JP2008244291A - Plasma treatment apparatus and quartz member used for same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize plasma treatment by suppressing a change in plasma treatment performance due to a remaining matter on the surface of a quartz component caused by repeated plasma treatment in a plasma treatment apparatus. <P>SOLUTION: An element hardly removed from a quartz-made member to be used for plasma treatment is mixed in advance to the quartz-made member provided in the plasma treatment apparatus, thereby allowing the plasma treatment environment in replacing the quartz-made member to become a plasma treatment environment having substantially less change, and thus, the performance of the plasma treatment apparatus is stabilized. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to plasma processing having a plasma generation mechanism and a quartz member used in the plasma processing apparatus, and more particularly to a semiconductor manufacturing apparatus suitable for fine processing of semiconductor elements and a quartz member used in the plasma processing apparatus.

  In the step of subjecting the workpiece to plasma treatment, in order to obtain a desired treatment result, it is important to appropriately control the composition of radicals (chemically reactive atoms and molecules) and ions in the plasma. That is, it can be said that the processing accuracy of plasma processing is determined by the controllability of radicals and ions.

  Examples of such plasma treatment include a step of plasma etching a semiconductor wafer, a glass substrate of a liquid crystal panel, and the like. In such a process, as processing dimensions of semiconductor elements are miniaturized year by year, requirements for processing accuracy are becoming stricter. In particular, in semiconductor logic devices, even a disorder of processing of only 1 nanometer has been regarded as defective. Under such circumstances, high precision is also required for radical / ion composition control.

  However, in the plasma processing apparatus, the processing performance of the apparatus changes with time even though the plasma processing conditions are kept constant, and the workpiece may eventually become defective. One of the causes of such problems is various atoms and molecules remaining in the plasma processing chamber. Residual atoms and molecules are desorbed into the plasma and change the ion / radical composition in the plasma, or change the electrical characteristics of the plasma and the device, and have a significant effect on the plasma processing performance. give.

  Since radicals and ions have high chemical reactivity, they not only react with the target object, but also cause chemical reaction or adsorption with the constituent members of the plasma processing chamber. In particular, halogen, especially fluorine, is highly reactive with silicon solids such as quartz, and thus often reacts with quartz parts and the like and remains in the plasma processing chamber.

  In addition, wear of parts occurs due to the reaction process by ions and radicals. If the degree of wear is significant, it will be necessary to replace it with a new part. However, the new quartz part is close to pure quartz in surface, and is used sufficiently, and the surface condition is very different from the quartz part in which a large amount of residue exists on the surface. This difference in the surface state causes a great difference in the result of the plasma treatment as a difference in electrical influence or chemical influence on the plasma. Therefore, the plasma processing apparatus after replacement with new quartz parts requires a break-in operation such as repeatedly generating fluorine-based plasma in order to put these parts into use. Until the break-in operation is completed, the plasma processing apparatus is not in a substantially usable state, which causes a reduction in the operating rate of the apparatus. Moreover, depending on the case, it becomes necessary to repeat the break-in operation by the processing of some workpieces. In many cases, the work for processing the object to be processed may be required 25 to 100 times or more, and it is necessary to prepare the object to be processed. . In addition, even if the processing characteristics of the plasma processing apparatus are stabilized by such a running-in operation, the plasma processing chamber is unnecessarily worn by plasma as a result of repeated unnecessary plasma processing and should be replaced. On the other hand, the number of parts increases, and on the other hand, foreign particles generated by the parts being worn out contaminate the object to be processed and cause defective products.

