Method for coating a resist film and resist coater

Abstract

A resist film having a thickness of 5500Å or less is coated on the wafer having a large diameter of 8 inches or more by the spin coat process. A resist is dripped while allowing the wafer to be rotated at a rotation speed of 500 rpm to 1200 rpm and the dripping of the resist is suspended at the time of spreading the resist on the whole surface of the wafer. The rotation speed is raised to the predetermined rotation speed which regulates the thickness of the resist film and is determined from the correlation of the predetermined rotation speed and the thickness of the resist film. The wafer is rotated for 1 second to 5 seconds at the predetermined rotation speed. Then, the wafer is rotated for 15 seconds or more at the rotation speed which is lower than the predetermined rotation speed.

What is claimed is:  
     
         1 . A coating method for a resist film wherein a resist film having a thickness of 5500Å or less is coated on a wafer having a large diameter of 8 inches or more by a spin coat process of coating a resist on a wafer by allowing the wafer to be rotated around an axis which is perpendicular to the surface of the wafer, the method comprising the steps of: 
 dripping a predetermined amount of the resist while allowing the wafer to be rotated at a rotation speed of 500 rpm to 1200 rpm and suspending the dripping of the resist at the time of spreading the resist on the whole surface of the wafer;  
 raising the rotation speed of the wafer from the rotation speed at the first step to a predetermined rotation speed of the wafer which is determined from a correlation of the predetermined rotation speed of the wafer which regulates the thickness of the resist film and the thickness of the resist film and allowing the wafer to be rotated at the predetermined rotation speed for 1 second or more to 5 seconds or less; and  
 lowering the rotation speed from the rotation speed at the second step and allowing the wafer to be rotated at a rotation speed which is lower than the predetermined rotation speed of the wafer at the second step for 15 seconds or more.  
 
     
     
         2 . The coating method for a resist film according to    claim 1   , wherein time of 1 second to 5 seconds which is defined as a period of the second step includes time of transition from the first step to the second step.  
     
     
         3 . The coating method for a resist film according to    claim 1   , wherein an organic resist having a viscosity of 40 cp or less is used, and the predetermined rotation speed at the second step is 4300 rpm to 6000 rpm.  
     
     
         4 . The coating method for a resist film according to    claim 3   , wherein the wafer is rotated at a rotation speed ranging between 3800 rpm and 4200 rpm at the third step.  
     
     
         5 . The coating method for a resist film according to    claim 1   , wherein there is provided after the third step a fourth step of rinsing the edge of the surface and the edge of the back surface of the wafer while allowing the wafer to be rotated at the rotation speed which is lower than the rotation speed at the third step.  
     
     
         6 . The coating method for a resist film according to    claim 5   , wherein the time of 10 seconds and 15 seconds, and the time of 10 seconds to 20 seconds are set respectively as time required for the first step and the time required for the fourth step, and a sequence from the first step to the fourth step is programmed, and a process of coating the resist film is automatically performed in accordance with the program.  
     
     
         7 . A resist coater for coating a resist film on a wafer by a spin coat process, comprising: 
 a wafer holding table for allowing a wafer to be rotated around an axis which is perpendicular to the wafer while holding the wafer with a wafer surface directed upwardly;    a resist supply nozzle for supplying a resist on the wafer which is held on the wafer holding table;    a coater cup surrounding the wafer holding table and the resist supply nozzle, the coater cup being of a tightly sealed type; and    a pressure reducing device for reducing a pressure within the coater cup.    
     
     
         8 . The resist coater according to    claim 7   , further comprising a back surface cleaning nozzle for rinsing the edge of the back surface of the wafer, and a surface cleaning nozzle for rinsing the edge of the surface of the wafer.  
     
     
         9 . The resist coater according to    claim 7   , wherein the coater cup is divided into two portions of an upper cup and a lower cup, and the upper cup and the lower cup are mutually connected to each other and but they are separable.  
     
     
         10 . The resist coater according to    claim 9   , wherein the resist supply nozzle and the surface cleaning nozzle are connected to the upper cup via flexible pipes, passes through the upper cup while the back surface cleaning nozzle passes through the lower cup and faces an appropriate portion of the back surface of the wafer.