JPH05129315A - Semiconductor device operated at low temperature - Google Patents

Abstract

PURPOSE:To obtain a bipolar transistor wherein it is provided with a base concentration distribution which shortens the base delay time at a low temperature of 200 deg. K or lower and it is suitable for a high-speed operation by a method wherein the impurity concentration on the side of a collector of a base region is set to a concentration which is higher than the impurity concentration on the side of an emitter of the base region. CONSTITUTION:A bipolar transistor is constituted in the following manner: it is operated at a low temperature of 200 deg. K or lower; carrier; to be used as an emitter current or a collector current flow from an emitter region 8 formed on the surface of a semiconductor substrate 1 toward a collector region 2 formed at the inside of the semiconductor substrate 1. In the bipolar transistor, the impurity concentration on the side of the collector 2 of a base region 7 is set to a concentration which is higher than the impurity concentration on the side of the emitter 8 of the base region 7. For example, when a base region 7 is formed by a low-temperature epitaxial growth operation, the amount of boron as a dopant is controlled, it is set at 3X10<19>/cm<3> at the beginning, and the amount of impurities is reduced to 3X10<18>/ cm<3> while 100nm is grown.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bipolar type semiconductor device, and in particular, it operates at a low temperature of 200 K or less, and has an emitter region formed on the surface of a semiconductor substrate and a collector region formed inside the semiconductor substrate. The present invention relates to a so-called forward operation bipolar transistor configured so that a carrier that becomes an emitter current or a collector current flows toward a so-called lateral transistor in which an emitter region and a collector region are formed on a semiconductor substrate surface.

[0002]

2. Description of the Related Art As a conventional example in which a base concentration distribution is devised for high speed operation of a bipolar transistor, for example,
Super-high-speed bipolar device supervised by Takuo Sugano, Baifukan, p
The graded base concentration distribution described in 36 is known. This is because the concentration of the base region 7 is high on the emitter side and low on the collector side, as shown in the concentration distribution of the conductive impurities in FIG. According to the concentration distribution of the base region 7, the potential energy becomes low on the collector side due to the difference in pseudo Fermi level depending on the concentration, and an internal electric field that accelerates the carriers traveling in the base region is generated.

Normally, carriers travel in the base by diffusion, but the built-in electric field produces an effect of traveling by drift, so that the base travel time is shortened from 1/2 to 1/3 of the normal time. Further, this concentration distribution can be easily formed by thermal diffusion of impurities or ion implantation generally used for forming a base.

[0004]

Although the conventional graded base concentration distribution is certainly effective at room temperature, it does not consider low temperature operation below 200K. That is, since the pseudo Fermi level is proportional to the temperature, the difference in the pseudo Fermi level due to the concentration becomes smaller as the temperature becomes lower. Therefore, as the temperature becomes lower, the built-in electric field in the base region also decreases, and the effect of shortening the base delay time decreases.

Further, in the conventional example, since the operation at room temperature was considered, sufficient consideration was not given to the bandgap reduction effect due to impurities. The bandgap reduction effect becomes stronger as the concentration increases, and hardly depends on the temperature. Therefore, at low temperatures, the built-in electric field due to the difference in bandgap reduction becomes relatively larger than the built-in electric field due to the difference in Fermi level. Since the higher the concentration is, the larger the bandgap reduction effect is, the bandgap on the emitter side becomes smaller in the conventional concentration distribution, and an internal electric field is generated in the direction in which carriers are pulled back to the emitter side. This causes a problem that the base delay time of the gradient concentration distribution becomes longer than the uniform concentration distribution at low temperature.

Further, in the conventional bipolar transistor having a gradient concentration distribution, the emitter region formed on the surface of the semiconductor substrate is operated as the collector, and the collector region formed inside the semiconductor substrate is operated as the emitter.
The above-mentioned problem does not occur in the so-called reverse operation mode in which the carrier serving as the emitter current or the collector current flows from the inside of the semiconductor substrate to the surface of the semiconductor substrate, but the emitter delay time peculiar to the reverse operation does not occur. Increase, high emitter resistance, and influence of carrier injection into the external base, there is a problem that it is not suitable for high speed operation.

