JPH0661190A - Dry etching method - Google Patents

Abstract

PURPOSE:To make a Y-shaped groove and hole in a single crystal silicon high in accuracy and selectivity by a method wherein mixed reaction gas is composed of HBr and a specific % oxygen to a total flow rate. CONSTITUTION:In a microwave plasma etching device, a specimen 10 is placed on a specimen pad 11 inside a reaction chamber 16, and a single crystal silicon 22 of the specimen 10 is etched with the mixed reaction gas of HBr gas and 1 to 5% hydrogen gas. Then, a tapered part 32 is formed as deep as an aspect ratio of 3 or so from the opening of a trench, and the rest of the trench is formed into a vertical part 33, and reaction gas is high in selectivity to the single crystal silicon 22 and an oxide film, so that an etching mask 21b is left enough, and an excellent Y-shaped etched trench can be obtained. By this process, reaction gas is enhanced in selectivity to a single crystal silicon and a silicon oxide which serves as an etching mask, whereby a Y-shaped trench suitable for element isolation or a capacitor can be accurately formed.

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, and more particularly to a dry etching method for forming a Y-shaped groove or a Y-shaped hole in dry etching of single crystal silicon.

[0002]

2. Description of the Related Art Dry etching of single crystal silicon in a semiconductor integrated circuit manufacturing process is performed by element isolation or dynamic R used in a bipolar transistor.
Used for trench type storage capacitor used for AM.

For dry etching of single crystal silicon, a halogen gas or a halogen compound gas is used. Further, in order to improve the selection ratio with an oxide film serving as an etching mask and prevent chemical contamination, no carbon atom is contained. An etching gas is used. In particular, in recent years, single crystal silicon has been etched using HBr gas as a main reaction gas. For dry etching of single crystal silicon using HBr gas,
As disclosed in Japanese Examined Patent Publication No. 63-278339, HBr gas or a mixture thereof with an inert gas such as He, Ar, N ₂ is used. However, the conventional etching does not consider the taper processing (Y-type trench) of the trench opening.

[0004]

With the miniaturization of semiconductor devices, the deposited film by the CVD method has been made thinner, and nowadays a very thin film of about 3 to 5 nm is required. The same thin film formation is necessary also in the formation of the trench type storage capacitor portion used in the dynamic RAM.

In the above-described conventional method of etching single crystal silicon, since the sidewalls of the trench are vertical, the coverage of the deposited film in the trench may be poor when the storage capacitor is formed in the trench. In the trench etching according to the present invention, a processed shape having a taper in the trench opening can be formed in a state where the selectivity with respect to the oxide film serving as the etching mask is kept high. Therefore, the deposited film can be formed in the trench with good coverage. Further, when the trench is filled with the CVD film, there is a problem that if the opening is not tapered, a cavity is formed and flat filling cannot be performed.

An object of the present invention is to provide a dry etching method capable of forming Y-shaped grooves and holes with high precision and high selectivity.

[0007]

This object can be achieved by mixing oxygen gas in a reaction gas mixture of HBr gas and oxygen gas in the range of 1% to 5% with respect to the total flow rate of the reaction gas. .

[0008]

In the reaction gas obtained by mixing the HBr gas and the oxygen gas, the Y-shaped trench can be easily formed by mixing the oxygen gas in the range of 1% to 5% with respect to the total flow rate of the reaction gas. Since the trench opening has a taper, a deposited film can be formed in the trench with good coverage.

[0009]

EXAMPLES Examples of the present invention will be described below.

FIG. 1 is an explanatory view of an apparatus used for etching of the present invention. The etching device is a microwave plasma etching device. The present apparatus has a structure capable of applying high-frequency power 12 to the sample stage 11, and has a structure capable of independently controlling the energy of ions incident on the etching sample 10 in addition to the generation of plasma. The high-frequency power has a frequency of 2 MHz and is connected to the sample table 11 through the matching circuit 13. The microwave that generates plasma is a magnetron 14 with a frequency of 2.45 GHz.
Is introduced into the reaction chamber 16 which is sealed in a vacuum by the quartz tube 20 by the waveguide 15. An electromagnet 17 is provided around the reaction chamber 16, and plasma is generated in the reaction chamber 16 by the synergistic effect of the microwave and the electromagnet 17.
The etching sample 10 is installed on the sample table 11 in the reaction chamber 16. The reaction gas is supplied into the reaction chamber 16 through the gas supply port 18. The gas after etching is exhausted to the outside of the reaction chamber 16 through an exhaust port 19 provided at the lower portion of the apparatus by an exhaust system of a turbo pump and a dry pump.

