JP3807598B2 - Etching method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an etching method.
[0002]
[Prior art]
For example, a semiconductor wafer (hereinafter referred to as a “wafer”) on which a semiconductor device such as an LSI is formed will be described as an example. An etching gas is introduced into a processing chamber that has been conventionally airtight, and high-frequency power is applied. Plasma is generated in the processing chamber, and an etching process for forming contact holes, for example, is performed on the wafer in the plasma atmosphere.
[0003]
This will be described based on, for example, etching of a silicon oxide film (SiO ₂ ). When etching is conventionally performed on a silicon oxide film formed on a wafer, an etching gas such as F (fluorine) such as CF _{4 is used.} ) Based gases, Cl (chlorine) based gases such as CCl _4, and F—Cl based gases such as CClF ₃ are often used.
Of the various gases, for example, CF ₄ , the silicon oxide film (SiO ₂ ) is removed by F ^* (fluorine radical) generated by dissociating gas molecules by plasma.
[0004]
Nowadays, with the high integration of devices, there is a demand for an etching method capable of ultra-fine processing corresponding to half micron and quarter micron. Therefore, for example, a contact hole needs to be formed to 0.35 μm or less. However, in order to form such a fine contact hole, it is necessary to realize anisotropic etching with a high selectivity in a high-density plasma atmosphere.
[0005]
However, under a high-density plasma atmosphere, the energy absorbed by the plasma is high, so the dissociation of gas molecules proceeds. As a result, for example, in the case of CF ₄ described above, excessive F ^* (fluorine radical) is generated. As a result, the selectivity is lowered and the etching tends to be isotropic.
[0006]
Therefore, it is necessary to remove the excess fluorine radicals by some means. Recently, however, it is easy to react with such fluorine radicals and disable them, for example, by a material such as Si (silicon), It has been proposed to constitute a member in the processing chamber such as an electrode plate.
[0007]
[Problems to be solved by the invention]
However, in such a method using Si alone as a member in the processing chamber, it is necessary to first heat the member itself to a high temperature of about 300 ° C. by appropriate heating means. In addition, as the number of treatments is repeated, the surface area of the member surface changes and the reaction surface area changes. As a result, the amount of reaction with fluorine radicals is not constant, and the important etching process itself varies from wafer to wafer. There is also a risk of coming.
Furthermore, maintenance is required every certain number of processing times, and throughput is also reduced.
[0008]
The present invention has been made in view of such a problem, and basically, an excess radical component that shifts to isotropic etching is absorbed and removed by a constant mixture gas, and anisotropic. The object is to improve the etching selectivity.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an etching method according to claim 1, wherein a processing gas is introduced into a processing chamber, and a predetermined etching process is performed on the silicon oxide film of the target object in a plasma atmosphere. In the etching method, the mixed gas of the gas containing C (carbon) and F (fluorine) and the gas containing S (sulfur) and O (oxygen) and not containing F (fluorine) is used as the processing gas. while using the S by adjusting the flow rate of the gas containing no one or include (sulfur) and O (oxygen) F (fluorine), dissociation of the C-containing gas (carbon) and F (the fluorine) It is characterized by controlling the suppression by reacting an excess fluorine radical generated by the reaction with a gas containing S (sulfur) and O (oxygen) and not containing F (fluorine).
[0010]
In the etching method, the plasma atmosphere is generated by applying high-frequency power to an upper electrode and a susceptor provided in the processing container, and the high-frequency power is separated from the processing container through a transformer. Matching may be performed with respect to the waveform on the secondary side supplied by the high frequency power source on the primary side and via the transformer.
[0011]
Examples of the gas containing carbon and fluorine in the present invention include CxFy-based halogenated carbon compound gases such as CF _{4 described} above .
[0012]
The gas containing S (sulfur) and O (oxygen) and not containing F (fluorine) is, for example, thionyls such as SOBr ₂ or SO, SO ₂ , SO ₃ , S ₂ O, S ₂ O _3. , S ₂ O ₇ , SO _{4 and} other sulfur oxide gases.
[0013]
In the present invention, the former gas containing C (carbon) and fluorine functions as a so-called reaction gas, and causes a dissociation reaction in plasma to generate an etchant such as a radical component for performing etching.
