JPH0242731A - Semiconductor device and its manufacturing method - Google Patents

Abstract

PURPOSE:To obtain an ultrahigh-speed bipolar transistor by a method wherein, while a substrate temperature is kept at 0 deg.C or lower, a hydrogen plasma sputtering operation is executed and fine-crystal silicon is deposited in order to enhance a current gain. CONSTITUTION:When an emitter composed of a fine-crystal silicon film is formed, an opening used to extract an emitter electrode 7 is made; after that, an emitter layer 6 is formed in this opening part. During this process, a sputtering operation by a hydrogen plasma 24 is executed; silicon which has been sputtered from a target 25 is deposited in the emitter opening part in a substrate 1 which has been cooled at 0 deg.C or lower; a fine-crystal Si film is formed. Since the silicon is deposited by the sputtering operation of the hydrogen plasma in a state that a substrate temperature has been kept at 0 deg.C or lower, it is possible to obtain the fine-crystal silicon film whose volume ratio is nearly 100% and whose average particle diameter is 100Angstrom or lower. Thereby, it is possible to obtain a high-performance bipolar transistor whose current gain is remarkably high.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor device and a method for manufacturing the same, and particularly relates to a semiconductor device using a microcrystalline silicon film in the emitter layer of a heterojunction bipolar transistor and a method for manufacturing the same. It is.

[Prior Art] To date, in order to realize ultra-high-speed silicon bipolar integrated circuit devices, heterojunction bipolar transistors have been developed that use a wide energy gap heterojunction emitter to reduce base resistance. In this case, the wide energy gap film material is generally amorphous silicon (hereinafter abbreviated as a-8i),
Three types have been proposed: amorphous silicon carbide (hereinafter abbreviated as a-9t c) and microcrystalline silicon (hereinafter abbreviated as μa-81).

Of the three materials mentioned above, when a-8i and a-3iC are actually used for the emitter layer of a bipolar transistor,
The current gain is lower than the value predicted from the band structure, and no particular advantage has been recognized compared to the normal homojunction emitter method. The reason for this is that both a-81 and a-3IC have high resistance, resulting in a large voltage drop at the emitter, and a defect current related to the energy level existing at the hetero interface and in the amorphous semiconductor. It is believed that this is due to the increase in

To compensate for this drawback, a method has been proposed that uses μc-8I film as an emitter material, which has higher doping efficiency and a band width comparable to that of amorphous semiconductors, and its potential is currently attracting attention. It is.

[Problems to be Solved by the Invention] However, in a heterojunction bipolar transistor that actually uses the μe-8l film described above as an emitter material, the current gain may increase in some cases. However, the following problems still remain.

(b) It is necessary to further improve the current gain.

(b) Even if transistors are formed under the same manufacturing conditions, characteristic parameters such as current gain vary.

The problems shown in (a) and (b) above are due to the fact that the band width of the μc-8i film is extremely sensitive to the film manufacturing conditions, and this can be seen by observing the formed μc-8t film using an electron microscope. As a result, the reason has become clear. In other words, the μc-8t film of the conventional method has a morphology in which microcrystalline silicon of different sizes is scattered within the a-3i film, and the volume fraction and microcrystal grain size of these microcrystals are within the band. This is because it has a strong influence on the gap width. Therefore, it has been desired to form a microcrystalline silicon film for emitter material that is insensitive to wide energy gap film fabrication characteristics, and to establish a method for manufacturing the same.

This invention was made to solve the above-mentioned problems, and aims to provide an ultra-high-speed bipolar transistor by establishing a manufacturing method using film forming conditions with uniform film characteristics over a wide energy gap. That is.

[Means for Solving the Problems] A semiconductor device according to the present invention is a heterojunction bipolar transistor in which an emitter layer is formed of a film consisting essentially only of microcrystalline silicon with an average grain size of 100 Å or less.

Furthermore, the method for manufacturing a semiconductor device according to the present invention includes a step of forming an emitter made of the above-mentioned microcrystalline silicon film, forming an opening for taking out an emitter electrode, and then forming an emitter layer in this opening. The method is characterized in that silicon sputtered from a target by hydrogen plasma sputtering is cooled to below 0° C., and silicon is deposited on the emitter opening of a substrate to form a microcrystalline S1 film.

[Function] In the method for manufacturing a semiconductor device according to the present invention, in forming the emitter layer, silicon is deposited by hydrogen plasma sputtering while the substrate temperature is maintained at 0° C. or less, so that a volume fraction of almost 100% can be achieved. A microcrystalline silicon film having an average grain size of 100 Å or less can be obtained. In this case, the inside of the microcrystal is silicon, and the outside is silicon hydride, and adjacent microcrystals are firmly bonded to each other via this hydride.

