JP2009140944A - Method of etching oxide film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remove an etching product adsorbed onto a semiconductor substrate substantially thoroughly in an interface cleaning process for removing an oxide film on the semiconductor substrate by dry etching. <P>SOLUTION: A method of etching an oxide film includes a dry etching step of forming an etching product consisting of an ammonium silicofluoride salt through reaction with an oxide film formed on a semiconductor substrate 1 by using one or a plurality of kinds of gas selected from NF<SB>3</SB>and H<SB>2</SB>, N<SB>2</SB>, HF and NH<SB>3</SB>, an annealing step of sublimating the etching product by heating the semiconductor substrate at a temperature of ≥100°C after execution of the etching step, and a step of removing the etching product remaining on the semiconductor substrate by introducing hydrogen radicals after the annealing step. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an oxide film etching method for removing a natural oxide film on a semiconductor substrate by a dry etching process.

  As semiconductor miniaturization advances, interface (surface) cleaning has become necessary when forming gate wiring and contact wiring. Conventionally, wet chemical cleaning has been introduced to clean the surface of gate wiring and contact wiring. However, when wet chemical treatment is performed, for example, voids may be generated in the insulating film between the gate wirings, and control of void suppression is becoming difficult.

In order to solve these problems, an interface cleaning treatment method in which dry etching treatment is introduced is considered. For example, when cleaning the interface of the gate wiring by this processing method, first, dry etching of the wafer is performed in the etching chamber using a reaction gas such as NF ₃ / H ₂ / N ₂ / HF / NH ₃ , An etching reaction is caused with the natural oxide film to adsorb the etching product onto the wafer. Thereafter, the wafer is heated in an annealing chamber at a temperature of 100 ° C. or higher, and the etching product adsorbed on the wafer is volatilized and removed.

However, in the interface cleaning process in which the above-described dry etching process is introduced, the etching product adsorbed on the wafer cannot be completely removed and may remain on the wafer. In such a case, for example, a leak or a short circuit occurs in the gate wiring or the contact wiring, or particles are generated and remain on the wafer. For example, in a salicide reaction in which a metal silicide is formed by annealing after forming a metal such as Co or Ni in a later step, the uniform etching reaction of the gate wiring is hindered by the etching product remaining without being removed. The problem occurred. As an example of a technique for removing etching products on the wafer, a method described in Patent Document 1 is known.
JP-A-5-152255

  An object of the present invention is to provide an oxide film etching method capable of almost certainly removing etching products adsorbed on a semiconductor substrate in an interface cleaning process in which a natural oxide film on a semiconductor substrate is removed by a dry etching process. It is to provide.

The oxide film etching method of the present invention uses NF ₃ and one or more gases of H ₂ , N ₂ , HF, and NH ₃ to react with the oxide film and the gas from an ammonium silicofluoride salt. A dry etching process for forming an etching product, an annealing process for sublimating the etching product by heating the semiconductor substrate at a temperature of 100 ° C. or higher after performing the etching process, and after performing the annealing process. And a hydrogen radical introduction step of introducing hydrogen plasma or hydrogen radicals to remove etching products remaining on the semiconductor substrate.

  According to the present invention, in the interface cleaning process in which the natural oxide film on the semiconductor substrate is removed by the dry etching process, the etching product adsorbed on the semiconductor substrate can be almost certainly removed.

  Hereinafter, a first embodiment in which the present invention is applied to, for example, a surface cleaning process of a gate wiring of a MOS transistor will be described with reference to FIGS. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. The drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones.

  First, FIG. 1 is a sectional view schematically showing a sectional structure of a MOS transistor. As shown in FIG. 1, a MOS transistor Tr includes a gate electrode 3 formed on a p-type (or n-type) silicon substrate 1 as a semiconductor substrate via a gate insulating film 2, and the gate. Source / drain regions 4 are formed on the surface layer side of the silicon substrate 1 on both sides of the electrode 3.

