JP2020091330A - Method for manufacturing photomask - Google Patents

Abstract

To provide a method for manufacturing a photomask, in which the number of processes of manufacturing a multi-gradation photomask can be reduced by forming a photoresist pattern with different film thicknesses on a photomask substrate by a single exposure process.SOLUTION: A micromirror array in which a plurality of micromirrors each independently variable for a tilt angle is arranged is irradiated with laser light; and a first state and a second state determined by the tilt angle of the micromirror are temporally controlled so as to allow a photoresist formed on a photomask substrate to be irradiated only with the laser light reflected by the micromirror in the first state. Thus, a photoresist pattern having different film thicknesses can be formed by a single exposure process.SELECTED DRAWING: Figure 1

Description

The present invention relates to a photomask manufacturing method. Specifically, the present invention relates to a photomask using a photomask drawing apparatus using a DMD (digital micromirror device), and particularly to a method for manufacturing a multi-tone mask.

When manufacturing a photomask used in a lithography process in the manufacturing process of a display device, a semiconductor device, etc., in order to draw a desired pattern on a photoresist on a photomask blank, for example, as described in Patent Documents 1 and 2 The device is in use.

The main steps of manufacturing a halftone mask (three-tone photomask) using such a known laser drawing apparatus will be described below.
12A to 12D are process cross-sectional views showing a method of manufacturing a typical bottom half type multi-tone mask.
First, a photomask blank in which a semi-transmissive film 101 such as Mo silicide (MoSi) and a light shielding film 102 such as chromium (Cr) are formed in this order on a transparent substrate 100 such as quartz is prepared, and the entire surface thereof is prepared. A photoresist 103 is formed on the substrate by a coating method or the like (FIG. 12A).
Next, the photoresist 103 is exposed by a drawing device and developed to form a photoresist pattern 103a (FIG. 12B).
Next, the light-shielding film 102 is etched by using the photoresist pattern 103a as a mask to form the light-shielding film pattern 102a (FIG. 12C), and the semi-transmissive film 101 is further etched to form the semi-transmissive film pattern 101a. Formed (FIG. 12D).
Next, after removing the photoresist pattern 103a by ashing or the like (FIG. 12E), a photoresist 104 is formed (FIG. 12F).
Next, the photoresist 104 is exposed by a drawing device and developed to form a photoresist pattern 104a (FIG. 12G).
Next, the light shielding film pattern 102a is selectively etched using the photoresist pattern 104a as a mask to form a light shielding film pattern 102b (FIG. 12H).
Finally, the photoresist pattern 104a is removed by ashing or the like (FIG. 12I).

JP, 2003-215782, A JP, 2014-95827, A

In order to manufacture a halftone mask (multi-tone mask) with a known drawing device, two kinds of drawing data, that is, a pattern for etching a semi-transmissive film and a stack of light-shielding films and a pattern for etching only the light-shielding film, are used. It must be made separately and requires two lithographic steps. As a result, the manufacturing period is lengthened and the manufacturing cost is increased due to the increase in the manufacturing process.
Furthermore, since two (plural) lithography processes are required, it is necessary to perform alignment for aligning the drawing patterns formed in each lithography process. In this case, since it is necessary to take measures such as expanding the drawing pattern in consideration of the alignment margin (margin), it becomes an obstacle to miniaturization of pattern and high integration.
Further, when forming a multi-tone mask having four or more tones, the number of lithography processes will be further increased.

The present invention has been made in view of the above, and provides a photomask drawing device capable of forming a multi-tone photomask by a single lithography process, and a method of manufacturing a multi-tone mask using the photomask drawing device. The challenge is to provide.
Needless to say, the photomask drawing apparatus according to the present invention is not limited to the production of a multi-tone photomask, but can be used for the production of a binary mask, for example.

The photomask manufacturing method according to the present invention is
A method of manufacturing a photomask using a drawing device, comprising:
The drawing apparatus includes a micromirror array composed of a plurality of micromirrors capable of independently changing an inclination angle in an optical path of laser light emitted from a semiconductor laser,
Installing a photomask substrate having a photoresist formed thereon,
Irradiating the micromirror array with a laser beam,
For each of the micro mirrors, controlling the tilt angle to control the irradiation state of the laser light temporally,
Relatively changing the irradiation position of the laser light on the photomask substrate.

With such a photomask manufacturing method, it is possible to control the exposure amount of the laser applied to the photoresist formed on the photomask substrate (photomask blanks) in pixel units of pattern formation. It becomes possible to form photoresist patterns having different thicknesses by a single exposure process.

