KR100861368B1

KR100861368B1 - Immersion lithography method to suppress water residue on back side of wafer

Info

Publication number: KR100861368B1
Application number: KR1020070049348A
Authority: KR
Inventors: 고성우; 안영배
Original assignee: 주식회사 하이닉스반도체
Priority date: 2007-05-21
Filing date: 2007-05-21
Publication date: 2008-10-01

Abstract

An immersion lithography method is provided to prevent an overlay failure caused by water residues on a wafer back side by forming a hydrophobic surface layer on the wafer back side. A resist layer(703) for exposing is formed on a front side of a wafer(701). A hydrophobic surface layer(800) is formed on a back side of the wafer to suppress water residues. An exposure process is then performed by loading the wafer on a chuck of an immersion lithography apparatus. The hydrophobic surface layer is formed by coating resist material with hydrophobicity on the back side of the wafer.

Description

Immersion lithography method to suppress water residue on back side of wafer}

1 to 3 are diagrams schematically illustrating a process in which moisture remains on a back surface of a wafer.

4 is a graph showing the wafer temperature drop due to the residual moisture on the back surface of the wafer.

FIG. 5 is a graph presented to illustrate overlay failure in immersion lithography due to residual moisture on the wafer backside.

Figure 6 is a graph measuring the degree of scaling (scaling) according to the contact angle of the hydrophobic surface layer according to an embodiment of the present invention.

7 through 9 are schematic diagrams for explaining an immersion lithography method according to an embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to semiconductor devices, and more particularly, to an immersion lithography method that suppresses water residues on the back surface of a wafer.

As circuit patterns of semiconductor devices are miniaturized, immersion lithography techniques have been proposed to transfer finer patterns of line width (CD) onto wafers. The immersion lithography technology introduces a high refractive index liquid immersion liquid that is larger than the refractive index of the vacuum state between the exposure apparatus and the wafer, and induces a shorter wavelength of light passing through the high refractive index medium, thereby enabling a finer pattern of exposure. I'm letting you. In this case, the liquid medium uses water having a refractive index of 1.33.

One of the problems to be solved in such immersion lithography may be to illustrate an overlay fail. Since the temperature sensitivity to water, which is the infiltration medium in the immersion exposure equipment, is about 100 times higher than in the vacuum state, a substantial wavelength change of the exposure light according to the change in the refractive index of the infiltration medium may be greatly generated. Accordingly, overlay failure during exposure due to temperature fluctuation of the infiltration medium is considerably greater than that of conventional dry exposure tools.

Referring to FIG. 1, although the current immersion lithography equipment is very precisely controlling the temperature of the feed to approximately ± 5 mK, this overlay failure is not only at the wafer back side, as shown in FIG. 1. This may be due to the residual water (water residue or water droplet) 13 or thus the moisture 23 remaining in the wafer chuck 20 of FIG. As shown in FIG. 3, as the moisture 33 remaining between the rear surface of the mounted wafer 31 and the wafer chuck 20 or holder is evaporated when the exposure process is performed, A change in temperature of the wafer or liquid infiltrating medium can be caused.

4 is a graph showing the wafer temperature drop due to the residual moisture on the back surface of the wafer. FIG. 5 is a graph presented to illustrate overlay failure in immersion lithography due to residual moisture on the wafer backside.

Referring to FIG. 4, it is measured that the wafer temperature in the case where residual moisture is present 43 decreases relative to the measurement wafer temperature in the case where there is no residual moisture 41. Accordingly, as shown in FIG. 5, the overlay failure degree is measured to increase three times when the residual moisture is present 53 as compared with the absence of residual moisture 51. The degree of overlay failure of FIG. 5 is three times the measured value, and shows the result of observing the degree of pattern shift in the X-axis direction and the Y-axis direction, that is, the scaling error. Giving. Therefore, the overlay failure can be controlled to a level of about 2 to 3 nm when there is no residual moisture (51), but the overlay failure becomes very severe when residual moisture is present (53).

SUMMARY OF THE INVENTION An object of the present invention is to provide an immersion lithography method capable of suppressing moisture from remaining on a wafer chuck or a wafer back surface of an immersion lithography apparatus.

One aspect of the present invention for the above technical problem, forming a main resist layer to be exposed on the front surface of the wafer, forming a hydrophobic surface layer to suppress moisture retention on the back surface of the wafer, and An immersion lithography method is disclosed that includes mounting on a wafer chuck of an immersion lithography apparatus to perform exposure.

The hydrophobic surface layer may be formed by coating a resist material having hydrophobicity against ultrapure water on the back surface of the wafer.

Coating of the hydrophobic resist material may be carried out continuously in the step of forming the main resist layer.

The hydrophobic surface layer may be formed to extend onto the main resist layer.

According to the present invention, it is possible to suppress the remaining of moisture on the wafer chuck or the back surface of the wafer of the immersion lithography apparatus, thereby providing an immersion lithography method which can suppress the overlay defect by suppressing the temperature change of the unwanted infiltration medium. .