  The gate insulating film 2 is formed of, for example, a silicon oxide film, and is configured, for example, by thermally oxidizing the silicon substrate 1. The gate electrode 3 is composed of, for example, a polysilicon film 5 doped with impurities and a metal silicide laminated on the polysilicon film 5 and constitutes a part of the gate wiring. FIG. 1 shows a state before metal silicide is formed (a state before depositing Co as a metal, for example), and an insulating film 6 is laminated on the polysilicon film 5. A gate sidewall insulating film 7 is formed on the sidewall of the gate electrode 3. The source / drain regions 4 are diffusion regions in which n-type (or p-type) impurities are diffused on both sides of the gate electrode 3 with respect to the surface layer portion of the silicon substrate 2.

When the gate electrode 3 is formed, a natural oxide film 8 is formed on the surfaces of the insulating film 6 and the source / drain regions 4. In order to remove the natural oxide film 8 (to perform a surface cleaning process), a dry etching process is performed (dry etching process). In this case, dry etching treatment of the wafer (silicon substrate 1) is performed in the etching chamber using one or more gases among reaction gases such as NF ₃ / H ₂ / N ₂ / HF / NH ₃ , An etching reaction is caused between the natural oxide film 8 (the natural oxide film on the surface of the insulating film 6 and the source / drain region 4). Then, as shown in FIG. 2, the etching product (that is, ammonium silicate fluoride) 9 generated by the above etching reaction is adsorbed on the wafer (the surface of the insulating film 6 and the source / drain region 4).

  Thereafter, as shown in FIG. 3, the wafer is heated at a temperature of, for example, 100 ° C. or higher in the annealing chamber to volatilize the etching product 9 adsorbed on the wafer (annealing step). In this case, only by heating the wafer, the etching product 9 adsorbed on the wafer cannot be completely removed, and as shown in FIG. 4, it remains on the wafer, that is, the residual product 10 remains. there were.

Therefore, in order to remove the residual product 10, a step of introducing the hydrogen radical H ^* in the state of FIG. 4 to remove the residual product (etching product) 10 remaining on the wafer (hydrogen radical introduction step) ). Specifically, the wafer is returned to the etching chamber again, and hydrogen radical H ^* processing is executed (see FIG. 5). In this embodiment, the hydrogen radical introduction step is performed at room temperature, for example. Further, the hydrogen radical introduction step may be executed by raising the wafer temperature above room temperature.

By executing the hydrogen radical introduction step, the SiFx-based residual product (etching product) 10 can be decomposed and removed by the following reaction formula.
aSiFx + nH ^* → aSi + nHF
As a result, as shown in FIG. 6, the interface of the wafer, that is, the surface of the insulating film 6 and the source / drain region 4 can be cleaned.

According to this embodiment having such a structure, in order to remove the etching product 9, after performing an annealing process for heating the wafer, hydrogen radicals H ^* are introduced to introduce the wafer (insulating film 6 and source / drain regions). Since the remaining product (etching product) 10 remaining on the surface 4 is removed, the natural oxide film on the surface of the insulating film 6 and the source / drain region 4 is almost certainly removed. The surface can be cleaned almost certainly. As a result, the gate wiring process can be uniformly formed.

  7 to 12 show a second embodiment of the present invention. The same components as those in the first embodiment are denoted by the same reference numerals. The second embodiment is an embodiment in which the present invention is applied to a cleaning process of the inner bottom surface of a contact wiring hole.

First, as shown in FIG. 7, an insulating film 11 is formed on the silicon substrate 1, and a contact hole 12 is formed in the insulating film 11. The surface of the inner bottom portion of the contact hole 12 is naturally oxidized, and a natural oxide film 8 is formed on the surface. In order to remove the natural oxide film 8 (in order to perform a surface cleaning process), a dry etching process is performed. In this case, the wafer (silicon substrate 1) is dry-etched in the etching chamber using one or more gases among reaction gases such as NF ₃ / H ₂ / N ₂ / HF / NH ₃ , An etching reaction is caused with the natural oxide film (natural oxide film on the inner bottom surface of the contact hole 12) 8 (dry etching process). Then, as shown in FIG. 8, the etching product (that is, ammonium silicofluoride salt) 9 generated by the etching reaction is adsorbed on the wafer (the surface of the inner bottom portion of the contact hole 12).

  Thereafter, as shown in FIG. 9, the wafer is heated at a temperature of, for example, 100 ° C. or higher in the annealing chamber to volatilize the etching product 9 adsorbed on the wafer (annealing step). In this case, only by heating the wafer, the etching product 9 adsorbed on the wafer cannot be completely volatilized and removed, and remains on the wafer (inner bottom of the contact hole 12) as shown in FIG. Residual product 10 may remain.

