JPH04722A - Heterojunction bipolar transistor - Google Patents

Abstract

PURPOSE:To provide a heterojunction bipolar transistor which decreases in base resistance and improves a high frequency characteristic by a method wherein an epitaxial layer is eliminated immediately before the base is exposed to implant Be ions after implanting oxygen ions. CONSTITUTION:Etching does not reach a base layer with a distance l left. The distance l between the etching surface and the base layer is, for example, a certain measure of 50 to 200Angstrom with the distance between the etching and a base surface 4 being formed with a margin. Next, Be ion is implanted at a certain measure of 40keV, 5X10<14>cm<-2>. Afterwards, an annealing is performed for 10 seconds at 750 deg.C so as to recover a crystalline characteristic of the base layer and activate an implanting dopant so that a HBT may be completed. That is, even if a distance is existent between the etching surface and the base surface 4, it becomes possible to come into contact with a base by implanting Be ions, thereby capable of obtaining a favorable ohmic contact.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a heterojunction bipolar transistor (hereinafter referred to as
In particular, the present invention relates to HBTs that are easier to manufacture and have improved performance.

<Prior Art> FIGS. 2(a) to 2(g) schematically show the manufacturing process of a conventional HBT. The process will be explained step by step.

Step (a) On a semi-insulating GaAs substrate, form an n" GaAs layer 2 with a thickness of 0.4 μm and an impurity concentration of 5×10'"C1-' and a thickness of 0.4 μm.
m, n-G-aAs with impurity concentration 5X10"CI-'J
Layer 3. Thickness 0.1. um, impurity concentration 3X10”cm-
“p” GaAs layer 4. 5. Undoped layer with a thickness of 001 μm. N with a thickness of 0.2 μm and an impurity concentration of lXl0"CI'
"AlGaAs layer 6, thickness 0.15 μm, impurity concentration 5
N'' GaAs layers 7 of X10''CI' are stacked one after another.

Step (b) An A1 layer 8 is formed on the n'' GaAs layer 7 on the surface by vapor deposition or the like, and this A1 layer is etched leaving the portion where the emitter and base are to be formed, and oxygen ions are etched using the remaining A1 layer as a mask. 200KeV.

Insulation is achieved by implanting up to n-GaAs (collector layer) 7 at a concentration of about 1X10' to C1-'.

Step (c) Remove the A1 layer 8, and remove the oxide film SiOχ9 and the A1 layer 8a.
, then emitter S pole and Bess $ If! The oxide film SiOx9 and the Af layer 8a are removed, leaving only the part where the emitter electrode is to be formed.

Step (d) N” GaAs layer 7°N-A by wet etching
lGaAs layer6. Undoped GaAs layer 5 is removed to expose P+ layer 4, which is a base layer.

As a result, the layer below the oxide film SiOx9 is under-etched. After that, oxygen ions are added to the p” GaA base layer.
The oxygen ions penetrate the P+ layer 4 and form an n-
Reached collector layer 3.

This contributes to insulating the n- layer and reducing the capacitance between the p+ layer 4 and the n+ layer 2.

Step (e) Remove the A1 layer 8a, apply a resist 10, remove the resist at the location where the collector electrode is to be formed by photolithography, and remove the removed portions of layers 4 and 3.
remove.

Step (f) The oxide film SiOx9 is removed and the emitter electrode 11 and collector electrode 12 are formed by vapor deposition or the like.

H+ ions are implanted around the HBT in order to separate it from the element on the same substrate of the same color from which the resist 10 has been removed.

Process (g) The base electrode 13 is formed by self-alignment.

<Problem to be solved by the invention> Step (d) in the above conventional HBT using GaAs
In etching to expose the base electrode, the concentration of the etching solution is adjusted while considering the type and thickness of the thin film, and the etching time is adjusted.
It is necessary to control on an order close to 008. However, it is difficult to etch to the desired depth (stop the etching the moment the base layer appears), and the etching amount must be monitored and removed little by little. Also, excessively etched HBT
However, there was a problem in that the base resistance became large and it was difficult to provide good high frequency characteristics.