As a conventional technique for coping with this problem, it has been proposed to remove residual fluorine with hydrogen plasma and keep the surface state of the quartz part constant (for example, see Patent Document 1).
JP 2003-178993 A

  It is not easy to remove fluorine that is chemically strongly bonded to the surface of the quartz part, and it is difficult to completely remove fluorine remaining on the surface of the quartz part by the method described in Patent Document 1. This is because the chemical bond strength between fluorine and hydrogen is about 5.91 electron volts at room temperature, whereas the chemical bond strength between silicon and fluorine is about 5.73 electron volts. This is because the reaction does not easily proceed even under plasma irradiation. Further, according to experiments by the inventors of the present invention, it was confirmed that it was not easy to remove fluorine bonded to silicon even by plasma using a hydrogen-containing gas.

  For this reason, it is not easy to remove residual fluorine from the quartz surface using hydrogen, and even if possible, it is considered difficult to remove all of it. Therefore, it is inevitable that the surface of the quartz part is gradually fluorinated, and this is not sufficient to keep the processing performance of the plasma processing apparatus stable. Moreover, the work time for performing the removal process is required, and accordingly, the time for the processing time of the target object to be processed is reduced, leading to a reduction in the apparatus operating rate.

  In view of the above problems, the present invention creates a plasma processing environment with substantially no change in the plasma processing apparatus, stabilizes the performance of the plasma processing apparatus, and reduces the need for a break-in operation when replacing quartz parts. The purpose is to do.

  In view of the above-mentioned problems, the present invention does not remove the residue generated on the surface of the quartz part as the plasma treatment is repeated, but maintains the state in which the residue is present in the quartz part from the beginning. Thus, the plasma processing performance of the plasma processing apparatus using quartz parts is kept constant.

  That is, for example, if residual fluorine has an effect on the plasma processing performance, fluorine is mixed in the quartz parts in advance, and the plasma processing environment has little change in surface condition when replacing the quartz parts. By realizing the above, the plasma processing performance of the plasma processing apparatus is kept constant.

  In this case, there are many plasma processing apparatuses other than halogen such as fluorine that are difficult to remove, such as carbon and sulfur that are strongly bonded to silicon in quartz. Or, the same problem occurs when the vapor pressure is very low, such as aluminum halides such as aluminum, yttrium, titanium, tungsten, and tantalum, and those that cannot be converted into high vapor pressure even after chemical reaction. Cause it to occur. As described above, when difficult-to-remove materials adhere to quartz and cause problems due to the accumulation of the number of times of plasma processing, the performance of the plasma processing equipment can be stabilized by mixing these materials in the quartz parts in advance. It can be made.

  Below, the case where a fluorine is mixed is demonstrated as the representative.

  As described above, according to the present invention, an element that remains in the plasma processing apparatus and is difficult to remove is mixed in advance into a quartz part used in the plasma processing apparatus, so that the plasma processing with substantially little change is performed. It can create an environment and stabilize the performance of plasma processing equipment.

In the examples described in this specification, the method of mixing fluorine has been described. However, other elements such as chlorine, bromine, carbon, and sulfur, which are frequently used in plasma processing, are removed because the vapor pressure is low. Difficult metals and their compounds may be mixed. For example, if the object to be processed contains platinum, ruthenium, or other metals, and the object to be processed is plasma-treated, residues containing these metals are generated on the surface of the quartz part and are difficult to remove. In addition, the present invention is effective. Further, aluminum or yttrium compounds used as a material for the plasma processing chamber, for example, AlF ₃ , YCl ₃ , YF _3, etc. may be mixed. The essence of the present invention is to use a quartz part in which an element that is difficult to remove is mixed in advance, and the substance to be mixed and the mixing method are not limited.

  In addition, the present invention is effective when quartz parts are used in a plasma processing apparatus, regardless of the type of plasma processing apparatus, particularly a so-called gate etching apparatus, insulating film etching apparatus, or metal etching apparatus. Can be applied.

  Hereinafter, as an application example of the present invention, a case where a semiconductor wafer mainly composed of silicon is processed by a plasma etching apparatus will be described. The configuration of a plasma etching apparatus to which the present invention is applied will be described with reference to FIG.