On the other hand, in the latter S (sulfur) -based gas containing S (sulfur) and O (oxygen) and not containing F (fluorine), dissociation of the reaction gas proceeds and an excessive radical component is generated. Sometimes it reacts with this excess radical component to remove it.
[0014]
Therefore, excessive state of generation of the radical components, i.e. depending on the degree dissociation of the reactant gases, for example, by a mass flow controller, not including the latter S and (sulfur) O (oxygen) and a and F (fluorine) S ( By controlling the flow rate of the (sulfur) -based gas, it is possible to suppress anisotropic radical components, improve the etching selectivity, and perform anisotropic etching with increased vertical anisotropy.
[0015]
Incidentally, in view of the functions of the respective gas, the process gas introduced into the processing chamber in actual etching process is not impeded by a combination of inert gases and the like such as other example N _2, Ar gas.
[0016]
When an S (sulfur) -based gas not containing F (fluorine) and containing O (oxygen) is used as in the present invention , this O (oxygen) reacts with, for example, excess C (carbon) in the processing gas. do it,
C + O ₂ → CO ₂ ↑
And exhaust it.
Therefore, it is possible to remove excess carbon that hinders anisotropic etching in the processing gas.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 schematically shows a cross section of a plasma etching apparatus 1 used for carrying out the present embodiment. The electrode plate is configured as a so-called parallel plate RIE apparatus in which the electrode plates face each other in parallel.
[0018]
The plasma etching apparatus 1 includes a processing container 2 formed in a cylindrical or rectangular shape made of, for example, aluminum whose surface is anodized with anodization, and the processing container 2 is grounded.
A substantially cylindrical shape for placing an object to be processed, for example, a semiconductor wafer (hereinafter referred to as “wafer”) W through an insulating plate 3 made of ceramic or the like at the bottom of the processing chamber formed in the processing container 2. The susceptor support 4 is accommodated, and a susceptor 5 constituting a lower electrode is provided above the susceptor support 4. In the present embodiment, the case where the silicon oxide film (SiO ₂ ) on the wafer W having a silicon substrate is etched will be described.
[0019]
A refrigerant chamber 6 is provided in the susceptor support 4, and a temperature adjusting refrigerant such as liquid nitrogen can be introduced into the refrigerant chamber 6 via a refrigerant introduction pipe 7. The refrigerant circulates in the refrigerant chamber 6, and the cold heat generated during this period is transferred from the refrigerant chamber 6 to the wafer W via the susceptor 5, thereby cooling the processing surface of the wafer W to a desired temperature. Is possible.
For example, when liquid nitrogen as described above is used as the refrigerant, nitrogen gas generated by the nucleate boiling is discharged out of the processing chamber 2 through the refrigerant discharge pipe 8.
[0020]
The susceptor 5 is formed into a convex disk shape at the center of the upper surface, and an electrostatic chuck 11 having substantially the same shape as the wafer W is provided thereon. The electrostatic chuck 11 has a configuration in which a conductive layer 12 is sandwiched between two polymer polyimide films, and a DC high-voltage power supply installed outside the processing container 2 with respect to the conductive layer 12. 13, by applying a DC high voltage of 1.5 kV, for example, the wafer W placed on the upper surface of the electrostatic chuck 11 is attracted and held at that position by Coulomb force.
[0021]
An annular focus ring 15 is disposed at the upper peripheral 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 reactive ions, and is configured so that the reactive ions generated by the plasma are effectively incident only on the wafer W inside.
[0022]
The focus ring 15 is made of, for example, SiO (silicon monoxide), so that it can be reacted with fluorine radicals and removed as will be described later.
[0023]
Above the susceptor 5, an upper electrode 21 is supported on the upper portion of the processing vessel 2 via an insulating material 22 at a position facing the susceptor 5 in parallel and spaced apart by about 15 to 20 mm therefrom. Has been.
[0024]
The upper electrode 21 has a number of diffusion holes 23 on the surface facing the susceptor 5, for example, an electrode plate 24 made of SiC or amorphous carbon, and is positioned in parallel to the electrode plate 24 and is hollow between the two. For example, a support plate 25 made of aluminum with an alumite oxide treatment, and a gas diffusion plate 26 is provided on the upper surface of the electrode plate 24.
[0025]
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 material of 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 materials such as ceramics or quartz. However, the former conductive material is preferable because it has the same potential as that of the electrode plate 24, and thus there is no possibility of abnormal discharge.
