JPS629624A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To unnecessitate the process in which the back side of a semiconductor substrate is coated with a photoresist film as well as to prevent the flaws and contamination generated by the coating of photoresist by a method wherein the thermally oxided film on the back side of the semiconductor substrate is coated with a protective film which can be removed by the same etching process. CONSTITUTION:A semiconductor substrate 11 is oxidized by heat, and thermally oxided films 14 and 15 are grown on the main surface 12 and the back side 13 of the substrate 11. Subsequently, a silicon dioxide film (protective film) 16 of approximately 8,000Angstrom in thickness is coated on a thermally oxided film 15 by performing a CVD method, and then a photoresist film 17 is made to spray-coat the thermally oxided film 14. Said photoresist film 17 is formed by patterning, and an etching is performed on the thermally oxided film 14 using the pattern-formed photoresist film 17 as a mask. Generally, as the etching speed of the silicon dioxide film 16 is approximately double the etching speed of the thermally oxided films 14 and 15, the thermally oxided film 15 of approximately 4,000Angstrom is left on the back side 13 even when the thermally oxided film 14 is entirely removed by etching. A thermally oxided film 15 is formed by patterning, and a thyristor, for example, can also be formed by introducing impurities using said film 15 as a mask.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method of manufacturing a semiconductor device, and in particular, to a method of manufacturing a semiconductor device, and particularly to a method for protecting the back surface of the main surface of a semiconductor substrate from impurities when introducing impurities into the main surface of the semiconductor substrate. The present invention relates to a method for forming a protective film.

<Conventional Technology> FIG. 2 is a process diagram showing a conventional method for manufacturing a semiconductor device. First, a single crystal silicon substrate 1 is thermally oxidized to form carbon dioxide on the main surface 2 and the back surface 3 of the substrate 1. Silicon films 4 and 5 are grown (FIG. 2(a)). Subsequently, a photoresist film 6 is applied on the silicon dioxide film 4 (FIG. 2(b)).
), after this, the photoresist film 6 is formed by a lithography process.
A pattern is formed (FIG. 2(C)). After this, board 1
is turned over and a photoresist film 7 is placed on the silicon dioxide film 5.
After being applied to the entire surface, it is cured through baking (Fig. 2(d)). After the back surface 3 is protected in this way, the silicon dioxide film 4 is etched using the patterned photoresist film 6 as a mask (FIG. 2(e)). After the photoresist film 6 is removed, a diffusion process is performed to remove the silicon dioxide film 4. A P-type impurity, such as boron, is introduced from the exposed main surface 2 (FIG. 2(f)). When the diffusion region 8 is formed in this way, the thickness of the silicon dioxide film 4 is increased and the diffusion region 8 is also covered with silicon dioxide (FIG. 2(g)). The silicon dioxide film 4 is removed together with the film 5, and an N-type impurity, for example, phosphorus, is introduced into the silicon dioxide film 4 and the exposed back surface 3.
In addition to passivation, the back surface 3 has an increased impurity concentration in preparation for ohmic contact.

<Problems to be solved by the invention> However, in the conventional manufacturing method, the silicon dioxide film 4
If the silicon dioxide film 5 is not covered with a photoresist film 7 before etching, the silicon dioxide film 5 will also be etched while the silicon dioxide film 4 is being etched, exposing the back surface 3 and forming the diffusion region 8. Since P-type impurities may be introduced into the back surface 3 during the process, making it impossible to form an ohmic contact, the process of coating the photoresist film 7 is absolutely necessary. Therefore, the substrate 1 is turned over and the silicon dioxide film 5 While applying the photoresist film 7 thereon, scratches and dirt are likely to adhere thereto.

Due to these factors, there has been a problem in that the yield of semiconductor devices is lowered, and further, the reliability is lowered.

Furthermore, if a photoresist film is coated on both sides, if the substrate 1 is placed on a silicone rubber belt and conveyed and the photoresist is applied by spraying, the photoresist will adhere to the belt, making it impossible to perform mass processing using such a continuous coating method. There was a problem.

