Detection of Effect of Strain on the Valence Band Structure of SiGe by HXPES with High Spatial Resolution

Since the aggressive scaling of the Si-based metal–oxide–semiconductor field effect transistors (MOSFET) is reaching its limits, the strained-Ge and III–V semiconductors are being studied extensively as one of the alternative channel materials due to their higher carrier mobility [1,2]. Recently, the channel strain engineering has become an essential technology for the future complementary metal oxide semiconductor. The process-induced local strain is currently the mainstream technology [3]. We reported that a selective-ion-implantation technique was developed as a novel method of creating uniaxially strained Si/Ge heterostructures [4]. We investigated the effect of the strain on the binding energy of valence band top, Si 1 s and Ge 2 p core level by Hard X-ray photoemission spectroscopy (HXPES) with the high spatial resolution. The sample was prepared as follows. A SiO 2 film was firstly deposited as a mask on a Si(100) substrate by plasma-enhanced chemical vapor deposition (PECVD), followed by the patterning of stripes with a standard photolithography process. Ar + ion were selectively implanted into the Si substrate through the SiO 2 mask windows at an energy of 25 keV with a dose of 1×10 15 cm -2 . The line widths of the implanted and unimplanted regions were fixed to be 20 and 2μm, respectively. A SiGe layer with a Ge content of 26% and thickness around 70 nm was pseudomorphically grown on the selectively ion-implanted Si substrate. Subsequently, postgrowth annealing was carried out to promote strain relaxation at 900°C. The hard X-ray (7.94 keV photons) excited Si 1 s , Ge 2 p , and valence band spectra arising from the sample were measured at photoelectron take-off angle (TOA) of 85 degrees with the energy resolution of 100 meV at undulator beam line (BL47XU at SPring-8 (JASRI, Proposal No. 2012B1269)) using high resolution electron energy analyzer R-4000 with the spatial resolution [11(|)0] direction is about 0.8µm [5]. The Si 1 s photoelectron spectra are changing in the position of a sample as shown in Fig. 1 (a). From Fig. 1 (b) and (c), the binding energies of Si 1 s and Ge 2 p core level are reduced at the position of 8, 30, and 52µm. Here, spectra are shown in figures as a parameter at the position of the [11(|)0] direction. On the other hand, the change of the binding energy of valence band top is less than that of peak of Si 1 s and Ge 2 p as shown in Fig. 1(d). The comparison of the position of the valence band top in the case in relatio