2 (a) to 2 (c) show a process of preparing a sample used for etching in the embodiment. An oxide film 21 having a thickness of 300 nm was formed on the single crystal silicon 22 (a), and a pattern 23 was formed on the oxide film 21 by photoresist (b). Using the photoresist pattern 23 as an etching mask, the oxide film 21 is dry-etched with a mixed gas of CF ₄ and CHF ₃ . After dry etching of the oxide film 21, a photoresist pattern 23 is formed using oxygen plasma.
Was removed and washed with HF diluted 200 times with water.
Minutes (c). Dry etching of single crystal silicon was performed using the sample having the structure of FIG. The opening dimension W of the oxide film 21 serving as an etching mask is 500 nm.

FIG. 3 shows the relationship between the etching rate of single crystal silicon and an oxide film and the oxygen gas mixture ratio with respect to the total flow rate of the reaction gas. The etching conditions are a gas flow rate of 40 sccm,
The pressure is 10 mTorr, the high frequency power is 25 W, the microwave power is 600 W, the cooling temperature is 20 ° C., and the etching time is 5 minutes. The etching rate a of single crystal silicon is 250 nm / min in the range of the oxygen gas mixture ratio of 0% to 5%.
Is constant, but it decreases when mixing more than 5%,
It becomes 120 nm / min at a mixing ratio of 10%. The etching rate b of the oxide film is reduced from 50 nm / min to 5 nm / min by mixing oxygen gas at 1% (0.4 sccm). Further increase the oxygen gas mixing ratio to 10% (4scc
No change was observed in the etching rate of the oxide film as m).

The results of etching performed under various conditions will be described below.

(1) Using the microwave plasma etching apparatus shown in FIG. 1, the sample shown in FIG. 2 was used to etch single crystal silicon only with HBr gas. The conditions used for etching are: HBr gas flow rate 40 sccm, microwave power 600 W, RF power 20 W, pressure 0.
5 mTorr, cooling temperature 20 ° C, etching time 20
Minutes. A schematic view of the processed shape at this time is shown in FIG.
The shape of the side surface of the trench is a barrel shape 30, and a sub-trench 31 is formed on the bottom surface. Further, since the etching mask 21a is thin because the selection ratio to the oxide film is as small as 5, it was not possible to obtain a good etching shape. The barrel shape 30 is formed because the side wall protection film that prevents side etching by ions from an oblique direction is not formed.

(2) Single crystal silicon was etched with a reaction gas obtained by mixing 2.5% oxygen gas with HBr gas. The condition used for etching is that the flow rate of HBr gas is
37.5 sccm, oxygen gas flow rate is 2.5 sccm, and other conditions are the same as in (1). A schematic diagram of the processed shape at this time is shown in FIG. A taper shape 32 is formed from the trench opening to a depth of about an aspect ratio of 3, and a vertical shape 33 is formed at a deeper portion. Further, since the selection ratio with respect to the oxide film is as large as 50, the etching mask 21b is sufficiently left, and a good Y-shaped trench etching shape can be obtained. This is because the oxide of silicon is generated during the etching of silicon, and more of the oxide is attached to the trench opening, so that a Y-shaped trench shape is obtained.

When the processed shape was examined by changing the oxygen gas mixing ratio, the oxygen gas mixing ratio capable of obtaining a good Y-shaped trench etching shape was in the range of 1 to 5%. Moreover, the total flow rate of the reaction gas is 20 sccm to 100 sccm.
However, in each case, the Y-shaped trench etching shape was obtained in the oxygen gas mixture ratio of 1 to 5%. The same effect was obtained by mixing an inert gas such as He or Ar.