  The plasma processing apparatus includes a plasma processing chamber 202 for plasma processing a wafer 201 that is an object to be processed, a gas supply unit 203 that supplies a processing gas, and a gas exhaust unit 204 that exhausts the processing gas in the plasma processing chamber 202. A pressure gauge 205, a valve 206, a plasma generation means 207, a power source 208, a tuner 209, a stage 210, a power source 211, a tuner 212, a cover 213, a distributor 214, and an inner wall 215. ing.

  When plasma processing is performed on the wafer 201, the pressure in the plasma processing chamber 202 is measured by a pressure gauge 205 so that the pressure in the plasma processing chamber 202 can be maintained at a desired value, and the exhaust speed of the processing gas is adjusted by the valve 206. In this state, a high frequency generated from the power source 208 is applied to the plasma generating means 207 to generate plasma in the plasma processing chamber 202. In order to maintain the plasma stably, a tuner 209 is provided between the plasma generating means 207 and the power source 208, thereby matching the impedance. Further, a stage 210 for supporting the wafer 201 to be processed is installed in the plasma processing chamber 202, and a power source 211 for applying a voltage to the stage 210 and a tuner 212 for adjusting impedance are provided. .

  The above is the minimum configuration of the plasma processing apparatus. In addition to this, a cover 213 for protecting the stage 210 from plasma, a distributor 214 for evenly distributing the gas supplied from the gas supply means 203 into the plasma processing chamber 202, and the plasma processing chamber 202 from the plasma. An inner wall 215 or the like for protection may be provided. The cover 213, the distributor 214, and the inner wall 215 are installed at positions very close to the plasma, and are easily damaged by the plasma. If these parts are made of a material such as metal or a metal non-moving body, the inside of the plasma processing chamber 202 and the object to be processed 201 are contaminated with metal elements when severely damaged by plasma. . Therefore, these parts are often made of a material mainly composed of silicon, for example, quartz, as a material constituting these parts. By doing in this way, the danger of contaminating the to-be-processed object 201 mainly having silicon can be eliminated.

However, since the workpiece 201 and these parts are similar in that they are mainly composed of silicon, the plasma causes a chemical reaction not only with the workpiece 201 but also with these quartz parts. . In particular, when plasma is generated using a gas such as SF ₆ , CF ₄ , or CHF ₃ , fluorine radicals or fluorine ions in the plasma react violently with these parts, and wear the surface of the parts. Furthermore, even after the plasma disappears, it remains chemically bonded to the surface of these quartz parts.

  The above has described the case where the workpiece 201 composed mainly of silicon is processed. However, such a problem is that the configuration of the workpiece includes not only silicon but also carbon or metal. Even so, it occurs in common with all plasma processing equipment that uses quartz for its parts.

In order to confirm this experimentally, the inventors of the present invention placed a 10 mm square and 1 mm thick quartz test piece on the workpiece 201 and exposed it to SF ₆ plasma, and then removed the test piece. The amount of fluorine adhering to the surface was measured by X-ray photoelectron spectroscopy. The result of this experiment is shown by a curve 301 in FIG. The horizontal axis represents the time during which the quartz test piece was irradiated with SF ₆ plasma, and the left vertical axis represents the concentration of fluorine atoms in the vicinity of the surface of the quartz test piece in atomic percent relative to quartz. The longer the exposure time to SF ₆ plasma, the greater the amount of fluorine atoms in the vicinity of the quartz surface, and finally reached about 10%. That is, it can be said that the surface of the quartz part in the plasma processing chamber also fluorinates with time. On the other hand, the result of measuring the Poly-Si etching rate by SF ₆ / CHF ₃ plasma between the SF ₆ plasmas is also shown by a curve 302 in FIG. The horizontal axis represents the total time during which the SF ₆ plasma was irradiated after exchanging quartz parts in the plasma processing apparatus, and the right vertical axis represents the etching rate per minute. It was found that the etching rate also increases with the SF ₆ plasma irradiation time. From the above, it was found that there is a strong relationship between the concentration of fluorine bonded to the surface of the quartz part and the etching rate.

