JP2000091343A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent oxidation as much as possible from an emitter polysilicon growth preprocessing to polysilicon growth on the manufacture method of the emitter of an NPN transistor. SOLUTION: In a manufacture method using the growth furnace of an NPN transistor having the emitter of polysilicon 8, a process for introducing a substrate 1 to the preparation room of a structure integrated with the growth furnace at a low temperature, setting oxygen concentration in the preparation room to be almost equal to that in the growth furnace, introducing the substrate 1 to the growth furnace from the preparation room and executing prescribed molding work is given.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a bipolar semiconductor device, and more particularly to a method for manufacturing a bipolar semiconductor device by introducing an oxide film at an interface between a substrate and an emitter polysilicon without oxidizing the substrate surface during introduction into a high temperature growth furnace. The present invention relates to a method for manufacturing a semiconductor device having an NPN transistor having a polysilicon emitter which can be eliminated.

[0002]

2. Description of the Related Art When a polysilicon emitter is used in a semiconductor device having an NPN transistor, it is very important to keep the interface between the substrate (base region) and polysilicon clean. By the way, since it is inevitably exposed to the air from the opening of the emitter region to the growth of the emitter polysilicon, a natural oxide film is formed. Subsequently, the substrate is heated at a high temperature by LPCVD (Low Pres
(Sure Chemical Vapor Deposition) When introduced into a growth reactor, oxidation proceeds further. The oxide film formed at the interface between the substrate and the polysilicon formed as described above functions as a barrier for holes injected from the base to the emitter, and the base current fluctuates due to the variation of the film thickness, and h _FE (= collector current / base) Current) becomes unstable. Also, the grain size of polysilicon changes depending on the thickness of the oxide film at the interface, which affects the characteristics of the NPN transistor.

A natural oxide film at room temperature is very fragile in film quality and has a small oxidation rate. Therefore, if the time from pre-growth treatment to growth is controlled, the progress of the oxidation does not become a serious problem. . However, if the substrate is hot LPC
When the substrate is introduced into a VD reduced-pressure growth furnace, the substrate is also exposed to high temperatures, and the oxide film oxidized at this time greatly affects the characteristics of the device. When thus the substrate is put without any countermeasures, the substrate surface is considerably oxidized and is, in the case where almost incapable its thickness control, the variation cause h _FE. Normally, in the prior art, in order to avoid this, when introducing a substrate into the growth furnace, as described above, nitrogen is allowed to flow in the growth furnace, and an atmosphere containing less oxygen is used.
Oxidation is suppressed. Also, there is a means for cleaning the surface of a silicon substrate before growing the emitter polysilicon.

[0004]

However, it has been difficult to keep the substrate surface sufficiently clean before silicon growth by the above conventional means. That is, when introducing the substrate into the growth furnace, nitrogen is caused to flow in the growth furnace to make the atmosphere low in oxygen, and even if an attempt is made to suppress oxidation, the oxygen concentration in the film forming furnace is sufficient to prevent oxidation. Therefore, oxidation could not be sufficiently suppressed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the conventional method of manufacturing a semiconductor device. It is an object of the present invention to provide a method of manufacturing a semiconductor device capable of minimizing oxidation during pre-treatment to polysilicon growth.

[0006]

According to a method of manufacturing a semiconductor device according to the present invention, a substrate is introduced at a low temperature into a preparatory chamber provided in front of a growth furnace, and the oxygen concentration in the preparatory chamber is extremely low.
That is, the above object is achieved by introducing a substrate into a high-temperature growth furnace after passing through a step of lowering the oxygen concentration to a state substantially equal to the oxygen concentration of the growth furnace.

In other words, the method of manufacturing a semiconductor device according to the present invention is a method of manufacturing a semiconductor device in which an NPN transistor having a polysilicon emitter is arranged, wherein a substrate is placed at a low temperature in a preparation room provided in front of a growth furnace. And introducing the substrate into the growth furnace from the preparation chamber and growing a predetermined amount of polysilicon after the oxygen concentration in the preparation chamber is made substantially equal to the oxygen concentration in the growth furnace. (A method for manufacturing a semiconductor device) (Claim 1).
It is assumed that.

