Method for fabricating a tunneling field-effect transistor
The present invention discloses a method for self-alignedly fabricating tunneling field-effect transistor (TFET) based on planar process, thereby lowering requirements on a photolithography process for fabricating the planar TFET. In the method, the source region and the drain region of the TFET are not directly defined by photolithography; rather, they are defined by another dielectric film which locates over an active region and on both sides of the gate and which is different from the dielectric film that defines the channel region. The influence due to the alignment deviation among three times of photolithography process for defining the channel region, the source and the drain regions may be eliminated by selectively removing the dielectric film over the source and drain regions by wet etching. Therefore, a planar TFET may be fabricated self-alignedly based on this process, thereby the rigid requirements on the alignment deviation of the photolithography during the fabrication procedure of a planar TFET is alleviated, which facilitates to fabricate a planar TFET device with stable and reliable characteristics.
1. A method for self-alignedly fabricating a tunneling field-effect transistor based on a planar process, comprising steps of:
1) defining an active region on a substrate by shallow trench isolation, and then sequentially growing a gate dielectric, depositing polysilicon, and carrying out a gate implantation with respect to the polysilicon;
2) depositing a first hard dielectric on the polysilicon and then etching the first hard dielectric to define a channel region, and then depositing a second hard dielectric and then a chemical mechanical polishing process is carried out on the second hard dielectric by using the upper surface of the first hard dielectric as the stop layer, wherein the first hard dielectric and the second hard dielectric comprise different materials and are selectively etchable by different chemical agents;
3) applying photoresist on a mask comprising both the first and second hard dielectric, carrying out photolithography to define a through hole over a region where a drain region is to be formed, carrying out wet etching on the second hard dielectric over the region through the through hole to remove the second hard dielectric over the region, removing the photoresist, removing the polysilicon over the region by etching, and carrying out a n-type ion implantation process to form the drain region of the device;
4) depositing the second hard dielectric to cover the drain region, and carrying out a chemical mechanical polishing process on the second hard dielectric by using the upper surface of the first hard dielectric as the stop layer, thereby forming a hard mask for protecting the drain region;
5) applying a photoresist on a mask comprising both the first and second hard dielectrics, carrying out photolithography to define a through hole over a region where a source region is to be formed, carrying out a wet etching on the second hard dielectric over the region through the through hole to remove the second hard dielectric over the region, removing the photoresist, removing the polysilicon over the region by etching, and carrying out a p-type ion implantation process to form the source region of the device;
6) depositing the second hard dielectric to cover the source region, and carrying out a chemical mechanical polishing process on the second hard dielectric by using the upper surface of the first hard dielectric as the stop layer, thereby forming a hard mask to protect the source region;
7) carrying out an anneal process to activate the impurities, and carrying out subsequent procedures for manufacturing the transistor.
2. The method according to claim 1 , wherein the first hard dielectric is silicon nitride and the second hard dielectric is silicon oxide, or the first hard dielectric is silicon oxide and the second hard dielectric is silicon nitride.
3. The method according to claim 1 , wherein the first hard dielectric and the second hard dielectric are deposited by chemical vapor deposition.
4. The method according to claim 1 , wherein a following step is added between the step 6) and the step 7): removing the first hard dielectric over the channel region by a wet etching, and then depositing and planarizing the second hard dielectric over the region, thereby the entire active region is protected by the second hard dielectric.
5. The method according to claim 1 , wherein, in the step 1), silicon oxide is grown as the gate dielectric by dry oxygen oxidation, and the polysilicon is deposited on the gate dielectric by chemical vapor deposition.
6. The method according to claim 1 , wherein the step of defining the channel region in the step 2) comprises: depositing the first hard dielectric and applying a layer of photoresist thereon, defining the channel region by photolithography, transferring patterns in the photoresist onto the first hard dielectric by etching, and then removing the photoresist.
7. The method according to claim 1 , wherein the first hard dielectric comprises silicon oxide, and in the steps 3) and 5), the second hard dielectric is removed by wet etching using hydrofluoric acid.
8. The method according to claim 1 , wherein, in the steps 3) and 5), the polysilicon is etched by anisotropic etching.
9. The method according to claim 1 , wherein, in the steps 4) and 6), the second hard dielectric are deposited by plasma-enhanced chemical vapor deposition.
10. The method according to claim 1 , wherein, in the step 7), a rapid thermal processing is carried out in nitrogen gas to activate the impurities.