JP2005310944A - Dry etching method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a round-bottom forming process independent from mask material, having little working dimensional dependence on etching shape. <P>SOLUTION: The dry etching method of a semiconductor device is used for performing formation of a slot or a hole in a semiconductor substrate 10. By using halogen system gas, such as Cl<SB>2</SB>and HBr as the source gas, a slot or a hole form is formed in the semiconductor substrate. The wafer bias output, impressed on a semiconductor substrate, is set to 0W, etching processing pressure is made into a low pressure of 1Pa or lower and contains no addition gas. Halogen system gas, such as Cl<SB>2</SB>and HBr, is used as independent gas 14. The radius of a circle (round bottom) 15 is formed in the bottom end of the formed slot or a hole. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a dry etching method, and more particularly to a method of forming a groove and a hole having a bottom round by etching.

  2. Description of the Related Art In recent years, STI (Shallow Trench Isolation) is used to make a semiconductor element fine as a semiconductor element isolation method. This is a method of separating elements by forming a groove in a silicon substrate by dry etching and then embedding an insulating film in the groove. The shape of this groove is configured by processing the side wall into a forward tapered shape in order to embed an insulating film without forming a cavity in a subsequent process. In order to prevent generation of crystal defects due to stress when an oxide film is formed in the groove, it is necessary to form a roundness at the lower end of the groove.

In a conventional etching method, a microwave plasma etching apparatus is used, and in a reaction gas obtained by mixing HBr (hydrogen bromide) gas and O ₂ (oxygen) gas, a range of 1% to 5% with respect to the total flow rate of the reaction gas. The groove is formed using the condition in which the O ₂ gas is mixed. Then, as the additional etching for forming the bottom round, the O ₂ gas mixing ratio of the precondition is set to 10% (for example, see Patent Document 1).

In the method shown in Patent Document 1, since a bottom round is formed by a method of depositing a reaction product by addition of O ₂ (oxygen) gas, a bottom round shape is formed depending on a trench size due to a bias of a reactive bioadhesion amount. There was a concern about the occurrence of foreign substances due to the reaction product.

On the other hand, the applicant of the present application uses a gas mainly composed of sulfur hexafluoride (SF ₆ ), nitrogen trifluoride (NF ₃ ), and fluorine (F) as a source gas, and carbon (C), hydrogen (H), F A method of forming a bottom round using (CHF ₃ ), (CH ₂ F ₂ ), and the like made of the above as an additive gas has been proposed (for example, see Patent Document 2). This method requires an additive gas.
JP-A-6-61190 Japanese Patent Application No. 2003-48867

  An object of the present invention is to provide a bottom round forming process that is less dependent on the processing size of an etching shape and does not depend on a mask material by a bottom round forming method that does not depend on an etching reactive organism in a dry etching method.

This problem can be achieved by setting the wafer bias output to 0 W in plasma using a halogen gas such as Cl ₂ gas or HBr gas as a single gas.

That is, in order to solve the above problems, the present invention relates to an etching method for forming a groove or a hole in a semiconductor substrate, using a halogen-based gas such as Cl ₂ or HBr as a source gas, and forming a groove or hole in the semiconductor substrate. A hole shape was formed, and roundness (bottom round) was formed at the lower end of the formed groove or hole.

  Further, according to the present invention, in the process of forming the bottom round, the wafer bias output applied to the semiconductor substrate is performed at 0 W or a bias close thereto. Furthermore, the present invention is a process for generating a bottom round, and the etching processing pressure is set to a low pressure of 1 Pa or less.

In the present invention, a halogen-based gas such as Cl ₂ or HBr that does not contain an additive gas is used as an etching gas. In addition, since the present invention can reduce products from the mask material and etching reactive organisms, the machining shape can reduce the dependence of the groove or hole on the machining dimension.

  The plasma etching method according to the present invention will be described below. 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 as 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, and an electron cyclotron resonance (ECR) is caused by a magnetic field generated therefrom and incident microwaves. As a result, the process gas is efficiently converted into plasma 5 at a high density. The processing wafer 6 is fixed to the electrode by electrostatic adsorption force by applying a DC voltage to the sample stage 8 by the electrostatic adsorption power source 7. Further, a high frequency power source 9 is connected to the electrode, and high frequency power is applied to give an acceleration potential in a direction perpendicular to the wafer to ions in the plasma. The gas after etching is exhausted from an exhaust port provided at the lower part of the apparatus by a turbo pump / dry pump (not shown).

  FIG. 2 is a diagram illustrating a method of manufacturing a semiconductor device using the apparatus of FIG. In the wafer used in this example, as shown in FIG. 2A, a pad oxide film 11 and a silicon nitride 12 as an etching mask are sequentially formed on a silicon substrate 10.

