KR20120081665A - Mask for extreme ultraviolet lithography amd method for adjusting reflectivity of the mask - Google Patents

Abstract

PURPOSE: A EUV(Extreme Ultra Violet) mask and a method for controlling reflectivity thereof are provided to improve line-width uniformity by radiating laser or etching a capping layer. CONSTITUTION: A EUV mask comprises a substrate, a reflecting layer(120), a capping layer(130), and an absorbing layer(140). The reflecting layer is formed on the substrate. The capping layer is formed on the reflecting layer. The absorbing layer is formed on the capping layer. The capping layer comprises a reflex controlling unit. The reflex controlling unit irradiates the capping layer with a laser beam. The reflex controlling unit is formed by etching the capping layer. The capping layer is a silicon layer, a ruthenium layer, or a chrome nitride layer.

Description

Mask for extreme ultraviolet lithography amd method for adjusting reflectivity of the mask}

The present invention relates to an EUV mask and a method of adjusting reflectivity of an EUV mask, and more particularly, to an EUV mask and an EUV mask reflecting method of improving line uniformity.

As circuit line widths of semiconductor devices are reduced, extreme ultraviolet lithography (EUVL) technology has been developed to transfer finer linewidth patterns onto wafers. Extreme ultraviolet lithography is expected to be the next generation technology to be used to produce smaller and faster microchips with 32nm line width. EUVL technology is expected to mainly use photolithography technology using Extreme Ultra Violet (EUV) light having a short wavelength of 13.5 nm.

In general, the EVU mask uses a laminated structure in which molybdenum (Mo) and silicon (Si) bilayers are stacked as a reflection mirror layer, and includes an absorbing layer pattern on the reflection layer. This EUV mask is irradiated with EUV light and reflected to cause the reflected image light to reach the wafer to transfer the pattern on the EUV mask onto the wafer. When performing the lithography process using such an EVU mask, since the image transfer process depends on the reflected light, the reflectivity of the EUV mask greatly affects the EUV lithography process.

In other words, the critical dimension (CD) implemented on the wafer varies according to the reflectance of the EUV mask, and when the defect occurs in the line width to the CD uniformity (CDU), the defect is caused by the change of the lithography process conditions. If this doesn't work, you may need to create a new EUV mask. However, since EUV masks are very expensive, fabrication of new masks is undesirable in terms of time and cost.

It is an object of the present invention to provide an EUV mask and a method of adjusting reflectivity of an EUV mask, which can improve line width uniformity.

In an embodiment of the present invention, the EUV mask includes a substrate, a reflective layer formed on the substrate, a capping layer formed on the reflective layer, and an absorbing layer formed on the capping layer, wherein the capping layer includes a reflection controller.

In one embodiment, the reflection control unit may be a structure change unit formed by irradiating a laser beam to the capping layer.

In one embodiment, the reflection control unit may be an etching portion formed by etching the capping layer.

In one embodiment, the capping layer may be a silicon layer, ruthenium layer or chromium nitride layer.

EUV mask reflectance control method according to an embodiment of the present invention after the lithography process using the EUV mask step of measuring the line width on the wafer by position, calculating the amount of reflectance adjustment of the EUV mask based on the measured line width And forming a reflection control unit in the capping layer of the EUV mask according to the calculated reflectance adjustment amount.

In an embodiment, the forming of the reflection control unit on the capping layer of the EUV mask according to the calculated reflectance adjustment amount may include forming a structure change unit on the capping layer by irradiating a laser beam on the capping layer. .

In one embodiment, the step of irradiating a laser beam to the capping layer to form a structural change in the capping layer, the irradiated laser beam may be a pulsed laser beam.

In one embodiment, in the step of forming a structural change in the capping layer by irradiating the laser beam to the capping layer, the energy of the laser beam may be greater than 0 or less than 550mW.

In an embodiment, the forming of the reflection control unit on the capping layer of the EUV mask according to the calculated reflectance adjustment amount may include forming an etching unit by etching the capping layer.

