Makoto Hanabata

Design concept for a high‐performance positive photoresist

An attempt was made to design a high‐performance positive photoresist from the standpoint of the image formation process. There are a lot of trade‐off relationships among performance of a positive photoresist. A study was made to raise performance without the decrease in other performances. It was necessary to design a new type of novolak resin that has a molecular structure different from the existing materials. Many kinds of cresol–formaldehyde type novolak resins were synthesized and evaluated lithographically. Such items as molecular weight, molecular weight distribution, isomeric structure of cresol, the position of methylene bond, and the content of quinonediazide in a positive photoresist were investigated. Three methods were found useful: (i) to apply high‐ortho novolak resins that have a high content of ortho–ortho’ methylene bonds (ii) to optimize molecular weight distribution of novolak resins, and (iii) to optimize the content of quinonediazides in a photoresist. These results are explained in...

Novolak Design For High Resolution Positive Photoresists

The mechanism of resolution improvement in novolak-based positive photoresists was investigated from the stand-point of the image formation process. The image formation process in the novolak-quinonediazide system involves the dissolution inhibition in unexposed parts and the dissolution promotion in exposed parts. The 4-(gamma)-value, which is one of the indexes of resolution capabilities, depends greatly on the difference between the solubility of unexposed parts and that of exposed parts, i.e.-the lower dissolution rate in unexposed parts(Ro) and the higher one in exposed parts(Rp) are desirable to obtain high γvalues.

High performance positive photoresists

An attempt was made to improve the sensitivity and heat resistance of positive photoresist applicable to very large‐scale integrated (VLSI) semiconductor processing. It was found out that, in general, when the lithographic sensitivity of resist was made higher, film thickness retention and heat resistance were lowered. A study was made on how to raise sensitivity without decrease in film thickness retention and heat resistance. It was necessary to design a new type of novolac resin that has a molecular structure and a molecular weight different from the existing materials. Many kinds of cresol‐formaldehyde type novolac resins were synthesized and evaluated. Such items as the isomeric structure of cresol, the position of the methylene bond, and the influence of molecular weight were investigated. As a result of the optimization of these items, a number of different resist materials that exhibit improved characteristics in sensitivity, film thickness retention, and/or heat resistance were obtained. It is al...

High Resolution Positive Photoresists

An attempt was made to improve the resolution capability of positive photoresists applicable to VLSI semiconductor processing. It was found out that in general, when the contrast (y(gamma)-value) of resists is made higher, the exposure latitude and the mask size reproducibility tend to be lowered. Study was made how to raise Y-value without decrease in the exposure latitude and the mask size reproducibility. It was necessary to design a new type of novolac resin that has a molecular weight and a molecular structure different from the existing materials. Many kinds of cresol-formaldehyde type novolak resins were synthesized and evaluated. Such items as the isomeric structure of cresol, the position of the methylene bond and the influence of molecular weight were investigated. As a result of the optimization of these items, a number of different resist materials that exhibit improved resolution capabilities were obtained. It is also remarkable that the introduction of the new polymer design not only enabled to improve resolution capabilities, but also made the process latitude much wider at various points of resist work including, prebaking temperature, developing time and developing temperature, compared to the so far commercially available products. This new material makes it possible to obtain fine pattern resolution required in VLSI processing. Moreover, wider latitude of processing conditions assures higher yields of the circuits.

A selection principle of phenolic compounds for novolak resins in high performance positive photoresists

The relationship between resist performance and the kinds of phenolic compounds for novolak resins was investigated from the standpoint of the image formation process. Dissolution rates were measured on photoresists containing novolak resins made from various phenolic compounds including phenol, cresol, ethylphenol, butylphenol, and their copolymers. It was found that there are suitable combinations of phenolic compounds to exhibit high resist performance. On the basis of the experimental results, we discuss the effect of the kinds of phenolic compounds on the dissolution characteristics and the structure of novolak resins. Finally, we propose a selection principle of phenolic compounds for novolak resins useful to design high performance positive photoresists.

Novolac design for high-resolution positive photoresist (III): a selection principle of phenolic compounds for novolac resins

The relationship between resist performance and the kinds of phenolic compounds for novolak resins was investigated from the standpoint of the image formation process. Dissolution rates were measured on photoresists containing novolak resins made from various phenolic compounds including phenol,cresol,ethylphenol,butylphenol,and their copolymers. It was fo.und that there are suitable combinations of phenolic compounds to exhibit high resist performance. On the basis of the experimental results,we discuss the effect of the kinds of phenolic compounds on the dissolution characteristics and the structure of novolac resins. Finally,we propose a selection principle of phenolic compounds for novolak resins useful to design high performance positive photoresists. 1.lntroduction

Design of PACs for high-performance photoresists (II): effect of number and orientation of DNQs and -OH of PACs on lithographic performances

PACs which have a defined number of DNQs and -OH groups were synthesized with high yield by the selective esterification method, and the relationship between number and orientation of DNQs, and lithographic performances and dissolution properties, were examined and measured by puddle development. From our present and previous examinations, it is concluded that existence of one -OH group and two DNQs, which are separated from each other on a ballast molecule, is the most preferable structure of PAC, which provides a photoresist not only a high (gamma) -value and resolution capability but also suitable sensitivity and a scum-free pattern. According to concept of polyphotolysis results are discussed quantitatively by dissolution inhibition effect and the number of DNQs of the PAC.

Design of PACs for high-performance photoresists (I): role of di-esterified PACs having hindered -OH groups

Steric hindrance on a ballast molecule causes selective esterification of -OH groups and provides novel di-esterified PACs having -OH group(s) with high selectivity. These novel PACs give photoresists higher sensitivities, (gamma) -values and resolutions, than those of fully esterified PACs. Also, these novel PACs provide scum-free patterns. Comparison of dissolution properties of a novel di-esterified PAC having a sterically hindered -OH with those of a di-esterified PAC suggests that the presence of -OH enhances dissolution rates, but it does not change the slope of logR-logE plots. DRMs agitated development reduces a large (gamma) -value of a novel PAC observed in puddle development. On the other hand, (gamma) -values of fully esterified PACs were not affected by the change of development methods. This observation suggests significance of (gamma) - value evaluation by puddle development for the investigation of high performance PACs.

Observation of internal structure of a positive photoresist image using cross-sectional exposure method

The internal structure of a novolak/quinonediazide type positive photoresist image was observed using a cross‐sectional exposure method. On the surface of a photoresist image, a photochemically inert layer was detected which does not return to diazo and phenolic compounds with acid treatment. This shows that this layer does not consist of the azoxy compounds. Fourier transform infrared spectrum indicates that this layer includes azocoupling reaction products. It was also found that the formation of the photochemically inert layer and the dissolution of the layer takes place simultaneously at the development front and a resist image is formed during the competition between these two reactions.