JP5054889B2 - Exposure method and exposure apparatus - Google Patents

Description

  The present invention relates to an exposure method and an exposure apparatus for a photosensitive material formed on a semiconductor wafer, and more particularly to a technique suitably applied to exposure for forming a photolithography pattern (color filter) on a radical polymerization type UV curable resin.

When the radical polymerization type UV curable resin is exposed, the radical polymerization type UV curable resin is cured by a radical polymerization reaction. During the curing, heat damage due to heat energy generated by absorbing ultraviolet rays and radical concentration distribution are generated in the film of the radical polymerization type UV curable resin. FIG. 9A shows the distribution of thermal damage in the film when the radical polymerization type UV curable resin is collectively exposed to a predetermined exposure amount. The horizontal axis represents the magnitude of thermal damage, and the vertical axis represents the film thickness. Although the thermal damage is small in the lower layer of the film, the thermal damage becomes larger as the surface becomes closer like the middle layer and the upper layer of the film. FIG. 9B shows the radical concentration distribution in the film when the radical polymerization type UV curable resin is collectively exposed. The horizontal axis represents the radical concentration height, and the vertical axis represents the film thickness. Although the radical concentration is low in the lower layer of the film, the radical concentration becomes higher as the surface becomes closer, as in the middle layer and upper layer of the film. The tendency for the thermal damage to increase and the radical concentration to increase becomes stronger as the exposure amount increases and the upper layer of the film.
As described above, when the thermal damage is large and the radical concentration is high, the performance of the circuit pattern profile formed by photolithography deteriorates, and a predetermined fine circuit pattern cannot be formed. In particular, when the radical polymerization type UV curable resin has an optimum photolithographic pattern profile performance at an appropriate illuminance, the optimum performance cannot be obtained if an exposure machine having an illuminance higher than the appropriate illuminance is used. Therefore, it is desirable to expose a photoconductor such as a radical polymerization type UV curable resin under the optimum conditions of the photoconductor.

For example, Patent Document 1 discloses a technique in which a single exposure is performed at a lower exposure amount than a predetermined exposure amount, and a predetermined exposure amount is obtained by repeating the exposure a plurality of times. In Patent Document 1, in order to prevent the temperature of the lens from rising during exposure and causing adverse effects on the optical system of the exposure apparatus, the exposure is intermittently repeated a plurality of times with an interruption time during the exposure. It is. As described above, Patent Document 1 intermittently repeats exposure at the same location of a semiconductor wafer a plurality of times, and performs a necessary amount of exposure at the same location.
JP-A-1-270225

When the radical polymerization type UV curable resin is collectively exposed as described above, the thermal damage is large and the radical concentration is high as shown in FIG. Further, when the same portion is repeatedly exposed N times as in Patent Document 1, an exposure interruption time t4 is taken for each exposure as shown in FIG. 6, so that the exposure processing time T1 for stepping and repeating the entire semiconductor wafer is T1 = [t3 · N + t4 · (N−1)] · X + t2 (X−1)
It becomes. Here, t2 is the stage moving time between shots, t3 is the exposure time for one shot, t4 is the interruption time, X is the number of shots, and N is the number of repetitions.
The exposure time Sr for exposing the semiconductor wafer by step-and-repeat is (Sr = t3 · N · X), and the stage moving time Sd is (Sd = t2 (X−1)). The exposure interruption time St is (St = t4 · (N−1) · X). Therefore, Patent Document 1 becomes longer by the exposure interruption time.
In view of the above problems, the present invention provides an exposure method and an exposure apparatus that have low thermal damage, a low radical concentration, and a short exposure time.

