JPH02235343A - Hetero junction bipolar transistor and its manufacture - Google Patents

Abstract

PURPOSE:To reduce base resistance and capacitance by providing a mesa type emitter and arranging a surface protecting layer epitaxially formed in the vicinity of an exposed emitter-base junction. CONSTITUTION:On a multilayer structure material, an emitter mask 8 composed of SiOx is formed; by etching wherein said mask 8 used as a mask, a base layer 4 is exposed, and an emitter mesa 7 is formed. This is used as a mask, and undoped GaAs (u-GaAs) 14 is formed from the oblique direction 15 by MBE. By anisotropic dry etching, wherein CHF3 gas is used, from the upper direction 16, the u-GaAs formed in an outside base region is eliminated so as to leave the surface protecting film 14 of u-GaAs formed just under the mask 8. By self-alignment method, the mask 8 is converted to an emitter electrode 11, and further a base electrode 12 is formed to be adjacent to a mesa 7. By etching wherein the electrode 11 is used as a mask, the outside u-GaAs is eliminated while the u-GaAs just under the electrode 11 is left, and a structure in which the electrode 12 is formed to be adjacent to the mesa 7 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a heterojunction bipolar transistor (HBT), which is promising as an ultra-high speed and ultra-high frequency device, and a method for manufacturing the same. Conventional technology In order to improve the high-speed and high-frequency characteristics of HBT, current gain cutoff frequency f, maximum oscillation frequency f. It is important to increase the [． is expressed concomitantly as . Here, R is a base resistance, and Cbc is a base-collector capacitance. In order to increase fm (as seen from 132), one of the issues is to decrease Rh. In a structure where base electrodes are provided on both sides of the emitter mesa, Rb is 12 Ls 2
It is expressed as Le. Here, R3 is the sheet resistance of the base, L6 is the length of the emitter, 26 is the width of the emitter, and l.
, is the distance between the emitter mesa and the base electrode, and ρ. is the contact resistivity of the base electrode. In HBT, the base can be highly doped, so R is small, and in high speed/high frequency devices, l. In order to make it small enough,
The first term in equation (2) is sufficiently small (I!), but in the method using normal photolithography, I! ．． Since ah cannot be made small, the second term becomes thick. To solve this? Seed self-alignment technology has been developed! A technology has been developed that can reduce (2) to the order of submicrons and reduce the second term. For example, Figure 2 is an example (for example,
(Patent Application No. 193294/1982). In this manufacturing method, the base Fi
．． 1, a highly doped semiconductor layer 2 for forming a collector contact, a semiconductor layer 3 for forming a collector, a highly doped semiconductor layer 4 for forming a base, and a semiconductor layer for forming an emitter. 5. An emitter mask 8 is formed on the part that will become the emitter on the multilayer structure material (FIG. 2(a)) consisting of the highly doped semiconductor layer 6 for forming the emitter contact, and wet etching is performed using this as a mask. When the emitter mesa is formed and the base layer 4 is exposed, a structure is formed in which the mask 8 covers the emitter mesa 7 like a parasol due to the undercut caused by wet etching (Fig. 2)). After that, the surface of the sample is covered with photoresist 9 and flattened (Fig. 2 (C)).
, the top of the mask 8 is exposed by dry etching (FIG. 2(dl)), and the mask 8 is selectively removed to form the opening part 10 where the upper surface of the emitter contact layer 6a is exposed (
FIG. 2(e)), the emitter electrode 11 is formed in that part by vapor deposition and lift-off (FIG. 2(f)), and then,
Using the emitter electrode 11 as a mask, the base electrode l2 is formed by vapor deposition in the vicinity of the emitter mesa 7 in a self-aligned manner (
Figure 2 (auto)). In this method, since the emitter electrode 11 covers the emitter mesa 7 like a parasol, the base electrode l
2 is formed close to the emitter mesa 7 on the order of submicrons. In this manufacturing method, since the emitter electrode l1 is formed by self-alignment, l0 can be made sufficiently small, and as mentioned above! ．． , can be made small on the order of submicrons, so there is an advantage that the first and second terms of equation (2) can be made sufficiently small and R can be made small.

