LB resists for traditional lithography
 

Development of super thin uniform electron beam sensitive coatings is of interest for high resolution lithography. Attempts to decrease the thickness of ordinary spin-coated electron beam resist materials always result in considerable density of pinholes and unacceptable level of non-uniformity of films.

Langmuir-Blodgett (LB) films are considered as promising candidates which can enable to overcome these problems as it permits the formation of regular  ultrathin films with low number of defects.

The following copolymers based on cyanoacrylates were used for the deposition of LB negative electron beam resists:

We tested the sensitivity of Langmuir-Blodgett films composed of 48 monolayers (the thickness of one monolayer  is about  0,7 nm) , finding a dose of less than 1 mC/cm2, and employed them  as masks for wet etching of Cr metal layers, with resolution up to 300 nm.

SEM images of exposed and developed samples with dense patterns with 2 mm and 1mm features and patterns with a resolution up to 300 nm are shown.

The CP-HCA-1 resist exhibits good EBL results obtained by a relatively easy experimental operation, having a required dose about one order of magnitude lower than chemically amplified resist of good sensitivity

An important characteristic of the protective film is its resistance to treatment with etching agents.

500 and 400nm Cr dense patterns obtained by etching Cr metal through the CP-HCA-1 mask 30 nm thick, and a Cr etched 300 nm single feature, displayed in AFM and SEM images of figures a and b respectively, exhibit an etched depth around 40 nm. This clearly demonstrates the resistance of the exposed CP-HCA-1 layers  (consisting of 48 monolayers with the total thicjness of 30nm) against etching agents. Further studies, aiming at investigating the effect of the CP-HCA-1 thickness and the ultimate achievable resolution, are currently in progress in our laboratories.

Results of present work demonstrate that super thin films of copolymers CP-HCA-1 and CP-HCA-2 based on heptylcyanoacrylate and deposited by LS technique satisfy the main requirements for their utilization as negative electron beam resists. Masks of high uniformity with thickness necessary for the reliable protection (about 15-18 nm) can be deposited in few minutes onto substrates of large dimensions normally used in microelectronics. The films possess the values of sensitivity and contrast suitable for their applications in real technological processes.

LB films of fluorocarbon polymer – a new electron beam sensitive material

Uniform LB films of poly(methacrylate) with fluorocarbon side groups (PPFPM) can be deposited at low surface pressure with a modified LS technique, which provides high speed of deposition. The quality of monolayer transfer does not vary during the deposition from ultra thin to relatively thick layers and thus the compound can be used for the development of nanostructured materials.

Positive pattern is produced if the irradiation dose does not exceed 75 mC/cm2. The film sensitivity is approximately the same as that of poly(methacrylate) LB resists, but the main advantage provided by PPFPM is the improved deposition quality. At high irradiation doses negative patterns can be also produced.

 

1. V.I. Troitsky, N.K. Matveeva, Thin Solid Films 327-329 (1998) 659.

2. T.S. Berzina, V.I. Troitsky, S. Vakula, A. Riccio, A. Morana, M. De Rosa, S. Dante, E. Maccioni, F. Rustichelli, P. Accossato, C. Nicolini, Mater. Sci. Eng. C 3 (1995) 13.

3. V.I.Troitsky, N.K.Matveeva, Thin Solid Films 327-329 (1998) 659.