JPH07169747A - Etching method - Google Patents

Abstract

PURPOSE:To provide excellent anisotropic etching by improving the selection ratio. CONSTITUTION:In an etching method which subjects a semiconductor wafer W to a prescribed etching is under a plasma atmosphere by introducing a treatment gas into a treatment vessel 2, a mixed gas of a halogen gas which generates an etchant and S(sulfur) gas containing no F(fluorine) is used as the treatment gas. Therefore, the excessive radical component which is generated by the dissociation of the halogen gas and hinders the anisotropy of the etching is removed and the selection ratio is improved, because the radical component is absorbed into the S gas containing no F.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching method.

[0002]

2. Description of the Related Art For example, a semiconductor wafer (hereinafter referred to as "wafer") having a semiconductor device such as an LSI formed on its surface will be described as an example. An etching gas is introduced into a processing chamber which is conventionally airtight. Plasma is generated in the processing chamber by applying high-frequency power, and an etching process for forming, for example, a contact hole is performed on the wafer in the plasma atmosphere.

For example, a silicon oxide film (SiO ₂ )
When etching is performed on a silicon oxide film formed on a wafer in the related art, an etching gas such as an F (fluorine) -based gas such as CF ₄ or Cl (such as CCl ₄ ) is used as an etching gas. Chlorine) -based gas, and further F-Cl-based gas such as CClF ₃ is often used. And among the various types of gas,
For example, in the case of CF ₄ , the silicon oxide film (SiO ₂ ) is removed by F ^* (fluorine radical) generated by dissociating gas molecules by plasma.

By the way, today, with the high integration of devices, there is a demand for an etching method capable of ultrafine processing corresponding to half micron and quarter micron. Therefore, for example, contact holes can be formed to 0.35 μm or less. Although it becomes necessary, in order to form such a fine contact hole, it is necessary to realize anisotropic etching having a high selection ratio in a high-density plasma atmosphere.

However, in a high-density plasma atmosphere, since the energy absorbed by the plasma is high, the dissociation of gas molecules proceeds, and as a result, in the case of CF ₄ mentioned above, F ^* (fluorine radical) is generated. It is generated excessively, the selectivity is lowered, and the etching tends to be isotropic.

Therefore, it is necessary to remove the above-mentioned excessive fluorine radicals by some means, but recently, in this respect, it easily reacts with such fluorine radicals to render them ineffective, such as Si (silicon). It has been proposed to configure members such as an electrode plate in the processing chamber depending on the material.

[0007]

However, in such a method in which a simple substance of Si is used for the member in the processing chamber, it is necessary to heat the member itself to a high temperature of about 300 ° C. by an appropriate heating means. In addition, as the number of times of treatment is increased, the surface area of the member surface changes and the reaction surface area changes, and as a result the amount of reaction with the fluorine radicals is not constant, and the essential etching process itself differs from wafer to wafer. There is also a fear of coming. Furthermore, maintenance is required every fixed number of times of processing, and throughput is also reduced.

The present invention has been made in view of such problems, and basically absorbs and removes an excessive radical component that shifts to isotropic etching by a constant mixing amount gas, The purpose is to improve the selection ratio of anisotropic etching.

[0009]

In order to achieve the above object, the etching method according to claim 1 introduces a processing gas into a processing chamber and performs a predetermined etching process on an object to be processed in a plasma atmosphere. In the etching method, etching is performed by using, as the processing gas, a processing gas containing a mixed gas of at least a CFC-based gas and an S (sulfur) -based gas not containing F (fluorine). .

The etching method according to claim 2 is
Fluorocarbon gas as a processing gas and O without F (fluorine)
S (sulfur) -based gas containing (oxygen), for example, SO, SO ₂ , SO ₃ , S ₂ O, S ₂ O ₃ , S ₂ O ₇ , S that are sulfur oxides
It is characterized in that a gas containing a mixed gas with O ₄ or the like is used.