In order to form a groove having a certain angle, chlorine (Cl ₂ ) gas and borohydride (HBr) gas were used as etching conditions and oxygen (O ₂₎ gas was used as an additive gas as etching conditions. At this time, a reaction product composed of an etching gas and a silicon substrate is etched in the vertical direction while adhering to the silicon sidewall, so that a silicon groove having a certain angle can be formed. In this way, the shape of FIG. 2B can be obtained. At this time, the reaction product is deposited on the side wall as shown in FIG. 2B, the side wall protective film 13 is formed, and the reaction product is less deposited on the bottom surface. This is a result of etching progressing in the vertical direction while attaching reactive organisms to the side surfaces.

  At this time, even if the sidewall protective film 13 in FIG. 2B is removed, the lower end of the groove has an angular shape as shown in FIG.

As an additional step for forming the bottom round from the state shown in FIG. 2B (that is, the state where the protective film is formed on the side wall of the groove after the formation of the silicon groove), the pressure is 0.4 Pa, the wafer bias output is 0 W, Cl Etching was performed for about 20 seconds using ₂ gases alone as a process gas.

  In the bottom round forming step, since no wafer bias is applied, the sidewall protective film 13 on the trench side wall formed in the groove forming step is not etched, and only the groove bottom portion is selectively etched. As shown in the enlarged view of the lower end of the groove (FIG. 3), since a gas that easily forms a deposition protective film is not used as a process gas, chlorine (Cl) 14 activated by plasma reaches the etching surface. The etching rate of the high bottom portion is increased. Chlorine (Cl) 14 reflected from the trench side wall reaches the bottom surface of the groove away from the square bottom of the groove, so that the probability of reaching the bottom surface away from the bottom of the groove is high, and the bottom surface of the groove has a round shape. Is etched. As a result, the bottom round 15 can be formed. Moreover, since there was little production | generation of a reaction product, the stable round shape independent of the magnitude | size of a trench width was obtained.

Note that when a gas that easily generates a reaction product (O ₂ or the like) is added to the process gas, the deposition distribution of the reaction product at the groove bottom portion is the same as the arrival probability of chlorine (Cl) 14, and the round shape Is not formed.

  As described above, according to this embodiment, when the protective film is formed on the side wall of the groove after the formation of the silicon groove, the bottom round can be formed by etching under the above conditions.

In the above embodiment, the CI ₂ gas alone that does not contain the same additive gas as the gas used for the groove (hole) formation etching process was used as the gas for the bottom round formation process, but the gas used for the groove (hole) formation etching process was used. A single HBr gas that does not contain the same additive gas as the gas can be used.

  Furthermore, in the present invention, in the process of forming the bottom round, the wafer bias output applied to the semiconductor substrate is set to 0 W, but the activated processing gas reflected by the protective film formed on the trench sidewall is at the bottom. The same effect can be obtained even if the bias is such that it reaches the wafer bias close to 0 W.

  In the above embodiment, the etching process pressure is 0.4 Pa in the process of generating the bottom round, but the process in which the activated process gas reflected by the protective film formed on the groove sidewall reaches the bottom. If pressure is applied, the same effect can be obtained by setting the pressure to 1 Pa or less.

  Furthermore, the present invention can reduce products from the mask material and etching reactive organisms, and the processing shape can be less dependent on the processing dimensions of the grooves or holes.

  In this embodiment, the STI has been described, but the bottom round can be formed by the same method even in the deep groove shape and the deep hole shape.

  Although the present invention uses a plasma etching apparatus using a microwave and a magnetic field, it can be applied regardless of the plasma generation method. Therefore, for example, by a helicon wave etching apparatus, an inductively coupled etching apparatus, or the like. Even if implemented, the same effect can be obtained.

The schematic sectional drawing of the microwave plasma etching apparatus used for one Example of this invention. The principal part sectional drawing of the semiconductor substrate for demonstrating one Example of this invention. The important point enlarged view for demonstrating one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Magnetron 2 ... Waveguide 3 ... Quartz plate 4 ... Solenoid coil 5 ... Plasma 6 ... Wafer 7 ... Electrostatic adsorption power supply 8 ... Sample stand 9 ... High frequency power supply 10 ... Silicon substrate 11 ... Pad oxide film 12 ... Silicon nitride film 13 ... Side wall protective film 14 ... Chlorine 15 ... Bottom round

Claims (5)

An etching method for forming a groove or a hole in a semiconductor substrate is formed by forming a groove or a hole shape in the semiconductor substrate using a halogen-based gas such as chlorine (Cl ₂ ) or bromine (HBr) as a source gas. A dry etching method characterized in that a roundness (bottom round) is formed at the lower end of a groove or hole.   2. The dry etching method according to claim 1, wherein a wafer bias output to be applied to the semiconductor substrate is 0 W or a bias close thereto in a process of forming a bottom round.   3. The dry etching method according to claim 2, wherein an etching process pressure is set to a low pressure of 1 Pa or less in a process for generating a bottom round. The dry gas according to any one of claims 1 to 3, wherein a halogen-based gas such as chlorine (Cl ₂ ) or bromine (HBr) that does not contain an additive gas is used as an etching gas. Etching method.   5. The dry etching method according to claim 4, wherein products from the mask material and etching reactive organisms are reduced, and the processing shape is less dependent on the processing dimensions of the grooves or holes.

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