JPH0648688B2 - Method of manufacturing heterojunction bipolar transistor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 / ultra high frequency transistor.

2. Description of the Related Art In recent years, HBT using a semiconductor material having a bandgap larger than that of a base as an emitter of a bipolar transistor (hereinafter referred to as BT) has been extensively studied as one of the promising candidates for an ultra-high speed / ultra high frequency transistor. I am sorry.

FIG. 2 shows a conventional HBT manufacturing method.

1 is a substrate, 2 is a highly-doped semiconductor material layer of the same type as the emitter for facilitating formation of an ohmic contact of the emitter, 2-a is an emitter electrode extraction region, and 3 is a semiconductor material layer for forming the emitter region , 3-a is an emitter region, 3-b is a semi-insulating region around the emitter, 4
Is a semiconductor material layer for forming a base region, 4-a is a base region, 4-b is an external base region for taking out a base electrode, 5 is a semiconductor material layer for forming a collector region, and 5-a is A collector region, 6 is a highly doped semiconductor material layer of the same type as the collector for facilitating the formation of an ohmic contact of the collector, 6-a is a cap layer above the collector region, and 7 is an epitaxy from which HBT is formed. -Formed multilayer structure material, 8 is collector electrode, 9
Is a base electrode, 10 is an emitter electrode, and 16 is a mask layer for introducing impurities into a layer for forming an emitter to form a minute emitter.

Using the multilayer structure material 7 (FIG. 2 (a)) epitaxially formed on the substrate 1, impurities are introduced into the layer forming the emitter as shown in FIG. 2 (b) to form a minute emitter. Then, by photolithography and etching, the second
As shown in FIG. 2C, a structure having a collector region composed of 6-a and 5-a, a base region composed of 4-a and 4-b, an emitter region 3-b, and an emitter electrode extraction region 2-a. To do. Then, as shown in FIG. 2D, a collector electrode 8, a base electrode 9, and an emitter electrode 10 are formed.

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

The f _t and f _m, which are indexes of the high-speed operation of the HBT, are expressed as follows.

Where τ _B (emitter depletion layer strike time) = y _E (C
_BC + C _EB + C _PB ), τ _B (base running time) = W
_B ² / πD _B , τ _C (collector depletion layer strike time) = W _C
² / 2Vs, τ _CC (collector depletion layer charging time) = (R
_EE + R _C ) (C _BC + C _PC ), R _B is the base resistance,
C _BC is the base-collector _{capacitance, C EB} is the base-emitter _{capacitance, C PB} base layer stray _{capacitance, C PC} is the collector layer stray capacitance, _{W B} is the base layer thickness, _{D B} is the base layer diffusion coefficient , W _C is the thickness of the collector depletion layer, Vs is the collector strike speed, R _EE is the emitter contact resistance, R
_C is a collector resistance.

The HBT suppresses the leakage of holes from the base to the emitter (in the case of npn type) by using a semiconductor material having a bandgap larger than that of the base as an emitter. The collector can be lightly doped. This makes it possible to reduce the base resistance R _B , which is important for increasing the speed and frequency of the transistor, and thus f _m becomes large. Furthermore, in general, in BT, C _EB , C _BC
Is the factor C _EB (n, h) due to the doping of the junction capacitance,
It is represented by the product of C _BC (n, h) and the junction areas A _EB and A _BC . In HBT, since the emitter and collector are lightly doped and the base is heavily doped, C _EB (n,
h) and C _BC (n, h) depend only on the emitter-collector doping, and C _EB and C _BC are as follows.

Therefore, in HBT, C _EB and C _BC are higher than those in normal BT _.
Becomes smaller, τ _E and τ _CC become smaller, and f _t can be increased. Further, since C _EB is small, it is possible to increase f _m together with the fact that R _B is small.

Thus, HBTs are inherently advantageous for speed-up due to their heterostructure-based reasons. However, in order to further increase the speed, in addition to this, it is important to miniaturize the device structure. For example, as in the conventional example, a structure in which the collector is on the upper side is formed, a minute collector is formed, and the junction area A _BC between the base and the collector is reduced to reduce C _{BC.
In order} to increase _m , further, impurities are introduced into the layer forming the emitter to form a minute emitter to reduce the base-emitter junction area A _EB to reduce C _EB ,
This makes it very important to increase f _t , and thus f _m .

Problems to be Solved by the Invention However, in the manufacturing method as shown in FIG. 2, a fine mask is used to introduce impurities into a layer forming a collector to form a fine emitter to reduce C _BC . However, except for this mask, it is necessary to form the collector and the collector electrode by using another two fine masks on the minute collector part, so that the process is extremely difficult and the mask alignment is difficult. Therefore, there is a problem that the yield is deteriorated.

In view of the above problems, the present invention uses one mask,
An extremely effective HB in which a fine emitter can be formed by introducing impurities into a layer forming an emitter and a collector electrode can be formed by self-alignment.
It is intended to provide a new manufacturing method of T.