The CFC-based gas referred to in the present invention is, for example, a C _x F _y- based halogenated carbon compound (so-called Freon gas) such as CF _{4 described} above, and further F.
₂ , Cl ₂ , Br ₂ , I ₂ , At ₂ , Cl ₃ F, ICl ₃ , C
IF, ICl, BrF, BrF ₃ , BrF ₅ , IF ₅ , I
Falogen gas such as F ₇ , interhalogen compound, HF, HC
l, HBr, HI, HAt and other hydrogen halides, B
Boron halides such as F ₃ , BCl ₃ , B ₂ Cl ₄ , B ₄ Cl ₄ , BBr ₃ , and BI ₃ , B ₂ H ₆ (diborane), B ₄ H ₁₀ (tetraborane), B ₅ H ₉ , B ₅ The concept includes boron hydrides such as H ₁₁ and B ₆ H ₁₀ , and boron hydride hydrides such as B ₂ H ₂ F ₄ .

The S (sulfur) -based gas containing no F (fluorine) includes thionyls such as SOBr ₂ (thionyl bromide), CS ₂ , H ₂ S, N ₂ S ₂ , N ₄ S ₄ and As. ₄ S ₄ , As
Sulfides such as ₂ S ₃ , P ₄ S ₇ , P ₂ S ₅ , SO, SO ₂ , S
Sulfur oxides such as O ₃ , S ₂ O, S ₂ O ₃ , S ₂ O ₇ , and SO ₄ are included.

[0013]

The former fluorocarbon gas functions as a so-called reaction gas and causes a dissociation reaction in plasma to generate an etchant such as a radical component for etching. On the other hand, the latter S (sulfur) -based gas that does not contain F (fluorine) reacts with the excess radical component when the dissociation of the reaction gas proceeds and an excess radical component is generated, Remove this.

Therefore, by controlling the flow rate of the latter S (sulfur) -based gas that does not contain F (fluorine) by, for example, a mass flow controller or the like, depending on the generation of excess radical components, that is, the degree of dissociation of the reaction gas. Therefore, it is possible to suppress the excessive radical component, improve the etching selection ratio, and perform the anisotropic etching treatment with the increased vertical anisotropy.

In view of the function of each gas, the processing gas introduced into the processing chamber in the actual etching processing is at least these fluorocarbon-based gases and F (fluorine).
It suffices to contain an S (sulfur) -based gas that does not contain, and it is not hindered to use an inert gas such as N ₂ or Ar gas together.

Further, as described in claim 2, instead of the S (sulfur) -based gas containing no F (fluorine), F (fluorine) is used.
When an S (sulfur) -based gas that does not contain O and contains O (oxygen) is used, this O (oxygen) is excessive C in the processing gas, for example.
It reacts with (carbon) and becomes C + O ₂ → CO ₂ ↑, which is exhausted. Therefore, it is possible to remove the excess carbon that interferes with the anisotropic etching in the processing gas.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 schematically shows a cross section of a plasma etching apparatus 1 used for carrying out this embodiment. 1 is configured as a so-called parallel plate type RIE device in which electrode plates face each other in parallel.

The plasma etching apparatus 1 has a processing container 2 formed into a cylindrical or rectangular shape, for example, made of aluminum whose surface is subjected to anodized aluminum oxide, and the processing container 2 is grounded. At the bottom of the processing chamber formed in the processing container 2, a substantially cylindrical column for mounting an object to be processed, for example, a semiconductor wafer (hereinafter referred to as “wafer”) W via an insulating plate 3 made of ceramic or the like. The susceptor support base 4 is housed therein, and the susceptor 5 forming a lower electrode is provided on the susceptor support base 4. In the present embodiment, the silicon oxide film (Si
A case of carrying out etching of O ₂ ) will be described.

A coolant chamber 6 is provided inside the susceptor support 4, and a coolant for temperature control such as liquid nitrogen can be introduced into the coolant chamber 6 through a coolant introduction pipe 7. The introduced refrigerant circulates in the refrigerant chamber 6,
Cold heat generated during that time is transferred from the coolant chamber 6 to the wafer W via the susceptor 5, and the processing surface of the wafer W can be cooled to a desired temperature. When liquid nitrogen as described above is used as the refrigerant, the nitrogen gas generated by the nucleate boiling of the liquid nitrogen is discharged from the refrigerant discharge pipe 8 to the outside of the processing chamber 2.

