Wafer bonding
The wafer bonding is a step in the semiconductor and microsystems technology, in which two wafers or wafers (silicon, quartz, glass and others) are interconnected. In microsystems technology wafer bonding is used to produce the necessary for the sensor cavities, such as the reference pressure chamber at an absolute pressure sensor or the vacuum chamber of some angular rate sensors.
Wafer bonding method
Process without intermediate layers
- Direct bonding: The silicon direct bonding ( SFB ) was first introduced in 1986 by JB Lasky. In this method, hydrophilic and hydrophobic surfaces are brought in contact at high temperatures. In this case, a wafer in the middle is pressed against the other wafer, there is formed the first contact point. The basis of the mechanical connecting hydrogen bonds and van der Waals interactions in the contact zone. The remaining area is separated from one another yet by means of spacers. Subsequently, the spacers are removed and the silicon junction spreads from the center. Usual processing temperatures are in the range between 1000 ° C and 1200 ° C. The pressure at which the wafers are pressed together, is approximately 18 MPa.
- Anodic bonding: If the glass anodic bonding is used with increased Na - ion concentration., This glass is brought into contact with the silicon wafer, and a voltage is applied so that the negative polarity is applied to the glass. And characterized by elevated temperature, the diffusion of sodium ions (Na ) to the electrode. Due to this, a space charge region at the interface is formed, resulting in a high field, and subsequent formation of Si -O- Si bonds. The Bond front now behaves as in SFB, only slower.
Method with intermediate layers
- Eutectic bonding: The principle is based on this combination the formation of a eutectic alloy such as Si - Ge or Au -Al.
- Glass frit bonding: bond formation by melting of glass solders / glass frit
- Adhesive bonding: bond formation by adhesive as an intermediate layer