KR20120100208A - Maskless exposure apparatus and method for compensating cumulative intensity of illumination using the same - Google Patents

Abstract

In the maskless exposure, a method for securing a uniform cumulative roughness of the entire field of the optical system is proposed.
By masking the cumulative illuminance caused by the distortion of the projection optical system in the maskless exposure, it is possible to ensure a uniform cumulative illuminance for the entire field of the optical system without causing a decrease in the line edge roughness (LER). As a result, the price of the optical system can be lowered and the CD (Critical Dimension) Uniformity is improved for all the optical systems.
Further, in maskless exposure, the cumulative illuminance correction separated from the exposure data generation is performed, even if the shape of the substrate to be exposed is changed, there is no need to perform the correction again, and the system configuration is simple.

Description

MASKLESS EXPOSURE APPARATUS AND METHOD FOR COMPENSATING CUMULATIVE INTENSITY OF ILLUMINATION USING THE SAME}

The present invention relates to a method capable of ensuring uniform cumulative illuminance of the entire field of the optical system in maskless lithography.

In general, a method of forming a pattern on a substrate (or semiconductor wafer) constituting a liquid crystal display (LCD), a plasma display panel (PDP), or a flat panel display (FPD) A pattern material is first formed by applying a pattern material to a substrate, and selectively exposing the pattern material using a photomask to selectively remove portions of the pattern material or other portions whose chemical properties are different.

However, as substrates become larger in size and patterns become more precise, maskless exposure can increase exponentially, resulting in the formation of patterns on substrates (or semiconductor wafers) without the use of photomasks. The device is being developed. The maskless exposure apparatus exposes the exposure beam to a substrate by transferring the exposure beam to the substrate with pattern information made of a control signal using a spatial light modulator (SLM) such as a digital micro-mirror device (DMD). It is a principle to expose a pattern on a surface.

In maskless exposure, a beam from a light source is formed as an exposure image on an exposure surface through a DMD and a projection optical system while scanning a stage for moving a substrate in the exposure direction. However, if distortion of the exposure image occurs due to the distortion of the projection optical system, cumulative illuminance becomes uneven to directly affect the exposure quality.

In the maskless exposure, we propose a method capable of software-correcting the unevenness of the cumulative illuminance caused by the distortion of the projection optical system.

To this end, a maskless exposure apparatus according to an aspect of the present invention, the light source for emitting an exposure beam; An optical modulator for modulating the exposure beam according to the exposure pattern; Projection optics for transmitting the modulated exposure beam onto a substrate in the form of a beam spot array; A beam measuring unit measuring beam data of the beam spot array; A correction mask generator for generating a correction mask for correcting cumulative illuminance using the measured beam data; And a control unit which transmits an exposure pattern whose cumulative illuminance is corrected to the optical modulation device by using the generated correction mask.

The maskless exposure apparatus according to an aspect of the present invention further includes an exposure data generation unit configured to generate exposure data of the optical modulation device according to an exposure pattern, and the controller performs an AND operation on the correction mask and the generated exposure data. An exposure pattern in which cumulative illuminance is corrected is generated.

The beam data includes position data, intensity data, horizontal size data, and vertical size data of the spot beams constituting the beam spot array.

The correction mask generator accumulates the intensity of the discretized spot beams for the entire field of the projection optical system, and performs digital correction on the intensity of the accumulated spot beams.

The correction mask generator calculates the spatial density at each point of the spot beams, and turns off the spot beam of the point with the highest spatial density calculated in order to ensure uniform accumulated illuminance for the entire field of the projection optical system.

The correction mask generator generates a correction mask by calculating a residual for the PEG at the y coordinate position of the spot beams.

In addition, the cumulative illumination correction method of the maskless exposure apparatus according to an aspect of the present invention includes: transmitting an exposure beam emitted from a light source onto a substrate in the form of a beam spot array through an optical modulation device and a projection optical system; Measure beam data of the beam spot array; Generating a correction mask for cumulative illuminance correction using the measured beam data; And transmitting the exposure pattern whose cumulative illuminance is corrected using the generated correction mask to the light modulation device.

In addition, the cumulative illuminance correction method of the maskless exposure apparatus according to one aspect of the present invention comprises: generating exposure data of an optical modulation element in accordance with an exposure pattern; And performing an AND operation on the correction mask and the generated exposure data to generate an exposure pattern having a cumulative roughness corrected.

