Cobalt sputtering target and sputter deposition of Co thin films for cobalt silicide metallization

Abstract

CoSi 2 is considered an alternative to TiSi2 for use as a contact in ultralarge scale integration due to its low resistivity, excellent chemical stability and lower formation temperature. Sputter deposition of Co thin films is one of the crucial steps in the cobalt salicide (a self-aligned silicide) process. One major problem with sputter deposition of Co thin films is that Co is a ferromagnetic material and is difficult to sputter. The dc magnetic field transmitted through a ferromagnetic material from one side to another is called the pass-through flux (PTF). In this study, the effects of target PTF and sputtering process parameters such as Ar pressure and sputtering power on the sputter process were studied. Co targets with PTF% of 65% (high PTF), 53% (medium PTF) and 32% (low PTF) were sputter tested. The sputter deposition rate, I–V characteristics, film sheet resistance and film uniformity were measured under various sputter conditions. The study indicated that, in magnetron sputtering of Co, a high magnetic flux intensity could be obtained by using a high PTF target that allowed maximum magnetic flux to permeate through the target. The I–V characteristics of different PTF targets followed the typical I=KVn relationship of dc planar magnetron sputtering. The exponents in the equation, n, increased with increasing target PTF%, indicating the sputtering impedance decreased with increasing target PTF%. The target with the highest PTF% demonstrated the best performance and film uniformity. Rapid thermal processing (RTP) was carried out to form cobalt silicides at temperatures between 300 and 850 °C in Ar atmosphere for various times. The sheet resistance of the Co and cobalt silicide films produced was monitored by a four-point probe before and after the RTP. The sheet resistance decreased significantly after annealing at 600 and 700 °C due to formation of CoSi2, which has lower resistivity. The significant increase in sheet resistance after annealing at 400 and 500 °C was attributed to formation of the CoSi phase. For the 16 nm thick Co film, a sheet resistance of 3.2 Ω/sq was obtained after RTP at 600 and 700 °C.