Means for Solving the Problems In order to solve the above problems, in the method for manufacturing an HBT according to the present invention, a protective layer is formed on an epitaxy-formed multilayer structure material which is a source of HBT formation, and the protection is performed. A mask material layer is formed on a portion of the layer corresponding to the collector, and the protective layer around the masked portion is removed or thinned by using the mask material layer as a mask to form the protective layer. Forming a temporary collector that includes at least, and using the temporary collector as a mask, introducing impurities into the material layer for forming the emitter to reduce the carrier concentration in a region outside the emitter region below the temporary collector. And a step of forming a base electrode take-out region using the temporary collector as a mask. Then, the entire surface is coated with photoresist and dry etching is performed. After the photoresist is etched to locate the temporary collector formed on the collector, the temporary collector is removed by etching, and the photoresist remaining on the periphery of the collector is used to collect the collector. By using at least the step of forming electrodes by vapor deposition and lift-off, fine emitter and collector electrodes can be formed in a self-aligned manner with a single mask.

Action In the method for producing HBT of the present invention, HBT having a fine size is used.
However, the fine emitter and collector electrodes can be formed by self-alignment using a single mask. For this reason, the process which has conventionally been performed using separate masks for forming a fine emitter and forming a collector and a collector electrode becomes remarkably easy. Further, in the present invention, since the collector electrode covers the entire surface of the upper part of the collector, the contact area between the electrodes is significantly increased even in the collector having the same size as the conventional one, and the contact resistance of the electrode becomes smaller than that in the conventional one. Therefore, f _t is increased, and larger f _t and a small C due to formation of minute emitters
It is possible to significantly increase the _{f m} and a _BC.

Example A method for manufacturing a heterojunction bipolar transistor (HBT) according to an example of the present invention will be described below with reference to the drawings.

FIG. 1 is an example of a method for manufacturing the HBT of the present invention. As shown in FIG. 1 (a), a highly doped GaAs (n ⁺ −) of the same type as the emitter for facilitating the formation of the ohmic contact of the emitter is formed on the (001) GaAs substrate 1.
GaAs) layer 2, the n-type to form the emitter region _{Al x Ga 1-x As (} N-Al x Ga 1-x As) layer 3, the P-type for forming the base region GaAs (p-
GaAs) layer 4, n-type GaAs (n-GaAs) layer 5 for forming a collector region, and highly-doped n-type GaAs (n ⁺ -GaAs) layer for facilitating the formation of a collector ohmic contact. 6 is epitaxially formed in this order to form a multilayer structure material 7. Then, the first
As shown in FIG. (B), a protective layer made of SiOx is provided,
A mask layer 12 made of Al is formed on the portion corresponding to the collector by lift-off or etching. Then, the protective layer 12 is dry-etched using the mask layer 12 as a mask, and a temporary collector 13 composed of the protective layer 11 and the mask layer 12 is formed as shown in FIG. 1 (c). Then, using the temporary collector as a mask, oxygen ions are ion-implanted into the layer 3 for forming the emitter as shown in FIG. 1 (d), and the outside of the temporary collector 13 outside the region 3-b is semi-insulated. The micro emitters 3a are formed to be substantially the same size as the temporary collector, and then heat treatment is performed to recover the crystallinity of the external base region 4-b damaged by the ion implantation. Then, as shown in FIG. 1 (e), the external base region 4-b is exposed by etching using the temporary collector 13 as a mask. Then, as shown in FIG. 1 (f), a photoresist is coated, and as shown in FIG. 1 (g), the temporary collector 13 is tentatively found by dry etching. Then, as shown in FIG. 1 (h), the temporary collector 13 is removed by etching, and the cap layer 6-a of the collector is removed.
Is exposed to form a recess 15. Then, as shown in FIG. 1 (i), a collector electrode metal is formed by vapor deposition and lift-off. Then, as shown in FIG. 1 (j), an HBT device structure is formed by photolithography and etching, and a collector electrode 8, a base electrode 9, and an emitter electrode 10 are formed.
To form.

In the embodiment, SiOx is used as the protective layer, but the protective layer is not limited to this. In short, any material that does not react with the underlying semiconductor material by the heat treatment after ion implantation and can be selectively removed with respect to the underlying semiconductor material may be used. The SiOx and SiNx shown in the examples can be used for various semiconductor materials of the base. In the case where the underlying layer is GaAs as shown in the examples, Al _x Ga _1-x A
s, Ge, Si, etc. can be used as the protective layer. These protective layers can be used quite widely when the base is a compound semiconductor material. The base is Ge or Si
In the case of a semiconductor material such as, a compound semiconductor material can be widely used as a protective layer.

Although Al is used as the mask layer in the examples, various metals other than this can be used. The mask layer serves as a mask for ion implantation, as a mask for forming a temporary collector made of a protective layer, and when the protective layer material is a material that is attacked by an etching solution of the underlying semiconductor material, Since it plays a role as a mask in etching the material, it is necessary to select a material suitable for the base material and the protective layer material. For example, Au
The system material can also be applied to various materials. Further, the mask material is not limited to metal, and any material satisfying the above conditions may be used.

