In Situ Fault Detection of Wafer Warpage in Microlithography

Abstract

Wafer warpage is common in microelectronics processing. Warped wafers can affect device performance, reliability and linewidth control in various processing steps. We proposed in this paper an in situ fault detection technique for wafer warpage in microlithography. Early detection will minimize cost and processing time. Based on first principle thermal modeling, we are able to detect warpage fault from available temperature measurements. Experimental results demonstrate the feasibility and repeatability of the approach. The proposed approach is applicable to other semiconductor substrates.

Temperature Control and In Situ Fault Detection of Wafer Warpage

“…The temperature drop is about 0.1 C. Notice a ten times reduction in the magnitude of the temperature disturbance when feedforward control was used. In contrast the temperature disturbance in [4] like Experiment (a) was larger than 1 C because feedforward control was not implemented making it less suitable for industrial implementation. Wafers Table I.…”

“…Hence, warpage can be detected from the temperature disturbances. Using temperature to detect warpage is also given in [4]. However, in [4], the temperature disturbance used as the signal for warpage computation had magnitude of more than a degree Celcius.…”

“…Using temperature to detect warpage is also given in [4]. However, in [4], the temperature disturbance used as the signal for warpage computation had magnitude of more than a degree Celcius. This may not be implementatable in practice as the temperature for some baking steps such as the postexposure bake have to be controlled to 0.1 C [5].…”

“…The center-to-edge warpage was given by the difference between height of proximity pin and thermal tape thickness. The model relating power , temperature disturbance , caused by the placement of a wafer at ambient on the hot bake-plate, and bake-plate temperature was given as where For details on how to derive the model, see [4]. Once the model was known, the optimal feedforward control signal was computed from linear programming with the constraints W W .…”

“…Consider Experiments (b) and (d) in Table I. The norminal air-gap changed by about 50 m from 167 to 118 m while the temperature drop changed by about 0.3 C from 0.12 C to 0.38 C. In contrast, the sensitivity in [4] for detecting was lower, i.e., 0.1 C change in temperature for a 50-m change in . Hence, in this paper, temperature is more sensitive to change in which is important for detecting warpage from temperature.…”