<Means for Solving the Problems> In view of the above-mentioned problems, the present invention provides a method for growing a thermal oxide film on the main surface of a semiconductor substrate and the back surface of the main surface, and then forming a thermal oxide film on the back surface of the semiconductor substrate. A protective film that can be removed in the same etching process as the thermal oxide film is deposited on the thermal oxide film, and when the thermal oxide film on the main surface of the semiconductor substrate is etched, the thermal oxide film is left on the back surface and the exposed parts are removed. When introducing impurities of a first conductivity type from the main surface of a semiconductor substrate, the back surface is protected with the remainder of a thermal oxide film in preparation for the step of introducing impurities of a second conductivity type into the back surface. .

<Example> FIGS. 1(a) to (g) are process diagrams showing an example of the present invention. First, a semiconductor substrate 11 is thermally oxidized,
The main surface 12 and the back surface 13 of the main surface 12 have a thickness of about 1.5 mm.
Thermal oxide films 14 and 15 of 6 μm are grown (Fig. 1(a)).
), Next, a silicon dioxide film 16 is deposited on the thermal oxide film 15 to a thickness of approximately 8,000 mm by the CVD method (FIG. 1(b)), and then a photoresist is deposited on the thermal oxide film 14. A membrane 17 is spray applied (FIG. 1(C));
This photoresist 9117 is patterned by a lithography process (FIG. 1(d)), and the thermal oxide film 14 is etched with hydrofluoric acid using the patterned photoresist film 17 as a mask. Generally, the etching speed of the silicon dioxide film 16 is about twice that of the thermal oxide film 14.15, so even if the thermal oxide film 14 is completely etched away, about 4000 thermal oxide films 15. remains. As a result, the semiconductor substrate 1
A part of the main surface 12 is exposed (FIG. 1(e)), and after removing the photoresist film 17, a P-type impurity 5 such as boron is introduced to form a diffusion region 18 (FIG. 1(f)). ')
After that, the diffusion region 18 is covered with a silicon dioxide film, and the back surface 13 is exposed.

Introducing an N-type impurity, for example, phosphorus (Figure 1 (g))
, As a result, passivation is achieved and
The impurity concentration of the back surface 13 increases, and a back surface 13 suitable for ohmic contact is obtained.

In one embodiment, a silicon dioxide film formed by CVD was used as the protective film, but the protective film only needs to be removed in the same etching process as the thermal oxide film, and if etching by ion milling is used, the material of the protective film can be removed. can be selected from a wide range.

Furthermore, it is not necessary to completely remove the thermal oxide film 15 on the back surface 13; it is also possible to pattern it and introduce impurities using the patterned thermal oxide film 15 as a mask to form, for example, a thyristor. can.

<Effects> As explained above, according to the present invention, the thermal oxide film on the back side is covered with a protective film that can be removed in the same etching process, so the process of covering the back side with a photoresist film is no longer necessary. , it is possible to prevent scratches and stains associated with the application of photoresist, and the effect of improving yield and reliability can be obtained.

Furthermore, since the photoresist is applied only to the thermal oxide film on the main surface, the photoresist can be spray applied while the semiconductor substrate is being transported by a conveyor, which also has the effect of increasing the throughput of the photoresist application process. .

[Brief explanation of the drawing]

FIGS. 1(a) to (g) are process diagrams representing one embodiment of the present invention, and FIGS. 2(a) to (h) are process diagrams representing a conventional example. 11...Semiconductor substrate 12...Main surface 13...Back surface 14.15...Thermal oxide film 16...Protective film patent Applicant ROHM Co., Ltd. Agent Patent Attorney Kiyoshi Kuwai - Figure 1 Figure 1 (f) Figure 1 Figure 2 (e) (↑) Figure 2 ζg)' Figure 2

Claims (1)

[Claims] A step of growing a thermal oxide film on a main surface of a semiconductor substrate and a back surface of the main surface, and a protective film that can be removed together with the thermal oxide film in the same etching step on the thermal oxide film grown on the back surface of the semiconductor substrate. a step of selectively removing the thermal oxide film grown on the main surface of the semiconductor substrate to expose a part of the main surface of the semiconductor substrate and leaving a thermal oxide film on the back surface;
A step of introducing an impurity of a first conductivity type from the exposed main surface of the semiconductor substrate, a step of removing at least a part of the thermal oxide film on the back surface, and a step of introducing an impurity of a second conductivity type from the exposed back surface. A method for manufacturing a semiconductor device comprising: