JPS63138774A - Manufacture of hetero junction bipolar transistor - Google Patents

Abstract

PURPOSE:To facilitate processes markedly by a method wherein a fine collector as well as an emitter and an emitter electrode are formed in self alignment using the same mask. CONSTITUTION:A temporary emitter 13 is removed by etching process to expose a cap layer 6a of emitter forming a recession 15. First, an emitter electrode metal is formed by evaporation and lift off process. Second, hydrogen ion is implanted in a layer 3 using an emitter electrode 8 as a mask to form a collector while an outer region 3b below the emitter electrode 8 is semiinsulated to form a fine collector region 3a in substantially the sane size as that of emitter electrode 8. Through these procedures, the processes can be facilitated markedly to improve the yield thereof notably.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a heterojunction bipolar transistor (hereinafter referred to as HBT), which is promising as an ultra-high speed and ultra-high frequency transistor.

Background of the Invention In recent years, HBTs, which use a semiconductor material with a larger bandgap than the base as the emitter of bipolar transistors (hereinafter referred to as BT), have been actively researched as one of the promising candidates for ultra-high speed and ultra-high frequency transistors. It's happening.

Figure 2 shows a normal HBT with a conventional emitter installed on the top.
1 is a GaAs substrate, 2 is a highly doped n-type GaAs to facilitate the formation of an ohmic contact of the collector, 2a is a collector electrode extraction region, and 3 is an n-type substrate for forming a collector region. type of GaAs,
3a is a collector region, 3b is a semi-insulating region around the collector, and 4 is p-type GaAs for forming a base region.
.

4a is a base region, 4b is an external base region for taking out the base electrode, and 5 is n for forming an emitter region.
5a is an emitter region, 6 is highly doped n-type GaAs to facilitate the formation of an emitter ohmink contact, 6a is a camp layer above the emitter region, 7 8 is an emitter electrode, 9 is a base electrode, 10 is a collector electrode, and 16
is a mask layer for forming a minute collector by introducing impurities into the layer for forming the collector.

A multilayer structure material 7 epitaxially formed on a substrate 1 (
Using FIG. 2(a), impurities are introduced into the layer forming the collector to form a minute collector as shown in FIG. 2[bl]. Then, by photolithography and etching, a structure having an emitter region 6a and 53, a base region 4a and 4b, a collector region 3a, and a collector electrode lead-out region 2a is formed as shown in FIG. Then, as shown in FIG. 2+dl, an emitter electrode 8, a base electrode 9, and a collector electrode 10 are formed. An inverted HBT with a collector provided on the upper side is formed by the same method as shown in FIG. 2, using a multilayer structure with 3 material layers forming the emitter and 5 material layers forming the collector.

The operation of the HBT configured as above will be explained.

ft and fm, which are indicators of high-speed operation of HBT, are expressed as follows.

Jt-1/2π(τ8+τe + r c + r c
c) fm-Jt /, /'i West 1 West 7 times, τB (emitter depletion layer strike time) - TE (C
BC"caa"CPB), τB (base running time) - W82/πDB, τ. (Collector depletion layer travel time)
-W. 2/2 vs, τ. . (Collector depletion layer charging time)
-(R8F:+R,)(CBC+CPC)'RB is base resistance, Cac hahebe collector capacitance 1, CEB is base-emitter capacitance, CPB is base layer stray capacitance, C
1° is the collector layer stray capacitance, WB is the base layer thickness, D
B is the base layer diffusion coefficient, Wo is the thickness of the collector depletion layer,
V5 is collector running velocity, RI:Il: is emitter contact resistance, and Ro is collector resistance.

HBT uses a semiconductor material with a larger bandgap than the base as the emitter, which suppresses hole leakage from the base to the emitter (in the case of npn type). The collector can be lightly doped. As a result, jm becomes large with a Q that can reduce the base resistance RB, which is important for increasing the speed and frequency of the transistor. Furthermore, in general in BT, CBBlCBc
is the junction capacitance doping factor CBB(n, h>
, CB, (n, h), and the junction area AEB%ABC. In HBT, the emitter and collector are lightly doped and the base is highly doped, so CBB
(n, h), CB.

(n, h) depends only on the emitter-collector doping, and Cas''ac is:

Cae"8 "AHB "B C""C"B CB
B Therefore, in HBT, compared to normal BT, CIEB'
Since CBC becomes smaller, τ8 and τcc become smaller, and j
It becomes possible to increase t. Further, since 08B becomes smaller, it becomes possible to increase 1 m in combination with the above-described small RB.

Thus, HBTs are inherently advantageous for higher speeds due to their heterostructure. However, in order to further increase the speed, it is extremely important to reduce floating elements by miniaturizing the device structure and reducing the contact resistance of the electrodes. For example, as shown in the conventional example, base-collector junction area ABC
By introducing impurities into the layer for forming the collector to form a minute collector, the CBG can be reduced and LJm can be increased. Similarly, in an inverted HBT, the Joint area ABB
It is important to reduce CB□ by decreasing , thereby increasing ft, and thus increasing fm.

In addition, in the normal type, the resistance R of the emitter contact is
66. In the inverted type, it is extremely important to reduce the contact resistance of the collector.

Problems to be Solved by the Invention However, in the manufacturing method of a normal HBT as shown in FIG. 2, a fine collector is formed by introducing impurities into the layer forming the collector using a fine mask.
Although CaC can be made smaller, the process is extremely complicated as it is necessary to look through this mask and use three other fine masks to form the emitter, emic electrode, and emitter IIT electrode wiring in the tiny emitter part. There was a problem in that it was difficult and the yield was poor due to the difficulty of mask alignment. Similarly, in the case of an inverted HBT, it is extremely difficult to form a minute collector, collector electrode, and collector electrode wiring.

In view of the above-mentioned problems, the present invention aims to form a fine collector (emitter in the inverted type) by introducing impurities into a layer forming the collector (emitter in the inverted type) using a single mask, and to form a fine collector (emitter in the inverted type). The present invention aims to provide a method for manufacturing an HBT in which the electrode (collector in the case of an inverted type) can be formed in a self-aligned cell line.

Means for Solving the Problems In order to solve the above problems, in the HBT manufacturing method of the present invention, a protective layer is added on the epitaxially formed multilayer structure material from which the normal type or inverted type HBT is formed. forming a mask material layer on the protective layer at a portion corresponding to the emitter (collector in the case of an inverted type), and etching the mask material layer using the mask material layer as a mask; a step of forming an emitter (a collector in the case of an inverted type), a step of etching the temporary emitter as a mask to expose the external base region, and a step of covering the entire surface with a photoresist and dry etching the photoresist to remove the emitter. Temporary emitter (collector in inverted type) formed on top of (collector in inverted type)
After positioning the temporary emitter (collector in the inverted type), the temporary emitter (collector in the inverted type) is removed by etching, and the photoresist left around the emitter (collector in the inverted type) is used to form the emitter (collector in the inverted type) electrode. A process of forming impurities by vapor deposition and lift-off, and using the emitter (collector in the inverted type) electrode as a mask, impurities are removed from the collector (
A step of reducing the carrier concentration in a region outside the lower collector (emitter in the inverted type) region of the emitter (collector in the inverted type) electrode by introducing it into a material layer for forming the emitter (in the inverted type) electrode. By using both, a fine emitter (collector in the inverted type), an emitter (collector in the inverted type) electrode, and a fine collector (emitter in the inverted type) can be formed using essentially one mask.

Function: In the HBT manufacturing method of the present invention, fine-sized HBT
However, formation of a fine collector (emitter in the inverted type) and formation of the emitter (collector in the inverted type) and emitter (collector in the inverted type) electrode can be performed by self-line using a single mask. For this reason, the conventional process of forming a fine collector (emitter 7 for an inverted type), emitter (collector for an inverted type), and emitter (collector for an inverted type) electrode using separate masks has significantly changed. becomes easier. In addition, in this invention, the emitter (collector in the inverted type) electrode covers the entire upper part of the emitter (collector in the inverted type), so even if the emitter is the same size as the conventional one (collector in the inverted type), the electrode and emitter (collector in the inverted type) The contact area with the electrode increases significantly, and as a result, the contact resistance of the electrode becomes smaller than in the past.

Therefore, it is effective to increase lt.

EXAMPLE Hereinafter, a method for manufacturing an HBT according to an example of the present invention will be described with reference to the drawings.

FIG. 1 shows an example of the method for manufacturing the HBT of the present invention.

As shown in FIG. 1, a (001) GaAs substrate l
On top of this, a highly doped GaAs layer 2 of the same type as the collector to facilitate the formation of an ohmic contact to the collector.
, an n-type GaAs layer 3 for forming a collector region,
P-type GaAs layer 4 for forming the base region, n-type AlxGa1-XAs for forming the emitter region
A layer 5 and a highly doped n-type GaAs layer 6 to facilitate the formation of an emitter ohmic contact are epitaxially formed in this order to form a multilayer structure material 7.

Next, as shown in FIG. 1 (bl), a protective layer 11 made of SiOx is provided, and a mask layer 12 made of AN is formed thereon by lift-off or etching at a portion corresponding to the emitter. By dry etching the protective layer 12 as a mask, a temporary emitter 13 consisting of the protective layer 11 and the mask layer 12 is formed as shown in FIG.

Next, as shown in FIG. 1 (1), a temporary emitter 13 is installed.
is used as a mask to expose the external base region 4b. Next, as shown in FIG. 1 (1) 1, the temporary emitter 13 is coated with a photoresist, and the temporary emitter 13 is located by dry etching as shown in FIG.
(As shown in the figure, the temporary emitter 13 is removed by etching, the emitter cap layer 6a is exposed, and the recess 15 is removed.
form. Then, as shown in FIG. 1 (hl), emitter electrode metal is formed by vapor deposition and lift-off.
As shown in FIG. 1(1), an HBT device structure is formed by photolithography and etching, a collector electrode 10 is formed, and then ohmic electrodes for the emitter and collector are formed by heat treatment. Next, using the emitter electrode as a mask, hydrogen ions are implanted into the layer 3 for forming the collector, as shown in FIG. A minute collector region 3a having substantially the same size is formed. Next, the base electrode 9 is connected to the base electrode 9 in FIG.
form like this.

In the example, 5tyx is used as the protective layer, but it is not limited to this.The point is that it does not react with the underlying semiconductor material by heat treatment after ion implantation, and is selectively removed with respect to the underlying semiconductor material. The Siox and SiNx shown in the examples can be used for various underlying semiconductor materials. When the base is GaAs as shown in the example, ANXGa, -XAs
.

Ge, SL, etc. can be used as the protective layer.

These protective layers can be used in a wide range of applications when the underlying material is a compound semiconductor material. When the underlying material is a semiconductor material such as Ge or Si, compound semiconductor materials can be used quite widely as the protective layer.

In the embodiment, AiL is used as the mask layer, but various other metals can be used. The mask layer serves as a mask for ion implantation, and also as a mask when forming a temporary emitter made of a protective layer.If the protective layer material is a material that is eroded by the etching solution of the underlying semiconductor material, it can be used as a mask for the underlying semiconductor material. Since it serves as a mask during material etching, it is necessary to select a material that is compatible with the underlying material and the protective layer material. For example, Au-based materials can also be applied to various materials.

In addition, the mask material may be not only metal but also any material that satisfies the above conditions.
It is not necessary after forming one temporary emitter.

In the example, S iox at the periphery of the temporary emitter
However, it is of course possible to leave a small amount of SiOx around 0 and use it as a surface protective layer in ion implantation and subsequent heat treatment, and then remove it afterwards.

In the embodiment, ion implantation is performed with the external base region exposed, but the invention is not limited to this. It is also possible to implant while a portion of the layer 5 for forming the emitter remains, and after the implantation to perform etching using the emitter electrode as a mask to expose the layer for forming the extrinsic base region.

In the examples, a method of implanting hydrogen ions is used, but in the case of hydrogen ions, it is not necessary to particularly restore the crystallinity of the external base region through which the hydrogen ions have passed. Any ion that can be heat treated after implantation to activate the extrinsic base layer without damaging the emitter and collector electrodes can be used.

In the embodiment, a normal type in which the emitter is provided on the upper side is described, but in FIG. 1, an n-type AlxGa1. , a multilayer structure is formed in which the XAs layer and the layer 5 are n-type GaAs for forming the collector region, and hereinafter, in the process of the example, by replacing the process related to the emitter and the collector, the collector is provided on the upper side. It can also be applied to an inverted HBT.

In the example, GaAs-All, Ca1
- Although the HBT using As-based material is shown,
Of course, other material systems are also possible. Further, as a material for forming the collector, a semiconductor material having a larger band gear than the base can also be used.

Effects of the Invention As described above, in the HBT manufacturing method of the present invention, HBT
There is a step of providing a temporary emitter (collector in the inverted type) on the emitter (collector in the inverted type) portion on the multilayer structure material to be formed, and etching using the emitter of the plate (collector in the inverted type) as a mask. After exposing the external base region and covering the surface with photoresist, dry etching is performed to locate the temporary emitter (collector in the case of the inverted type), and then the temporary emitter 7 is exposed.
A process of removing the emitter (collector in the inverted type) by etching and forming an emitter (collector in the inverted type) electrode on that part by vapor deposition and lift-off. Using the electrode as a mask, impurities are introduced into the layer for forming the collector (emitter in the inverted type) to remove carriers in the region outside the collector (emitter in the inverted type) area below the emitter (collector in the inverted type) electrode. Using at least the step of reducing the concentration, the formation of fine collector (emitter in the inverted type), emitter (collector in the inverted type), and emitter (collector in the inverted type) electrodes is performed using a single mask in the Selfa line. It is now possible to form.

As a result, since conventionally, the formation of a minute collector (emitter for inverted type), emitter (collector for inverted type), and emitter (collector for inverted type) electrodes was performed using three separate masks, the mask A process that was previously difficult to align and had a low yield can now be performed using a single mask, making the process much easier and significantly improving the yield. Furthermore, since the emitter (collector in the inverted type) electrode covers the entire upper surface of the emitter (collector in the inverted type), the contact resistance becomes smaller than in the past, and jt and frn can be increased.

FIG. 2 is a process diagram showing a conventional HBT manufacturing method.

1...GaAs substrate, 2...Highly doped n-type GaAs layer for facilitating the formation of a collector ohmink contact, 2a...Collector electrode extraction region, 3...N-type GaAs layer for forming a collector region, 3a...Collector region, 3b...Semi-insulating region around the collector,
4...p-type Ga for forming the base region
As layer, 4a...Base region, 4b...
・External base area for taking out the base electrode, 5...
...N-type AlXG for forming the emitter region
a1-XAs layer, 5a... emitter region, 6.
...Highly doped n-type GaAs layer 6a to facilitate formation of emitter ohmic contact...
...Emitter camp layer above the emitter, 7...
...Multilayer structure material formed by epitaxy, 8...
...Emitter electrode, 9...Base electrode, lO.
... Collector electrode, 11 ... SiO2 protective layer for forming a temporary emitter, 12 ...
...Metal mask layer for temporary emitter part, 13...
...Temporary emitter, 14...Photoresist,
15... A recess formed in the emitter portion in the photoresist 14, 16... A mask layer for forming a micro collector in the conventional method.

Claims (4)

[Claims] (1) To form a normal type heterojunction bipolar transistor in which a semiconductor material with a larger band gap than the base is used as the emitter and the emitter is provided on the upper side, an n-type semiconductor material layer for forming the collector and the base. In the manufacturing method of forming a multilayer structure material including an npn junction consisting of a p-type semiconductor material layer and a large bandgap n-type semiconductor material layer for forming an emitter, a protective layer is formed on the multilayer structure material. forming a mask material layer on the protective layer in a portion corresponding to the emitter, and etching the protective layer around the masked portion using the mask material layer as a mask,
forming a temporary emitter comprising at least the protective layer, and etching the multilayer structure material using the temporary emitter as a mask to expose an external base region or with a layer of material for forming the emitter; Then, the surface is covered with a photoresist, and then the photoresist is etched by dry etching to locate the temporary emitter formed above the emitter, and the photoresist left around the emitter is removed. forming an emitter electrode by evaporation and lift-off, and using the emitter electrode as a mask, impurities are introduced into the material layer for forming the collector to reduce carrier concentration in a region outside the collector region below the emitter. The process of
If a material layer for forming the emitter remains, etching the emitter material layer using the emitter electrode as a mask to expose the external base region. A method for manufacturing a junction bipolar transistor. (2) n-type A as the semiconductor material layer forming the emitter
l_xGa_1_-_xAs, p-type GaAs is used as the semiconductor material layer for forming the base, n-type GaAs or n-type Al_xGa_1_-_xAs is used as the material layer for forming the collector, and SiO_2 or SiN_x is used as the protective layer. A method for manufacturing a heterojunction bipolar transistor according to claim (1), characterized in that a metal is used as the mask layer. (3) To form an n-type semiconductor material layer for forming the collector and the base of an inverted heterojunction bipolar transistor using a semiconductor material with a larger band gap than the base as the emitter and with the collector provided on the upper side. In the manufacturing method of forming a multilayer structure material including an npn junction consisting of a p-type semiconductor material layer and a large bandgap n-type semiconductor material layer for forming an emitter, a protective layer is formed on the multilayer structure material. forming a mask material layer on the protective layer in a portion corresponding to the collector, and etching the protective layer around the masked portion using the mask material layer as a mask,
forming a temporary collector consisting of at least the protective layer, and etching the multilayer structure material using the temporary collector as a mask to expose an external base region or with a layer of material for forming the collector; Then, the surface is covered with a photoresist, and then the photoresist is etched by dry etching to locate the temporary collector formed on the upper part of the collector, and then the photoresist left around the collector is removed. a step of forming a collector electrode by vapor deposition and lift-off using the collector electrode; and using the collector electrode as a mask, impurities are introduced into the material layer for forming the emitter to reduce the carrier concentration in a region outside the emitter region below the collector. The process of
If a material layer for forming the collector remains, etching the collector material layer using the collector electrode as a mask to expose the external base region. A method for manufacturing a junction bipolar transistor. (4) n-type A as the semiconductor material layer forming the emitter
l_xGa_1_-_xAs, p-type GaAs is used as the semiconductor material layer for forming the base, n-type GaAs or n-type Al_xGa_1_-_xAs is used as the material layer for forming the collector, and SiO_2 or SiN_x is used as the protective layer. A method for manufacturing a heterojunction bipolar transistor according to claim 3, characterized in that a metal is used as the mask layer.