The center portion of the upper surface of the susceptor 5 is formed in a convex disk shape, and an electrostatic chuck 11 having substantially the same shape as the wafer W is provided thereon. This electrostatic chuck 11
Has a structure in which the conductive layer 12 is sandwiched between two polymer polyimide films, and the conductive layer 12 is supplied from the DC high-voltage power supply 13 installed outside the processing container 2 to, for example, 1 By applying a DC high voltage of 0.5 kV, the wafer W placed on the upper surface of the electrostatic chuck 11 is attracted and held at that position by the Coulomb force.

An annular focus ring 15 is arranged around the upper edge of the susceptor 5 so as to surround the wafer W placed on the electrostatic chuck 11. The focus ring 15 is made of an insulating material that does not attract the reactive ions, and is configured so that the reactive ions generated by the plasma are effectively incident only on the wafer W inside thereof.

The focus ring 15 is made of, for example, SiO (silicon monoxide) so that it can be removed by reacting with fluorine radicals, as will be described later.

An upper electrode 21 of the processing container 2 is disposed above the susceptor 5 so as to face the susceptor 5 in parallel and to be spaced apart from the susceptor 5 by about 15 to 20 mm, with an insulating material 22 interposed therebetween. It is supported at the top.

This upper electrode 21 has an electrode plate 24 made of, for example, SiC or amorphous carbon, which has a large number of diffusion holes 23 on the surface facing the susceptor 5, and is located parallel to this electrode plate 24. A support plate 25 made of, for example, aluminum whose surface has been subjected to anodized aluminum is formed to form a hollow portion, and a gas diffusion plate 26 is provided on the upper surface of the electrode plate 24.

The gas diffusion plate 26 has a form as shown in FIG. 2, and is fixed to the electrode plate 24 by a fixing member 27 such as a bolt as shown in FIG. The gas diffusion plate 26 is made of a conductive material such as carbon or glass carbon having a large number of holes, but may be made of other insulating material such as ceramics or quartz. However, the former conductive material is preferable because it has the same potential as the electrode plate 24 and the possibility of abnormal discharge disappears.

As shown in FIG. 3, a gas inlet port 28 is provided in the center of the support plate 25 of the upper electrode 21, and the gas inlet port 28 is provided with a gas inlet port as shown in FIG. The introduction pipe 29 is connected. As shown in FIG. 1, a gas supply pipe 31 is connected to the gas introduction pipe 29, and the gas supply pipe 31 is further divided into three parts via a valve 32 and a mass flow controller 33, respectively. , Corresponding processing gas sources 34, 35,
36. In this embodiment, CF ₄ gas is supplied from the processing gas supply source 34 and S is supplied from the processing gas supply source 35.
The O 2 and processing gas supply sources 36 are set to supply N ₂ gas.

An exhaust pipe 41 is connected to a lower portion of the processing container 2, and an exhaust pipe 44 of a load lock chamber 43 adjacent to the processing container 2 via a gate valve 42, a turbo molecular pump, and the like. It communicates with the exhaust means 45 and is constructed so that it can be evacuated to a predetermined reduced pressure atmosphere. Then, the wafer W, which is the object to be processed, is carried in and out between the processing container 2 and the load lock chamber 43 by the carrying means 46 such as a carrying arm provided in the load lock chamber 43. It is configured.

The power unit in the plasma etching apparatus 1 has a so-called power split structure in which the high frequency power source section is separated from the processing container 2. That is, for example, a high frequency power source 51 that oscillates a high frequency of 13.56 MHz is installed on the primary side of a transformer unit 52 including an induction coil and the like.
A slide controller 53 that is grounded is provided on the secondary side of the second induction coil or the like.

