JPH11251212A - Method and device for exposure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct an alignment error due to the expansion or contraction in an exposure shot region occurring during exposure, related to method and device for exposure. SOLUTION: A lighting calculation part 12a, wherein based on a phenomenon where alignment error due to expansion or contraction in each exposure shot region occurs, the energy of exposure light, transmissivity of a mask 4, and reflectivity of a sensitized substrate 2 are measured, and an optical energy given to each exposure shot region of the sensitized substrate 2 is calculated from the measurement information, and a calculation part 12b wherein the amount of expansion and contraction in the exposure shot region is obtained from the energy for correcting the alignment error are provided, for correcting the alignment error according to the exposure shot region which expands or contracts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure method and an apparatus for forming a fine or ultra-fine pattern on a semiconductor substrate.

[0002]

2. Description of the Related Art Usually, in a semiconductor manufacturing process, a desired pattern is transferred onto a wafer which is a semiconductor substrate.
A photosensitive agent is applied to the wafer, and the exposure light is reduced and projected onto the wafer through a mask, which is an original plate magnified about 5 or 4 times the pattern, to transfer a pattern to the wafer, and then to develop the wafer. Was obtained by doing.

In addition, when a base pattern is already formed on a wafer and a photosensitive agent pattern is formed on the wafer so as to overlap with the base pattern, it is necessary to form the photosensitive agent pattern at a predetermined position relative to the base pattern on the wafer. Because
Exposure has been performed after performing an alignment operation on an alignment mark formed on a wafer by an exposure apparatus. However, during the exposure processing or during the exposure processing after the alignment work, the exposure light causes the photosensitive substrate as a wafer and the substrate older on the substrate stage to generate heat and expand. Due to this expansion, expansion and development of the entire photosensitive substrate occurs around the center of the photosensitive substrate, which causes a problem that a so-called scaling-type alignment error occurs.

A method of forming a pattern by correcting such an alignment error due to thermal expansion is disclosed in Japanese Patent Laid-Open No. 5-9012.
No. 4 discloses this. In this method, the position shift at which the photosensitive agent pattern is displaced from the base pattern to be formed is measured by measuring the reflectance of the photosensitive substrate, and the light energy absorbed by the photosensitive substrate is obtained. The amount of heat generation and expansion of the entire photosensitive substrate is calculated to correct the alignment.

[0005]

In the conventional pattern forming method disclosed above, the so-called diametrical extension of the photosensitive substrate causes a positional shift with respect to the expansion of the entire photosensitive substrate centered on the center of the photosensitive substrate. Although the correction of the alignment error due to the scaling is effective, in the actual stepper, each time an exposure shot is sequentially exposed to a square exposure shot area arranged vertically and horizontally on the photosensitive substrate, the exposure shot is exposed. The area expands or contracts due to cooling when moving to the next exposure position,
Each time exposure is performed, an alignment position shift occurs in the exposure shot area, and the direction and amount of the position shift change.

For example, a photoresist film is formed on a single semiconductor wafer to serve as a photosensitive substrate, and when this photosensitive substrate is exposed, the amount of X-axis alignment error was examined for each exposure shot area position. As a result, data as shown in FIG. 5 was obtained.

The order of exposure shots is shown in the upper part of the rectangular exposure shot area in FIG. 5, and the amount of alignment error is shown in the lower part. As can be seen from this figure, the average value (X) of the alignment error amount is listed for each exposure shot row, but an odd row has an alignment error in the positive direction and an even row has an alignment error in the negative direction. I understand.

FIG. 6 is a graph of the alignment error values shown in FIG. 5, and the average value (X) and the absolute value are both 1 and 1.
The values of the alignment errors in the odd columns 3, 5, 7 and the even columns 2, 4, 6, 8 have a total range of about R = 80 nm, which is the superimposition value of the odd and even columns. Therefore, they are shifted in opposite directions. This means that R
The / 2 value is considered to be a substantial value of the alignment error in one row, and an alignment error of about 40 nm has occurred. This value poses a serious problem in the manufacture of devices of 16 MDRAM second generation or later.

