| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
LL9, Comprehensive Investigation of Ge-Si Bonded Interfaces Using Surface Activation |
| Author(s) |
Ki Yeol Byun, Isabelle Ferain, Brenda Long, Susan Holl, Cindy Colinge |
| On-Site Speaker (Planned) |
Ki Yeol Byun |
| Abstract Scope |
Germanium (Ge) has been considered as a promising candidate to overcome the limitation of silicon (Si) for next generation CMOS devices and optoelectronics due to higher mobility and smaller absorption coefficient. Epitaxial crystal growth is a well-known method for integration of hetero-structures between dissimilar materials. However, conventional epitaxial Ge growth on Si requires careful processing and device design to minimize the impact of the dislocations caused by the lattice mismatch and large thermal expansion coefficient difference between Ge and Si. Low temperature wafer bonding is a simple and easy alternative method for forming hetero-structures without these limitations. In this work, our chemical and structural investigations of bonded interface show that successful low temperature Ge-Si hetero integration can be achieved utilizing wafer bonding. In the experiment, 4-inch ‹100› oriented p-type Ge (Ga doped, resistivity = 0.016 Ω.cm) were selected for bonding. Prior to bonding, the Ge and Si wafers were cleaned in an SC1-equivalent solution with ozone for Si and without ozone for Ge. Wafers were then loaded into bonder and vacuum was applied. The wafers were then exposed for 10 minutes to either oxygen or nitrogen free radicals (chamber pressure was 1 mbar at 100 W) generated by a remote plasma ring. After exposure the wafers were bonded in-situ under a pressure of 1kN applied for 5 minutes at a chamber pressure of 10−5 mbar. The wafers were annealed in-situ at 100°C for 1 hour with an applied pressure of 500N in vacuum followed by an ex-situ anneal at 200°C for 24 hours in order to enhance bond strength. The same wafers were then annealed again at 300°C for 24 hours. The ramp-up rate was set to 0.5°C/min in both cases. After anneal Ge-Si bonded pairs remained intact due to a slow ramp-up rate. X-ray Photoelectron Spectroscopy (XPS) data is presented which provides the chemical composition of the Ge surfaces as a function of the hydrophilic bonding reaction at the interface. Additionally, the hetero interfaces were characterized by Atomic Force Microscopy (AFM), High Resolution Transmission Electron Microscopy (HR-TEM), and synchrotron x-ray topography. The reaction product at Ge-Si bonded interfaces has been investigated comprehensively. It is demonstrated that radical exposure prior to bonding can achieve less defective and a lower strained interface by means of a conversion of the bulk Ge to GeO2. The stable passive film contributes to a reduction of bubbles (“voids”) caused by Ge desorption. This conclusion is very useful for high quality hetero-structure integration of thermally mismatched materials such as those used for photonic devices. In particular, we have found that to achieve void-free, strain free Ge-Si interface it is necessary to “passivate” the Ge surface prior to bonding. This is accomplished using oxygen free radical exposure. |
| Proceedings Inclusion? |
Undecided |