JP2004259927A - Dry etching method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method of a semiconductor device which forms a bottom round at the lower end corner of the groove or the hole of the semiconductor device. <P>SOLUTION: The wafer bias output of a semiconductor substrate 10 employing a photo resist 13 and an insulating film 11 as masks is made OW employing a reaction gas consisting of a source gas and an additional gas, whereby the bottom round 15 is formed utilizing isotropic etching and a sidewall protective film 14. In this case, the source gas is constituted of the principal constituent of fluorine (F) such as 6-sulfur fluoride (SF<SB>6</SB>), 3-nitrogen fluoride (NF<SB>3</SB>) or the like. The reaction gas is constituted of an additional gas (CHF<SB>3</SB>, CH<SB>2</SB>F<SB>2</SB>or the like) constituted of carbon (C), hydrogen (H), and F. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a dry etching method, and more particularly, to formation of a groove and a hole having a bottom round by etching.
[0002]
[Prior art]
In recent years, STI (Shallow Trench Isolation) has been used as an element isolation method due to miniaturization of semiconductor elements. This is a method of forming a groove in a silicon substrate by dry etching and then embedding an insulating film in the groove to isolate elements. The shape of this groove needs to be tapered on the side surface in order to bury the insulating film without voids, and the lower end of the groove needs to be rounded in order to prevent crystal defects due to stress when the oxide film is formed.
[0003]
In the conventional etching, a microwave plasma etching apparatus is used, and in a reaction gas in which HBr (hydrogen bromide) gas and O ₂ (oxygen) gas are mixed, in a range of 1% to 5% with respect to the total flow rate of the reaction gas. A groove is formed by using a condition in which O ₂ gas is mixed. Then, as the additional etching for forming the bottom round, an etching in which the O ₂ gas mixture ratio of the previous condition is set to 10% is used (for example, see Patent Document 1).
[0004]
[Patent Document 1]
JP-A-6-61190 [0005]
[Problems to be solved by the invention]
In STI, in addition to forming a groove mainly by anisotropic etching, it is necessary to incline the silicon groove angle to about 80 ° to 85 °, and it is difficult to round the bottom corner of the groove. In the conventional method, after forming a certain groove, the bottom round is formed under the condition that the silicon groove angle is more inclined. However, a further round shape has been required to improve device performance.
[0006]
It is an object of the present invention to form an additional bottom round at the corner of the groove bottom in STI.
[0007]
[Means for Solving the Problems]
The problem is that when forming the bottom round, a gas mainly composed of fluorine (F) such as nitrogen trifluoride (NF ₃ ) is composed of a source gas and carbon (C) · hydrogen (H) · F (CHF _3. CH ₂ F _2, etc.) can be achieved by setting the wafer bias output to 0 W in a reaction gas mixed with an additional gas.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the plasma etching method according to the present invention will be described. FIG. 1 shows an etching apparatus used in the present invention. The present embodiment is an example of a microwave plasma etching apparatus using a microwave and a magnetic field for plasma generation means. The microwave is oscillated by the magnetron 1, passes through the waveguide 2, passes through the quartz plate 3, and enters the vacuum vessel. A solenoid coil 4 is provided around the vacuum vessel. Electromagnetic cyclotron resonance (ECR) is caused by a magnetic field generated by the solenoid coil 4 and an incident microwave. As a result, the process gas is efficiently converted to high density plasma 5. The processing wafer 6 is fixed to the electrodes by electrostatic attraction by applying a DC voltage to the sample table 8 by the electrostatic attraction power supply 7. A high-frequency power supply 9 is connected to the electrodes, and high-frequency power is applied to give ions in the plasma an acceleration potential in the vertical direction to the wafer. The gas after the etching is exhausted from an exhaust port provided in the lower part of the apparatus by a turbo pump / dry pump (not shown).
[0009]
FIG. 2 is a diagram illustrating a method of manufacturing a semiconductor device using the etching apparatus of FIG.
As shown in FIG. 2A, the wafer used in this embodiment has a pad oxide film 11, a silicon nitride 12, and a photoresist pattern 13 formed in this order on a silicon substrate 10.
[0010]
FIG. 2B shows the silicon nitride etched using the photoresist pattern as an etching mask. Next, in order to form a groove having a certain angle in the silicon substrate 10, a mixed gas of HBr gas and O ₂ gas was used as an etching condition. At this time, since the etching product and the reaction product 14 composed of the silicon substrate 10 are vertically etched while being attached to the silicon side wall, a silicon groove having a certain angle can be formed. Thus, the shape shown in FIG. 2C can be obtained. At this time, a protective film 14 is provided on the side wall as shown in FIG. The protective film adheres to the side walls, and the bottom surface has a small amount of the protective film. This is a result of the etching progressing in the vertical direction while attaching the reaction product to the side surface.
[0011]
At this point, even if the side wall protective film (reaction product) 14 in FIG. 2C is removed, a bottom round is not formed at the lower end of the groove, and the groove has a square shape as shown in FIG. 2D.
