Nanoline Formation by Using Small-Aggregate Resist and Supercritical Resist Drying
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NANOLINE FORMATION BY USING SMALL-AGGREGATE RESIST AND SUPERCRITICAL RESIST DRYING Hideo Namatsu NTT Basic Research Laboratories, NTT Corporation 3-1 Morinosato Wakamiya, Atsugi-shi, Kanagawa, 243-0198 JAPAN ABSTRACT Nanolines as small as 7 nm wide have been formed using a small-aggregate resist and supercritical resist drying. Aggregates consisting of resist polymers cause pattern roughness and cause nanolines to break. Hydrogen silsesquioxane (HSQ) is a resist material in which the aggregates are small due to its three-dimensional network. Development with an aqueous solution of TMAH provides high-contrast patterns. The problem that nanolines formed in HSQ collapse after development is solved by a supercritical resist drying technique. Supercritical drying suppresses the swelling of the resist by the rinse solution during development and thereby prevents nanolines from collapsing. The use of both small-aggregate HSQ resist and supercritical resist drying enables free-standing nanolines with a high aspect ratio to be formed without collapse. INTRODUCTION The dramatic advances in lithography have now given birth to the age of nanolithography. There are two trends in the development of nanolithography: the sub-100-nm and sub-10-nm regimes. For 100- or sub-100-nm lithography, the most promising exposure sources are EUV light, X-rays, e-beams, and ion-beams which will be essential in future generations of lithography. For sub-10 nm lithography, the range of subjects being researched is much broader, and include scanning probe techniques and non-lithographic techniques such as self-organizing processes, in addition to those for conventional lithography. Though the development of lithographic tools like exposure sources are important, the development of resist materials and processes is also crucial to nanolithography and nanopatterning, because a resist is the medium through which a beam from an exposure sources is converted into a pattern. Resolution is the primary issue in the formation of nanolines in a resist. The formation of lines 10 nm wide and even finer has already been reported, but in many cases the resist was not thick enough for use as an etching mask. In addition, the lines were not straight but wavy [1,2]. Excess waviness results in pattern collapse. So, there is an urgent need for a method of forming thick enough resist patterns while keeping the line width at the nanometer scale, which requires the development of new resist materials and processes. In addition to resolution, another serious issue in the formation of nanolines is pattern roughness. This is generally called line-edge roughness (LER), and it causes linewidth fluctuations, which give rise to variations in device characteristics. If the fluctuations are 3 nm (σ) and a line 10 nm wide is formed, then the maximum variation in the line width is 10 ± 9 nm (3σ). This means that the line will break. So, reducing LER, or linewidth fluctuations, is very important for nanopatterning. It has been reported that the polymer aggregates in resist films ar
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