ABSTRACT:A diphenyliodonium salt with an environment-friendly dye as anion was designed. This salt was shown to possess photosensitivity suitable for use as a chemically amplified resist at both 365 and 405 nm. PAG of tris(diphenyliodonium) 9-hydroxy-pyrene-1,4,6-trisulfonate had a negative Ames test, showed good thermal stability, and had a decomposition temperature of 199.9C. The quantum yield of acid generation upon irradiation was 0.63. The mechanism of acid generation was intramoleculor electron transfer from the excited dye moiety to the iodonium structure. The photosensitivities of PAG in a polymer with a t-butoxycarbonyl protecting group were 31 and 58 mJ/cm 2 for 365 and 405 nm light, respectively.
Chemically amplified resists based on acid catalyzed reaction have been widely utilized in the development of semiconductor technology and resists.Photo-acid generator (PAG) that generated acids upon irradiation with light has been played an important role on the progress of chemically amplified resist.In general, the required properties for PAGs are high sensitivities, high thermal stability, strong acid generation and high solubility in solvents and matrixes. In addition, it is important that PAG and precursor of acid are non-mutagen.PAG's molecules were classified into ionic structure such as onium salts of sulfonate derivatives and non-ionic structure such as sulfonate derivatives of N-hydroxynaphthaleneimide.In the PAGs, onium salts have advantage of easy structure modification to alter their spectral absorption characteristics.Then various onium salts were applied as a PAG in photolithography. [1][2][3][4][5][6][7][8] The PAGs that have photosensitivity at 193 nm or 248 nm have been studied, however, there were a few reports about the onium salt's PAGs for 365 nm light 9-13 and moreover, few reports about PAGs and the precursor of acid considered the safety and environmentally sensitive technology.In this study, we reported a new type PAG with environment-friendly dye that has photosensitivity at 365 nm light. The PAG is triiodonium salt of 9-hydroxypyrene-1,4,6-trisulfonic acid (PC-DPI, 1). The dye (2) is referred to as pyranine conk that contained cosmetic and shampoo, recently.
EXPERIMENTAL
ReagentAll of the solvents used in this study were commercially available, and used after being dehydrated with molecular sieves.
MaterialsPyranine conk, 2 (Hodogaya Chemical) and diphenyliodonium chloride (Tokyo Kasei, DPI-Cl) were used as received. Tetrabromophenol blue (TBPB) and ptoluenesulfonic acid was purchased from Wako Pure Chemicals. Tetrabutylammonium hydroxide (TMAH) 2.38 wt % solution was purchased from Tama Chemical Company.
A half-tone phase shift mask process has been developed. The writing and process for normal masks are found to be applicable to HT-PSMs. A dry etch process has been adopted to etch the shifter. Several characteristics of HT-PSMs such as CD uniformity, CD linearity, edge roughness and corner rounding, positional accuracy in the EB process, selectivity in dry etch, pattern profile, durability against cleaning, pelliclization and a blind pattern are evaluated. The process shows a good performance sufficient for first generation 64MDRAM mask making. The EB writing causes no charge-up problem. The selectivity of HTshifter to an i-line resist and an new type EB resist in dry etch is satisfactory and the selectivity to a fused silica substrate is more than 300.An exposure test was conducted with our HT-PSM. Coherency factor () of a stepper is founds to strongly affect the defocus range and exposure latitude.Recently, we have developed HT-PSMs with a practical multilayer structure for our shifter. Blanks with a shifter layer and an opaque layer were used, the properties of which have been described in paper I. The writing and process for normal masks are found to be applicable to HT-PSMs because our shifter is made of Cr compounds only. At present a dry process has been adopted to etch the shifter layer because of the ease of obtaining a side-wall angle of nearly 90° in the pattern.Specifications for new generation masks are so strict that both high accuracies of writing machines and tight process control are required. Table 1 lists the requirements for conventional masks for three generations of DRAMs. HT-PSMs will be used from the first generation of 64MDRAM manufacturing. We set our target of specifications for HT-PSMs as follows;248
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