QuaSiC™ substrates can be obtained by transferring a single crystal SiC layer onto a poly SiC substrate using the Smart Cut ™ technology. The structure evolution of metal bonding (W-Si silicide) layer has been investigated by Transmission Electron Microscopy and X-ray diffraction. Results indicate that the metal bonding film is made of W5Si3. The film is discontinuous and strained. Annealing releases stress at least partially.