed for a long time, in FIG. 1, the impurities 5 and 6 attached on the oxide films 2 and 3 react with the oxide films 2 and 3, and the oxide film 2 and Problems such as pinholes on 3 occur. To prevent this, firstly impurities
5 and 6 are heated at 1000 to 1300 ° C. for about 30 to 60 minutes to dope the diffusion regions 7 and 8 of the semiconductor substrate 1 with impurities 5 and 6, respectively. During this doping, since the diffusion time is relatively short, the reaction between the oxide films 2 and 3 and the impurities 5 and 6 hardly occurs.

Then, after removing the impurities 5 and 6 attached on the oxide films 2 and 3, only the impurities doped in the diffusion regions 7 and 8 are removed by the second etching.
The impurities are diffused deeply into the substrate 1. At this time, the impurities in the diffusion regions 7 and 8 may not be sufficient in the amount of diffusion of the impurities. Therefore, the impurities 5 and 6 are left in the oxide film removing portion 4, and the impurities at the time of the second impurity diffusion are used. It is effective for pushing in. Of course, at the time of the second impurity diffusion, the impurities 5 and 6 do not exist on the oxide films 2 and 3, so that the reaction between the oxide film and the impurities does not occur. By thus performing the first impurity diffusion before the second impurity diffusion, the occurrence of pinholes and the like in the oxide film is reduced.

In the above embodiment, both the first impurity diffusion and the second impurity diffusion are practical at a heating temperature of 1000 to 1300 ° C. The time for the second impurity diffusion may be selected within the range of 100 to 200 hours depending on the diffusion width.

In the semiconductor substrate 1 on which the isolation layer 9 is formed as described above, the impurity layers on the oxide films 2 and 3, that is, the boron source is removed at the time of diffusion at high temperature for a long time. The degree of reaction with is small, and therefore the number of pinholes formed on the semiconductor substrate 1 is also small. Schematically, the pinholes 10 of the semiconductor wafer (substrate) 1 obtained by the method of this embodiment are in the state shown in FIG. 3 (a), which is slightly generated at the boat position and the orientation flat portion. A yield of 95% was obtained. The pinhole 10 of the semiconductor wafer 1 produced by the conventional method has a pinhole 10 on the entire surface of the wafer as shown in FIG. 3 (b), and the yield is about 40 to 70%. .

Further, as shown in FIG. 4 (a), QAT (reliability evaluation time) at high temperature reverse bias when the present invention is applied to SCR.
With respect to the characteristic of −I _DRM (leakage current of peak off voltage), the variation width is much smaller than that of the conventional example shown in FIG. 4 (b).

Further, in the above embodiment, the photolithographic etching method is used to remove the impurity layer on the oxide film.
Alternatively, the boron rich layer on the oxide film may be removed by hydrofluoric acid light etching.

(F) Effect of the Invention According to the present invention, the first impurity diffusion is performed by heating at a temperature of 1000 ° C. to 1300 ° C., then the impurity layer on the oxide film is removed, and then the temperature of 1000 ° C. 100 hours ~ 2 at a temperature of 1300 ℃
Since the second impurity diffusion is performed by heating for 00 hours to form the diffusion region in the semiconductor substrate, the impurities are removed from the oxide film during the high temperature diffusion for a long time, and thus the oxidation is performed. The reaction between the film and impurities is small, and the occurrence of pinholes is reduced. Therefore, the film quality of the oxide film is improved, the reliability test, the bias test, and the like are strengthened, and the yield reduction due to the withstand voltage failure is remarkably improved.

[Brief description of drawings]

1 (a), 1 (b), 1 (c), 1 (d), 1 (e) and 1 (f) show an embodiment of the present invention. FIG. 2A is a cross-sectional view of the semiconductor substrate for explaining the diffusion process shown in FIG.
FIG. 2B is a diagram showing an example of a temperature process of impurity diffusion of Al.
Is a diagram showing a temperature process example of the second impurity diffusion in the same process, FIG. 3 (a) is a diagram showing pinhole distribution of the semiconductor wafer obtained by the same embodiment, and FIG. 3 (b). FIG. 4 is a diagram showing a pinhole distribution of a semiconductor wafer obtained by carrying out the conventional method, FIG. 4 (a) is a diagram showing the QAT-I _DRM characteristics of the SCR manufactured by the above-mentioned embodiment, FIG. ) Is a diagram showing the QTA-I _DRM characteristics of the SCR obtained by the conventional example, and FIGS. 5 (a), 5 (b), 5 (c) and 5 (d) are conventional. FIG. 6 is a cross-sectional view of a semiconductor substrate for explaining the impurity diffusion treatment process of FIG. 1: Semiconductor substrate, 2.3: Oxide film, 4: Oxide film removal part, 5: 6:
Boron layer, 7/8: Diffusion region.

Claims (1)

[Claims] 1. An oxide film is formed on a semiconductor substrate, the oxide film in a region to be diffused next is removed, and thereafter, an impurity is applied to the oxide film and the upper surface of the oxide film removing portion of the semiconductor substrate.
℃ ~ 1300 ℃ to heat the first impurity diffusion,
Next, the impurity layer on the oxide film is removed, and then 1000
Second by heating for 100 to 200 hours at a temperature of ℃ to 1300 ℃
And a method for manufacturing a semiconductor element, wherein a diffusion region is formed in a semiconductor substrate by performing the impurity diffusion.