JP2010003872A - Dry etching method of zinc oxide film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dry etching method of a zinc-oxide film in which processing accuracy or working speed is high. <P>SOLUTION: When processing a zinc-oxide film into a requested shape by dry etching, an etching or cleaning treatment is performed in a mixed gas atmosphere containing methane and hydrogen. The supply of methane is stopped in the middle of an etching or cleaning treatment, or the supply of methane is decreased by step or consecutively to make methane to be zero in a process gas which is supplied, and an etching or cleaning process is continuously performed in an atmosphere not containing methane preferably containing only hydrogen, thereby a processing method stably having high accuracy without generating an amorphous carbon based deposit on a zinc-oxide film is obtained. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a dry etching method for a zinc oxide film when processing the zinc oxide film.

  In recent years, transparent electrodes have become indispensable as electrodes for solar cells, image sensors, flat panel displays and the like. As this transparent electrode, zinc oxide (ZnO) has an advantage that a good crystal having low transparency and high transparency has been obtained so far, and therefore research and development on the growth conditions and processing conditions of the film has been made. ing.

  In order to use the ZnO film for the above-described various applications, it is necessary to process the ZnO film, and the reproducibility is high, and various etching methods have been studied in order to obtain a desired shape. This etching method is roughly classified into a wet etching method in which a sample is immersed in a chemical and a dry etching method using a gas phase etching medium. In the wet etching method, since the etching reaction isotropically progresses, there is a problem that the processing accuracy for processing into a desired shape deteriorates when the ZnO film is processed into a concavo-convex shape. In addition, in wet etching, there is a problem that the etching residue floats in the liquid and remains on the device.

  On the other hand, in the dry etching method, chemically active ions generated in the plasma have straightness, so that the etching reaction has anisotropy by being perpendicularly incident on the workpiece, and the processed shape is It has the advantage of being faithful to the desired shape.

  As a general dry etching method, a reactive ion etching (RIE) method is used. In the RIE method, an etching gas is introduced into a vacuum vessel having parallel plate electrodes, and high-frequency power is applied to the electrode, so that electrons accelerated to a high-frequency electric field ionize and ionize the etching gas to be in a plasma state. Radicals and ions generated in the plasma are reacted and etched on the surface of the substrate placed on the electrode.

  The etching reaction mechanism in the RIE method includes an etching reaction in which a chemical reaction that advances the reaction by removing secondary products generated by adsorption of radicals and an accelerated positive ion colliding with the substrate. There are two types of etching reactions in which the sputtering effect that is physically excavated is dominant.

  Regarding conventional dry etching, fluorine-based gas is often used as an etching medium, but the etching rate for the zinc oxide film is slow, which is disadvantageous for mass production.

  Regarding dry etching of a zinc oxide film, it is known that a process gas containing methane and argon is used for dry etching (Patent Document 1).

In addition, a reaction using a mixed gas of hydrogen and hydrocarbons while heating the ITO film when dry etching is performed on a transparent conductive film made of In ₂ O ₃ : Sn (ITO) formed on a glass substrate It is known to use reactive dry etching (Patent Document 2).
JP-A-11-335874 JP-A-3-77209

  However, the above-described dry etching method has various problems as described below.

  In the dry etching method described in Patent Document 1, argon is used as a dilute gas material of methane, and since the sputtering effect by argon ions is the dominant etching reaction as an etching reaction, the surface shape after the etching process is There is a problem that a desired shape is difficult to obtain due to roughening.

  Further, in the dry etching method described in Patent Document 2, when the transparent conductive film is not heated, amorphous carbon-based deposits are generated on the transparent conductive film, and an etching result having a predetermined shape cannot be obtained. There is a problem.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for processing a zinc oxide film with high processing accuracy.

  The present invention has the following configuration.

  1). In the dry etching or cleaning method of the zinc oxide film, the etching or cleaning process is performed in a mixed gas atmosphere containing methane and hydrogen, and the supply of methane is stopped in the middle of the etching or cleaning process, or stepwise or continuously. A dry etching method for a zinc oxide film, characterized in that an etching or cleaning process is performed while reducing supply.

  2). In the dry etching or cleaning method of the zinc oxide film, the etching or cleaning process is performed in a mixed gas atmosphere containing methane and hydrogen, and the supply of methane is stopped in the middle of the etching or cleaning process, or stepwise or continuously. The dry etching method for a zinc oxide film according to 1), wherein the supply is reduced and a process gas not using methane is supplied to perform etching or cleaning treatment.

  3). The mixed gas used for the etching or cleaning process is stopped immediately or the mixed gas immediately before the supply of methane is reduced stepwise or continuously is within a range where the proportion of methane in methane and hydrogen is 20% by volume or less. The method for dry etching a zinc oxide film as described in 1) or 2), wherein

  4). The dry etching of a zinc oxide film according to any one of 1) to 3), wherein the etching or cleaning process is finished after methane becomes substantially zero in the gas atmosphere in the chamber where the etching or cleaning process is performed. Method.

