The diameter and depth of the hole, shown in Fig. 1 for C4F6, are 200 nm and 1.32 mm, respectively. The fluorocarbon polymer film deposited in the C4F6 plasma has a rough surface and the lowest density as described previously. Hence, it seems that etch reaction products are released easily and the SiO2 etch rate is consequently in an acceptable range. The good etch profile is due to the appropriate balance between the high-density CF+ ions with a low etching efficiency and the low-density fluorocarbon polymers. In the C5F8 plasma, the etch profile exhibits a slight side etching since the ions reflected at the tapered resist are more than in the C4F6 plasma. The microloading effect is also higher than in the C4F6 plasma because the CFx (x=1~3) radical densities and the film density of fluorocarbon polymers in the C5F8 plasma are higher than in the C4F6 plasma.

Fig. 1. Etch profiles of 0.2 mm contact holes at 3 mTorr, 600 W source power and 200 W bias power. Фmax and D represent the maximum diameter and depth of etched contact holes, respectively.

Fig.2 shows the SEM cross section of the fine contact holes etched with C4F6, C4F6/O2 (10%), C4F6/Ar (25%) and C5F8/Ar (50%) plasmas. Figure 3 shows the positive ion content in the C4F6, C4F6/O2 (10%) and C4F6/Ar (25%) plasmas. The CF+ is the dominant etching species and the others are less significant in these plasmas. Figure 4 shows CFx (x =1~3) radical densities in the C4F6/O2 (10%) and C4F6/Ar (25%) plasmas. Certain radicals do not contribute to etching the fine contact hole in both plasmas. It is possible that both the polymeric radicals except CFx (x=1~3) and the CF+ ion play an important role in etching the fine holes in the C4F6, C4F6/O2 (10%) and C4F6/Ar (25%) plasmas.

Figure 5 shows the SiO2 etch rate and selectivity for theetch plasmas. The SiO2 etch rates for the C3F6, C4F8 and cC4F8 plasmas are slightly higher than those for the C4F6 andC5F8 plasmas. The selectivity against resist or Si is smallerin the C3F6, C4F8 and c-C4F8 plasmas than in the C4F6 andC5F8 plasmas.

Fig. 5. SiO2 etch rate and selectivity at 3 mTorr, 600 W source power and 200W bias power.