Wafer Smart Technology
Smart technology is a method which has been developed since 1993. It really is based on the direct bonding of two wafers, certainly one of that has first been implanted by light gas ions, with splitting induced in the implanted zone.
Implantation of ions, such as for instance hydrogen or helium, contributes to the formation of a weakened buried zone, located during the mean depth of ion penetration. Following the implanted wafer is bonded to a second wafer, splitting may occur, for which a thin layer is transferred from the implanted wafer onto the second wafer. Comparable scenarios occur as soon as the second wafer is replaced by a thick layer stiff adequate to allow splitting.
Semiconductor testing for Wafer Smart Technology was initially developed for Solar Projects and then it was later adapted for wafer applications. It really is now mature adequate to allow industrial-volume production of high-quality SOI wafers. The Smart process for producing SOI wafers is composed of listed here steps:
• A first Si wafer is thermally oxidized.
• Ions (H, He, etc.) are implanted in this first oxidized wafer to induce a buried weak zone.
• The first implanted wafer will be cleaned and directly bonded to an extra support wafer.
• Splitting is induced when you look at the weakened zone, transferring a thin layer from the first implanted wafer to your second support wafer.
• A final stage of treatment removes the roughness left in the surfaces after splitting, resulting in the last SOI structure. This enables the rest of the the main donor wafer to be reclaimed.
Fourier transform infrared spectroscopy operated in a multiple internal reflection mode, FTIR-MIR, enables the character of bonds and their densities in the bonding interface to be measured. Thermally grown oxide layers are 10 nm thick.65 Figure 1.16 shows clearly that –OH band peaks, into the 3000–3700 cm− 1 wave number range, are strongly modified at annealing temperatures over 250 °C. Water peaks, located into the 3200–3500 cm− 1 range, decrease continuously. Si–OH peaks into the 3500–3700 cm− 1 range first increase with temperature, up to 350 °C, and then decrease for higher temperatures.
Direct bonding, which occurs in the nanometer scale, is induced by hydrogen bonds either via water molecules adsorbed on silanol groups (Si–OH) or between silanols through the two surfaces. So, an initial approach is to increase silanol density and, specifically, water diffusion into the oxide subsurface. A surface preparation process such as for instance CMP in a basic solution (pH within the selection of 9–11) is well suited to induce these changes.