JP7220066B2 - Photomask drawing equipment - Google Patents

Description

The present invention relates to a photomask drawing apparatus. Specifically, the present invention relates to a photomask drawing apparatus using a DMD (digital micromirror device).

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, drawing as described in Patent Documents 1 and 2 is used. Device is in use.

Principal processes for manufacturing a halftone mask (three-tone photomask) using such a known drawing apparatus will be described below.
17A to 17D are process cross-sectional views showing a method of manufacturing a typical bottom-half type multi-tone mask.
First, a photomask blank is prepared in which a semi-transmissive film 101 such as Mosilicide (MoSi) and a light shielding film 102 such as chromium (Cr) are formed in this order on a transparent substrate 100 such as quartz. A photoresist 103 is formed on the surface by a coating method or the like (FIG. 17(A)).
Next, the photoresist 103 is exposed by a drawing device and developed to form a photoresist pattern 103a (FIG. 17B).
Next, the light shielding film 102 is etched using the photoresist pattern 103a as a mask to form the light shielding film pattern 102a (FIG. 17C). A pattern 101a is formed (FIG. 17(D)).
Next, after removing the photoresist pattern 103a by ashing or the like (FIG. 17(E)), a photoresist 104 is formed (FIG. 17(F)).
Next, the photoresist 104 is exposed by a drawing device and developed to form a photoresist pattern 104a (FIG. 17(G)).
Next, using the photoresist pattern 104a as a mask, the light shielding film pattern 102a is selectively etched to form a light shielding film pattern 102b (FIG. 17(H)).
Finally, the photoresist pattern 104a is removed by ashing or the like (FIG. 17(I)).

Japanese Patent Application Laid-Open No. 2003-215782 JP 2014-95827 A

In order to manufacture a halftone mask (multi-tone mask) with a known drawing apparatus, two types of drawing data are prepared: a pattern for etching the semi-transmissive film and the light shielding film and a pattern for etching only the light shielding film. It has to be made separately and requires two lithography steps. As a result, an increase in the number of manufacturing processes results in a longer manufacturing period and a higher manufacturing cost.
Furthermore, since two (a plurality of) lithography steps are required, alignment is required for aligning drawing patterns formed in each lithography step. In this case, it is necessary to take measures such as expanding the drawing pattern in consideration of the alignment margin (allowance), which becomes an obstacle to miniaturization of the pattern and high integration.
Further, when forming a multi-tone mask with four or more gradations, the number of lithography steps is further increased.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a photomask drawing apparatus capable of forming a multi-tone photomask by a single lithography process.
Needless to say, the drawing apparatus according to the present invention is not limited to use for manufacturing multi-tone photomasks, but can also be used for manufacturing binary masks, for example.

A photomask drawing apparatus according to the present invention includes:
a semiconductor laser; a DMD having a micromirror array composed of a plurality of micromirrors whose tilt angles can be changed independently in the optical path of the laser emitted from the semiconductor laser ; a stage; an optical system; , a DMD control unit, a light amount measurement unit, and an arithmetic processing unit,
the storage unit stores a micromirror control condition that defines a time for maintaining a first state and a second state determined by the tilt angle for each of the micromirrors of the DMD;
The light amount measuring unit measures the intensity distribution of the laser reflected from the micromirror in the first state,
The arithmetic processing unit sets a micromirror control region such that the variation width of the intensity distribution is smaller than a preset threshold value,
The DMD control unit always maintains the second state of the micromirrors other than the micromirror control area according to the micromirror control conditions, and controls each of the micromirrors in the micromirror control area,
The optical system irradiates only the laser reflected from the micromirror in the first state in the micromirror control area onto the photoresist formed on the photomask substrate placed on the stage. characterized by comprising

By using such a photomask drawing apparatus,
The optical path of the laser emitted from the semiconductor laser, which is a laser generator, is controlled in units of micromirrors of the DMD to flexibly correspond to various photomask patterns and facilitate pattern drawing.

Further, the photomask drawing apparatus according to the present invention includes:
comprising a stage, an optical system, a storage unit, and a DMD control unit,
the storage unit stores a micromirror control condition that defines a time for maintaining a first state and a second state determined by the tilt angle for each of the micromirrors of the DMD;
The DMD control unit controls each of the micromirrors according to the micromirror control conditions,
the optical system is arranged so that only laser reflected from the micromirror in a first state is incident;
It is characterized in that the laser incident on the optical system irradiates the photoresist formed on the photomask substrate placed on the stage.

By using such a photomask drawing apparatus,
The amount of laser exposure applied to the photoresist formed on the photomask substrate can be controlled in units of pixels for pattern formation, and the photoresist pattern having different film thicknesses can be formed by a single exposure process. can be formed.

Further, the photomask drawing apparatus according to the present invention includes:
Equipped with a light intensity measurement unit,
The light amount measuring unit measures an intensity distribution of laser reflected from the micromirror in the first state of the DMD.

By using such a photomask drawing apparatus,
It is possible to measure the intensity distribution of the laser with which the photoresist formed on the photomask substrate is irradiated, and to monitor the laser intensity distribution over time.

