JP2010118418A - Method of cleaning plasma processing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of cleaning a plasma processing device by which the surface of a plasma processing chamber is efficiently cleaned to improve throughput, and further to provide a method of removing a resist mask formed on a low-dielectric-constant film (Low-k film) being a workpiece simultaneously with the cleaning. <P>SOLUTION: As a method for improving the throughput, a plasma cleaning using CO<SB>2</SB>gas is carried out in a state wherein the low-dielectric-constant film (Low-k film) etched by using CxFx-based gas is mounted on a lower electrode as it is to remove deposits deposited on the surface of the plasma processing chamber. At this time, the resist mask patterned on the Low-k film can be removed simultaneously, so a processing time can be greatly shortened. Further, an electrode surface where a wafer is installed is not exposed to plasma during the cleaning, so that the electrode is prevented from deteriorating. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a plasma processing apparatus, and more particularly to a plasma cleaning method in a plasma processing chamber.

  In recent years, the device structure of semiconductor elements has become increasingly complex, and high speed processing and small number of processes are required in these manufacturing processes. That is, with the demand for miniaturization, for example, a width between wirings of about 0.1 μm or less, a semiconductor integrated device has a relatively large capacitance between adjacent wirings. When a conventional silicon oxide film is used as an insulating material between the wirings of such devices, it is not possible to enjoy the benefits of high-speed transistors obtained by miniaturization. For this reason, a material having a low dielectric constant (k value), for example, SiOC, is employed as the inter-wiring insulating material.

  These materials having a low dielectric constant (k value) are mainly used in combination with copper, which is a wiring material, and are formed by a method called dual damascene. Therefore, a step of etching the insulating film is required. The dual damascene formation process includes, for example, a process of obtaining a predetermined shape by processing and transferring a groove shape to a porous insulating film using a hard mask on a sample whose hole shape has been processed in the previous step. Such a technique is disclosed in Patent Document 1, for example.

  In plasma processing of a semiconductor substrate, there are many processes in which deposition of reaction products (also referred to as deposits) occurs on the surface in a plasma processing chamber (hereinafter referred to as a processing chamber). For example, when etching the above-described film types and the like, CxFx-based gas is used, and a CF-based deposit as a reaction product adheres and deposits on the surface of the processing chamber. When this deposit peels and becomes a foreign material and adheres on the substrate to be processed, a defect is caused in the fine structure, which becomes a big problem.

  In order to prevent this problem, the plasma cleaning is performed every certain number of plasma treatments, for example, 1 sheet, 25 sheets, or 100 sheets, or every day, and the accumulation of deposits is suppressed. The generation of foreign matter is delayed.

  Further, as a deposit removal method, the processing chamber may be opened to the atmosphere and the deposit may be wiped off using water or the like. However, this method takes a very long time to restore the apparatus.

  For this reason, there is a desire to remove the plasma processing chamber by plasma cleaning that does not open to the atmosphere. This plasma cleaning is disclosed in Patent Document 2.

JP-A-9-115878 JP-A-8-319586

  Conventionally, in an apparatus for plasma processing an object to be processed such as a semiconductor substrate, plasma cleaning is performed in order to remove substances deposited in the processing chamber during the plasma processing. In order to improve the operating rate of the plasma processing apparatus, There was a demand to increase the efficiency of this plasma cleaning and shorten the time.

  Plasma cleaning includes a method using a dummy wafer (Si substrate) and a method using a waferless method without using a dummy wafer. The former method has a problem that throughput is lowered because it takes time to transfer a dummy wafer after processing a patterned wafer (for example, a semiconductor product wafer).

  In the latter method, since plasma is generated on the lower electrode without cleaning the wafer and the surface in the processing chamber is cleaned, the lower electrode may be damaged. For example, a decrease in adsorption force occurs due to a change in the resistance value / surface state of the electrode.

  Therefore, plasma cleaning without damage to the lower electrode was put into practical use by wafer screening without using a dummy wafer (Si substrate).

  An object of the present invention is to provide a cleaning method for a plasma processing apparatus capable of efficiently cleaning the processing chamber surface of the plasma processing chamber and improving the throughput. It is another object of the present invention to provide a cleaning method for a plasma processing apparatus capable of removing (ashing) a patterned resist mask on a low dielectric constant film (Low-k film) which is an object to be processed simultaneously with cleaning.

  As a technique to improve the throughput, the sample of the low dielectric constant film (Low-k film) etched using CxFx gas is plasma-cleaned with it placed on the lower electrode as it is, and it adheres to the surface of the plasma processing chamber Remove the deposited material.