  In this experiment, the change in the etching rate was described as an example. However, as long as the properties of the plasma have changed due to the influence of residual fluorine, various processing performance changes occur in addition to the etching rate. For example, when a three-dimensional object is constructed on an object to be processed by etching, the three-dimensional dimension and shape also change. Alternatively, since the amount of ions incident from the plasma changes, the object to be processed may be excessively charged in some cases, causing an abnormal potential difference in the internal structure, and causing problems such as dielectric breakdown. Thus, for example, when the fluorine concentration changes, the etching performance of the plasma etching apparatus also changes.

There are two main ways to deal with this problem. The first method is a method of performing a fluorine removal operation as described above. For example, plasma is generated by hydrogen gas or a gas containing hydrogen, and fluorine remaining on the surface of the quartz part is reacted with hydrogen radicals or hydrogen ions in the plasma to be exhausted out of the plasma processing chamber as hydrogen fluoride. It is a method to do. However, when the inventors of the present invention tried to remove fluorine by HBr plasma, it was found that this reaction hardly occurs on the surface of a quartz part, and it is difficult to completely remove fluorine. The second method is a method in which a break-in operation is repeated to stabilize the etching performance of the apparatus, and then processing of a desired object to be processed is started. The running-in operation referred to here is a method in which, for example, SF ₆ gas is converted into plasma and sufficient fluorine is adhered to the surface of the quartz part. However, in this method, it takes time to deposit sufficient fluorine on the surface of the quartz part, and during that time, processing of a desired object to be processed cannot be started. In addition, there are cases where a workpiece for break-in operation is required, and in many cases, 25 to 100 or more such workpieces for break-in operation must be prepared, resulting in extra costs. .

  Therefore, the inventors of the present invention do not remove the remaining fluorine from the surface of the quartz part, but use a part that is premixed in the quartz part and whose surface state does not substantially change. I thought. First, according to the present invention, it is necessary to mix fluorine or the like into a quartz part. Three examples will be described below as to how to mix them.

In the first embodiment, when melting quartz, which is a material, fluorine atoms are mixed, and a quartz part manufactured using quartz mixed with fluorine is used. Usually, in order to produce a quartz part, a process such as melting and molding a material mainly composed of quartz is required. In this embodiment, when a quartz component containing fluorine is prepared, when quartz is melted, a material containing fluorine atoms, for example, CaF ₂ or AlF ₃ is mixed with quartz, or F ₂ gas or SF _{6 is used.} Quartz may be melted in an atmosphere of a gas containing fluorine atoms. According to this embodiment, a quartz member containing a desired amount of fluorine atoms in quartz can be obtained.

  However, in the first embodiment, there are cases where sufficient hardness cannot be maintained when fluorine or the like is mixed at a high concentration.

  In order to deal with such a case, a second embodiment is proposed. In the second embodiment, quartz already doped with a high concentration of fluorine is placed on a part made of pure quartz so that the concentration of fluorine atoms can be concentrated only near the surface of the shaped quartz member. Thermal spray. The quartz part thus produced has a high mechanical strength because the base material is pure quartz, and the surface is made of quartz to which fluorine is added at a high concentration. The same effect is obtained. Quartz parts usually need to be replaced when they are worn by plasma from the surface to a thickness of a few millimeters, so that the sprayed thickness of the fluorine-added quartz need only be a few millimeters. Moreover, as a 2nd Example, the same components can be obtained even if the thermal spraying of the quartz to the quartz member is performed in a fluorine atmosphere.

  On the other hand, in the second embodiment, since thermal spraying is used, the smoothness of the surface may not be sufficiently secured. The rough surface is advantageous in that the chemical components in the plasma can be adsorbed well. However, if the surface is too rough, the surface is chipped and foreign particles are generated. In order to improve this point, a third embodiment will be described.