In the embodiment, all SiOx in the peripheral portion of the temporary collector is removed, but it is not always necessary. It is of course possible to leave a small amount of SiOx in the peripheral portion, use it as a surface protective layer in ion implantation and subsequent heat treatment, and then remove it.

In the embodiment, the ion implantation is performed in the state of the multilayer structure material 7, but it is not limited to this. Ion implantation can also be performed with part or all of the layer 5 for forming the collector remaining, or with the layer 4 for forming the base exposed. When the ion implantation is performed with part or all of the layer 5 for forming the collector remaining, the layer 5 for forming the collector is removed by etching after the implantation, or
In the layer 5 for forming the collector, impurities may be introduced into the peripheral portion of the mask using the temporary collector as a mask to replace the region with carriers of the same type as the base.

In the embodiment, the ion implantation method is used as the impurity introduction method, but the diffusion method can also be used.

EFFECTS OF THE INVENTION As described above, according to the method for producing an HBT of the present invention, the HBT
A protective layer is formed on the epitaxy-formed multi-layered structure material, which is the source of the formation, a mask material layer is formed on the protective layer at a portion corresponding to the collector, and the mask material layer is used as a mask. Removing or thinning the protective layer in the peripheral portion of the exposed portion to form a temporary collector including at least the protective layer; and using the temporary collector as a mask to form an emitter of impurities. Introducing into the material layer to form the temporary collector to reduce the carrier concentration outside the emitter region below the temporary collector, and with the temporary collector as a mask The step of forming a region, and then coating the entire surface with a photoresist and etching the photoresist by dry etching to form an area above the collector. After the cueing of the provisional collector formed in step 1) is performed, the provisional collector is removed by etching, and the collector electrode is formed by vapor deposition and lift-off using the photoresist left in the peripheral portion of the collector. At least the fine emitter and collector electrodes can be formed in a self-aligned manner using a single mask.

As a result, conventionally, the formation of the minute emitter and the formation of the collector and the collector electrode have been performed using three separate masks, so that mask alignment is difficult and the process with poor yield can be performed with one mask. Therefore, the process is remarkably facilitated and the yield is remarkably improved. As a result, both the emitter and collector have a small HB
T can be formed, which is remarkably effective in increasing f _t and f _m of HBT.

[Brief description of drawings]

FIG. 1 is a process drawing showing the method for producing an HBT of the present invention, FIG.
The drawings are process diagrams showing a conventional method of manufacturing an HBT. 1 ... Substrate, 2 ... Highly doped layer for facilitating formation of emitter ohmic contact, 2-a ... Emitter electrode extraction region, 3 ... Semiconductor material layer for forming emitter region, 3- a: emitter region, 3-b ...
... Semi-insulating region around emitter, 4 ... Semiconductor material layer for forming base region, 4-a ... Base region,
4-b ... external base region for taking out base electrode, 5 ... semiconductor material layer for forming collector region, 5-a ... collector region, 6 ... facilitating formation of collector ohmic contact Highly doped layer for
6-a ... collector cap layer on top of collector, 7 ...
Multilayer structure material formed by epitaxy, 8 ... Collector electrode, 9 ... Base electrode, 10 ... Emitter electrode, 11 ...
... Protective layer for forming a temporary collector, 12 ... Mask layer in the part of the temporary collector, 13 ... Temporary collector, 1
4 ... Photoresist, 15 ... Recesses formed in the photoresist 14 in the collector portion, 16 ... Mask layer for forming minute emitters in the conventional method.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-59-210669 (JP, A) Extended Abstracts of the 18th (1986 Integrated) Conference on SOLID STATE DE VICES AND MATERIALS P. 769 ~ 770 1986-8-20

Claims (1)

[Claims] 1. A semiconductor having a large bandgap for forming an emitter of a heterojunction bipolar transistor in which a semiconductor material having a bandgap larger than that of a base is used as at least one of an emitter and a collector, and the collector is provided on the upper side. In the manufacturing method, which comprises at least a material layer, a semiconductor material layer for forming the base, and a semiconductor material layer for forming the collector, and forming from a multilayer structure material epitaxially formed in this order, A protective layer is formed, and a mask material layer is formed on the protective layer at a portion corresponding to the collector.
And a step of etching the protective layer around the masked portion using the mask material layer as a mask to form a temporary collector including the protective layer; and the multilayer structure material using the temporary collector as a mask. To expose the material layer for forming the base, or with the material layer for forming the collector attached, impurities are introduced into the layer for forming the emitter using the temporary collector as a mask. Then, the step of reducing the carrier concentration in the region outside the emitter region below the temporary collector, and when the material layer for forming the collector is left, the collector material layer is used as a mask for the temporary collector. Before the base material layer is exposed by etching or impurities are introduced into the collector material layer using the temporary collector as a mask. A step of changing to a region having a carrier of the same type as the base material layer, then coating the entire surface with a photoresist, and etching the photoresist by dry etching to locate a temporary collector formed on the collector. After that, the heterojunction bipolar transistor is characterized by at least the steps of removing the temporary collector by etching and forming a collector electrode by vapor deposition and lift-off using the photoresist left in the peripheral portion of the collector. Manufacturing method.