JPS6334925A - Formation of photoresist film - Google Patents

Abstract

PURPOSE:To relatively slowly form a photoresist and to widen it uniformly on the whole surface of a silicon wafer by dropping the photoresist on the wafer, and then providing the step of rotating it until it arrives at the speed of the wafer for providing the thickness of the photoresist to be of a target. CONSTITUTION:A time T1 is a time of dropping a photoresist on a silicon wafer, a time T3 is a time for providing the step of rotating it until it arrives at the speed of the wafer to be of a target, and a time T2 is a time of rotating at the speed to be of a target. The time T3 for providing the step of rotating it is provided to widen the photoresist dropped on the wafer on the whole surface of the wafer while slowly drying it, i.e., slowly raising its viscosity. As a result, the thickness difference between the photoresist film formed at the center on the wafer and the photoresist film formed on the periphery of the wafer is reduced.

Description

[Detailed description of the invention] [Industrial application field].

The present invention involves dropping positive type and negative type photoresists onto a silicon wafer for semiconductor integrated circuit manufacturing.
The present invention relates to a method of forming a photoresist film by rotating and applying the silicon wafer.

[Conventional technology]

Conventionally, in this type of photoresist coating method, in order to make the photoresist film uniform in thickness, a method has been adopted in which the photoresist is dropped onto a silicon wafer and then the wafer is rotated to spread the photoresist over the entire surface of the wafer.

At this time, as shown in FIG. 2, a method was used in which the silicon wafer was rapidly stood up and rotated up to the target rotational speed of the rotating shaft.

[Problem that the invention seeks to solve]

In the conventional photoresist coating method described above, the rotational speed of the silicon wafer at the time of photoresist dropping was increased all at once to the target rotational speed, so the photoresist dropped onto the silicon wafer was coated onto the silicon wafer in a relatively short time. Since the photoresist spreads to the periphery and a large amount of scattering occurs, it was necessary to drop a large amount of photoresist onto the silicon wafer. Additionally, as silicon wafers become larger in diameter, the phenomenon that the photoresist film is thinner at the center of the silicon wafer and thicker at the periphery becomes more severe. There was a drawback that the dimensions varied greatly within the silicon wafer.

[Means for solving problems]

The method for forming photoresist films 1 to 1 of the present invention includes dropping photoresist onto a silicon wafer for manufacturing a semiconductor integrated circuit and rotating the silicon wafer. This method is characterized by providing at least two stages of rotation speed from the rotation speed at the time of cyst dropping to the target rotation speed.

〔Example〕

Next, the present invention will be explained with reference to the drawings. FIG. 1 is a graph of silicon wafer rotation speed versus elapsed time according to one embodiment of the present invention. Time T1 is the time during which the photoresist is being dropped onto the silicon wafer, time T3 is the time during which the rotation speed steps to reach the target rotation speed, and time T2 is the time during which the rotation is being performed at the target rotation speed. It's time.

The photoresist 1 to 1 dropped onto the silicon wafer is
spreads over the entire surface of the wafer while slowly drying, that is, slowly increasing its viscosity. As a result, the difference in film thickness between the photoresist film formed at the center of the wafer and the photoresist film formed at the periphery of the wafer becomes smaller. The present invention focuses on the fact that the viscosity of the photoresist greatly affects the photoresist film thickness, and provides steps in the number of revolutions in order to make the viscosity change of the photoresist as gradual as possible in the process of forming the photoresist film. . In this example, the number of revolutions was set to 10 steps as shown in FIG. 1, and as a result, as shown in FIG. Compared to FIG. 4, the maximum value - minimum value of the film thickness is approximately 1/3, which is greatly improved. Furthermore, as shown in FIG. 5, even if the amount of photoresist dropped is small, coating unevenness in which the maximum value minus the minimum value of the photoresist film thickness is 100 Å or more is less likely to occur. As mentioned above, this is due to the fact that the photoresists 1 to 1 dropped onto the silicon wafer are gradually spread over the entire surface of the wafer in steps.

(Effects of the Invention) As described above, the present invention provides the following advantages: After dropping a photoresist onto a silicon wafer, the number of revolutions b of the silicon wafer that provides the target photoI/cyst film thickness is increased by steps of the number of revolutions until reaching the target photoI/cyst film thickness. By having a The cost of photoresist can be reduced by increasing the amount of photoresist.Also, even when silicon wafers have a large diameter, uniformity of the photoresist film thickness within the silicon wafer surface can be ensured, making it possible to reduce the cost of photoresist! It has the effect of making it less likely that uneven coating will occur.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the rotational speed of a silicon wafer versus elapsed time in an embodiment of the present invention, and FIG. 2 is a diagram showing the conventional silicon wafer rotational speed versus elapsed time. Figure 3 is a characteristic diagram showing the in-plane uniformity of a silicon wafer when a photoresist film is formed using the method shown in Figure 1, and Figure 4 is a characteristic diagram showing the in-plane uniformity of a silicon wafer using the conventional method shown in Figure 2. Characteristic diagram showing the characteristics, 5th
The figure is a characteristic diagram showing the photoresist drop amount versus coating unevenness occurrence rate when a photoresist film is formed using the method shown in Fig. 1, and Fig. 6 is a characteristic diagram showing the coating unevenness rate when a photoresist film is formed using the method shown in Fig. 2. FIG. 3 is a characteristic diagram showing the unevenness occurrence rate. T1...Time for dropping the photoresist onto the silicon wafer, T3...Time to maintain the rotation speed until reaching the rotation speed that gives the target photoresist film thickness, T2...・Time during which the silicon wafer rotates at the rotation speed that provides the target photoresist film thickness. 1st figure, 1 unit, 31st sword change; Shi--color Ll-ro

Claims (1)

[Claims] In a method for forming a photoresist film in which a photoresist is dropped onto a silicon wafer for manufacturing semiconductor integrated circuits and the silicon wafer is rotated, at least two steps are required from the rotational speed at the time of dropping the photoresist to the target rotational speed. A method for forming a photoresist film, characterized by providing a step with a rotational speed higher than or equal to the number of rotations.