In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of miniaturization. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation such as g-line and i-line radiation has been used as the exposure light source, but recently, KrF excimer lasers (248 nm) have been introduced.
Furthermore, one example of a resist material that satisfies the high resolution conditions required to enable reproduction of a pattern of minute dimensions is a chemically amplified resist composition, which includes a base resin that undergoes a change in alkali solubility under the action of acid, and an acid generator that generates acid on exposure. Chemically amplified resist compositions include negative compositions, which contain an alkali-soluble resin (a base resin), an acid generator, and a cross-linking agent, and positive compositions, which contain a resin that exhibits increased alkali solubility under the action of acid (a base resin) and an acid generator.
Currently, onium salts are the most commonly used acid generators.
In recent years, with the rapid miniaturization of semiconductor elements, ever higher levels of resolution are being demanded, and for example, line and space resolutions of 90 nm or less are now being sought. As a result, LER (line edge roughness) is becoming a serious problem.
However, currently, the anion portions (the acid portions) of the onium salts used as acid generators are almost all chain-like fluorinated alkylsulfonate ions, and other acids are not used due to problems with the degree of acidity. In terms of enabling favorable control of the diffusion length of the acid within the resist film, the alkyl chain within these fluorinated alkyl groups preferably contains a large number of carbon atoms, but fluorinated alkylsulfonic acids in which the alkyl chain contains 4 or more carbon atoms are starting to attract comment over concerns about safety, and the use of such compounds is now being restricted on a worldwide basis.
Accordingly, an acid generator that provides a short diffusion length within the resist film without using the above types of long-chain fluorinated alkylsulfonic acids is now required.
(Patent Reference 1)
Japanese Unexamined Patent Application, First Publication No. 2003-160612
(Patent Reference 2)
Japanese Unexamined Patent Application, First Publication No. 2003-140346
(Patent Reference 3)
Japanese Patent (Granted) Publication No. 3,390,702