Further, the photomask drawing apparatus according to the present invention includes:
Equipped with an arithmetic processing unit,
The arithmetic processing unit is
The uniformity of the intensity distribution of the laser measured by the light amount measuring unit is calculated.

By using such a photomask drawing apparatus,
By evaluating the uniformity of the intensity distribution of the laser, the condition of the DMD can be monitored, and by comparing it with a predetermined threshold value, it is possible to prompt the operator or the like to take action such as replacement or maintenance of the DMD.

Further, the photomask drawing apparatus according to the present invention includes:
The arithmetic processing unit is
The micromirror control area is determined from the intensity distribution of the laser measured by the light amount measuring unit.

By using such a photomask drawing apparatus,
The variation width of the pattern dimension of the photoresist formed on the photomask substrate can be set within a predetermined range according to, for example, customer requirements.

Further, the photomask drawing apparatus according to the present invention includes:
The micromirror control conditions stored in the storage unit are the micromirrors belonging to a first micromirror area, a second micromirror area, and a third micromirror area for which the first state is maintained at different times. is characterized by including a control condition of

By using such a photomask drawing apparatus,
It is now possible to form a photoresist pattern with three different film thicknesses in a single exposure process, which reduces the number of lithography processes and eliminates the need to include a margin for overlay in the pattern, miniaturizing patterns and designing work. It becomes possible to contribute to the reduction of the load.
For example, the time for maintaining the first state in the first micromirror region is set to 0 (zero), and the time for maintaining the first state in the second mirror region is set to the first state in the third mirror region. A halftone mask having a transparent portion, a light shielding portion, and a semi-transmissive portion can be easily manufactured by making the time longer than the time for which the state is maintained.

Further, the photomask drawing apparatus according to the present invention includes:
The storage unit stores correlation data between a laser exposure dose and a photoresist pattern width,
The first micromirror area, the second mirror area and the third mirror area are corrected from the correlation data.

By using such a photomask drawing apparatus,
Even if the exposure amount of the photoresist is changed corresponding to the first, second and third micromirror regions, it is possible to easily suppress the variation in the photoresist pattern dimension due to the difference in the exposure amount.

Further, the photomask drawing apparatus according to the present invention includes:
Equipped with a drive system control unit,
The driving system control unit moves the relative position between the optical system and the stage, and exposes the photoresist formed on the photomask substrate placed on the stage by a step-and-repeat method. characterized by

By using such a photomask drawing apparatus,
The DMDs are used to continuously connect the exposure sections irradiated with the laser, and the photoresist on the photomask substrate can be patterned over a predetermined area.

With the photomask drawing apparatus according to the present invention, resists having different film thicknesses can be formed by one lithography process, and the number of steps for manufacturing a multi-tone photomask can be reduced.
In addition, by eliminating the need for pattern design in consideration of the overlay margin, it is possible to contribute to miniaturization of patterns.

1 is a diagram showing the configuration of a drawing apparatus according to the present invention; FIG. FIG. 2(A) shows how the laser is irradiated onto the light reflecting portion, and FIG. 2(B) schematically shows the laser intensity distribution. FIG. 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 irradiated onto the photoresist. FIG. 4 is a diagram showing a situation in which a photoresist is exposed by a step-and-repeat method; FIG. 5(A) shows the position dependence of the measured intensity distribution of the laser reflected from the AA' portion of the micromirror control region C, and FIG. 5(B) shows the patterned photoresist line The distribution (position dependence) of measured width values is shown. FIG. 6(A) shows the position dependence of the measured intensity distribution of the laser reflected from the AA' portion of the micromirror control region C, and FIG. 6(B) shows the patterned photoresist line The distribution (position dependence) of measured width values is shown. FIG. 4 is a diagram showing a setting example of a micromirror control region C; 4 is a graph showing the relationship between the amount of laser exposure and the amount of dimensional variation in resist pattern width after development. FIG. 9A is an enlarged view of a partial region of the light reflecting portion; FIG. 9B is a graph showing a comparison of the timings of the first state and the second state of the micromirror. FIG. 4 is a cross-sectional view of a photoresist patterned by a laser whose irradiation time is controlled for each region by a DMD; 4A to 4C are cross-sectional views showing main steps of a method for manufacturing a halftone mask (multi-tone mask); 4A to 4C are cross-sectional views showing main steps of a method for manufacturing a halftone mask (multi-tone mask); The figure which shows the mechanism which moves an optical system (a DMD is included). FIG. 14A schematically shows circuit patterns to be patterned. FIGS. 14B and 14C show an example of dividing the circuit pattern into exposure sections. The figure which shows the outline|summary of the system of a drawing device. FIG. 10 illustrates correction of areas of micromirrors to suppress pattern dimension variations. 4A to 4C are cross-sectional views showing main manufacturing steps 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 provide a restrictive interpretation in identifying the gist of the present invention. Also, the same reference numerals are given to members of the same or similar type, and description thereof may be omitted.