Considering the reason why such an alignment error occurs, as shown in FIG. 7, when an exposure shot area is exposed to an exposure shot area, it receives incident light energy and the exposure shot area is indicated by a dotted line. To expand.
Assuming that the next shot area is exposed after a time lag from the expansion step, the shot area at that time is cooled from the expansion step and is shifted to the contraction step, and the exposure shot area is It is considered that an alignment error occurs in a direction opposite to the exposure direction because the film is pulled by the contraction. In addition, the exposure shot area in which the exposure direction changes has the same change as the exposure shot area similar to the exposure shot area similar to the exposure shot area. From this, it is considered that different alignment errors occur in odd-numbered columns and even-numbered columns as described above.

Further, in the conventional method, the amount of alignment error due to thermal expansion of the photosensitive substrate is used as information for calculating only the reflectance of the photosensitive substrate. Patterns are different. Since the patterns are different, the irradiation power of the light source that transmits the exposure light through the mask is also different. If the irradiation powers are different, the irradiation power for irradiating the photosensitive substrate with the light source is not considered in the correction value calculation. For this reason, it is not possible to calculate an accurate and proper correction amount.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an exposure method and apparatus capable of correcting an alignment error caused by expansion or contraction of an exposure shot area generated during exposure.

[0012]

The present invention is characterized in that a plurality of rectangular exposure shot areas are arranged vertically and horizontally on one main surface, and a pattern is formed on each of the exposure shot areas of a photosensitive substrate to which a photosensitive agent is applied. In an exposure method for sequentially transmitting and reducing exposure light through a mask having a pattern formed thereon and transferring the pattern to each of the exposure shot areas, the energy of the exposure light and the transmission of the mask are determined. The exposure and the reflectance of the photosensitive substrate are measured, the one-shot exposure energy absorbed in the exposure shot area is determined from these measured values, and the one-shot exposure energy is sequentially applied to the exposure shot area. The amount of displacement due to expansion or contraction of the exposure shot area is defined as an alignment error, and is determined by the exposure shot area due to the one exposure energy. Seeking Zhang amount, the alignment error in the amount of expansion depending on whether Thereafter the exposure shot area is or contracting expansion - is an exposure method for correcting.

Another feature of the present invention is that a projection lens for transmitting a mask through exposure light to reduce and project a pattern image of the mask onto a photosensitive substrate, and mounting the photosensitive substrate and moving the photosensitive substrate An exposure apparatus comprising: a substrate stage to be moved; and an interferometer for measuring a moving distance of the substrate stage.
A first power sensor for measuring a light intensity of the exposure light that branches a part of the exposure light, and a second power sensor for measuring the light intensity of the exposure light transmitted through the mask; A reflection sensor which irradiates the portion of the photosensitive substrate on which pattern formation is unnecessary with the reflected light and measures the light intensity of the reflected light; and inputs the light intensity values to reflectivity of the photosensitive substrate and transmittance of the mask. And an irradiation calculation unit that calculates one exposure energy input to the photosensitive substrate, and an exposure shot region generated when the exposure light is sequentially applied to the exposure shot regions arranged vertically and horizontally on the photosensitive substrate. In order to correct an alignment error due to expansion or contraction, a thermal expansion amount due to the one exposure energy is calculated, and the alignment error corresponds to expansion or contraction of the exposure shot area. An arithmetic processing unit for calculating an amount for correcting the alignment error in consideration of the thermal expansion amount; and a relative position between the mask and the exposure shot area corresponding to the correction amount output from the arithmetic processing unit. And a stage control circuit for converting the amount into a change amount and outputting the converted amount to a moving mechanism.

The moving mechanism is provided on the substrate stage or a stage for mounting the mask.
It is desirable to be provided in the device.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a view showing an exposure apparatus according to an embodiment of the present invention. As shown in FIG. 1, the exposure apparatus includes a projection lens 3 for transmitting exposure light from a light source lamp 11 through a mask 4 through a shutter 7a and reducing and projecting a pattern image of the mask 4 onto a photosensitive substrate 2. A substrate stage 1 on which the photosensitive substrate 2 is placed and moved by a motor 13 and an interferometer 15 for measuring a moving distance of the substrate stage 1 are provided as in the conventional case.

