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We demonstrate an approach for fabricating relaxed SiGe layers on Si substrate with low threading dislocation density using commercially available low-pressure chemical vapor deposition epitaxy systems. This approach involves a thin epitaxial buffer layer with a reversed Ge composition gradient, i.e., the Ge composition decreases from the Si substrate to the growing surface. On a 90 nm thick buffer, growth of SiGe layer with composition up to 32% Ge was demonstrated with a strain relaxation Ͼ80% and a threading dislocation density below 10 6 cm Ϫ2 .

We have recently developed a novel reverse-graded ͑RG͒ buffer system, in which the Ge content decreases with distance from the Si interface. These thin ͑90 nm͒ RG layers are capable of supporting the growth of relaxed SiGe layers ͑85% relaxed͒ with defect densities as low as 10 5 /cm 2 . Good quality strained Si has also been successfully grown on these substrates. However, the thermal stability of this novel heterostructure has not been explored. In this paper, we establish, by high-resolution X-ray diffraction, Raman spectroscopy, atomic force microscopy, and transmission electron microscopy, that the heterostructure is stable up to 1000°C with no further strain relaxation in both the RG layer and strained Si layer. Hence, it is clear that this thin RG heterostructure is highly suitable as a buffer system for the growth of high-mobility strained Si or Ge devices.The execution of Moore's law beyond the 45 nm node has become possible with the recent innovation of strained channel technology. It has been reported that effective mobility of electrons and holes increased by up to three times in strained Si channels and eight times in strained Ge channels, respectively. 1-3 The integration of strained channels into Si wafer processing is critically dependent on the success of heteroepitaxy technology, which remains a challenging proposition. The 4.2% lattice constant mismatch between pure Si ͑a = 0.543 nm͒ and Ge ͑a = 0.569 nm͒ must be accommodated with minimum threading dislocation density ͑TDD͒ in the strained Si channel, so far achieved by the use of various buffer layers. The most widely accepted buffer approach is via continuous forward grading of SiGe on Si, followed by a relaxed SiGe layer with constant concentration, topped by a thin strained Si or Ge channel layer. 4 This approach can reduce the TDD to 10 5 /cm 2 ; however, up to a 5-m-thick buffer layer is needed to grow the high quality SiGe layer. Earlier studies have found that the self-heating effect of a device on a relaxed SiGe buffer is proportional to the square root of the buffer thickness. 5,6 Thus, investigations on a high-quality thin buffer layer are relevant and necessary in order to improve device performance.Recently, we proposed a novel reverse-graded ͑RG͒ buffer grading system, where the Ge concentration decreases gradually from the Si substrate towards the relaxed SiGe layer. 7 We have demonstrated that the defect density of this heteroepitaxy system is comparable to, if not better than, the current state of the art, with a thickness only 10% of the forward graded buffer system. 7 We believe that the success of this method depends on the residual strain in the RG layer, which exerts force on the misfit dislocations and prevents them from propagating upwards and terminating on the top SiGe layer as threading dislocations. Nevertheless, it has been reported that, during high-temperature anneals encountered in a typical semiconductor fabrication, strain relaxation of strained SiGe, 8 strained Si, 9 and diffusion of Ge into the strained Si la...

We report different loading effects in selective epitaxial deposition of silicon germanium on silicon ͑001͒ using different silicon sources, such as silane or dichlorosilane, and other conventional sources, such as germane, and hydrogen chloride in hydrogen carrier gas, in a low-pressure chemical vapor deposition system. Silane leads to lower relative deposition rates in a smaller silicon area, while dichlorosilane shows the opposite trend. Flowing silane and dichlorosilane simultaneously during deposition results in a similar deposition rate independent of exposed silicon area. Decreasing hydrogen chloride partial pressure is found to improve the loading effect for both the silane-and dichlorosilane-based process for a small active window of about 0.01 m 2 . The results point to the importance of availability of the adsorbed species on the active silicon windows when their size is below 0.04 m 2 .The selective epitaxial growth of SiGe has been used in volume production of mainstream complementary metal-oxide semiconductor products 1 following the introduction of SiGe heterojunction bipolar transistor technologies. For productivity improvement in manufacturing advanced Si technology, higher growth rate and less dependence of the growth rate on the exposed Si active size are ideal. Dichlorosilane ͑DCS͒ has been the Si source of choice for selective growth, but more chemically active sources, such as SiH 4 , Si 2 H 6 , or Si 3 H 8 , have been considered for growth rate improvements. No matter which Si source was used, it is widely reported that there is a difference between epitaxial SiGe growth rates on patterned and blanket wafers. [2][3][4][5][6][7][8][9] The loading effect depends on the Si/dielectrics filling ratio ͑global effect͒ and the opening size of the windows ͑local effect͒. Reducing the total pressure or increasing HCl flow has been found to improve loading performance. 2-4 Previous studies, however, have focused on structures larger than 0.1 m 2 . 2-9 Advanced Si technologies usually involve active areas less than 0.01 m 2 , which pushes the previously termed "local effect" into more like a "global effect." In this paper we discuss the selective growth behavior of SiGe using SiH 4 and DCS as Si sources, with an emphasis on the growth rate on Si͑001͒ with different active area sizes down to 0.01 m 2 .The SiGe layers were grown in a commercially available lowpressure chemical vapor deposition ͑LPCVD͒ system using different Si sources, SiH 4 or DCS and other conventional sources, such as GeH 4 or HCl in H 2 carrier gas. Blanket and patterned wafers with exposed Si areas of different sizes ranging from 0.01 to 3600 m 2 were used. Thickness and Ge composition were measured by X-ray diffraction ͑XRD͒ for SiGe grown on active area. Cross-sectional transmission electron microscopy ͑TEM͒ was used to verify thickness measurements. All data were collected on the same die location on 300 mm wafers. Figure 1 shows the normalized deposition rate vs the Si area for different selective processes with different Si sou...