[0026]
As shown in FIG. 3, a gas introduction port 28 is provided in the center of the support plate 25 in the upper electrode 21. Further, as shown in FIG. 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 branched into three parts via a valve 32 and a mass flow controller 33. To the corresponding process gas supply sources 34, 35, 36, respectively.
In the present embodiment, the processing gas supply source 34 is set to supply CF ₄ gas, the processing gas supply source 35 to SO gas, and the processing gas supply source 36 to N ₂ gas.
[0027]
An exhaust pipe 41 is connected to the lower part of the processing container 2, and the exhaust pipe 45 of the load lock chamber 43 adjacent to the processing container 2 via a gate valve 42 and an exhaust means 45 such as a turbo molecular pump. And is configured to be able to be evacuated to a predetermined reduced pressure atmosphere.
Then, the wafer W, which is an object to be processed, is loaded and unloaded between the processing container 2 and the load lock chamber 43 by a transfer means 46 such as a transfer arm provided in the load lock chamber 43. It is configured.
[0028]
The power unit in the plasma etching apparatus 1 has a so-called power split configuration in which a high-frequency power source is separated from the processing container 2.
That is, for example, the high frequency power source 51 that oscillates a high frequency of 13.56 MHz is installed on the primary side of the transformer unit 52 configured by an induction coil or the like, and further on the secondary side of the transformer coil such as the induction coil, A slide controller 53 to be grounded is provided.
[0029]
The secondary side of the transformer 52 is connected to the electrode plate 24 of the upper electrode 21 via the first matching unit 54 and the blocking capacitor 55, the second matching unit 56 and the blocking capacitor 57, respectively. Each is connected to the susceptor 5, and is configured to perform matching on the waveform on the secondary side, respectively, and apply high-frequency power that is 180 ° out of phase to the upper electrode 21 and the susceptor 5. .
[0030]
The plasma etching apparatus 1 for carrying out the present embodiment is configured as described above. Next, its operation and the like will be described. First, after the gate valve 42 is opened, the wafer W that is the object to be processed is opened. Then, it is carried into the processing container 2 from the load lock chamber 43 by the conveying means 46 and placed on the electrostatic chuck 11. The wafer W is attracted and held on the electrostatic chuck 11 by application of the high-voltage DC power supply 13. After that, after the conveying means 46 is retracted into the load lock chamber 43, the processing container 2 is evacuated by the exhaust means 45.
[0031]
On the other hand, the valve 32 is opened and the flow rate is adjusted by the mass flow controller 33, while the CF ₄ gas is supplied from the processing gas supply source 34, the SO gas is supplied from the processing gas supply source 35, the gas supply pipe 31, and the gas introduction It is introduced into the hollow portion of the upper electrode 23 through the tube 29 and the gas inlet 28.
Further, from this hollow portion, the mixed gas of the CF ₄ gas and SO gas is discharged to the wafer W through the gas diffusion plate 26 and the diffusion hole 23. As shown in FIG. The gas diffusion plate 26 is made of a porous material, and is combined with the configuration of the plurality of diffusion holes 23 serving as direct discharge ports, so that the gas diffusion plate 26 is discharged evenly onto the wafer W. .
[0032]
Then, after the pressure in the processing container 2 is set and maintained at, for example, 10 mTorr, the high frequency power source 51 is operated, and the output adjustment is performed by the slide controller 53 of the transformer 52, while the upper electrode 21 and the susceptor 5 are applied. On the other hand, a high frequency power having a phase difference of 180 ° is applied, plasma is generated between the upper electrode 21 and the susceptor 5, and the wafer W is caused by radical components generated by dissociation of the introduced CF ₄ gas. Is subjected to predetermined etching.
[0033]
At this time, CF ₄
・ CF ₃ + F ⁻
CF ₃ ^- + · F
CF ₃ ⁺ + F ⁻
CF ₃ ⁺ + F + e ⁻
In this way, the dissociation takes place in multiple stages, and F ⁻ → F ^* + e ^−, and this F ^* (fluorine radical) etches SiO _{2 on the} surface of the wafer W.
[0034]
However, if the dissociation described above proceeds to the final stage and fluorine radicals are generated excessively, the vertical anisotropy of etching is impaired and the selectivity is lowered, resulting in isotropic etching as a whole. End up.