In this exposure apparatus, a part of exposure light is transmitted to a shutter 7b by a pair of half mirrors 8a and 8b.
A reflection sensor 6a for irradiating the photosensitive substrate 2 or the power sensor 6a through the optical fiber 9 and detecting its reflected light, and a power sensor 6b for detecting the intensity of the exposure light transmitted through the half mirror 8b. An irradiation calculator 12a for inputting the light intensity signal, the light intensity signal from the reflected light sensor 5, and the light intensity signal from the power sensor 6a to calculate the reflectance of the photosensitive substrate 2 and the transmittance of the mask, and the interferometer 15. A processing unit 12b for inputting the exposure shot position information of the photosensitive substrate 2, the reflectance from the illumination calculation unit 12a, the light intensity of the exposure light, and the transmittance, and calculating the amount of alignment error correction; A stage control circuit 14 for inputting information, controlling the motor 13 and positioning the photosensitive substrate 2 is provided.

A photosensitive agent, which is a photoresist film, is applied to a thickness of about 1.0 μm to form a photosensitive substrate 2. The photosensitive substrate 2 is held on the substrate stage 1 by vacuum suction. Further, an interferometer 15 having a resolution of 5 nm
And the substrate stage 1 is positioned with high accuracy. A power sensor 6a that monitors irradiation power and converts an optical signal into an electric signal is provided on the substrate stage 1, and can measure the same irradiation power as that at the time of exposure.

On the other hand, the photosensitive substrate 2 is exposed, but has a stage 10 on which a mask 4 having an exposure pattern is set, and the mask 4 can be positioned with an accuracy of 20 nm or more. The pattern of the mask 4 is reduced to 1/4 by the projection lens 3.
The pattern is projected onto the photosensitive substrate 2 after being reduced by about 1/5 to transfer the pattern.

FIG. 2 is a flowchart for explaining a method of exposing using the exposure apparatus of FIG. First, the mask 4 is set and positioned on the mask stage 10 in a start step to prepare for exposure. Next, the photosensitive substrate 2 is mounted on the substrate stage 1 and waits for exposure.

Next, in step A, the shutter 7a is opened, and the illumination light reflected from the half mirror 8a and transmitted through the half mirror 8b is measured by the power sensor (light source) 6b for the illumination power of the current light source. . This measurement result is stored in the irradiation calculation unit 12.
a is transferred as information and stored in the storage unit.

Next, in step B, the substrate stage 1 is moved to the position of the irradiation light power sensor (stage) 6a installed on the substrate stage 1 directly below the projection lens 3,
Then, the shutter 7a is opened again, and the irradiation power transmitted through the mask 4 and the projection lens 3 is measured. Then, similarly to the illumination power, the measurement information is transferred to the irradiation calculation unit 12a and stored. Here, the illumination operation unit 12a calculates the illumination power of the light source that has been transferred to the illumination operation unit 12a and the measured value to calculate the transmittance of the mask 4. Since the transmission of the mask 4 differs depending on the exposure process, the measurement is performed by measuring each time the mask 4 is installed.

Next, in step C, the light branched by the half mirror 8b and introduced into the optical fiber 9 through the shutter 7b is emitted from the reflected light sensor 5, and the non-photosensitive agent pattern forming portion ( The emitted light is applied to the portion where the pattern does not need to be transferred, and the reflected light is measured by the reflected light sensor 5 for the amount of reflected light. This measurement information is transferred to the irradiation calculation unit 12a and stored. Since the surface reflectivity of the photosensitive substrate 2 varies depending on the use process, this is measured and calculated for each new process.

