Method of manufacturing bonded substrate stack
A method of manufacturing a bonded substrate stack includes a bonding surface processing step of processing at least one of first and second substrates each containing silicon and having a bonding surface, and a bonding step of bonding the bonding surface of the first substrate and the bonding surface of the second substrate. The bonding surface processing step includes an OH group increasing step of increasing OH groups on the bonding surfaces, and a moisture content decreasing step of heating the bonding surfaces where the OH groups have been increased at a temperature falling within a range of 50° C. to 200° C. to decrease moisture contents of the bonding surfaces.
1. A method of manufacturing a bonded substrate stack comprising:
increasing a concentration of OH groups to ≧5×10 13 atoms/cm 2 on a surface of a first substrate which contains silicon;
cleaning the surface of the first substrate with pure water;
heating the first substrate to decrease a moisture concentration on the surface of the first substrate to ≦5×10 13 atoms/cm 2 while maintaining the concentration of OH groups ≧5×10 13 atoms/cm 2 ;
joining the surface of the first substrate to a surface of a second substrate which contains silicon; and
bonding the surfaces of said substrates;
wherein voids are not present in the bonded substrate stack.
2. The method according to claim 1 , wherein the moisture concentration is decreased by heating the first substrate to a temperature falling within a range of 50 to 200° C.
3. The method according to claim 1 , wherein the moisture concentration is decreased in one of an air atmosphere, an inert gas atmosphere, or a reduced pressure atmosphere.
4. The method according to claim 1 , wherein the concentration of OH groups is increased by cleaning the surface of the first substrate with a cleaning liquid that increases the concentration of OH groups.
5. The method according to claim 1 , wherein the concentration of OH groups is increased by activating the surface of the first substrate and thereafter providing water to said surface.
6. The method according to claim 1 , wherein bonding is performed such that a bonding portion of the first and second substrates enlarges with a speed of not more than 10 mm/sec.
7. The method according to claim 1 , wherein a substrate having a silicon layer and silicon oxide layer sequentially on a separation layer is employed as the first substrate, and a silicon substrate is employed as the second substrate.
8. The method according to claim 1 , wherein a substrate having a silicon layer and silicon oxide layer sequentially on a separation layer is employed as the first substrate, and a substrate having a silicon oxide layer on a surface thereof is employed as the second substrate.
9. The method according to claim 1 , wherein a substrate having a silicon layer on a surface thereof and a separation layer thereunder is employed as the first substrate, and a substrate having a silicon oxide layer on a surface thereof is employed as the second substrate.
10. The method according to claim 2 , wherein the moisture concentration is decreased by heating the first substrate to a temperature falling within a range of 60 to 175° C.
11. The method according to claim 5 , wherein the concentration of OH groups is increased by irradiating the surface of the first substrate with light or a plasma to activate said surface.
12. The method according to claim 7 , 8 , or 9 , further comprising dividing the bonded substrate stack by using the separation layer.