FIG. 1A shows the main configuration of the drawing apparatus 1. As shown in FIG.
A laser LD (e.g., 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. be. The laser beam reflected by the light reflecting portion 8 of the DMD 4 is projected on a photomask substrate 7 placed on a stage 6 at the same magnification or reduced size by an optical system 5 composed of, for example, a lens, as indicated by a dotted line arrow. be. As the semiconductor laser 2, a single mode can be preferably used.
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. there is
The stage 7 moves in X and Y directions perpendicular to each other, and can move the photomask substrate 7 in a predetermined direction by a predetermined distance.

The light reflecting part 8 of the DMD 4 has a plurality of micromirrors 9 as will be described later, and the tilt angle of each micromirror 9 is electrically controlled. can be changed alternatively, as indicated by the white or black arrows in .
The laser reflected in the direction of the white arrow passes through (passes through) the optical system 5 and is irradiated onto 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 does not irradiate the photomask substrate 7 . By arranging the optical system 5 in this way, it is possible to select whether or not to irradiate the photomask substrate 7 with the laser by means of the DMD 4 .

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

When the laser beam (indicated by the dotted line arrow in FIG. 1(B)) that has entered the light reflecting portion 8 is reflected by the micromirror 9a set at the first tilt angle, for example, as shown in FIG. The light enters the optical system 5 as indicated by the white arrow, and then irradiates the photomask substrate 7 . When the light is reflected by the micromirror 9b whose tilt angle is set to the second tilt angle, it does not enter the optical system 5 as indicated by the black arrow in FIG. ) are arranged as follows.

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 according to the tilt angle of each micromirror 9 . The area irradiated onto the photomask substrate 7 from one micromirror 9 via the optical system 5 is the minimum exposure area (pixel) on the photomask substrate 7 .
By controlling the tilt angle for each micromirror 9, it is possible to flexibly cope with laser drawing of various patterns.
In addition, the inclination angle is an example and is not limited to this.

In this way, the DMD 4 changes the tilt angle of each micromirror 9 to locally change the course of the laser (for each micromirror 9) to irradiate the photomask substrate 7 (the first state). state) and no irradiation state (second state).

FIG. 2(A) shows how the laser is irradiated onto the light reflecting portion 8, and FIG. 2(B) schematically shows the laser intensity distribution in the cross section of the dashed-dotted line ZZ' in FIG. 2(A). show.
A region surrounded by a circle indicated by a dotted line in FIG. 2(A) indicates a laser irradiation region S, and this circle corresponds to a laser spot diameter (for example, 1 [mm]). 2A is a micromirror control area C set within the laser irradiation area S. The rectangular area indicated by solid lines in FIG. The micromirror control area C is set so as to be within the laser irradiation area S without fail, taking into consideration variations in the diameter of the laser spot and variations in the optical axis.

As shown in FIG. 2B, outside the laser irradiation region S, the laser intensity rapidly decreases and becomes 0 (zero), but inside the laser irradiation region S, the laser intensity is ideally is constant, and the micromirror control region C is set in a region where the intensity distribution is highly uniform.
Since the surface of the light reflecting portion 8 of the DMD 4 is not necessarily perpendicular to the incident direction of the laser, the laser irradiation area S is not necessarily a circle, but may be an ellipse to be precise. Also, the micromirror control area C is not limited to a square, and may be a rectangle.

Inside the micromirror control area C, each micromirror is an area in which the first state or the second state can be selectively controlled. Set to state 2.

FIG. 3A shows 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. FIG. 3B is a cross-sectional view showing a state in which the laser LD is reflected by the micromirror 9 and irradiated onto the photoresist 10 formed on the photomask substrate 7 via the optical system 5 .
In FIG. 3A, hatched micromirrors 9a are in the first state, and unhatched micromirrors 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 irradiated onto the photoresist 10 on the photomask substrate 7 in a desired pattern shape (see FIG. 3). (B)). Therefore, the photoresist 10 can be exposed in a desired pattern shape.
Each micromirror 9 in the micromirror control area C constitutes one picture element (pixel) on the photomask substrate 7, and a photoresist pattern is formed as a set of pixels, which is the minimum unit of the exposure area. Become.

The exposure area (for simplicity, referred to as an exposure section) of the photoresist 10 that can be exposed by one exposure process (one drawing process) is an area that can be irradiated by the laser reflected from the micromirror control area C. be.
Therefore, as shown in FIG. 4, when the exposure processing for one exposure section determined in the micromirror control area C is completed, the stage 6 moves the distance corresponding to the size of the exposure section so that continuous pattern formation is possible. The photomask substrate 7 is moved by (L in the figure). After that, exposure processing is performed by controlling the ON state and the second state of the micromirrors 9 of the desired pattern for the next exposure section.

That is, by repeating the exposure processing of the surface of the photomask substrate 7 and the movement of the photomask substrate 7 by a step-and-repeat method, a desired pattern is formed on the entire surface of the photomask substrate 7 (or on the photoresist 10). 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 be relatively moved. Therefore, 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.