In the exposure method of the present invention, light emitted from a UV light source is imaged on a semiconductor wafer through one reticle, a wafer stage on which the semiconductor wafer is placed is moved, and exposure shot 1 to exposure shot X by performing exposure to a step-and-repeat exposure Return to exposure 1 a N times repeated exposure method, suitable equivalent exposure time, or when the appropriate illumination, a radical polymerization type UV having an optimal photolithography pattern profile performance Each exposure shot for exposing the photoconductor to a semiconductor wafer coated with a photoconductor made of a curable resin adjusts the optimal exposure time, the optimal illuminance, or both the exposure time and the illuminance, thereby providing a predetermined exposure. An exposure step of exposing at 1 / N of the amount,
The exposure time To per one semiconductor wafer is expressed by the following formula, and the above-mentioned problem is solved.
To = [t3 * X + t2 * (X-1)] * N + t5 * (N-1)
Where t3 is the exposure shot time
X is the number of exposure shots
t2 is the movement time of the wafer stage during step-and-repeat
t5 is a time for returning the wafer stage to the initial position. In the exposure method of the present invention, the exposure time is adjusted to 1 / N of a predetermined exposure amount by adjusting the opening time of the shutter. It is characterized by doing.
The exposure method of the present invention, the illumination intensity, and characterized in that the voltage adjustment of the UV light source, the insertion distance adjustment or exposure adjustment plate between the UV light source and the semiconductor wafer is exposed with a predetermined exposure amount of 1 / N To do.
Further, the exposure method of the present invention is a prepolymer having a photosensitive body having an unsaturated group such as an acrylic group or a methacryl group, a system in which a vinyl monomer such as styrene is dissolved in an unsaturated polyester, or a thiol-olefin resin system. It is a radical polymerization type UV curable resin (photo radical polymerization initiator: benzophenone series, benzoin ether series, acetophenone series, thioxanthone series, etc.) .
In the exposure method of the present invention, the N is 2 or more and 10 or less .
The exposure method of the present invention, the exposure amount of the exposure process, initially less than 1 / N of a predetermined exposure amount, the end is characterized by greater than 1 / N of a predetermined exposure amount.
The exposure apparatus of the present invention is characterized by comprising a control unit for performing the projection exposure method as described above .

In the exposure method of the present invention, the semiconductor wafer is exposed at 1 / N of the required exposure amount, so that the thermal damage to the surface layer of the radical polymerization type UV curable resin and the uneven concentration distribution of radicals generated in the film are reduced. Therefore, a good pattern profile and line width characteristic can be obtained regardless of the ultraviolet exposure illuminance of the exposure machine. And, it is possible to form a photolitho pattern with good performance using the same radical polymerization type UV curable resin even in exposure machines having greatly different ultraviolet illuminances, and the radical polymerization type UV curable resin can obtain the same line width characteristics. it can. If the present invention is used, when a radical polymerization type UV curable resin having an optimum photolithographic pattern profile performance at an appropriate illuminance is used, exposure can be performed with the optimum illuminance. Moreover, the performance of the pattern profile can be controlled (improved) for the radical polymerization type UV curable resin once introduced without changing the composition and additives.
In addition, since the exposure interruption time can be taken naturally by performing exposure by repeating step and repeat N times, the present invention significantly increases the processing time compared to the exposure method using the conventional intermittent exposure method that takes the exposure interruption time. Can be shortened.
The exposure apparatus of the present invention adjusts the exposure amount by setting the exposure time (exposure shutter opening time) to 1 / N or using a UV light source having an illuminance of the exposure amount 1 / N. It can be carried out.

  The exposure method of the present invention is configured using a reduced projection exposure apparatus as shown in FIG. The exposure apparatus condenses light 2 emitted from a UV light source 1 such as an ultra-high pressure mercury lamp by a condenser lens 3, transmits this light through a reticle 4 on which a predetermined circuit pattern is formed, and further reduces a lens 5. Thus, an image is formed on the semiconductor wafer 6. As a result, the circuit pattern formed on the reticle 4 is reduced and projected onto the semiconductor wafer 6, and the photosensitive layer (radical polymerization type UV curable resin) applied on the semiconductor wafer is exposed. The semiconductor wafer 6 is placed on a wafer stage 7 that can move in the X and Y directions, and step and repeat exposure is performed by moving the wafer stage 7 in the X and Y directions. As the light source, i-line, g-line, KrF, ArF, F2, KR2 excimer laser, or electron beam may be used. In addition, as a photosensitive layer, a prepolymer having an unsaturated group such as an acrylic group or a methacryl group, a system in which a vinyl monomer such as styrene is dissolved in an unsaturated polyester, a radical polymerization type UV curable resin such as a thiol-olefin resin system ( Photo radical polymerization initiators: benzophenone series, benzoin ether series, acetophenone series, thioxanthone series, etc.) can be used. Further, instead of the reticle, a phase difference plate may be used.

