Microcrystalline silicon thin film transistor

A method for forming a microcrystalline silicon containing layer on a substrate comprising:

• providing a substrate in a processing chamber;
• supplying a first gas mixture in the processing chamber;
• maintaining a process pressure at greater than about 6 Torr;
• forming a first microcrystalline silicon layer on the substrate, wherein the first microcrystalline silicon layer has a crystalline fraction greater than about 70 percent;
• and
• forming a second microcrystalline silicon layer on the first microcrystalline silicon layer, wherein the second microcrystalline silicon layer has a crystalline fraction less than the crystalline fraction of the first microcrystalline silicon layer.

A method of depositing a microcrystalline silicon layer, comprising:

• providing a substrate into a processing chamber;
• supplying a gas mixture into the chamber, wherein the gas mixture includes a first gas mixture and a second gas mixture, wherein the first gas mixture includes at least a H2 gas, SiH4 gas and an inert gas and the second gas mixture includes at least a H2 gas and SiH4 gas;
• and
• depositing a microcrystalline silicon containing layer on the substrate in the presence of a plasma formed from the gas mixture, wherein the process pressure is adjusted during deposition.

A method of forming a device structure, comprising:

• providing a substrate in a processing chamber;
• forming a dual microcrystalline silicon layer on the substrate, wherein the dual microcrystalline silicon layer has a first microcrystalline silicon layer and a second microcrystalline silicon layer formed over the first microcrystalline silicon layer, wherein the first microcrystalline silicon layer has a higher crystalline fraction than the second microcrystalline silicon layer and the first microcrystalline silicon layer is formed at a process pressure greater than about 6 Torr;
• and
• forming an amorphous silicon layer over the dual microcrystalline silicon layer.