JP2940021B2 - Etching method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching method that can be used for manufacturing a device having a heterostructure multilayer film.

2. Description of the Related Art In recent years, devices having a heterostructure multilayer film have attracted attention as light-emitting devices or ultra-high-speed devices. However, in order to fabricate these devices, fine shape processing is required, and various etching methods have been studied. ing.

Hereinafter, an example of the above-described conventional etching method will be described with reference to the drawings.

3 (a), 3 (b) and 3 (c) are structural cross-sectional views showing a conventional etching method for each process, taking formation of a base electrode in a heterojunction bipolar transistor as an example. 3 (a), 3 (b) and 3 (c), 21 is an etching mask, 22 is an emitter layer made of GaAs, and 23 is
An In _0.47 Ga _0.53 base layer made of As, 24 is In _0.47 Ga _0.53 As
, A substrate 25 made of InP, and 26 a base electrode.

First, the obtained substrate 25 made of InP, the base layer made of an In _0.47 Ga _0.53 collector layer 24 composed of As, In _0.47 Ga _0.53 As
23. An emitter layer 22 made of GaAs is sequentially epitaxially grown, and an etching mask 21 is formed using photolithography (FIG. 3A). Next, using the etching mask 21 as a mask, the emitter layer 22 made of GaAs is etched with an etching solution containing phosphoric acid and hydrogen peroxide, the base layer 23 made of In _0.47 Ga _0.53 As is caught, and the emitter mesa is etched. Is formed (FIG. 3 (b)). Thereafter, a base electrode 26 is formed (FIG. 3C).

However, in such a method, GaAs and In _y Ga _1-y As
Since there is almost no difference in the etching rate (0 ≦ y ≦ 1), it is necessary to strictly control the etching time at the cue of the base layer 23. In particular, in a heterojunction bipolar transistor, the base layer 23 is thinner than other layers, and the thickness of the emitter layer 22 and the collector layer 24 is 4 to 5000 A, while the thickness of the base layer 23 is 700 A.
It is about. For example, when cueing the base layer in this heterojunction bipolar transistor, if the etching rate of the etching solution is 6000 A / min, the base layer 23 is exposed in 4 to 50 seconds.
If it shifts by 2%, the etching depth changes by about 200A. This means that the base layer becomes about 500 A, and the sheet resistance of the base layer becomes 1.4 times, which deteriorates transistor characteristics. As described above, it is difficult to strictly locate the base layer in the conventional etching method, and thus there is a problem that the transistor characteristics are likely to deteriorate.

In view of the above problems, the present invention provides an etching method capable of selectively etching an emitter layer with respect to a base layer when cueing the base layer 23 and strictly cueing the base layer. Things.

Means for Solving the Problems To solve the above problems, the etching method of the present invention uses an Al _x Ga _{1 -x} As (0) layer on an In _y Ga _{1 -y} As (0.4 ≦ y ≦ 1) layer.
In a multilayer film having ≦ x ≦ 1) layer, the In _y Ga _1-y As
(0.4 ≦ y ≦ 1) layer with respect to the Al _x Ga _1-x As (0 ≦ x ≦
1) When the layer is selectively etched, Cl ₂ is converted into plasma by electron cyclotron resonance, the plasma is extracted by a diverging magnetic field, and irradiated on a substrate support to which a high-frequency bias is applied, and a multilayer film is formed on the substrate support. (Hereinafter referred to as bias ECR stream etching).

Using the bias ECR stream etching with Cl ₂ of the present invention, the etching rate of In _y Ga _1-y As is Al _x Ga _1-x
Less than the etching rate of As, 0.4 ≦ y ≦ 1, 0 ≦ x
In the case of ≦ 1, since it is 1/5 or less, Al _x Ga _{1 -x} As (0 ≦
x ≦ 1) can be selectively etched with respect to _{In y Ga 1-y As (} 0.4 ≦ y ≦ 1), strictly _{In y Ga 1-y As (} 0.4
≦ y ≦ 1) It has been found that cueing of the layer can be performed.

Example An etching method according to an example of the present invention will be described below with reference to the drawings.

1 (a), 1 (b) and 1 (c) are structural cross-sectional views showing the etching method of the present invention for each process, taking formation of a base electrode in a heterojunction bipolar transistor as an example. In FIGS. 1 (a), (b) and (c), 11
Is an etching mask, 12 is an emitter layer made of GaAs, 13
Is a base layer made of In _0.47 Ga _0.53 As, 14 is In _0.47 Ga _0.53
A collector layer made of As, 15 is a substrate made of InP, and 16 is a base electrode.

