JPS6348863A - Manufacture of heterojunction bipolar transistor - Google Patents

Abstract

PURPOSE:To form a base electrode readily even in a minute external base region in a self-aligning method, by forming the base electrode at a part very close to the junction part of an emitter and a base, thereby reducing the resistance of the outer base to a remarkably small value. CONSTITUTION:With a temporary emitter 13 as a mask, wet etching is performed to a layer 4 for forming a base, and emitter region comprising an emitter 5-a and a cap layer 6-a is formed. Both sides of the region along the extending direction of a stripe are formed in an inverted mesa shape. The entire surface of the upper part of the emitter region is covered with an emitter electrode 8. The emitter electrode has a mesa shape, i.e., an undercut part, which is formed by etching at the lower part of the emitter electrode. Then, a base mesa and a collector mesa are formed by photolithography and etching, and a collector electrode is formed. Then a mask is applied on a part other than parts including both ends of the stripe and a baseelectrode forming part. Base electrode metal is evaporated and liftoff is performed. Thus a base electrode 9 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a petrojunction 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.

FIG. 6 shows the structure and manufacturing method of a conventional HBT.

1 is a substrate, 2 is a highly doped semiconductor material layer of the same type as the collector to facilitate the formation of an ohmic contact with 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, 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 the base electric machine, and 5 is 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 to facilitate the formation of an ohmic contact with the emitter; 6-a is an emitter camp layer above the emitter region; 7 is a multilayer structure material formed from 1 to 6 semiconductor material layers, 8 is an emitter electrode, 9 is a base electric machine, and 10 is a collector electrode. Multilayer structure material 7 epitaxially formed on substrate 1
(Fig. 6 (5)), by photolithography and etching, as shown in Fig. 6 (bl), 6-a
The structure has an emitter region consisting of and s-b, a base region 4-a and 4-b, a collector region 3-b, and a collector region 2-a.
As shown in C1, an emitter electrode 8, a base electrode 9, and a collector electrode 10 are formed.

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

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

Here, τB (emitter depletion layer travel time) = γE
(CBC 108B + CPB)' τB (Base running time) - WB2/πDB% τ. (Collector depletion layer running time) "W./2Vs, rco (Collector depletion layer charging time') - (RF36+Ro) (C3°+CPc), R
B is the base resistance, CBC is the base-collector capacitance, C
IEB is the base-emitter capacitance, cpB is the base layer stray capacitance, C6° is the collector layer stray capacitance, WB is the base layer thickness, DB is the base layer diffusion coefficient, Wo is the collector depletion layer thickness, and Vs is the collector layer stray capacitance. The strike velocity, RBB is the emitter contact resistance, and Ro is the collector resistance.

In HBT, leakage of holes from the base to the emitter (in the case of n p n type) is suppressed by using a semiconductor material with larger band gears than the base as the emitter. and the collector can be lightly doped. This makes it possible to reduce the base resistance RB, which is important for increasing the speed and frequency of the transistor, thereby increasing fm. Furthermore, in general in BT, CBB'C
Bo is a factor 08B (n, h
), CB c (n, h) and junction area AEB, Aac
It is expressed as the product of In HBT, the emitter and collector are lightly doped and the base is highly doped, so C(
n, h), CB C(n.

RB h) is τ8, τ since C58 and CBG are smaller in HBT than in normal BT, depending only on the emitter-collector doping. . becomes smaller, making it possible to increase ft. Furthermore, since CEB becomes small, it becomes possible to increase fm 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 speed, it is important to miniaturize the device structure in addition to this6.
By reducing the collector-collector junction area ABC, CB
By decreasing C and thereby increasing fm, by decreasing the resistance of the external base region (external base resistance), f
It is very important to increase m.

Problems to be Solved by the Invention However, with the structure and manufacturing method shown in FIG. It was extremely difficult to form the base electrode 9 thereon. Furthermore, in order to reduce the external base resistance, it is nearly impossible to form the base electrode several thousand people close to the emitter-base junction using normal mask alignment.

In view of the above problems, the present invention allows the base electrode 9 to be formed extremely close to the emitter-base junction, thereby significantly reducing the external base resistance and increasing fm.
The present invention aims to provide a new method for manufacturing HBT that can produce BT.

