JPH0684841A - Formation method of groove in silicon substrate - Google Patents

Abstract

PURPOSE:To achieve that a deep groove in which the selective ratio of a silicon substrate with reference to a mask is high and whose aspect ratio is high is formed without any damaged part by a method wherein a plasma etching operation is performed by making use of a silicon oxide film as a mask and by using a gas composed mainly of heavy hydrogen. CONSTITUTION:In a method wherein a groove 3 is formed on the main surface of a silicon substrate 1 by a plasma etching operation, the etching operation is performed by making use of a silicon oxide film 2 as a mask and by using a gas composed mainly of heavy hydrogen. For example, a parallel plate-type RIE apparatus on which a permanent magnet has been set is used, a plasma etching operation is performed by using a silicon oxide mask 2 having a stripe shape at an opening width of 1mum and at a length of 1mm by using a single gas of D2, at an ion impinging energy of 110eV and at an operating pressure of 10mTorr with reference to a repeated pitch of 1000 lines at 2.6mum. As a result, it is possible to form a groove 3 having a depth of 4mum at a selective ratio of 100 in such a way that an undercut part 5 and a damaged part 4 are hardly recognized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a groove on the main surface of a silicon substrate used for a semiconductor device.

[0002]

2. Description of the Related Art Conventionally, individual semiconductor devices using a silicon single crystal substrate and semiconductor devices such as semiconductor integrated circuits have been widely used. There is also known a semiconductor device in which a groove is formed in a well shape, a stripe shape, a surrounding shape, or the like on a main surface of a silicon single crystal substrate, and the groove forms a high breakdown voltage structure, an insulation separation structure, or the like.

In recent years, as a method of forming a groove in a silicon substrate in the manufacture of a semiconductor device, dry etching using an excitation means by plasma discharge has come to be used as opposed to wet etching. In other words, dry etching has the advantage that there is no reduction in processing accuracy due to undercutting, and the effect of ions that are vertically incident on the surface of the processing material makes it possible to obtain a vertical processing shape whose processing dimensions are faithful to the mask. Has been.

Currently, the most widely used dry etching apparatus for manufacturing semiconductor devices is a reactive ion etching apparatus (RIE). Usually, disk-shaped electrodes are arranged in parallel in a vacuum container, high-frequency power is applied to one of the electrodes to generate plasma between the electrodes, and ions in the plasma are generated on the semiconductor substrate installed on the electrodes. Incident vertically. There are various types of improved RIE, for example, there is one that increases the plasma density by increasing the number of collisions of electrons and gas molecules in plasma with a magnetic field.

Various reaction gases used for RIE have also been developed. These are gases containing a halogen element such as F and Cl as a main component, and the processing material is made into a volatile halogen compound. To be removed. In actual etching, the processing performance is controlled by mixing various additive gases and reaction gases.

For example, in the manufacture of a trench type Schottky barrier diode whose main purpose is to increase the breakdown voltage, a known SF6 gas and CCl are formed on the main surface of an N type epitaxial substrate.
There is a RIE using 2F2 gas in which 1000 stripe-shaped grooves having a width of 1 μm, a depth of 2 μm and a length of 3 mm are formed at a repeating pitch of 2.6 μm using a silicon oxide film as a mask.

[0007]

The problems to be solved are, in particular, improvement of selectivity, high aspect ratio (ratio between the depth of the pattern to be etched and the plane size of the space) processing, and the processing part. Is the prevention of damage. That is, with the progress of fine processing technology and the improvement of the performance of semiconductor devices, high aspect ratio processing is required for forming grooves on the main surface of a silicon substrate. However, the selectivity between the mask including the silicon oxide film and the silicon substrate as the processing material is, for example, 1
It is about 0 to 20, and the silicon oxide film, which is a mask material, is simultaneously etched, the mask effect is lost, and it becomes difficult to form a deep groove with a high aspect ratio. Further, in the case of the conventional reaction gas, since ions having a large mass enter the substrate, a damage is generated at the bottom and inner wall of the groove formed. (3)

[0008]

According to the present invention, in a method of forming a groove on a main surface of a silicon substrate by plasma etching, etching is performed with a gas containing deuterium as a main component using a silicon oxide film as a mask. And
As a result, it is possible to obtain an improved individual semiconductor device or semiconductor integrated circuit device in which grooves are formed with a high aspect ratio.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional structural view for explaining an embodiment of the present invention. Reference numeral 1 is a silicon substrate made of an epitaxial growth layer, 2 is a mask of a silicon oxide film, 3 is a groove, 4 is a damage portion, 5 is an undercut portion, and FIG. 1 shows a groove after plasma etching. A structural drawing is shown.