In order to remove the residual product 10, a step (hydrogen radical introduction step) of introducing hydrogen radical H ^* to remove the residual product (etching product) 10 remaining on the wafer is performed. Specifically, the wafer is returned to the etching chamber again, and hydrogen radical H ^* treatment is performed using hydrogen plasma (see FIG. 11). In addition, the said hydrogen radical introduction | transduction process is performed at room temperature, for example. Further, the hydrogen radical introduction step may be executed by raising the wafer temperature above room temperature.

By executing the hydrogen radical introduction step, the SiFx-based residual product (etching product) 10 can be decomposed and removed by the following reaction formula.
aSiFx + nH ^* → aSi + nHF
As a result, as shown in FIG. 12, the wafer interface, that is, the inner bottom surface of the contact hole 12 can be cleaned.

  The configuration of the second embodiment other than that described above is the same as that of the first embodiment. Therefore, in the second embodiment, substantially the same operational effects as in the first embodiment can be obtained.

In each of the embodiments described above, when the hydrogen radical introducing step for introducing hydrogen radical H ^* is executed, it is preferable to use the plasma etching apparatus 13 having the configuration shown in FIG. 13 as the third embodiment of the present invention. This plasma etching apparatus 13 has the same basic configuration as a dry etching apparatus having a well-known configuration, and includes an etching chamber 14, a stage 16 provided in the etching chamber 14 for mounting and fixing the wafer 15, and the etching chamber 14. A supply unit 17 for supplying gas to the gas and an exhaust unit 18 for exhausting the gas in the etching chamber 14 are provided.

The supply unit 17 includes a first supply unit 19 that supplies HF, a second supply unit 20 that supplies H _2, and a third supply unit 21 that supplies NH ₃ . The second supply unit 20 and the third supply unit 21 are provided with waveguides 22 and 23 for irradiating the internal gas with microwaves. In the case of this configuration, when the microwave output from the waveguide 22 is irradiated to H ₂ in the second supply unit 20, H ₂ is turned into plasma, and hydrogen plasma, that is, active species (hydrogen radical or (Including ions and the like) is supplied into the etching chamber 14. Similarly, when the microwave output from the waveguide 23 is irradiated onto the NH ₃ in the third supply unit 21, the NH ₃ is turned into plasma, and active species (including hydrogen radicals, ions, etc.) ) Is supplied into the etching chamber 14.

  The stage 16 is provided with a refrigerant flow path 24 for cooling the stage 16 and thus the wafer 15. When the wafer 15 is cooled, the etching product (ammonium silicofluoride salt) 9 is easily adsorbed on the wafer 15.

(Other embodiments)
The present invention is not limited to the above embodiments, and can be modified or expanded as follows.

First, in each of the above embodiments, the wafer is put in an etching chamber and dry-etched, then the wafer is put in an annealing chamber and heated, and then the wafer is returned to the etching chamber to perform hydrogen radical H ^* treatment. However, the present invention is not limited to this, and a function for heating the wafer is provided in the etching chamber, and the wafer is dry-etched in the same etching chamber, heated, and treated with hydrogen radical H ^*. It may be configured. Further, in each of the embodiments and the modifications described above, the wafers may be configured to be processed one by one (that is, configured as a single wafer device), or the wafers may be processed at the same time (that is, a plurality of wafers are processed simultaneously (that is, (It may be configured as a batch type apparatus).

  In each of the above embodiments and each of the above modifications, it is preferable to introduce a gas purge process during the heating (annealing process) of the wafer or during the conveyance after the annealing process. When the gas purge process is introduced, the amount of etching products remaining on the wafer can be reduced.

Further, in each of the above embodiments and each of the above modifications, the hydrogen radical H ^* may be introduced when the wafer is dry-etched to form an etching product (ammonium silicofluoride salt). . With this configuration, the amount of etching products remaining on the wafer can be reduced. In this case, when supplying N ₂ and H _2, constituting active species using microwave radiation to supply part N ₂ and H ₂ flow (radicals, ions, etc.) this as to introduce into the etching chamber It is preferable.