Means for Solving the Problems In order to solve the above problems, in the HBT of the present invention, H
Using the epitaxy-formed multilayer structure after BT formation, a striped protrusion consisting of a high-dorf cap layer provided on the top of the emitter or a layered structure of an emitter and an emitter cap layer is formed, and the striped protrusion is Both sides of the striped protrusion along the direction of extension are substantially vertical, or one side is substantially vertical and the other side is inverted mesa-like, or both sides are inverted mesa-like, and at least both sides of the striped projection in the direction of extension. After the step of forming the striped protrusions having the electrically scraped metal that protrudes like an umbrella, or after the step, the upper surface of the material is formed into an emitter electrode,
The base electrode and the heterojunction bipolar transistor forming material are covered with a protective film made of a material that can be selectively removed, and the upper surface of the emitter electrode metal and the upper surface of the base electrode extraction area are removed using an anisotropic dry etching method. Then, a step of forming a sidewall made of a protective film made of the material on the sidewall of the emitter electrode and the emitter sidewall portion protruding in the striped shape, a step of forming an external base region, and a step of forming a base electrode metal from above. The base electrode is formed into an emitter electrode using at least a step of vapor deposition and forming a base electrode on the emitter electrode metal cap or the peripheral area directly under the emitter electrode metal cap having the sidewalls.
Formed very close to the base joint.

Function: In the method for producing HBT of the present invention, HBT of minute size is produced.
However, the base electrode can be easily formed close to the emitter-base junction in a self-aligned manner. Therefore, the external base resistance becomes extremely small, which is extremely effective in reducing the base resistance RB. This has a remarkable effect on increasing fm.

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

Example 1 FIG. 1 shows an example of the method for manufacturing an HBT of the present invention. As shown in FIG. 1 (al), on a (001) GaAs substrate 1, a highly doped GaAs (
n"-GaAs) layer 2, an n-type GaAs (n-GaAs) layer 3 for forming a collector region, a P-type Ga, As (p-GaAs) layer 4 for forming a base region, and an emitter region. n-type A 1 x to form
G a 1-x A s (N A 1 x G a
1- x As) layer 5, highly doped n-type Ga to facilitate the formation of the emitter ohmic contact.
An As (n"-GaAs) layer 6 is epitaxially formed in this order to form a multilayer structure material 7, and then wet-etched to form a layer 6 that can be selectively removed with respect to the underlying n"-GaAs. A SiOx protective film 11 made of a material that is not substantially corroded by etching is formed, and a temporary emitter of metal AI is set on the film in a portion corresponding to the emitter region so that the extending direction of the stripe is in the <110> direction. Then, using the metal emitter of the plate as a mask, anisotropic dry etching is performed to form a temporary emitter 13 consisting of the SiOx protective film 11 and the metal 112, as shown in FIG. , As shown in Figure 1 (C1), using the emitter 13 of the strip as a mask, etching was performed until the base 4 was etched by W-type etching, so that both sides along the extending direction of the stripe became an inverted mesa shape. , an emitter region consisting of an emitter 5-a and a camp layer 6-a is formed. Then,
As shown in FIG. 1 (dl), the entire surface is coated with photoresist 14, the temporary emitter 13 is located by dry etching, the temporary emitter is removed by etching, and the first
As shown in the figure (el), the emitter electrode 8 covers the entire upper part of the emitter region, as shown in FIG.
Further, an umbrella-shaped emitter electrode having an undercut portion formed by etching is formed at the lower part of the emitter electrode.

Next, as shown in FIG. 1Fgl, a base mesa and a collector mesa are formed by photolithography and etching, and a collector electrode is formed. Next, the parts including both ends of the stripes and the part where the base electrode is formed are masked, and the base electrode metal is vapor deposited and lifted off.
A base electrode 9 is formed as shown in FIG. As a result, the base electrode 9 is placed on the periphery directly under the emitter electrode metal cap.
It is formed very close to the emitter-base junction.

Further, since the sidewalls along the extending direction of the stripes have an inverted mesa shape, the base electrode will not be short-circuited with the emitter when a highly linear evaporation beam is used.

Embodiment 2 FIG. 2 shows that after forming the structure shown in FIG.
-a, and prevents the vapor-deposited metal from wrapping around the side wall portion of the emitter by vapor deposition when forming the base electrode, thereby preventing short circuits. First, cover the entire surface with a thin 5iOxi film 1.
6 to 5I as shown in Fig. 2 (al), and then remove the SiOx on the upper part of the emitter and the part where the base electrode was removed by anisotropic dry etching,
A side wall 16-a made of Ox is formed. Next, the base electrode 9 is formed by the method shown in Example 1, and then,
The 5iOx16a on the sidewall is removed by etching, and the base electrode metal that wraps around and adheres to the emitter sidewall is removed to prevent a short circuit between the emitter and the base electrode. With this method, the base electrode can be formed without problems even in the case of a deposition beam with poor linearity.