The method of manufacturing a semiconductor device according to the present invention may further comprise: the preparation chamber has an integral structure with the growth furnace, and the preparation chamber is separated from the growth furnace by a partition which can be opened and closed. (Claim 2) ・ Achieved by making the oxygen concentration in the preparation chamber the same degree of vacuum as that in the growth furnace (Claim 3) ・ The growth furnace Is always maintained at a predetermined degree of vacuum (Claim 4). The oxygen concentration in the growth chamber is adjusted by introducing an inert gas into the preparation chamber to expel oxygen. The inert gas is nitrogen gas (Claim 6). The introduction of the substrate into the growth furnace is performed by using an inert gas in the growth furnace. (Invention 7), ・ Introducing into the growth furnace The inert gas is a nitrogen gas (claim 8).

The operation of the present invention will be described below.
According to the present invention, in the manufacture of a semiconductor device in which an NPN transistor having a polysilicon emitter is arranged, when performing emitter polysilicon growth, a preparation chamber is provided before a growth furnace, and a substrate is introduced into the preparation chamber at a low temperature. Then, after making the oxygen concentration in the preparation chamber approximately the same as the oxygen concentration in the growth furnace,
By introducing the substrate into the growth furnace, the surface of the substrate is not oxidized during the introduction into the growth furnace at a high temperature, and the oxide film at the interface between the substrate and the emitter polysilicon is minimized.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a cross-sectional structure of an NPN transistor in a semiconductor device obtained by a manufacturing method of the present invention. In FIG. 1, 1 is a substrate, 2 is an N ⁺ buried collector region, 3 is an N ⁻ collector region, 4 is an N ⁺ collector region, and 5 is a P base region. Emitter and an N ⁺ region 7 is diffused into the base during the heat treatment from which the polysilicon 8 that high dose of A _s. Further, the oxide film 101, the insulating film 102, the insulating film 10
3 is an insulating film for separating an electrode and a wiring, respectively;
Reference numeral 01 denotes a metal for making contact between base, emitter and collector electrodes, and reference numeral 202 denotes a metal of the first wiring.

(First Embodiment) FIGS.
(B), FIGS. 3 (c) to (d), FIGS. 4 (e) to (f), and FIG. 5 (g) show N by the method of manufacturing a semiconductor device of the present invention.
FIG. 5 is a diagram showing a state in which PN transistors are sequentially formed. FIG. 2A shows that the substrate surface on which the N ⁻ collector region 3 and the N ⁺ collector region 4 have already been formed has an insulating film 10.
2B shows a state in which the insulating film 102 is etched to the substrate, that is, the base after the formation of the photoresist 301, and FIG. 3C shows a state in which the photoresist 301 is formed. 3D shows a state after a patterning step of the emitter polysilicon, FIG. 3D shows a state after the insulating film is grown, and FIG. 4E shows a state after the photolithography. FIG. 4F shows a state after the contact metal is buried, and FIG. 5G shows a cross-sectional structure of the NPN transistor after the first metal wiring step.

Hereinafter, a process of sequentially forming the NPN transistors will be described. On the substrate surface on which the N ⁻ collector region 3 and the N ⁺ collector region 4 have already been formed, an insulating film 102 (for example, 2000 °) is grown by the CVD method to form the state shown in FIG. Then
A photoresist 301 is applied thereon, and thereafter, an emitter region (for example, 0.60 _{μm in} width) is opened by photolithography, and the insulating film 102 is etched to a substrate, that is, a base by dry etching.
The state shown in (b) is formed.

Next, after the photoresist 301 is stripped, polysilicon 8 serving as an emitter is grown by LPCVD. At this time, care must be taken so that the exposed surface is not oxidized as much as possible until the growth. In addition, the natural oxide film formed after the opening is once removed, and as a means for removing the oxide film, a commonly used means, for example,
Means such as a hydrofluoric acid treatment performed as a pretreatment immediately before the polysilicon growth step is applied. A time limit is provided until growth to prevent natural oxidation as much as possible.

