| AVS 59th Annual International Symposium and Exhibition | |
| Plasma Science and Technology | Thursday Sessions |
| Session PS2-ThM |
| Session: | Low Damage Processing |
| Presenter: | N. Kuboi, Sony Corporation, Japan |
| Authors: | N. Kuboi, Sony Corporation, Japan T. Tatsumi, Sony Corporation, Japan M. Fukasawa, Sony Corporation, Japan J. Komachi, Sony Corporation, Japan T. Kinoshita, Sony Corporation, Japan H. Ansai, Sony Corporation, Japan H. Miwa, Sony Corporation, Japan |
| Correspondent: | Click to Email |
The Si recess, which is caused after post-wet treatment in the Si gate etching process, can have a big effect on transistor properties such as threshold voltage (Vth) and off-state leakage current (Ioff). We previously studied what caused the Si recess [1] and found through our analysis of a molecular dynamics (MD) calculation and a beam experiment that it could be the oxidation enhanced diffusion induced by incident hydrogen during HBr/O2 gate etching [2]. The fluctuation in the Si recess depth (ΔdR) as well as in the critical dimension (ΔCD) is one of the key factors causing fluctuations in Vth (ΔVth) and Ioff (ΔIoff). The pattern dependence of the incident particle flux is related to ΔdR, therefore a prediction technology that considers this dependence is necessary in order to understand the effects on ΔVth and ΔIoff.
To model the dependence, we assumed that three factors–mask open area ratio at the wafer level (global), chip level (semi-local), and local level (local)–affect ΔCD and ΔdR. We performed experiments using a dual frequency capacitively coupled plasma system. We used wafers ranging from 60 to 91 % (the global range (RG) and the semi-local (RS)) with various patterns of the photo-resist mask on the Poly-Si film. These samples were treated by the HBr/O2 process under a pressure of 30 mTorr.
We found that ΔCD had positive and linear correlations with the global, semi-local, and local levels, which was consistent with the trend of the by-product (SiBrx) intensity and with that of the taper angles of the etched profiles. We also clarified that ΔCD was affected by the amount of SiBrx generated within several times of the mean free path area for the semi-local dependence, and that it was the solid angle (S) viewing from a pattern, not the pattern space, that had a good correlation with variations in ΔCD as a control indicator. We used this experimental knowledge to model the SiBrx flux and created a Si gate etching simulation that demonstrated the ΔCD value and etched profile trends. We also found that ΔdR depended on (RG+RS)S as well as on the dosage of incident particles, considering the relationship between dR and the ion energy reduced by the SiBrx deposition depth [3]. Furthermore, when we used the analytical transistor model [3], we could predict ΔVth and ΔIoff enhanced by the Si recess with (RG+RS)S.
These results show that it is crucial to control plasma processes such as ion energy, gas flux, and over-etch time considering the effect of pattern dependence of fluctuations in ΔCDand the Si recess.[1] T. Ohchi et al., JJAP 47, 5324 (2008).
[2] T. Ito et al., JJAP 50, 08KD02 (2011).
[3] K. Eriguchi et al., JJAP 49, 08JC02 (2010).