Etching a substrate: processes – Gas phase etching of substrate – Application of energy to the gaseous etchant or to the...
Reexamination Certificate
1999-04-30
2001-11-27
Gulakowski, Randy (Department: 1746)
Etching a substrate: processes
Gas phase etching of substrate
Application of energy to the gaseous etchant or to the...
C252S079100, C438S710000
Reexamination Certificate
active
06322715
ABSTRACT:
TECHNICAL FIELD
This invention relates to a fluorocarbon gas-containing gaseous composition for dry etching, and a dry etching process using the gaseous composition. More particularly, it relates to a gaseous composition for dry etching, and a dry etching process, by which the etching can be conducted at a high rate with good selectivity to a protective thin film such as a photoresist or a polysilicon.
BACKGROUND ART
In recent years, a rapid progress has been achieved in the field of electronics. One reason therefor exists in that extremely highly integrated semiconductor devices have been put into practice. A dry etching technique is very important for forming a fine pattern on a silicon wafer for achieving the high integration, and is constantly progressing.
In dry etching, in order to produce fluorine-containing active ingredients by plasma discharge or other means, gases of compounds containing many fluorine atoms have heretofore been used as the etching gas. As examples of the fluorine-containing etching gas, there can be mentioned highly fluorinated compounds such as carbon tetrafluoride, sulfur hexafluoride, nitrogen trifluoride, carbon trifluoro-monobromide, trifluoromethane, hexafluoroethane and octafluoropropane.
International efforts for conserving the global environment are being made, and especially those for preventing or minimizing the global warming are now attracting a great interest. For example, in IPCC (Intergovernmental Panel on Climate Change), regulations on control of the total amount of carbon dioxide emission have been established in the international agreement. Under these circumstances, it is pointed that, from a viewpoint of prevention of the global warming, there is an increasing need of developing alternatives for the highly fluorinated compounds which have heretofore widely been used and which have a long life in the air and cause the global warming. More specifically, it is said that carbon tetrafluoride, hexafluoroethane and sulfur hexafluoride have a life in the air of 50,000, 10,000 and 3,200 years, respectively. These fluorinated compounds exhibit a large absorbability for infrared rays and exert a considerable influence upon the global warming. Thus, it is eagerly desired to develop an etching process utilizing a novel etching gas which does not cause the global warming and has etching performances comparable to those of the heretofore used etching gases.
Various proposals have been made for enhancing the selectivity to a protective thin film such as a photoresist or a polysilicon in a dry etching process. For example, a proposal has been made in Japanese Unexamined Patent Publication No. H4-170026 wherein a silicon compound is etched by using a gas containing an unsaturated fluorocarbon such as perfluoropropene or perfluorobutene while the temperature of the substrate to be etched is controlled to a temperature not higher than 50° C. Another proposal has been made in Japanese Unexamined Patent Publication no. H4-258117 wherein etching is effected in a manner similar to the above proposal by using a gas containing a cyclic saturated or cyclic unsaturated fluorocarbon such as perfluorocyclopropane, perfluorocyclobutane, perfluorocyclobutene or perfluorocyclopentene, while the temperature of the substrate to be etched is controlled to a temperature not higher than 50° C.
However, the dry etching techniques heretofore proposed in the above patent publications have problems such that the etching gas is not sufficiently decomposed by the plasma discharge, depending upon the particular dry etching conditions, to polymerize on the substrate whereby a polymer deposition in the form of a brown thin film is produced on the substrate, and further that the rate of etching is not high and the selectivity to a protective thin film such as a photoresist or a polysilicon is low.
DISCLOSURE OF THE INVENTION
In view of the foregoing conventional techniques, an object of the present invention is to provide a gaseous composition for dry etching by which dry etching is conducted with a high selectivity to a protective thin film such as a photoresist or a polysilicon and at a high rate of etching without production of a polymer film by deposition in the etching step, and thus, good etching results are obtained.
Another object of the present invention is to provide a dry etching process by which dry etching can be industrially advantageously conducted by using the above-mentioned gaseous dry etching composition.
The inventors have continued researches into dry etching of a silicon compound by using dry etching gases containing various saturated and unsaturated, and straight chain and cyclic fluorine-containing compounds, and surprisingly, found that, when a dry etching gas composition containing octafluorocyclopentene is used, and a small amount of oxygen gas or a gaseous oxygen-containing compound is incorporated in the dry etching gas composition, satisfactory etching can be achieved at a high rate of etching with a high selectivity to a photoresist and a high selectivity to a polysilicon and without deposition of an undesirable polymer film.
In accordance with the present invention, there is provided a gaseous composition for dry etching, comprising a octafluorocyclopentene and 1 to 40% by mole, based on the octafluorocyclopentene, of at least one oxygen ingredient selected from oxygen gas and oxygen-containing gaseous compounds.
In accordance with the present invention, there is further provided a dry etching process, characterized in that dry etching is conducted by using a gaseous composition comprising a octafluorocyclopentene and 1 to 40% by mole, based on the octafluorocyclopentene, of at least one oxygen ingredient selected from oxygen gas and oxygen-containing gaseous compounds.
BEST MODE FOR CARRYING OUT THE INVENTION
The gaseous composition for dry etching used in the present invention is characterized by containing octafluorocyclopentene. When octafluorocyclopentene is used, the etching rate and the selectivity are sufficiently high, and there is no problem of polymer deposition and volatility.
In the present invention, a perfluorocarbon selected from perfluorocycloolefins other than octafluorocyclopentene, straight chain unsaturated perfluorocarbons, and perfluoroalkanes and perfluorocycloalkanes may be used, in combination with octafluorocyclopentene. However, if these optional perfluorocarbons are used in a salient amount, the object of the present invention cannot be achieved. Therefore, the amount of these perfluorocarbons is usually not larger than 30% by weight, preferably not larger than 20% by weight and more preferably not larger than 10% by weight, based on the total amount of the fluorocarbons.
In the gaseous composition for dry etching, at least one oxygen ingredient selected from oxygen gas and oxygen-containing gaseous compounds is contained in addition to octafluorocyclopentene. The term “oxygen-containing gaseous compounds” used herein we mean oxygen-containing compounds which are gaseous under the etching conditions employed. As specific examples of the oxygen-containing gaseous compounds, there can be mentioned carbon oxide gas such as carbon monoxide and carbon dioxide, nitrogen oxide gas, and sulfur oxide gas. Of the oxygen ingredients, oxygen gas is preferable. By using a dry etching gas containing a perfluorocycloolefin, and oxygen gas and/or an oxygen-containing gaseous compound, a higher selectivity to a photoresist and a higher selectivity to a polysilicon are obtained and etching can be conducted at a higher rate, than those attained in the case when a dry etching gas containing a perfluorocycloolefin, but, containing neither oxygen gas nor an oxygen-containing gaseous compound. The oxygen gas and the oxygen-containing gaseous compounds may be used either alone or as a combination of at least two thereof.
The amount of the oxygen ingredient is in the range of 1 to 40 moles, preferably 3 to 30 moles and more preferably 5 to 15 moles, per 100 moles of the octafluorocyclopentene. If the amount of the oxygen ingredient is to
Goto Kuniaki
Sekiya Akira
Takagaki Tetsuya
Yamada Toshiro
Armstrong Westerman Hattori McLeland & Naughton LLP
Gulakowski Randy
Japan as represented by Director General of the Agency of Indust
Olsen Allan W.
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