O ₂ gas, which has been used as a conventional plasma cleaning, reacts with C (carbon atoms) contained in the etched low dielectric constant film (Low-k film) and desorbs, so the film quality changes and the dielectric constant is high. (Also referred to as film damage) occurs.

Therefore, by selecting carbon dioxide-containing CO ₂ gas as the cleaning gas, reaction with the low dielectric constant film (Low-k film) can be suppressed, film damage can be reduced, and patterning is performed on the Low-k film. The resist mask can be removed.

  Hereinafter, an embodiment of the present invention will be described. First, the configuration of a plasma etching apparatus to which the sample surface treatment of the present invention is applied will be described.

  FIG. 1 is a plan view of a plasma etching apparatus having a single wafer type multi-chamber used in the present invention. 1, this apparatus includes a vacuum transfer chamber 20 provided with a transfer robot 21, two or more processing chambers 1a and 1b interposed by gates 24a and 24b, load lock chambers 22a and 22b, and an atmospheric loader unit. 25 and a cassette mounting portion 23 on which a wafer cassette 26 is mounted. Processing the same processes performed in the processing chambers 1a and 1b in parallel is also configured so that different processes in the processing chambers 1a and 1b can be sequentially processed.

  Since the processing chamber 1a and the processing chamber 1b of this apparatus have substantially the same structure, the details of the processing chamber 1a will be described with reference to FIG.

  This apparatus is a UHF plasma etching apparatus that forms plasma using UHF (Ultra High Frequency) and a magnetic field.

  In FIG. 2, the processing chamber 1 a is a vacuum vessel, and a coil 9 for generating a magnetic field for electron cyclotron resonance (ECR) is installed around the inner wall of the processing chamber 1 a, for example, at 30 ° C. Temperature controlled. The substrate 13 to be processed is placed on the substrate electrode 18 provided with the electrostatic chuck 7. A DC power supply (not shown) is connected to the electrostatic chuck 7 so that the substrate 13 to be processed can be attracted to the electrostatic chuck 7. A substrate bias power supply 11 is connected to the substrate electrode 18 via the matching unit 10 so that a high frequency bias can be applied to the substrate 13 to be processed.

Is a conventional main etching gas _{CF 4, CHF 3, CH 2} F 2 or the like _{chlorofluorocarbons, C 2 F 6, C 3} F 8, C 4 F 6, C 4 F 8, C 5 F 8 or the like of the C / Additive gases with high F ratio, inert gases such as Ar, Xe, Kr, etc. are supplied from the gas cylinders 19-1, 19-2, 19-3, respectively, and the flow rate is controlled by the mass flow controller 12 and connected to the process gas source. Through the gas supply pipe 14, the gas is introduced into the processing chamber 1 a from a gas supply plate 8 made of silicon or glassy carbon having many holes.

  The antenna electrode 2 is disposed on the upper side of the gas supply plate 8, and power is supplied from the coaxial terminal 16 to the antenna electrode 2 from the high frequency power source 3 and the high frequency power source 5 through the matching circuit 4 and the matching circuit 6. The high frequency is radiated from the dielectric window 15 around the antenna electrode 2 and a resonance electric field is introduced into the processing chamber 1a through the gas supply plate 8, and the processing target substrate 13 is etched by the generation of plasma. The

  Below the processing chamber 1a, vacuum evacuation means (not shown) consisting of a turbo molecular pump (TMP) and pressure regulating means (not shown) consisting of an auto pressure controller (APC) are arranged, while maintaining a predetermined pressure, The etching gas after processing is discharged from the processing chamber 1a.

  Next, referring to FIG. 3, the film configuration, device process, and etching flow will be described.

  FIG. 3A shows an initial film structure, and the film structure includes an ArF resist mask 302, a silicon oxide film 303, an inorganic film (low-k film) 304, and a Si substrate 305 from the top. Next, the etching flow will be described. 3B and 3C, the silicon oxide film 303 and the inorganic film (low-k film) 304 are etched using the ArF resist mask 302 as a mask. At that time, an additive gas having a high C / F ratio such as CxFx is often used in order to increase the selection ratio with the mask. FIG. 3D shows the removal (ashing) process of the ArF resist mask 302. After the etching process, the ArF resist mask 302 is removed (ashing) using another vacuum processing chamber in the same apparatus or another apparatus. )It is carried out.

  Next, a film damage generation mechanism will be described with reference to FIG.

