JPH0648687B2 - 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 collector for facilitating the formation of an ohmic contact of the collector, 2-a is a collector electrode extraction region, and 3 is a semiconductor material layer for forming the collector region. , 3-a is a collector region, 3-b is a semi-insulating region around the collector, 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 an emitter region, 5-a is An emitter region, 6 is a highly-doped semiconductor material layer of the same type as the emitter for facilitating the formation of an ohmic contact of the emitter, 6-a is a cap layer above the emitter region, and 7 is an epitaxy from which HBT is formed. -Formed multilayer structure material, 8 is an emitter electrode, 9
Is a base electrode, 10 is a collector electrode, and 16 is a mask layer for introducing impurities into a layer for forming a collector to form a minute collector.

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

Here, τ _B (emitter depletion layer strike time) = γ _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, it is possible to increase the f _m together that C _EB is smaller R _B mentioned above becomes smaller.

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 shown in the conventional example, the base-collector junction area A _BC is reduced by introducing impurities into a layer for forming a collector to form a minute collector, thereby reducing C _BC. Therefore, it is very important to increase f _m .

Problem 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 the collector to form a fine collector, thereby reducing C _BC . However, except for this mask, it is necessary to form the emitter and the emitter electrode by using two other minute masks on the minute emitter part, so the process is extremely difficult and it is difficult to align the mask. Therefore, there is a problem that the yield is deteriorated.

In view of the above problems, the present invention uses one mask,
An HB that is extremely effective in a process, in which impurities can be introduced into a layer forming a collector to form a fine collector and an emitter 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 the layer in a portion corresponding to the emitter, and the protective layer in the peripheral portion of the masked portion is removed or thinned by using the mask material layer as a mask to form the protective layer. Forming a temporary emitter including at least, and using the temporary emitter as a mask, introducing impurities into a material layer for forming a collector to reduce a carrier concentration in a region outside the collector region below the temporary emitter. And a step of forming a base electrode take-out region using the temporary emitter as a mask, followed by coating the entire surface with photoresist and dry etching. After the photoresist is etched to locate the temporary emitter formed on the emitter, the temporary emitter is removed by etching, and the photoresist remaining on the periphery of the emitter is used to form the emitter. Using at least the process of forming electrodes by vapor deposition and lift-off,
Fine collector and emitter 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 collector and emitter electrodes can be formed by self-alignment using a single mask. Therefore, the process in which the fine collector and the emitter and the emitter electrode are conventionally formed by using different masks is remarkably facilitated. Further, according to the present invention, the emitter electrode covers the entire upper surface of the emitter, so that the contact area between the electrode and the emitter remarkably increases even in the case of an emitter having the same size as the conventional one, and the contact resistance of the electrode becomes smaller than that of the conventional one. Therefore, f _t is increased, and larger f _t and a small C due to the formation of very small collector
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 collector for facilitating the formation of the ohmic contact of the collector is formed on the (001) GaAs substrate 1.
GaAs) layer 2, n-type GaAs (n-GaAs) layer 3 for forming a collector region, P-type GaAs (p-GaAs) layer 4 for forming a base region, and emitter region n-type _{Al x Ga 1-x As (} a
1 _x Ga _1-x As) layer 5, highly doped n-type Ga for facilitating the formation of ohmic contact of the emitter.
An As (n ⁺ -GaAs) layer 6 is epitaxially formed in this order to form a multilayer structure material 7. Then, Fig. 1
As shown in (b), a protective layer made of SiOx is provided, and a mask layer 12 made of Al is formed on the portion corresponding to the emitter by lift-off or etching.
Then, the protective layer 12 is dry-etched by using the mask layer 12 as a mask to form a temporary emitter 13 composed of the protective layer 11 and the mask layer 12 as shown in FIG. 1 (c). Then, using the temporary emitter as a mask, oxygen ions are ion-implanted into the layer 3 for forming the collector as shown in FIG. After activating, a minute collector 3-a having substantially the same size as the temporary emitter is formed, and then heat treatment is performed to recover the crystallinity of the external base region 4-b damaged by the ion implantation. Next, as shown in FIG. 1 (e), the external base region 4-b is exposed by etching using the temporary emitter 13 as a mask. Then, as shown in FIG. 1 (f), a photoresist is coated, and as shown in FIG. 1 (g), the temporary provision of the emitter 13 is performed by dry etching. Then, as shown in FIG. 1 (h), the temporary emitter 13 is removed by etching, and the cap layer 6-a of the emitter is removed.
Is exposed to form a recess 15. Then, as shown in FIG. 1 (i), the emitter 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 the emitter electrode 8, the base electrode 9, and the collector 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 functions as a mask for ion implantation, as a mask for forming a temporary emitter made of a protective layer, and when the protective layer material is a material that is attacked by the 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 emitter 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 emitter remaining, or with the layer 4 for forming the base exposed. When ion implantation is performed with part or all of the layer 5 for forming the emitter remaining, the layer 5 for forming the emitter is removed by etching after the implantation, or
The layer 5 for forming the emitter may be replaced with a region having carriers of the same type as the base by introducing impurities into the peripheral portion of the mask using the temporary emitter as a mask.