Generating a correction mask for cumulative illuminance correction is to accumulate the intensity of the discretized spot beams for the entire field of the projection optical system and to perform digital correction on the intensity of the accumulated spot beams.

Creating a correction mask for cumulative illuminance correction calculates the spatial density at each point of the spot beams, and calculates the spot beam of the point with the highest spatial density calculated to ensure uniform cumulative illuminance for the entire field of projection optics. To turn it off.

Generating a correction mask for cumulative illuminance correction is to generate a correction mask by calculating a residual for the PEG at the y coordinate position of the spot beams.

According to the proposed maskless exposure apparatus and the cumulative illuminance correction method using the same, the cumulative illuminance caused by the distortion of the projection optical system in the maskless exposure is software-corrected, so that the LER (Line Edge Roughness) deterioration does not occur, Uniform cumulative roughness can be secured. As a result, the price of the optical system can be lowered and the CD (Critical Dimension) Uniformity is improved for all the optical systems.

1 is a schematic configuration diagram of a maskless exposure apparatus according to an embodiment of the present invention.
2 is a view showing an exposure head of a maskless exposure apparatus according to an embodiment of the present invention.
3 is a perspective view showing a DMD configuration of a maskless exposure apparatus according to an embodiment of the present invention.
4 is a detailed configuration diagram of FIG. 2.
5 is a plan view illustrating a beam spot array by a maskless exposure apparatus according to an exemplary embodiment of the present invention.
6 is a control block diagram of a maskless exposure apparatus according to an embodiment of the present invention.
7 is a flowchart illustrating a control method for performing cumulative illuminance correction in a maskless exposure apparatus according to an exemplary embodiment of the present invention.
8 is a conceptual diagram illustrating a method of calculating a spatial density for correcting cumulative illuminance in a maskless exposure apparatus according to an embodiment of the present invention.
9 and 10 are graphs comparing the cumulative illuminance after correction with the cumulative illuminance before correction in the maskless exposure apparatus according to the exemplary embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic configuration diagram of a maskless exposure apparatus according to an embodiment of the present invention.

In FIG. 1, the maskless exposure apparatus 10 according to an exemplary embodiment of the present invention includes a stage 20 for moving a substrate 30 to be exposed (all objects to form a predetermined pattern such as a film, a wafer, and a glass). And an exposure head 100 for transferring the exposure beam to the substrate 30 to expose a photosensitive film (pattern forming material) coated on the substrate 30.

The stage 20 also moves the substrate 30 in the X-axis direction, the Y-axis direction, and if necessary, the Z-axis direction. The stage 20 includes guides 22 and 24 extending along the moving direction of the stage 20. The stage 20 is reciprocated by the guides 22 and 24 in the X-axis direction which is a sub-scanning direction, or the Y-axis direction (scanning direction) which is a scanning direction.

In addition, the stage 20 includes a chuck 26 that fixes the substrate 30 to the stage 20, and an isolator 28 that blocks vibration of the stage 20.

The exposure head 100 is fixed to the stage gantry 102 to irradiate the substrate 30 with an exposure beam to form image data in a desired pattern shape. This exposure head 100 is composed of a single head or multiple heads.

In the exemplary embodiment of the present invention, the stage 20 on which the substrate 30 is mounted is moved with respect to the exposure head 100 as an example. However, the present invention is not limited thereto, and the stage 20 is fixed and the exposure head is fixed. 100 may move, and further, both the stage 20 and the exposure head 100 may move.

The maskless exposure apparatus 10 according to the exemplary embodiment of the present invention is provided with a beam measuring unit 40 for measuring the position of the exposure beam irradiated from the exposure head 100 to the substrate 30.

2 is a view showing an exposure head of a maskless exposure apparatus according to an embodiment of the present invention, Figure 3 is a perspective view showing a DMD configuration of the maskless exposure apparatus according to an embodiment of the present invention.

In FIG. 2, the exposure head 100 includes a light source 110 for emitting the exposure beam 115, an illumination optical system 120 for correcting the exposure beam 115 emitted from the light source 110 with uniform illuminance, and outputting the light. The light modulation element 130 for modulating the exposure beam 115 passing through the illumination optical system 120 according to the pattern information (image data), and the beam spot array for the exposure beam 115 modulated by the light modulation element 130. It includes a projection optical system 140 for transmitting on the substrate 30 in the form of a beam spot array.

The light source 110 emits a beam for exposure, and includes a semiconductor laser or an ultraviolet lamp. The beam emitted from the light source 110 is output to the substrate 30 placed on the stage 20 via the light modulation device 130 and the projection optical system 140.