Further, the method for manufacturing a photomask according to the present invention,
The micromirror array is divided into a first area, a second area and a third area,
The micromirror arranged in the first region maintains the first state during the first control time, while maintaining the second state during the other time,
The micromirror disposed in the second region maintains the first state for the second control time, while maintaining the second state for the other time,
The micromirror arranged in the third region maintains the first state during the third control time, and maintains the second state during the other time,
The first control time, the second control time, and the third control time are set to be different from each other.

With such a photomask manufacturing method, it is possible to form a photoresist pattern having photoresists of three different film thicknesses by a single exposure process.
Further, for example, by setting the first control time to zero for a negative photoresist, it becomes possible to form a photoresist pattern having a film thickness of zero, that is, an opening.

Further, the method for manufacturing a photomask according to the present invention,
The first region, the second region, and the third region are corrected in units of micromirrors based on the correlation between the exposure amount of the photoresist by the laser and the pattern width variation amount.

By using such a photomask manufacturing method, it becomes possible to form photoresist patterns having different film thicknesses with a small pattern width dimensional variation.

Further, the method for manufacturing a photomask according to the present invention,
The step of exposing the photoresist and the step of relatively moving the area irradiated by the reflection laser from the micromirror control area may be repeated.

With such a photomask manufacturing method, it becomes possible to expose all the photoresist in a necessary region by the step-and-repeat method.

Further, the method for manufacturing a photomask according to the present invention,
The photomask substrate is characterized in that a semi-transmissive film and a light shielding film are formed in this order on a transparent substrate.

By using such a photomask manufacturing method, it is possible to easily manufacture three-tone halftones.

The photomask manufacturing method according to the present invention is
A method of manufacturing a photomask using a drawing device that includes a micromirror array composed of a plurality of micromirrors capable of independently changing an inclination angle in an optical path of laser light emitted from a semiconductor laser,
Preparing a photomask substrate in which a semi-transmissive film and a light-shielding film are formed in this order on a transparent substrate,
Forming a photoresist on the photomask substrate,
The first state and the second state determined by the tilt angle are maintained for each of the micromirrors arranged in the first region, the second region and the third region in the micromirror array. Controlling the time,
By individually controlling the tilt angles of the micromirrors arranged in the first to third regions,
Controlling time for each of the micromirrors to maintain a first state and a second state determined by the tilt angle;
The micromirrors installed in the first area maintain a second state determined by an inclination angle, and the micromirrors installed in the second area maintain a first state determined by an inclination angle. For a second control time, and the micromirror installed in the third region maintains a first state determined by a tilt angle for a third control time shorter than the second control time. Keep and
Irradiating the photoresist only with the laser reflected by the micromirror in the first state;
Developing the photoresist to form a photoresist pattern having openings, a photoresist of a first thickness and a photoresist of a second thickness;
Etching the light-shielding film and the semi-transmissive film using the photoresist pattern as a mask,
Etching back the photoresist pattern by an amount larger than the second film thickness and smaller than the first film thickness to reduce the film thickness of the photoresist pattern;
Etching the light-shielding film using the photoresist pattern with a reduced film thickness as a mask,
Removing the photoresist pattern,
It is characterized by including.

By using such a photomask manufacturing method, it is possible to reduce the number of man-hours for manufacturing three halftones.

By the photomask manufacturing method according to the present invention, resists having different film thicknesses can be formed by one lithography process, and the manufacturing process of the multi-tone photomask can be reduced.
Further, it is possible to contribute to the miniaturization of the pattern by eliminating the need for the pattern design considering the overlay margin.

The figure which shows the structure of the drawing apparatus concerning this invention. FIG. 2A shows how the laser is irradiated onto the light reflecting portion, and FIG. 2B schematically shows the laser intensity distribution. 3A is an enlarged view of a part of the micromirror control region C, and FIG. 3B is a cross-sectional view showing a state in which the laser reflected by the micromirror 9 is applied to the photoresist. The figure which shows the condition which exposes a photoresist by a step and repeat system. FIG. 5A shows measured values of the intensity distribution of the laser reflected from the AA′ portion of the micromirror control region C, and FIG. 5B shows the line width distribution of the patterned photoresist ( The measured value) is shown. FIG. 6A is an enlarged view of a part of the light reflecting portion. FIG. 6B is a graph showing the timings of the first state and the second state of the micromirror in comparison. FIG. 5 is a cross-sectional view of a photoresist patterned by a laser, the irradiation time of each region is controlled by DMD. Sectional drawing which shows the main processes of the manufacturing method of a half-tone mask (multi-tone mask). Sectional drawing which shows the main processes of the manufacturing method of a half-tone mask (multi-tone mask). The graph which shows the relationship between the exposure amount of a laser, and the dimension variation of the resist pattern width after development. FIG. 11A is a diagram showing the correction situation of the area of the micromirror based on the measured value of the dimensional variation of the resist pattern width. FIG. 11B is a diagram showing a pattern for obtaining the correlation data between the exposure amount and the dimensional variation of the resist pattern width. Sectional drawing which shows the main manufacturing processes of a typical bottom half type multi-tone mask.

