JP2007110152A - Thin film semiconductor epitaxial substrate and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film semiconductor epitaxial substrate whereby a semiconductor device with high reliability can be manufactured by suppressing the effect of a carrier concentration of its sub-collector layer on a current amplification factor and to provide a manufacturing method thereof. <P>SOLUTION: A boron added layer 42A resulting from adding boron (B) to a collector layer 42 is formed to part of the collector layer 42 in the thin film semiconductor epitaxial substrate 1 formed with the sub collector layer 41 and the collector layer 42 so as to thereby prevent the current amplification factor from being decreased even when the sub collector layer 41 is doped with a high concentration. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thin film semiconductor epitaxial substrate suitable for manufacturing a heterojunction bipolar transistor (HBT) and a method for manufacturing the same.

  High performance heterojunction bipolar transistors (HBTs) have recently been manufactured using excellent crystal growth techniques such as MOCVD as semiconductor elements used in the frequency region above the microwave band. The HBT uses a material having a band gap larger than that of the base layer for the emitter layer to make the emitter-base junction a heterojunction, and has a higher energy barrier when holes flow from the base layer to the emitter layer, compared to a homojunction bipolar transistor. In addition, the emitter injection efficiency is increased by suppressing the inflow of holes into the emitter.

  The conventional HBT current amplification mechanism configured as described above is basically the same as a conventional homojunction bipolar transistor. Therefore, in order to improve the current amplification factor, it is necessary to reduce the probability that electrons recombine with holes in the base region. For this reason, conventionally, for example, a composition gradient in the emitter layer and the base layer is required. An electric field for accelerating electrons is generated by using AlGaAs with a base, and the flow of electrons in the base region is caused by diffusion caused by the concentration gradient of conventional electrons and the electric field created in the AlGaAs crystal. A configuration is known that accelerates by a synergistic effect with the flow of electrons traveling, shortens the traveling time of electrons in the base region, and reduces the probability that electrons recombine with holes in the base region. In addition, Patent Documents 1 and 2 disclose configurations for improving crystallinity.

In addition, attempts have been made to improve the crystallinity of the emitter layer and the base layer or the interface thereof in order to improve the current amplification factor of the HBT. The relationship has not been well examined so far.
JP-A-6-85239 JP 2000-183076 A

  However, recently, in order to reduce the contact resistance between the collector layer and the collector electrode, the carrier concentration of the sub-collector layer, which is a thin film layer having a high conductivity provided between them, has a large current gain. It turns out that it is influencing. In designing a semiconductor device, it is desirable that the carrier concentration of the subcollector layer can be set freely. However, if the carrier concentration has a large effect on the current amplification factor, the degree of freedom in device design is severely restricted. Thus, there arises a problem that the design of a device having desired characteristics is complicated.

  An object of the present invention is to provide a thin-film semiconductor epitaxial substrate and a method for manufacturing the same, which can solve the above-mentioned problems in the prior art.

  Another object of the present invention is to provide a thin film semiconductor epitaxial substrate and a method for manufacturing the same, which can suppress the influence on the current amplification factor due to the carrier concentration of the subcollector layer.

  It is another object of the present invention to provide a thin-film semiconductor epitaxial substrate and a method for manufacturing the same, which make it possible to manufacture a highly reliable semiconductor device.

  In order to solve the above problems, in the present invention, when a sub-collector layer, a collector layer, a base layer, and an emitter layer are grown on a substrate by vapor phase growth, a sub-collector layer is manufactured. And a step of adding boron (B) to at least a part of the layer portion comprising the collector layer. Therefore, in the thin film semiconductor epitaxial substrate manufactured as described above, boron (B) is present in at least a part of the subcollector layer or the collector layer or in the vicinity of the interface between the subcollector layer and the collector layer. It will be in the added state.

  Thus, when boron (B) is added to at least a part of the layer portion composed of the sub-collector layer and the collector layer, it is generated in this sub-collector layer when the sub-collector layer is highly doped. Propagation of complex crystal defects in the base layer and the emitter layer is suppressed. As a result, it is possible to effectively prevent a complex crystal defect generated in the subcollector layer from becoming a recombination center in the base layer or the emitter layer and increasing the base current and decreasing the current amplification factor. Therefore, even when the subcollector layer is doped at a high concentration, it is possible to suppress the influence on the current amplification factor, to prevent a decrease in the current amplification factor, and to improve the reliability of the semiconductor device at the same time.

