ETCHING METHOD

Abstract

In an etching method of the present invention, a first etching step for etching a silicon semiconductor region at a first etching rate with use of a first etching gas is first performed. Then, after the first etching step, a second etching step is performed in order to etch the silicon semiconductor region at a second etching rate that is lower than the first etching rate by using a second etching gas that includes carbon and fluoride, with the ratio of the fluoride in the second etching gas being higher than that of the carbon therein. Carbon is included in the second etching gas in order to chemically bind to at least either oxygen or hydrogen used in the first etching step. Therefore, it is possible to inhibit the generation of black silicon (i.e., a residue composed of silicon needles) which is caused as a result of attachment of oxygen and hydrogen on the etching surface. The resulting etched surface is smoothly formed, and black silicon is not formed thereon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of this original disclosure:

FIG. 1 is a partial vertical cross-sectional view of a semiconductor substrate in one step of a selective anisotropic plasma etching method in accordance with a first embodiment of the present invention;

FIG. 2 is a partial vertical cross-sectional view of the semiconductor substrate in one step of the selective anisotropic plasma etching method in accordance with the first embodiment of the present invention;

FIG. 3 is a partial vertical cross-sectional view of the semiconductor substrate in one step of the selective anisotropic plasma etching method in accordance with the first embodiment of the present invention;

FIG. 4 is a partial vertical cross-sectional view of the semiconductor substrate in one step of the selective anisotropic plasma etching method in accordance with the first embodiment of the present invention;

FIG. 5 is a partial vertical cross-sectional view of the semiconductor substrate in one step of the selective anisotropic plasma etching method in accordance with the first embodiment of the present invention;

FIG. 6 is a flow chart explaining steps of the selective anisotropic plasma etching method in accordance with the first embodiment of the present invention;

FIG. 7 is an electrophotograph showing a bottom portion of a trench formed by etching a silicon substrate under conditions in which an etching gas comprised of a SF₆ gas and an O₂ gas is used and the etching rate is set to be 3.2 μm min;

FIG. 8 is an electrophotograph showing a bottom portion of a trench formed by etching a silicon substrate under conditions in which an etching gas comprised of a SF₆ gas and a CF₄ gas is used and the etching rate is set to be 0.375 μm/min;

FIG. 9 is a partial vertical cross sectional view showing the vertical cross sectional shape of a trench formed as a result of a finishing etching step under conditions in which the ratio of the gas flow rate of CF₄ to that of SF₄ is set to be low;

FIG. 10 is a partial vertical cross-sectional view explaining the relaxation of stress applied to a silicon substrate when a thermal oxide film is formed on a sidewall of the trench and a bottom portion shown in FIG. 9;

FIG. 11 is a partial vertical cross sectional view showing the vertical cross sectional shape of a trench formed as a result of an finishing etching step under conditions in which the ratio of the gas flow rate of CF₄ to that of SF₆ is set to be low; and

FIG. 12 is a partial vertical cross-sectional view explaining an increase in stress applied to the silicon substrate when a thermal oxide film is formed on a bottom portion of a trench shown in FIG. 11 and a laminated structure comprised of a thermal oxide film and polysilicon is formed on a sidewall.

Claims

1. An etching method, comprising: a first etching step of etching a silicon semiconductor region with a first etching gas at a first etching rate; anda second etching step of etching the silicon semiconductor region after the first etching step with a second etching gas comprising carbon and fluoride at a second etching rate that is lower than the first etching rate, the percentage of the fluoride in the second etching gas being larger than that of the carbon therein.

2. The etching method according to claim 1, wherein the first etching gas comprises at least either hydrogen or oxygen.

3. The etching method according to claim 1, wherein the second etching gas is comprised of CF4 and at least either SF6 or NF4.

4. The etching method according to claim 1, wherein the second etching gas is set so that the weight ratio of fluoride to carbon is in a range of 90:1 to 6:1.

5. The etching method according to claim 1, wherein the second etching gas is set so that the weight ratio of fluoride to carbon is in a range of 40:1 to 6:1.

6. The etching method according to claim 1, wherein anisotropic etching is performed in the first and second etching steps, and the percentage of a second etching amount performed in the second etching step to the sum of a first etching amount in the first etching step and the second etching amount is in a range of 3 to 20%.

7. The etching method according to claim 1, further comprising an etching mask forming step of selectively forming an etching mask comprised of an oxide on the silicon semiconductor region before the first etching step.

8. The etching method according to claim 1, wherein the second etching step is started by discharging the first etching gas from the interior of an etching chamber after the first etching step, and then providing the second etching gas in the interior of the etching chamber.

9. The etching method according to claim 1, wherein the first etching gas comprises SF6 and O2.

10. The etching method according to claim 9, wherein the first etching gas comprising SF6 and O2 is changed to the second etching gas comprising SF6 and CF4 after the first etching step by stopping a supply of O2 and starting a supply of CF4 while a supply of SF6 is maintained, until the second etching step is started.

11. The etching method according to claim 1, wherein the first etching gas comprises Cl2 and O2.

12. The etching method according to claim 1, wherein the first etching gas comprises Cl2 and HBr.

13. The etching method according to claim 1, wherein the first etching gas comprises Cl2, HBr, and O2.

14. The etching method according to claim 1, wherein in the second etching step, a cleaning process is performed by causing a substitution reaction between Cl2, SF6 and CF4 simultaneously with selective anisotropic etching.

15. An etching method, comprising: a first etching step in which an anisotropic dry etching is performed so that a first etching amount in a silicon semiconductor region, which corresponds to 80 to 97% of a predetermined objective etching amount, is etched at a first etching rate by using a first etching gas comprising at least either hydrogen or oxygen; anda second etching step, performed after the first etching step, in which an anisotropic dry etching is performed so that a second etching amount of the silicon semiconductor region, which corresponds to 3 to 20% of the objective etching amount, is etched at a second etching rate that is lower than the first etching rate by using a second etching gas that is free of both hydrogen and oxygen and comprises carbon and fluoride, the weight ratio of the fluorine to the carbon in the second etching gas being in a range of 6:1 to 90:1.