JPS6227539B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, such as a mesa-type bipolar transistor.

A silicon layer containing a predetermined amount of oxygen (hereinafter referred to as
SIPOS) is an excellent surface film for improving the surface passivation of semiconductor devices. this
Regarding the SIPOS layer, the applicant has, for example,
-36175 (Patent No. 925898) has already been proposed.

When applying the SIPOS layer to the passivation of mesa-type bipolar transistors, there were problems, especially in the photoetching process. As shown in FIG. 1, an N ⁺ type collector region 1, an N type collector region 2, a P ⁺ type base region 3, and an N ⁺ type emitter region 4.
is formed on a semiconductor substrate and then etched into a mesa structure. Next, a SIPOS layer 5 is formed on the surface by vapor phase growth, and the photoresist layer 6 formed on the SIPOS layer 5 is selectively etched in order to take out the emitter and base electrodes. However, the photoresist layer 6 is difficult to adhere to, or sometimes does not adhere to, especially the shoulder portion of the mesa structure shown by the arrow 7.
If you do etching in this state, the SIPOS of shoulder part 7 will be removed.
This will also result in being etched. As a result, the passivation effect of SIPOS becomes insufficient.

The present invention was made to correct these defects, and includes a surface protective film made of semi-insulating polycrystalline or amorphous silicon containing 2 to 45 at% oxygen on a mesa-shaped semiconductor substrate. a step of implanting nitrogen ions into a predetermined region of the surface protective film to make the predetermined region at least partially have a nitrogen content of 10 at% or more in the thickness direction; The present invention relates to a method of manufacturing a semiconductor device, comprising a step of selectively removing a region other than the predetermined region into which the nitrogen ions have not been implanted. By this method, only predetermined regions of the surface layer can be selectively removed while retaining the surface layer well on the semiconductor substrate.

Next, the principle of the method of forming and etching a surface protective film applied to the present invention will be explained with reference to FIGS. 2 and 3.

As shown in FIG. 2, a SIPOS layer 15 made of polysilicon or amorphous silicon containing 2 to 45 at % (atomic ratio) of oxygen is grown on the surface of the Si substrate 11 in a vapor phase. This SIPOS layer is easily grown by feeding SiH ₄ and N ₂ O onto the substrate 11 using a carrier gas and decomposing them at a low temperature of about 650° C., similarly to the method of the prior application described above. Then SIPOS
A photoresist layer 16 is applied to the surface of the layer 15 and selectively etched away using an exposure technique, leaving the photoresist layer 16 only at predetermined locations. Then, using this photoresist layer as a mask,
Irradiating the SIPOS layer 15 with N ₂ ions 20,
Ion implantation is performed only into the SIPOS layer 15 where the mask 16 does not exist. As a result, _N2 ions are implanted into at least the surface region of the SIPOS layer 15, converting it into nitrogen-doped polysilicon. The conditions for this ion implantation are, for example, an acceleration energy of 100 KeV and a dose of 1 to 5×10 ¹⁶ cm ⁻² . After ion implantation, the mask 16 is removed using O ₂ plasma.

Next, the etching solution for SIPOS (H ₂ O ₂ and HF
and NH ₄ F, H ₂ O ₂ :HF:NH ₄ F=6:1:
10) The surface of the substrate 11 is immersed in the solution. As a result, as shown in FIG. 3, the etching rate of the SIPOS surface region 17 doped with nitrogen and the undoped SIPOS in the step of FIG. Directly below 16
Only SIPOS is selectively etched away,
An opening 18 is formed in the SIPOS layer. Therefore, the region excluding this opening has a two-layer structure of a polysilicon layer 15 containing oxygen and a polysilicon layer 17 containing nitrogen.

An embodiment of the present invention in which the above-described surface protective film formation and etching method is applied to a mesa-type bipolar transistor will be described with reference to FIGS. 4 and 5.

First, as shown in FIG. 4, collector regions 11, 12, base region 13, and emitter region 14 are formed in the same manner as in FIG. 1, and an oxygen-containing SIPOS layer 1 is formed on the surface.
5 is grown in a vapor phase, and then a photoresist layer 16 is formed in a predetermined pattern on the electrode lead-out portion in the same manner as in FIG. Next, using the photoresist layer 16 as a mask, N ₂ ions are irradiated as described above to dope the SIPOS layer 15 without the mask 16 with N ₂ ions. Next, the mask 1 is immersed in etching solution for SIPOS as shown in FIG. 3, and as shown in FIG.
Openings 18 are formed at positions 6, and the two-layer structure of oxygen-containing polysilicon layer 15 and nitrogen-containing polysilicon layer 17 is left in the other regions. Then, a metal electrode is applied to the opening 18 by a conventionally known method to form an emitter and a base electrode.

As is clear from the above, in the method according to this embodiment, a mask 16 is provided on the SIPOS layer 15, _N2 ions are implanted into the region without the mask, the mask 16 is removed, and the desired etching is performed. The opening for electrode formation can be made into a window. This is based on the effective use of the difference in etching rate between the nitrogen-containing portion and the oxygen-containing portion in SIPOS. Therefore, as before
Since there is no need to attach photoresist during etching of SIPOS, there is no room for etching of SIPOS, which was inevitable at the shoulder portion of the mesa structure. That is, at the shoulder of the mesa structure, the surface of SIPOS is covered with a nitrogen-containing layer 17 with a slow etching rate, so this two-layer structure is covered with an oxygen-containing layer 17.
Stable and virtually unchanged upon etching of SIPOS. Furthermore, the nitrogen-containing layer 17 can be uniformly formed over the entire surface of the oxygen-containing polysilicon layer 15 without the need for etching by N ₂ ion implantation, and can therefore be uniformly formed on the shoulders of the mesa structure. Therefore, the underlying oxygen-containing layer can be effectively protected from etching. Furthermore, since the difference in etching speed of SIPOS is utilized,
In this embodiment, only the lower part of the photoresist layer 16 is removed, and an opening pattern opposite to the conventional opening pattern after etching is formed. Because of this reverse pattern, the photoresist occupies less area in FIG. 2 than in FIG. 1.