  According to the first aspect of the present invention, in the thin film semiconductor epitaxial substrate, an AlGaAs-based HBT functional layer having a subcollector layer, a collector layer, a base layer and an emitter layer is formed on the substrate as a thin film semiconductor epitaxial layer. A thin film semiconductor epitaxial substrate is proposed in which boron (B) is added to at least a part of a layer portion composed of a subcollector layer and the collector layer.

  According to a second aspect of the present invention, in the thin film semiconductor epitaxial substrate, on the substrate, an InGaP-based HBT functional layer having a subcollector layer, a collector layer, a base layer and an emitter layer is formed as a thin film semiconductor epitaxial layer. A thin film semiconductor epitaxial substrate is proposed in which boron (B) is added to at least a part of a layer portion composed of a subcollector layer and the collector layer.

  According to a third aspect of the present invention, there is proposed a thin film semiconductor epitaxial substrate according to the first or second aspect, wherein the subcollector layer is a GaAs layer.

  According to a fourth aspect of the invention, in the first or second aspect of the invention, boron (B) is added to the entire surface of at least a part of the layer portion composed of the sub-collector layer and the collector layer. A thin film semiconductor epitaxial substrate is proposed.

  According to the fifth aspect of the present invention, an AlGaAs-based HBT functional layer having a subcollector layer, a collector layer, a base layer, and an emitter layer is formed on a substrate as a thin film semiconductor epitaxial layer to manufacture a thin film semiconductor epitaxial substrate. In this method, there is proposed a method for manufacturing a thin film semiconductor epitaxial substrate including a step of adding boron (B) to at least a part of a layer portion composed of the subcollector layer and the collector layer.

  According to the sixth aspect of the present invention, a thin film semiconductor epitaxial substrate is manufactured by forming an InGaP-based HBT functional layer having a subcollector layer, a collector layer, a base layer and an emitter layer as a thin film semiconductor epitaxial layer on the substrate. In this method, there is proposed a method for manufacturing a thin film semiconductor epitaxial substrate including a step of adding boron (B) to at least a part of a layer portion composed of the subcollector layer and the collector layer.

  According to the invention of claim 7, in the invention of claim 5 or 6, a method of manufacturing a thin film semiconductor epitaxial substrate in which the subcollector layer is a GaAs layer is proposed.

  According to the present invention, as described above, when a sub-collector layer, a collector layer, a base layer, and an emitter layer are vapor-phase grown on a substrate to manufacture a thin-film semiconductor epitaxial substrate for HBT manufacturing, Since the step of adding boron (B) to at least a part of the layer portion made of the collector layer is included, in the thin film semiconductor epitaxial substrate manufactured as described above, the subcollector layer or collector layer Boron (B) is added at least partially or near the boundary between the sub-collector layer and the collector layer, and is generated in this sub-collector layer when the sub-collector layer is highly doped. Propagation of complex crystal defects in the base layer and the emitter layer is suppressed. As a result, it is possible to effectively prevent a complex crystal defect generated in the subcollector layer from becoming a recombination center in the base layer or the emitter layer and increasing the base current and decreasing the current amplification factor. Therefore, even when the subcollector layer is doped at a high concentration, it is possible to suppress the influence on the current amplification factor, to prevent a decrease in the current amplification factor, and to improve the reliability of the semiconductor device at the same time.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a layer structure diagram schematically showing an example of a thin-film semiconductor epitaxial substrate for HBT manufactured by the method of the present invention. The thin film semiconductor epitaxial substrate 1 is for use in manufacturing a GaAs-based HBT. Hereinafter, the thin film semiconductor epitaxial substrate 1 shown as an example of the embodiment of the present invention will be described.

  The structure of the thin film semiconductor epitaxial substrate 1 shown in FIG. 1 is as follows. The thin-film semiconductor epitaxial substrate 1 is formed by laminating a plurality of semiconductor thin-film crystal growth layers one after another on the GaAs substrate 2 which is a semi-insulating GaAs compound semiconductor crystal using the MOCVD method as described below. Is. The thin film semiconductor epitaxial substrate 1 will be described with reference to FIG. 1. The GaAs substrate 2 is composed of a semi-insulating GaAs (001) layer, and a buffer layer 3 composed of an i-GaAs layer is formed on the GaAs substrate 2.

