(Invited) Epitaxial Growth of Low Defect SiGe Buffer Layers for Integration of New Materials on 300 mm Silicon Wafers

Abstract

We report on the structural characterization of state-of-the-art SiGe graded buffers on Si(001) substrates with a diameter of 300 mm with and without a backside stressor. The main beneficial effect of the backside stressor is a clear improvement in surface morphology in terms of reduced surface roughness and substantially decreased density of threading dislocation pile-ups all across the wafer. X-ray diffraction furthermore proves that the relaxation of the various layers in the SiGe buffer is triggered by the misfit stress of the subsequently deposited layer. In addition, spatially resolved microRaman studies demonstrate that the formed cross hatch pattern surface morphology is clearly correlated with strain field and not with Ge concentration fluctuations.

Imaging Structure and Composition Homogeneity of 300 mm SiGe Virtual Substrates for Advanced CMOS Applications by Scanning X-ray Diffraction Microscopy

“…The polished sample (Figure 3d) has a higher average composition (68.4%) and lower fwhm (0.8%), with a symmetric distribution. This may result from a Ge concentration gradient across the whole 300 mm wafer with lower x toward the edges, as previously observed by Kozlowski et al 20 on similar samples. The quite homogeneous distribution of the strain and composition was also observed during previous measurements for the unpolished as well as polished samples (see Supporting Information).…”

“…It is noted again that no difference can be detected between the unpolished and polished samples. Although such a strain fluctuation was already demonstrated by Raman investigations, 20,26 we are not aware of any study clearly demonstrating the correlation of strain and composition modulation. It is clearly established by the K-map technique that less compressively strained regions at growth temperature (more tensile strained at room temperature) are characterized by a higher germanium concentration.…”

“…Since the vibration modes of the Ge−Ge, Ge−Si, and Si−Si bonding and, respectively, their signals ω GG , ω GS , and ω SS shift according to stoichiometry and strain, it is possible to determine these values by experimentally approximated equations. 20,27,28 Because of the high germanium concentration, the corresponding Ge−Ge and Ge−Si vibrations give the highest signal intensities and enable the best data evaluation. Thus, ω GG and ω GS peaks were used to map ε ∥ and x for the unpolished sample in Figure 3e and f, respectively.…”

“…The process gases were dichlorosilane (SiCl 2 H 2 ) and germanium tetrachloride (GeCl 4 ) in a high temperature process. 20 To avoid bowing of the wafer by lattice and thermal mismatch with respect to the Si substrate, a BSS of constant Si 1−x Ge x concentration was deposited prior to the VS growth on the frontside of the wafer. 7 The graded Si 1−x Ge x buffer layer on the wafer frontside consists of a graded buffer layer and a constant composition layer on top of the graded part.…”

“…As a result of the high deposition temperature of the epi process, all parts of the SiGe buffer layer are almost fully relaxed. 20 Figure 1a provides the schematic of the layer stacking. Differential interference contrast (DIC) microscopy images of a selected 90 μm × 90 μm area of the two samples show the characteristic cross-hatch pattern on the ⟨110⟩-equivalent directions of the as-grown sample (Figure 1b), which is clearly absent on the polished surface of the CMP-processed wafer (Figure 1c).…”