The secondary side of the transformer 52 is connected through the first matching unit 54 and the blocking capacitor 55 to the electrode plate 24 of the upper electrode 21 and the second matching unit 56, respectively.
Via the blocking capacitor 57, the susceptor 5 mentioned above is connected.
Are connected to the upper electrode 21 and the susceptor 5, respectively.
Each of them is configured to apply high-frequency power that is 180 ° out of phase with each other.

The plasma etching apparatus 1 for carrying out the present embodiment is constructed as described above. Next, the operation thereof will be described. First, the wafer W which is the object to be processed.
After the gate valve 42 is opened, the carrier is carried into the processing container 2 from the load lock chamber 43 by the carrying means 46 and placed on the electrostatic chuck 11. Then, the wafer W is attracted and held on the electrostatic chuck 11 by the application of the high-voltage DC power supply 13. After that, the transport means 46 retracts into the load lock chamber 43, and then the inside of the processing container 2 is evacuated by the exhaust means 45.

On the other hand, while the valve 32 is opened and the flow rate thereof is adjusted by the mass flow controller 33, the CF ₄ gas from the processing gas supply source 34, the SO gas from the processing gas supply source 35, and the gas supply pipe 31. The gas is introduced into the hollow portion of the upper electrode 23 through the gas introducing pipe 29 and the gas introducing port 28. Further, from this hollow portion, the CF
A mixed gas of ₄ gas and SO gas is discharged to the wafer W through the gas diffusion plate 26 and the diffusion holes 23. As shown in FIG. 3, the gas diffusion plate 26 is a porous body. In combination with the configuration of the plurality of diffusion holes 23 that are direct ejection ports, the ejection is extremely evenly performed on the wafer W.

The pressure inside the processing container 2 is, for example, 10 m.
After being set and maintained at Torr, the high frequency power supply 51 operates and the output is adjusted by the slide controller 53 of the transformer 52, and the phase of the upper electrode 21 and the susceptor 5 differs by 180 °. A high frequency power is applied to generate plasma between the upper electrode 21 and the susceptor 5, and the wafer W is subjected to predetermined etching by radical components generated by dissociation of the introduced CF ₄ gas. It

At this time, CF ₄ is dissociated in multiple stages, such as ^: · CF ₃ + F ⁻ CF ₃ ⁻ + · F CF ₃ ⁺ + F ⁻ CF ₃ ⁺ + · F + e ⁻ , and F ⁻ → F ^* +
This becomes e ^−, and this F ^* (fluorine radical) etches SiO _{2 on the} surface of the wafer W.

However, if the above-mentioned dissociation proceeds to the final stage and the fluorine radicals are excessively produced, the vertical anisotropy of etching is impaired and the selection ratio is lowered, resulting in isotropic etching as a whole. Will be.

However, in this embodiment, since SO ₄ gas is mixed with CF ₄ gas and introduced into the processing container 2, for example, the following reaction occurs and excess fluorine radicals are absorbed and removed. It That is, F ^* + SO → SF ₆ ↑ + O ₂ ↑ (coefficient is arbitrary), and excessive C (carbon) in CF ₄ becomes C + O ₂ → CO ₂ ↑ and is exhausted.

Therefore, it is possible to suppress excessive fluorine radicals that lower the selection ratio, and to carry out etching with good vertical anisotropy. Moreover, in this example, S (sulfur) containing O (oxygen) but not F (fluorine) was used.
Since SO gas, which is a system gas, is used, excess C (carbon) reacts with O in SO to cause CO as described above.
It becomes ₂ (carbon dioxide) and is exhausted. Therefore, when used as a CFC-based gas mixed with a gas containing C (carbon), it is possible to prevent C from accumulating on the surface of the object to be processed and impeding anisotropic etching.

Moreover, since the control of such excess fluorine radical suppression can be performed by adjusting the flow rate of SO gas, for example, the corresponding mass flow controller 33.
It is possible to easily do this by controlling the.

