Abstract

In this paper, we report the temperature variation response of silicon grating and the release of thermal strains in such a grating. The periodical corrugations of such a silicon grating were directly ablated by the interference fringe of the fourth-harmonic of a Q-switched Nd:YAG laser. The grating period can be varied from 180 through 550 nm. Such a grating has the application potential for temperature measurement of silicon wafer in thermal process facilities of integrated circuits. We found that the crests in the corrugations were composed of silicon oxide, which could be removed with HF dip. After HF dip, the crests became troughs. Figure 1 shows a typical set of results under the condition of laser ablation with an air gap between a prism and the sample and nitrogen purge. The dark diamonds represent the measurement results before rapid thermal annealing (RTA). The gray diamonds and crosses stand for the results after nitrogen-purged RTA (800 °C for 30 sec) in the increasing and decreasing temperature measurements, respectively. We can see that the variations of the data points are consistent with theoretical predictions. Notice that after RTA the room temperature grating period has been increased implying that in this case the built thermal strains become compressive. Then, the gray triangles and X marks in Fig. 1 stand for the results after nitrogen-purged RTA (800 °C for 30 sec) and after 30 sec 10 % HF dip in the increasing and decreasing temperature measurements, respectively. Now, the room temperature grating period is reduced back to the value before RTA implying that the existence of oxide causes tensile strain after RTA. It was found that the results relied on the environmental condition and laser pulse energy during grating formation. The details of silicon oxida-tion and the release of thermal strains will be reponed.

© 1998 IEEE