In the first embodiment of the present invention, in order to suppress the unnecessary oxidation described above, the substrate is introduced into a closed preparation room at a low temperature (for example, room temperature) before the substrate is introduced into the growth furnace. Then, a vacuum is applied to reduce the oxygen concentration (for example, about the oxygen concentration in a vacuum state of the growth furnace), and then the substrate is introduced into a high-temperature growth furnace. Specifically, an airtight container (sealing preparation room) is installed in a portion located just before the growth furnace entrance, a substrate is put in the airtight container, and the airtightness is evacuated. Reduce the vacuum to about the furnace level. The growth furnace is always in a vacuum state. The sealed container is the target vacuum degree (vacuum degree equal to the vacuum degree of the growth furnace)
Is reached, the growth furnace inlet connected in an airtight state is opened, and the substrate is introduced into the high-temperature growth furnace.

After introducing the substrate into the growth furnace, polysilicon for forming the emitter is grown. After the polysilicon deposition, a A _s is ion implanted into the polysilicon 8, by thermal treatment, formation of the N ⁺ region 7 by diffusion into the activation of A _s and the base region, the emitter - performs formation of base junction Next, the emitter polysilicon is patterned. The cross-sectional structure of the NPN transistor obtained in this way has a structure as shown in FIG.
Thereafter, an insulating film 103 is grown as shown in FIG.
A photoresist 301 is applied, the photoresist 301 is opened at a portion where a contact is to be formed by photolithography technology, and the insulating film 103 and the insulating film 102 are further opened by dry etching, as shown in FIG. Such a cross-sectional structure is obtained. Next, a metal is buried in a portion where a contact is to be formed, and a metal contact 201 is formed, resulting in a cross-sectional structure as shown in FIG. Further, after the growth of the first wiring metal 202, a photoresist is applied and patterned to obtain a sectional structure as shown in FIG. 5 (g).
Is etched to obtain the cross-sectional structure of the NPN transistor shown in FIG.

As described above, the sealed preparation room (sealed container)
May be manufactured as a sealed preparation chamber separate from the growth furnace, and may be hermetically connected to the inlet of the growth furnace at the time of use. The chamber and the growth furnace may be manufactured by a design such that they are separated by a partition that can be opened and closed.

As described above, in this embodiment, before the substrate is introduced into the high-temperature growth furnace, the substrate is completely shielded from the outside air at a low temperature in advance, and is heated in an atmosphere containing very little oxygen. The substrate is not exposed to a high temperature in the open air when the substrate is introduced into the growth furnace as in the conventional method. Therefore, in this embodiment, the vacuum is maintained before and after the substrate is introduced into the high-temperature growth furnace, so that oxidation hardly occurs, and even if polysilicon is grown thereafter,
The natural oxide film hardly exists at the interface between the substrate surface and the polysilicon.

(Second Embodiment) The method of manufacturing a semiconductor device according to the present invention is characterized by suppressing oxidation when a substrate is introduced into an LPCVD growth furnace. Is not an essential requirement, as shown in the first embodiment, to use a sealed preparation room as the preparation room and to make it a vacuum state.

Therefore, in the present embodiment, when the oxygen concentration in the sealed preparation chamber is made substantially equal to the oxygen concentration in the growth furnace in the first embodiment, the closed preparation chamber and the growth furnace are evacuated. Instead, the following means are applied, and the rest is the same as the first embodiment.

That is, in the present embodiment, the preparatory chamber provided in front of the high-temperature growth furnace is purged with an inert gas (for example, nitrogen) to reduce the oxygen concentration as much as possible. The substrate is introduced at a low temperature (the oxygen concentration is reduced, for example, to 50 _ppm ). Thereafter, the entrance of the high-temperature growth chamber is opened, and the substrate is introduced from the preparation chamber into the high-temperature growth chamber. At this time, although the high temperature growth chamber is at atmospheric pressure,
By flowing the inert gas into the growth furnace,
The oxygen concentration in the growth furnace is also reduced. This treatment is because the inside of the growth furnace is at a high temperature, and therefore, when the substrate is introduced in the atmosphere, it is easily oxidized.

