Proximity effect

If electrons are used for the irradiation of resist films, always a certain amount of scattered radiation will occur, either as forward scattering due to an interaction with the resist material or as backscattering from the substrate (wafer). This phenomenon is called proximity effect and results in undesirable changes of the structures. The proximity effect is significantly more pronounced if sensitive resists (CAR) as compared to e.g., PMMA resists are used.

In the following example, AR-N 7700.18 was applied by spin coating to yield a film thickness of 1100 nm, tempered (85 °C, 2 min, hot plate) and irradiated with different doses (20 kV). The crosslinking bake was carried out at 105 °C, 3 min on a hot plate. After development (AR 300-46 undilute., 2 min), the following structures were obtained. Clearly visible is an increased widening of the 250-nm bars with higher exposure doses.

電子束曝光時,總有ㄧ部份電子會產生散射. 前向散射來自電子束與阻劑材料的相互作用; 反向散射則來自基板,此現像稱為鄰近效應. 鄰近效應會導致所寫的圖案結構改變. 比起像PMMA阻劑,化學放大型阻劑的鄰近效應較明顯.

如下圖以AR-N 7700.18為例, 膜厚1100nm, 軟烤85℃ x 2 min(熱板), 以20kV加速電壓做不同劑量曝光. 隨後在熱板上以105℃ x 3min做曝後烤. 顯影(AR 300-46 x 2 min)後結構如下圖. 曝光劑量越高底部變寬現像越明顯.