JP5058667B2 - Exposure apparatus and device manufacturing method - Google Patents

Description

The present invention relates to an exposure apparatus that exposes a pattern of an original such as a mask or a reticle onto a substrate such as a wafer or a glass plate in a manufacturing process of a semiconductor integrated circuit, a liquid crystal display element, or the like.

When the deformation factors of the original plate such as a mask and a reticle are classified, it is possible to consider deformation due to its own weight, polishing accuracy of the glass substrate itself, mask adsorption, deformation due to thermal expansion, and the like.
Such deformation may vary from mask to mask and from exposure apparatus to exposure apparatus. In order to accurately measure the amount of deformation, it is necessary to measure on the mask stage which is the actual use environment.
As shown in FIGS. 1 and 2, the correction plate 12 is placed on and closely adhered to the mask 11, and the bending of the mask 11 is corrected by changing the pressure between the mask 11 and the correction plate 12 from the pipe 13. Yes.
At that time, each time the mask 11 changes, the amount of deflection of the mask 11 is measured by the laser displacement meter 14, and the pressure is changed and measured many times so as to be within the predetermined amount of deflection.
In addition, even when the pressure is initially determined, the amount of deflection may change depending on the environment in the exposure apparatus and the usage state of the mask 11 while the substrate 20 is exposed. In that case, exposure is performed again by setting a pressure value by trial and error.

FIG. 4 is a flowchart showing the conventional lot processing. Exposure is started (step 101), and a substrate such as a wafer or a glass plate is prepared (step 102).
The mask surface, which is the original surface, is measured, and the measured value and the specified pressure value are stored (step 103).
If it exceeds the allowable range within the predetermined deflection amount (step 103), an error occurs (step 105).
If the allowable range within the predetermined deflection amount is not exceeded, exposure is started (step 106).
If there is a next substrate (step 107), the substrate is prepared again (step 102).
If there is no next substrate, the exposure ends (step 108).
Japanese Patent Application Laid-Open No. 2005-85833 proposes a mask inspection method that can accurately predict and correct the position of each subfield when the mask is set in the exposure apparatus, and can improve the exposure accuracy in the exposure apparatus. Has been.
JP 2005-85833 A

Since there is deformation of the mask due to factors such as bending due to its own weight, polishing accuracy of the glass substrate itself, mask adsorption, and thermal expansion, it is necessary to increase the flatness of the entire mask.
For example, when the deformation factor of the mask is only the deflection due to the weight of the mask, the difference between the center where the deflection of the mask is expected to be the largest and the mask reference plane should be small.
However, among the deformation factors of the mask described above, it is impossible to predict deformation due to glass polishing, deformation due to mask adsorption, and deformation due to thermal expansion.
When correcting including these, it is necessary to measure and correct the entire mask.
Next, it is necessary to correct the change with time of the deflection of the mask.
Possible deformation factors of the mask and reticle original plate include bending due to its own weight, polishing accuracy of the glass substrate itself, deformation due to mask adsorption, deformation due to thermal expansion, and the like.
Among these, deformation due to mask adsorption, thermal expansion, and the like change with time.
Even in the case where there is a change due to the passage of time, in the conventional example, the exposure apparatus is stopped when the pressure value once determined is used until it exceeds the allowable range of deflection and exceeds the allowable range.

Further, the pressure is determined every time the mask 11 is changed as described above, and it is necessary to automate the process of determining the two control pressures for setting the pressure value by trial and error again for the initially determined pressure.
In the conventional example, the amount of deflection of the mask is measured when the exposure apparatus is adjusted, when exposure is started, and when the substrate 20 is carried in. When the allowable range is exceeded, the exposure apparatus is stopped.
It was necessary to set the pressure manually and repeat the measurement to set the optimum pressure value. At that time, production was not possible, productivity was lowered, and personnel were required.
Therefore, an object of the present invention is to provide an exposure apparatus that reduces defocus due to deformation of a pattern surface of an original, for example.