Embodiment 3 FIG. 3 shows that in the multilayer structure material 7 shown in FIG.
A case where the setting is made so that the OQ>direction is shown is shown. In this case, the walls on both sides along the extending direction of the stripe and the walls at both ends of the stripe are wet-etched using the temporary emitter 13 as a mask, so that a substantially vertical stripe shape is formed as shown in FIG. A protrusion is formed.

Next, by converting the temporary emitter into an emitter electrode using the same method as in Example 1, the emitter electrode formed on the upper part of the striped emitter region protrudes into the peripheral part of the stripe by undercutting by wet etching. The umbrella-shaped emitter electrode is shown in Figure 3 ('b).
It is formed as follows. Using this, a base electrode 9 is formed as shown in FIG. 3(C) by the same method as in Example 1. However, in this case, since the emitter electrode umbrella is formed over the entire peripheral portion of the stripe, it is not necessarily necessary to cover both end portions of the stripe as in the case of the first embodiment.

Example 4 FIG. 5 shows that after forming the structure of FIG. 3Cb) shown in Example 3, the structure of FIG.
As shown in FIG. 3, the surface of the material having the structure of Al is covered with a 5iOxEi film 15 as shown in FIG.
form like this. Using this, a base electrode metal is formed by vapor deposition and lift-off, and then the side wall 15-a of the Siox thin film is removed by etching, and the metal attached to the emitter side wall is removed to prevent the base electrode from shorting the emitter. To prevent. Even in the case of Example 4, if a vapor deposition beam with good linearity is used, the base electrode will not be short-circuited with the emitter, but in the case of this example, it is extremely effective even when the linearity of the vapor deposition beam is poor. becomes.

Example 5 In Example 1, instead of forming a temporary emitter on the multilayer structure material 7, an emitter electrode 8 made of AuGe/Au was formed as shown in FIG. Etching is performed up to layer 4 to form a base as a mask, and both sides of the stripe along the direction of extension of the stripe form an inverted mesa shape, covering the entire upper surface of the stripe, and from the sides along the direction of extension of the stripe. An emitter electrode 8 protruding like an umbrella is formed as shown in FIG.

Although an example has been shown as a method of etching using the emitter electrode gold hawk 8 as a mask, this embodiment can also be applied to cases corresponding to embodiments 2 to 4.

In the method of using a temporary emitter as a mask shown in Examples 1 to 4, three masks are used as a mask in contact with the underlying semiconductor material.
Although iQx is used, Siox and SiNx are also available as materials that can be selectively removed from the underlying semiconductor material.
can be used as a general material. Also,
When the underlying semiconductor material is a compound semiconductor material, Ge or Si can be used as a temporary emitter, and when the underlying semiconductor material is Ge or 3i, a compound semiconductor material can be used as a temporary emitter. This method has the advantage of being able to be combined with processes that require heat treatment, such as ion implantation, by selecting SiOx, SiNx, or other materials that do not react with the corners of the base material during heat treatment as the temporary emitter.

In the method of using the emitter electrode as a mask shown in Embodiment 5, it is necessary to select a metal material that will not be corroded by the etching solution during wet etching of the underlying semiconductor material. In addition, by selecting a metal material that does not react with the underlying semiconductor material during heat treatment, it can be combined with processes such as ion implantation that require heat treatment.

In Examples 1 to 4, etching was performed up to the layer 4 forming the base using the temporary emitter 13 as a mask, but after etching the layer forming the emitter halfway and performing a process involving heat treatment such as ion implantation, The method of the embodiment can also be applied after forming the emitter electrode 8 and then exposing the external base layer by etching.

Also, using the temporary emitter 13 as a mask, etching is performed to the layer that will form the emitter, forming striped protrusions mainly consisting of a highly doped cap layer, and then ion implantation is performed to form the external base region of the layer that will form the emitter. It is also possible to change the portion corresponding to the external base region by ion implantation, form the emitter electrode, and apply the method of the embodiment.

In Examples 1 to 4, the base electrode is formed after changing the temporary emitter to an emitter electrode, but with the temporary emitter attached, the temporary emitter's umbrella or the temporary emitter and striped emitter are formed. The base electrode can also be formed by using a temporary emitter whose sidewalls are coated with a Siox thin film.

