In Situ Growth Rate Measurement of Selective LPCVD of Tungsten

The ref lec tance m e a s u r e m e n t dur ing the select ive depos i t ion of W on Si covered wi th an insula tor grat ing is p roven to be a conven i en t m e t h o d to mon i to r the W deposi t ion. The ref lectance change dur ing depos i t ion al lows the in s i tu measu r e m e n t of the depos i t ion rate: The inf luence of surface roughen ing due to e i ther the W growth or an e tch ing p re t r ea tmen t of the wafer is mode led , as wel l as the effect of select ivi ty loss and lateral overgrowth. A grat ing has been successfu l ly used in the past to monitor in s i tu the e tch rate of, e.g., Si for dry t r ench e tch ing (1-3). W can be depos i t ed select ivi ty by means of L P C V D us ing the reduc t ion react ion of WF6 by e i ther Si, H2, or Sill4 (4, 5). The reac t ion condi t ions can be chosen so that W does not depos i t on insula tors l ike SIO2, Si3N4, etc., bu t only grows on (semi-)conductors l ike Si and A1 (4, 6-8). When W is depos i t ed on a grat ing s t ruc ture as p resen ted in Fig. 1, the ref lec tance will change dur ing depos i t ion due to the changing dif f ract ion caused by the m o v i n g W surface. The d is tance be tween the m a x i m u m and a m i n i m u m in ref lectance is re la ted to M4, wi th k the wave l eng th by which the ref lec tance is measured .