Embodiments of the present invention will be described below with reference to the drawings. However, none of the following embodiments gives a limited interpretation in the recognition of the gist of the present invention. Further, the same or similar members are denoted by the same reference numerals, and description thereof may be omitted.

FIG. 1A shows a main configuration of the drawing device 1.
A laser LD (eg, g-line, h-line, i-line, etc.) emitted from a semiconductor laser 2 which is a laser generator is guided to a DMD (digital micromirror device) 4 by a reflecting mirror 3 as indicated by a dotted arrow. It The laser reflected by the light-reflecting portion 8 of the DMD 4 is projected in the same size or reduced size on the photomask substrate 7 mounted on the stage 6 by the optical system 5 including a lens, as shown by a dotted arrow. It
The photomask substrate 7 is, for example, a photomask blank in which a semi-transmissive film and a light-shielding film are formed on a transparent substrate, and a photoresist having photosensitivity to a laser irradiated on the photomask blank is applied. There is.
The stage 7 can move in the X and Y directions orthogonal to each other, and can move the photomask substrate 7 in a predetermined direction by a predetermined distance.

The light reflecting portion 8 of the DMD 4 has a plurality of micromirrors 9 as will be described later, the tilt angle of each micromirror 9 is electrically controlled, and the reflection angle of the laser is shown in FIGS. 1(A) and 1(B). Alternately, as indicated by a white arrow or a black arrow in FIG.
The laser reflected in the white arrow direction passes through (passes through) the optical system 5 and is applied to the photomask substrate 7. On the other hand, the laser reflected in the direction of the black arrow does not enter the optical system 5, and therefore is not irradiated on the photomask substrate 7. By arranging the optical system 5 in this way, the DMD 4 can selectively realize the state where the photomask substrate 7 is irradiated with the laser and the state where the photomask substrate 7 is not irradiated with the laser.

FIG. 1B is a perspective view showing a part of the surface of the light reflecting portion 8 of the DMD 4.
As shown in FIG. 1B, the light reflecting portion 8 has a plurality of minute mirrors (micromirrors 9) each having a side of 10 to 15 [μm], for example, 1980×1080, in a grid pattern. It is configured by a micromirror array (arrangement of micromirrors) aligned and arranged. Each micro mirror 9 can be independently controlled, and its tilt angle can be switched to the first tilt angle or the second tilt angle, for example, −12 [°] or +12 [°].

The laser incident on the light reflecting portion 8 (indicated by a dotted arrow in FIG. 1B) is reflected by the micromirror 9a set to the first tilt angle, as shown in FIG. The light enters the optical system 5 as indicated by the white-filled arrow, and then is irradiated on the photomask substrate 7. When reflected by the micro mirror 9b whose inclination angle is set to the second inclination angle, it does not enter the optical system 5 as shown by the black arrow in FIG. 1B (the photomask substrate 7 is not irradiated). ) Is arranged.

It is possible to select whether or not to irradiate the photomask substrate 7 with the laser by controlling the reflection direction of the laser for each micromirror 9 depending on the inclination angle. The area irradiated from one micro mirror 9 to the photomask substrate 7 via the optical system 5 is the minimum exposure area (pixel) on the photomask substrate 7.
It should be noted that the inclination angle is an example and is not limited to this.

In this way, the DMD 4 locally (for each micro mirror 9) changes the laser path by changing the tilt angle of each micro mirror 9, and irradiates the photo mask substrate 7 with the laser light (first). State) and a state in which irradiation is not performed (second state) can be selected.

FIG. 2(A) shows how the laser is radiated onto the light reflecting portion 8, and FIG. 2(B) schematically shows the laser intensity distribution in the cross section taken along the alternate long and short dash line ZZ′ of FIG. 2(A). Show.
A region surrounded by a circle indicated by a dotted line in FIG. 2A indicates a laser irradiation region S, and this circle corresponds to a laser spot diameter (for example, 1 [mm]). Further, a rectangular area shown by a solid line in FIG. 2A is a micromirror control area C set in the laser irradiation area S. The micromirror control area C is set so as to be always within the laser irradiation area S in consideration of the fluctuation of the laser spot diameter and the fluctuation of the optical axis.
As shown in FIG. 2B, the laser intensity sharply decreases outside the laser irradiation region S and becomes 0 (zero), but inside the laser irradiation region S, ideally, the laser intensity decreases. Is constant, and the micromirror control region C is set to a region where the intensity distribution is uniform, for example, a region within the uniformity required by the customer.
Since the surface of the light reflecting portion 8 of the DMD 4 is not necessarily perpendicular to the laser incident direction, the laser irradiation area S is not necessarily a circle but may be an ellipse to be exact.

