JPH09320920A - Adjustment method of exposure equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent error exposure by detecting an error in calibration of a device which is performed before exposure in an aligner. SOLUTION: In calibration before exposure of a series of substrates, that is, position measurement or alignment of a specific measurement point such as a position sensor and a reticle, a position of at least one identical measurement point is measured at least twice, at first and at the end, for example in the middle of calibration and measured positions are compared. When a difference of positions obtained in the two measurements is not less than a preset minute allowable value, the calibration is an error.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus for manufacturing semiconductors or liquid crystals, and more particularly to a method of adjusting the apparatus before and during exposure.

[0002]

An exposure apparatus for manufacturing semiconductors and liquid crystal substrates (hereinafter referred to as an exposure apparatus) irradiates a reticle installed at a predetermined position of the apparatus with exposure light to expose an image of the reticle to an exposure stage of the apparatus. The wafer or glass substrate is exposed by projecting it onto a semiconductor wafer or a glass substrate for liquid crystal placed thereon. At this time, the reticle and the substrate (wafer or glass substrate) must be accurately aligned so as to have a predetermined positional relationship. Therefore, alignment is performed to align the reticle and the substrate with respect to the device at a predetermined position.

Of these, the alignment of the substrate is performed by detecting an alignment mark formed on the substrate using a sensor provided in the apparatus and measuring the position thereof. Furthermore, it is necessary to calibrate a certain device as a preparation for exposure. This is to align the reticle, which is the original image at the time of exposure, with the device, and at the same time, to measure the positions of a plurality of position sensors used to align the wafer or glass substrate with the device (measure the position of the substrate) (or Alignment) and is usually called baseline measurement. That is, since the alignment mark position of the substrate measured by the position sensor is a relative position with respect to the sensor, in order to determine the absolute position of the substrate with respect to the coordinate system of the apparatus, the absolute position of the position sensor with respect to the exposure apparatus is beforehand determined. It is necessary to determine in advance, and that is why calibration is performed here. As will be described later in connection with the embodiments, the position referred to here is strictly measured and managed with a resolution of about 0.01 μm using a laser interferometer.

The alignment of the sensor is usually performed together with the alignment of the reticle with respect to the apparatus. However, the alignment is not performed for each exposure of each substrate, but in most cases, the same reticle is used for one lot or several lots. Perform each time the substrate is exposed. However, this is always done when the reticle is replaced when changing lots.

[0005]

Conventionally, when performing the above-mentioned calibration, a slight drift of the sensor position, such as drift of an interferometer for managing the sensor position or position drift of a reference mark for aligning the sensor Occasionally, there were cases where accurate calibration could not be performed.

Further, in the above-mentioned exposure apparatus, if there is a change in the substrate position or a change in the interferometer during alignment / exposure of the substrate, the exposure pattern will not be exposed at an accurate position. This abnormality in the exposure position could not be found without inspection after the substrate was developed.

[0007]

In order to solve the above problems, in the method of the present invention, a calibration performed before exposure of a series of substrates, that is, position measurement of a specific measurement point such as a position sensor and / or a reticle, or When performing the alignment, the position of at least one same measurement point is measured twice during the calibration, and the measured positions are compared. If the difference between the positions obtained by the two measurements is equal to or greater than a preset small permissible value, an error is generated. If this error occurs, the calibration can be automatically performed again.

When exposing each substrate, a plurality of alignment marks provided on the substrate are position-measured and aligned using the position sensor, and then exposure is performed. In the method, the position of at least one of the alignment marks on the substrate is measured again after the exposure is completed, and the difference between the position measured before the exposure and the position measured after the exposure is set to a fine tolerance value or more. If it is, the error is detected and the defect is detected.

According to the present invention as described above, even if there is a defect in the alignment in the calibration before exposure of a series of substrates, it is possible to detect before the exposure, which can be judged only after the exposure is completed. become.

Further, in the case of alignment / exposure of individual substrates, if a shift in exposure position occurs during exposure, defective products can be detected without developing and inspecting.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An exposure apparatus to which the method of the present invention is applied usually has a wafer stage which is movable in two directions (X direction and Y direction) orthogonal to each other and on which a wafer is placed. Position (movement amount) of the wafer stage in the X and Y directions
Is strictly measured by an interferometer, for example, in units of 0.01 μm. The information on the wafer stage is provided with a position sensor for detecting an alignment mark on the wafer placed on the stage. A reference mark used for measuring the position of the position detection device and the reticle is formed on the stage.