In this method, a sealed preparation room (vacuum chamber) is not necessarily required, and it is sufficient that the preparation room is sealed to some extent. If a purge preparation chamber using an inert gas (nitrogen) as described above is used instead of the closed preparation chamber, the same effect can be obtained for the purpose of not oxidizing. In addition, if the temperature in the growth furnace is lowered (for example, room temperature) before the substrate is introduced into the growth chamber, the vacuum preparation chamber and the nitrogen purge are not required, but the temperature in the growth furnace is changed rapidly. Is very difficult, so it is impractical at present if considering the throughput and the maintainability of the furnace.

[0022]

As described above, according to the present invention, when forming the emitter of the NPN transistor, it is possible to minimize oxidation during the pre-growth process from the pre-emitter polysilicon growth to the polysilicon growth. Since the oxide film at the interface can be made extremely free,
It is possible to manufacture a semiconductor device in which NPN transistors having stable characteristics with little manufacturing variation are arranged. That is, conventionally, when an NPN transistor is operated, if an oxide film is present, the oxide film becomes a barrier against the injection of holes from the base to the emitter, which is the base of the base current, and the base current becomes small. _FE increases,
It has been known that this oxide film affects even a very thin oxide film of 20 ° or less, and the thickness of the oxide film determines the degree of the hole barrier, which is one of the causes of _hFE instability. In this method, it was very difficult to control the ultra-thin oxide film.However, in the present invention, by using a preparatory room and entering the furnace at a low temperature, oxidation during the entrance was suppressed, so that the polysilicon and the substrate could be removed. A state in which an oxide film on the surface interface is extremely small can be stably manufactured, and an NPN transistor having stable characteristics can be manufactured.

[Brief description of the drawings]

FIG. 1 shows a cross-sectional structure of an NPN transistor manufactured by a semiconductor manufacturing method according to the present invention.

FIGS. 2A and 2B are diagrams showing steps of a method for manufacturing a semiconductor according to the present invention, wherein FIG. 2A is a view after a step of covering a substrate surface with an insulating film, and FIG. It is.

FIGS. 3A and 3B are views showing the steps of the method of manufacturing a semiconductor according to the present invention, wherein FIG. 3C is a view after a patterning step of emitter polysilicon, and FIG.

FIG. 4 is a view showing steps of a method for manufacturing a semiconductor according to the present invention, wherein (e) is a view after photolithography,
(F) is a view after embedding the contact metal.

FIG. 5 is a view showing a step of the method for manufacturing a semiconductor according to the present invention, in which (g) is a view after a first metal wiring step.

[Explanation of symbols]

1 substrate 2 N ⁺ buried collector region 3 N ^- collector region 4 N ⁺ collector region 5 P base region 7 N ⁺ region 8 polysilicon 101 oxide film 102 and 103 insulating film 201 for contact metal 202 first wiring Metal 301 Photoresist

Claims (8)

[Claims] 1. An NPN having a polysilicon emitter.
In the method for manufacturing a semiconductor device in which transistors are arranged, a substrate is introduced at a low temperature into a preparation chamber provided in front of a growth furnace, and the oxygen concentration in the preparation chamber is made approximately equal to the oxygen concentration in the growth furnace. A method of manufacturing a semiconductor device, comprising: introducing a substrate from the preparation chamber into the growth furnace to grow polysilicon by an LPCVD method. 2. The preparation chamber has an integral structure with the growth furnace, and the preparation chamber and the growth furnace are separated by a partition which can be opened and closed. The manufacturing method of the semiconductor device described in the above. 3. The method according to claim 1, wherein the oxygen concentration in the preparation chamber is set to a degree of vacuum similar to the degree of vacuum in the growth furnace. A method for manufacturing a semiconductor device. 4. The method for manufacturing a semiconductor device according to claim 1, wherein the growth furnace is always maintained at a predetermined degree of vacuum. 5. The oxygen concentration in the growth chamber is made substantially the same as the oxygen concentration in the growth furnace by introducing an inert gas into the preparation chamber to drive out oxygen. 3. The method for manufacturing a semiconductor device according to any one of 2. 6. The method according to claim 5, wherein the inert gas is a nitrogen gas. 7. The method according to claim 1, wherein the introduction of the substrate into the growth furnace is performed while injecting an inert gas into the growth furnace. The manufacturing method of the semiconductor device described in the above. 8. The method according to claim 7, wherein the inert gas is a nitrogen gas.