In the case of supplying NF ₃ and NH ₃ , it is preferable that NF ₃ and NH ₃ are converted into active species (radicals, ions, etc.) by remote plasma and introduced into the etching chamber. Further, NH ₃ and HF may be directly introduced into the etching chamber to generate NH ₄ Fx-based active species (radicals, ions, etc.). Furthermore, when N ₂ and NH ₃ are supplied, the supply part through which N ₂ and NH ₃ flow is irradiated with microwaves to introduce it into the etching chamber as active species (radicals, ions, etc.). It is even more preferable.

Sectional drawing which shows the 1st Example of this invention and demonstrates the surface cleaning process of a gate wiring (the 1) Sectional drawing explaining the surface cleaning process of a gate wiring (the 2) Sectional drawing explaining the surface cleaning process of a gate wiring (the 3) Sectional drawing explaining the surface cleaning process of a gate wiring (the 4) Sectional drawing explaining the surface cleaning process of a gate wiring (the 5) Sectional drawing explaining the surface cleaning process of a gate wiring (the 6) Sectional drawing which shows the 2nd Example of this invention and illustrates the surface cleaning process of a contact wiring (the 1) Sectional drawing explaining the surface cleaning process of contact wiring (the 2) Sectional drawing explaining the surface cleaning process of contact wiring (the 3) Sectional drawing explaining the surface cleaning process of contact wiring (the 4) Sectional drawing explaining the surface cleaning process of contact wiring (the 5) Sectional drawing explaining the surface cleaning process of contact wiring (the 6) Sectional drawing of the dry etching apparatus which shows the 3rd Example of this invention

Explanation of symbols

  In the drawing, 1 is a silicon substrate (semiconductor substrate), 2 is a gate insulating film, 4 is a source / drain region, 5 is a polysilicon film, 6 is an insulating film, 8 is a natural oxide film, 9 is an etching product, 10 is Residual product, 12 is a contact hole, 13 is a plasma etching apparatus, 14 is an etching chamber, and 15 is a wafer.

Claims (5)

In an oxide film etching method for etching and removing an oxide film on a semiconductor substrate,
Dry etching using NF ₃ and one or more gases in H ₂ , N ₂ , HF, NH ₃ to form an etching product made of ammonium silicofluoride by reaction of the oxide film and the gas Process,
After performing the etching step, an annealing step of sublimating the etching product by heating the semiconductor substrate at a temperature of 100 ° C. or higher;
An oxide film etching method comprising: a hydrogen radical introduction step for removing etching products remaining on the semiconductor substrate by introducing hydrogen plasma or hydrogen radicals after the annealing step. Forming a gate electrode of a transistor on a semiconductor substrate;
After the electrode forming step, the natural oxide film formed on the gate electrode and the semiconductor substrate is dry-etched using one or more gases of NF ₃ and H ₂ , N ₂ , HF, and NH _3. And forming an etching product comprising an ammonium silicofluoride salt on the gate electrode and the semiconductor substrate;
After the etching product forming step, the step of sublimating the etching product by heating the semiconductor substrate at a temperature of 100 ° C. or higher;
An oxide film etching method comprising: after the sublimation step, introducing hydrogen plasma or hydrogen radicals to remove etching products remaining on the semiconductor substrate. Forming an insulating film on the semiconductor substrate and then forming a contact hole reaching the surface of the semiconductor substrate;
After the contact hole forming step, a natural oxide film formed on the surface of the semiconductor substrate at the bottom of the contact hole is formed using one or more gases among NF ₃ and H ₂ , N ₂ , HF, and NH _3. Performing a dry etching process to form an etching product made of ammonium silicofluoride salt on the surface of the semiconductor substrate;
After the etching product forming step, the step of sublimating the etching product by heating the semiconductor substrate at a temperature of 100 ° C. or higher;
An oxide film etching method comprising: after the sublimation step, introducing hydrogen plasma or hydrogen radicals to remove etching products remaining on the surface of the semiconductor substrate.   4. The oxide film etching method according to claim 1, wherein a gas purge process is introduced during or after the semiconductor substrate is heated.   5. The oxide film etching method according to claim 1, wherein hydrogen radicals are introduced during the dry etching.

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