  In the third embodiment, fluorine is doped on the surface of the shaped quartz member using an accelerator. For example, when fluorine ions are implanted with an accelerator at an energy of about 500 kiloelectron volts, they can be implanted to a depth of about several hundred micrometers. Furthermore, by heat-treating the quartz part into which fluorine ions are implanted, fluorine atoms can be further expanded by thermal diffusion, and it is easy to diffuse to a depth of several millimeters. By doing so, it is possible to obtain a quartz part having a high fluorine atom concentration in the vicinity of the surface as in the second embodiment while maintaining the surface smoothness.

Through such steps, a quartz part containing fluorine can be produced. FIG. 1 shows a result of comparison between a plasma processing apparatus using a part containing 7% fluorine in quartz and a plasma processing apparatus using a part made of pure quartz as usual. In the plasma processing apparatus using a part made of pure quartz, the etching rate using SF ₆ / CHF ₃ gas gradually increases as shown by the curve 101, but the quartz containing fluorine is used. In the plasma etching apparatus using the parts prepared in (1), the etching rate was high from the beginning as shown by the curve 102, and the change with time was small. Since the etching characteristics became stable, there was no change in the plasma treatment result even when the treatment was repeated, and both the processing dimension and the cross-sectional shape of the workpiece 201 could be kept constant.

  As described above, it has been found that the fluorine-based etching characteristics can be stabilized by incorporating fluorine into the quartz part. However, as described above, if the impurities are excessively contained in the quartz, there are cases where the hardness of the quartz cannot be maintained. From the viewpoint of stabilizing the etching performance, a higher fluorine concentration is preferable, but from the viewpoint of mechanical strength, 0.01 atomic% or more and 20 atomic% or less is suitable. However, this method is not particularly limited in the case where a high fluorine concentration can be achieved while maintaining the mechanical strength by the method described in the second and third embodiments of the present invention. In this experiment, since a quartz member having an appropriate fluorine concentration was used, the mechanical strength was sufficient and the generation of foreign particles was small. In addition, since a stable plasma treatment can be performed from the beginning, no break-in operation is required, and an improvement in the operating rate of the apparatus can be realized. Furthermore, since the parts inside the plasma processing apparatus are not consumed unnecessarily, the generation of foreign particles can be reduced as compared with the normal operation method.

  In the above examples, the method and effect of incorporating fluorine into a quartz part have been described. In addition to fluorine, elements that cause changes in plasma processing performance over time include chlorine, bromine, iodine, carbon, and sulfur.

  Chlorine and bromine have a high reactivity with silicon like fluorine (for example, the bond energy between fluorine and silicon at room temperature is 5.73 electron volts, whereas 4.21 electrons between chlorine and silicon. Bolt, between bromine and silicon is 3.81 electron volts), causing the problem of remaining on the quartz surface. Residual chlorine and bromine may still change the composition of radical ions in the plasma to an undesirable state. Therefore, even when performing plasma etching mainly composed of chlorine or bromine, a method for stabilizing processing performance such as break-in discharge and removal work is required as in the case of fluorine.

Carbon and sulfur also have a high bond energy with silicon (the bond energy between carbon and silicon at room temperature is 4.68 eV, and the bond energy between sulfur and silicon is 6.46 eV), and these elements are also fluorine. Like, it tends to remain. In addition, carbon and sulfur can form a solid film, especially on the surface of quartz parts. When the film is formed, the surface of the component is chemically not a quartz but a carbon or sulfur compound, and can be removed by oxygen plasma alone, but cannot be easily removed in a compound state. If the surface of the quartz part is coated with these carbon and sulfur compounds, the chemical reaction with the plasma may be different or the electrical characteristics of the plasma may be affected. Iodine has a high bond energy with silicon (iodine-silicon bond energy is 3.04 eV at room temperature), and SiI ₄ has low volatility. Causes problems similar to carbon and sulfur.

