JPH0613286A - Position measuring method in semiconductor exposure apparatus - Google Patents

Abstract

(57) [Summary] [Purpose] To reduce the effects of errors due to differences in the postures of structures and errors due to differences in the temperature environment with a simple method when measuring position errors related to shot areas. When measuring the positions of a plurality of measured patterns on a wafer in a semiconductor exposure apparatus and calculating the overall pattern position on the wafer from these measured values, each measured pattern is divided into a plurality of sets 1 to 4. And divide into 5 to 8 and measure the wafer stage by driving the wafer stage from different directions, calculate the average of the measured values of each set, and calculate the overall pattern position on the wafer based on the average. It is characterized by doing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position measuring method for estimating a whole pattern position by measuring a part of pattern position on a wafer in a semiconductor exposure apparatus.

[0002]

2. Description of the Related Art In a step-and-repeat type exposure apparatus for manufacturing a semiconductor, a so-called stepper, a position or a position error associated with several shot areas on a semiconductor wafer is measured, and from these, each shot area on the wafer is measured. A positioning method for determining a shot arrangement and sequentially aligning each shot area on the wafer with a position related to the reticle using the determined shot arrangement has been proposed, for example, in Japanese Patent Laid-Open No. 63-232321. . Further, there has been proposed a method of calculating the reliability of measurement obtained from a measurement signal or the like by weighting the measurement position data when determining the shot arrangement.

[0003]

However, in the above proposal and in the related art, regarding the measurement of the position or position error related to some shot areas on the wafer, the wafer at the time of the measurement is in the posture of the stage. And the influence of errors due to changes in temperature environment was not considered. For example, when measuring a position error relating to a certain shot area, the wafer stage is driven so that the shot area comes to the measurement position. At this time, the method of driving the wafer stage and the position of the wafer stage before driving are
An error is given to the position error measurement.

In the conventional case where the pattern width formed on the semiconductor wafer was about 0.3 μm or more, such an influence was negligible. However, the above-mentioned method of driving the wafer stage and the position of the wafer stage before the driving cause an error factor of about 0.02 to 0.04 μm according to the experiments of the applicant, and form a pattern with a width of 0.2 μm or less. The amount required is now negligible. In the future, as the resolution of the stepper is further improved, and as the stepper is required to have higher alignment accuracy, such an influence cannot be ignored.

The present invention has been made in view of the above circumstances, and an object thereof is to simply measure the influence of an error due to a difference in posture of a structure and an error due to a difference in temperature environment in measuring a position error relating to a shot area. It is to reduce.

[0006]

In order to solve the above problems, a position measuring method of the present invention is to measure the positions of a plurality of measured patterns on a wafer in a semiconductor exposure apparatus, and to measure the positions on the wafer from the measured values. When calculating the overall pattern position, each measured pattern is divided into a plurality of groups, the wafer stage is driven from a different direction for each group to perform measurement, and the average of the measured values of each group is calculated. It is characterized in that the overall pattern position on the wafer is calculated based on an average.

In a preferred embodiment of the present invention, the wafer stage is driven in a reciprocating driving sequence for each set, such as clockwise and counterclockwise.
Further, the measured patterns that are close to each other are divided into different sets. In this case, the same measured pattern may be measured by a plurality of different sets instead of the measured patterns that are close to each other.

[0008]

In the past, the order of position measurement has been determined so that the total movement distance of the wafer stage is minimized from the viewpoint of throughput. Therefore, the measurement is performed while moving to the closest shot. If the measurement is performed in this order, the change of the temperature with time and the influence of the attitude difference of the wafer stage structure cause an error in the obtained shot arrangement.

In the present invention, for example, three shots at positions as far apart as possible on the wafer are selected and a plurality of shots are set as one shot. The shots are shot in order while changing the driving direction of the wafer stage for each shot. Measure the position. From this measurement result, the measurement value of the shot array error on the wafer is calculated for each set, for example, the translation component, the rotation component and the magnification component, and finally the shot array is calculated from the average of the shot arrays obtained from the measurement values of each set. . By selecting the measurement order in this way, the errors due to the stage attitude and the temperature environment difference that occur for each set are averaged.

[0010]

According to the present invention, as described above, the method of measuring the positions of the shot areas is devised, and the effects of the posture difference of the structure and the ambient temperature difference are averaged. It was possible to reduce the influence of the error due to the difference in the posture of the structure and the error due to the difference in the temperature environment.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the drawings.

FIG. 1 shows an embodiment of a step-and-repeat type semiconductor exposure apparatus (so-called stepper) according to the present invention. RT is a reticle on which a pattern PT for manufacturing a semiconductor element is formed, WF is a semiconductor wafer having a large number of shots SH, LN is a projection lens for reducing and projecting the pattern PT on the reticle RT onto one shot SH of the wafer WF, CU is a control unit for controlling the entire stepper, and CS is a console for inputting necessary information such as alignment data and exposure to the control unit CU. AM is a mark for alignment which is formed in advance on each shot SH on the semiconductor wafer WF. AS is an alignment scope for detecting the position of the mark AM for alignment. ST is a wafer stage for moving the wafer, and the position of this wafer stage ST is the laser interferometer IM.
Is constantly monitored by.

The semiconductor wafer WF is exposed by the following procedure. First, the reticle RT is aligned with the projection lens LN, and then the alignment scope AS detects the positions of the alignment marks AM on some shots SH on the semiconductor wafer WF. This position is stored in the control unit CU as a combined value of the reading value of the laser interferometer IM and the detection value of the alignment scope AS. The control unit CU estimates the position of the entire shot from this shot position, and the estimated shot position is the projection lens L.
Exposure is performed while sequentially driving the wafer stage ST so that it is directly below N.

When measuring the positions of several shots SH on the semiconductor wafer WF, an error occurs due to the following causes.

(1) Measurement error of laser interferometer IM (2) Error due to posture variation (distortion) of wafer stage ST (3) Measurement error of alignment scope AS

The errors (1) and (2) are error factors closely related to the history of the wafer stage, and an object of the present invention is to reduce their influence. The error of (3) is not the object of the present invention.

The error (1) is mainly due to the change in the refractive index of air with temperature. In the case of an interferometer using a HeNe laser, this amount is known as 0.93 ppm / ° C. For example, when the measured distance is 200 mm and the temperature change is 0.1 ° C., this corresponds to a measurement error of 0.019 μm. On the other hand, it is difficult to keep the temperature of the air around wafer stage ST within 0.1 ° C. Even if it is kept constant over time, it takes a great deal of cost to suppress the variation in the spatial temperature distribution caused by the movement of the wafer stage.

FIG. 2 shows the mechanism of temperature change caused by the movement of the stage ST. In FIG. 2, the stage ST moves from the measurement position of the shot SHB to the shot S.
When the stage ST moves to the measurement position of HA, the stage ST moves across the air flow F, so that the surrounding air EA flows into the optical path of the laser interferometer IM. However, when the stage ST moves in parallel with the air flow F, for example, from the shot SHC measurement position to the shot SHA measurement position, this phenomenon does not occur. If the position of the shot SHA is measured, the stage ST
Has moved from the measurement position of the shot SHB or has moved from the measurement position of the shot SHC.

The error in (2) above is caused by the wafer stage ST.
Is an error component caused by not being a perfect rigid body.
For example, when the wafer stage ST stops at a certain position,
The attitude of wafer stage ST differs depending on whether it has moved from the right direction or from the left direction. This posture change returns to the original posture with a fairly long time constant of several seconds, but since the shot SH position is measured immediately after the stage is stopped, the posture of wafer stage ST remains distorted.

FIG. 3 shows a shot arrangement determination method according to the present invention. 3 measurement shots each in step 1
Divide into multiple sets, each containing at least one. In step 2,
For example, the first set is driven in the clockwise direction, the second set is driven in the counterclockwise direction, and so on. In step 3, the entire shot array is estimated from each measured value. The method of estimating the entire shot arrangement in step 3 may be a method of estimating the entire shot arrangement by averaging translational components, rotational components, and magnification components obtained from the measurement values of each set,
Further, approximate calculation of the shot array may be performed by direct square approximation or the like from the individual measurement values of each set.

The grouping of the measurement shots in the above step 1 is determined by using the fuzzy inference composition rule based on the following inference rules.

(Rule 1) if the number of shots in each set is 3 or more then GOO
D (Rule 2) if The sum of the distances between shots of each pair is large
then GOOD (Rule 3) if the sum of the distances between shots in each group is small
then POOR (rule 4) if the number of if sets is large then GOOD (rule 5) if the number of if sets is small then POOR (rule 6) if there are few shots that belong to multiple sets
then GOOD (Rule 7) if Many shots belong to multiple groups th
en POOR

FIG. 4 shows an example of the order of shot measurement created by the above inference. Shot SH in FIG.
A, SHB, and SHC correspond to those in FIG. Figure 4
In, the measurement shot is divided into two sets, the first set of measurements is counterclockwise, and the second set of measurements is clockwise. The shot SHA and the shot SHC are located close to each other and should have the same amount of measurement error.
While the wafer stage ST (FIG. 1) moves from the upper left when measuring HA, it is largely driven from the upper right when measuring shot SHC. Therefore, shot SH
The measured value of A and the measured value of shot SHC include approximately the same amount of errors due to the above-described posture distortion of the wafer stage and the ambient temperature distribution in opposite directions, and these error components are canceled by the averaging process. Will be.

FIG. 5 shows an example of a conventional shot measurement order. In this case, the measured value of the shot SHC includes an attitude distortion of the wafer stage and an error component due to temperature distribution. However, since the wafer stage moves from the adjacent shot SHC during the shot SHA measurement, the error component mixed in this measurement value is small, and since it is in the same direction as the shot SHC measurement value, the averaging effect is expected. Can not.

Table 1 shows an experimental example of measured values of the orthogonality component of the same wafer in the conventional measurement order and the measurement order of the present invention.

[0026]

[Table 1] In this example, in the conventional measurement order, the average is −0.24 μ.
While the error of rad occurs, the average of the measurement errors is reduced to about 0.04 μrad in the measurement order according to the present invention.

[0027]

[Embodiment] If the measurement shot SH is allowed to be measured twice, as shown in FIG. 6, the distortion of the wafer stage is distorted by using two measurement groups in which the driving directions of the wafer stage are opposite to each other. It is possible to eliminate the influence of the above and the influence of the fluctuation of the ambient temperature distribution. In this case, the overall measurement time is delayed, but a more accurate measurement result can be obtained as compared with the above-described embodiment. In FIG. 6, numbers and arrows indicate the order of measurement.

[Brief description of drawings]

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

2 is an explanatory diagram of a cause of a shot position measurement error in the apparatus of FIG.

3 is a flowchart showing a shot position measuring procedure in the apparatus of FIG.

4 is a diagram showing an example of a shot position measurement sequence in the apparatus of FIG.

FIG. 5 is a diagram showing an example of a conventional shot position measurement sequence.

6 is a diagram showing another example of the shot position measurement order in the apparatus of FIG.

[Explanation of symbols]

RT: reticle, WF: semiconductor wafer, LN: projection lens, CU: control unit, CS: console, AM: alignment mark, AS: alignment scope, ST: wafer stage, IM: laser interferometer, S
H: Shot, SHA, SHB, SHC: Shot to be measured.

Claims (5)

[Claims] 1. When measuring the positions of a plurality of measured patterns on a wafer in a semiconductor exposure apparatus to calculate the overall pattern position on the wafer, each measured pattern is divided into a plurality of groups, A position measuring method characterized in that the wafer stage is driven from a different direction for each set to perform measurement, an average of the measurement values of each set is obtained, and the overall pattern position on the wafer is calculated based on the average. . 2. The measuring method according to claim 1, wherein the driving order for each set is a reciprocating operation. 3. The measuring method according to claim 1, wherein the measured patterns that are close to each other are divided into different sets and measured. 4. The measuring method according to claim 1, wherein the same measured pattern is measured by a plurality of different sets. 5. The measuring method according to claim 1, wherein the averaged measurement values are a translation component, a rotation component, and a magnification component of an array error of each shot on the wafer.