JP2008172253A - Electrode for plasma etching - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vitreous carbon-made electrode for plasma etching which can significantly reduce the contamination of a silicon wafer with metal impurities. <P>SOLUTION: The vitreous carbon-made electrode for plasma etching is one in which the iron adhering amount adhered on the whole surface, including through-hole inner walls, is 2 μg/cm<SP>2</SP>or smaller, with respect to the entire surface area. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a glassy carbon plasma etching electrode used in a dry etching apparatus in a semiconductor device manufacturing process.

  One of the semiconductor device manufacturing processes is an etching process for forming a circuit pattern on a silicon wafer. Among these, in the parallel plate type plasma etching apparatus, a silicon wafer is disposed on the lower electrode, and high-frequency plasma is generated between the silicon wafer and the upper electrode having a large number of through holes for circulating the reaction gas. Then, the silicon wafer is etched. The upper electrode itself is etched by plasma when the silicon wafer is etched.

  Conventionally, the upper electrode (electrode for plasma etching) has conductivity as shown in Japanese Patent Application Laid-Open No. 57-185982, etc., has excellent chemical stability, and does not contaminate a silicon wafer with metal impurities. Highly purified graphite materials have been used. However, because graphite material is an aggregate of particles composed of aggregate and matrix, the constituent particles fall off due to etching by plasma, the wear increases, and the particles fall on the silicon wafer, which impedes circuit pattern formation. There were problems such as becoming. In order to solve such problems, glassy carbon has recently been used for plasma etching electrodes as disclosed in JP-A-62-109317.

  Whereas a general carbon material such as a graphite material is an aggregate of particles composed of an aggregate and a matrix, glassy carbon obtained by carbonizing and baking a thermosetting resin is a glassy, very homogeneous and dense material. It has a simple structure. For this reason, glassy carbon has excellent characteristics that are not found in general carbon materials, such as chemical stability, heat resistance, self-lubricating property, and the like, and that constituent particles do not fall off. For this reason, it is supposed that glassy carbon is suitable for a semiconductor manufacturing apparatus member.

In the manufacture of semiconductor devices, contamination of a silicon wafer with metal impurities causes deterioration of characteristics and a reduction in device yield. For this reason, the plasma etching electrode is required to have a high purity with a low content of metals, particularly heavy metals such as iron and lead. However, even in the case of high purity as a whole, or even if the amount of metal attached to the surface is very small in view of the total amount of impurities, the influence on silicon wafer contamination is significant at the initial stage of electrode use.
JP 57-185982 A JP 62-109317 A

  The present invention provides a glassy carbon plasma etching electrode capable of significantly reducing contamination of a silicon wafer with metal impurities.

The present invention relates to a glassy carbon plasma etching electrode in which the amount of iron attached to the entire surface including the inner wall of the through hole is 2 μg / cm ² or less with respect to the total surface area.

  The plasma etching electrode according to the present invention can greatly reduce the contamination of the silicon wafer by metal impurities, so that the device yield can be improved and stable plasma etching processing can be performed, which is extremely industrially difficult. Is preferred.

  The glassy carbon in the present invention is a carbon material obtained by carbonizing and firing a thermosetting resin cured product, and there is no particular limitation on the thermosetting resin used to obtain the thermosetting resin cured product. Although there are no phenol resins, epoxy resins, unsaturated polyester resins, furan resins, melamine resins, alkyd resins, xylene resins, and the like. A mixture of these resins may also be used. A furan resin and / or a phenol resin are preferable.

  Although the thermosetting resin used for this invention is shape | molded with various shaping | molding methods according to the target shape before hardening, there is no restriction | limiting in particular about the shaping | molding method. After forming into a predetermined shape, it is further cured at a temperature of 130 to 200 ° C. The thermosetting resin is molded and cured at a heating condition and a temperature rising rate at which condensed water easily escapes to the outside, or a catalyst amount for curing is set to an appropriate amount to obtain a stable resin plate.

  Next, after performing predetermined processing to form the electrode plate, in an inert atmosphere (usually inert gas such as helium and argon, nitrogen, hydrogen, halogen gas, etc.) using a high-purity jig and furnace Calcination carbonization is performed at a temperature of about 1000 ° C. in an oxygen-free atmosphere composed of at least one non-oxidizing gas (under reduced pressure or under vacuum). Further, a plasma etching electrode made of glassy carbon is obtained by high-temperature treatment at a temperature of 1300 ° C. or higher, preferably 2000 ° C. or higher. As a method for obtaining an electrode for plasma etching, glassy carbon may be obtained in addition to the above method, and then processed into an electrode plate having a predetermined shape by electric discharge machining or ultrasonic machining. In addition, the electrode for plasma etching is subjected to finish processing such as surface polishing if necessary.