Problems to be Solved by the Invention However, wet etching exposes the eminter-base junction 13 to the surface, which increases the base current due to increased surface recombination around the exposed junction. I increase, the following formula, β= ・
(3) There was a problem in that the current amplification factor β, represented by Ib, decreased. Means for Solving the Problems In order to solve the above problems, the HBT of the present invention has a structure in which a surface protective film is epitaxially formed in the vicinity of the exposed emitter-base junction. This structure is realized by the following manufacturing method. Using an emitter mask covering the eminota mesa like a parasol as a mask, a surface protective film is formed by epitaxy, and then anisotropic dry etching is performed from above using the emitter mask as a mask to form an epitaxy layer in the area directly under the emitter mask. The surface protective film formed by epitaxy on the base region outside this region is removed while leaving the formed surface protective film as it is. The emitter mask is then converted to an emitter electrode and the base electrode is formed proximate to the emitter mesa using conventional self-alignment methods. Function: In the HBT structure of the present invention, the vicinity of the exposed emitter-base junction is covered with an epitaxy-formed surface protective film, so surface dangling ponds that cause surface recombination centers in this region are removed from the surface. It combines with the protective film and reduces the number of recombination centers. For this reason, the recombination current decreases and β does not decrease even in a micro-sized HBT. In addition, since the base electrode can be close to the emitter mesa on the order of submicrons, the base resistance can also be reduced. Furthermore, since the emitter electrode is formed by self-alignment, even a fine HBT can be manufactured, which has the advantage of reducing capacitance and improving high-speed and high-frequency characteristics. In addition, in the manufacturing method of the present invention, since the emitter mask covers the emitter mesa in a parasol shape, after forming the surface protective film by epitaxy, dry etching is performed from above to form the emitter-base junction where surface recombination is greatest. It is possible to effectively remove the epitaxially formed surface protective film from other parts, leaving the surface protective film only in the vicinity of the area. EXAMPLE Hereinafter, an example of the present invention will be described in detail with reference to the drawings. First, using a conventional method, an emitter mask 8 made of Siox is formed on the part that will become the emitter on the multilayer structure material shown in FIG. , So4-H202-H2
The emitter mesa 7 is formed by etching using a 0-based etchant to expose the base layer 4. As a result, the structure shown in Figure 2 (2) is formed in which the emitter mesa 7 is covered with a SiOx emitter mask in a parasol shape. Next, molecular beam epitaxy (MB) is performed using the emitter mask 8 as a mask.
E), from the diagonal direction l5 as shown in FIG. 1(a),
Undoped GaAs (u-GaAs) l4 is epitaxially formed to a thickness of about 200 mm. Then, upward direction 1
From 6 onwards, anisotropic dry etching using CHF gas is performed to form a y
-The u-GaAs formed on the outer base region is removed, leaving the GaAs surface protection film l4 (see Fig. 1 (
c)). Next, Figure 2 (C), which is the conventional self-alignment method,
(Using the rumored process, the emitter mask 8 is converted into an emitter electrode 11, and the base electrode 12 is further formed close to the emitter mesa 7 to form the structure shown in FIG. 1(C). After the process of FIG. 1(a), the structure of FIG. 2(C) to (
After converting the emitter mask 8 into the emitter electrode 11 using the process of f), the u-C in the area directly under the emitter electrode 2 is removed by anisotropic dry etching using CHF8 gas using the emitter electrode l1 as a mask. ;aAs
, and remove the u-GaAs in the outer base area, and then form the base electrode l2 close to the emitter mesa 7 using the process shown in FIG.
Form the structure of C). Furthermore, the structure shown in FIG. 1(C) can also be formed as follows. After performing dry etching using the emitter mask B as a mask, a base electrode 12 is formed by vapor deposition using the emitter mask 8 as a mask, and then the emitter mask 8 is formed in the vicinity of the emitter mesa by the processes shown in FIGS. 2(C) to 2(f). is converted into an emitter electrode l1 to form the structure shown in FIG. 1(C). In the example, n-Alo. z Gao,t As emitter, P''-U-G as GaAs-based surface protection film
゜Using aAs is the same as GaAs ■Undoped uAl which is a 1V group material! GaAs and other ■−
Of course, V group materials can be used. In addition, Group 1 materials such as St and Ge can also be used since they can be epitaxed to Group 2-- Group materials. In short, it is sufficient if the dangling bonds exposed on the surfaces of the emitter and base materials can be removed by epitaxy. In addition, in the examples, Aj! is used as the HBT material. Although a GaAs-GaAs material is used, it goes without saying that the structure and manufacturing method of the present invention can be applied to HBTs made of other materials, and in the examples, SiOx is used as the emitter mask. But, S
Various materials such as INx or other materials can be used as long as they do not react with the emitter contact layer and can be selectively removed with respect to the photoresist.

