Mechanism of SiN etching rate fluctuation in atomic layer etching

Abstract

Note: This paper is part of the Special Topic Collection Commemorating the Career of John Coburn. a)This article is based on material presented at the 66th Symposium of the American Vacuum Society.

In Situ Monitoring of Etching Characteristic and Surface Reactions in Atomic Layer Etching of SiN Using Cyclic CF4/H2 and H2 Plasmas

“…It has been reported that the residual CF layer, as F-containing radicals, was released back into the plasma from the reactor walls, which lead to a gradual increase of EPC. ,, Conversely, in the F-deficient condition plasma using CH 3 F/Ar, the buildup of CF x on the chamber walls was observed to cause a decrease of EPC. This is because the C–C bonds in the HFC polymer are difficult to be removed via physical ion bombardment with low energy . Hence, various approaches have been attempted, such as using additional ashing processes or adding O 2 into gas mixtures, to inhibit the formation of residual carbon. ,, Unlike the SiN ALE using CH 3 F/Ar, which presented a decrease in EPC with respect to etch cycle, in this work, the increase in EPC after four cycles is likely due to the reason that the H 2 plasma in the etching step can incorporate with residual carbon, resulting in the formation of HCN by-products with the N in SiN .…”

“…Consequently, the etch depth deviates from a linear relationship with the cycle number. This phenomenon is a common problem, which has been observed in many systems, particularly in the FC-assisted ALE or cyclic processes. ,,,,, To assess the relationship between the EPC and cycle time (ALE fluctuation), the dependence of EPC on the cycle number of the SiN and SiO 2 films with the HFC deposition step using H 2 /(CF 4 + H 2 ) = 85% plasma for 30s is presented in Figure . The results show that for the SiN ALE, the EPC exhibited a linear relation with the cycle number being increased until 3 with a magnitude of 3.47 nm/cycle.…”

“…32 Hence, various approaches have been attempted, such as using additional ashing processes or adding O 2 into gas mixtures, to inhibit the formation of residual carbon. 11,30,32 Unlike the SiN ALE using CH 3 F/Ar, which presented a decrease in EPC with respect to etch cycle, in this work, the increase in EPC after four cycles is likely due to the reason that the H 2 plasma in the etching step can incorporate with residual carbon, resulting in the formation of HCN by-products with the N in SiN. 47 Furthermore, the ALE fluctuation also introduces difficulties in error analysis of EPC, as it strongly depends on the parameters used in the deposition half-cycle.…”

“…This is because the C−C bonds in the HFC polymer are difficult to be removed via physical ion bombardment with low energy. 32 Hence, various approaches have been attempted, such as using additional ashing processes or adding O 2 into gas mixtures, to inhibit the formation of residual carbon. 11,30,32 Unlike the SiN ALE using CH 3 F/Ar, which presented a decrease in EPC with respect to etch cycle, in this work, the increase in EPC after four cycles is likely due to the reason that the H 2 plasma in the etching step can incorporate with residual carbon, resulting in the formation of HCN by-products with the N in SiN.…”

“…30 In addition, fluorocarbon (FC)assisted ALE has also been reported to realize the self-limiting process and high selectivity among these materials, not only for SiO 2 6,9,11 but also for SiN. 31,32 The behavior of self-limiting etch reactions has been found to strongly depend on the FC deposition in the ALE of SiO 2 and SiN. However, a more comprehensive understanding of surface reactions at an atomistic level is required to further develop ALE.…”