In order to solve the above problems, an exposure apparatus of the present invention is an exposure apparatus that has a projection optical system that projects light from an original and exposes a substrate through the pattern surface of the original and the projection optical system. And
Measuring means for obtaining a measurement value relating to the distance from the reference surface at a plurality of locations of the pattern surface in the optical axis direction of the projection optical system;
Means for applying a force to the original plate in a direction perpendicular to the pattern surface,
The means for applying the force applies the force based on the ratio of the amount of change in the force applied to the original plate and the amount of change in the measured value obtained by the measuring means, and the measured value obtained by the measuring means. Changing the force that the means apply to the original,
When the force applying means changes the force applied to the original plate, the ratio of the change amount of the force applied by the force applying means to the original plate and the change amount of the measured value obtained by the measuring means is obtained. Updated,
When the measurement value obtained by the measurement means for at least one place on the pattern surface exceeds an allowable range, based on the measurement values obtained by the measurement means and the updated ratio, The force applying means changes the force applied to the original so that the measurement values obtained by the measuring means regarding the plurality of locations are within an allowable range;
An exposure apparatus characterized by that .

According to the present invention, for example, it is possible to provide an exposure apparatus which Ru reduce defocus due to deformation of the pattern surface of the original.

  Embodiments of the present invention will be described below with reference to the drawings.

First, Embodiment 1 of the present invention for automatically increasing the flatness of the entire mask will be described.
FIG. 1 schematically shows the arrangement of an exposure apparatus according to the first embodiment of the present invention.
The exposure apparatus has a projection optical system that projects light from an original such as a mask and a reticle, and exposes a substrate such as a wafer and a glass plate through the pattern surface of the original and the projection optical system.
The exposure apparatus has a mask stage 10 on which a mask 11 which is an original is loaded and held by suction with a vacuum chuck.
A correction plate 12 for correcting the deflection of the mask 11 is mounted on the mask 11. The correction plate 12, which is a means for applying a force to the original, is a means for applying a force to the mask 11, which is the original, in a direction orthogonal to the pattern surface.
The correction plate 12 includes a pipe 13 for adjusting the pressure between the mask 11 and the correction plate 12, and the exposure apparatus includes a control system for controlling the pressure.

The pressure is changed to an appropriate pressure value by the pressure control by the pipe 13, and the mask 11 bent as shown in FIG. 2 is lifted up to the mask reference plane 30 shown in FIG.
Further, a displacement meter 14 that is movable in the X direction for measuring the distance of the mask reference surface 30 to the mask 11 surface is provided, and a control system for controlling it is provided.
To move in the Y direction, the mask stage 10 is scan-driven, and the laser displacement meter 14 measures the entire surface of the mask 11.
The laser displacement meter 14 serving as detection means is means for detecting the positions of a plurality of positions on the pattern surface in the optical axis direction of the projection optical system.
A force is generated in the correction plate 12 which is a means for applying a force to the original so that the positions of a plurality of positions on the pattern surface detected by the laser displacement meter 14 which is the detection means are within a predetermined allowable range.
The laser displacement meter 14 is adjusted in advance using the reference surface 30 of the mask 11 as the origin of the laser displacement meter 14 and measures the distance of the mask reference surface 30 to the surface of the mask 11.

Next, Embodiment 1 of the present invention will be described with reference to FIG.
The flatness of the mask 11 is affected by the deflection due to its own weight, the polishing system of the glass substrate itself, the deformation at the time of mask adsorption, the thermal expansion, etc., and is measured and corrected for the entire surface of the mask 11.
In step 202 shown in FIG. 5, the entire surface of the mask 11 is measured.
The pressure value at that time is P1, the average value of the displacement measurement values is d1, and the measurement value d1 and the pressure value P1 are stored.
In step 203, a correction pressure is calculated. In the correction calculation, the following formula is used.

When the correction pressure value is P2, K is a coefficient at the time of the previous measurement. In this case, the value measured at the time of device adjustment or the like is used, or the initial value at the time of factory shipment is used.
The pressure is controlled with the pressure value of P2.
In step 204, measurement is performed on the entire mask as in step 201.
The pressure value at that time is P2, the average value of the displacement measurement values is d2, and the measurement value d2 and the pressure value P2 are stored.