An HBT functional layer 4 is formed on the buffer layer 3. In the HBT functional layer 4, an n ⁺ -GaAs layer (carrier concentration 3 to 5 × 10 ¹⁸ cm ⁻³ ) serving as a subcollector layer 41 is formed on the buffer layer 3 to a thickness of 500 nm. N ⁻ -GaAs layers (carrier concentration 1 × 10 ¹⁶ cm ⁻³ ) functioning as a semiconductor epitaxially grown crystal layer with a thickness of 700 nm.

  Here, boron (B) is added to a portion of the collector layer 42 in contact with the sub-collector layer 41, thereby forming a B-added layer 42 A in the collector layer 42. In the present embodiment, the thickness of the B-added layer 42A is 10 nm. The B-added layer 42A is formed by using triethylboron (TEB), which is a raw material for boron (B), as a raw material gas necessary for forming the collector layer 42 only for a predetermined period from the start of the growth of the collector layer 42 until the thickness reaches 10 nm. By supplying them into the reactor together with arsine and trimethylgallium (TMG), a thin film semiconductor epitaxial layer containing boron (B) can be formed.

On the collector layer 42, a p ⁺ -GaAs layer (carrier concentration 2 × 10 ¹⁹ cm ⁻³ ) serving as the base layer 43 is formed as a semiconductor epitaxially grown crystal layer with a thickness of 90 nm. On the base layer 43, an n ⁻ -AlGaAs layer (carrier concentration 5 × 10 ¹⁷ cm ⁻³ ) serving as the emitter layer 44 is formed to a thickness of 110 nm. On the emitter layer 44, an n ⁻ -GaAs layer (carrier concentration 1 × 10 ¹⁷ cm ⁻³ ) serving as the emitter layer 45 is formed with a thickness of 150 nm. On the emitter layer 45, a sub-emitter layer 46 is formed. A working n ⁺ -GaAs layer (carrier concentration 3 × 10 ¹⁸ cm ⁻³ ) is formed to a thickness of 100 nm. On the sub-emitter layer 46, an n ⁺ -InGaAs layer (carrier concentration 4 × 10 ¹⁹ cm ⁻³ ) serving as the emitter contact layer 47 is formed to a thickness of 120 nm.

  The thin film semiconductor epitaxial substrate 1 shown in FIG. 1 is characterized in that the B-added layer 42A is formed in a part of the collector layer 42. In this manner, by forming the B-added layer 42A, which is a layer region to which boron (B) is added, in the collector layer 42, the sub-collector layer 41 is generated in the sub-collector layer 41 when doped at a high concentration. Propagation of the composite crystal defect in the base layer 43 and the emitter layers 44 and 45 is suppressed. As a result, it is possible to effectively prevent the complex crystal defects generated in the subcollector layer 41 from becoming a recombination center in the base layer 43 and the emitter layers 44 and 45 to increase the base current and lower the current amplification factor. it can. Therefore, according to the HBT manufactured using the thin film semiconductor epitaxial substrate 1, even when the subcollector layer 41 is doped at a high concentration, the influence on the current amplification factor is suppressed, and the current amplification factor of the HBT is reduced. Can be prevented, and at the same time, the reliability of the HBT can be improved.

  In the case of the layer structure of the thin-film semiconductor epitaxial substrate 1 having the B-added layer 42A shown in FIG. 1 and in the case of the thin-film semiconductor epitaxial substrate in which the collector layer 42 is formed without providing the B-added layer 42A. Samples were prepared for each case in order to examine how they differ.

(Sample A)
The MOCVD method is used for growth. After the growth of the subcollector layer 41 is completed, triethylboron (TEB) is simultaneously flowed together with a source gas of arsine and TMG from the start of the growth of the collector layer 42, and boron (B) is added. The additive layer 42A was grown to a thickness of 10 nm, and then only the TEB supply was stopped, and the n ⁻ -GaAs layer was grown to a thickness of 680 nm. As a result, a collector layer 42 having a B-added layer 42A having a thickness of 10 nm was formed at a portion in contact with the sub-collector layer 41, and a sample (sample A) of the thin film semiconductor epitaxial substrate having the layer structure shown in FIG.