FIG. 13 shows an example of the configuration of the drawing apparatus 1 provided with a mechanism for moving the optical system 4. As shown in FIG.
The drawing device 1 includes a first travel guide 16 and a second travel guide 18 .
The longitudinal direction of the first travel guide 16 is parallel to the X direction in the figure, and the longitudinal direction of the second travel guide 18 is parallel to the Y direction in the figure.

The first traveling guide 16 has a fixed reflecting mirror 31 and a movable reflecting mirror 32 inside. A first driving device 17 moves the movable reflecting mirror 32 , DMD 4 and optical system 5 along the first traveling guide 16 . A second drive device 19 moves the first travel guide 16 along the second travel guide 18 .
Therefore, the movable reflecting mirror 32, DMD 4 and optical system 5 are movable in the X and Y directions in the figure.

A laser LD emitted from the semiconductor laser 2 is reflected by the fixed reflecting mirror 31 and irradiates the movable reflecting mirror 32 . After that, the laser beam is reflected by the movable reflecting mirror 32 and irradiates the photomask substrate 7 via the DMD 4 and the optical system 5 . As a result, it becomes possible to scan the laser LD on the photomask substrate 7 in the X direction and the Y direction by using the first and second driving devices 17 and 19 .

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

Since the drawing apparatus 1 includes the light amount detector 15 , the intensity distribution of the laser reflected by the light reflecting portion 8 of the DMD 4 and irradiated onto the photomask substrate 7 can be measured.
The light amount detector 15 uses an image sensor or the like, sets all the micromirrors 9 of the light reflection part 8 of the DMD 4 to the first state, and irradiates the light receiving surface of the light amount detector 15 with the reflected laser beam. It becomes possible to measure the laser irradiation intensity distribution two-dimensionally.
By setting the light receiving surface of the light amount detector 15 at the same height (level) as the irradiated surface of the photomask substrate 7, the intensity can be measured accurately.

As shown in FIG. 15, the drawing apparatus 1 is configured as a system further including a pattern data input unit 51, a storage unit 52, an arithmetic processing unit 53, a DMD control unit 54, a drive system control unit 55, and a light intensity measurement unit 56. may
The light amount measuring unit 56 controls the light amount detector 15 and stores the detected two-dimensional information in the storage unit 52 as image data (two-dimensional array data), for example. The arithmetic processing unit 53 can obtain the in-plane intensity distribution of the laser irradiated from each pixel of the image data, calculate the uniformity of the in-plane intensity distribution, and monitor the state of the light reflecting unit 8. .

5A and 6A show the results of extracting the intensity distribution of the laser reflected from the AA' portion of the micromirror control region C from the measured values of the detected two-dimensional intensity distribution. 5(B) and 6(B) are patterned by laser reflected from micromirror 9 controlled by DMD controller 54 to form a row of 5 μm wide line patterns. 3 shows the actual measured line width of the photoresist.
The micromirrors 9 forming a row of line patterns are extracted according to the pattern data stored in the storage section 52 via the pattern data input section 51, and are controlled to be in the first state.

As shown in FIG. 5A, the actual laser intensity distribution shows a downwardly convex intensity distribution with a finite fluctuation width. As shown in FIG. 5(B), the measured value of the line width of the photoresist exhibits slight periodic fluctuations reflecting the intensity distribution of the laser.

FIG. 6(A) shows the result of measuring the intensity distribution of the reflected laser using a DMD different from the DMD having the intensity distribution shown in FIG. 5(A). The intensity distribution shown in FIG. 6(A) shows a downwardly convex intensity distribution similar to FIG. 5(A), but compared to the laser intensity distribution shown in FIG. .
The uniformity (=standard deviation/average value) of the intensity distribution shown in FIG. 5(A) is 11%, but that of the intensity distribution shown in FIG. 6(A) increases to 23%.
As shown in FIG. 6B, when the variation width of the intensity distribution increases and the uniformity increases (deteriorates), the variation width of the measured value of the line width of the photoresist also increases, and the uniformity of the line width increases ( to degrade.

For example, while the laser intensity distribution was initially shown in FIG. 5A, the laser intensity distribution changes to the intensity distribution shown in FIG. When the uniformity deteriorates, the distribution of the photoresist pattern changes from the distribution shown in FIG. 5B to the distribution shown in FIG. 6B.
In such a case, it is possible to take measures such as exchanging the DMD.

Therefore, by monitoring and managing the intensity distribution of the laser beam reflected by the light reflecting portion 8 of the DMD 4, fluctuations in the line pattern of the photoresist can be suppressed and a predetermined uniformity can be maintained. For example, when the intensity distribution exceeds a predetermined threshold value, for example, a specification value requested by a customer, the arithmetic processing unit 53 of the drawing apparatus 1 displays a warning on a lamp or a display screen to prompt the operator to replace the DMD. Action can be taken. As a result, it becomes possible to control and guarantee the quality of the manufactured photomask.

In order to detect the light intensity, the light intensity may be two-dimensionally detected by the light amount detector 15 with all the micromirrors 9 in the first state. The light intensity may be detected one-dimensionally by the light amount detector 15 in sequence by setting the micromirrors 9 to the first state row by row in the direction parallel to the line indicated by Z'. A pattern for placing the micromirror 9 for detecting the light intensity distribution in the first state can be appropriately set.