Although the reason why a microcrystalline silicon film can be obtained by hydrogen plasma sputtering at such a low temperature has not yet been fully elucidated, the present inventors have considered the following.

■ Reason for crystallization: Hydrogen plasma discharge emits a large amount of ultraviolet rays, and upon receiving this irradiation, silicon atoms or hydrogen compounds in the gas become excited, which allows the deposited silicon to recrystallize.

■ Reason for forming microcrystals: Due to the presence of dangling bonds or silicon hydrogen compounds in silicon crystals, which are microcrystals, the free energy increases, and when the grain size reaches a certain level, growth stops, and new growth occurs. The next microcrystal grows.

In addition, since the semiconductor device obtained by the manufacturing method of the present invention uses a high-quality microcrystalline silicon film as described above for the emitter layer, especially in the case of a bipolar transistor, the microcrystalline silicon film has an average grain size of 100 Å or less. Once formed, the energy gap required for ultra-high-speed silicon bipolar transistors is a silicon-specific value, that is, 1.
A wide energy gap of 1 eV or more can be obtained, and especially when formed under optimal conditions to a thickness of 50 Å or less, a wide energy gap of 2 eV or more can be obtained.

[Examples] Example 1; FIG. 1 is a schematic cross-sectional view of a heterojunction bipolar transistor showing an example of the present invention. Note that in this cross-sectional view, illustration of the element isolation region is omitted.

In the figure, 1 is an n/n+ type silicon (St) epitaxial wafer substrate (hereinafter referred to as a shrimp substrate), 2 is a p-type base layer formed within the n-type layer of the shrimp substrate 1, and 3 is a shrimp substrate. The collector electrode C is an insulating film made of a St oxide film formed on the surface of the substrate 1, and the collector electrode C is taken out from the n-soil layer of the shrimp substrate 1.

The base electrode B is taken out from an opening provided in the insulator film 3 via a metal electrode 5 formed so as to be in contact with the base layer 2 . 6 is an emitter layer formed so as to be in contact with the base layer 2 at the emitter opening of the insulating film 3, and is made of an n-type microcrystalline Si film formed by the manufacturing method of the present invention (explained in Example 2). It has become. The emitter electrode E is taken out via a metal electrode 7 formed on the upper surface of the emitter layer 6.

The npn type heterojunction bipolar transistor formed with the above structure achieves a reduction in base resistance due to the heterojunction between the emitter layer 6 and the base layer 2, which has an enlarged energy gap, and improves current gain. A bipolar transistor has been obtained. That is, as a result of measuring the current gain of this heterojunction bipolar transistor, it showed a maximum of 1000, which was higher than that of the conventional μc
It was confirmed that this transistor has a significant advantage over a heterojunction bipolar transistor using a -81 film.

Example 2: In this example, we will first explain the manufacturing apparatus for the microcrystalline St film used to form the emitter layer 6 shown in the example of FIG. 1, and then explain the method for forming the microcrystalline Si film. The method for manufacturing a heterojunction bipolar transistor will be mainly explained.

FIG. 2 is a schematic cross-sectional view of a plasma sputtering apparatus used in a method for manufacturing the emitter layer 6 of a heterojunction bipolar transistor, taking the semiconductor device of the embodiment shown in FIG. 1 as an example. In the figure, reference numeral 21 denotes a vacuum vessel, which is provided with an exhaust hole 31 connected to a vacuum device (not shown) and a gas introduction hole 22 for adjusting the atmosphere of the vacuum vessel 21. 27.2
9 is an electrode for plasma discharge, and the electrode 27 has a permanent magnet 2.
A target 25 made of a semiconductor material (Sl in this case) is installed on the upper surface of the electrode 27, and a shrimp substrate 28 before the emitter layer 6 is formed is installed on the electrode 29.

The electrode 29 is provided with a cooling medium inlet/outlet hole 30 connected to a cooling device (not shown). 23 is the electrode 27°29
This is a high-frequency power supply that supplies power to the Note that 24 is the formed hydrogen plasma.

The table below lists specific operating conditions when forming the emitter layer 6 in this example.

Hereinafter, a method for manufacturing a heterojunction bipolar transistor will be described using the plasma sputtering apparatus shown in FIG. 2 in part and taking the embodiment shown in FIG. 1 as an example.