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-layer structure material that is the basis of the formation, a mask material layer is formed on the protective layer at a portion corresponding to the emitter, and the mask material layer is used as a mask. Removing or thinning the protective layer in the peripheral portion of the formed portion to form a temporary emitter including at least the protective layer; and using the temporary emitter as a mask to form an impurity collector. Introducing into the material layer to form the temporary emitter to reduce the carrier concentration outside the collector region below the temporary emitter; and taking out the base electrode using the temporary emitter 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 emitter. After cueing the temporary emitter formed in step 1, the temporary emitter is removed by etching, and the emitter electrode is formed by vapor deposition and lift-off using the photoresist left on the periphery of the emitter. At least the fine collector and emitter electrodes can be formed in a self-aligned manner with a single mask.

As a result, since the formation of the minute collector and the formation of the emitter and the emitter electrode have conventionally been performed using three separate masks, it is difficult to align the masks, 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 collector ohmic contact, 2-a ... Collector electrode extraction region, 3 ... Semiconductor material layer for forming collector region, 3- a: collector area, 3-b ...
... semi-insulating region around collector, 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 emitter region, 5-a ... Emitter region, 6 ... Facilitating formation of emitter ohmic contact Highly doped layer for
6-a ... Emitter cap layer on the upper part of the emitter, 7 ...
Multilayer structure material formed by epitaxy, 8 ... Emitter electrode, 9 ... Base electrode, 10 ... Collector electrode, 11 ...
... a protective layer for forming a temporary emitter, 12 ... a mask layer for a portion of the temporary emitter, 13 ... a temporary emitter, 1
4 ... Photoresist, 15 ... Recesses formed in the photoresist 14 in the emitter portion, 16 ... Mask layer for forming a minute collector 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 material layer for forming a collector of a heterojunction bipolar transistor in which a semiconductor material having a band gap larger than that of a base is used as at least one of an emitter and a collector, and the emitter is provided on the upper side. A manufacturing method comprising at least a semiconductor material layer for forming the base and a semiconductor material layer having a large band gap for forming the emitter, wherein the multilayer structure material is epitaxially formed in this order. A protective layer is formed thereon, a mask material layer is formed on the protective layer in a portion corresponding to the emitter, and the protective layer around the masked portion is etched using the mask material layer as a mask. And forming a temporary emitter including at least the protective layer,
Using the temporary emitter as a mask, the multilayer structure material is etched to expose a material layer for forming a base, or with the temporary emitter as a mask, the temporary emitter is used as a mask. Introducing impurities into the material layer for forming the collector to reduce the carrier concentration in the region outside the collector region below the temporary emitter; and leaving the material layer for forming the emitter. Etches the emitter material layer with the temporary emitter as a mask to expose the base material layer, or introduces an impurity into the emitter material layer with the temporary emitter as a mask to obtain the same type as the base material layer. The process of changing to a region having carriers, then coating the entire surface with a photoresist, and performing dry etching to obtain the photoresist Of the temporary emitter formed above the emitter by etching the strike, the temporary emitter is removed by etching, and the emitter electrode is vapor-deposited using the photoresist left on the peripheral portion of the emitter. And a step of forming by lift-off at least, a method of manufacturing a heterojunction bipolar transistor.