An object of the present invention is to have a base concentration distribution that shortens the base delay time at a low temperature of 200 K or less,
It is to provide a bipolar transistor suitable for high speed operation.

[0008]

As shown in FIG. 1, a so-called forward operation bipolar transistor basic concentration distribution according to a typical embodiment of the present invention is shown in FIG. The impurity concentration on the collector side of 7 is set higher than that on the emitter side.

[0009]

The operation of the present invention will be described below with reference to the band potential diagram (FIG. 3) at 77K. In the base concentration distribution of the present invention, the concentration on the collector side of the base region 7 is higher than that on the emitter side. Therefore, the built-in electric field due to the difference in pseudo-Fermi level causes carriers to flow to the emitter side, contrary to the conventional gradient concentration distribution type. It is working to pull back. However, since the pseudo Fermi level is proportional to temperature, this built-in electric field is 77
At K, it is about 1/4 of room temperature. On the other hand, according to the bandgap reduction effect, the collector-side bandgap Eg2 of the base region 7 becomes smaller than the emitter-side bandgap Eg1, and an internal electric field that accelerates carriers to the collector side is generated. Since the bandgap reduction effect hardly depends on temperature, the built-in electric field does not decrease even at low temperature.
Therefore, at 77K, the built-in electric field due to the bandgap reduction effect exceeds the built-in electric field due to the Fermi level, and as a whole, the built-in electric field acts in the direction of accelerating the carriers running in the base to the collector side. This built-in electric field can reduce the base delay time. Also,
In the forward operation or the lateral operation, the emitter delay and the emitter resistance are small, so that the reduction of the base delay time can be largely reflected in the improvement of the delay time of the entire transistor.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. In the embodiment, the forward operation npn-type bipolar will be described as an example, but the operation principle is the same for a so-called lateral transistor that performs lateral operation and a pnp-type bipolar transistor.

FIG. 2 is a sectional view showing a first embodiment of the present invention. In the manufacturing method of this embodiment, the surface of the Si substrate 1 is made to have a high concentration by ion implantation, the collector region 2 is formed by epitaxial growth, and the element isolation insulating film 3 is formed by oxidation. An opening is formed in the element isolation insulating film 3, and a base region 7 is formed on the semiconductor surface of the opening by low temperature epitaxial growth. At the time of this epitaxial growth, the amount of boron as a dopant is controlled and the initial value is 3 × 10 ¹⁹
/ Cm ^3, and the amount of impurities is reduced to 3 × 10 ¹⁸ / cm ³ while growing 100 nm. Then, polysilicon 4 containing boron at a high concentration is deposited on the element isolation insulating film 3 to form an external base electrode for connection with the base electrode 9. A polysilicon 8 is deposited on the base / emitter separating silicon oxide film 5 and ion-implanted with phosphorus or arsenic and annealed to form an emitter region.

The concentration distribution on the line aa 'in FIG. 2 is the basic concentration distribution of the present invention shown in FIG. 1. At a low temperature of 200 K or less, a built-in electric field that accelerates carriers to the collector side is generated. The concentration of the base region is set to 1 × 10 ¹⁸ / cm ³ or more of the Mott transition concentration in order to prevent the carrier freeze-out effect at low temperatures.

As an effect of this embodiment, FIG. 4 shows the temperature dependence of the base delay time in the reverse gradient concentration distribution type base of the present invention and the conventional gradient concentration distribution type base. As can be seen from the above, the delay time of the conventional gradient concentration type base is shorter at a temperature of 200 K or higher, but the delay time of the reverse gradient concentration type base of the present invention is gradually shorter at a temperature of 200 K or lower, and the temperature becomes lower. The difference becomes bigger. In this embodiment, at 77K, the base delay time can be reduced to about 1/4 of the conventional value.