  When there are many metal impurities contained in the entire glassy carbon, the silicon wafer is contaminated regardless of the surface contamination. Therefore, the amount of metal impurities contained in the entire glassy carbon is preferably 50 ppm or less, and more preferably 20 ppm or less. The amount of metal impurities is determined from the amount of ash obtained by firing glassy carbon in an atmosphere containing oxygen.

Iron deposition amount adhered to the surface of the plasma etching electrode of the present invention, the total surface area including the through-hole inner walls, 2 [mu] g / cm ² or less, preferably 1.8μg / cm ² or less, more preferably 1 [mu] g / cm ² If it exceeds ² μg / cm ² , the silicon wafer is significantly contaminated when used for plasma etching, and the product yield decreases. The iron adhesion amount is usually 0.09 μg / cm ² , and it is difficult to make it more.

  In the present invention, the amount of iron adhering to the entire surface including the inner wall of the through-hole of the glassy carbon plasma etching electrode refers to the amount of iron component that is acid extracted from the surface of the plasma etching electrode. It is obtained by immersing the electrode for plasma etching in hydrochloric acid and measuring the concentration of iron eluted in the concentrated hydrochloric acid. The immersion time in concentrated hydrochloric acid is the time until the iron concentration is substantially saturated. The analysis of the iron concentration is performed by a known method such as electrochemical analysis such as atomic absorption analysis, ICP method, potentiometric stripping method, and the amount of iron adhering to the electrode for plasma etching from the obtained iron concentration. Is calculated.

When the amount of iron adhering to the entire surface including the inner wall of the through-hole of the plasma etching electrode obtained in the present invention exceeds ² μg / cm ² , the amount of iron adhering can be reduced by performing acid cleaning or heat treatment. Can be reduced.

  Acid cleaning is performed by immersing the electrode for plasma etching in an acid such as hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid or a mixture thereof or an aqueous solution thereof (hereinafter collectively referred to as a cleaning solution). The time is preferably 1 hour or longer. The concentration of the cleaning liquid varies depending on the type, but is preferably 2% by weight or more. 5 weight% or more is more preferable, and the range of 10-60 weight% is further more preferable. If it is less than 2% by weight, the ability to remove the iron component tends to be reduced, and the effect tends not to be exhibited. Further, hydrogen peroxide may be added in order to improve the cleaning effect. The addition amount is preferably 10% by weight or more, more preferably 20% by weight or more, and further preferably in the range of 25 to 40% by weight with respect to the cleaning liquid. Furthermore, in order to make acid cleaning more effective, cleaning may be performed by a method such as applying ultrasonic vibration as necessary. The time for applying the ultrasonic vibration is preferably 1 minute or more, and more preferably 5 minutes or more.

  The heat treatment is preferably heat-treated at a temperature of 1000 ° C. or higher, and more preferably heat-treated at a temperature of 1000 to 2000 ° C. If the temperature is lower than 1000 ° C., the removal ability of the target iron component is lowered, and the effect tends not to be exhibited. This method is a method of heating and evaporating and removing the iron adhering to the entire surface including the inner wall of the through hole. For example, in an inert gas atmosphere such as nitrogen gas or argon gas, or in a vacuum (reduced pressure) Heat treatment is preferably performed in an oxidizing atmosphere.

Hereinafter, the present invention will be described in detail with reference to examples.
Examples 1-6 and Comparative Examples 1-3
To 100 parts by weight of furan resin (manufactured by Hitachi Chemical Co., Ltd., trade name VF-303), 0.3 parts by weight of paratoluenesulfonic acid and 0.3 parts by weight of ethylene glycol are added and mixed thoroughly. After pouring into a mold and drying and curing by holding at 50 ° C for 3 days, 70 ° C for 3 days and 90 ° C for 3 days, the temperature was increased up to 160 ° C at a rate of 5 ° C / hour, and 3 hours at 160 ° C. It was kept for a day and cured to obtain a disk-shaped resin molded body having a thickness of 4 mm and a diameter of 250 mm.

  The molded body is processed into a predetermined shape that allows for dimensional shrinkage (20% shrinkage) in advance, and then heated up to 160 ° C. at a rate of 5 ° C./hour and held at 160 ° C. for 3 days for curing treatment. A disk-shaped resin cured product was obtained. The cured body is placed in an electric furnace, heated up to 1000 ° C. at a rate of 5 ° C./hour in a nitrogen stream, and held at 1000 ° C. for 10 hours for firing and carbonization, and then a high-purity jig and atmosphere furnace Is heated to 2000 ° C. at a rate of 30 ° C./hour in a nitrogen atmosphere and is subjected to a high temperature treatment at a temperature of 2000 ° C. for 6 hours, having a thickness of 3.5 mm and a diameter of 200 mm. Got carbon.