Further, in this example, the nitrogen-containing polysilicon layer 1
7 not only functions as a so-called etching mask for the underlying polysilicon layer 15, but also functions to improve the passivation effect on the transistor surface. In other words, the patent application previously proposed by the applicant in 1973
Similar to the passivation membrane according to No.-123765,
Since the lower polysilicon layer 15 contains a predetermined amount of oxygen, charges are not induced on the substrate side unlike in the case of SiO. Further, since the nitrogen-containing polysilicon layer 17 is present on the polysilicon layer 15, the moisture resistance of the device is greatly improved, and a device resistant to humidity can be obtained. For this purpose, the nitrogen content in the polysilicon layer 17 must be 10 at % or more; if it is less than this, the moisture resistance will deteriorate and dielectric breakdown will easily occur on the surface. In the apparatus disclosed in Japanese Patent Application No. 49-123765, an oxygen-containing polysilicon layer and a nitrogen-containing polysilicon layer are sequentially grown in a vapor phase, but in the method of this embodiment, it is sufficient to grow only an oxygen-containing polysilicon layer. , just dope with nitrogen by implanting _N2 ions. In addition, the nitrogen-containing polysilicon layer 17 does not undergo any etching and only needs to be left as it is after ion implantation, making it easy to control etching.

In the process shown in FIG. 4, by taking measures to selectively implant N ₂ ions into the SIPOS layer 15 without using the mask 16, the mask formation and removal process can be omitted, and the ion implantation → etching process can be performed. can be performed continuously, and in this way, the manufacturing process can be streamlined.

Oxygen is added to the semiconductor substrate having a mesa shape for 2~
forming a surface protective film made of semi-insulating polycrystalline or amorphous silicon containing 45 at%, and implanting nitrogen ions into a predetermined region of the surface protective film to reduce the thickness of the predetermined region. Both of the steps included a step of partially increasing the nitrogen content to 10 at % or more, and a step of selectively removing regions of the surface protective film other than the predetermined regions into which the nitrogen ions were not implanted.

Therefore, first, an oxygen-containing silicon layer (surface protective film) is formed on a semiconductor substrate, and then nitrogen ions are implanted into a predetermined region of the silicon layer, so that the predetermined region is at least partially reduced in nitrogen content in its thickness direction.
By forming a silicon layer containing 10at% or more of nitrogen, and then selectively removing areas other than the above-mentioned predetermined areas, as long as nitrogen ions are implanted into the predetermined areas of the surface protective film, no nitrogen ions will be implanted. There is no particular need for a mask to selectively remove the removed areas. Therefore, it is extremely easy to selectively form a surface protective film having a nitrogen-containing silicon layer on a semiconductor substrate having a mesa shape, and therefore the manufacturing efficiency can be greatly improved. In addition, in order to prevent unnecessary removal of the oxygen-containing silicon layer (surface protective film) formed on the mesa-shaped semiconductor substrate, the nitrogen-containing silicon layer formed on the mesa-shaped shoulder portion is also uniformly removed. can be formed. Therefore, it is possible to effectively prevent the surface protective film from being removed unnecessarily at the shoulder portion of the mesa shape, such as when a mask for selectively removing the surface protective film is particularly required. Therefore, the yield during manufacturing of semiconductor devices having a mesa shape can be greatly improved.

Furthermore, the semi-insulating polycrystalline or amorphous silicon layer containing 2 to 45 at% oxygen is implanted with nitrogen ions so that the nitrogen content becomes at least partially 10 at% or more in the thickness direction. The presence of oxygen can effectively suppress the induction of charges on the surface of the semiconductor substrate, and the presence of nitrogen can improve moisture resistance, thereby providing an excellent passivation effect.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a conventional mesa-type bipolar transistor when a window for electrode formation is opened. 2 and 3 show the principle of the method of forming and etching a surface protective film applied to the present invention, and FIG. 2 is a cross-sectional view of the substrate during N ₂ ion implantation;
FIG. 3 is a cross-sectional view of the etched substrate after ion implantation. 4 and 5 show an embodiment in which the present invention is applied to a mesa-type bipolar transistor. FIG. 5 is a sectional view similar to FIG. 4 in the etched state shown in FIG. 3. In the symbols used in the drawings, 15... oxygen-containing polysilicon layer, 16... photoresist layer, 17... nitrogen-containing polysilicon layer, 20... N ₂ ion.

Claims (1)

[Claims] 1. Oxygen is 2.
forming a surface protective film made of semi-insulating polycrystalline or amorphous silicon containing ~45 at%, and implanting nitrogen ions into a predetermined region of the surface protective film to form a surface protective film in the thickness direction of the predetermined region. The method is characterized by comprising a step of at least partially increasing the nitrogen content to 10 at% or more, and a step of selectively removing a region of the surface protective film other than the predetermined region into which the nitrogen ions have not been implanted. A method for manufacturing a semiconductor device.