In example embodiments, the etching may be dry etching in the etching of the capping layer to form an etching unit.

In an embodiment, in the forming of the reflection control unit in the capping layer of the EUV mask according to the calculated reflectance adjustment amount, the capping layer may be a silicon layer, ruthenium layer or chromium nitride layer.

EUV mask according to the present invention can improve the line width uniformity by adjusting the reflectance of the reflective layer through laser irradiation or capping layer etching. In addition, it is not necessary to manufacture a new mask for line width uniformity correction, which can significantly reduce time and cost.

1 is a cross-sectional view of an EUV mask according to an embodiment of the present invention.
2 is a cross-sectional view of an EUV mask according to another embodiment of the present invention.
3 is a flowchart illustrating a method of adjusting an EUV mask reflectance according to an embodiment of the present invention.
4 shows an example of a line width uniformity map.
5 and 6 are graphs of reflectivity of the capping layer when the capping layer is a silicon layer and a ruthenium layer, respectively.
7 is a graph showing the amount of change in reflectance according to laser beam energy.

1 is a cross-sectional view of an EUV mask according to an embodiment of the present invention. Referring to FIG. 1, an EUV mask according to an embodiment of the present invention includes a substrate 100, a reflective layer 120, a capping layer 130, and an absorbing layer 140, and the capping layer 130 includes a reflection controller. 130a is present.

The substrate 100 may be formed of a quartz substrate having a light transmittance and a low thermal expansion coefficient (LTE), but the present invention is not limited to the substrate material.

The reflective layer 120 may be a multi-layered thin film in which a double layer including a scattering layer 121 for scattering incident EUV and a spacer layer 122 spaced apart from the scattering layers is repeated. The bilayer reflects EUV on the principle of Distributed Bragg reflector. Specifically, a bilayer consisting of a scattering layer 121 including a molybdenum (Mo) layer and a spaced apart layer 122 including a silicon (Si) layer is formed of about 20 nm to 120 layers of about 7 nm to about 8 nm to about 13 nm. Bragg reflection of the EUV of the wavelength. As another example, a bilayer structure of beryllium (Be) / silicon (Si), ruthenium (Ru) / silicon (Si) may be used, or may be formed as a triple layer structure instead of a double layer structure.

A capping layer 130 is provided on the reflective layer 120 to protect the reflective layer. The capping layer 130 may be formed of a silicon (Si) layer, a chromium nitride (CrN) layer, or a ruthenium (Ru) layer. , 3 nm to 50 nm thick. The capping layer 130 has a reflection control unit 130a, and the reflection control unit 130a may be a structural change unit formed by laser beam irradiation. By adjusting the laser beam energy for each position of the EUV mask it is possible to adjust the degree of structural change of the capping layer by the laser beam irradiation, thereby improving the linewidth uniformity (CDU) by adjusting the reflectance of the EUV.

The absorber layer 140 may have a plurality of openings H exposing a portion of the capping layer 130. The absorber layer can be used without limitation as long as it absorbs substantially all of the incident EUV. For example, it may be a single layer film or a multilayer film including any one or more of tantalum boron nitride (TaBN), tantalum nitride (TaN), tantalum boron oxynitride (TaBON), or titanium nitride (TiN).

On the back side of the substrate there may be a conductive layer 110 which guides the mounting of the substrate by electrostatic action when the substrate is mounted on an electrostatic chuck of the EUV lithography equipment. The conductive layer 110 may be, for example, a chromium nitride (CrN) layer. In addition, a buffer layer (not shown) may further exist between the capping layer 130 and the absorber layer 140, and a lower layer (not shown) may further exist between the substrate 100 and the reflective layer 120.