Inside the micromirror control region C, each micromirror is a region in which the first state or the second state can be selectively controlled, and the micromirrors in the regions other than the micromirror control region C are always in the first state. Set to state 2.

FIG. 3A is an enlarged view of a part of the micromirror control area C and shows an example of the control state of each micromirror 9. FIG. 3B is a cross-sectional view showing a state in which the laser LD is reflected by the micromirror 9 and is applied to the photoresist 10 formed on the photomask substrate 7 via the optical system 5.
In FIG. 3A, the hatched micro mirrors 9a are in the first state, and the unhatched micro mirrors 9b are in the second state.
By arranging the micromirrors 9a in the first state in a desired pattern, the laser reflected by the micromirrors 9a is applied to the photoresist 10 on the photomask substrate 7 in a desired pattern shape (FIG. 3). (B)). Therefore, the photoresist 10 can be exposed to a desired pattern shape.
Each micromirror 9 in the micromirror control region C constitutes one pixel on the photomask substrate 7, and a photoresist pattern is formed as a set of pixels which is the minimum unit of this exposure region. Become.

The exposure region of the photoresist 10 that can be exposed by one exposure process (one drawing process) (referred to as an exposure section for simplicity) is a region that can be irradiated by the laser reflected from the micromirror control region C. is there.
Therefore, as shown in FIG. 4, when the exposure process of one exposure section determined in the micromirror control area C is completed, the distance corresponding to the size of the exposure section is adjusted by the stage 6 so that continuous pattern formation can be performed. The photomask substrate 7 is moved by (L in the figure). After that, the exposure process is performed by controlling the first and second states of the micromirror 9 having a desired pattern for the next exposure section.
That is, it is necessary to form a desired pattern on the entire surface of the photomask substrate 7 (or on the photoresist 10) by repeating the exposure process of the surface of the photomask substrate 7 and the movement of the photomask substrate 7 by the step-and-repeat method. Area).

Although the photomask substrate 7 is moved by the moving stage 6, when the photomask substrate 7 is exposed by the step-and-repeat method, the photomask substrate 7 and the optical system 5 may move relatively. The optical system 5 (and the DMD 4) may be moved, or both the optical system 4 and the photomask substrate 7 may be moved.

The exposure amount of the laser for exposing the photoresist can be controlled by the time of the first state of the micromirror 9a. The exposure time of the desired pattern can be easily set by setting the micromirror 9a to the second state after a predetermined time has elapsed.
Furthermore, since one micro mirror 9 constitutes one pixel on the photomask substrate 7, the exposure time can be controlled for each pixel.

FIG. 5A shows measured values of the intensity distribution of the laser reflected from the AA′ portion of the micromirror control region C, and FIG. 5B shows a line pattern row having a width of 5 μm. An actual measurement value of the line width of the photoresist patterned by the laser reflected from the micromirror 9 controlled to be formed is shown.

As shown in FIG. 5A, the actual laser intensity distribution shows a downward convex intensity distribution and has a finite fluctuation range. As shown in FIG. 5B, the measured value of the line width of the photoresist shows a slight periodic fluctuation reflecting the intensity distribution of the laser.
Variations in the photoresist line width depend on the intensity distribution of the reflected laser. Therefore, if the fluctuation of the line width exceeds the allowable range, the micromirror control region C may be set so as to reduce the fluctuation width of the laser intensity distribution. For example, in FIG. 5A, the variation in the line width of the photoresist can be further suppressed by limiting the area to the central area (area indicated by the arrow BB′). In this way, the threshold value of the variation amount of the desired line width is determined by reflecting the design requirements (or the target of miniaturization) of the circuit of the final product, and the micromirror control area C Should be decided.
Note that the same applies to the direction perpendicular to BB'.

FIG. 6A is an enlarged view of a partial region of the light reflecting portion 8 of the DMD 4 for manufacturing the multi-tone photomask. As shown in FIG. 6A, the light reflecting portion 8 has three regions Ra (cross hatching region in the drawing), region Rb (single hatching region in the drawing), and region Rc (white area in the drawing). ing.

FIG. 6B shows the first state (“ON” state) and the second state (“OFF”) of the micromirrors 9a, 9b and 9c in the regions Ra, Rb and Rc when performing one exposure process. It is a graph which shows the timing of "state." In the region Rc (first region), each micromirror 9c keeps the time of the first state zero (first control time), that is, always maintains the second state, and in the region Rb (second region). Each micro mirror 9b maintains the first state for a predetermined period (second control time tb) and the second state for the other period, and each micro mirror 9a has a predetermined state in the region Ra (third region). The first state is maintained during the period (third control time ta), and the second state is maintained during other periods. As shown in FIG. 6B, tb is set shorter than ta. For example, when ta is 100%, tb is 30% to 50%.

