Silicon-on-insulator substrate with built-in substrate junction
View Patent ↗A method of forming a SOI substrate, diodes in the SOI substrate and electronic devices in the SOI substrate and an electronic device formed using the SOI substrate. The method of forming the SOI substrate includes forming an oxide layer on a silicon first substrate; ion-implanting hydrogen through the oxide layer into the first substrate, to form a fracture zone in the substrate; forming a doped dielectric bonding layer on a silicon second substrate; bonding a top surface of the bonding layer to a top surface of the oxide layer; thinning the first substrate by thermal cleaving of the first substrate along the fracture zone to form a silicon layer on the oxide layer to formed a bonded substrate; and heating the bonded substrate to drive dopant from the bonding layer into the second substrate to form a doped layer in the second substrate adjacent to the bonding layer.
1. A method, comprising:
forming an oxide layer on a silicon first substrate;
ion-implanting hydrogen through said oxide layer into said first substrate, to form a fracture zone in said substrate;
forming a doped dielectric bonding layer on a silicon second substrate;
bonding a top surface of said bonding layer to a top surface of said oxide layer;
thinning said first substrate by thermal cleaving of said first substrate along said fracture zone to form a silicon layer on said oxide layer to form a bonded substrate; and
heating said bonded substrate to drive dopant from said bonding layer into said second substrate to form a doped layer in said second substrate adjacent to said bonding layer.
2. The method of claim 1 , wherein said forming said oxide layer includes thermal oxidation of a top surface of said first substrate in the presence of water vapor.
3. The method of claim 1 , wherein said forming said bonding layer includes depositing a doped glass onto a top surface of said second substrate.
4. The method of claim 1 , wherein said forming said bonding layer includes:
thermal oxidation of a top surface of said second substrate in the presence of water vapor to form an undoped bonding layer; and
ion implanting a dopant species into said undoped bonding layer.
5. The method of claim 1 , wherein said dopant species is selected from the group consisting of arsenic, antimony, phosphorus and boron.
6. The method of claim 1 , further including:
after said thinning smoothing a top surface of said silicon layer by chemical-mechanical polishing of said top surface of said silicon layer or by performing a post-cleave heating.
7. The method of claim 1 , further including:
after said heating, forming a photoresist layer on a top surface of said silicon layer;
forming an opening in said photoresist layer, a region of said top surface of said silicon layer exposed in a bottom of said opening;
ion implanting an additional dopant species into a portion of said doped layer under said opening to form an ion-implanted region in said doped layer, said photoresist layer blocking ion-implantation of said additional dopant species into said silicon layer, said dopant species of an opposite type than dopant in said doped layer;
after said ion-implanting, removing said photoresist layer; and
performing an additional heating to activate said additional dopant species in said ion-implanted region of said doped layer to form a doped region in said doped layer, said doped region and said doped layer comprising a diode.
8. The method of claim 7 , wherein said doped region has a net doping of P-type and said doped layer is doped N-type.
9. The method of claim 1 , further including:
forming a photoresist layer on a top surface of said silicon layer;
forming an opening in said photoresist layer, a region of said top surface of said silicon layer exposed in a bottom of said opening;
ion implanting a dopant species into a portion of said doped layer under said opening to form an ion-implanted region in said doped layer, said photoresist layer blocking ion-implantation of said dopant species into said silicon layer, said dopant species of an opposite type than dopant in said doped layer;
after said ion-implanting, removing said photoresist layer; and
heating said silicon-on-insulator substrate to activate said dopant species in said ion-implanted region of said doped layer to form a doped region in said doped layer, said doped region and said doped layer comprising a diode.
10. The method of claim 9 , wherein said doped region has a net doping of P-type and said doped layer is doped N-type.
11. The method of claim 1 , further including:
forming dielectric isolation in said silicon layer, said dielectric isolation separating said silicon layer into electrically isolated silicon islands;
forming dynamic random access memory (DRAM) cells in respective silicon islands, each DRAM cell comprising a field effect transistor (FET) and a respective trench capacitor, each trench capacitor of said respective trench capacitors comprising a dielectric layer isolating a doped polysilicon inner plate from a diffused outer plate, said diffused outer plate formed in said doped layer and said substrate, said doped layer electrically contacting said outer plate, and
forming an electrically conductive contact extending through said trench isolation and said buried dielectric layer into said doped layer.
12. The method of claim 11 , further including:
said inner plates of said trench capacitors contacting first source/drains of said respective FETs;
connecting second source/drains of said respective FETs to bitlines of a memory array;
connecting gates of said FETS to wordlines of said memory array; and
connecting said contact to a ground rail of a power distribution network.
13. The method of claim 12 , further including:
forming additional FETs in respective silicon islands; and
connecting said additional FETs into logic circuits.