Method for molecular adhesion bonding at low pressure
A method for bonding first and second wafers by molecular adhesion. The method includes placing the wafers in an environment having a first pressure (P1) greater than a predetermined threshold pressure above which initiation of bonding wave propagation is prevented, bringing the first wafer and the second wafer into alignment and contact, and spontaneously initiating the propagation of a bonding wave between the wafers after they are in contact solely by reducing the pressure within the environment to a second pressure (P2) below the threshold pressure.
1. A method for bonding at least a first wafer and a second wafer by molecular adhesion, which comprises:
placing the first and second wafers in an environment having a first pressure (P1) greater than a predetermined threshold pressure above which initiation of a bonding wave propagation is prevented, and then bringing the first wafer and the second wafer into alignment and contact; and
spontaneously initiating the propagation of a bonding wave between the first and second wafers after the wafers are in contact solely by reducing the pressure within the environment to a second pressure (P2) below the threshold pressure.
2. The method according to claim 1 , wherein the predetermined threshold pressure is between 20 millibar and 5 millibar.
3. The method according to claim 1 , which further comprises aligning the wafers before initiating the propagation of the bonding wave.
4. The method according to claim 3 , wherein the wafers are aligned by applying a force to an edge of one of the wafers.
5. The method according to claim 3 , which further comprises arranging the first wafer and the second wafer such that the surfaces to be brought into contact are facing one another, while interposing spacer elements to maintain a space between the two wafers before aligning the wafers.
6. The method according to claim 4 , wherein the lateral force is applied to the edges of the wafers by a pusher that moves from a retracted position to an alignment position.
7. The method according to claim 1 , which further comprises: interposing spacer elements between the wafers to maintain the space between them; and aligning the wafers before initiating the propagation of the bonding wave.
8. The method according to claim 1 , wherein the second pressure (P2) is less than 1 mbar.
9. The method according to claim 1 , wherein the first wafer and the second wafer have alignment marks that interact with a holding finger, and further wherein the lateral force is exerted to place the wafers in abutment against at least the holding finger interacting with the alignment marks.
10. The method according to claim 1 , which further comprises thinning the first wafer after bonding to form a thin layer.
11. The method according to claim 10 , which further comprises producing a second layer of microcomponents on the face of the first wafer opposite the face having the first layer of microcomponents prior to bonding the first and second wafers.
12. The method according to claim 10 , wherein the first substrate is a silicon-on-insulator structure.
13. The method according to claim 10 , wherein at least the first layer of microcomponents on the first wafer are image sensors.
14. The method according to claim 11 , which further comprises forming an oxide layer on the face of the first substrate comprising the first series of microcomponents prior to bonding of the first and second substrates.