Therefore, the period (exposure time) during which the laser is reflected in the three regions Ra, Rb, and Rc and irradiated on the photomask substrate 7 during one exposure process is ta, tb, and tc (0: none), respectively. Is.
Note that the irradiation period (exposure time) does not necessarily need to be continuous, and the total may be ta, tb, tc (0: none).

FIG. 7 shows the film thickness of the photoresist 10 patterned by using the drawing apparatus 1. The laser LD is reflected in the regions Ra, Rb, and Rc shown in FIG. 7, and irradiates the regions Pa, Pb, and Pc of the photoresist 10 on the photomask substrate 7, respectively. Since the photoresist 10 in the regions Pa, Pb, and Pc have different exposure times, the film thickness of the photoresist after development also differs.
For example, in the case of a negative photoresist, the exposure time of the laser irradiated through the region Rc is 0, so the film thickness of the photoresist 10 in the region Pc is 0. The film thickness (Hb) of the photoresist 10 in the region Pb and the film thickness (Ha) of the photoresist 10 in the region Pa are Hb<Ha because the exposure time tb is shorter than the exposure time ta (tb<ta).

The photoresist 10 having a desired film thickness can be obtained from the correlation data (sensitivity curve) between the film thickness of the photoresist 10 and the exposure time. By acquiring the data of the sensitivity curve of the photoresist 10 to be used in advance, the exposure time for forming the photoresist 10 having a desired film thickness in each region can be determined. The determined exposure time can be controlled by setting the time for maintaining the first state for each micro mirror 9. Therefore, by controlling the laser irradiation using the DMD 4, it is possible to set an arbitrary exposure time in an arbitrary region in which one micro mirror 9 is a unit.

FIG. 7 shows an example in which the photoresist 10 having three kinds of film thickness (Ha, Hb, 0) is formed. In this way, the light reflecting portion 8 is divided into a plurality of regions, for example, the first to n-th (n≧3) regions, and the micromirrors arranged in the respective regions are set to the first state. By setting the control time for n (including time 0), it is possible to form n types (including film thickness 0) of resist patterns having different film thicknesses. Therefore, it is possible to form a photoresist having three or more kinds of film thickness.
It is also possible to form a photoresist having a cross section that is inclined stepwise.

As will be described later, the photomask substrate 7 is moved after exposing the photoresist 10 using the laser reflected from the light reflecting portion 8, and the exposure process and the movement of the photomask substrate 7 are repeated by the step-and-repeat method, The pattern of the photoresist 10 having a plurality of film thicknesses can be formed on the photomask substrate 7.
Incidentally, also for the positive type photoresist, a photoresist having a plurality of different film thicknesses can be formed by one exposure process.

If a conventional drawing apparatus is used to form a photoresist pattern having such a different film thickness, it is necessary to expose the photoresist by a plurality of drawing processes. For this reason, it is necessary to incorporate a width (dimension) corresponding to an overlay margin (margin) into the pattern in consideration of overlay misalignment (positional misalignment) of the patterns in different drawing processes.
However, when the drawing apparatus 1 using the DMD 4 is used as in the present embodiment, the photoresist 10 having different film thickness can be patterned by one exposure, so that it is not necessary to design the pattern considering the overlay margin. Therefore, it is possible to reduce the size corresponding to the overlap margin. Further, the design rule for the overlay margin is relaxed, the pattern design is facilitated, and the labor of the pattern designer is reduced.

FIG. 8 is a cross-sectional view showing the main steps of the method for manufacturing a halftone mask (multi-tone mask).
As shown in FIG. 8A, a semi-transmissive film 12 (for example, MoSi, Ti) and a light shielding film 13 (for example, Cr) are formed in this order on a transparent substrate 11 such as quartz by a vapor deposition method or a sputtering method. The photomask blanks are prepared, and the photoresist 10 is formed on the light-shielding film 13 by coating or the like.
The light transmittance of the semi-transmissive film 12 is arbitrarily set between the light transmittance of the transparent substrate 11 and the light transmittance of the light shielding film 13.

Next, as shown in FIG. 8B, the photoresist 10 is exposed by controlling the exposure time in units of each micromirror 9, and then developed to pattern the photoresist 10.
As described above (see FIGS. 6 and 7), since the exposure time can be controlled for each micro mirror 9, the first photoresist 10a and the second photoresist 10b having different film thicknesses can be formed by one exposure process. It can be formed at the same time. It is also possible to form patterns of the photoresist 10 having three or more different film thicknesses.

Next, as shown in FIG. 8C, with the photoresist 10 (the first photoresist 10a and the second photoresist 10b) as a mask, the light-shielding film 13 and the half-shield film are formed by a known wet etching method or dry etching method. The permeable film 12 is sequentially etched.

