JPS62125670A - Manufacture of bipolar transistor - Google Patents

Abstract

PURPOSE:To improve high frequency characteristic and noise characteristic by implanting first conductivity type impurity from a polysilicon film into a predetermined region by removing a mask layer to form an emitter region. CONSTITUTION:A second conductivity type impurity is implanted to the surface of a first conductivity type semiconductor substrate 11 to form a base region 13, while the base region is covered with a polysilicon film 14, and the polysilicon film on the predetermined region in the base region is covered with a mask layer 15 wider than the predetermined region. Then, the polysilicon film is isotropically etched to expose a base region surface except the predetermined region, the mask layer is formed in overhang state, second conductivity type impurity is implanted to the exposed base region except the base region under the mask layer to form a graft base region 17. Thereafter, the mask layer is removed, the first conductivity type impurity is implanted from the polysilicon film into the predetermined region to form an emitter region 18. Thus, the regions 17, 18 are not superposed to obtain a preferable high frequency characteristic and noise resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Application in Industry> The present invention relates to a method for manufacturing a bipolar transistor device, and particularly relates to a method for manufacturing a bipolar transistor device in which a graft base region and an emitter region are formed in a self-aligned manner. .

<Prior Art> FIGS. 2(a) to 2(e) are cross-sectional views showing each step of a conventional method for manufacturing a bipolar transistor device. is thermally oxidized to grow a silicon dioxide film 2 (see Fig. 2(a)
)). Subsequently, the silicon dioxide film 2 is selectively removed by photoetching to expose the region where the graft base is to be formed. A p-type impurity is introduced into this region where the graft base is to be formed to form the graft base region 3 (second
Figure (b)). Thereafter, the silicon dioxide film 2 is selectively removed through a photoresist process to expose a region where a base is to be formed, and an n-type impurity is introduced to form a base region 4 (FIG. 2(C)).

When the step of forming the base region 4 is completed, the conductor substrate 1 is transferred to the base region 1.
Since the surface of is again covered with the silicon dioxide film 2, the silicon dioxide film 2 is selectively removed in the photoresist step 1 to expose the area where the emitter is to be formed in the base region 4, and the area where the emitter is to be formed is covered with an electrode. It is covered with a polysilicon film 5 to prevent removal (FIG. 2(d)). In the next step, n-type impurities are introduced into the region where the emitter is to be formed to form the emitter region 6 (FIG. 2(e)), and the bipolar one helangister device is completed through standard steps.

<Problems to be Solved by the Invention> In the above conventional manufacturing method, the formation of the graft base region 3, the formation of the base region 4, and the formation of the emitter region 6 are performed in independent resist steps that have no relation to each other. Since the emitter region 6 was formed over a long period of time, there is a risk that a part of the emitter region 6 may extend into the graft base region 3 with a high impurity concentration due to an error in mask alignment, as shown in FIG. There is a drawback that the high frequency characteristics of the bipolar transistor device deteriorate due to an increase in the capacitance between the two and an imbalance in emitter injection efficiency. Such graph I - base region 3
In order to prevent overlap between the graft base region and the emitter region 6, it is necessary to provide a large distance between the inner circumference of the graft base region and the outer circumference of the emitter region.

Generally, the base resistance Rb of a bipolar transistor device
b' is expressed as Rbb' = (ρ, WE/12L+ρ, S, /2L + ρ3S 2 / 2 T-) / rn.

Here, ρ3. ρ2. ρ3 is the specific resistance, WE is the width of the emitter region 6, S, and S2 are the distance between the outer circumference of the graft base region and the outer circumference of the emitter region, and graph 1 - the distance between the inner circumference of the base region and the inner circumference of the base electrode, respectively. The interval, 7, is the length of one emitter electrode, and m is the number of base electrodes. Therefore, in order to prevent the graft base region 3 and the emitter region 6 from overlapping, graph 1 to base region;
By increasing the distance between the inner circumference of the emitter region and the outer circumference of the emitter region,
As Sl increases and this region has a higher specific resistance than the graft base region 3, the base resistance Rbb'
leading to an increase in As a result, there has been a problem in that the high frequency characteristics and noise characteristics of the bipolar transistor device are deteriorated. Therefore, in order to avoid inconveniences due to mask alignment errors, it has been impossible to avoid deterioration of high frequency characteristics due to an increase in base resistance.

Therefore, the present invention enables self-alignment between the base region and the emitter region as shown in graph 1, and enables the interval between the inner circumference of the graft base region and the outer circumference of the emitter region to be set as small as possible, thereby improving high frequency characteristics. The purpose of this invention is to provide a method for manufacturing a bipolar transistor device with excellent noise characteristics.