In Examples 2 and 4, a SiOx thin film is used as the material for forming the striped protrusions and the sidewalls of the emitter electrode, but SiNx or other materials that can be selectively removed with respect to the emitter electrode metal, base electrode metal, and HBT forming material are used. materials can be used.

In Examples 1 to 5, GaAs-An! is used as the HBT forming material. Although XGa and -XAs-based zinc blend materials are used, the examples can also be applied to zinc blend materials other than these. Furthermore, the method of this embodiment can also be applied to the manufacture of an HBT using a multilayer structure material consisting of a zinc blend material and a diamond material such as Ge or Si.

In Examples 1 to 5, epitaxy was formed (100)
Although an emitter region protruding in a stripe shape is formed on the surface, it can also be used on surfaces formed by epitaxy other than this. The striped projections of the emitter can be provided in such a way that the elongation direction is uniform in the <110> direction within the plane of the multilayer structure material. In this case, one [1
111 plane is parallel to the stripe and perpendicular to the plane, one rll
Since the 11 planes are parallel to the stripes and located in an inverted mesa shape, it is possible to form a striped emitter in which one side on both sides along the extension direction is perpendicular and the other side is in an inverted mesa shape. Therefore, an umbrella-shaped emitter electrode can be formed similarly to the cases shown in Examples 1 to 4. As described above, in the manufacturing method of the present invention, (100
) Using grown multilayered materials to form emitter stripes with substantially vertical or inverted mesas on both sides along the elongation direction; It can also be applied to the case of forming an emitter region of a stripe-like protrusion in which both sides in the extending direction of the stripe are vertical and an inverted mesa, or one side is perpendicular and the other is an inverted mesa to form an umbrella-like emitter electrode. .

Effects of the Invention As described above, in the present invention, a semiconductor material having a larger band gap than the base is used for at least the emitter of the emitter and the collector, and the HBT is provided with the emitter above.
In the process of forming the HBT from a multilayer structure material formed by epitaxy, which is the source of HBT formation, a highly doped semiconductor material layer provided on the top of the emitter or a striped protrusion made of a layered structure of the emitter and the highly doped layer is formed. Both sides of the striped protrusion along the extending direction are substantially vertical, one side is substantially vertical and the other side is in an inverted mesa shape, or both sides are in an inverted mesa shape, and the stripe covering the entire upper part of the protrusion, and
A step of forming the stripe-like protrusion having an emitter electrode metal protruding like a umbrella on at least both sides along the extension direction of the stripe-like protrusion, or after the step, forming the upper surface of the material as an emitter electrode and a base. The upper surface of the emitter electrode metal and the upper surface of the base electrode extraction area are covered with a protective film made of a material that can be selectively removed with respect to the electrode and IBT forming material, and an anisotropic dry etching method is used to remove the upper surface of the emitter electrode metal and the upper surface of the base electrode extraction area. forming a protective film made of the material on the sidewalls of the emitter electrode metal and the sidewalls of the emitter portion protruding from the upper surface; forming an external base region; depositing the base electrode metal from above; A manufacturing method is used, which comprises at least the step of forming a base electrode on the emitter electrode metal umbrella or on the periphery immediately below the emitter electrode metal and the sidewall umbrella.

As a result, the base electrode can be easily formed in a self-aligned manner even in a minute external base region, which has extremely large process advantages.Also, the base electrode can be formed extremely close to the emitter-base junction. ,
The external base resistance of the HBT can be significantly reduced, thereby making it possible to manufacture an HBT with a large fm.

[Brief explanation of drawings]

1 to 5 are process diagrams showing the HBT manufacturing method of the present invention, and FIG. 6 is a process diagram showing the conventional HBT manufacturing method. 1...71.2... Highly doped layer to facilitate formation of collector ohmic contact,
2-a... Collector electrode extraction area, 3...
・・・Semiconductor material layer for forming a collector region,
3-a... Collector region, 4... Semiconductor material layer for forming base region, 4-a...
... Base region, 4-b ... External base region for taking out the base electrode, 5 ... Semiconductor material layer for forming the emitter region, 5-a ...・
Emitter region, 6. Old... Highly doped layer to facilitate formation of emitter ohmic contact, 5-a...
...Emitter cap layer above the emitter, 7...
...Multilayer structure material formed by epitaxy, 8...
・・Emitter electrode, 9・・・・Sumi electrode, 10・
... Collector electrode, 11. Old... Protective film layer for forming temporary emitter, 12... Metal layer for temporary emitter part, 13... Temporary Emitter, 1
4... Photoresist, 15... Concavity formed in the emitter portion of the photoresist 14, 1
6... Protection for forming emitter electrode and sidewall of emitter region, 16-a... Protective film 1
The emitter electrode and the sidewall of the emitter region formed from 6. Name of agent: Patent attorney Toshio Nakao and one other person Figure 1! -11 board 16cL-11 flight J2 wall No. 2 Figure 3 Figure 4 Figure 8-m-Emi So9 skin I pole ball Tsuta happy 5 Figure 6