In step 205, it is determined whether or not the measured value d2 is within the predetermined allowable range. If the measured value d2 is not within the allowable range, the process returns to step 203, and K is calculated from P1, P2, d1, and d2 according to equation (2). Calculate and save.
Therefore, the next specified pressure P3 is calculated from the equation (1) and K · P2 · d2. The pressure is controlled with that value.
In step 204, measurement is again performed on the entire mask surface, the pressure value at that time is P3, the average value of the displacement measurement values is d3, and the measurement value d3 and the pressure value P3 are stored.
In step 205, it is determined whether or not the measured value d3 is within the predetermined allowable range. If the measured value d3 is not within the allowable range, the process returns to step 203 again to repeat the measurement.
If it is within the allowable range, it can be determined that the mask surface is flat enough not to defocus, and the process ends (step 206).

As described above, by averaging the displacement difference at each measurement point and bringing the average value close to 0, it is possible to finally correct the displacement difference that is not defocused.
If it takes time to measure the entire surface of the mask 11, first, the method of the first embodiment is performed by measuring only one point of the displacement difference at the center of the mask 11.
As a result, the number of steps in which steps 203 to 205 are repeated is reduced and the time is shortened.

Next, referring to FIG. 6, a second embodiment of the present invention that automatically corrects the change with time of the mask during the lot processing and maintains the mask flatness will be described.
The apparatus configuration of the second embodiment is the same as that of the first embodiment, and the amount of change over time for at least one detection point on an original plate such as a mask is calculated by a laser displacement meter 14 serving as detection means.
Further, when the amount of change exceeds an allowable range, the force is generated on the correction plate 12 which is a means for applying a force to the original.
As a premise for performing the second embodiment, it is assumed that the first embodiment is performed and a certain degree of mask flatness is maintained.
When the exposure of the lot is started (step 301), in step 302, the lot leading substrate 20 is carried into the apparatus.
Mask surface measurement (step 303) is performed during the loading of the substrate 20 or after the loading of the substrate 20.
In the mask surface measurement (step 303), measurement is performed on the entire mask surface or several predetermined points are measured.

The number of measurement points is determined so as not to delay the entire operation according to the performance of the apparatus.
Save the average displacement measurement value as d1 and the pressure value at that time as P1.
It is determined whether or not the measured value d1 is within a predetermined allowable range (step 304).
If not within the allowable range, the pressure calculation for measuring the mask surface is performed again (step 305).
As for the pressure value, d1 is the average value of the displacement meter measurement value of the first mask surface measurement (step 303), P1 is the pressure value, and K is a coefficient stored at the time of previous measurement or stored at the time of apparatus adjustment. Using the numerical value, the pressure value P2 to be changed can be obtained.
The pressure value controls the pressure between the mask of the apparatus and the correction plate.
Mask surface measurement is performed again (step 303), and the average value d2 of the displacement meter measurement values and the pressure value at that time are stored as P2.
It is determined whether or not the measured value d2 is within the predetermined allowable range (step 304). If not, K is calculated from P1, P2, d1, and d2 according to the equation (2) and stored.
The next specified pressure P3 is calculated from the formula (1) and K · P2 · d2.
Returning to step 303, the mask surface measurement is repeated.

If it is within the allowable range in step 304, it can be determined that the mask surface is flat enough not to defocus, and an exposure operation (step 306) is performed.
If there is a next substrate 20 after the exposure is completed, the process returns to the substrate preparation (step 302) and is repeated until there are no more substrates in the lot.
As described above, the displacement difference of the mask surface is measured for each substrate, the displacement difference at each measurement point is averaged, and the average value is brought close to 0, so that the displacement difference that is not defocused is finally corrected. It becomes possible to do.
As described above, it is possible to perform exposure by correcting temporal changes such as deformation due to suction of the mask 11 and deformation due to thermal expansion.