In addition, in order to clarify the relationship between the position of the micromirror 9 and the position in the image data of the light quantity detector 15, for example, the micromirror 9 in the micromirror array is set to the cross shape in the first state, and the light quantity detector 15 The intensity distribution may be measured by The crossed micromirrors 9 and the intersection points of the intensity distribution detected by the photodetector 15 are made to correspond to each other. By correlating such intersections at a plurality of locations, the relationship between the position of the micromirror 9 and the coordinates in the image data of the light amount detector 15 can be clarified.

As shown in FIGS. 5(A) and 6(A), both intensity distributions exhibit a relatively flat distribution in the central portion while the intensity increases in the peripheral portion. This tendency is the same in the direction perpendicular to AA', and although the intensity distribution is relatively flat near the center of the laser irradiation area S, the intensity increases in the peripheral area of the laser irradiation area S. do.
Therefore, by selecting a region exhibiting a relatively flat intensity distribution, the uniformity of the resist pattern is reduced (improved).
A region indicated by BB' in FIGS. 5A and 6A is a region where the uniformity of the light intensity distribution is improved.

As shown in FIG. 7, from the light intensity distribution detected by the light amount detector 15, the micromirror control region C is set to, for example, B The area determined by -B' may be set again. Similarly, in the direction perpendicular to BB', the variation width is set to be smaller than the threshold value.
For example, a threshold is set according to specifications (customer-requested values) such as the minimum line width and minimum spacing of the photomask to be manufactured, and micromirror 9 micromirror control regions C may be set

If the micromirror control area C is set narrow, the exposure processing time by the step-and-repeat method is lengthened, so it may be appropriately set according to the required photomask specifications.
Since the DMD 4 can control each micromirror 9 independently, the setting of the micromirror control area C can also be easily controlled.

By setting the spatial resolution of the light intensity detection of the light amount detector 15 to be smaller than that of the pixels for writing the photoresist, the laser irradiation intensity for each pixel can be measured. By clarifying the correlation between the coordinates of the intensity distribution data of the light amount detector 15 and the positions of the micromirrors by the above method, the intensity of the laser reflected by each micromirror can be measured. Therefore, by multiplying the time for each micromirror to maintain the first state by a coefficient that is inversely proportional to the laser reflection intensity, the intensity distribution may be corrected and the photoresist may be uniformly irradiated with the laser. However, such a control method also has the drawback of complicating the control of the micromirror.

FIG. 8 shows the correlation between the amount of laser exposure and the amount of dimensional variation in the resist pattern width after development, plotting the amount of dimensional variation on the vertical axis and the amount of laser exposure on the horizontal axis.
The exposure dose is normalized with the exposure dose for forming a resist pattern with a line width of 5 [μm] being 1. Such a relationship between the exposure amount and the resist pattern dimension after development depends on the resist to be used, and is obtained by actual measurement for each pattern dimension (for example, for a plurality of line widths, space widths, or a plurality of hole diameters). be able to.

From the laser intensity distribution of FIG. 5A (or FIG. 6A) and the correlation data between the exposure amount and the resist pattern dimension of FIG. 8, FIG. 5B (or FIG. 6B) A distribution of pattern dimensions (widths) can be calculated.
By storing the basic data on the correlation between the exposure amount and the pattern dimension shown in FIG. can be calculated automatically. Further, by acquiring correlation data for a plurality of resists, it is possible to present candidates for the photoresist to be used.

FIG. 9A is an enlarged view of a partial region of the light reflecting portion 8 of the DMD 4 for manufacturing a multi-tone photomask. As shown in FIG. 9A, the light reflecting portion 8 has three regions Ra (cross-hatched region in the drawing), Rb (single-hatched region in the drawing), and Rc (white-painted region in the drawing). there is

FIG. 9B shows the first state (“ON” state) and the second state (“OFF” state) of the micromirrors 9a, 9b, and 9c in the regions Ra, Rb, and Rc when one exposure process is performed. "state)" is a graph showing the timing. In the region Rc, each micromirror 9c stays in the first state for zero (first control time), that is, always maintains the second state. In the region Ra, each micromirror 9a is in the first state for a predetermined period (third control time ta) and is otherwise maintained in the second state. The period remains in the second state. As shown in FIG. 9B, tb is set shorter than ta. For example, when ta is 100%, tb is 30% to 50%.

Therefore, the periods (exposure times) during which the laser is reflected in the three regions Ra, Rb, and Rc and irradiated onto the photomask substrate 7 during one exposure process are ta, tb, and tc (none), respectively. .
Note that the irradiation period (exposure time) does not necessarily have to be continuous, and the total period for maintaining the first state may be, for example, ta and tb.

FIG. 10 shows the film thickness of the photoresist 10 patterned using the drawing apparatus 1. As shown in FIG. Laser LD is reflected at regions Ra, Rb, and Rc shown in FIG. 10 to irradiate regions Pa, Pb, and Pc of photoresist 10 on photomask substrate 7, respectively. Since the regions Pa, Pb, and Pc of the photoresist 10 have different exposure times, the 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).