  FIG. 4A shows a processed shape after the etching process. 4A, the film structure is composed of an ArF resist mask 402, a silicon oxide film 403, an inorganic film (low-k film) 404, and a Si substrate 405 from the top.

FIG. 4B shows a case where processing is performed consistently up to removal (ashing) of the ArF resist mask 402 without carrying out the substrate to be processed from the processing chamber after the etching processing in order to shorten the device process. This is a film damage generation mechanism. Considering, for example, the case of O ₂ gas used in plasma cleaning as the gas species, O radicals react with (1) CF-based deposits attached to the surface of the processing chamber (plasma cleaning), and (2) ArF. Reaction (ashing) with the resist mask 402, (3) Reaction (film damage) with the side surface of the inorganic film (low-k film) 404 after the etching process.

The above (3) will be described. The C-based component in the inorganic film (Low-k film, eg, SiOC film) 404 is extracted by O radicals attached to the side surface of the inorganic film (Low-k film) 404 to be converted into SiO _{2 and} dielectric. A higher rate is a factor that changes device characteristics.

In this evaluation, the SiO ₂ film thickness was taken as the film damage amount, and the gas type was examined. A method for measuring the film damage amount will be described. When HF cleaning (hydrofluoric acid cleaning) is performed, the inorganic film (Low-k film) 404 (SiOC film) with good film quality cannot be cut, but the portion where the C component is extracted and converted to SiO ₂ reacts with HF and is cut off. Using this characteristic, the processed substrate after removal of the ArF resist mask 402 was compared with before and after being immersed in 0.10% HF for 20 s, and the film damage amount of the inorganic film (Low-k film) 404 (from the cross-sectional SEM photograph ( Formula (1)) is calculated.

That is, in FIG.
Film damage amount = D−C (1)
(C: Dimensions after etching treatment D: Dimensions after HF cleaning)
It becomes.

Next, the gas type comparison of the film damage amount will be described using FIG. The film damage amount when treated with O ₂ gas conventionally used in plasma cleaning was 22.7 nm, whereas the film damage amount treated with CO ₂ gas of the present invention was 12.3 nm. From this result, it can be seen that the CO ₂ gas can suppress film damage as compared with the O ₂ gas and can remove (ash) the ArF resist mask 402.

Therefore, in order to actually confirm the effect as plasma cleaning, the reaction product C ₂ in the plasma (wavelength: 516.5 nm) formed by reacting the CF deposit deposited on the surface of the processing chamber with the cleaning gas. The amount of deposits deposited on the surface of the processing chamber was confirmed. Here, it is assumed that the CF-based deposit attached to the processing chamber can be removed by stabilizing the light emission level of C ₂ (no fluctuation).

FIG. 6 shows a comparison of C ₂ emission intensity under each condition. In FIG. 6, C ₂ emission in O ₂ gas plasma cleaning after etching by the conventional method is stable in 3 s from the start of discharge. This indicates that deposits adhered to the surface of the processing chamber during the etching process are removed and the state before the etching process is restored.

Next, the case where discharge is performed with a wafer with a resist using O ₂ gas will be described. The time required for resist removal is 16 s from the result calculated from the remaining film of the ArF resist mask 402 and the ArF resist rate (ashing speed) of O ₂ gas separately measured, but the change in C ₂ emission is It is stable in 8s from the start of discharge. Further, as a result of performing O ₂ plasma cleaning after removing the resist, no change was observed in C ₂ emission. From this, it can be said that the deposit deposited in the processing chamber can be removed within the time required for resist removal, and plasma cleaning can be performed. However, when O ₂ gas is used in ashing, film damage occurs in SiOC as described above.

Next, the case where discharge is performed with a wafer with a resist using CO ₂ gas will be described. The resist removal time needs 23 s from the result calculated from the remaining film of the ArF resist mask 402 and the ArF resist rate (ashing speed) of CO ₂ gas measured separately, and the change in C ₂ emission is 15 s from the start of discharge. And stable. In addition, when O ₂ plasma cleaning was performed after removing the resist with CO ₂ gas, no C ₂ emission change was observed. From this, it can be said that the deposit deposited in the processing chamber can be removed within the time required for resist removal, and plasma cleaning can be performed. Further, as described above, it has been found that CO ₂ gas discharge can reduce film damage.

From the above results, it is understood that plasma cleaning in the processing chamber can be performed while suppressing film damage by performing discharge with a wafer with a resist using CO ₂ gas.

FIG. 7 shows a processing time comparison under each condition. In FIG. 7, in the conventional method, after the product wafer is etched, the product wafer is once taken out of the chamber and the chamber is cleaned. The product wafer that has been subjected to the etching process is collected from the etching processing apparatus, transferred to a resist removal (ashing) processing apparatus, and then subjected to an ashing process. When the time required for product wafer processing in this conventional method is 100%, the time required per product is reduced by 50% when O ₂ gas cleaning is applied and 55% when CO ₂ gas cleaning is applied. be able to.

  This is because, by removing the resist in the same chamber, plasma cleaning can be performed in a state where it is placed on the lower electrode without carrying out the wafer after the etching process, so that the wafer transfer time after the etching process can be omitted. One reason is that the subsequent resist removal processing can be omitted by performing processing chamber cleaning with a wafer with resist.

  In the conventional method, since the ashing process is performed in another chamber (another apparatus), it takes time for wafer transfer and resist removal processing. However, according to the present invention, the resist removal process is performed in the same chamber and plasma. Processing can be performed in parallel during cleaning, and processing time can be greatly reduced.

  Furthermore, one of the features of the present invention is that after a patterned wafer (Low-k film) is processed, plasma cleaning can be performed in a state where the wafer is continuously placed on the lower electrode. As a result, the lower electrode is not exposed to plasma, preventing physical deterioration due to ions generated by plasma potential, etc., and deterioration of the lower electrode surface due to chemical reaction due to gas, etc., and extending the electrode replacement cycle. It becomes. Thus, it can be said that the replacement period of the lower electrode can be extended and the maintenance cost of the apparatus can be reduced.

  As described above, according to the present embodiment, the plasma cleaning can be performed without replacing the wafer, so that the throughput can be improved. At the same time, the lower electrode on which the wafer is installed is not exposed to the plasma during the cleaning, so that Deterioration of the electrode can be suppressed.

  Further, since the resist mask patterned on the low dielectric constant film (Low-k film) can be removed, the device process can be shortened.

It is drawing explaining the structure of the plasma etching apparatus in this invention. It is sectional drawing explaining the structure of the process chamber in this invention. It is a device process in this one Example, and an etching flow figure. It is a film damage generation | occurrence | production mechanism figure in a present Example. It is a gas type comparison figure of the film | membrane damage amount in a present Example. A C ₂ emission intensity comparison diagram under the situation in the present embodiment. It is a throughput comparison figure in each situation in this one Example.

Explanation of symbols

1a, 1b Processing chamber 2 Antenna electrode 3, 5 High frequency power supply 4, 6 Matching circuit 7 Electrostatic chuck 8 Gas supply plate 9 Coil 10 Matching device 11 Substrate bias power supply 12 Mass flow controller 13 Substrate 14 Gas supply tube 15 Dielectric window 16 Coaxial terminal 17 Focus ring 18 Substrate electrode 19 Gas cylinder 20 Vacuum transfer chamber 21 Transfer robot 22a, 22b Load lock chamber 23 Cassette mounting portion 24a, 24b Gate 25 Atmospheric loader portion 26 Wafer cassette 302, 402 ArF resist mask 303 Silicon oxide film 304,404 Inorganic film (Low-k film)
305,405 Si substrate 403 Silicon oxide film

Claims (4)

A processing chamber, a high-frequency power source for forming plasma in the processing chamber, a substrate electrode provided below the processing chamber on which a substrate to be processed can be placed, and a substrate bias power source for applying a bias to the processing substrate A plasma processing apparatus cleaning method for etching a multilayer film using ArF resist on the substrate to be processed using a CxFx-based gas as an etching gas.
A cleaning method for a plasma processing apparatus, wherein after the substrate to be processed is etched, cleaning is performed by introducing CO ₂ gas into the processing chamber to remove reaction products adhering to the surface of the processing chamber. In the cleaning method of the plasma processing apparatus according to claim 1,
The substrate to be processed is patterned with an ArF resist as a first film, a silicon oxide film as a second film, an inorganic film (Low-k film) as a third film, and a Si substrate as a fourth film. A plasma processing apparatus cleaning method comprising a wafer (product wafer). In the cleaning method of the plasma processing apparatus of Claim 2,
A cleaning method for a plasma processing apparatus, characterized in that the etching gas is etched with plasma mainly composed of a gas composed of C and F, and cleaning is continuously performed without carrying out the processed wafer. . In the cleaning method of the plasma processing apparatus of Claim 2,
A plasma processing apparatus cleaning method, wherein the ArF resist mask, which is the first film, is removed (ashed) simultaneously with the plasma cleaning.

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