Next, at step D, it is determined whether or not the exposure process is a process requiring superposition. If superposition is required, at step E, a conventional alignment process is performed by using an alignment mark. The pattern position deviation of the photosensitive substrate 2 is measured by the method, and the measurement information is transferred to the arithmetic processing unit 12b and stored. If there is no need for superposition, proceed to the next step.

Next, in step F, the expansion amount due to the incident energy of one exposure shot of the photosensitive substrate 2 is calculated in the arithmetic processing section 12b based on the measurement information collected in the irradiation arithmetic section 12a from step A to step C. Next, step G
Then, each alignment error correction amount corresponding to the expansion amount calculated in step F is calculated. This alignment error amount corresponds to half of the expansion amount. This is because the center of the exposure shot area is used as a reference. Further, in the contracted area in the exposure shot area, the correction amount is obtained by setting the half of the expansion amount to plus.

For example, when irradiation is performed at a required exposure light intensity, if the expansion amount is 40 nm, the correction amount is -20 nm in an expanding exposure shot region, and the correction amount is -20 nm in a contracting exposure shot region. +20 nm.

Next, in step H, if the exposure shot area to be exposed is an expanding area, an alignment error correction amount corresponding to the expansion amount is set. If the exposure shot area is a contracting area, an alignment error correction amount corresponding to the contraction amount is set. -Extract the correction amount and transfer it to the stage control circuit 14. If in step E,
If there is a correction amount in the alignment method, the alignment error correction amount is corrected in consideration of the extracted alignment error correction amount and transferred to the stage control circuit 14.

Next, in step I, the stage control circuit 1
4 transfers an output signal corresponding to the alignment error correction amount to the motor 13 and synchronizes the output signal with the interferometer 15 to the motor 1.
3 is driven to position the exposure shot area. Then, in step J, the shutter 7a opens to perform an exposure process.

Next, when the shot exposure is completed, it is determined in a step K whether or not there is a next exposure shot area. If there is, the substrate stage 1 moves to position the next exposure shot area, and the process proceeds to step H to perform exposure processing of the next exposure shot area. If there is no next exposure shot area, the process ends.

FIG. 3 is a graph showing alignment errors in the exposure shot area on the photosensitive substrate. By performing such correction processing, it is possible to reduce an alignment error generated due to expansion and contraction during an exposure shot. In other words, as shown in FIG. 5, the alignment error in the X direction was ± 20 nm or more in average value (X), but within ± 5 nm, 80n in range (R).
m was greatly improved to 50 nm or less.

FIG. 4 is a view showing a modification of the exposure apparatus of FIG. In this exposure apparatus, as shown in FIG. 4, the stage 10 for holding the mask 4 has a function of correcting an alignment error due to a thermal surge or shrinkage.

That is, a stage moving mechanism 16 for moving the stage 10 and an alignment error correction amount signal obtained from the arithmetic processing unit 12b are input to control the output of the motor 13 and the position control by the interferometer 15a. And a stage control circuit 14a for performing the above. Other power sensors 6
a, 6b, reflected light sensor 5, irradiation operation unit 12a, optical fiber 9, shutters 7a, 7b, half mirrors 8a, 8b
Is provided with the same one as the exposure apparatus in the above embodiment.

A motor 13 and an interferometer 15 for performing a step feed to an exposure shot area on the photosensitive substrate 2;
A stage controller 17 for controlling the output of the motor 13 for feeding the substrate stage 1 and controlling the position by the interferometer 15 is provided in the same manner as in the prior art.

The operation of this exposure apparatus is the same as that of the flowchart shown in FIG. However, since the mask 4 is above the projection lens 3, the amount of movement of the mask 4 is reduced by the magnification of the projection lens. Therefore, FIG.
In step G, it is necessary to multiply the magnification of the projection lens. For example, if it is four times, the amount of alignment error correction in step G becomes four times. This means that the error of the corrected position is reduced, and alignment with higher accuracy can be performed.