First, an n/f1+ type 81 epitaxial substrate 1 with a crystal plane orientation (111) was washed and dried in a predetermined process, and then a normal silicon process was applied to this shrimp substrate 1.
The insulator film 3 is formed by thermal oxidation, the base window is opened, boron (B) ions are implanted, and the base layer 2 is formed by thermal oxidation.
Formed within the layer. Thereafter, the emitter was opened to form an emitter opening. The shrimp substrate 1 (corresponding to the shrimp substrate 28 in FIG. 2) which had been formed to this process state was placed on the electrode 29 of the plasma sputtering apparatus shown in FIG. 2 and opposed to the target 25.

Next, an n-type microcrystalline Sl film constituting the emitter layer 6 is formed.The procedure is to introduce hydrogen (H2) gas and a predetermined amount of pH 3 gas through the gas introduction hole 22 to create an atmosphere in the vacuum vessel 21. As 1. After creating a gas pressure of approximately OTorr, a voltage from a high frequency type [23] is applied to the electrodes 27 and 29. At this time, a plasma 24 is formed, and the hydrogen ions in the plasma 24 sputter St constituting the target 25, and liquid nitrogen is introduced from the cooling medium inlet/outlet hole 30 onto the shrimp substrate 28 cooled to the liquid nitrogen temperature. The emitter layer 6 is formed by forming a thin film of. In this case, the cooling medium may be water cooled to below 0°C.

When the formed Si thin film, that is, the emitter layer 6 was observed using a dummy layer (not shown), it was found that the average grain size was 100 Å.
It was found that the following 91 microcrystals were formed by almost continuous bonding.

Furthermore, this shrimp substrate 28 is taken out from the plasma sputtering device, and after dry etching removes the portion other than the emitter layer 6, metal vapor deposition is performed by a normal process to form the emitter electrode 7, the base electrode 5, and the collector C. The steps for forming a heterojunction bipolar transistor up to the stage shown in the embodiment of FIG. 1 are completed.

In the above embodiment, the shrimp substrate 28 was used for ease of experiment.
A case has been described in which a microcrystalline Si film is formed by keeping it cooled to the temperature of liquid nitrogen. However, as can be deduced from the mechanism of microcrystalization, it is thought that the microcrystalline structure according to the present invention can be obtained even if the temperature is not so low.
It is sufficient if the diffusion of t atoms on the substrate is suppressed. According to another preliminary experiment, it has been confirmed that microcrystalization is possible even near 0°C. Generally speaking, microcrystallization is considered to be easier as the temperature decreases, and the lower limit of the temperature can be achieved up to the liquid helium temperature (4K).

[Effects of the Invention] As explained above, according to the method for manufacturing a semiconductor device of the present invention, a microcrystalline Si film with a volume fraction close to 100% and an average grain size of 100 Å or less is formed in the emitter layer of a heterojunction bipolar transistor. Having established the formation method used, bipolar transistors that take advantage of the advantages of heterojunctions can now be formed on silicon substrates. Therefore, this manufacturing method has the effect of providing a high-performance bipolar transistor with a significantly high current gain.

[Brief explanation of the drawing]

FIG. 1 is a schematic structural diagram of a heterojunction bipolar transistor showing an embodiment of the present invention, and FIG. 2 is a schematic diagram of a plasma sputtering apparatus used in the method for manufacturing the emitter layer of a bipolar transistor like the embodiment of FIG. 1. It is a diagram. In the figure, 1 is the substrate for the n/r′1+ type silicon epitaxial wafer (shrimp substrate), 2 is the base layer,
3 is an insulator layer, 5 is a base electrode, 6 is an emitter layer, 7 is an emitter electrode, 21 is a vacuum container, 22 is a gas introduction hole, 2
3 is a high frequency power supply, 24 is hydrogen plasma, 25 is a target, 2B is a permanent magnet, 27 is an electrode, 28 is a shrimp substrate, 2
9 is an electrode, 30 is an inlet/outlet hole for a cooling medium, and 31 is an exhaust hole.

Claims (2)

[Claims] (1) A semiconductor device constituted by a heterojunction bipolar transistor, characterized in that the emitter layer is formed of a film consisting essentially only of microcrystalline silicon with an average grain size of 100 Å or less. (2) In a method for manufacturing a semiconductor device configured with a heterojunction bipolar transistor, a base layer is formed on an epitaxial wafer, an insulating film is formed on the entire surface, and openings for taking out the emitter and base electrodes are formed in this insulating film. A method for manufacturing a semiconductor device, comprising: forming an emitter layer, and performing hydrogen plasma sputtering on the emitter opening while maintaining the substrate temperature at 0° C. or lower to deposit microcrystalline silicon.