[0035]
However, in the present embodiment, the SO ₄ gas is mixed with the CF ₄ gas and introduced into the processing container 2, so that, for example, the following reaction occurs, and excess fluorine radicals are absorbed and removed. That is,
F ^* + SO → SF ₆ ↑ + O ₂ ↑ (coefficient is arbitrary)
And the excess C (carbon) in CF ₄ is
C + O ₂ → CO ₂ ↑
And exhausted.
[0036]
Therefore, excessive fluorine radicals that reduce the selectivity can be suppressed, and etching with good perpendicular anisotropy can be performed.
Moreover, in this embodiment, since SO gas, which is an S (sulfur) -based gas not containing F (fluorine) but containing O (oxygen), is used, as described above, excess C (carbon) is converted into SO. It reacts with O in the inside and becomes CO ₂ (carbon dioxide) and is exhausted. Accordingly, when mixed with a gas containing C (carbon) as a chlorofluorocarbon-based gas, it is possible to prevent C from depositing on the surface of the object to be processed and inhibiting anisotropic etching.
[0037]
Moreover, since the control of the excessive fluorine radical suppression can be performed by adjusting the flow rate of the SO gas, for example, this can be easily achieved by the control of the corresponding mass flow controller 33.
[0038]
Since the high frequency power applied to the upper electrode 21 and the susceptor 5 is matched by the first matching unit 54 and the second matching unit 56 on the secondary side, as shown in FIG. It is possible to apply high-frequency power having a normal sine wave without distortion.
In this respect, in this type of apparatus having a conventional power split configuration, matching is performed with a matching unit provided only on the primary side, so that a substantially lumped waveform having distortion as shown in FIG. It was. For this reason, there is a possibility that the etching characteristics deteriorate due to the distortion or that the desired etching process cannot be performed due to difficulty in control.
[0039]
In this regard, since the plasma etching apparatus 1 includes the first matching unit 54 and the second matching unit 56 on the secondary side, respectively, high-frequency power having a sine waveform without distortion as shown in FIG. 4 is applied. It is possible to make it. Therefore, a predetermined etching process can be performed also from this point.
In this case, the first matching unit 54 and the second matching unit 56 may be configured to be controlled by a differential variable capacitor, for example.
[0040]
The gas diffusion plate 26 used in the upper electrode 23 of the plasma etching apparatus 1 used in the above-described embodiment is different from the conventional aluminum-based material, and as described above, carbon, glass carbon, ceramics, quartz, etc. It consists of Therefore, even when a chlorine-based gas such as CCl ₄ is used as an etching gas, it does not corrode.
[0041]
Conventionally, a plurality of diffusion plates having a large number of diffusion holes are used for uniform discharge, which is complicated during installation and maintenance. In the plasma etching apparatus 1 used in the above embodiment, however, Since a porous gas diffusion plate 26 is used, a sufficient uniform discharge effect can be obtained even by using only one of them, and it is possible to attach by fixing with a fixing member 27 such as a bolt. . Therefore, installation and maintenance are extremely easy.
[0042]
In the above-described embodiment, CF ₄ gas is used as a gas for generating an etchant, and SO is used as a gas for generating a component for absorbing and removing excess radical components. However, the present invention is of course limited to these gases. It is not something.
For example, as a gas for generating an etchant, it is possible to use CxFy-based halogenated carbon compounds such as CF ₄ .
[0043]
On the other hand, as a gas for generating a component that absorbs and removes excess radical components, S (sulfur) -based gas not containing F (fluorine), for example, thionyls such as SOBr ₂ (thionyl bromide), CS ₂ , H ₂ S, N ₂ S ₂ , N ₄ S ₄ , As ₄ S ₄ , As ₂ S ₃ , P ₄ S ₇ , sulfides such as P ₂ S ₅ , SO, SO ₂ , SO ₃ , S ₂ O, S ₂ It is possible to use a sulfur oxide gas such as O ₃ , S ₂ O ₇ or SO ₄ .
[0044]
Moreover, it does not contain F (fluorine) like sulfur oxides such as SO ₂ , SO ₃ , S ₂ O, S ₂ O ₃ , S ₂ O ₇ , SO ₄ such as SO used in the embodiment. If an S (sulfur) -based gas containing O (oxygen) is used, when mixed with a CxFy-based halogenated carbon compound (so-called freon gas) such as CF ₄ , 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 growing on the surface of the object to be processed.