Embodiments of the present invention propose a method of introducing a surface layer of a hydrophobic resist to suppress the occurrence of an overlay failure during exposure of immersion lithography due to moisture remaining on the back surface of a wafer. After forming a main resist layer on the wafer, and forming a top coating on the resist layer by inhibiting the reaction with the infiltration medium to suppress and protect the infiltration medium, a hydrophobic surface layer is formed on the back side of the wafer. do. In this case, the hydrophobic surface layer may be formed to extend on the front surface of the wafer. Such hydrophobic surface layer can suppress the moisture remaining on the back surface of the wafer. As a result, it is possible to suppress the moisture remaining on the wafer chuck of the immersion lithography apparatus.

Referring to FIG. 6, after the hydrophobic resist is coated on the front and back surfaces of the wafer, the contact angle of water as an infiltration medium with respect to the surface layer of the hydrophobic ledge is measured as a result of exposure and measurement of the degree of overlay failure such as wafer scaling. And the degree of scaling is measured to vary as shown in FIG. 6. After the coating of the surface layer, the exposure was performed after one day and two days, and the pattern shift in the X-axis direction by scaling and the pattern shift in the Y-axis direction were set. As a result of measuring the change degree with respect to the pattern size, the degree of scaling change obtained in the range 600 whose contact angle is about 60 degrees-about 70 degrees is measured relatively low. That is, it can be seen that scaling is reduced in hydrophobic resists compared to hydrophilic resists.

In the embodiment of the present invention using the results of FIG. 6, after forming the main resist layer to be exposed in actual immersion lithography, the surface layer of hydrophobic resist is introduced on the backside or the backside and the frontside of the wafer to overlay by residual moisture. A method of suppressing defects is presented. The hydrophobic surface layer introduced as described above suppresses the presence of ultra pure water (UPW: Ultra Purified Water) introduced into the rinse liquid during the wafer pre-rinse process performed before exposure. Thereby, when the wafer is mounted on the wafer chuck of the immersion lithography apparatus, it is possible to suppress the transfer of residual moisture onto the wafer chuck. Therefore, moisture remains on the wafer chuck and the wafer temperature is changed during exposure of the wafer, whereby the temperature of the infiltrating medium is changed to suppress occurrence of overlay failure.

Referring to FIG. 7, a main resist layer 703 to be exposed is formed on the wafer 701 by coating. At this time, after the coating of the main resist layer 703, as shown in FIG. 8, the hydrophobic surface layer 800 is coated on the rear surface of the wafer 701. In this case, the hydrophobic surface layer 800 is formed of a hydrophobic photoresist (PR) material, it may have a hydrophobicity that the contact angle to the ultrapure water or water is preferably implemented about 60 ° to 70 °. Hydrophobic surface layer 800 may be coated to extend over main resist layer 703. This coating of the hydrophobic surface layer 800 may be performed subsequent to the coating of the main resist layer 703. Subsequently, after coating the main resist layer 703 or the like, a soft bake process is performed, and a top coating layer for suppressing defects caused by the reaction between the infiltration medium and the main resist layer 703 and the like (top coating) layer: 850). Thereafter, the upper coating layer 850 is baked.

Referring to FIG. 9, a wafer 701 is mounted on a wafer chuck 901 of an immersion lithography apparatus, an infiltration medium 905 is introduced between the lens of the exposure unit 903 and the wafer 701, and exposed. Do this. Before the wafer 701 is mounted on the wafer chuck 901, that is, after baking of the upper coating layer 850, a process of prerinsing the wafer 701 may be performed.

At this time, in the conventional case, the ultrapure water used as the rinse liquid may remain on the rear surface of the wafer 701, but in the embodiment of the present invention, the hydrophobic surface layer 800 is introduced on the rear surface of the wafer 701, and thus the residual water may be retained. Moisture is suppressed. Therefore, the residual or introduction of moisture on the wafer chuck 901 can be suppressed. Accordingly, temperature fluctuations of the wafer 701 and temperature fluctuations of the infiltration medium 905 during the exposure process due to residual moisture can be suppressed. Therefore, overlay failure during exposure can be suppressed, and thus pattern deformation can be suppressed.

After performing the exposure, the wafer 701 is separated to absorb the residual infiltrating medium 905 on the wafer chuck 901. The detached wafer 701 is rinsed afterwards and subjected to post exposure bake (PEB). After baking after exposure, the upper coating layer 850 is removed, and a development process is performed to form a resist pattern.

According to the present invention described above, it is possible to prevent the overlay failure due to moisture that may remain on the wafer chuck or the wafer back during the immersion lithography process.

As mentioned above, although this invention was demonstrated in detail through the specific Example, this invention is not limited to this, It is clear that the deformation | transformation and improvement are possible by the person of ordinary skill in the art within the technical idea of this invention.

Claims

Forming a main resist layer to be exposed on the front side of the wafer;

Forming a hydrophobic surface layer on the backside of the wafer to inhibit moisture retention; And

Mounting the wafer onto a wafer chuck of an immersion lithography apparatus to perform exposure.

The method of claim 1,

And the hydrophobic surface layer is formed by coating a resist material having hydrophobicity against ultrapure water on a back surface of the wafer.

The method of claim 2,

And the coating of the hydrophobic resist material is carried out continuously in the step of forming the main resist layer.

The method of claim 1,

And the hydrophobic surface layer is formed to extend onto the main resist layer.