According to the present invention, by using a process gas containing methane, zinc oxide and methane react to form a reaction product such as volatile Zn (CH ₃ ) _2, which can be detached from the substrate for dry etching. . Furthermore, since this etching reaction appears strongly in the direction perpendicular to the substrate, it has anisotropy. Depending on the etching conditions, a very fast rate can be achieved and mass production is possible.

  Further, in the etching or cleaning method of the present invention, the methane supply ratio is preferably lowered by stopping the supply of methane during the etching process or decreasing the supply of methane stepwise or continuously. Will eventually supply process gas in the absence of methane and perform the above treatment in a state where substantially no methane is used in the atmosphere of the etching or cleaning process (including the case of substantially zero). Therefore, it is possible to provide a method for cleaning a zinc oxide film, which can avoid the adverse effect of the reaction product, and realize a reliable high etching rate and high uniformity.

  Hereinafter, a preferred embodiment of a method for etching or cleaning a zinc oxide film according to the present invention will be described with reference to the drawings. In each drawing of the present application, dimensional relationships such as thickness and length are appropriately changed for clarity and simplification of the drawings, and do not represent actual dimensional relationships. Moreover, in each figure, the same referential mark represents the same part or an equivalent part.

  In the embodiment of the etching process described here, as shown in FIG. 1, a photoelectric conversion device 2 formed on a transparent substrate 1 is formed, a zinc oxide film 3 is formed on the photoelectric conversion device 2, and A mask metal electrode 4 is formed on the surface of the zinc oxide film 3.

  A plate-like member or a sheet-like member made of glass, transparent resin or the like is used for the transparent substrate 1 used in a photoelectric conversion device of a type in which light enters from the substrate side. The photoelectric conversion device 2 is a semiconductor element having a photoactive layer, and the photoelectric conversion device is preferably formed using a thin film forming method such as CVD, sputtering, or vapor deposition. Next, a zinc oxide film 3 is formed on the photoelectric conversion device 2 by CVD or sputtering. Further, a metal mask 4 is deposited on the patterning mask to form a back electrode. Next, the zinc oxide film 3 is dry etched using an etching apparatus.

  As this etching apparatus, for example, an apparatus utilizing a reactive ion etching method is used. This apparatus is an apparatus for performing an etching process by converting a process gas into plasma by a high frequency applied from a high frequency power source between parallel plate type electrodes. In addition to the reactive ion etching method, the etching apparatus may be, for example, a high frequency inductively coupled plasma method (ICP: Inductively) as long as it can generate radicals and ions by plasma and gasify the metal in the oxide semiconductor film. Those using various plasma generation sources such as Coupled Plasma (ECR) and Microwave Plasma Etching (ECR) can be applied.

  A mixed gas of methane and hydrogen is used as a process gas introduced into the etching apparatus. The mixing ratio of methane in the mixed gas immediately before the methane supply of the mixed gas of methane and hydrogen used as the process gas is stopped or the supply of methane is reduced stepwise or continuously is set to a range of 20% by volume or less. Is preferred. Furthermore, the mixing ratio of methane is preferably 10% by volume or less, and particularly preferably 7% by volume or less, because generation of amorphous carbon deposits during the etching process can be further suppressed.

  Moreover, it is preferable that the minimum of the mixing ratio of methane in the said mixed gas is 1 volume%, Furthermore, it is 2 volume%. If the mixing ratio of methane is too low, the number of reactive species in the etching or cleaning process decreases and the etching process speed decreases.

  The process is characterized in that the methane supply is stopped in the middle of the etching or cleaning process or the methane supply is decreased stepwise or continuously to perform the etching or cleaning process, but preferably the process does not contain methane finally. It is preferable to perform etching or cleaning treatment by supplying a gas. More preferably, the etching or cleaning process is performed by adjusting the amount of methane and finally supplying only hydrogen.

  As a process gas supply method, it is preferable to perform the etching process by stopping the supply of methane gas in the middle of the etching or cleaning process.

  It is preferable to perform the etching or cleaning process in an atmosphere substantially free of methane at the final stage of the process. As a method for supplying methane, the flow rate may be decreased stepwise or continuously, or the supply of methane may be stopped quickly.

  In the preferred embodiment of the method for etching a zinc oxide film according to the present invention, although not shown, the dry etching process of the present invention can also be performed to control the uneven shape of the zinc oxide film produced on the substrate. It is.

  The cleaning process in the present invention is a process for etching a zinc oxide film adhering to the inside of a thin film forming apparatus such as a CVD, and the same process as the process used for the etching process is executed in the apparatus. By doing so, the zinc oxide film adhering to the inside of the apparatus can be stably removed without opening the apparatus.

  Hereinafter, specific examples of the dry etching method for a zinc oxide film according to the present invention will be described, but the present invention is not limited thereto.