[0045]
By the way, an annular focus ring 15 is arranged at the upper peripheral edge of the susceptor 5 in the processing container 2 of the plasma etching apparatus 1 used in the present embodiment. The material of the focus ring 15 is, for example, SiO. When composed of (silicon monoxide), the following effects are obtained.
[0046]
That is, as shown in FIG. 6, SiO easily forms passive SiO ₂ on the surface thereof. Then, when the silicon oxide film is etched on the wafer W, the SiO _{2 on the} surface of the focus ring 15 is simultaneously etched, and the internal SiO is exposed.
Then, this SiO reacts with the above-mentioned F ^* (fluorine radical),
SiO + F ^* → SiF ₄ + O ₂ ↑
It is possible to absorb and remove excess fluorine radicals. Further, since the product reaction product at that time is SiF ₄ , there is no possibility of contaminating the inside of the processing container. Moreover, since the non-moving body SiO ₂ is formed on the surface of SiO at room temperature, for example, even if the focus ring 15 is made of SiO, no special heating means is required, and handling is easy. is there. In addition, for example, the same effect can be obtained even if the inner wall of the processing container 2 is made of SiO.
[0047]
The apparatus used in the above embodiment is a so-called parallel plate type plasma etching apparatus. However, the present invention is not limited to this, and other etching apparatuses such as a magnetron RIE apparatus and an ECR etching apparatus are used. An apparatus 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]
【The invention's effect】
According to the present invention, since the radical component that hinders the vertical anisotropy can be suppressed by the processing gas introduced into the processing container, anisotropic etching with improved selectivity can be realized. In addition, the suppression can be easily controlled by controlling the flow rate of the processing gas. Even if excess C (carbon) that hinders anisotropic etching is present in the processing gas, it can also be removed, and the selectivity can be improved from this point.
[Brief description of the drawings]
FIG. 1 is an explanatory view of a side surface of a plasma etching apparatus used in carrying out an embodiment of the present invention.
2 is a perspective view of a gas diffusion plate used in an upper electrode in the plasma etching apparatus of FIG. 1. FIG.
3 is an explanatory view of a longitudinal section of an upper electrode in the plasma etching apparatus of FIG. 1. 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 apparatus.
6 is an explanatory view of a longitudinal section when SiO is used for the focus ring in the plasma etching apparatus of FIG. 1;
[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 device 55 Second matching device W Wafer

Claims (6)

In an etching method in which a processing gas is introduced into a processing chamber, and a predetermined etching process is performed on the silicon oxide film of the object to be processed in a plasma atmosphere.
As the processing gas, the use a gas containing C (carbon) and F (fluorine), a mixed gas of gas containing no S (sulfur) and O (oxygen) and a and F (fluorine), wherein S (sulfur) and O (oxygen) and by adjusting the flow rate of the gas containing no one or contain F (fluorine), excess fluorine produced by dissociation reaction of the gas containing the C (carbon) and F (fluorine) An etching method comprising controlling reaction by reacting a gas containing radicals, S (sulfur) and O (oxygen) and not containing F (fluorine). The gas containing C (carbon) and F (fluorine) is a gas of a CxFy-based halogenated carbon compound,
The gas containing S (sulfur) and O (oxygen) and not containing F (fluorine) is thionyl such as SOBr ₂ , or SO, SO ₂ , SO ₃ , S ₂ O, S ₂ O ₃ , S _2. The etching method according to claim 1, wherein the etching method is a sulfur oxide gas such as ₂ O ₇ or SO ₄ . The etching method according to claim 2, wherein the CxFy-based halogenated carbon compound is CF ₄ . The plasma atmosphere is generated by applying high frequency power to an upper electrode and a susceptor provided in a processing container,
The high-frequency power is supplied by a primary-side high-frequency power source separated from the processing container via a transformer, and each of the secondary-side waveforms via the transformer is matched. The etching method according to claim 1, wherein: The etching method according to claim 4, wherein the high frequency power applied to the upper electrode and the susceptor is 180 degrees out of phase . The etching method according to claim 1, wherein the processing gas further contains N ₂ or an inert gas .

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