The light modulator 130 includes a spatial light modulator (SLM). The optical modulation device 130 may be, for example, a digital micro-mirror device (DMD) of a MEMS type, a two-dimensional grating light valve (GLV), and a transparent zirconate (PLZT) that is a transparent ceramic. an electro-optic device using a titantate, a ferroelectric liquid crystal (FLC), or the like may be used, and DMD may be preferably used. Hereinafter, the present invention will be described using the optical modulation device 130 made of DMD for convenience of description.

As shown in FIG. 3, the DMD includes a memory cell 132 (for example, an SRAM cell) and a plurality of micro mirrors 134 arranged in a matrix type of L rows x M columns on the memory cell 132. ) Is a mirror device comprising a. By varying the angle of each micromirror 134 based on the control signal generated in accordance with the image data, the desired light is reflected by the projection optical system 140, and other light is sent by a different angle to block.

When a digital signal is written to the memory cell 132 of the optical modulation element 130 made of the DMD, the micromirror 134 is inclined at a predetermined angle (for example, ± 12 °) around a diagonal line. On / off control of each micromirror 134 is controlled by the control part 46 mentioned later, respectively. Light reflected by the micro mirror 134 in the on state exposes an exposure object (usually PR: Photoresist) on the substrate 30, and light reflected by the micro mirror 134 in the off state is the substrate 30. The above exposure object is not exposed.

4 is a detailed configuration diagram of FIG. 2.

In FIG. 4, the projection optical system 140 includes the first imaging optical system 142 and the second imaging optical system 144, the micro lens array 146, and the aperture array 148 along a path through which the exposure beam 115 passes. Include.

The first imaging optical system 142 is composed of double telecentric optical systems, and enlarges the image passing through the optical modulation device 130 by about 4 times, for example, to open the opening surface of the micro lens array 146 ( It forms in the aperture plane.

The second imaging optical system 144 is also composed of double telecentric optical systems, and is imaged on the substrate 30 by, for example, about one-fold multiple beam spots formed on the focal plane of the micro lens array 146. do. In the exemplary embodiment of the present invention, the magnifications of the first imaging optical system 142 and the second imaging optical system 144 are 4 times and 1 times, respectively. However, the present invention is not limited thereto and the first imaging optical system ( 142 and the magnification of the second imaging optical system 144 depend on the size of the desired beam spot, the minimum feature size of the pattern to be exposed, and the number of exposure heads 100 to be used in the maskless exposure apparatus 10. Therefore, an optimal combination of magnifications can be derived.

The microlens array 146 is formed by arranging a plurality of microlenses corresponding to the micromirrors 134 of the light modulation element 130 in two dimensions. For example, when the light modulation element 130 is composed of 1920 × 400 micromirrors 134, correspondingly, 1920 × 400 microlenses are also disposed. In addition, the arrangement pitch of the microlenses may be substantially the same as the value obtained by multiplying the arrangement pitch of the micromirrors 134 of the light modulation device 130 by the magnification of the first imaging optical system 142.

The aperture array 148 is a two-dimensional array of a plurality of pin holes in the focal plane of the micro lens corresponding to the micro lens. The pin hole serves to shape the size of the beam spot focused through the micro lens to a certain size or to block noise generated in the projection optical system 140. The diameter of the pinhole is, for example, 6 mu m.

5 is a plan view illustrating a beam spot array by a maskless exposure apparatus according to an exemplary embodiment of the present invention.

In FIG. 5, the exposure beam 115 focused on the focal plane of the microlens array 146 from the light modulation element 130 via the first imaging optical system 142 may have a circular or elliptic shape. An image of the exposure beam 115 formed on the exposure surface on the substrate 30 via the second imaging optical system 144 is called a beam spot array 131, and the beam spot array 131 is formed in a matrix form. It consists of a number of spot beams 133 arranged. For example, the arrangement pitch of the spot beam 133 may be about 55 μm, and the spot beam 133 may have a circular shape having a Gaussian distribution having a full width at half maximum (FWHM) of about 2.5 μm.

The array direction of the beam spot array 131 is disposed to be inclined at a predetermined alignment angle θ with respect to the scanning direction (Y-axis direction). This is to increase the resolution of the maskless exposure apparatus 10.

As such, the exposure beam 115 emitted from the light source 110 is formed as an exposure image on the exposure surface of the substrate 30 via the light modulation device 130 and the projection optical system 140. However, when the distortion of the exposure image occurs due to the distortion of the projection optical system 140, cumulative illumination becomes uneven and directly affects the exposure quality.