Next, as shown in FIG. 8D, the photoresist 10 is entirely etched (etched back) by an ashing method until the portion of the second photoresist 10b is removed.
That is, the film thickness of the photoresist 10 is reduced by etching back by an amount larger than the film thickness Hb and smaller than the film thickness Ha.
Since the film thickness Ha of the first photoresist 10a is larger than the film thickness Hb of the second photoresist 10b, the film thickness of the first photoresist 10a decreases (becomes less than Ha-Hb) but is left as it is. Is possible.
In the step of FIG. 8C, when at least one of the light shielding film 13 and the semi-transmissive film 12 is etched by the dry etching method, the etching gas (etchant) is optimized and the selection ratio is adjusted to adjust the photoresist 10. May be simultaneously etched to remove the portion of the second photoresist 10b.

Next, as shown in FIG. 9E, the light shielding film 13 is selectively etched by a wet etching method or a dry etching method using the photoresist 10 (first photoresist 10a) as a mask. The etching of the semi-transmissive film 12 is suppressed by using a known etchant (etching liquid, etching gas) and sufficiently increasing the selection ratio (for example, 10 or more).

Next, as shown in FIG. 9F, the photoresist (first photoresist 10a) is removed by an ashing method or the like.
Through the above steps, the transparent substrate 11 is exposed, the semi-transmissive film 12 is formed on the transparent substrate 11, and the semi-transmissive film 12 and the light-shielding film 13 are formed on the transparent substrate 11. A halftone mask 14 with gradation can be obtained.

The above shows a method of forming a halftone mask of three gradations. It is also possible to pattern the photoresist 10 so as to have three or more types of film thickness by controlling the time of the first state for the micromirror 9 with respect to the photoresist 10.
Thereby, it is possible to manufacture a photomask having more gradations.
In order to form patterns of semi-transmissive films having different film thicknesses, etching back of resist patterns having different film thicknesses and partial etching (half etching) of the semi-transmissive film may be sequentially repeated.

FIG. 10 shows the relationship between the laser exposure amount and the dimensional variation amount of the resist pattern width after development, in which the vertical axis represents the dimensional variation amount and the horizontal axis represents the laser exposure amount.
The exposure amount is standardized with an exposure amount of 1 at which a resist pattern having a line width of 5 [μm] is formed. The relationship between the exposure amount and the resist pattern width after development depends on the resist used and is obtained by actual measurement for each pattern width (for example, for a plurality of line widths, space widths or a plurality of hole diameters). be able to.

As shown in FIG. 10, when the exposure amount is smaller than 1, the resist pattern width is small, and when the exposure amount is larger than 1, the resist pattern width is large. That is, the pattern width becomes narrower when the exposure amount is reduced in order to reduce the film thickness of the formed resist. Therefore, in the region with a small exposure amount (region Pb in FIG. 7), the resist pattern becomes narrower than in the region with a large exposure amount (region Pa in FIG. 7).
This means that when a region having a large resist film thickness and a region having a thin resist film thickness are simultaneously formed by the exposure apparatus 1 using the drawing apparatus 1, the pattern width of the thin region becomes narrower than that of the region having a large resist film thickness. To do.

Therefore, in order to form a resist pattern having a desired width, as shown in FIG. 11A, the width of the area of the micromirror 9b (the middle area Rb in FIG. 11A) corresponding to the area with a small exposure amount. Should be set (corrected) so as to be wider than the area of the micro mirror 9a (the area Ra in FIG. 11A).
Here, in FIG. 11A, the dotted line shows the area (area Rb) of the micromirror 9b before correction.
Although the example in which the area of the micro mirror 9b is corrected has been described, the area of the micro mirror 9a may be corrected, both areas may be corrected, and the correction may be appropriately performed to obtain a desired pattern shape. Good.

Further, as for the correlation between the exposure amount and the dimensional variation of the resist pattern width, for example, as shown in FIG. 11B, the regions W1, W2, W3 in which the micromirrors 9 are arranged in a plurality of rows are prepared, and the microscopic regions in the respective regions are set. The correlation between the number of rows of the mirrors 9 and the resist pattern width may be acquired by changing the exposure time. In this case, the required number of micromirrors 9 (the number of rows) can be directly obtained with respect to the dimension of the resist pattern width. Further, a plurality of regions having different exposure times are prepared for the regions W1, W2, and W3 (for example, regions Ra and Rb in FIG. 11B), and data for changing a plurality of exposure amounts by one exposure is acquired. Is also possible. By using this method, the drawing apparatus 1 can reduce the labor for acquiring the data of the variation amount of the sensitivity curve of the photoresist and the pattern width, and can reduce not only the photomask manufacturing but also the development cost.