FIG. 6 shows the concentration distribution of the second embodiment in which the present invention is applied to a pseudo hetero bipolar transistor (hereinafter referred to as PHBT). The cross-sectional structure is shown in FIG. PHB
T is a transistor for obtaining high performance at a low temperature. By increasing the concentration of the base region 7 to be higher than that of the emitter region 6 to increase the band gap reduction, an operation similar to that of a narrow-gap base hetero-bipolar transistor is achieved. It is something that tries to let you do. The manufacturing method up to the base formation of FIG. 7 is the same as that of the first embodiment, but the insulating film 5 is used.
After depositing, a hole for an emitter is opened, and a low concentration emitter region 6 is formed again by low temperature epitaxial growth. At this time, polysilicon is deposited in regions other than the base region 7 as polysilicon. Then, a high impurity concentration emitter polysilicon electrode 8 and a metal electrode 9 are deposited and completed. In this embodiment, the delay time of the base is shortened at a low temperature, the current amplification factor is increased by the effect of the pseudo-hetero bipolar transistor, and the delay time of the emitter is also reduced, so that a high speed bipolar transistor can be provided.

The present invention is not limited to the above embodiments, but various modifications can be made within the scope of its technical idea. For example, in a so-called lateral transistor in which an emitter region and a collector region are formed on the surface of a semiconductor substrate and operates laterally, the impurity concentration on the collector side of the base region should be higher than the impurity concentration on the emitter side of the base region. Thus, similarly, excellent characteristics can be obtained at a low temperature of 200 K or less.

[0016]

As explained above, according to the reverse slope type base concentration distribution of the present invention, the built-in electric field due to the bandgap reduction greatly reduces the delay time of the base at a low temperature of 200 K or less, and the high speed. A bipolar transistor can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a concentration distribution of a basic embodiment of the present invention.

FIG. 2 is a diagram showing a cross-sectional structure of a first embodiment of the present invention.

FIG. 3 is a diagram showing a band potential in the case of a basic concentration distribution of the present invention.

FIG. 4 shows the temperature dependence of the base delay time showing the effect of the present invention.

FIG. 5 is a diagram showing a conventional density distribution.

FIG. 6 is a concentration distribution diagram showing a second embodiment in which the present invention is used in a pseudo hetero bipolar transistor.

FIG. 7 is a diagram showing a cross-sectional structure of a second embodiment in which the present invention is applied to a pseudo hetero bipolar transistor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Silicon substrate, 2 ... Collector layer, 3 ... Element isolation silicon oxide film, 4 ... Polysilicon external base electrode, 5 ... Base emitter isolation silicon oxide film, 6 ... Low concentration emitter region, 7 ... Base region, 8 ... Polysilicon emitter region, 9 ... Aluminum electrode, 10 ... Polysilicon low concentration emitter region.

Claims (5)

[Claims] 1. Operating at a low temperature of 200 K or less,
A bipolar transistor configured such that an emitter current or a carrier serving as a collector current flows from an emitter region formed on a surface of a semiconductor substrate toward a collector region formed inside the semiconductor substrate, the collector side of a base region. The impurity concentration of is higher than the impurity concentration of the base region on the emitter side. 2. The bipolar transistor according to claim 1, wherein the impurity concentration on the emitter side of the base region is higher than 1 × 10 ¹⁸ / cm ³ . 3. The bipolar transistor according to claim 1, wherein the emitter region in contact with the base region has a lower concentration than the emitter side of the base region. 4. The bipolar transistor according to claim 1, wherein the base region is formed by epitaxial growth. 5. While operating at a low temperature of 200 K or less,
A lateral transistor having an emitter region and a collector region formed on a surface of a semiconductor substrate, wherein a collector side impurity concentration of a base region is higher than an emitter side impurity concentration of the base region. Transistor.