The present invention has been made to solve the problems of the prior art described above.
By implanting Be ions (hereinafter referred to as Be ions), the purpose is to provide etching tolerance and facilitate etching, as well as to lower the base resistance and improve high frequency characteristics.

Means for Solving the Problems> In order to solve the problems of the prior art described above, the present invention has a structure in which a collector (n
In a petrojunction Vibora transistor manufactured by laminating a base (P+ layer), a base (P+ layer), and an emitter layer made of Aj7GaAs by epitaxial growth, when exposing the base electrode formation surface, the epitaxial layer is removed until just before the base is exposed. After oxygen ion implantation, Be
It is characterized by implantation of ions.

Effect> Since Be ions are implanted after oxygen ion implantation, contact with the base layer is possible even if the emitter layer and undoped layer remain. Furthermore, since Be is injected into the base layer, the base resistance is reduced. Furthermore, if it is possible to leave a very small amount of layer 6 so that GaAs is not exposed on the surface, 1
The surface recombination current is reduced, and the amplification factor of the HBT can be improved.

<Embodiment> FIGS. 1(a) and 1(b) show an embodiment of the present invention, and since the steps of the conventional example shown in FIG. 2 are the same except for step (d), the other steps will be omitted.

In Fig. 1(a), the etching has not reached the base layer and the distance! have. The distance between this etching surface and the base! may be, for example, about 50 to 2005, and is formed with a greater distance from the base surface 4 than in the past.

Next, as shown in Figure 1(b), Be ions were applied at 40 keV.
, 5xl □l ' C11-2.

Thereafter, annealing is performed at 750° C. for about 10 seconds to restore the crystallinity of the base layer and activate the implanted dopant, and the HBT is completed through the conventional steps (e), (f), and (g).

According to the above structure, even if there is a distance between the etched surface and the base surface 4, contact with the base can be made by implanting Be ions, and a good ohmic contact can be obtained.

Here, the index fy (cutoff frequency...frequency at which gain Ic (collector current)/Ib (base current) becomes OdB) and flaX (maximum oscillation frequency...power The frequency at which the gain becomes 0) can be expressed as follows.

fv=1/(2π(τe+τb×τC+τC−))fr
gax=Tyr b-cbc)"Here.

τe: Emitter charging time τb; Travel time of electrons passing through the base τC: Travel time of electrons passing through the collector τC-: Yaw: Charging time of ta Rb: Base resistance Cbc; Base-collector capacitance and τC- is τc = (Re + Rc) ・CbcRe,
Emitter resistance Rc: Served as collector resistance.

Here, since CBC is reduced by oxygen ion implantation and Rh is reduced by Be ion implantation, the above-mentioned fv and f laX can be improved. As a result, an HBT with excellent frequency characteristics can be realized.

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, when exposing the surface after base formation, the epitaxial layer is removed until just before the base is exposed, and Be ions are removed after oxygen ion implantation. By implanting GaAs, it is possible to facilitate etching and improve the high frequency characteristics.If GaAs can be prevented from being exposed on the surface, the surface recombination current will be reduced and the amplification factor of the HBT can be improved.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIGS. 1(a) and 1(b) are diagrams showing an oxygen injection process and a Be injection process showing an embodiment of the present invention, and FIGS. 2(a) to (
g) is a diagram showing the process of manufacturing a conventional HBT. 1-...Semi-insulating GaAs substrate, 2-n"GaAs layer, 3-...-n-GaAs layer (collector), 4-P"Ga
As layer (base) 5...Undoped layer 6...N"
AlGaAs layer (emitter 1.7-n” GaAs layer,
8...AlF layer, 9...SiOx. Agent Patent Attorney Shinsuke Kozawa

Claims (1)

[Claims] Collector (n^- layer) made of GaAs layer, base (p^+ layer) and AlGaA layer on semi-insulating GaAs substrate.
In a heterojunction bipolar transistor manufactured by laminating an emitter layer consisting of S by epitaxial growth, when exposing the base electrode formation surface, the epitaxial layer was removed until just before the base was exposed, and beryllium ions were implanted after oxygen ion implantation. A heterojunction bipolar transistor characterized by: