Back-gated fully depleted SOI transistor
View Patent ↗A fully depleted semiconductor-on-insulator (FDSOI) transistor structure includes a back gate electrode having a limited thickness and aligned to a front gate electrode. The back gate electrode is formed in a first substrate by ion implantation of dopants through a first oxide cap layer. Global alignment markers are formed in the first substrate to enable alignment of the front gate electrode to the back gate electrode. The global alignment markers enable preparation of a virtually flat substrate on the first substrate so that the first substrate can be bonded to a second substrate in a reliable manner.
1. A method of forming a semiconductor structure comprising:
forming a doped semiconductor region in an upper portion of a first semiconductor layer of a first substrate by implanting dopant ions through a portion of a first oxide cap layer on said first semiconductor layer;
forming a layer of hydrogen atoms in a second semiconductor layer of a second substrate by implanting hydrogen ions through an entirety of a second oxide cap layer on said second semiconductor layer;
forming a bonded substrate by bonding said first substrate and said second substrate at an interface of said first oxide cap layer and said second oxide cap layer, wherein said first and second oxide cap layers form a buried oxide layer, and a portion of said second semiconductor layer on one side of said layer of hydrogen atoms constitute a semiconductor-on-insulator (SOI) layer; and
forming a dual gate field effect transistor on said bonded substrate, wherein said doped semiconductor region constitutes a back gate electrode and a front gate electrode overlies an entirety of said back gate electrode.
2. The method of claim 1 , further comprising forming alignment marks in said first substrate prior to bonding said first substrate with said second substrate.
3. The method of claim 2 , wherein said alignment marks are formed in said first semiconductor layer.
4. The method of claim 3 , wherein said front gate electrode is aligned to said back gate electrode employing said alignment marks during lithographic patterning of a material layer, wherein a portion of said material layer is conductive and constitutes said front gate electrode after said lithographic patterning.
5. The method of claim 4 , wherein said alignment marks are global alignment marks that are laterally separated by a distance greater than a size of an exposure field of a lithography tool.
6. The method of claim 1 , wherein said first substrate is a bulk substrate comprising said first semiconductor layer and said first oxide cap layer.
7. The method of claim 1 , wherein said first substrate is a semiconductor-on-insulator (SOI) substrate comprising a stack, from bottom to top, of a first handle substrate, a first buried insulator layer, said first semiconductor layer, and said first oxide cap layer.
8. The method of claim 7 , wherein said doped semiconductor region contacts a surface of said first oxide cap layer and does not contact said first buried insulator layer upon formation by said implantation of said doped ions.
9. The method of claim 1 , wherein said second substrate is a bulk substrate comprising said second semiconductor layer and said second oxide cap layer.
10. The method of claim 1 , wherein said second substrate is a semiconductor-on-insulator (SOI) substrate comprising a stack, from bottom to top, of a handle substrate, a buried insulator layer, said second semiconductor layer, and said second oxide cap layer.
11. The method of claim 1 , wherein a thickness of said buried oxide layer is the same as the sum of a thickness of said first oxide cap layer and a thickness of said second oxide cap layer.
12. The method of claim 1 , wherein said second semiconductor layer is divided into a surface semiconductor portion and a bulk semiconductor portion by said layer of hydrogen atoms after said implantation of said hydrogen ions.
13. The method of claim 12 , wherein said bulk semiconductor portion is cleaved off said surface semiconductor portion after said bonding of said first substrate and said second substrate, wherein said surface semiconductor portion constitutes a semiconductor-on-insulator (SOI) layer in said bonded substrate.
14. The method of claim 1 , wherein said SOI layer comprises a semiconductor material selected from silicon, germanium, silicon-germanium alloy, silicon carbon alloy, silicon-germanium-carbon alloy, gallium arsenide, indium arsenide, indium phosphide, III-V compound semiconductor materials, II-VI compound semiconductor materials, organic semiconductor materials, and other compound semiconductor materials.
15. The method of claim 1 , wherein said SOI layer comprises a single crystalline semiconductor material.
16. The method of claim 1 , wherein said back gate electrode does not underlie an entirety of source and drain regions of said dual gate field effect transistor.
17. The method of claim 1 , further comprising forming a back gate contact through a portion of said SOI layer and said buried oxide layer.
18. The method of claim 1 , further comprising forming raised source and drain regions on said SOI layer by selective epitaxy and ion implantation, wherein top surfaces of said raised source and drain regions protrude above a surface of said SOI layer.
19. The method of claim 1 , further comprising forming metal semiconductor alloy portions on said SOI layer.
20. The method of claim 1 , wherein a p-n junction is formed between said back gate electrode and said first semiconductor layer.
21. The method of claim 1 , further comprising thinning said SOI layer by oxidation of a surface portion of said SOI layer and removal of an oxidized portion of said SOI layer.