In the exposure process on the semiconductor wafer according to the present invention, as shown in the explanatory diagram of FIG. 2A, the exposure shot 1, the exposure shot 2,... And repeat exposure is performed. The exposure amount of each exposure shot at this time is 1 / N of the predetermined exposure amount E. Since the exposure amount is the product of the illuminance of the light source and the exposure time, the exposure time is set to 1 / N without changing the illuminance of the light source, or the illuminance of the light source is set to 1 / N without changing the exposure time. Or by changing both the exposure time and the illuminance so that the exposure amount becomes 1 / N. For adjusting the exposure time, the opening time of the exposure shutter is set to 1 / N. The illuminance adjustment includes a method of adjusting the voltage of the UV light source, a method of adjusting the distance from the surface of the semiconductor wafer by changing the position of the UV light source, and a method of inserting an exposure adjustment plate between the light source and the semiconductor wafer. In particular, when the photosensitive layer (radical polymerization type UV curable resin) has an optimum exposure time (exposure shutter opening time) or an optimum photolithographic pattern profile performance at an appropriate illuminance (the above-mentioned photo radical polymerization initiator), The exposure is performed with the optimum exposure time (exposure shutter opening time) or with the optimum illuminance. In the present invention, this step-and-repeat is repeated N times.
FIG. 2B shows an exposure sequence when exposure is performed with the exposure time (exposure shutter opening time) set to 1 / N without changing the illuminance of the UV light source in the present invention, and exposure shot 1 with exposure amount E / N. , Exposure shot 2,..., Step and repeat until exposure shot X.
The exposure time for one shot is t3. The stage moving time for each exposure shot is t2. Next, the wafer stage 7 is returned to the initial position for repeated exposure. The time to return to this initial position is t5. Then, the second exposure is performed. This exposure is performed N times. Thereby, a predetermined exposure amount E is irradiated onto the semiconductor wafer.

  In the present invention, by setting the exposure amount of each exposure shot to 1 / N of the predetermined exposure amount E, the exposure amount per time can be set to E / N. In the present invention, when the exposure time (exposure shutter opening time) is set to 1 / N without changing the illuminance of the UV light source, it is 2 from the first exposure shot of the same chip (or the same chip group) on the semiconductor wafer. The interval between exposure shots is the step-and-repeat time for each semiconductor wafer. If only the time during which exposure is not performed is calculated, the stage movement time is 0.3 seconds, and the wafer stage is returned to the initial position. When the time of 3 is 3 seconds and the number of exposure shots is 100, 32.7 seconds. In addition to this, the time required for exposure is added, so that a sufficient exposure interruption time can be taken. In the present invention, since the exposure interruption time is sufficiently long, the thermal damage is almost uniformly reduced from the lower layer to the upper layer as shown in FIG. Further, as shown in FIG. 3B, the radical concentration is almost uniformly lowered from the lower layer to the upper layer.

  As an example, the pattern profile and line width characteristics as shown in FIG. 4 (shape A) are obtained by batch exposure with an ultraviolet light exposure amount E [mJ / cm2] with an exposure machine having a color resist S of ultraviolet illuminance A [mW / cm2]. Suppose that it is obtained. If this is performed in the same manner with an exposure machine having a high illuminance B [mW / cm 2] (for example, B> A × 2), the pattern profile is deteriorated and the line width characteristic is also deteriorated as shown in FIG. 4 (shape B-1). . On the other hand, by using the divided exposure method as in the present invention, the ultraviolet exposure amount E [mJ / cm2] necessary for the color resist is divided into N parts in an exposure machine with high illuminance B [mW / cm2], and ultraviolet exposure is performed. The amount E / N [mJ / cm2] is divided and exposed to the same portion N times. Here, if the division number N is 2, 4, and 8, the pattern profile is improved as the division number N increases as shown in FIG. 4 (shapes B-2, B-4, and B-8). When the number of divisions N is 8, the pattern profile is better than that of an exposure machine with illuminance A [mW / cm2], and it has the same line width characteristics as an exposure machine with illuminance A [mW / cm2]. It can be seen that the thermal damage to the film and the concentration distribution of radicals generated in the film are reduced, thereby preventing and improving the adverse effect on the pattern profile. The number of divisions may be determined in consideration of the characteristics of the photoconductor, the shape of the circuit pattern, restrictions on the manufacturing process, etc., but 2 to 10 is usually appropriate. If it is 2 or less, thermal damage and radical concentration increase, and if it is 10 or more, the production time becomes long.