Next, a large number of small through-holes having a diameter of 0.8 mm were drilled in glassy carbon at a pitch of 3 mm, polished to a thickness of 3.0 mm with a diamond lap machine, and mirror-finished to obtain an electrode for plasma etching. The total surface area including the through holes of the plasma etching electrode was 950 cm ² . The average values of physical properties of the obtained plasma etching electrode were as follows: bulk density 1.50 g / cm ² , porosity 0.5 volume%, electrical resistivity 42.5 μΩm, bending strength 135 MPa and Shore hardness Was 123. The total impurity amount (ash content) of the plasma etching electrode produced in the same lot was 15 ppm.

Next, two plasma etching electrodes were each acid-washed under the conditions shown in Table 1, and one of them was immersed in concentrated hydrochloric acid for 10 hours. The concentration of iron in the concentrated hydrochloric acid was measured by atomic absorption analysis, and the amount of iron adhered to the entire surface including the inner wall of the through hole was calculated. The results are also shown in Table 1. Next, the remaining one plasma etching electrode was set in the plasma etching apparatus, and the reaction gas: trifluoromethane (CHF ₃ ) carrier gas: argon (Ar), the gas pressure in the reaction chamber: 1 Torr, the power frequency: Oxide film etching of a 6-inch diameter silicon wafer was performed under the condition of 13.5 MHz. The product yield of the semiconductor device obtained from the silicon wafer at this time is also shown in Table 1.

Examples 7-12 and Comparative Examples 4-6
A disk having a thickness of 5.5 mm and a diameter of 350 mm through the same steps as in Examples 1 to 6 and Comparative Examples 1 to 3, using the same materials as in Examples 1 to 6 and Comparative Examples 1 to 3. A molded resin molded body was obtained. The molded body was fired and carbonized through the same steps as in Examples 1 to 6 and Comparative Examples 1 to 3, and then up to 2300 ° C. in a nitrogen atmosphere using a high-purity jig and an atmospheric furnace at 30 ° C./hour. The temperature was raised at a speed of 2300 ° C. and kept at a temperature of 2300 ° C. for 6 hours to carry out a high temperature treatment to obtain glassy carbon having a thickness of 4.4 mm and a diameter of 280 mm.

Next, a large number of through-holes having a diameter of 0.5 mm were formed in glassy carbon at a pitch of 7 mm, polished to a thickness of 4.0 mm with a diamond wrap machine, and mirror-finished to obtain an electrode for plasma etching. The total surface area including the through holes of this plasma etching electrode was 1300 cm ² . The average physical properties of the obtained plasma etching electrode were as follows: bulk density of 1.51 g / cm ² , porosity of 0.1% by volume, electrical resistivity of 42.5 μΩm, bending strength of 145 MPa, and shore hardening Was 123. The total impurity amount (ash content) of the plasma etching electrode produced in the same lot was 15 ppm.

Next, two plasma etching electrodes were each heat-treated under the conditions shown in Table 2, and one of them was immersed in concentrated hydrochloric acid for 10 hours. The concentration of iron in the concentrated hydrochloric acid was measured by atomic absorption analysis, and the amount of iron adhered to the entire surface including the inner wall of the through hole was calculated. The results are also shown in Table 2. Next, the remaining one plasma etching electrode was set in the plasma etching apparatus, and the reaction gas: trifluoromethane (CHF ₃ ) carrier gas: argon (Ar), the gas pressure in the reaction chamber: 1 Torr, the power frequency: Oxide film etching of a 6-inch diameter silicon wafer was performed under the condition of 13.5 MHz. Table 2 also shows the product yield of devices obtained from the silicon wafer at this time.

As shown in Tables 1 and 2, the plasma etching electrode according to the present invention has a low iron adhesion amount of 1.90 μg / cm ² or less, which indicates that the product yield of the device is good. On the other hand, the electrode for plasma etching of the comparative example has a large iron adhesion amount of 2.20 μg / cm ² or more, indicating that the product yield of the device is poor.

  The plasma etching electrode according to the present invention can greatly reduce the contamination of the silicon wafer by metal impurities, so that the device yield can be improved and stable plasma etching processing can be performed, which is extremely industrially difficult. Is preferred.

Claims (1)

An electrode for plasma etching made of glassy carbon in which the amount of iron adhered to the entire surface including the inner wall of the through hole is 2 μg / cm ² or less with respect to the total surface area.