Method of fabrication of a AL/GE bonding in a wafer packaging environment and a product produced therefrom
A method of bonding of germanium to aluminum between two substrates to create a robust electrical and mechanical contact is disclosed. An aluminum-germanium bond has the following unique combination of attributes: (1) it can form a hermetic seal; (2) it can be used to create an electrically conductive path between two substrates; (3) it can be patterned so that this conduction path is localized; (4) the bond can be made with the aluminum that is available as standard foundry CMOS process. This has the significant advantage of allowing for wafer-level bonding or packaging without the addition of any additional process layers to the CMOS wafer.
1. A method for bonding a CMOS wafer and a MEMS wafer, the CMOS wafer including an integrated circuit, the MEMS wafer including a MEMS device, the method comprising:
depositing a germanium bonding layer on the MEMS wafer;
forming a substantially aluminum bonding layer on the CMOS wafer, wherein the CMOS wafer is placed in a first chuck and the MEMs wafer is placed in a second chuck;
aligning CMOS wafer and the MEMS wafer; and
forming a eutectic bond between the germanium bonding layer on the MEMS wafer and the substantially aluminum metalization bonding layer on the CMOS wafer, wherein the eutectic bond is formed by keeping the CMOS wafer and the MEMS wafer apart until the temperature on each of the top and bottom chucks reaches a first predetermined temperature that is less than 450° C., inducing forming gas at an atmospheric pressure prior to bonding, providing a vacuum to remove the forming gas, applying a uniform force across the first chuck and the second chuck, and then ramping the temperature over the eutectic point of the aluminum/germanium bond to a second predetermined temperature that is less than 500° C. for a period not to exceed thirty minutes.
2. The method of claim 1 wherein the CMOS wafer and the MEMs wafer is cleaned before forming the eutectic bond.
3. The method of claim 2 , wherein cleaning the CMOS wafer and the MEMS wafer comprises one or more of:
dipping the CMOS wafer and the MEMS wafer in deionized water;
dipping the CMOS wafer and the MEMS wafer in a 50:1 HF solution;
placing the CMOS wafer and the MEMS wafer in a dump rinse; and
placing the CMOS wafer and the MEMS wafer through a spin-rinse-dry process.
4. The method of claim 1 , wherein the substantially aluminum metalization bonding layer on the CMOS wafer is a ratio mix of 97.5:2:.5 Al:Si:Cu (Aluminum:Silicon:Copper)
5. The method of claim 1 , wherein forming a eutectic bond includes creating a hermetic seal between the CMOS wafer and the MEMS wafer.
6. The method of claim 1 wherein the first predetermined temperature is approximately 420° C.
7. The method of claim 1 wherein the second predetermined temperature is approximately 450° C.
8. The method of claim 1 wherein the MEMS layer is doped to provide an ohmic contact to the CMOS once the aluminum/germanium eutectic bond is formed.
9. The method of claim 1 wherein the forming gas is utilized to deoxidize the surfaces of the germanium layer and the aluminum layer to initiate the reflow process of aluminum/germanium eutectic bond.
10. The method of claim 1 wherein the germanium layer can be deposited on a MEMS substrate layer that is highly doped such that the resulting contact with the CMOS wafer is an ohmic contact.