  Here, in the color resist S, when the division exposure method of Patent Document 1 is used, when the exposure interruption time t4 having the same line width characteristic as that of the present invention when the division number N is 8, as shown in FIG. It will be 3.5 seconds. The horizontal axis in FIG. 5 is the exposure interruption time, and the vertical axis is the shift amount from the line width target, that is, the extra size (μm) of the pattern remaining portion. That is, when the exposure interruption time is 0 second, the extra size of the pattern remaining portion is 0.16 μm. When the exposure interruption time is 0.3 seconds, the size of the pattern remaining portion is 0.05 μm. When the exposure interruption time is 3.5 seconds or more, the extra size of the pattern remaining portion becomes zero. Thus, it can be seen that the exposure interruption time is required to be 3.5 seconds or more in order to obtain a good pattern with the color resist S. In the embodiment of the present invention, the time for the wafer stage 7 to return to the initial position is 32.7 seconds even if the exposure time is excluded, and it is longer if the exposure time is included. .

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications based on the technical idea of the present invention are possible. For example, determine how many times the required exposure is performed and how to divide the exposure, etc., depending on the necessity of the composition of the subject irradiation object, the illuminance of the exposure machine, the line width dimension, etc. Is possible. That is, the divided exposure amounts may or may not be the same each time. The initial exposure amount may be less than 1 / N, and the final exposure amount may be greater than 1 / N. It is also possible to balance the pattern profile and the line width dimension by, for example, increasing / decreasing the divided exposure by N ± α times the ultraviolet exposure amount E / N [mW / cm 2].
By the way, it is possible to obtain a better pattern profile by using the technique of the present invention even in the above-described exposure apparatus having the illuminance A [mW / cm 2], and the line width dimension at that time can be adjusted by resizing the mask pattern. good.

In the present invention, FIG. 2B shows an exposure sequence in which the illuminance of the UV light source is not changed and the exposure time (exposure shutter opening time) is set to 1 / N. Here, the fact that the illuminance of the UV light source is not changed specifically means that it is the same as the illuminance in the case of batch exposure as shown in FIG. The exposure time To per semiconductor wafer in this embodiment can be calculated as follows. Assuming that exposure shot time t3, exposure shot count X, stage movement time t2 during step-and-repeat, repetition count N, and time t5 for returning the wafer stage to the initial position,
To = [t3 * X + t2 * (X-1)] * N + t5 * (N-1)
It becomes. Here, the total time t1 of the exposure shot is t1 = t3 · N
Then,
To = t1, X + t2, (X-1), N + t5, (N-1)
It is.
Excluding the exposure time t1 · X, and calculating only the non-exposure time So, t2 is 0.3 seconds, t5 is 3 seconds, X is 100 times, and N is 8 times.
So = t2 * (X-1) * N + t5 * (N-1)
= 0.3 * (100-1) * 8 + 3 * (8-1)
= 237.6 + 21≈259 (seconds)
It becomes.
(Comparative example)

  FIG. 6 shows intermittent exposure with an exposure interruption time as described in Patent Document 1. FIG. 6A is an explanatory diagram of exposure shots on a semiconductor wafer, where exposure shot 1, exposure shot 2,... Are sequentially performed. As shown in the exposure sequence in FIG. 6B, there is an exposure interruption time t4 in one exposure shot. In the case of this comparative example, the exposure illuminance per time can be reduced to 1 / N, where N is the number of exposures, so the thermal damage in this case is comparable to that of the present invention as shown in FIG. Can be reduced. Further, the radical concentration is comparable to that of the present invention as shown in FIG.

In the exposure process on the semiconductor wafer of this comparative example, as shown in the explanatory diagram of FIG. 6A, exposure and interruption are repeated N times on the exposure shot 1 on the chip (or chip group) on the semiconductor wafer 6. When an exposure shot is completed with one chip (or chip group), the stage is moved to the next chip (or chip group), and exposure and interruption are repeated N times in exposure shot 2. This exposure sequence is shown in FIG.
The exposure time T1 per one semiconductor wafer is, as described above, T1 = [t3 · N + t4 · (N−1)] · X + t2 (X−1)
It is. The exposure time Sr is (Sr = t3 · N · X = t1 · X), and the stage moving time Sd is (Sd = t2 (X−1)). The exposure interruption time St is (St = t4 · (N−1) · X). Excluding the exposure time Sr and calculating only the non-exposure time Sd + St, if t2 is 0.3 seconds, t4 is 3.5 seconds, X is 100 times, and N is 8 times,
Sd + St = t2 * (X-1) + t4 * (N-1) * X
= 0.3 * (100-1) + 3.5 * (8-1) * 100
= 29.7 + 2450≈2480 (seconds)
It becomes. Compared to the present invention, the time is about 9 times or more.
(Reference example)