The position of the position sensor can be measured, for example, by reading the position of the stage when the reference mark formed on the stage and the position sensor are aligned with an interferometer.

In the method of the present invention, position measurement is performed twice for at least one specific mark. Although the accuracy of the calibration error detection is increased by increasing the number of the specific marks, the time required for the calibration is increased, however, it may be appropriately determined according to the request in each case.

Although it is not particularly limited when the same specific mark is measured twice, the error can be detected during the calibration if the measurement is performed at the beginning and the end of the measurement. It is suitable.

Further, in the method of the present invention applied when exposing a series of substrates, in the case where a positional deviation of a specific alignment mark of the substrate between before and after exposure, which indicates an error of exposure of each substrate, occurs. , It is possible to terminate the exposure of the substrate and terminate the subsequent exposure of the substrate without error, or to continue the exposure of the substrate just by recording the substrate in which the error occurred and to record the error later. It is also possible to exclude certain substrates.

[0016]

EXAMPLE An example of an exposure apparatus for liquid crystals for carrying out the method of the present invention is shown schematically in FIG. The exposure apparatus has an XY stage 5 movable in the X and Y directions shown at right angles to each other. The substrate is placed on the XY stage when the glass substrate for liquid crystal is exposed. The XY stage can be moved independently of each other in two directions of the X direction and the Y direction by the stage drive unit 9. Mirrors 6a and 6b for reflecting the laser light from the laser interferometer are provided on the side surface of the stage 5 respectively in the X and Y directions. Stage 5 of 2
Dimensional (X direction, Y direction) position is determined by laser interferometer
It is constantly detected with a resolution of about 0.01 μm. FIG. 2 shows only the laser interferometer 7 which detects the position of the stage in the X direction by irradiating the mirror 6a with a laser for convenience of illustration.
In fact, a similar laser interferometer is also provided in the Y direction. The laser interferometer 7 is fixed to the main body of the device. The detection result of the laser interferometer is input to the control unit 10. The control unit 10 controls the movement of the stage by the stage driving unit 9.

A reticle holder (not shown) or a reticle 1 held by a reticle stage is located above the stage. During exposure, the reticle 1 is illuminated with illumination light from an illumination optical system (not shown), and the image of the pattern on the reticle 1 is projected onto the substrate on the stage through the projection optical system projection 3 to expose the substrate. Be seen.

The apparatus further has a substrate alignment sensor 4 used for measuring the position of the alignment mark of the substrate placed on the stage. In the apparatus of this embodiment, four substrate alignment sensors 4 are shown, but the number of substrate alignment sensor sensors 4 is determined according to the number of substrate position correction parameters, and is not particularly limited to four. .

The calibration of each sensor and reticle position is performed before alignment / exposure of each substrate. For measuring the position of each substrate alignment sensor 4 for calibration, an XY stage 5 is used.
Is appropriately moved so that the reference mark 8 comes to the detection position of each substrate alignment sensor 4, and the position indicated by the laser interferometer at that time is read.

In the apparatus of this embodiment, the reticle position is also calibrated using the reference mark 8. In such a case, the reference mark 8 and the reticle alignment mark 2 formed on the reticle are configured so that the reference mark 8 can be projected upward by irradiating light such as laser light from below the reference mark. Is detected by a reticle alignment sensor 11 provided above the reticle, and the position of the XY stage (reticle alignment mark) is measured by reading the position of the XY stage at that time with a laser interferometer. It should be noted that the above configuration can be applied to the case where exposure is performed while switching a plurality of reticles using the reticle changer, and in such a case, alignment of the reference mark and the reticle alignment mark is performed for each reticle.

The calibration operation described above is a series of alignment operations of the reference mark 8, the reticle alignment mark 2 and the substrate alignment sensor 4. During this time, the drift as described above, that is, the position of the reference mark. If there is a movement or movement of the interferometer or a position movement of the alignment sensor including a position variation of the alignment light beam, the calibration result will be inaccurate.