A desired film thickness of the photoresist 10 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, it is possible to determine the exposure time for forming the photoresist 10 with a desired film thickness in each region. The determined exposure time can be controlled by setting the time to maintain the first state of each micromirror 9 of DMD 4 . Therefore, by controlling the laser irradiation using the DMD 4, any exposure time can be set in any region with one micromirror 9 as a unit.

FIG. 10 shows an example of forming the photoresist 10 with three different film thicknesses (Ha, Hb, 0). In this way, the light reflecting section 8 is divided into a plurality of regions, for example, first to n-th (n≧3) regions, and each micromirror arranged in each region is in the first state. By setting n control times (including time 0), resist patterns having n different film thicknesses (including film thickness 0) can be formed. Therefore, it is also possible to form a photoresist with three or more different film thicknesses.
It is also possible to form a photoresist with a stepwise sloped cross-section.

In addition, when the exposure time changes as described above, the pattern dimension of the photoresist fluctuates. Therefore, the width of the area of the micromirror 9 in the micromirror control area C may be changed based on the correlation between the exposure amount and the pattern dimension, as will be described later.

After exposing the photoresist 10 using the laser reflected from the light reflecting portion 8, the photomask substrate 7 is moved, and the exposure process and the movement of the photomask substrate 7 are repeated by a step-and-repeat method to obtain a plurality of film thicknesses. A pattern of photoresist 10 having a pattern can be formed on the photomask substrate 7 .
It should be noted that a photoresist having a plurality of different film thicknesses can be formed by one exposure process even for a positive photoresist.

If a conventional drawing apparatus is used to form a photoresist pattern with such different film thicknesses, it is necessary to expose the photoresist by a plurality of drawing processes. Therefore, it is necessary to take into consideration the misalignment of patterns in different drawing processes, and to include in the pattern a width (dimension) corresponding to the margin of overlay.
However, when the drawing apparatus 1 using the DMD 4 is used as in the present embodiment, the photoresist 10 having different film thicknesses can be patterned by one exposure, so there is no need for pattern design considering the overlay margin. , it is possible to miniaturize the dimension corresponding to the overlay margin. Furthermore, the design rule for the overlay margin is relaxed, pattern design is facilitated, and pattern designer's labor is reduced.

FIG. 11 is a cross-sectional view showing main steps of a method for manufacturing a halftone mask (multi-tone mask).
As shown in FIG. 11A, 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 made of quartz or the like by vapor deposition or sputtering. A photomask blank is prepared, and a 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. 11B, the photoresist 10 is exposed by controlling the exposure time in units of the micromirrors 9 of the DMD 4, and then developed to pattern the photoresist 10. Next, as shown in FIG.
As described above, since the exposure time can be controlled for each micromirror 9, the first photoresist 10a and the second photoresist 10b having different film thicknesses can be simultaneously formed by one exposure processing step. Further, it is also possible to form patterns of the photoresist 10 having three or more different film thicknesses.

Next, as shown in FIG. 11C, using a photoresist 10 (a first photoresist 10a and a second photoresist 10b) as a mask, a known wet etching method or dry etching method is performed to remove the light-shielding film 13 and the semiconductor film. The permeable film 12 is sequentially etched.

Next, as shown in FIG. 11D, the entire surface of the photoresist 10 is 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 is reduced (Ha-Hb or less) but left. is possible.

In the process of FIG. 11C, when at least one of the light-shielding film 13 and the semi-transmissive film 12 is etched by a dry etching method, the etching gas (etchant) is optimized and the selection ratio is adjusted so that the photoresist 10 is simultaneously etched. Etching may be performed to remove portions of the second photoresist 10b.

Incidentally, the film thickness of the photoresist may be determined from the viewpoint of the process such as the etching resistance to the etchant, the uniformity of the amount of etching back, and the like.

Next, as shown in FIG. 12E, using the photoresist 10 (first photoresist 10a) as a mask, the light shielding film 13 is selectively etched by wet etching or dry etching. Etching of the semi-transmissive film 12 is suppressed by using a known etchant (etching liquid, etching gas) and setting the selectivity to a sufficiently high value (for example, 10 or more).

Next, as shown in FIG. 12F, the photoresist (first photoresist 10a) is removed by an ashing method or the like.
Through the above steps, a region 3 where the transparent substrate 11 is exposed, a region where only the semi-transmissive film 12 is formed on the transparent substrate 11, and a region where the semi-transmissive film 12 and the light shielding film 13 are formed on the transparent substrate 11 are provided. A grayscale halftone mask 14 can be obtained.

Note that the method for forming a halftone mask, which is a three-tone mask, has been described above. It is also possible to pattern the photoresist 10 to have three or more film thicknesses by controlling the first state time of the micromirrors 9 of the DMD 4 with respect to the photoresist 10 .
This makes it possible to manufacture photomasks with even more tones.
In order to form patterns of semi-transmissive films with different thicknesses, etching back of resist patterns with different thicknesses and partial etching (half-etching) of the semi-transmissive film may be repeated in sequence.