A feature of the present invention is that etching is performed with a gas containing deuterium as a main component from the opening of the mask 2 of the silicon oxide film. Deuterium is an isotope of hydrogen having a mass number of 2, and is also called deuterium or deuterium.
Expressed as 2.

Next, the embodiments of the present invention will be described more specifically. The equipment used was a parallel plate type RIE equipped with a permanent magnet, and the silicon oxide film mask had an opening width of 1 μm and a length of 1 mm, and had a repeating pitch of 2.
Plasma etching was performed on 1000 μm of 6 μm with a single gas of D 2, ion incident energy of 110 eV, and operating pressure of 10 mTorr. As a result, the selection ratio is 10
0, the undercut portion 5 and the damage portion 4 were hardly recognized, and a groove having a depth of 4 μm was formed. In FIG. 1, the undercut portion 5 and the damage portion 4 are shown in an enlarged manner for the sake of explanation, but they were in a negligible range in the embodiment. Even when the damage portion 4 is large, a removal process such as soft etching is usually required in a post process,
In this case, heat treatment at 500 ° C. (4) for 30 minutes sufficiently recovers the damage layer.

FIG. 2 is a data diagram of the etching rate of a silicon substrate based on experimental data in comparison with plasma using H2 gas in order to demonstrate the effectiveness of plasma using deuterium D2 gas used in the present invention. Is. The horizontal axis is the self-bias voltage applied to the silicon substrate during plasma irradiation, and corresponds to the incident energy of ions. The vertical axis represents the etching rate of silicon. The self-applied voltage depends on the rf power and the pressure of the plasma gas. As is clear from FIG. 2, with the same self-applied voltage, hydrogen plasma hardly etches silicon. On the other hand, with deuterium plasma, about 70 nm per minute
(700 Å) silicon can be etched. The etching rate of the silicon oxide film is shown in FIG.
Although not shown, it was almost zero for both hydrogen plasma and deuterium plasma. Therefore, when performing silicon etching, the thickness of the silicon oxide film used for the mask can be made as thin as possible. That is,
The thickness of the silicon oxide film required as a mask is determined by the incident energy of ions (self-applied voltage). The thickness of the silicon oxide film is required so that the incident ions do not pass through the silicon oxide film and reach the underlying substrate. From the calculation using the Monte Carlo method, at the incident energy of 200 eV, the silicon oxide film thickness of 300 angstrom is sufficient. Therefore, in the etching of silicon by deuterium plasma, the thickness of the silicon oxide film used as the mask is 1 as compared with the case where the conventional method is used (the silicon oxide film of 1 to 2 μm is conventionally used as the mask). It can be thin near the order. By making this mask thin, it becomes easy to perform fine processing control.

The groove forming method of the present invention can be variously modified within the scope of the gist of the present invention. For example, in the case of forming a composite layer mask by depositing a resist film or the like on the mask 2 of silicon oxide film in FIG. 1, or in addition to deuterium D2 which is the main component in the reaction gas, other (5) additive gas or This includes the case of designing a reaction gas that controls the processing performance with a mixed gas.

[0014]

As described above, a deep groove having a high selection ratio of a silicon substrate and a high aspect ratio with respect to a mask of a silicon oxide film can be formed without damaging portions. It is possible to realize the performance improvement and the simplification of the manufacturing process by forming the groove with high precision and miniaturization, and the industrial application effect is extremely large.

[Brief description of drawings]

FIG. 1 is an explanatory cross-sectional structural diagram of an embodiment of the present invention.

FIG. 2 is a data diagram of an etching rate of a silicon substrate.

[Explanation of symbols]

 1 Silicon substrate 2 Silicon oxide film 3 Groove 4 Damage part 5 Undercut part

Claims (1)

[Claims] 1. A method for forming a groove on a main surface of a silicon substrate by plasma etching, which comprises etching with a gas containing deuterium as a main component using a silicon oxide film as a mask. .