As described above, halogens such as fluorine, chlorine, bromine, iodine, carbon, and sulfur have been described as elements that are difficult to remove from quartz parts, but other elements that are difficult to remove include compounds of various metal elements. Aluminum and yttrium are used as materials for plasma processing chambers, but sometimes they react with radicals such as chlorine and fluorine in the plasma to form compounds such as AlF ₃ , YCl ₃ , YF _3, etc. May adhere to the surface. In addition, tungsten, tantalum, and titanium have recently been used as semiconductor components. Platinum and ruthenium are also sometimes used as semiconductor components. Such metal used in the construction of the object to be processed may react with the plasma to form, for example, TiFx (x = 2 to 4) or TiO ₂ , and may remain on the surface of the quartz part. These compounds do not remain on the quartz surface due to bonding with silicon like fluorine and carbon, but remain due to low vapor pressure. Residual points cause problems similar to those of carbon and sulfur, and cause changes in plasma processing performance in terms of chemical reactions with plasma and changes in plasma electrical characteristics. Therefore, as in the case of fluorine, the performance of the plasma treatment can be kept stable by preliminarily containing the metal compound as described above inside the quartz part.

It is a figure explaining that etching performance is maintained over a long period of time when fluorine is contained in a quartz part inside a plasma processing apparatus based on the present invention. It is a figure explaining the example of a structure of the plasma processing apparatus to which this invention is applied. Exposing the quartz specimen plasma of SF ₆ gas, compared to the results of measuring the residual amount of the surface of fluorine, and a state in which the etching rate by SF 6 _/ CHF ₃ plasma changes with time using a SF ₆ plasma It is a figure.

Explanation of symbols

101 ... Time variation of etching rate when pure quartz is used as a component in the plasma processing apparatus 102 ... Time variation of etching rate when using the quartz component of the present invention 201 ... Process object 202 of plasma treatment ... Plasma Plasma processing chamber 203 of processing apparatus ... Gas supply means 204 ... Gas exhaust means 205 ... Pressure gauge 206 ... Valve 207 ... Plasma generation means 208 ... Power source 209 ... Tuner 210 ... Stage 211 ... Power source 212 ... Tuner 213 ... Cover 214 ... Distributor 215... Inner wall 301... Fluorine atom density on the surface of the quartz test piece 302.

Claims (9)

A plasma processing apparatus,
A plasma processing apparatus, wherein a quartz member used in the processing apparatus contains a plasma generation gas component in advance. The plasma processing apparatus according to claim 1,
A plasma processing apparatus comprising at least one of a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a sulfur atom, and a carbon atom as a component of a plasma generation gas. The plasma processing apparatus according to claim 2,
A plasma processing apparatus, wherein the concentration of each substance that is a component of a plasma generation gas is 0.01 atomic% or more and 20 atomic% or less with respect to quartz. The plasma processing apparatus according to claim 2, wherein
A plasma processing apparatus, wherein the concentration of each substance that is a component of a plasma generation gas is 0.01 atomic% or more and 20 atomic% or less on the surface of a quartz member. A quartz member used in a plasma processing apparatus,
A quartz member comprising 0.01 atom% or more and 20 atom% or less of at least one of fluorine atom, chlorine atom, bromine atom, iodine atom, sulfur atom and carbon atom in the quartz member. The quartz member according to claim 5,
A quartz member obtained by melting a quartz member in an atmosphere of a fluorine molecular gas or a molecular gas containing fluorine. The quartz member according to claim 5,
A quartz member obtained by spraying quartz that already contains fluorine atoms on the surface of a shaped quartz member. The quartz member according to claim 7,
A quartz member obtained by performing thermal spraying in a fluorine gas or a molecular gas containing fluorine when spraying quartz onto the surface of the shaped quartz member. The quartz member according to claim 8, wherein
A quartz member obtained by implanting fluorine ions on the surface of a shaped quartz member using an ion accelerator and then incorporating fluorine by heat treatment.

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