JPH04350931A - Method of dry etching - Google Patents

Abstract

PURPOSE:To provide a method of vertical anisotropic dry etching using chemical reaction, wherein an under cut does not occur on side walls. CONSTITUTION:When an InP substrate 6 is etched using chlorine gas and an argon ion beam 5, a very small amount of XeF, having a stronger affinity for indium than chlorine has, is added to the etchant. As a result, an indium fluoride film 2 is formed. Since the indium fluoride film is not volatile, it forms a side-wall protective film. On the bottom surface, separation is promoted by the ion beam, the addition of XeF causes no problem. This realizes vertical anisotropic etching.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method using a reactive gas.

0002

2. Description of the Related Art Dry etching methods using reactive gases include reactive ion etching (RIE), reactive ion beam etching (RIBE), and ion beam excited etching (IBAE). These etching methods increase etching speed and smoothness by creating products with high vapor pressure using chemically reactive gases.

However, since chemical reactions occur isotropically, undercutting of the sidewalls occurs due to chemical etching under etching conditions where products are actively desorbed. in this case,
Carbon-based etchants allow vertical anisotropic etching because a polymer is deposited to protect the sidewalls from chemical etching.

0004

[Problems to be Solved by the Invention] Since a polymer made of carbon-based etchant is used for the above-mentioned side wall protection,
Carbon pollution becomes a problem. Especially in compound semiconductors, carbon becomes a dopant, which is a problem. As described above, conventional reactive dry etching has problems to be solved.

An object of the present invention is to provide a dry etching method that performs vertical anisotropic etching without sidewall undercuts.

[0006]

[Means for Solving the Problems] In order to achieve the above object, a dry etching method according to the present invention includes a dry etching method in which a substrate is dry etched using a reactive gas formed by a combination of an etchant gas and an additive gas. The additive gas has a stronger binding force to the substrate element than the etchant gas, and
The vapor pressure of the product is lower than that of the product produced by the etchant gas, and a small amount of the additive gas is added to the etchant gas, and dry etching is performed using the reaction gas resulting from this combination.

[0007]

[Operation] Since the additive gas has a stronger binding force to the substrate element than the etchant gas, it reacts more easily than the etchant gas and forms a compound on the substrate surface. Because the product has a low vapor pressure, it will not be chemically etched, preventing sidewall undercuts. At this time, since the etching of the bottom surface is promoted by ion bombardment in addition to chemical etching, the influence of the products of a small amount of added gas is small. In this way, vertical anisotropic etching without undercut can be performed without carbon contamination.

[0008]

EXAMPLES The dry etching method of the present invention will be explained below with reference to Examples.

FIG. 2 shows an example in which XeF is used as an additive gas in InP etching by the IBAE method in which argon ion beam is irradiated in a chlorine gas atmosphere. Argon is introduced into the ECR plasma chamber 7 through the argon introduction gas line 8 at a rate of 9 sccm to cause discharge. Chlorine gas is sprayed onto the InP substrate 6 from the nozzle 12, and then the extraction electrode 1 is
An ion beam accelerated at a zero voltage of 500V is irradiated. At this time, the substrate temperature is set to 210° C. by heating by the substrate heating heater 13, and the vacuum level in the etching chamber 11 is set to 8×10 −4 Torr by evacuation by the cryopump 14. Under these conditions, a smooth surface morphology is obtained, but the side wall has an undercut due to chemical etching. Here XeF
XeF is added through the introduction gas line 9.

[0010] Since P has a much higher vapor pressure than In,
The rate of etching is determined by the removal of In. Since fluorine has a stronger bonding force with In than chlorine, indium fluoride is produced on the substrate surface where fluorine is adsorbed, as shown in FIG. Indium fluoride has a boiling point of 1200
Since it is a non-volatile substance at temperatures above .degree. C., it does not undergo thermal desorption and forms an indium fluoride film 2 as a sidewall protective film. Since the ion beam promotes desorption at the bottom surface, a trace amount of indium fluoride 3 does not interfere with etching. In this way, by adding a small amount of XeF, argon/chlorine IBA
Vertical anisotropic etching of InP can be performed using E. Furthermore, Figure 1
, 1 is a SiO2 mask, 3 is indium fluoride, 4 is indium chloride, 5 is an argon ion beam, 6
indicates an InP substrate.

[0011] The etching method is not limited to IBAE,
RIE, RIBE, electron or photoexcitation etching, etc. may also be used.

[0012] The additive gas may also be fluorine-based, such as SF6
, HF, NF, etc. are also acceptable. Also, the combination of substrate, etchant gas, and additive gas is InP, chlorine, and Xe.
The additive gas is not limited to F, as long as it satisfies the conditions that the additive gas has a stronger bonding force to the substrate element than the etchant gas and the vapor pressure of the product is low. For example, a similar effect can be obtained by adding SF6 when performing chlorine RIBE on a GaAs substrate.

A similar effect can be obtained by adding HF when performing chlorine RIBE on an Al substrate.

Similar effects can be obtained by adding oxygen or the above-mentioned fluorine-based gas when performing chlorine RIE on the Si substrate.

[0015]

As described above, according to the present invention, a gas which has a stronger binding force to the substrate element than the etchant gas and whose vapor pressure is lower than that of the product produced by the etchant gas. Vertical anisotropic etching can be performed by adding a small amount of to the etchant gas and performing dry etching.

[Brief explanation of drawings]

FIG. 1 is a diagram showing vertical anisotropic etching for forming a sidewall protective film using indium fluoride.

FIG. 2 is a diagram showing a XeF-added argon/chlorine IBAE method.

[Explanation of symbols]

1　SiO2 mask 2 Indium fluoride film 3 Indium fluoride 4 Indium chloride 5 Argon ion beam 6 InP substrate 7 ECR plasma chamber 8 Argon introduction gas line 9 XeF introduction gas line 10 Extraction electrode 11 Etching chamber 12 Chlorine introduction nozzle 13　Substrate heating heater 14 Cryopump

Claims (1)

[Claims] 1. A dry etching method in which a substrate is dry etched using a reactive gas consisting of a combination of an etchant gas and an additive gas, wherein the additive gas has a stronger bonding force to the substrate elements than the etchant gas. and the vapor pressure of the product is lower than that of the product produced by the etchant gas, adding a small amount of the additive gas to the etchant gas, and performing dry etching using the reaction gas resulting from this combination. A dry etching method characterized by: