Systems and methods for bidirectional device fabrication
Methods and systems for double-sided semiconductor device fabrication. Devices having multiple leads on each surface can be fabricated using a high-temperature-resistant handle wafer and a medium-temperature-resistant handle wafer. Dopants can be introduced on both sides shortly before a single long high-temperature diffusion step diffuses all dopants to approximately equal depths on both sides. All high-temperature processing occurs with no handle wafer or with a high-temperature handle wafer attached. Once a medium-temperature handle wafer is attached, no high-temperature processing steps occur. High temperatures can be considered to be those which can result in damage to the device in the presence of aluminum-based metallizations.
1. A method of fabricating a semiconductor device, comprising:
introducing first-conductivity-type dopants into first regions on a first face of a semiconductor mass; introducing second-conductivity-type dopants into second regions on said first face;
attaching a high-temperature-resistant handle wafer to said first face;
introducing first-conductivity-type dopants into third regions on a second face of said semiconductor mass which is parallel to said first face; introducing second-conductivity-type dopants into fourth regions on said second face;
performing a high-temperature diffusion step; whereby said diffusion step diffuses the first-conductivity-type dopants in said first and third regions and the second-conductivity-type dopants in said second and fourth regions to corresponding desired depths in said semiconductor mass;
performing medium-temperature fabrication steps on said second face;
attaching a medium-temperature-resistant handle wafer to said second face;
removing said high-temperature-resistant handle wafer; and
performing medium-temperature fabrication steps on said first face.
2. The method of claim 1 , wherein both p-type and n-type dopants are introduced, in respective patterns and not overall, on both said first and second surfaces of the wafer.
3. The method of claim 1 , wherein the medium-temperature-resistant handle wafer has a different composition than the high-temperature-resistant handle wafer.
4. The method of claim 1 , wherein the diffusion step uses a higher sustained temperature than any step thereafter.
5. The method of claim 1 , wherein the steps of introducing dopants into said first and second regions on said first face use the same patterns as the steps of introducing dopants into said third and fourth regions on said second face, respectively.
6. The method of claim 1 , wherein the connection between each said handle wafer and said semiconductor mass is substantially unaffected by temperatures used after the respective attaching step.
7. The method of claim 1 , wherein said medium-temperature fabrication steps are performed at temperatures below about 450° C.
8. The method of claim 1 , wherein said diffusion step uses temperatures above about 600° C.
9. The method of claim 1 , further comprising forming trench gates on the respective face before introducing the dopants into each said face.
10. The method of claim 1 , wherein said semiconductor mass is made of silicon.
11. The method of claim 1 , wherein the first conductivity type is N type.
12. The method of claim 1 , wherein said medium-temperature fabrication steps are performed substantially identically both on said first face and also on said second face.
13. The method of claim 1 , wherein said high-temperature-resistant handle wafer is silicon.
14. The method of claim 1 , wherein said high-temperature-resistant handle wafer is silicon dioxide.
15. The method of claim 1 , wherein said high-temperature-resistant handle wafer is silicon carbide.
16. The method of claim 1 , wherein said high-temperature-resistant handle wafer is sapphire.
17. The method of claim 1 , wherein said high-temperature-resistant handle wafer is gallium nitride.
18. The method of claim 1 , wherein said medium-temperature-resistant handle wafer is quartz.
19. A method of fabricating a semiconductor device, comprising:
performing high-temperature fabrication steps on a first face of a semiconductor wafer;
introducing first-conductivity-type dopants into first regions on said first face; introducing second-conductivity-type dopants into second regions on said first face;
bonding a high-temperature-resistant handle wafer to said first face;
performing high-temperature fabrication steps on a second face of said semiconductor wafer which is parallel to said first face;
introducing first-conductivity-type dopants into third regions on said second face; introducing second-conductivity-type dopants into fourth regions on said second face;
performing a diffusion step at temperatures above about 600° C.; whereby said diffusion step diffuses the first-conductivity-type dopants in said first and third regions and the second-conductivity-type dopants in said second and fourth regions to corresponding desired depths in said semiconductor wafer;
performing medium-temperature fabrication steps on said second face at temperatures below about 450° C.;
bonding a medium-temperature-resistant handle wafer to said second face;
removing said high-temperature-resistant handle wafer from said first face;
performing medium-temperature fabrication steps on said first face at temperatures below about 450° C.;
removing said medium-temperature-resistant handle wafer from said second face; and
performing low-temperature processing steps on said semiconductor wafer at temperatures below about 240° C.;
wherein at least some of said high-temperature fabrication steps are performed at temperatures above about 600° C.
20. A method of fabricating a semiconductor device, comprising:
performing high-temperature fabrication steps on a first face of a semiconductor wafer;
introducing first-conductivity-type dopants into first regions on a first face of a semiconductor wafer; introducing second-conductivity-type dopants into second regions on said first face;
forming a protective layer on said first face;
bonding a high-temperature-resistant handle wafer to said protective layer on said first face;
thinning said semiconductor wafer, from a second face of said semiconductor wafer which is parallel to said first face, to a desired thickness;
performing high-temperature fabrication steps on said second face;
introducing first-conductivity-type dopants into third regions on said second face; introducing second-conductivity-type dopants into fourth regions on said second face;
performing a diffusion step; whereby said diffusion step diffuses the first-conductivity-type dopants in said first and third regions and the second-conductivity-type dopants in said second and fourth regions to corresponding desired depths in said semiconductor wafer;
performing medium-temperature fabrication steps on said second face; forming patterned metallization on said second face;
bonding a medium-temperature-resistant handle wafer to said second face, over said patterned metallization;
removing said high-temperature-resistant handle wafer from said first face;
removing said protective layer from said first face;
performing medium-temperature fabrication steps on said first face; forming additional patterned metallization on said first face;
removing said medium-temperature-resistant handle wafer from said second face; and
performing low-temperature processing steps on said semiconductor wafer at temperatures below about 240° C.;
wherein the bond between each said handle wafer and said semiconductor wafer is substantially unaffected by temperatures used after the respective bonding step;
wherein said diffusion step, and at least some said high-temperature fabrication steps, are performed at temperatures above about 600° C.;
wherein said medium-temperature fabrication steps are performed at temperatures below about 450° C.