<Means for Solving the Problems> The present invention involves introducing impurities of a second conductivity type into the surface of a semiconductor substrate of a first conductivity type to form a base region, and converting the surface of the base region into a first conductivity type. After covering with a polysilicon film containing type impurities, the polysilicon film on a predetermined region in the base region is covered with a mask layer that is wider than the predetermined region. Subsequently, the polysilicon film is isotropically etched to expose the surface of the base region outside the predetermined region, the mask layer is left in an overhanging state, and etching is performed on the exposed base region except for the base region under the mask layer. A graft base region is formed by introducing impurities of two conductivity types.

Thereafter, the mask layer is removed and a first conductivity type impurity is introduced from the polysilicon film into the predetermined region to form an emitter region.

<Embodiment> FIGS. 1(a) to 1(e) are cross-sectional views showing each step of a first embodiment of the present invention, and explain the cases of NPN type bipolar 1 to transistor. First, the surface of the n-type semiconductor substrate 11 is thermally oxidized to form a silicon dioxide film 12 of about 50%
000 people (Figure 1 (a)). Subsequently, the region where the base is to be formed is exposed by photo-etching, and 1013 to 014 boron is implanted. Thereafter, heating is performed at approximately 900° C. for approximately 30 minutes in a nitrogen atmosphere to form a base region 3 with a depth of approximately 0.15 to 0.2 μrn (see Fig. 1).
b)). After this, approximately 5,000 layers of P-type doped polysilicon (11%) 4 to cover the exposed surface of the semiconductor substrate 11 and silicon dioxide IIIX+12 are deposited, and approximately 2,000 layers of silicon nitride film 154 is further deposited. (1st
Figure (c)). A photoresist film ]-6 is applied on the silicon nitride film 15 and patterned to form a base region]
- Cover a predetermined area in 73 with a photoresist film]-(3.

Thereafter, the silicon nitride film 15 is selectively removed using the photoresist film 16 as a mask, and the exposed polysilicon film 1
4 isotropically etched. As a result of such isotropic etching, the polysilicon I under the silicon nitride film 1-5 is removed.
I*14 is also approximately 50o from the outer periphery of the silicon nitride film 15.

It is etched inward by about λ. Next, using the photoresist film 16 as a mask, boron ions are implanted in approximately 60 keys to define a region of the semiconductor substrate 1 where a graft base is to be formed (FIG. 1(d)).

After removing photoresist film]-6, approximately 800 to 90
The base region 17 is formed by heating in an oxidizing atmosphere of 0"C, and an n-type impurity, such as phosphorus, is diffused from the doped polysilicon film 14 into the semiconductor substrate ]-1 to form the emitter region 18. Form.

During this time, the surface of the semiconductor substrate 11 is oxidized and covered with a silicon dioxide film (FIG. 1(e)). Thereafter, electrodes are formed to complete the bipolar transistor device.

In this way, the graft base region 17 and the emitter region】-
8 is determined in accordance with the thickness of the polysilicon film 1-7'1, so that the distance S1 between the outer periphery of graph 1-base region]-7 and the outer periphery of emitter region 18 can be accurately controlled. Moreover, the emitter region 18 is formed inside the semiconductor substrate 1-1 of the mask layer 15, and the base regions 1-7 are formed outside thereof, so that they do not overlap with each other. Therefore, as in the conventional example, the interval S is set in anticipation of errors in mask alignment.

It is no longer necessary to set a large distance, and by reducing the interval S1, the high frequency characteristics and noise characteristics of the bipolar transistor device can be improved.

<Effects> As described in 1 above, according to the present invention, the graft base region is formed outside the predetermined region of the base formation planned region covered by the mask layer, and the emitter region is formed within the predetermined region. The graft base region and the emitter region do not overlap, and a bipolar transistor device having good high frequency characteristics and noise characteristics can be obtained.

[BRIEF DESCRIPTION OF THE DRAWINGS] Figures 1 (a) to (e) are sectional views showing each process of the embodiment of the present invention, and Figures 2 (a) to (e) are each process of the conventional example. FIG. 3 is a cross-sectional view illustrating the problems of the conventional example. 1] -... Semiconductor substrate, 13... Base region, ]4... Polysilicon film. ]-5...Mask layer, 17...Graph 1 to base region, 18...
...Emitter area. Patent Applicant: ROHM Co., Ltd. Representative Patent Attorney Kiyoshi Kuwai - (b) (C) Figure 1 (C1) Figure 1 (q) (b) (C) Figure 2 (cl) (e) Figure Z

Claims (1)

[Claims] A step of introducing impurities of a second conductivity type into the surface of a semiconductor substrate of a first conductivity type to form a base region, and a step of covering the surface of the base region with a polysilicon film containing impurities of a first conductivity type. a step of covering the polysilicon film on a predetermined region in the base region with a mask layer wider than the predetermined region; and isotropically etching the polysilicon film to expose the surface of the base region outside the predetermined region. and forming a graft base region by introducing impurities of a second conductivity type into the exposed base region excluding the base region under the mask layer, and removing the mask layer. and forming an emitter region by introducing impurities of a first conductivity type into the predetermined region from the polysilicon film.