|
The majority of VLSI exposure tools used in production are optical systems that use UV light. Optical lithograpy is capable of resolution below 1 urn. Reduced feature size and increased circuit complexity in modern VLSI devices, therefore, impose stringent requirements on photomasks. Photomasks used in wafer steppers and high resolution IX full-field projection systems require high performance such as good chemical durability, pattern stability during cleaning, and high resolution. Chromium films used for conventional photomasks do not adhere well to quartz substrates, resulting in pattern defects due to exfoliation. Furthermore, the fabrication of a Cr mask with high resolution patterns using dry etching is difficult. Pattern defects, caused by poor adhesion, can be generated during photomask cleaning by ultrasonic methods or scrubbing. Dry etching of Cr masks has the problem of low throughput and marginal resist protection. To solve these problems, we have developed a new photomask blank Page 2 using a molybdenum sillclde (MoSi) film deposited on the quartz substrates. A MoSi film deposited on a quartz substrate offers major advantages as a high performance photomask material for VLSI fabrication. There Is no missing pattern due to exfoliation after ultrasonic cleaning with frequency of 28 kHz and 300 W of power, and after being scrubbed over 10 cycles with a high pressure water Jet. Reflectivity and optical density of the MoSi film are not affected by acidic chemicals. Moreover, dry etching with CF4+02 can be aone at a rate 50 nanometers per minute for CMS resist, which is more than five times as fast as the etch rate for chromium masks. Dry etching of MoSi films with a PBS resist has been realized in fabrication of subraicron patterns. In addition a photomask with a MoSi Is easier to repair by PIB than one with chromium because of the higher sputter yields for a MoSi.
|