In the maskless exposure apparatus 10, even if there is some distortion in the projection optical system 140, the position and the illumination intensity of each spot beam 133 are measured to provide a kind of mask to the optical modulation device 130 to achieve the cumulative illumination. Uniformity can be secured, but if the mirror of the optical modulation device 130 is arbitrarily manipulated to ensure the uniformity of the accumulated illuminance, the lattice property of the spot beam 133 is destroyed, and thus a decrease in LER (Line Edge Roughness) may occur during exposure. Can be.

Thus, one embodiment of the present invention is to propose a method that can ensure a uniform cumulative roughness for the entire field of the optical system without a decrease in LER (Line Edge Roughness) during exposure. This will be described with reference to FIG.

6 is a control block diagram of a maskless exposure apparatus according to an embodiment of the present invention.

In FIG. 6, the maskless exposure apparatus 10 includes a beam measuring unit 40, a correction mask generating unit 42, an exposure data generating unit 44, and a control unit 46.

The beam measuring unit 40 is a position (X coordinate, Y coordinate) of the plurality of spot beams 133 arranged in a matrix in the beam spot array 131 where the exposure beam 115 is formed on the exposure surface on the substrate 30. Coordinates), the intensity of the spot beam 133, the horizontal size of the spot beam 133, and the vertical size of the spot beam 133 are measured.

The correction mask generator 42 calculates the uniformity of the accumulated illuminance by using the beam position data (X coordinate, Y coordinate), the beam intensity data, and the beam size data (horizontal direction and vertical direction) measured by the beam measuring unit 40. Software correction mask is created to secure. In this case, the beam data used for generating the correction mask may be data measured by the beam measuring unit 40 as a whole, or after measuring only some sample beams for shortening the time, the total data may be predicted from the beam data.

The key when generating the correction mask in software in the correction mask generator 42 is to prevent the LER (Line Edge Roughness) degradation from occurring.

To this end, the correction mask generator 42 generates a correction mask through the following process.

① First, in order to correct the unevenness of the cumulative illuminance, the characteristics of the respective spot beams 133 measured by the beam measuring unit 40 (beam position, beam intensity, beam horizontal size, and beam vertical size) To data.

(2) Subsequently, the shape of the spot beams 133 obtained as data is taken into consideration to form a continuous Gaussian model.

③ Discretize data shaped by Gaussian model at appropriate intervals. If the discretization is too dense, it takes too much time to perform the calibration, and if the discretization is too sparse, the accuracy of the calibration is lessened, so the designer sets the appropriate interval in advance.

④ Finally, the intensity of each spot beam 133 discretized with respect to the field before the projection optical system 140 is accumulated, and digital correction is performed on the intensity of the accumulated spot beam 133. A method of performing digital correction on the intensity of the accumulated spot beam 133 will be described later with reference to FIGS. 7 and 8.

The exposure data generation unit 44 generates exposure data of the optical modulation device 130 according to the exposure pattern. The exposure data generation unit 44 switches exposure of some of the optical mirrors 134 to the off state. Generate on / off data or exposure on / off data that turns some rows of the micro lens array 146 off.

The controller 46 performs an AND operation on the correction mask generated by the correction mask generator 42 and the exposure on / off data generated by the exposure data generator 44 to generate an exposure pattern whose cumulative illuminance is corrected. Transfer to the optical modulation device 130.

Next, a method of performing digital correction on the intensity of the spot beam 133 accumulated in the correction mask generator 42 will be described with reference to FIGS. 7 and 8.

7 is an operation flowchart illustrating a control method for performing cumulative illuminance correction in a maskless exposure apparatus according to an embodiment of the present invention, and FIG. 8 is a cumulative illuminance correction in a maskless exposure apparatus according to an embodiment of the present invention. Is a conceptual diagram illustrating how to calculate the spatial density.

In FIG. 7, the residual for the Position Event Generator (PEG) of the Y coordinate of each spot beam 133 is calculated using Equation 1 below (200).

For example, when the Y coordinate position of the spot beam 133 is 76.1 μm and the PEG is 1.0 μm, the residual becomes 0.1.

[Equation 1]

Residual = mod (76.1, 1.0) = 0.1

Subsequently, the spatial density within the Gaussian range (see FIG. 8) at each point of the spot beams 133 is calculated using Equation 2 below (202).