Furthermore, in the examples, a method of growing obliquely using MBH is used as a method for forming the surface protective film, but this is because MBE causes anisotropic growth. It is also possible to use an epitaxy growth method without anisotropy, and in that case, unlike the case of MBH, it is not necessary to perform epitaxy from an oblique direction. Effects of the Invention In the HBT structure of the present invention, the vicinity of the exposed emitter-base bond at the periphery of the emitter mesa is covered with a surface protective film formed by epitaxy, so surface recombination can be suppressed. Therefore, it is possible to prevent the current amplification factor β from decreasing due to surface recombination in an HBT having a micro-sized emitter mesa. In addition, since the eminota electrode can be formed by self-alignment, it can be bent to create a minute H
Since it can also be manufactured using BT, it is possible to reduce the capacity, and from this point of view it is also advantageous for improving the high-speed and high-frequency characteristics of HBT. Furthermore, since the base electrode can be formed close to the emitter on the order of submicrons, it is possible to reduce the base resistance, and this structure is also advantageous in improving the high-speed and high-frequency characteristics of the HBI'.

The manufacturing method of the present invention uses an emitter mask that does not react with the eminta mesa even at high temperatures, so the surface can be maintained even at high temperatures. ! #
can be formed by epitaxy, and since the emitter mask covers the emitter mesa like a parasol, the surface protective film can be formed only on the areas where surface recombination is greatest by dry enoching. Furthermore, since the base electrode can be formed close to the eminomesa using this parasol-like mask or an emitter electrode formed by converting it, the base resistance can be significantly reduced. Furthermore, since the emitter electrode can be formed by self-alignment, the HBT can be made finer and the capacitance can be lowered.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the manufacturing method and structure of the HBT of the present invention, and FIG. 2 is a sectional view showing the conventional manufacturing method and structure. l... Semi-insulating GaAs substrate, 2...
・n”-GaA for forming collector contact
s, 3...n-- for forming a collector
GaAs, 4...P'-GaAs for forming the base, 5...n Alm. for forming the emitter. 3 Gaa. ,As,5a・
'・'''5 emitter region, 6... n''-GaAs for forming emitter contact, 6a...
... 6 emitter contact region, 7 ... emitter mesa, 8 ... SiOx emitter mask,
9...Photoresist, lO...6a
Exposed opening on the top surface, 11...Eminota electrode, 12...Base electrode, 13...
Exposed emitter-base junction, l4...U
-GaAs surface protective film, l5...molecular beam epitaxy, l6...dry etching. 1st
Figure j5 / / 5:)" 14 , ~4 ゝ~3 = 2222 = 22 \{ I14 1 = = child H--'ftfk'r'l (suAsLM anti-2-n"-
GaAsxQ*Li3-. n-CmA5 hook 91 +-P''-θA5N-Z tatami SL-n-4L.zQaa.7.'Is Emmy-, 94x
Collection k-Jl'Qkyu A5Lb) 4jy da 7) 447--L
Mi・j4zop 9--SiOx Emi Q Tamasu 2 l-・Eshi: 9t Le f2・-・～-zu Denseki & 13-1 Nigu. To l9゜1 or 7 Fa layer +4-u-hA
x person kho L<#< 15--ra・each ^ pear epic ~ IC-・-k la {L-nokinge■=# d (ku