Therefore, in the present invention, at the beginning and the end of the calibration operation, the same specific measurement point (for example, one of the substrate alignment sensor or one of the reticle alignment marks) and the reference mark are aligned and the difference between them is determined. Try to calculate. If each drift factor does not exist, this difference is at most about the reproducibility of alignment (that is, the normal error range of alignment when alignment is performed multiple times without drift). It will be a large value that exceeds. Therefore, a value that occurs in the reproducibility of alignment is set in advance as an allowable value, and if this difference exceeds the allowable value, it is not possible to shift to exposure as an error, or a sequence for performing calibration again To do.

FIG. 1 shows the sequence at this time. This sequence will be described below with reference to FIG.

When the sequence starts in step S101, first, the position of one of the predetermined measurement points, that is, the substrate alignment sensor or the reticle alignment mark, is measured, and the initial value of the position of the specific measurement point is obtained. (Step S102).

Subsequently, the position of each measurement point other than the specific measurement point measured in step 102 is measured (step 1
03).

When step 103 is completed, it means that the position measurement of all measurement points including the specific measurement point is completed.
Therefore, in step 104, the position of the first measured specific measurement point is measured again to obtain the final value of the position of the specific measurement point.

Then, in step 105, step 1
02 and the difference between the initial value and the final value of the position of the specific measurement point obtained in step 104 are determined, and it is determined whether the difference is equal to or greater than the degree of alignment reproducibility. Specifically, a predetermined value is set, and the difference between the predetermined value and the initial value and the final value is compared.

If the difference between the initial value and the final value is greater than or equal to the predetermined value in step 105, it means that an error due to drift has occurred during the calibration.
In, it is determined whether or not to perform calibration retry (retry). In practice, the operator may select whether to retry or end in error at the time of step 106, or the operator may set in advance whether to retry or end in error when a drift occurs. A control system may be configured in advance.

If it is decided to retry in step 106, the process returns to step 102 to restart the calibration process from the beginning. If the retry is not performed, the processing ends with an error, the subsequent exposure operation is not performed, and the cause of the error is investigated.

Returning to step 105, when it is determined that the difference between the initial value and the final value is less than or equal to the predetermined value,
It is determined that the calibration operation has been performed normally without the occurrence of drift, and the process proceeds to step 108.

In step 108, the substrate is placed on the stage and a normal series of substrate alignment and exposure operations are performed.

In the above embodiment, the initial position measurement (initial value) and re-position measurement (final value) of a specific measurement point are performed at the beginning and end of the position measurement of all measurement points. This is preferable because it is possible to investigate the influence of drift throughout the calibration if performed at the beginning and at the end. However, the present invention is not necessarily limited to this, and the present invention includes all that the same measurement point is measured twice during the calibration of each measurement point and their measurement positions are compared.

Further, in this embodiment, only one measurement point (one of the substrate alignment sensor or one of the reticle alignment marks) is set as the specific measurement point,
Only one measurement point is re-measured,
It is also possible to set two or more specific measurement points and perform re-measurement and comparison with a predetermined value for each of them. Of course, the more specific measurement points, the higher the accuracy of calibration error detection.

Next, an example of another method of the present invention applied to substrate exposure will be described.

The apparatus used in the method is shown in FIG. Since this device is similar to the device of FIG. 2, the same reference numerals are given and the description of the configuration of the device is omitted. The difference from FIG. 2 is that the substrate 12 placed on the XY stage 5 is shown. In this apparatus, the pattern image of the reticle 1 illuminated from above by an illumination optical system (not shown) is imaged on the substrate 12 via the projection optical system 3,
Exposure is performed.

Four substrate alignment marks 13 are provided on the substrate. This board alignment mark 1
The substrate alignment mark 1 is read by the laser interferometer 7 by reading the position of the stage when the substrate alignment sensor 3 and the substrate alignment sensor 4 corresponding to each are aligned.
3 position measurements are performed.

The position of the substrate alignment mark (alignment) is usually measured before the exposure of the substrate, but in the method of the present invention, the position of a specific substrate alignment mark is measured again after the exposure, and the position is measured before the exposure. When the difference from the above-mentioned position is not less than the reproducibility of the alignment of the substrate, it is judged as an error.

The method of the present invention will be described with reference to the flowchart of FIG.

When the sequence starts at step 201, normal substrate alignment operation is performed at step 202.
That is, the position of each substrate alignment mark is measured.

Then, in step 203, a normal substrate exposure operation is performed.

After the exposure of the substrate is completed, the repositioning of the specific substrate alignment sensor is performed in step 204.