FIG. 2 shows that In _y Ga _1-y As (0 ≦ y ≦ 1) is converted to an ultimate pressure of 1 ×
The In composition ratio y in In _y Ga _1-y As when the bias ECR stream was etched under the conditions of 10 ⁻⁶ Torr, Cl ₂ flow rate of 10 sccm, Cl ₂ gas pressure of 8 × 10 ⁻⁴ Torr, and microwave power of 500 W It shows the relationship between the etching rates.

First, on a substrate 15 made of InP, the base layer made of an In _0.47 Ga _0.53 collector layer 14 composed of As, In _0.47 Ga _0.53 As
13. An emitter layer 12 made of GaAs is sequentially epitaxially grown, and an etching mask 11 is formed using photolithography (FIG. 1A). Next, the second
The emitter layer 12 is etched under the etching conditions shown to form an emitter mesa (FIG. 1B). At this time, the thickness of the emitter layer 12 and the collector layer 14 is 4 to 5000
In the case of a heterojunction bipolar transistor having a thickness of about A and a thickness of the base layer 13 of about 700 A, from FIG.
The etching rate of GaAs is 4170 A / min, y = 0.47, ie, I
Since the etching rate of n _0.47 Ga _0.53 As is 800 A / min, even if the etching time is shifted by ± 2%, the base layer
The etching depth of 13 changes only about 32A. This means that the thickness of the base layer 13 hardly changes and the sheet resistance of the base layer does not change, so that the transistor characteristics do not deteriorate. Thereafter, a base electrode 16 is formed on the base layer 13 (FIG. 1C).

As described above, according to the present embodiment, the emitter layer is formed of GaAs, the base layer is formed of In _0.47 Ga _0.53 As, and the collector layer is formed of In _0.47 Ga _0.53 As. the layers were etched, when performing the beginning of the base layer, if a bias ECR stream etching using Cl _2, GaA
Selective etching of s and In _0.47 Ga _0.53 As becomes possible, so that the cue of the base layer can be strictly performed.

Although the emitter layer 12 is made of GaAs, the etching rate of Al _x Ga _{1 -x} As (0 ≦ x ≦ 1) is almost equal in the present etching method, so that Al _x Ga _{1 -x} As (0 ≦ x ≦ 1) is used. ).

The base layer 13 is set to In _0.47 Ga _0.53 As, may be sufficient selectivity for Al than the second FIG _{x Ga 1-x As (0} ≦ x ≦ 1) is Torere, an In _y Ga _{1- y} As (0.4 ≦ y ≦ 1) may be set.

In addition, although the structure of the multilayer film is a heterojunction bipolar transistor structure, an A y layer is formed on the In _y Ga _1-y As (0.4 ≦ y ≦ 1) layer.
Any structure may be used as long as the structure is a multilayer film having l _x Ga _1-x As (0 ≦ x ≦ 1) layers.

Effect of the Invention As described above, the present invention provides In _y Ga _1-y As (0.4 ≦ y ≦ 1)
In a multilayer film having the _{Al x Ga 1-x As (} 0 ≦ x ≦ 1) layer on the layer, if a bias ECR stream etching using Cl _2, the _{Al x Ga 1-x As (} 0 ≦ x ≦ 1) Layer the In _y G
a _1-y As (0.4 ≦ y ≦ 1) layer can be selectively etched, and the In _y Ga _1-y As (0.4 ≦ y ≦
1) Cueing of a layer can be performed, which greatly contributes to improvement in performance of a device using this layer.

[Brief description of the drawings]

FIG. 1 is a sectional view of a process for explaining an etching method in an embodiment of the present invention, FIG. 2 is a diagram showing a relationship between a composition ratio and an etching rate, and FIG. 3 is a diagram for explaining a conventional etching method. 11: etching mask, 12: emitter layer, 13: base layer, 14: collector layer, 15: substrate, 16: base electrode.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/3065 H01L 29/72

Claims (1)

(57) [Claims] An Al _x Ga is formed on an In _y Ga _1-y As (0.4 ≦ y ≦ 1) layer.
_In a multilayer film having a _1-x As (0 ≦ x ≦ 1) layer,
n _y Ga _1-y As the relative (0.4 ≦ y ≦ 1) layer _{Al x Ga 1-x As (} 0
≦ x ≦ 1) When selectively etching the layer, Cl ₂ is converted into plasma by electron cyclotron resonance, the plasma is extracted by a divergent magnetic field, and irradiated on a substrate support to which a high frequency bias is applied. And etching the multilayer film.