As a reference example, the case of batch exposure is shown in FIG. FIG. 8A shows an explanatory diagram of an exposure process on a semiconductor wafer, and FIG. 8B shows an exposure sequence. Each exposure shot is exposed with a necessary exposure amount. The exposure time T2 in FIG. 8 is T2 = t1 · X + t2 · (X−1)
It is. t1 · X is the exposure time, and t2 · (X−1) is the total stage moving time. If t2 is 0.3 seconds and the number of shots X is 100, the stage moving time is 29.7 seconds. In the case of collective exposure, since exposure is performed with a large exposure amount, the thermal damage in this case increases as shown in FIG. 9A, and the radical concentration increases as shown in FIG. 9B.

It is a figure explaining the structure of a reduction projection exposure apparatus. It is explanatory drawing of the exposure process on the semiconductor wafer of this invention, and explanatory drawing of an exposure sequence (When illumination intensity of UV light source is not changed and exposure time (exposure shutter opening time) is set to 1 / N). It is a figure explaining the thermal damage at the time of exposing with the exposure apparatus of this invention, and the change of a radical concentration. It is explanatory drawing of a pattern profile. It is a figure explaining the relationship between exposure interruption time and the amount of shifts from a line width target. It is explanatory drawing of the exposure process on the semiconductor wafer of a comparative example, and explanatory drawing of an exposure sequence. It is a figure explaining the thermal damage at the time of exposing with the exposure apparatus of a comparative example, and the change of a radical concentration. It is explanatory drawing of the exposure process on the semiconductor wafer of a reference example, and explanatory drawing of an exposure sequence. It is a figure explaining the thermal damage at the time of exposing with the exposure apparatus of a reference example, and the change of a radical concentration.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 3 Condenser lens 4 Reticle 5 Reduction lens 6 Semiconductor wafer 7 Wafer stage

Claims (7)

The light emitted from the UV light source onto a semiconductor wafer passes through a single reticle is imaged, by moving the wafer stage for placing a semiconductor wafer, by performing exposure with exposure shot X or from exposure shot 1, An exposure method in which step-and-repeat exposure returning to exposure shot 1 is repeated N times,
Suitable equivalents exposure time, or when the appropriate illumination, the semiconductor wafer coated with a photosensitive member consisting of a radical polymerization type UV curable resin having an optimal photolithography pattern profile performance, each one exposure shot of exposing the photosensitive member Comprises an exposure process in which exposure is performed at 1 / N of a predetermined exposure amount by adjusting the optimal exposure time, optimal illuminance, or both exposure time and illuminance,
An exposure method characterized in that an exposure time To per one semiconductor wafer is expressed by the following equation .
To = [t3 * X + t2 * (X-1)] * N + t5 * (N-1)
Where t3 is the exposure shot time
X is the number of exposure shots
t2 is the movement time of the wafer stage during step-and-repeat
t5 is a time for returning the wafer stage to the initial position.   2. The exposure method according to claim 1, wherein the exposure time is 1 / N of a predetermined exposure amount by adjusting a shutter opening time. The exposure method according to claim 1, wherein the illuminance is exposed at 1 / N of a predetermined exposure amount by adjusting a voltage of a UV light source, adjusting a distance between the UV light source and a semiconductor wafer, or inserting an exposure amount adjusting plate. .   The photoreceptor is a prepolymer having an unsaturated group such as an acrylic group or a methacryl group, a system in which a vinyl monomer such as styrene is dissolved in an unsaturated polyester, or a radical polymerization type UV curable resin such as a thiol-olefin resin system. 2. The exposure method according to claim 1, wherein the exposure method is a photo radical polymerization initiator (benzophenone series, benzoin ether series, acetophenone series, thioxanthone series, etc.).   5. The projection exposure method according to claim 1, wherein the N is 2 or more and 10 or less. 6. The exposure amount according to claim 1, wherein an exposure amount in the exposure step is initially smaller than 1 / N of a predetermined exposure amount , and the end amount is larger than 1 / N of a predetermined exposure amount . Projection exposure method. An exposure apparatus comprising a control unit that implements the projection exposure method according to claim 1.

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