Then, in step 205, it is determined whether or not the difference between the position of the specific mark initially measured in step 202 and the position measured again in step 204 is equal to or more than a predetermined value.

If the value is equal to or more than the predetermined value, it means that the substrate is displaced during the exposure of the substrate. Therefore, the process proceeds to step 206 and ends with an error (step 207) or an error occurs during the exposure of the substrate. It is determined whether to record (step 208). Actually step 2
At the time of 06, the operator may select whether to terminate the error or record an error, or the control system of the apparatus may be configured so that which is selected in advance can be set.

When the process proceeds to the error recording in step 208, the number of the substrate in which the positional deviation has occurred is recorded as an error, and the following process (including the process of the next substrate) is performed without interrupting the operation of the apparatus. ) Continues (step 20)
9). The substrate for which an error is recorded will be rejected as a defective product in a later process.

When the processing proceeds to the error end in step 207, the operation of the apparatus is once stopped, the apparatus is inspected, and the cause of the error is investigated.

If the difference between the first measurement position and the re-measurement position of the specific mark is less than the predetermined value at step 205, it is possible to determine that the exposure has been performed without any misregistration at the time of exposure. Proceed to continue processing.

In the above description, the number of substrate alignment marks for position measurement is four, and the number of specific alignment marks for repositioning is one. However, the present invention is not limited to this, and two or more alignment marks are used. The mark may be remeasured. If the number of specific alignment marks is increased, the processing time becomes longer, but the error detection accuracy of the positional deviation is improved. Therefore, the number of specific alignment marks may be determined according to the required conditions.

[0048]

As described above, according to the method of the present invention, when there is an abnormality during the calibration of the apparatus before the exposure of a series of substrates, the abnormality can be detected before the exposure and the exposure can be blocked. Therefore, it is possible to prevent defective exposure in advance and reduce the defective rate.

Further, since it is possible to detect an abnormality such as a positional deviation occurring on the substrate during the exposure of the substrate, it is possible to detect a defective substrate without developing and inspecting each substrate. Alternatively, it is possible to prevent the inconvenience of continuing the exposure in a defective state by detecting that an error has occurred during the exposure and stopping the subsequent exposure.

[Brief description of drawings]

FIG. 1 is a flowchart of a calibration operation of an exposure apparatus that is an embodiment of the present invention.

FIG. 2 is a diagram schematically showing an example of a liquid crystal exposure apparatus to which the method of the present invention is applied.

FIG. 3 is a diagram showing a state during substrate exposure of a liquid crystal exposure apparatus similar to that of FIG.

FIG. 4 is a flowchart of substrate alignment and exposure operation during substrate exposure.

[Explanation of symbols]

 1 reticle 2 reticle alignment mark 3 projection optical system 4 substrate alignment sensor 5 XY stage 6a, 6b mirror 7 laser interferometer 8 reference mark 9 stage drive unit 10 control unit 11 reticle alignment sensor 12 substrate 13 substrate alignment mark

Claims (5)

[Claims] 1. An exposure apparatus performs position measurement of at least one same measurement point twice during calibration in which position measurement of a plurality of measurement points related to exposure position accuracy is performed before exposure of a substrate in an exposure apparatus, The positions obtained by the two measurements are compared, and if the difference between the positions obtained by the two measurements is equal to or more than a preset allowable value, a calibration error is determined. Adjustment method. 2. The method of adjusting an exposure apparatus according to claim 1, wherein the two position measurements performed on the same measurement point are performed at the beginning and end of the position measurement of a plurality of measurement points. 3. The measurement point is either a substrate alignment sensor used for aligning an alignment mark of a substrate to be exposed or a reticle alignment mark used for aligning a reticle having a pattern projected on the substrate. 3. One or both of the above, and the method for adjusting an exposure apparatus according to claim 1, wherein: 4. When exposing a substrate in an exposure apparatus, the position of a plurality of alignment marks on the substrate is measured before the exposure, and at least one of the plurality of alignment marks measured after the exposure and before the exposure is measured. If the position is re-measured for one and the two positions thus measured for the same alignment mark before and after exposure are compared, and the difference between the positions is equal to or greater than a preset allowable value, an error occurs. And an exposure error detecting method in an exposure apparatus. 5. The exposure error detection according to claim 4, wherein when the exposure of a plurality of substrates is continuously performed, it is recorded which one of the substrates is determined as the exposure error. Method.