RESIST HEATING IN CELL PROJECTION ELECTRON-BEAM DIRECT WRITING

Electron beam (EB) direct, writing systems have often been used for fa bricating sun-half-micron advanced devices because EB direct writing i s the most practical method for making the required patterns. Recently , the cell projection (CP) method has become indispensable for increas ing the writing throughput in the EE: direct writing system. However, it is considered that resist heating may be seriously aggravated below the quarter-micron level when tile CP method is used, because the tot al deposited energy: which is irradiated by one CP EB shot, is almost the same as that irradiated by one variably shaped (VS) EB maximum siz e shot, Resist healing in the case of the CP method is calculated by a finite element. method using the ANSYS (Ver. 5.0A: ANSYS, Inc.) progr am. In particular. thermal diffusion calculation is mainly carried out under the conditions of 50kV acceleration voltage and 10A/cm(2) curre nt density for practical application to advanced device fabrication. T he calculated results suggest that resist heating in the CP method is mainly caused by the horizontal thermal flux between plural EB shots w ithin the area of one CP shot, by the same mechanism as proximity resi st heating under the VS method. Therefore, CP EB writing causes horizo ntal-made resist heating. In particular, when a low current density is used, this resist heating mode arises significantly. However: CP writ ing. with high acceleration voltage causes a reduction in the rise of the resist temperature, which causes resist heating, When the EB irrad iation time is longer than 1.0 mu s under practical EB writing conditi ons, the resist temperature increases proportionally to the decrease o f writing pattern size in the case of the CP writing with a maximum sh ot size of 5.0 x 5.0 mu m. It is also shown that the larger the beam b lur of an incident beam, the more serious is the resist heating. When a highly sensitive resist (10 mu C/cm(2)) is used under these practica l conditions, however, resist heating in the CP method is prevented wi thout writing throughout degradation regardless of the CP maximum shot size, because the resist temperature does not rise above the thermal denaturation temperature of standard EB resists, Accordingly, the maxi mum CP shot size: which affects the writing throughput, is determined by the proximity effect and the Coulomb interaction for fine pattern f abrication.