When a Y-type groove isolation and a Y-type trench capacitor were prepared under the etching conditions of this example, it was confirmed that a thin film was deposited with good coverage.

(3) Single crystal silicon was etched with a reaction gas in which HBr gas was mixed with 10% oxygen gas. The condition used for etching is that the flow rate of HBr gas is 3
6 sccm, the flow rate of oxygen gas is 4 sccm, and other conditions are the same as in (1). An explanatory view of the processed shape at this time is shown in FIG. The etching depth is about half of that when HBr is used alone or when 2.5% oxygen is mixed. The processed shape is a V-shape 34 having a roundness 35a on the bottom surface. The etching mask 21c remains without being etched. This is because more oxide of silicon is generated during etching, which hinders etching.

(4) After etching the single crystal silicon under the condition (1) using a reaction gas prepared by mixing 2.5% oxygen gas with HBr gas, an oxygen gas mixture ratio of 10% is used as additional etching. Other conditions were the same as (1), and etching was performed for 5 minutes. An explanatory view of the processed shape at this time is shown in FIG. The processed shape is a Y-shaped trench shape similar to that of the second embodiment, and the bottom surface of the trench is rounded.
It came to have b. On the bottom surface of the trench having a large aspect ratio, the oxide of silicon serving as a protective film is hard to reach, and only ions having directionality contribute to the etching of the bottom surface, so that the bottom surface of the trench is rounded.

As described above, by using the condition (2), it is possible to obtain a shape in which the CVD film can be easily formed in the groove. Further, by performing additional etching as in (4), the bottom surface can be rounded, and the generation of crystal defects can be suppressed in a process with large stress such as formation of an oxide film in a groove.

[0021]

According to the present invention, the HBr gas contains 1% to 5%.
By mixing the oxygen gas in the range of%, the selectivity with respect to the oxide film serving as the etching mask can be increased, and the Y-shaped trench groove shape suitable for element isolation or a capacitor can be formed with high precision.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a microwave plasma etching apparatus used in an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a process of preparing a sample used in an example of the present invention.

FIG. 3 is a characteristic diagram showing etching rates of single crystal silicon and an oxide film with respect to a mixing ratio of oxygen gas with respect to a total flow rate of HBr gas and oxygen gas.

FIG. 4 is a cross-sectional view of a trench etched only with HBr gas.

FIG. 5: HBr gas and 2.5% according to an embodiment of the present invention
FIG. 6 is a cross-sectional view of a trench etched with a reaction gas mixed with the oxygen gas of FIG.

FIG. 6 is a cross-sectional view of a trench etched with a reaction gas in which HBr gas and 10% oxygen gas are mixed according to an embodiment of the present invention.

FIG. 7 shows HBr gas and 2.5% according to an embodiment of the present invention.
Etching is performed with a reaction gas mixed with oxygen gas,
Sectional drawing of the trench which carried out overetching with the reaction gas which mixed HBr gas and 10% oxygen gas.

[Explanation of symbols]

21, 21a, 21b, 21c ... Oxide film, 22 ... Single crystal silicon, 32 ... Tapered shape, 33 ... Vertical shape.

Claims (7)

[Claims] 1. A dry etching method characterized by forming a Y-shaped groove or a Y-shaped hole in single crystal silicon by using a reaction gas in which HBr gas and oxygen gas are mixed. 2. The dry etching method according to claim 1, wherein oxygen gas is mixed in the range of 1% to 5% with respect to the total flow rate of the reaction gas. 3. The method according to claim 1, wherein in order to make the bottom surface of the etching round, 10% to 10% of the total flow rate of the reaction gas is used.
A dry etching method in which additional etching is performed using a reaction gas mixed with 20% oxygen gas. 4. A dry etching method according to claim 1, wherein a Y-shaped U-shaped groove or hole having a round bottom is formed in the single crystal silicon. 5. The dry etching method according to claim 1, wherein microwave plasma etching is used. 6. A semiconductor device in which the Y-shaped groove formed by the dry etching method according to claim 1 is used for element isolation of a semiconductor integrated circuit. 7. A semiconductor device using the Y-shaped hole formed by the dry etching method according to claim 1 for a trench capacitor.