The EUV mask of the present invention may be a phase inversion mask in which a phase shift layer (not shown) exists between the capping layer 130 and the absorption layer 140. The phase shift layer changes the phase of the reflected light transmitted through the phase shift layer depending on the difference between the material constituting the phase shift layer and the material constituting the reflective layer 120 and the thickness of the phase shift layer. For example, the phase shift layer is formed such that the first reflection light reflected directly by the reflective layer 120 and the second reflection light reflected through the phase shift layer have a 180 ° phase difference. The phase shift layer may include tantalum nitride (TaN) having a thickness of 58.3 to 62.4 nm. When the phase shift layer is a TaN layer, it can act as such a phase shifter when the thickness is 58.2 to 62.4 nm so that the first reflected light has a 180 ° phase difference from the second reflected light.

2 is a cross-sectional view of an EUV mask according to another embodiment of the present invention. 2, an EUV mask according to another embodiment of the present invention includes a substrate 100, a reflective layer 120, a capping layer 130, and an absorbing layer 140, and the capping layer 130 includes a reflection controller. 130b may exist and the conductive layer 110 may further exist. The remaining substrate 100, the reflective layer 120, the capping layer 130, the absorbing layer 140, etc. except for the reflection controller 130b are the same as described above, and thus description thereof will be omitted.

In the present exemplary embodiment, the reflection control unit 130b may be an etching unit 130b formed by etching the capping layer 130. The etching unit 130b may vary the degree (depth) of etching for each position of the EUV mask, thereby improving the line width uniformity by adjusting the reflectance of the EUV. For example, in the case where the line width (DICD or FICD) on the wafer is larger (or smaller) than the specification, the etching portion 130b may be formed in the capping layer 130, and the portion in which the line width is in the specification is the capping layer. The etching unit 130b may not be formed at 130. An etching depth of the etching unit 130b may vary according to positions of the EUV mask.

3 is a flowchart illustrating a method of adjusting an EUV mask reflectance according to an embodiment of the present invention.

Referring to FIG. 3, first, after performing a lithography process using an EUV mask, the line width CD on the wafer is measured for each position (S100). Specifically, a photoresist film is coated on a wafer, and the photoresist film is exposed and developed using an EUV mask to form a photoresist pattern. The line width (DICD: Develop Inspection Crictical Dimension) of the photoresist pattern may be measured for each position on the wafer. Alternatively, the etching target layer may be etched using the photoresist pattern as an etching mask instead of DICD, and the final inspection CD (FICD) of the etching target layer may be measured for each position. A line width uniformity (CDU) map may be created based on the DICD or FICD measured for each location.

4 shows an example of a line width uniformity map. In FIG. 4, the black circle is the portion where the line width is smaller than the spec (or average), the gray circle is the portion where the line width is larger than the spec (or the average), and the diameter of the circle is the difference in line width from the specification (or average). It is shown. In other words, the larger the line width difference, the larger the diameter of the black (or gray) circle. That is, the line width uniformity map may display an error value or an error rate of the line width CD for each position of the wafer. Through this, it is possible to determine at a glance which part of the wafer has a large line width and which part has a small line width. For example, the portion indicated by the reference numeral 200 is a portion where the line width is larger than other portions, and the portion that needs to further reduce the line width.

Next, the amount of reflectance adjustment of the EUV mask is calculated based on the measured line width CD (S110). FIG. 5 shows the reflectance according to the thickness of the capping layer when the capping layer is a silicon layer. As can be seen from Figure 5 it can be seen that the reflectance (Blank reflectivity) decreases from approximately 0.75% to 0.70% while the thickness of the silicon layer is changed from 0nm to 20nm. FIG. 6 shows the reflectance according to the thickness of the ruthenium layer when the capping layer is a ruthenium (Ru) layer. As in the case of the silicon layer, it can be seen that the reflectance decreases with increasing thickness.

7 shows the amount of change in reflectance according to the laser beam energy. As shown, it can be seen that the reflectance decreases as the energy of the laser beam irradiated onto the capping layer increases. It is interpreted that the reflectance is lowered because the capping layer is locally melted by laser beam irradiation and then cooled, or the structure is changed in the process of expanding / contracting the grating. The energy of the irradiated laser beam may be greater than 0 and less than or equal to 550 mW. Specifically, when the capping layer is a silicon layer, it is preferable to irradiate a laser beam energy of more than 0 and 300 mW or less, and a laser beam energy of more than 0 and 550 mW or less in the case of a ruthenium layer.