Claims (7)

[Claims] (1) A multilayer structure material in which a heterojunction bipolar transistor in which the emitter and collector of a bipolar transistor are formed using a semiconductor material with a larger bandgap than the base at least as the emitter, and the emitter is provided above by epitaxy on a substrate. A highly doped semiconductor material layer provided on the top of the emitter or a striped protrusion formed of a layered structure of the emitter and the highly doped layer, the striped protrusion extending along the extending direction of the striped protrusion. Both sides of the side surface are substantially vertical, one side is substantially vertical and the other side is in an inverted mesa shape, or both sides are in an inverted mesa shape, and the striped projection covers the entire upper part of the striped protrusion, and After the step of forming the striped protrusion having the emitter electrode metal protruding like a umbrella on both sides of the protrusion at least along the extension direction, or after the step, the upper surface of the material is formed into an emitter electrode, a base electrode and a heterojunction bipolar. The emitter is covered with a protective film made of a material that can be selectively removed with respect to the transistor forming material, and the upper surface of the emitter electrode metal and the upper surface of the base electrode extraction area are removed using an anisotropic dry etching method. forming a protective film made of the material on the sidewalls of the electrode metal and the sidewalls of the emitter portion protruding from the upper surface; forming an external base region; depositing the base electrode metal from above; 1. A method for manufacturing a heterojunction bipolar transistor, comprising at least the step of forming a base electrode in a peripheral area immediately below the umbrella or emitter electrode metal and the side wall. (2) The emitter electrode metal is formed by lift-off to the size of the emitter, or the emitter electrode metal is deposited on the entire surface and the surrounding area of the emitter is removed by etching, and the emitter electrode is etched using the emitter electrode as a mask to form a striped shape. A method for manufacturing a heterojunction bipolar transistor according to claim 1, characterized in that a protruding region is formed. (3) As the multilayer structure material, use a zinc blend type material epitaxially grown in the <001> direction or a multilayer structure material consisting of a zinc blend type material and a diamond type material, and align the extension direction of the striped protrusions with the surface of the multilayer structure material. The heterojunction bipolar according to claim (2), characterized in that a silicon oxide or silicon nitride thin film is used as a protective film provided in the <100> direction or <110> direction and forming the side walls. Method of manufacturing transistors. (4) selectively removing the material for forming the heterojunction bipolar transistor in a portion that will become an emitter region;
and providing a temporary emitter made of a material that is not substantially corroded by the etching solution of the underlying material, etching the temporary emitter as a mask, and then covering the entire surface with photoresist and exposing the upper part of the temporary emitter by dry etching; The method for manufacturing a heterojunction bipolar transistor according to claim 1, wherein the temporary emitter is removed, and after the removal, the emitter electrode metal is formed by lift-off. (5) As a multilayer structure material, use a zinc blend material epitaxially grown in the <001> direction or a multilayer structure material consisting of a zinc blend material and a diamond material, and align the extension direction of the striped protrusions within the plane of the multilayer structure material. Claim (4) characterized in that silicon oxide or silicon nitride is used as a protective film provided in the <100> direction or <110> direction and forming the sidewall.
) A method for manufacturing a heterojunction bipolar transistor according to item 1. (6) As the multilayer structure material, use a zinc blend type material epitaxially grown in the <001> direction or a multilayer structure material consisting of a zinc blend type material and a diamond type material, and set the extension direction of the striped projections to the surface of the multilayer structure material. The method for manufacturing a heterojunction bipolar transistor according to claim (1), wherein the heterojunction bipolar transistor is provided in the <110> direction or the <100> direction. (7) A method for manufacturing a heterojunction bipolar transistor according to claim (1), characterized in that a silicon oxide or silicon nitride thin film is used as the protective film forming the sidewall.