T-gate forming method for high electron mobility transistor and gate structure thereof

Abstract

A T-gate forming method for a high electron mobility transistor includes the steps of: coating a first, a second and a third resist, each having an electron beam sensitivity different from each other, on a semiconductor substrate; performing a first exposure process by using an electron beam on the semiconductor substrate and then selectively developing the third resist; defining a gate head area by selectively developing the second resist to have a developed width wider than that of the third resist; performing a second exposure process by using an electron beam on the semiconductor substrate and then selectively developing the first resist in a bent shape at a temperature lower than in the development of the second and the third steps; and depositing metallic materials on the resists and then removing them to form a T-gate.

1 . A T-gate forming method for a high electron mobility transistor, the method comprising the steps of:
 a first step of coating a first resist, a second resist and a third resist, each having an electron beam sensitivity different from each other, on a semiconductor substrate;   a second step of performing a first exposure process by using an electron beam on the semiconductor substrate where the first resist, the second resist and the third resist are coated and then selectively developing the third resist;   a third step of defining a gate head area by selectively developing the second resist to have a developed width wider than that of the third resist;   a fourth step of performing a second exposure process by using an electron beam on the semiconductor substrate where the third resist and the second resist are selectively developed and then selectively developing the first resist in a bent shape at a temperature lower than in the development of the second and the third steps; and   a fifth step of depositing metallic materials on the first resist, the second resist and the third resist which are selectively developed and then removing the first resist, the second resist and the third resist to form a T-gate with the gate head and a gate foot.   
     
     
         2 . The method of  claim 1 , wherein, as the first resist, a PMMA (Polymethyle Methacrylate) resist is coated with a thickness from 90 nm to 110 nm. 
     
     
         3 . The method of  claim 1 , wherein, as the second resist, a PMGI (Poly-Dimethylgutarimide) resist is coated with a thickness from 450 nm to 550 nm. 
     
     
         4 . The method of  claim 1 , wherein, as the third resist, a PMMA-MAA (Polymethyle Methacrylate-Methyle Methacrylate) resist is coated with a thickness from 180 nm to 220 nm. 
     
     
         5 . The method of  claim 1 , wherein the first exposure process is performed at an energy level of 90 μC/cm 2  to 100 μC/cm 2 . 
     
     
         6 . The method of  claim 1 , wherein the development at the second step is performed by using a developing solution with a ratio of MIBK:IPA being 1:3. 
     
     
         7 . The method of  claim 1 , wherein the development at the third step is performed by using a developing solution of PMGI-101. 
     
     
         8 . The method of  claim 1 , wherein the second exposure process is performed at an energy level of 1000 μC/cm 2  to 4000 μC/cm 2 . 
     
     
         9 . The method of  claim 1 , wherein the development at the fourth step is performed by using a developing solution with a ratio of MIBK:IPA being 1:3. 
     
     
         10 . The method of  claim 9 , wherein the development at the fourth step is performed at a temperature from −15° C. to −25° C. 
     
     
         11 . The method of  claim 1 , wherein a transversal cross section of the bent shape at the fourth step is of a patterned shape having trapezoids, where each trapezoid is connected to its two adjacent trapezoids without the base lines. 
     
     
         12 . The method of  claim 1 , wherein a transversal cross section of the bent shape at the fourth step is of a patterned shape having alternating sharp bends at each apex. 
     
     
         13 . The method of  claim 1 , wherein a transversal cross section of the bent shape at the fourth step is of a patterned shape having curved bends alternating right and left. 
     
     
         14 . The method of  claim 1 , wherein, as the metallic materials, Ti, Pt and Au are sequentially deposited. 
     
     
         15 . The method of  claim 12 , wherein, as the metallic materials, Ti with a thickness from 25 nm to 35 nm, Pt with a thickness from 10 nm to 20 nm and Au with a thickness from 230 nm to 270 nm are deposited.