JP2913988B2 - How to measure heat treatment effect - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the effect of heat treatment, and more particularly to a method for measuring the effect of heat treatment in a resist process.

[0002]

2. Description of the Related Art FIG. 3 is a view schematically showing a hot plate type heat treatment apparatus. Usually, in the resist process, a hot plate type heat treatment apparatus shown in FIG. 3 is used. In this hot plate heat treatment apparatus, a semiconductor substrate is placed on a hot plate 23 via a pin 22, accelerated, a heating temperature is detected by a temperature measuring element 24, and feedback control is performed by a temperature control unit 26 to obtain a temperature of 0.1 ° C. ] It is a device that controls accurately to the extent. Further, the hot plate 23 and the semiconductor substrate 21 are separated by the pins 22 interposed between the hot plate 3 and the semiconductor substrate 21.
A gap of about [μm] is provided. And the semiconductor substrate 2
1 is heated by the hot plate 23 through this gap.

Conventionally, the effect of this heat treatment is determined by the temperature of the hot plate 23 and the processing time of the semiconductor substrate 21 on the hot plate 23. In this hot plate type heat treatment apparatus, both the temperature and the treatment time can be controlled to about 0.1 [° C.] and 0.1 [S], and have sufficient accuracy to express the heat treatment effect.

FIGS. 4 (a) and 4 (b) are schematic cross-sectional views of a semiconductor substrate for explaining the measurement of the sensitivity of a photoresist film to be removed. The measurement of the film-peeling sensitivity is generally used as one factor indicating the characteristics of the photoresist. For this measurement, first, the photomask 3
2 is used to expose UV light 3. In this case, a region in which the exposure amount is changed stepwise is formed in the photoresist film 33 by using a photomask in which the transmittance of the UV light changes stepwise or by changing the irradiation time of the UV light stepwise. (FIG. 4 (a)). Next, as shown in FIG. 5B, by developing this, a stepwise change in the photoresist film can be obtained in the case of a positive type photoresist. As the exposure amount increases, the remaining photoresist film decreases, and the minimum exposure amount at which the remaining photoresist film becomes zero is defined as the photoresist film removal sensitivity. In addition, since the sensitivity of the photoresist to film removal greatly depends on the heat treatment, this sensitivity measurement has actually been used as one of the methods for measuring the effect of the heat treatment applied to the semiconductor substrate.

[0005]

Conventionally, the heat treatment effect is determined by the temperature of the hot plate and the processing time on the hot plate. However, no matter how precisely the temperature and the time can be measured, the semiconductor substrate is actually subjected to the heat treatment. It is only a measure of the heat treatment effect. The heat treatment effect actually applied to the semiconductor substrate is greatly affected by the thermal conductivity from the hot plate to the semiconductor substrate.

FIGS. 5A to 5C are views for explaining two methods of the hot plate heat treatment method.
5A shows a proximity type method in which a slight gap is provided between the hot plate and the semiconductor substrate, and FIG. 5B shows a contact type method in which the hot plate and the semiconductor substrate 1 are directly contacted with each other. (C) is a graph of the temperature rise by both methods. FIG. 5C shows the actual wafer temperature by these two methods, and the temperature rise is completely different due to the difference in thermal conductivity. That is, between devices having different thermal conductivity, the hot plate temperature and the processing time are merely guidelines. As described above, the resist film removal sensitivity has been used to measure the heat treatment effect actually received by the semiconductor substrate, but has a disadvantage that it is easily affected by other process conditions. Factors such as the coating film thickness, exposure amount, and development time have a greater effect on the resist film removal sensitivity than the heat treatment effect.
That is, the method of measuring the heat treatment effect based on the resist film removal sensitivity has a large error due to other process conditions and is unsuitable.

An object of the present invention is to provide a method of measuring a heat treatment effect that can quantitatively measure a heat treatment effect without being influenced by factors of other process conditions or the magnitude of thermal conductivity.

[0008]

A feature of the present invention is a step of measuring the thickness of a photoresist film formed on a semiconductor substrate before heat treatment, and a step of measuring the thickness of the photoresist film after heating. a measurement method of the heat treatment effects to evaluate the effect of heat treatment using a thickness reduction amount of by that the photoresist film on the heating.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1A is a cross-sectional view of a semiconductor substrate for explaining one embodiment of a method for measuring a heat treatment effect of the present invention. It is assumed that a photoresist film 11 is formed on a semiconductor substrate 12 by a spin coating method or the like. The value of the thickness of the photoresist film 11 measured by an optical measuring device or the like is defined as t0. Next, as shown in FIG. 1B, the semiconductor substrate 12 is subjected to a heat treatment on the hot plate 13. As a result, the heat transmitted from the semiconductor substrate into the photoresist film evaporates the solvent in the photoresist, and the density of the photoresist film increases. As a result, as shown in FIG. Film thickness decreases. The measured value of the photoresist film at this time is defined as t. Assuming that the thickness of the photoresist film reduced by the heat treatment is Δt, Δt
Is represented by an equation Δt = t0−t.

FIG. 2 is a graph showing the relationship between δt and resist pattern dimensions. It is known that the amount of decrease Δt of the film thickness changes faithfully with the heat treatment conditions (temperature, time). Further, Δt has a strong relationship with the characteristics of the photoresist. If other conditions (resist film thickness, exposure amount, development time, etc.) during the resist process are not changed and only Δt is changed, the dimension of the resist pattern changes faithfully with respect to Δt. This is probably because the removal of the solvent changes the density of the photoresist film and changes the permeability of the developer. That is, Δt represents the amount of the removed solvent, and the effect of the heat treatment for removing the solvent in the photoresist can be represented by the thickness reduction Δt.

[0011]

As described above, the present invention measures the thickness of the photoresist film before and after the heat treatment and quantifies the effect of the heat treatment using the difference between the thicknesses, that is, the amount of decrease in the film thickness. Regardless of changes in thermal conductivity between semiconductor substrates,
The effect of the heat treatment actually received by the semiconductor substrate can be measured. Further, since exposure, development, and the like are not performed, there is an effect that there is no influence from other process factors.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a semiconductor substrate for explaining one embodiment of a method for measuring a heat treatment effect of the present invention.

FIG. 2 is a diagram showing a relationship between Δt and resist pattern dimensions.

FIG. 3 is a view schematically showing a hot plate type heat treatment apparatus.

FIG. 4 is a schematic cross-sectional view of a semiconductor substrate for explaining photoresist film detachment sensitivity measurement.

5A and 5B are diagrams for explaining two methods in a hot plate heat treatment, in which FIG. 5A is a dimension by a proxy type having a slight gap between a hot plate and a semiconductor substrate, and FIG. 7A is a graph of a contact type method in which a hot plate and a semiconductor substrate are directly contacted, and FIG.

[Description of Signs] 11, 33 Photoresist film 12, 21, 34 Semiconductor substrate 13, 23 Hot plate 24 Temperature detector 25 Heater 26 Temperature controller 31 UV light 32 Photomask

Claims (1)

(57) [Claims] [Claim 1 further comprising the steps of measuring before the heat treatment the thickness of the photoresist film formed on a semiconductor substrate, and measuring the thickness of the photoresist film after heating, the photoresist film that by the heating A method for measuring the effect of a heat treatment, wherein the effect of the heat treatment is evaluated using the thickness reduction amount of the heat treatment.