As described above, if the data on the correlation between the exposure amount of the laser and the resist pattern width after development is acquired in advance, the pattern of the micro mirror 9 of the reflecting section 8 can be corrected based on the data. A resist pattern having a desired film thickness and a desired width can be formed.
Since the micromirrors 9 can be individually controlled, the pattern can be easily modified. For example, in the case of a negative photoresist, in order to expand the resist pattern, it is sufficient to increase the number of micromirrors 9 in the first state by a predetermined number according to the expanding width. May be reduced by a predetermined number of micromirrors 9 in the first state according to the width to be reduced.

Hereinafter, a method of controlling the DMD 4 for forming the drawing pattern of the photomask will be described.
For example, when forming a three-tone halftone mask, a resist pattern of a photomask (halftone mask) can be formed according to the following procedure.

(1) Using a design tool such as CAD, pattern data (coordinate data) of the transparent portion (light transmitting portion or transparent substrate exposed portion) that is the first pattern area, and pattern of the light shielding portion that is the second pattern area Desired pattern data (for example, data (coordinate data) and desired pattern data divided into three regions, that is, pattern data (coordinate data) of a semi-transmissive portion having a transmittance between a light-shielding portion and a transparent portion, which is a third pattern area Confirm (design) the electric circuit pattern. The pattern data is stored in a storage device built in the drawing device 1 or an external storage device.
(2) The film thickness of the photoresist to be formed is determined from the requirements of the manufacturing process corresponding to each of the above regions.

(3) Each pattern data is divided into exposure sections (irradiation areas on the photoresist of the laser reflected by the micromirror control area) defined by the micromirror control area, and transparent sections (first sections) are formed for each exposure section. The exposure time of the photoresist corresponding to each region of the first pattern region), the light-shielding portion (second pattern region), and the semi-transmissive portion (third pattern region) is determined. The exposure time is calculated from the sensitivity curve measured in advance and the photoresist film thickness determined for each region.
At this time, it is also possible to adjust so that the important circuit portion of the pattern data does not overlap the boundary portion of the divided exposure sections.
By doing so, it becomes possible to avoid the fluctuation of the pattern width of the important circuit portion even when the fluctuation of the exposure amount occurs.
That is, an important circuit portion is specified and designated in advance as an undividable portion, and the size of the exposure division is changed around the undividable portion so that the boundary portion of the exposure division does not overlap the undividable portion. do it.

From the calculated exposure time, the control conditions (tilt angle (that is, the first state or the second state) and the holding time of each micromirror 9 of the DMD 4 corresponding to the first, second and third pattern areas are calculated. ) Is provisionally determined.
Here, the micromirrors corresponding to the first, second, and third pattern areas mean micromirrors that reflect laser and irradiate the first, second, and third pattern areas, respectively. Areas formed by micromirrors corresponding to the first, second and third pattern areas are referred to as first, second and third micromirror areas, respectively.
The sensitivity curve may be stored in a storage device and calculated by an arithmetic processing device such as a microcomputer.

(4) From the previously obtained correlation between the exposure amount and the pattern width variation amount, the first, second, and third patterns corresponding to the first, second, and third pattern regions are set for the micromirror control region. The micromirror region is corrected (enlarged or reduced) in units of micromirrors, the control conditions (tilt angle and holding time) of the micromirrors 9 are corrected, and the control conditions are determined.
Note that the micromirror control conditions for regions other than the first, second, and third micromirror regions, that is, regions other than the micromirror control region C, are conditions that always maintain the second state.
The corrected micromirror control conditions are stored in the storage device in association with each exposure section.

(5) A photomask substrate 7 having a photoresist 10 formed thereon is prepared on a photomask blank having a light transmitting portion and a light shielding portion formed in this order on a transparent substrate, and placed on a stage 6.
(6) The micromirrors 9 of the DMD 4 are controlled according to the stored micromirror control conditions corresponding to the respective exposure sections, and the photoresist 10 on the photomask substrate 7 is irradiated with the laser.

(7) The photomask substrate 7 is moved with respect to the optical system 5 by a distance corresponding to one exposure section.
In this step, the relative distance between the photomask substrate 7 and the optical system 5 is moved, and either the photomask substrate 7 or the optical system 5, or both the photomask substrate 7 and the optical system 5 are moved. Good. As a result, it is possible to move the exposure section on the photoresist 10 and expose the entire area of the photoresist 10 that requires exposure processing.
The relative movement can be performed, for example, in each of the two orthogonal axes of the so-called orthogonal coordinate system, the X axis, and the Y axis.

When the optical system 5 is moved, the laser reflected from the micromirror 9 in the first state needs to be configured to irradiate the photomask substrate 7 via the optical system 5. Therefore, the DMD 4 may be moved simultaneously with the optical system 5. As a method for moving the optical system 5, known methods such as the methods disclosed in Patent Documents 1 and 2 can be adopted.

