Heated Ion Implantation Technology for High Performance Metal-Gate/High-k CMOS SOI Finfets

1. Introduction

Thinning of the fin channel is a key technology for CMOS FinFET scaling. For sub-14nm- node FinFETs, the fin channel becomes thinner than 10 nm. Furthermore, lowering of the sheet resistance (R_s) in the source/drain extension (SDE) is essential for performance improvement [1]. However, in the case of conventional I/I, it is difficult to reduce R_s because conventional I/I generally causes poly-crystallization and/or crystal defects to be formed in ultrathin fin region, even after activation annealing [2, 3]. This problem is particularly severe for SOI FinFETs. Recently, a novel I/I technology called heated I/I has been proposed. By using the heated I/I technology, the crystallinity of the implanted layer for Si is maintained during heated I/I, and defect-free crystal can be realized by activation annealing [4, 5]. Furthermore, it has been reported that the I_on-I_offcharacteristics are improved in bulk Si-channel nMOS FinFETs by heated I/I [6].

In this paper, we report heated I/I technology for high-performance metal-gate/high-k CMOS SOI FinFETs.

2. Experimental

Both nMOS and pMOS SOI FinFETs were fabricated. (110) fin channel was formed on (100) SOI substrate. Doped-poly-Si/TiN/HfO₂/SiO₂ gate stacks were formed, patterned, and etched. SDE was formed by room temperature (RT) or 500^oC I/I. As⁺ or BF₂⁺ was implanted at 5keV with total doses of 2x10¹⁵cm^-2. RTA was performed at 915^oC for 2s. Finally, the back-end process was carried out.

3. Results and Discussion

To understand the crystal condition in the ultrathin fin region after heated I/I, we investigated the crystallinity of the SOI layer after RT and heated I/I by cross-sectional TEM observation (Figs. 1 and 2). The I/I was performed under the same conditions as those for the SDE formation in FinFETs (Figs. 1(a) and 2(a)). In the case of RT I/I, the SOI layer is fully amorphized by I/I (Fig. 1(b)), and polycrystals and twins are observed even after annealing (Fig. 1(c)). Since there are no seed crystals in the SOI layer after I/I, the implanted region cannot be crystallized by activation annealing. On the other hand, in the case of heated I/I, the crystallinity is maintained in the SOI layer after I/I (Fig. 2(b)). The crystal perfectly recovers by activation annealing (Fig. 2(c)). These results indicate that the defect-free SDE can be formed in ultrathin fin region by heated I/I.

We investigated the impact of heated I/I on the SOI FinFET performance. Figures 3 (a) and (b) show the I_on distribution in the nMOS and pMOS FinFETs, respectively, processed by RT or heated ion implantation. For the nMOS FinFETs, the 50% I_on value of heated I/I is about 7% higher than that of RT I/I. Also, for the pMOS FinFETs, the 50% I_on value in the case of heated I/I is about 1.5% higher. The resistance (R_sd) of the SDE becomes lower in the case of heated I/I (Fig. 4), owing to perfect crystal recover [7]. This is the main reason for the improvement in I_onby heated I/I. Thus, by using heated I/I, the SOI FinFET performance is improved as compared with conventional RT I/I.

4. Conclusion

Heated I/I contributes to the formation of the defect-free SDE in ultrathin fin region and is effective for improving the performance of ultrathin FinFETs. Thus, heated I/I technology is promising for SDE formation in future SOI FinFETs.

References

[1] C.-H. Jan et al., IEDM Tech. Dig., 2012, p. 44.

[2] M. J. H. van Dal et al., 2007 Symp. on VLSI Tech. Dig. (2007) 110.

[3] R. Duffy et al., ESSDERC (2008) 334.

[4] H. Onoda et al., Ext. Abs. the 13th Int. Workshop on Junction Tech. (2013) 66.

[5] H. Onoda et al., Ext. Abs. the 14th Int. Workshop on Junction Tech. (2014) 126.

[6] M. Togo et al., Symp. on VLSI Tech. Dig. (2013) T196.

[7] W. Mizubayashi et al., IEDM Tech. Dig. (2013) 538.