Spin coating apparatus and method
In one embodiment, a spin coating apparatus includes a coating liquid feeding module to drop a coating liquid onto a substrate, and a motor to rotate the substrate. The module drops a first drop amount of the coating liquid onto the substrate at a first discharge rate, while the motor rotates the substrate at a first number of rotations. The module drops a second drop amount of the coating liquid onto the substrate at a second discharge rate larger than the first discharge rate, while the motor rotates the substrate at a second number of rotations smaller than the first number of rotations, after the first drop amount of the coating liquid is dropped. The module discharges the coating liquid onto the substrate at a third discharge rate smaller than the second discharge rate, after the coating liquid is discharged onto the substrate at the second discharge rate.
1. A spin coating method comprising:
starting to rotate a substrate;
starting to drop coating liquid onto a portion of the substrate, wherein, when the dropping of the coating liquid is started, the coating liquid is dropped at a first discharge rate while rotating the substrate at a first number of revolutions per minute; and
after a first drop amount of the coating liquid is dropped at the first discharge rate, dropping a second drop amount of the coating liquid onto the portion of the substrate at a second discharge rate which is larger than the first discharge rate while rotating the substrate at a second number of revolutions per minute which is smaller than the first number of revolutions per minute; and
wherein the discharge rate of the coating liquid is changed from the first discharge rate to the second discharge rate while the number of revolutions per minute of the substrate is changed from the first number of revolutions per minute to the second number of revolutions per minute.
2. The method of claim 1 , wherein
the coating liquid is discharged onto the substrate at a third discharge rate which is equal to or larger than the first discharge rate and smaller than the second discharge rate, after the coating liquid is discharged onto the substrate at the second discharge rate, and
when the coating liquid is dropped while the substrate is rotated at the second number of revolutions per minute, the coating liquid is discharged onto the substrate at the second discharge rate and then discharged onto the substrate at the third discharge rate.
3. The method of claim 1 , further comprising dropping a pre-wet liquid which has a vapor pressure of 6 hPa or less at 23° C. onto the substrate and rotating the substrate, before the coating liquid is dropped onto the substrate.
4. The method of claim 3 , wherein the pre-wet liquid has a vapor pressure lower than a vapor pressure of di-n-butyl ether.
5. The method of claim 1 , wherein the coating liquid contains silazanes or siloxanes.
6. The method of claim 3 , wherein time from a start of rotating the substrate to spread the pre-wet liquid on the surface of the substrate to a start of dropping of the coating liquid is 1 second or more.
7. The method of claim 3 , wherein time from a start of rotating the substrate to spread the pre-wet liquid on the surface of the substrate to an end of dropping of the coating liquid is 1.5 seconds or more.
8. The method of claim 1 , wherein, when dropping the second drop amount of the coating liquid onto the portion of the substrate, the second discharge rate and the second number of revolutions per minute are held constant.