In addition, from the relationship between the exposure time and the pattern width shown in FIG. 8, the pattern width may change if the exposure time is changed depending on the region in order to form different resist film thicknesses.
For example, in FIG. 9A, the exposure amount is reduced in region Rb as compared with region Ra, and the pattern width is reduced (thinned). Therefore, as shown in FIG. 16A, the width of the region (region Rb) of the micromirror 9b corresponding to the region with a small amount of exposure is reduced by the variation of the pattern width (region Ra) of the micromirror 9a. It may be set (corrected) so that it becomes wider by the amount of decrease. Alternatively, as shown in FIG. 16B, conversely, the area (area Ra) of the micromirror 9a corresponding to the area where the amount of exposure is small may be reduced by the variation of the pattern width.
Dotted lines in FIGS. 16A and 16B indicate regions before correction.

Hereinafter, a method for forming a resist pattern of a photomask (halftone mask) will be described in detail, taking as an example the case of forming a three-gradation halftone mask.

(1) Using a design tool such as CAD, the pattern data (coordinate data) of the transparent portion (light transmitting portion or transparent substrate exposed portion) that is the first pattern region, and the pattern of the light shielding portion that is the second pattern region. Desired pattern data 20 (for example, , electrical circuit patterns) are determined (designed). The pattern data 20 are stored in the storage unit 52 via the pattern data input unit 51 of the drawing apparatus 1 .
(2) The intensity distribution of the laser beam reflected from the reflecting portion 8 of the DMD 4 is measured by the light amount measuring section 56 using the light amount detector 15 and the measurement result is stored in the storage section 52 .
The laser intensity distribution may be periodically measured in advance and stored in the storage unit 52 of the drawing apparatus 1, or may be measured each time a photomask is manufactured.

(3) The arithmetic processing unit 53 determines the micromirror control region C so that the uniformity of the pattern width satisfies the threshold value based on the light amount measurement result. The threshold is determined depending on design requirements such as customer specifications.
(4) The pattern data 20 is divided into exposure sections 21 defined by the micromirror control areas C (irradiation areas on the photoresist of the laser reflected by the micromirror control areas).
At this time, it is also possible to adjust so that the important circuit portion of the pattern data 20 does not overlap the boundary portion of the divided exposure section 21 .
By doing so, it is possible to avoid fluctuations in the pattern width of the important circuit portion even when the exposure amount fluctuates.
That is, an important circuit portion is specified and designated in advance as an undivided portion, and the size of the exposed portion 21 is adjusted around the undivided portion so that the boundary portion of the exposed portion 21 does not overlap with the undivided portion. should be changed with

FIG. 15 shows an example of dividing the circuit pattern 18 (FIG. 14A) into exposure sections 21 (FIGS. 14B and 14C). FIGS. 14B and 14C show examples of division into exposure sections 21 corresponding to different micromirror control regions C depending on the threshold value.

(5) Determine the photoresist film thickness corresponding to each region from the requirements of the manufacturing process.
(6) The exposure time of the photoresist corresponding to the first, second, and third pattern regions (transparent portion, light shielding portion, and semi-transmissive portion) is measured in advance on the sensitivity curve and the photoresist film corresponding to each region. Calculate from the thickness.
From the calculated exposure time, the control conditions (tilt angle (that is, first state or second state) and its holding time) of the micromirror 9 corresponding to the first, second and third pattern regions are determined. do.

Here, the micromirrors corresponding to the first, second and third pattern regions refer to micromirrors that reflect the laser and irradiate the first, second and third pattern regions, respectively. The pattern area (Pc in FIG. 10) is irradiated with a laser, and the area (Rc in FIG. 10) composed of micromirrors is the first micromirror area, and the second pattern area (Pa in FIG. 10) is irradiated with a laser. A region composed of mirrors (Ra in FIG. 10) is referred to as a second micromirror region, and a region composed of micromirrors (Rb in FIG. 10) for irradiating laser onto a third pattern region (Pb in FIG. 10) is referred to as a third micromirror region. It is called a micromirror area. The first, second and third micromirror regions belong to the micromirror control region C. FIG.

The micromirror control conditions including the arrangement (coordinate) information in the micromirror array of the micromirrors 9 belonging to the first, second and third micromirror regions and the duration of the first state are stored in the storage unit 52. Keep
Note that the sensitivity curve may be stored in advance in the storage unit 52 and the exposure time may be calculated by the arithmetic processing unit 53 .

(7) The first, second and third micromirror regions corresponding to the first, second and third pattern regions are determined in units of micromirrors based on the correlation between the exposure amount and the pattern width variation obtained in advance. After correcting (enlarging or reducing), the corrected arrangement (coordinate) information of the micromirror 9 in the micromirror array is stored in the storage unit 52 .

(8) The corrected micromirror control conditions for the first, second, and third micromirror regions are divided for each exposure section 21 by the arithmetic processing section 53 and stored in the storage section 52 .
The micromirror control condition for the regions other than the first, second, and third micromirror regions, ie, the micromirror control region C, is to always maintain the second state.