Claims (10)

[Claims] (1) A heterojunction bipolar transistor having a collector, a base, and an emitter in this order on a substrate has a mesa-type emitter and a surface protective film formed by epitaxy near the exposed emitter-base junction. Characteristics of heterojunction bipolar transistors. (2) The heterojunction bipolar transistor according to claim (1), further comprising an emitter electrode covering the emitter mesa in a parasol shape. (3) The heterojunction bipolar transistor according to claim (2), further comprising a base electrode adjacent to the base region directly under the emitter electrode. (4) On a multilayer structure material for producing a heterojunction bipolar transistor having semiconductor layers for forming a collector, a base, and an emitter in this order on a substrate,
Step 1 of etching using an emitter mask formed on a portion that will become an emitter, forming an emitter mesa whose upper surface is covered with the emitter mask in a parasol shape, and exposing a semiconductor layer for forming a base; Step 2 of epitaxially forming a surface protective film on the exposed surfaces of the emitter and base using the mask as a mask;
step 3 of dry etching from above using the emitter mask as a mask to remove the surface protective film epitaxially formed on the base region outside the base region directly under the emitter mask. A method of manufacturing bipolar transistors. (5) After step 3, the surface of the sample was covered with photoresist and planarized, and the top of the emitter mask was exposed by dry etching, and then the emitter mask was selectively removed to expose the top surface of the emitter mesa. Claim (4) characterized by comprising a step 4 of forming an opening and forming an emitter electrode in the opening by vapor deposition and lift-off.
A method of manufacturing the described heterojunction bipolar transistor. (6) After step 4, the heterojunction bipolar according to claim 5, further comprising step 5 of forming a base electrode adjacent to the base region directly under the emitter electrode by vapor deposition using the emitter electrode as a mask. Method of manufacturing transistors. (7) After step 3, the method further comprises step 6 of forming a base electrode adjacent to the base region directly under the emitter mask by vapor deposition using the emitter mask as a mask. A method for manufacturing a junction bipolar transistor. (8) After step 6, the surface of the sample was covered with photoresist and planarized, and the top of the emitter mask was exposed by dry etching, and then the emitter mask was selectively removed to expose the top surface of the emitter mesa. 8. The method of manufacturing a heterojunction bipolar transistor according to claim 7, further comprising the steps of forming an opening and forming an emitter electrode in the opening by vapor deposition and lift-off. (9) A mask (emitter layer) is formed on the multilayer structure material for producing a heterojunction bipolar transistor having semiconductor material layers for forming a collector, base, and emitter in this order on a substrate. form an emitter mesa by etching using a
and a step of exposing a semiconductor layer for forming a base, a step of epitaxy forming a surface protective film on the exposed surfaces of the emitter and base using the emitter mask as a mask, and a step of covering the surface with a photoresist. Planarize, expose the head of the emitter mask by dry etching, selectively remove the emitter mask to form an exposed opening on the top surface of the emitter mesa, and form an emitter electrode in the opening by vapor deposition and lift-off. and a step of dry etching from above using the emitter electrode as a mask to remove the surface protective film epitaxially formed on the base region outside the base region immediately below the emitter electrode. A method for manufacturing a heterojunction bipolar transistor. (10) Manufacturing a heterojunction bipolar transistor, characterized in that after the step of the method for manufacturing a heterojunction bipolar transistor according to claim (9), a base electrode is formed by vapor deposition in proximity to the emitter mesa using the emitter electrode as a mask. Method.