&Quot; (2) "

In FIG. 8, the area indicated by the circle based on the spot beam 133 displayed in black is an effective area of influence within the Gaussian range.

Using the distances d1, d2, d3, and d4 from the other spot beams 133 within the Gaussian range with respect to the spot beam 133 shown in black, as shown in [Equation 2], Calculate At this time, the spatial density is calculated within the Gaussian range for each spot beam 133.

In addition, the spot beams 133 having the highest spatial density, that is, the spot beams 133 having the most dense spatial density, are compared by comparing the spatial densities of the respective spot beams 133 calculated using Equation 2 below. ) To prevent the deterioration of LER (Line Edge Roughness) (204).

As described above, the maskless exposure apparatus 10 according to an exemplary embodiment of the present invention corrects the cumulative illuminance by software to uniform cumulative illuminance for the entire field of the optical system without causing a decrease in LER (Line Edge Roughness) during exposure. Can be secured. This is shown in FIGS. 9 and 10.

9 and 10 are graphs comparing the cumulative illuminance after correction with the cumulative illuminance before correction in the maskless exposure apparatus according to the exemplary embodiment of the present invention.

As shown in FIG. 9, it can be seen that the cumulative illuminance before correction is uneven with respect to the field before the optical system.

On the other hand, as shown in Figure 10, it can be seen that the cumulative roughness after the correction is uniform for the entire field of the optical system.

10: maskless exposure apparatus 20: stage
30 substrate 40 beam measuring unit
42: correction mask generator 44: exposure data generator
46: control unit 100: exposure head
110: light source 115: exposure beam
130: optical modulator 131: beam spot array
133 spot beam 140 projection optical system

Claims (12)

A light source emitting an exposure beam;
An optical modulator for modulating the exposure beam according to an exposure pattern;
Projection optics for transmitting the modulated exposure beam onto a substrate in the form of a beam spot array;
A beam measuring unit measuring beam data of the beam spot array;
A correction mask generator which generates a correction mask for correcting cumulative illuminance using the measured beam data;
And a control unit which transmits an exposure pattern whose cumulative illuminance is corrected to the light modulation device by using the generated correction mask. The method of claim 1,
And an exposure data generation unit configured to generate exposure data of the light modulation device according to the exposure pattern.
And the control unit performs an AND operation on the correction mask and the generated exposure data to generate the exposure pattern in which the cumulative illuminance is corrected. The method of claim 1,
And the beam data includes position data, intensity data, horizontal size data, and vertical size data of spot beams constituting the beam spot array. The method of claim 3,
And the correction mask generator accumulates the intensity of the discretized spot beams for the entire field of the projection optical system, and performs digital correction on the accumulated intensity of the spot beams. The method of claim 4, wherein
The correction mask generator calculates a spatial density at each point of the spot beams, and masks off the spot beam of the point having the highest spatial density calculated to ensure uniform cumulative illuminance for the entire field of the projection optical system. Lease exposure apparatus. The method of claim 5,
And the correction mask generation unit generates the correction mask by calculating a residual for the PEG at the Y coordinate position of the spot beams. Transmitting the exposure beam emitted from the light source to the substrate in the form of a beam spot array via an optical modulation device and a projection optical system;
Measure beam data of the beam spot array;
Generating a correction mask for cumulative illuminance correction using the measured beam data;
And a cumulative illuminance correcting method of the maskless exposure apparatus that transmits the exposure pattern whose cumulative illuminance is corrected to the light modulation device by using the generated correction mask. The method of claim 7, wherein
Generating exposure data of the light modulator according to an exposure pattern;
And generating the exposure pattern of which the cumulative illuminance is corrected by performing an AND operation on the correction mask and the generated exposure data. The method of claim 7, wherein
And the beam data includes position data, intensity data, horizontal size data, and vertical size data of spot beams constituting the beam spot array. 10. The method of claim 9,
Generating a correction mask for the cumulative illumination correction,
And accumulating the intensity of the discretized spot beams over the entire field of the projection optical system, and performing digital correction on the accumulated intensity of the spot beams. The method of claim 10,
Generating a correction mask for the cumulative illumination correction,
Accumulation of the maskless exposure apparatus that calculates the spatial density at each point of the spot beams, and turns off the spot beam of the point with the highest spatial density calculated to ensure uniform cumulative illuminance for the entire field of the projection optical system. Illumination correction method. The method of claim 11,
Generating a correction mask for the cumulative illumination correction,
And calculating a residual for the PEG at the Y coordinate of the spot beams to generate the correction mask.

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