[0035]

As described above, according to the present invention, the energy of exposure light, the transmittance of a mask and the sensitivity of a mask are based on the phenomenon that an alignment error occurs due to expansion or contraction in each exposure shot area due to repeated exposure shots. Means for measuring the reflectivity of the substrate, means for calculating and calculating light energy applied to each exposure shot area of the photosensitive substrate based on the measurement information, and calculating the amount of expansion and contraction in the exposure shot area based on the energy. Means for calculating the amount of alignment error correction, and correcting the alignment error according to the exposure shot area that expands or contracts, thereby improving the alignment accuracy and transferring a fine pattern to the photosensitive substrate. effective.

[0036]

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an exposure apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining a method of performing exposure using the exposure apparatus of FIG. 1;

FIG. 3 is a graph showing alignment errors in an exposure shot area on a photosensitive substrate.

FIG. 4 is a view showing a modification of the exposure apparatus of FIG. 1;

FIG. 5 is a map diagram showing an alignment error of each exposure shot area on a photosensitive substrate.

FIG. 6 is a graph showing the alignment error in FIG. 5;

FIG. 7 is a diagram showing an expanded and contracted state of each exposure shot area.

[Explanation of symbols]

 Reference Signs List 1 substrate stage 2 photosensitive substrate 3 projection lens 4 mask 5 reflected light sensor 6a, 6b power sensor 7a, 7b shutter 8a, 8b half mirror 9 optical fiber 10 stage 11 light source lamp 12a irradiation operation unit 12b operation processing unit 13 , 13a Motor 14, 14a Stage control circuit 15, 15a Interferometer 16 Stage moving mechanism 17 Stage control unit

Claims (4)

[Claims] 1. A plurality of square exposure shot areas are arranged vertically and horizontally on one main surface, and a pattern is formed on each of the exposure shot areas of a photosensitive substrate to which a photosensitive agent is applied via a mask. Exposure light is sequentially transmitted and reduced and projected,
In an exposure method for transferring the pattern to each of the exposure shot areas, the energy of the exposure light, the transmittance of the mask, and the reflectance of the photosensitive substrate are measured, and the exposure shot area is measured based on the measured values. The one shot exposure energy absorbed by the exposure shot area is determined, and the deviation amount caused by the expansion or contraction of the exposure shot area caused by sequentially applying the one shot exposure energy to the exposure shot area is defined as an alignment error. -To determine the expansion amount due to the exposure shot area,
Then, depending on whether the exposure shot area expands or contracts, the alignment error is obtained with the expansion amount.
An exposure method characterized by correcting the following. 2. A projection lens for transmitting a mask through exposure light to reduce and project a pattern image of the mask onto a photosensitive substrate, and a substrate stage for mounting the photosensitive substrate and moving the photosensitive substrate. An exposure apparatus including an interferometer for measuring a moving distance of the substrate stage, a first power sensor for branching a part of the exposure light and measuring the intensity of the branched light, and a transmission through the mask. A second power sensor for measuring the light intensity of the exposure light, and a reflection sensor for irradiating the branched light to a portion of the photosensitive substrate that does not require pattern formation and measuring the light intensity of the reflected light. An irradiation calculator for inputting the light intensity values and calculating the reflectance of the photosensitive substrate, the transmittance of the mask, and one exposure energy input to the photosensitive substrate, and are arranged vertically and horizontally on the photosensitive substrate. Exposure shot area In order to correct an alignment error caused by expansion or contraction of the exposure shot area generated when the exposure light is sequentially irradiated with the exposure light, a thermal expansion amount due to the one exposure energy is calculated, and the alignment error is corrected by the exposure shot area. An arithmetic processing unit for calculating an amount for correcting the alignment error in consideration of the thermal expansion amount in accordance with the expansion or contraction of the mask, and the mask and the exposure corresponding to the correction amount output from the arithmetic processing unit An exposure apparatus, comprising: a stage control circuit for converting the relative position with respect to a shot area into an amount to be changed and outputting the converted amount to a moving mechanism. 3. An exposure apparatus according to claim 1, wherein said moving mechanism is provided on said substrate stage. 4. The exposure apparatus according to claim 1, wherein the moving mechanism is provided on a stage on which the mask is mounted.