Next, an embodiment of a device manufacturing method using the above-described exposure apparatus will be described with reference to FIGS.
FIG. 7 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, etc.). Here, a semiconductor chip manufacturing method will be described as an example.
The method comprises the steps of exposing a wafer using an exposure apparatus and developing the wafer, and specifically comprises the following steps.
In step 1 (circuit design), a semiconductor device circuit is designed.
In step 2 (mask production), a mask is produced based on the designed circuit pattern.
In step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon.
Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer using the mask and the wafer by the above exposure apparatus using the lithography technique.
Step 5 (assembly) is referred to as a post-process, and is a process for forming a semiconductor chip using the wafer produced in step 4, and an assembly process such as an assembly process (dicing, bonding), a packaging process (chip encapsulation), or the like. including.
In step 6 (inspection), the semiconductor device manufactured in step 5 undergoes inspections such as an operation confirmation test and a durability test.
Through these steps, a semiconductor device is completed and shipped (step 7).

FIG. 8 is a detailed flowchart of the wafer process in Step 4.
In step 11 (oxidation), the surface of the wafer is oxidized.
In step 12 (CVD), an insulating film is formed on the surface of the wafer.
In step 13 (electrode formation), an electrode is formed on the wafer.
In step 14 (ion implantation), ions are implanted into the wafer.
In step 15 (resist process), a photosensitive agent is applied to the wafer.
Step 16 (exposure) uses the exposure apparatus to expose a circuit pattern on the mask onto the wafer.
In step 17 (development), the exposed wafer is developed.
In step 18 (etching), portions other than the developed resist image are removed.
In step 19 (resist stripping), the resist that has become unnecessary after the etching is removed.
By repeatedly performing these steps, multiple circuit patterns are formed on the wafer.

It is the figure which showed the structure of the exposure apparatus of Example 1 of this invention partially partially, and was shown roughly. It is a state figure of the bending of the mask by which the mask of Example 1 of this invention, a correction board, and a displacement meter are shown. It is a state figure after the deflection correction of the mask of Example 1 of the present invention. It is a flowchart figure during the lot process of a prior art example. It is a flowchart figure of the pressure correction at the time of adjustment of Example 1 of this invention. It is a flowchart figure in the lot process of Example 2 of this invention. It is a flowchart for demonstrating manufacture of the device using an exposure apparatus. It is a detailed flowchart of the wafer process of step 4 of the flowchart shown in FIG.

Explanation of symbols

10: Mask stage 11: Original plate 12: Correction plate 13: Pressure pipe 14: Laser displacement meter 20: Substrate 21: Plate stage

Claims (4)

An exposure apparatus having a projection optical system for projecting light from an original, and exposing a substrate through the pattern surface of the original and the projection optical system,
Measuring means for obtaining a measurement value relating to the distance from the reference surface at a plurality of locations of the pattern surface in the optical axis direction of the projection optical system;
Means for applying a force to the original plate in a direction perpendicular to the pattern surface,
The means for applying the force applies the force based on the ratio of the amount of change in the force applied to the original plate and the amount of change in the measured value obtained by the measuring means, and the measured value obtained by the measuring means. Changing the force that the means apply to the original,
When the force applying means changes the force applied to the original plate, the ratio of the change amount of the force applied by the force applying means to the original plate and the change amount of the measured value obtained by the measuring means is obtained. Updated,
When the measurement value obtained by the measurement means for at least one place on the pattern surface exceeds an allowable range, based on the measurement values obtained by the measurement means and the updated ratio, The force applying means changes the force applied to the original so that the measurement values obtained by the measuring means regarding the plurality of locations are within an allowable range;
An exposure apparatus characterized by that. The exposure apparatus according to claim 1, wherein the at least one location is less than the plurality of locations . If the measured value obtained by the measuring means for the at least one place exceeds an allowable range, the force is calculated based on the measured value obtained by the measuring means for the at least one place and the updated ratio. The means for applying the force changes the force applied to the original plate, and then the force applied by the means for applying the force to the original plate based on the measured values for the plurality of locations obtained by the measuring means and the updated ratio. changing the exposure apparatus according to claim 1 or claim 2, characterized in that. A step of exposing the substrate using the exposure apparatus according to any one of claims 1 to 3 ;
A step of developing the substrate exposed in the step,
Device manufacturing method characterized by having a.

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