METHOD FOR BONDING TWO SUBSTRATES
The invention relates to a method for bonding two substrates by applying an activation treatment to at least one of the substrates, and performing the contacting step of the two substrates under partial vacuum. Due to the combination of the two steps, it is possible to carry out the bonding and obtain high bonding energy with a reduced number of bonding voids. The invention is in particular applicable to a substrate of processed or at least partially processed devices.
1 . A method for bonding two substrates comprising the steps of:
providing each substrate with a surface for contact;
applying an activation treatment to at least one surface of the two substrates to be bonded; and
contacting the surfaces of the two substrates under partial vacuum to bond the substrates together.
2 . The method according to claim 1 , wherein the surfaces of both substrates are flat and polished to facilitate molecular bonding therebetween during the contacting step.
3 . The method according to claim 1 , wherein at least one of the substrates comprises processed or at least partially processed devices are on the surface or within the substrate.
4 . The method according to claim 3 , wherein the devices are present within the substrate by providing the processed devices on the surface of one substrate, and providing a dielectric layer over the processed devices as the surface of that substrate, wherein the surface of the dielectric layer is bonded to the surface of the other substrate.
5 . The method according to claim 4 , wherein the dielectric layer is an oxide layer and the substrates comprise silicon so that a silicon on insulator structure can be achieved.
6 . The method according to claim 1 , wherein the partial vacuum has a pressure of 1 to 50 Torr (1.33 to 66.7 mbar).
7 . The method according to claim 1 , wherein the contacting step is carried out at a temperature of from 18° C. to 26° C.
8 . The method according to claim 1 , wherein the bonded substrates have a bonding energy of about 700 to 1000 mJoule/m 2 and a reduced number of edge voids compared to substrates conventionally bonded at temperatures of above 1000° C.
9 . The method according to claim 1 , wherein after bonding and during subsequent treatment steps, the bonded substrates are exposed to temperatures of at most 300° C. to 500° C.
10 . The method according to claim 1 , wherein the activation treatment comprises at least one of a plasma activation, a polishing step, a cleaning step or a brushing step conducted on the surface of one or both of the substrates.
11 . The method according to claim 3 , wherein the activation treatment for the substrate that includes the processed devices comprises conducting sequentially a cleaning step, a plasma activation, a cleaning step and a brushing step.
12 . The method according to claim 3 , wherein the activation treatment for the substrate that includes the processed devices comprises conducting sequentially a polishing step and a cleaning step.
13 . The method according to claim 12 , wherein the activation treatment further comprises a plasma activation step or brushing step after the cleaning step.
14 . The method according to claim 1 , wherein the contacting step is carried out in a dry atmosphere that contains less than 100 ppm H 2 O molecules.
15 . The method according to claim 1 , wherein the contacting step is carried out in a neutral atmosphere that contains argon, nitrogen or mixtures thereof.
16 . The method according to claim 1 , further comprising a step of thinning at least one of the two substrates after bonding.
17 . An electronic or opto-electronic device comprising a bonded substrate fabricated according to the method of claim 1 .