  Reactive ion etching apparatus: A reactive ion etching (RIE) system in which a substrate is placed on a cathode electrode using a general parallel plate type 13.56 MHz high frequency power source (CE-C manufactured by ULVAC, Inc.) 300R). After putting the sample in the chamber of the apparatus and evacuating, the process gas was flowed to excite the plasma and etching was performed.

  Calculation of etching rate: After completion of etching, the film thickness of the sample was evaluated with a spectrophotometer and an ellipsometer, and the dry etching rate was calculated.

Example 1
The zinc oxide film was subjected to a dry etching process by supplying pure hydrogen at a flow rate of 140 sccm for 50 seconds at a pure methane flow rate of 7 sccm, a hydrogen flow rate of 140 sccm, an RF power of 200 W, and a process pressure of 30 Pa. For a second. FIG. 2 shows the result of conversion of the relative variation in the ratio of the amount of methane and the amount of hydrogen remaining in the etching apparatus in this embodiment from the variation in the partial pressure of each gas in the apparatus.

  The amount of methane in the etching apparatus gradually decreases after the supply of methane is stopped, and methane staying in the apparatus becomes substantially zero at the final stage of processing, and etching is performed in an atmosphere containing only hydrogen. . As a result of performing the dry etching process under the above conditions, it was found that the etching rate of the zinc oxide film was 80 angstroms / min, and that etching could be performed stably without generating a non-volatile product.

(Example 2)
The zinc oxide film was subjected to a dry etching process by supplying pure hydrogen at a flow rate of 140 sccm for 60 seconds at a pure methane flow rate of 10 sccm, a hydrogen flow rate of 140 sccm, an RF power of 200 W, and a process pressure of 30 Pa, and then supplying only hydrogen gas at a flow rate of 140 sccm. For a second. Also in this embodiment, the amount of methane in the etching apparatus gradually decreases after the supply of methane is stopped, as in the case of Embodiment 1, and the methane staying in the apparatus becomes substantially 0 at the final stage of the process. Etching is performed in an atmosphere containing only hydrogen. As a result of performing the dry etching process under the above conditions, it was found that the etching rate of the zinc oxide film is 100 angstrom / min, and that etching can be performed stably without generating a non-volatile product.

(Comparative Example 1)
When the zinc oxide film was dry-etched at room temperature, a pure methane flow rate of 7 sccm, a hydrogen flow rate of 140 sccm, an RF power of 200 W, and a process pressure of 30 Pa, the etching rate of the zinc oxide film was 60 Å / min.

(Comparative Example 2)
The zinc oxide film was dry-etched under conditions of room temperature, pure methane flow rate 10 sccm, hydrogen flow rate 100 sccm, RF power 200 W, and process pressure 30 Pa. As a result of performing the dry etching process under the above conditions, the etching rate of the zinc oxide film was 39 Å / min.

(Comparative Example 3)
The zinc oxide film was dry-etched under conditions of room temperature, pure methane flow rate 30 sccm, hydrogen flow rate 140 sccm, RF power 200 W, and process pressure 30 Pa. As a result of performing the etching process under the conditions of this comparative example, non-volatile amorphous carbon-based deposits were generated and etching did not proceed.

  According to the present invention, a zinc oxide film formed on a substrate can be dry-etched, and a photoelectric conversion device having stable and uniform electrical characteristics can be provided on the substrate.

  In addition, the zinc oxide film | membrane used as the object of a process is used not only for what is used as a transparent conductive electrode layer of a photoelectric conversion apparatus but for various uses as a transparent conductor used for a flat panel display, a touch panel, etc.

Structural sectional drawing which shows position embodiment of the zinc oxide film | membrane field processing method which concerns on this invention Example of time variation of relative methane / hydrogen ratio according to the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Photoelectric conversion apparatus 3 Zinc oxide film 4 Metal electrode layer

Claims (4)

  In the dry etching or cleaning method of the zinc oxide film, the etching or cleaning process is performed in a mixed gas atmosphere containing methane and hydrogen, and the supply of methane is stopped in the middle of the etching or cleaning process, or stepwise or continuously. A dry etching method for a zinc oxide film, characterized in that an etching or cleaning process is performed while reducing supply.   In the dry etching or cleaning method of the zinc oxide film, the etching or cleaning process is performed in a mixed gas atmosphere containing methane and hydrogen, and the supply of methane is stopped in the middle of the etching or cleaning process, or stepwise or continuously. 2. The method of dry etching a zinc oxide film according to claim 1, wherein the supply is reduced and a process gas not using methane is supplied to perform etching or cleaning.   The mixed gas used for the etching or cleaning process is stopped immediately or the mixed gas immediately before the supply of methane is reduced stepwise or continuously is within a range where the proportion of methane in methane and hydrogen is 20% by volume or less. The method for dry etching a zinc oxide film according to claim 1, wherein the method is dry etching.   The dry etching of a zinc oxide film according to any one of claims 1 to 3, wherein the etching or cleaning process is finished after methane becomes substantially zero in the gas atmosphere in the chamber in which the etching or cleaning process is performed. Method.