Mechanistic Studies of Wafer Bonding and Thin Silicon Film Exfoliation
- PDF / 445,457 Bytes
- 13 Pages / 612 x 792 pts (letter) Page_size
- 10 Downloads / 200 Views
Abstract In this paper, we review and highlight the central role that infrared spectroscopy has played in elucidating the microscopic details of the bonding and exfoliation processes and we introduce a novel technique for imaging and measuring strain with submicron resolution. The mechanism for chemical bond formation between two interfaces is derived from monitoring the chemical evolution of interfacial species as a function of annealing. The mechanism for silicon shearing upon Himplantation/ annealing is understood as an evolution of H-passivated point defects into Hstabilized internal surfaces, together with H2 formation. The nucleation and propagation of microbubbles that form prior to exfoliation is imaged with x-rays and a detailed strain map in the vicinity of bubbles just prior to exfoliation can be made.
INTRODUCTION Wafer bonding and thin-film exfoliation represent interesting alternatives to epitaxy. In particular, it is now possible with the technique coined “SmartCut” [1] to deposit thin (500Å to microns) crystalline films of most semiconductors onto many substrates [2]. This technique, based on mono-energetic H-ion implantation of a “device” wafer, a bonding step to a support (or handle) wafer and then subsequent annealing, has been perfected for the manufacturing of silicon-oninsulator (SOI) wafers [3] and is being actively worked on for other materials. Yet, there is relatively little fundamental understanding of the mechanisms behind these fascinating processes. The initial characterization, based on transmission electron microscopy (TEM) images of the implanted region [1,4], revealed the presence of cracks in Si samples implanted with 1017 H+/cm2 and annealed to 400-500oC, but the underlying physics and chemistry that led to the development of such internal cracks was completely unexplored. In this paper, we review the infrared spectroscopic studies of the thermal evolution both of species at the bonded interface between the device and handle wafers and of hydrogen in the Himplanted device wafer. Along with complementary techniques such as TEM, forward recoil scattering (FRS), atomic force microscopy (AFM) and mass spectrometry, IR spectroscopy has been key in providing a mechanistic picture of the bonding and exfoliation processes [5-7]. We also present a novel technique, micro x-ray scattering, that makes it possible to image and quantify the strain gradients associated with the H-implantation/annealing process.
EXPERIMENTAL The infrared study of interfaces is best performed using multiple internal transmission (MIT) spectroscopy [8]. With this geometry, the essential feature is the large enhancement (×30) occurring for the perpendicular component of the interfacial species’ vibrations. This enhancement arises from the large mismatch in refractive indices between the bulk substrate (nsi = 3.47 ) and the
ultra-thin interface (ninterface < 1.5). As a result, the IR beam tunnels through the interface, that is it would be totally reflected if the interface was thicker than the wavelength. Using
Data Loading...