The high frequency power applied to the upper electrode 21 and the susceptor 5 is
Since they are matched by the first matching unit 54 and the second matching unit 56, respectively, as shown in FIG. 4, it is possible to apply high frequency power having a normal sine wave without distortion. In this respect, in the device of this type having the conventional power split configuration, since the matching device is provided only on the primary side, matching is performed as shown in FIG. Was becoming. Therefore, there is a possibility that the distortion deteriorates the etching characteristics or makes the control difficult, and the desired etching process cannot be performed.

In this respect, in the plasma etching apparatus 1, the first matching box 54 and the second matching box 56 are provided on the secondary side, respectively.
Since it is provided, it is possible to apply high frequency power having a sinusoidal waveform without distortion as shown in FIG. Therefore, from this point as well, it is possible to perform the predetermined etching process. In this case, each of the first matching unit 54 and the second matching unit 56 may be configured to be controlled by a differential variable capacitor, for example.

The gas diffusion plate 26 used in the upper electrode 23 of the plasma etching apparatus 1 used in the above-mentioned embodiment is different from the conventional aluminum-based material, and as described above, carbon, glass carbon, ceramics, It is made of quartz or the like. Therefore, even if a chlorine-based gas such as CCl ₄ is used as the etching gas, it will not corrode.

Further, conventionally, a structure is adopted in which a plurality of diffusion plates having a large number of diffusion holes are used for uniform discharge, and therefore, it was complicated at the time of mounting and maintenance, but the plasma etching apparatus used in the above-mentioned embodiment. In 1,
Since the gas diffusion plate 26 of a porous body is used, a sufficient uniform discharge effect can be obtained by using only one of the gas diffusion plate 26, and the gas diffusion plate 26 can be fixed by a fixing member 27 such as a bolt. Therefore, mounting and maintenance are extremely easy.

Although CF ₄ gas was used as the gas for generating the etchant and SO was used as the gas for generating the component that absorbs and removes the excessive radical component in the above-mentioned embodiments, the present invention is not limited to these gases. It is not limited. For example, as a gas for generating the etchant, C _x F _y type halogenated carbon compounds that including the CF ₄ (so-called Freon gas), and further _{F 2, Cl 2, Br 2} , I 2, At 2, Cl 3 F, IC
l ₃ , ClF, ICl, BrF, BrF ₃ , BrF ₅ , I
F _5, halogen gas IF ₇ or the like, interhalogen compounds, H
Hydrogen halide such as F, HCl, HBr, HI, HAt, BF ₃ , BCl ₃ , B ₂ Cl ₄ , B ₄ Cl ₄ , BBr ₃ ,
Boron halide such as BI ₃ , B ₂ H ₆ (diborane), B ₄ H
It is possible to use boron hydride such as ₁₀ (tetraborane), B ₅ H ₉ , B ₅ H ₁₁ and B ₆ H ₁₀ and boron borohydride such as B ₂ H ₂ F ₄ .

On the other hand, as a gas for generating a component for absorbing and removing an excessive radical component, an S (sulfur) type gas containing no F (fluorine), for example, thionyls such as SOBr ₂ (thionyl bromide), CS ₂ , H ₂ S, N ₂ S ₂ , N
Sulfides such as ₄ S ₄ , As ₄ S ₄ , As ₂ S ₃ , P ₄ S ₇ , P ₂ S ₅ , SO, SO ₂ , SO ₃ , S ₂ O, S ₂ O ₃ , S ₂ O ₇ , S
It is possible to use a gas of sulfur oxide such as O ₄ .

In particular, like sulfur oxides such as SO ₂ , SO ₃ , S ₂ O, S ₂ O ₃ , S ₂ O ₇ , and SO ₄ including SO used in the examples, F (fluorine) is used. If an S (sulfur) -based gas that does not contain O (oxygen) is used, when mixed with a C _x F _y- based halogenated carbon compound (so-called Freon gas) such as CF ₄ , the excess C (Carbon) and O
Since it reacts with (oxygen) and becomes CO ₂ (carbon dioxide) and is exhausted, it is possible to prevent the carbon compound that inhibits anisotropic etching from accumulating on the surface of the object to be processed.