(8) By repeating step (6) and (7) according to the step-and-repeat method, the photoresist 10 formed on the photomask substrate 7 is sequentially exposed. After the exposure is completed, the patterning of the photoresist 10 is completed by the developing process.
After that, the photomask can be completed by the manufacturing process described in FIG.

The steps (3) and (4) can be substantially interchanged.
That is, the pattern data (coordinate data) of the semi-transmissive portion and the pattern data (coordinate data) of the light-shielding portion are corrected based on the previously obtained correlation between the exposure amount and the pattern width variation amount, and then each pattern data is converted into a micromirror. Dividing the exposure section to be determined in the control area, determining the control conditions (tilt angle and its holding time) of each micromirror 9 of the DMD 4 corresponding to the light transmitting section, the light shielding section, and the transparent section for each exposure section, It may be stored in the storage device.

According to the present invention, it is possible to form photoresist patterns having different film thicknesses on a photomask substrate by a single exposure process, and it is possible to reduce the number of steps for manufacturing a multi-tone photomask. It is also possible to contribute to the miniaturization of the photomask pattern. The photomask manufactured according to the present invention can be used in the lithography process in the manufacturing process of electronic devices and the like, and has high industrial applicability.

1 Drawing device 2 Semiconductor laser 3 Reflector 4 DMD
5 optical system 6 stage 7 photomask substrate 8 light reflecting portions 9, 9a, 9b, 9c micromirror 10 photoresist 10a first photoresist 10b second photoresist 11 transparent substrate 12 semi-transmissive film 13 light-shielding film 14 halftone Mask 15 Light intensity detector 100 Transparent substrate 101 Semi-transmissive film 101a Semi-transmissive film pattern 102 Light-shielding films 102a and 102b Light-shielding film pattern 103 Photoresist 103a Photoresist pattern 104 Photoresist 104a Photoresist pattern

Claims (6)

A method of manufacturing a photomask using a drawing device, comprising:
The drawing apparatus includes a micromirror array composed of a plurality of micromirrors capable of independently changing an inclination angle in an optical path of laser light emitted from a semiconductor laser,
Installing a photomask substrate on which a photoresist film is formed,
Irradiating the micromirror array with a laser beam,
For each of the micro mirrors, controlling the tilt angle to control the irradiation state of the laser light temporally,
A step of relatively changing an irradiation position of the laser beam with respect to the photomask substrate. The micromirror array is divided into a first area, a second area and a third area,
The micromirror arranged in the first region maintains the first state during the first control time, while maintaining the second state during the other time,
The micromirror disposed in the second region maintains the first state for the second control time, while maintaining the second state for the other time,
The micromirror arranged in the third region maintains the first state during the third control time, and maintains the second state during the other time,
The method of manufacturing a photomask according to claim 1, wherein the first control time, the second control time, and the third control time are set to be different from each other. The first region, the second region, and the third region are corrected in units of micromirrors based on a correlation between an exposure amount of the photoresist by the laser and a pattern width variation amount. 2. The method for manufacturing a photomask according to 2. 4. The photo according to claim 1, wherein the step of exposing the photoresist and the step of relatively moving the area irradiated by the reflection laser from the micromirror control area are repeated. Mask manufacturing method. The method of manufacturing a photomask according to claim 1, wherein the photomask substrate has a semi-transmissive film and a light-shielding film formed in this order on a transparent substrate. A method of manufacturing a photomask using a drawing device that includes a micromirror array composed of a plurality of micromirrors capable of independently changing an inclination angle in an optical path of laser light emitted from a semiconductor laser,
Preparing a photomask substrate in which a semi-transmissive film and a light-shielding film are formed in this order on a transparent substrate,
Forming a photoresist on the photomask substrate,
The first state and the second state determined by the tilt angle are maintained for each of the micromirrors arranged in the first region, the second region and the third region in the micromirror array. Controlling the time,
By individually controlling the tilt angles of the micromirrors arranged in the first to third regions,
Controlling time for each of the micromirrors to maintain a first state and a second state determined by the tilt angle;
The micromirror installed in the first area maintains the second state, and the micromirror installed in the second area maintains the first state for a second control time. , The micromirror installed in the third region maintains the first state for a third control time shorter than the second control time,
Irradiating the photoresist only with the laser reflected by the micromirror in the first state;
Developing the photoresist to form a photoresist pattern having openings, a photoresist of a first thickness and a photoresist of a second thickness;
Etching the light-shielding film and the semi-transmissive film using the photoresist pattern as a mask,
Etching back the photoresist pattern by an amount larger than the second film thickness and smaller than the first film thickness to reduce the film thickness of the photoresist pattern;
Etching the light-shielding film using the photoresist pattern with a reduced film thickness as a mask,
Removing the photoresist pattern,
A method of manufacturing a photomask, comprising:

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