[0012]
As an additional step for forming a bottom round from the state of FIG. 2C, etching is performed for about 20 seconds using a pressure of 0.4 Pa, a wafer bias output of 0 W, and a gas flow ratio of SF ₆ / CHF ₃ of about 1/6. Was done.
[0013]
When the wafer bias output is 0 W and SF ₆ , isotropic etching is performed. CHF ₃ functions as a gas for controlling the amount of isotropic etching.
[0014]
In the bottom round forming step, the isotropic etching is selectively performed from the bottom surface with less protective film, and the groove below the groove is etched so as to draw an arc. FIG. 3 shows an enlarged view of the isotropically etched state at the lower end of the groove. In FIG. 3, arrows indicate the direction of isotropic etching, and the size thereof generally indicates the amount of etching. This makes it possible to form the bottom round 15 as shown in FIG.
[0015]
In forming grooves and / or holes, the silicon groove angle and the type and thickness of the sidewall protective film differ depending on the processing conditions such as the type of gas. At this time, a desired bottom round can be obtained by adjusting the conditions of the round forming step, the ratio of SF ₆ / CHF ₃ , the pressure, and the etching time.
[0016]
FIG. 4 shows an application example using the bottom round forming step. First, as shown in FIG. 4A, as etching for forming a groove, a groove having a desired groove angle and a desired depth of about 80 to 90% is formed by etching. Next, the remaining depth is used as a taper forming step under the conditions of HBr / CHF ₃ , a flow ratio of 20/3, a pressure of 2.0 Pa, and a wafer bias of 80 W, and the lower part of the groove is formed as a groove with a more tapered angle. From this state, bottom round formation etching is performed. This enables bottom round formation without excessively etching the lower side wall. Therefore, as shown in FIG. 4B, the bottom round 15 can be formed while maintaining the silicon groove angle.
[0017]
Thereafter, by removing the groove side wall protection film 14, a groove having a taper and a bottom round shown in FIG. 4C can be formed.
[0018]
As described above, according to the present embodiment, after the silicon groove is formed, when the protective film is formed on the groove side wall, the bottom round can be formed by etching under the above conditions.
[0019]
In the present embodiment, the STI is described. However, the bottom round can be formed by a similar method in a deep groove shape or a deep hole shape.
[0020]
Although the present invention uses a plasma etching apparatus using a microwave and a magnetic field, the present invention can be applied regardless of a method of generating plasma. Therefore, for example, a helicon wave etching apparatus, an inductively coupled etching apparatus, etc. Even if it is carried out, the same effect can be obtained.
[0021]
In the present invention, in addition to sulfur hexafluoride (SF ₆ ), a gas mainly containing fluorine (F) such as nitrogen trifluoride (NF ₃ ) can be used as a source gas at the time of forming the bottom round. In addition to CHF ₃ , a gas containing hydrogen such as CH ₂ F _{2 made of} carbon (C) · hydrogen (H) · F can be used as the gas.
[0022]
【The invention's effect】
According to the present invention, a bottom round can be formed by using a reactive gas mainly containing SF ₆ gas and adding a gas containing hydrogen such as CHF ₃ and setting the wafer bias output to 0 W.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a microwave plasma etching apparatus used in one embodiment of the present invention.
FIG. 2 is an essential part cross-sectional view of a semiconductor substrate for explaining one embodiment of the present invention;
FIG. 3 is an enlarged view of an essential part for explaining an embodiment of the present invention.
FIG. 4 is an application example of the present invention.
[Explanation of symbols]
1: magnetron, 2: waveguide, 3: quartz plate, 4: solenoid coil,
5 ... plasma 6 ... wafer 7 ... electrostatic power supply 8 ... sample stand
9: high frequency power supply, 10: silicon substrate, 11: pad oxide film,
12: silicon nitride film, 13: photoresist pattern,
14: reaction product (protective film), 15: bottom round,
16 ... Taper forming step

Claims (4)

Regarding the step of forming grooves and holes in a semiconductor substrate, that is, an etching method using a mask material (resist) and a reaction product as a side wall protective film, sulfur hexafluoride (SF ₆ ) and nitrogen trifluoride (NF ₃ ) For example, a gas mainly composed of fluorine (F) is used as a source gas, and a gas (such as CHF ₃ , CH ₂ F ₂ ) composed of carbon (C), hydrogen (H), and F is used as an additional gas. A dry etching method characterized in that roundness (bottom round) is formed and controlled at the lower ends of the grooves and holes. 2. A dry etching method according to claim 1, wherein the wafer bias output applied to the semiconductor substrate is 0 W or a bias close thereto, as the method of forming and controlling the bottom round. 2. A dry etching method according to claim 1, wherein the bottom round is formed on the bottom surface of the groove and the hole formed in the semiconductor substrate by using a side wall protective film made of a reactive substance as a method of forming and controlling the bottom round. 2. A dry etching method according to claim 1, wherein a bottom round is formed on the bottom surface of the processed groove or hole by inserting a taper forming step at the time of forming the groove or hole.

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