By the way, an annular focus ring 15 is arranged at the upper peripheral portion of the susceptor 5 in the processing container 2 of the plasma etching apparatus 1 used in this embodiment. , SiO
When it is made of (silicon monoxide), the following operational effects are obtained.

That is, as shown in FIG. 6, SiO easily forms SiO ₂ as an immovable body on the surface thereof. Then, when the silicon oxide film on the wafer W is etched, SiO _{2 on the} surface of the focus ring 15 is also etched at the same time to expose the internal SiO. Then, this SiO reacts with the above-mentioned F ^* (fluorine radical) to cause a reaction of SiO + F ^* → SiF ₄ + O ₂ ↑, and it is also possible to absorb and remove an excessive fluorine radical. Further, since the reaction product produced at that time is SiF ₄ , there is no possibility of contaminating the inside of the processing container. Moreover, SiO _2, which is an unmoving body, is Si at room temperature.
Since it is formed on the surface of O, even if the above-mentioned focus ring 15 is made of, for example, SiO, a dedicated heating means or the like is not required and the handling is easy. Other,
For example, even if the inner wall of the processing container 2 is made of SiO 2, the same effect can be obtained.

The apparatus used in the above-mentioned embodiments was a so-called parallel plate type plasma etching apparatus. However, the present invention is not limited to this, and other etching apparatuses such as magnetron RIE apparatus, An ECR etching device may be used. Of course, the object to be processed is not limited to the semiconductor wafer as described above, and the same effect can be obtained even if it is an LCD substrate, for example.

[0048]

According to the first aspect of the present invention, the radical gas that prevents the vertical anisotropy can be suppressed by the processing gas introduced into the processing container, so that anisotropic etching with an improved selection ratio can be realized. is there. Moreover, by controlling the flow rate of the processing gas, it is possible to easily control the suppression.

According to the second aspect, even if excess C (carbon) that prevents anisotropic etching is present in the processing gas, it can be removed, and from this point also the selection ratio is improved. Can be made.

[Brief description of drawings]

FIG. 1 is an explanatory view of a side surface of a plasma etching apparatus used when carrying out an embodiment of the present invention.

FIG. 2 is a perspective view of a gas diffusion plate used in an upper electrode of the plasma etching apparatus of FIG.

3 is an explanatory view of a vertical cross section of an upper electrode in the plasma etching apparatus of FIG.

4 is an explanatory diagram showing a waveform of a high frequency applied in the plasma etching apparatus of FIG.

FIG. 5 is an explanatory diagram showing a waveform of a high frequency applied in a conventional power split type plasma device.

FIG. 6 is an explanatory view of a vertical section when SiO is used for a focus ring in the plasma etching apparatus of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma etching apparatus 2 Processing container 5 Susceptor 21 Upper electrode 23 Diffusion hole 26 Gas diffusion plate 29 Gas introduction pipes 34, 35, 36 Processing gas supply source 45 Exhaust means 51 High frequency power supply 54 First matching box 55 Second matching box W Wafer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Masahiro Ogasawara 2-3-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo Within Tokyo Electron Co., Ltd. (72) Makoto Aoki 2-3-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo In Tokyo Electron Ltd. (72) Inventor Isamu Wakui 7-30-2, Sumiyoshi-cho, Fuchu-shi, Tokyo Inside Tokyo Electron FE Ltd.

Claims (2)

[Claims] 1. An etching method in which a processing gas is introduced into a processing chamber and a predetermined etching process is performed on an object to be processed in a plasma atmosphere, wherein at least the processing gas contains a fluorocarbon gas and F (fluorine). An etching method comprising: a mixed gas with an S (sulfur) -based gas that does not contain. 2. An etching method of introducing a processing gas into a processing chamber and subjecting an object to be processed to a predetermined etching treatment in a plasma atmosphere, wherein at least the processing gas contains a fluorocarbon gas and F (fluorine). A method for etching, comprising a mixed gas of an S (sulfur) -based gas containing O (oxygen) but not containing it.