(9) A photomask substrate 7 having a photoresist 10 formed thereon is prepared on a photomask blank in which a light transmission portion and a light shielding portion are formed in this order on a transparent substrate, and placed on the stage 6 .
(10) The micromirror 9 of the DMD 4 is controlled by the DMD controller 54 according to the stored micromirror control conditions corresponding to each exposure section 21, and the photoresist 10 on the photomask substrate 7 is irradiated with the laser.

(11) At least one of the stage 6, the first driving device 17 and the second driving device 19 is driven by the drive system control unit 55, and the stage 6 (and the stage 6) is moved by a distance corresponding to one exposure section. The relative distance between the photomask substrate 7) placed on the optical system 5 and the optical system 5 is moved.
In this step, the relative distance between the photomask substrate 7 and the optical system 5 is moved. good too. Thus, the exposure section on the photoresist 10 can be moved to expose all areas on the photoresist 10 that require exposure processing.
Relative movement can be performed, for example, in each direction of two orthogonal axes, the X-axis and the Y-axis of a so-called orthogonal coordinate system.

When the optical system 5 is moved, it is necessary to configure so that the laser reflected from the micromirror 9 in the first state can irradiate the photomask substrate 7 via the optical system 5 . Therefore, as shown in FIG. 13, the DMD 4 is moved together with the optical system 5 .

(12) The arithmetic processing unit 53 controls the driving system control unit 55 and the DMD control unit 54, repeats (10) and (11) according to the step-and-repeat method, and removes the photoresist formed on the photomask substrate 7. 10 are exposed sequentially.

Through the above procedure, exposure of the photoresist 10 on the photomask substrate 7 is completed, and then patterning of the photoresist 10 is completed by development.
After that, the photomask can be completed by the manufacturing process described with reference to FIGS.

Note that the above steps can be replaced as appropriate.
For example, (4) may be performed after (7). That is, the pattern data (coordinate data) of the first, second, and third pattern regions are corrected based on the correlation between the exposure dose and the pattern width variation obtained in advance, and then each pattern data is subjected to micromirror control. The area C may be divided into the exposure sections 21 determined, and the control conditions (tilt angle and its holding time) for each micromirror 9 of the DMD 4 may be determined for each exposure section 21 and stored in the storage section 52 . .

According to the drawing apparatus 1, it is possible to form photoresist patterns with different film thicknesses on a photomask substrate with a single exposure process, and it is also possible to satisfy the demand for a desired pattern variation width. becomes. As a result, it is possible to reduce the number of manufacturing steps of the multi-tone photomask, and further contribute to miniaturization of the pattern of the photomask.
A photomask manufactured using this drawing apparatus 1 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 reflecting mirror 31 fixed reflecting mirror 32 movable reflecting mirror 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 amount detector 16 First traveling guide 17 First driving device 18 Second traveling guide 19 Second driving device 20 Pattern data 21 Exposure section 51 Pattern data input unit 52 Storage unit 53 Arithmetic processing unit 54 DMD control Part 55 Drive system control part 56 Light quantity measurement part 100 Transparent substrate 101 Semi-transmissive film 101a Semi-transmissive film pattern 102 Light-shielding films 102a, 102b Light-shielding film pattern 103 Photoresist 103a Photoresist pattern 104 Photoresist 104a Photoresist pattern

Claims (4)

semiconductor laser and
a DMD having a micromirror array composed of a plurality of micromirrors whose tilt angles can be changed independently in the optical path of the laser irradiated from the semiconductor laser ; a stage; an optical system; a storage unit; comprising a control unit, a light amount measurement unit, and an arithmetic processing unit,
the storage unit stores a micromirror control condition that defines a time for maintaining a first state and a second state determined by the tilt angle for each of the micromirrors of the DMD;
The light amount measuring unit measures the intensity distribution of the laser reflected from the micromirror in the first state,
The arithmetic processing unit sets a micromirror control region such that the variation width of the intensity distribution is smaller than a preset threshold value,
The DMD control unit always maintains the second state of the micromirrors other than the micromirror control area according to the micromirror control conditions, and controls each of the micromirrors in the micromirror control area,
The optical system irradiates only the laser reflected from the micromirror in the first state in the micromirror control area onto the photoresist formed on the photomask substrate placed on the stage. A photomask drawing apparatus characterized by: The micromirror control conditions stored in the storage unit are for the micromirrors belonging to a first micromirror area, a second mirror area, and a third mirror area that maintain the first state for different times. 2. The drawing apparatus according to claim 1 , further comprising a control condition. The storage unit stores correlation data between a laser exposure dose and a photoresist pattern width,
3. The writing apparatus according to claim 2 , wherein said first micromirror area, said second mirror area and said third mirror area are corrected from said correlation data. The drawing device
Equipped with a drive system control unit,
The driving system control unit moves the relative position between the optical system and the stage, and exposes the photoresist formed on the photomask substrate placed on the stage by a step-and-repeat method. 4. The drawing apparatus according to any one of claims 1 to 3, characterized by:

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