Based on this, we can calculate how much the reflectance of the large and small portions of the line width should be changed. For example, the depth of the capping layer to be etched or the amount of energy during laser beam irradiation, or the laser beam irradiation time may be calculated to reduce (or increase) the reflectance of the portion indicated by 200 in FIG. 4.

Next, the reflection control unit is formed in the capping layer of the EUV mask according to the calculated reflectance adjustment amount (S120). The reflection control part may be a structural change part formed by irradiating a laser beam on the capping layer or an etching part formed by etching a part of the thickness of the capping layer.

The structural change portion may be generated by irradiating the capping layer of the mask by passing the laser beam from the laser oscillator through a predetermined optical device, for example, an expander, a beam steering device, a focusing device, or the like. . The laser may be Nd: YAG laser, Ti: Sapphire laser, He-Ne laser, Ar, CO ₂ laser, excimer laser such as ArF, KrF, XeCl or semiconductor laser such as GaAs, InP, InAs, etc. It is not limited to this. In addition, the laser beam coming from the laser oscillator may be a pulsed laser. An example of a femtosecond pulsed laser is a Ti: Sapphire laser. By adjusting the energy, irradiation time, or frequency of the laser beam, the width, depth, etc. of the structure changer in the capping layer can be adjusted, and thus the reflectance of the EUV mask can be controlled.

Formation of the etching portion may be wet etching or dry etching, but dry etching is preferred. An etching mask such as a photoresist layer may be formed on the absorption layer of the EUV mask for the etching, and the capping layer may be etched through the opening of the absorption layer. There is no restriction on the etching gas for forming the etching portion. For example, when the capping layer includes a silicon layer, the etching portion may be formed by dry etching using an etching gas such as CF ₄ , CCl _4, or SF ₆ .

100 substrate 110 conductive layer
120: reflective layer 130: capping layer
130a, 130b: reflection control unit 140: absorption layer

Claims (11)

Board;
A reflective layer formed on the substrate;
A capping layer formed on the reflective layer; And
Including an absorbing layer formed on the capping layer,
The capping layer is a reflection control unit
EUV mask comprising a. The method of claim 1,
The reflection control unit is a EUV mask structure change unit formed by irradiating the laser beam to the capping layer. The method of claim 1,
The reflection control unit is an EUV mask is an etching portion formed by etching the capping layer. The method of claim 1,
The capping layer is a silicon layer, ruthenium layer or chromium nitride layer EUV mask. Measuring a line width on a wafer by position after a lithography process using an EUV mask;
Calculating a reflectance adjustment amount of the EUV mask based on the measured line width; And
Forming a reflection control unit on the capping layer of the EUV mask according to the calculated reflectance adjustment amount
EUV mask reflectance adjustment method comprising a. The method of claim 5,
The forming of the reflection control unit on the capping layer of the EUV mask according to the calculated reflectance adjustment amount includes the step of forming a structure change unit on the capping layer by irradiating a laser beam on the capping layer. The method of claim 6,
And irradiating a laser beam to the capping layer to form a structural change part in the capping layer, wherein the irradiated laser beam is a pulsed laser beam. The method of claim 6,
And irradiating a laser beam to the capping layer to form a structural change part in the capping layer, wherein the energy of the laser beam is greater than 0 and less than or equal to 550 mW. The method of claim 5,
The forming of the reflector on the capping layer of the EUV mask according to the calculated reflectance adjustment amount comprises the step of etching the capping layer to form an etching portion EUV mask reflectance control method. 10. The method of claim 9,
And etching the capping layer to form an etching portion, wherein the etching is a dry etching. The method of claim 5,
And forming a reflection control unit in the capping layer of the EUV mask according to the calculated reflectance adjustment amount, wherein the capping layer is a silicon layer, a ruthenium layer, or a chromium nitride layer.

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