(Sample B)
After the growth of the subcollector layer 41, an n ⁻ -GaAs layer was grown to a thickness of 700 nm without supplying TEB to form the collector layer 42 without the B-added layer 42A. A thin film semiconductor epitaxial substrate sample (sample B), which is exactly the same as in the case of sample A, was prepared.

Sample A and sample B were processed to produce an HBT having an emitter size of 100 μm × 100 nm, and then the current amplification factor was measured at a current density of 1 kA / cm ² . The current amplification factor of the HBT (B) manufactured by the sample B without the B-added layer 42A was 50, but the current amplification factor of the HBT (A) prepared by the sample A having the B-added layer 42A was as large as 89. It was confirmed that

The boron (B) addition concentration of the B addition layer 42A of the sample A was 6 × 10 ¹⁸ cm ⁻³ by secondary ion mass spectrometry.

  In the above embodiment, the B-added layer 42A is provided in the lower 10 nm portion of the collector layer 42. However, considering the cause of the decrease in the current gain, the B-added layer 42A is provided between the sub-collector layer 41 and the base layer 43. In other words, it is considered that the same effect can be obtained at any position within the region of the collector layer 42.

  In the above embodiment, boron (B) is added to the collector layer 42 in order to reduce vacancy diffusion from the subcollector layer 41 to the base layer 43. In order to suppress the diffusion of vacancies into the substrate, it is expected to be obtained by adding boron (B) to at least a part of the emitter layer 44, the emitter layer 45, and the sub-emitter layer 46. In this case, the method for adding boron (B) can be the same as in the above embodiment.

  Although the present invention has been described with respect to an AlGaAs-based HBT, the present invention is not limited to an AlGaAs-based HBT, and even in the case of a thin-film semiconductor epitaxial substrate for manufacturing an InGaP-based HBT. The same effect can be obtained.

Sectional drawing which shows an example of embodiment of the thin film semiconductor epitaxial substrate by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thin film semiconductor epitaxial substrate 2 GaAs substrate 3 Buffer layer 4 HBT functional layer 41 Subcollector layer 42 Collector layer 43 Base layers 44 and 45 Emitter layer 46 Subemitter layer 47 Emitter contact layer

Claims (7)

  A thin-film semiconductor epitaxial substrate in which an AlGaAs-based HBT functional layer having a sub-collector layer, a collector layer, a base layer, and an emitter layer is formed as a thin-film semiconductor epitaxial layer on the substrate. A thin-film semiconductor epitaxial substrate, wherein boron (B) is added to at least a part of the layer portion.   A thin-film semiconductor epitaxial substrate in which an InGaP-based HBT functional layer having a sub-collector layer, a collector layer, a base layer, and an emitter layer is formed as a thin-film semiconductor epitaxial layer on a substrate. A thin-film semiconductor epitaxial substrate, wherein boron (B) is added to at least a part of the layer portion.   3. The thin film semiconductor epitaxial substrate according to claim 1, wherein the subcollector layer is a GaAs layer.   3. The thin film semiconductor epitaxial substrate according to claim 1, wherein boron (B) is added to the entire surface of at least a part of a layer portion composed of the subcollector layer and the collector layer.   A method for manufacturing a thin-film semiconductor epitaxial substrate by forming an AlGaAs-based HBT functional layer having a sub-collector layer, a collector layer, a base layer and an emitter layer as a thin-film semiconductor epitaxial layer on a substrate. A method of manufacturing a thin film semiconductor epitaxial substrate, comprising: adding boron (B) to at least a part of a layer portion including the collector layer.   A method for manufacturing a thin-film semiconductor epitaxial substrate by forming an InGaP-based HBT functional layer having a sub-collector layer, a collector layer, a base layer and an emitter layer as a thin-film semiconductor epitaxial layer on a substrate. A method of manufacturing a thin film semiconductor epitaxial substrate, comprising: adding boron (B) to at least a part of a layer portion including the collector layer.   7. The method of manufacturing a thin film semiconductor epitaxial substrate according to claim 5, wherein the subcollector layer is a GaAs layer.

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