No abstract

Dense 0.1Op.m hole pattern formation has been achieved by optical lithography with KrF wavelength. Double exposure utilizing two alternative phase shift masks of lines and spaces pattern produces dense small hole images with enough focus and exposure latitudes. Applying this method with a KrF stepper and chemically-amplified negative-tone resist, 2-dimensional 0 . 1 3~ hole array with the pitch of 0.4Opn has been resolved with 1 . 0~ DOF, and resolution limit size and pitch are less than 0.1Op.m and 0.28p1, respectively.

The minimum feature size for the LSI circuit geometry will reach 20 nm in the upcoming 45 nm technology node. In order to achieve this target, various new lithography technologies, such as Electron-beam (EB) and Extreme-ultraviolet (EUV) lithography, are now being intensively developed. However, as shrinking gate length, line edge roughness (LER) of fabricated resist patterns becomes one of the most significant issues [1][2][3]. For the resist material aspect, the application of compounds with low molecular weight and/or narrow polydispersity may be one of the key concepts to dissolve this issue due to its reduced molecular weight and controlled structure [4][5][6][7]. We have reported the characteristics and LER properties of molecular resists based on low molecular weight polyphenols as a chemically amplified (CA) positive-tone EB resist [8][9]. In this paper, new molecular resist based on cholate derivatives for EB lithography will be reported. Figure 1 shows the structures of two cholate derivatives (C2ChDM and C2E) prepared for resist base matrix. The etch rates of C2ChDM and C2E, which were measured under CF4/CHF3/He mixed gas process, were almost the same as polyhydroxystyrene (PHS) as shown in Fig. 2. From the dissolution rate measurement by using alkaline developer, the model resist samples formulated with C2ChDM or C2E as base matrix and photo-acid generator originated from onium-salt (resist-A and B, respectively) showed good sensitivity and the dissolution behavior of common CA positive-tone resist. Furthermore, the FT-IR spectra of resist-A and B films unexposed and exposed with the EB lithography tool was measured. A cleavage reaction of acetal bonds occurred by EB irradiation and PEB treatment as the characteristic signals for acetal bonds at around 949 cm-' and 1735 cm-' became weak. From the dissolution rate measurement and the FT-IR spectra changes, we confirmed that the resist-A and B could work as common CA positive-tone resist. The evaluation results with the resist-A and B by using EB exposure tool indicated the resolution of 120 nm lines and spaces pattern as shown in Fig. 4. References[1] C.

Although ArF excimer laser lithography is expected to attain the highest resolution possible in optical lithography, its application to 0.13-pm devices has not yet adequately demonstrated. In next generation sub-0.10 pm devices, it is believed that the mix and match process is indispensable with optical lithography and other types of lithography. One of the reason is the difficulty of fabricating contact holes with a larger process margin. Here, we demonstrate that it is possible to make 0.13-pm patterns using a single layer resist in combination with resolution enhancement techniques, and to make sub-0.10 ym contact holes using the Top Surface Imaging (TSI) process. Figure 1 shows a pattern formed by using a single layer resist of the alicyclic group. The process for this high resolution resist is based on an analysis of methacrylate copolymer by percolation theory. Figure 2 shows the diffusion contrasts calculated by simulation and experiment results of dissolution rate measurement for methacrylate copolymer. This resist has excellent performance through the use of an alternating phase shifting mask (PSM), as shown in Fig. 3. We observed that bottom anti-reflective coating (BARC), and annular illumination could extend the depth of focus (Table 1, Table 2). Using such techniques, we obtained 0.12-pm resist patterns of actual devices (Fig. 4).We have already reported that the TSI process can be used to fabricate a sub-0.10 pm L&S.We tried to make contact holes using NTS-4 (Sumitomo Chemical Co., Ltd.). Silylation was done by dimethylsilyldunethylamine (DMSDMA) in the vapor phase. Then, silylated resist was developed in 02-SO2 plasma. The exposure tool was an IS1 stepper (1OX reduction and 0.6-NA).A good pattern profile for a 0.09-pm contact hole was obtained ( Fig. 5(a)). A high sensitivity of 20 mJ/cm2 was also achieved. This process was optimized by theoretical calculation methods.We etched 1.0-pm thickness Si02 film using this resist pattern as a mask. A vertical contact hole pattern (aspect ratio 12) was obtained, as shown in Fig. 5 (b). After dry etching, the resist was successfully removed by 0 2 ashing without residue, as shown in Fig. 5 (c). We evaluated the process margin for this procedure. A exposure latitude of +/-lo% was obtained with a 0.10-pm contact hole (Fig. 6). A focus latitude of 0.3 pm was obtained for the Cr mask (Fig. 7).We obtained a 0.5-pm DOF using an attenuated phase shifting mask. This indicate that this process is suitable for dynamic planarization substrates such as those in the CMP process.We demonstrated that ArF lithography is able to be applied to multi-generation device fabrication of 0.13-ym process using a single layer resist and a sub-0.10 pm process using TSI.

Probabilistic gel formation theory in negative tone chemically amplified resists used in optical and electron beam lithography J.In KrF or ArF resist processing, a chemically amplified resist is widely used for ultralarge scale integrated device fabrication. Decomposition ͑positive resist͒ or cross linking ͑negative resist͒ is amplified by an acid catalytic reaction during post-exposure baking ͑PEB͒. T-top forming becomes a serious problem in these resists. In resist simulation, to take these characteristics into account, percolation theory is introduced. The acid and product distributions during PEB are iteratively calculated. Thus, we can conclude that the acid and product distribution in resist films are time dependent. Moreover, a resist simulator that can take into account macroscopic feature changes from microscopic molecular structural change is necessary. From resist surface observation and slow positron annihilation measurements, free volume generation is confirmed. A new resist process model, including prebake, PEB, and development for chemically amplified resists is established by the cluster model. CPU time is 1 min each for a three dimensional image and for development, which is fast enough for practical evaluation use. The defocus dependence of the resist profile agrees well with the experiment. For chemically amplified resists, decomposition or cross linking proceeds vertically rather than horizontally. Thus, a rectangular resist profile can be obtained. Simulation results based upon this model can describe T-tops or resist bridges.