JPH1140488A - Aligning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the alignment, without doing uselessly by counting the number of times that alignment mark position cannot be computed, and changing so that the relative moving parallel to computation is down after the computing step ends, if the count exceeds a specified value. SOLUTION: The method comprises S101 of receiving a reflected light of a detecting light irradiating an alignment mark and computing the mark position from the received light, thereby measuring the mark position, S102 of moving in a wafer station immediately, without waiting for the mark direction result, irradiating the next alignment mark with detection light and judging whether the computer result of the mark position is valid or not, S103 of counting the number of times that the mark position computation result is invalid if any, S104 of judging whether the count N exceeds a threshold S, and S105 of, if N is judged to exceed S, changing the process so as to do the stage moving after the position computation ends.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment method, and more particularly, to an exposure apparatus used when a semiconductor or a substrate such as a liquid crystal display element is manufactured by a photolithography process, and to a method of aligning the substrate.

[0002]

2. Description of the Related Art For example, in a photolithography process (a process of forming a resist image of a mask pattern on a substrate) for manufacturing a semiconductor device or the like, a reticle pattern as a mask is exposed to a photoresist through a projection optical system. A projection exposure apparatus for exposing a substrate (or a wafer or the like) coated with is used.

In recent years, as a projection exposure apparatus of this type, a photosensitive substrate is mounted on a two-dimensionally movable stage, and the photosensitive substrate is stepped by this stage, so that a reticle pattern image is formed on each photosensitive substrate. An exposure apparatus of a so-called step-and-repeat method, for example, a reduction projection type exposure apparatus (stepper), which repeats an operation of sequentially exposing a shot area, is frequently used.

A semiconductor element is formed by laminating a large number of circuit patterns on a wafer coated with a photosensitive agent as a photosensitive substrate. Therefore, when projecting and exposing the second and subsequent circuit patterns on the wafer, In this method, it is necessary to accurately perform alignment between each shot area on which a circuit pattern is already formed on the wafer and a pattern image of a reticle to be exposed, that is, alignment (alignment) between the wafer and the reticle. Therefore, before the exposure operation, the alignment of the wafer is usually performed.

Here, a large number of identical circuit patterns are formed on a wafer, and if the respective circuit patterns are aligned, the circuit patterns can be superposed most accurately. However, if positioning is performed for each of a large number of circuit patterns, it takes a long time to expose one wafer. Therefore, EGA (Enhanced Global) as disclosed in JP-A-6-275496 is disclosed.
Alignment method (hereinafter, abbreviated as EGA method) has been proposed.

[0006] In the EGA method, the positions of three or more measurement points on one wafer are measured to determine the attitude (residual rotation error, orthogonality error, etc.) of the wafer, and based on the attitude, each circuit pattern is determined. The position is estimated and the circuit patterns are to be superimposed. More specifically,
Irradiating a plurality of alignment marks on the wafer with detection light,
The reflected light is received, the position of the alignment mark is calculated based on the reflected light, and the posture of the wafer is detected based on the calculated positions of all the alignment marks.

[0007]

In order to shorten the time required for such alignment, a process of receiving reflected light from an alignment mark and calculating the position of the alignment mark based on the received reflected light is another process. A method has been proposed in which a process of immediately moving a stage holding a wafer is performed in parallel so that detection light is applied to an alignment mark.

However, the reflected light may be inappropriate due to, for example, the amount of the received reflected light being low or the detection light being irradiated off the alignment mark. If the position of the alignment mark is calculated based on such inappropriate reflected light, an error occurs in the calculation.

Therefore, when the method of calculating the alignment mark and moving the stage in parallel is used as described above, the stage has already been moved to a position where another alignment mark is irradiated with the detection light. Even so, once such an error occurs,
In order to measure the erroneous mark again, the stage must be reversed.

In order to prevent such a double effort, in the prior art, a method of calculating the alignment mark and moving the stage in parallel according to the judgment of the operator, a method of calculating the alignment mark, One of the methods of moving the stage after the processing is completed can be selected before wafer positioning.

However, such selection is based on the experience of the operator and is not always correct. On the other hand, when the operator cannot judge immediately based on experience, he or she often chooses a method of moving the stage after calculating the alignment mark, because of the fear of taking a lot of trouble.
This does not speed up the alignment.

Therefore, in view of such a problem, the present invention provides:
For example, it is an object of the present invention to provide a positioning method capable of quickly positioning a wafer.

[0013]

In order to achieve the above object, a positioning method for positioning a substrate according to the present invention comprises the steps of: irradiating one of a plurality of positioning marks with detection light; Receiving the detection light reflected from the alignment mark, calculating the position of the alignment mark based on the received detection light, and moving the detection light and the substrate relative to each other in parallel with the calculation step; Irradiating the detection light on another alignment mark; and counting the number of calculation steps in which the position of the alignment mark could not be calculated when the calculation step was repeated. When the number of times exceeds the predetermined number, the relative movement step performed in parallel with the calculation step is changed to be performed after the calculation step is completed. Characterized by a step.

According to the positioning method of the present invention, when the calculation step is repeated, the step of counting the number of calculation steps in which the position of the alignment mark could not be calculated, and the step of counting the predetermined number of times. A step of changing the relative movement step, which was performed in parallel with the calculation step, to be performed after the calculation step, when the error has occurred a predetermined number of times in the calculation of the alignment mark. As there is a high possibility that an error will occur, the calculation step and the relative movement step are stopped in parallel, and the relative movement step is performed after the calculation step is completed. I have.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described.
This will be described in detail below with reference to the drawings. In the present embodiment, the present invention is applied to an alignment process of an exposure apparatus (stepper) for exposing a reticle pattern to each shot area on a wafer as a photosensitive substrate by a step-and-repeat method.

FIG. 1 is a schematic diagram showing an exposure apparatus according to the present embodiment. In FIG. 1, the exposure light IL emitted from the illumination optical system 1 has a substantially uniform illuminance.
Lighting. The reticle 2 is held on a reticle stage 3, and the reticle stage 3 is supported such that it can move and minutely rotate in a two-dimensional plane on a base 4. A main control system 6 that controls the operation of the entire apparatus controls the operation of the reticle stage 3 via the drive device 5 on the base 4.

Under the exposure light IL, a pattern image of the reticle 2 is projected onto each shot area on the wafer 8 via the projection optical system 7. The wafer 8 is mounted on a wafer stage 10 via a wafer holder 9. The wafer stage 10 holds the wafer 8 in a plane perpendicular to the optical axis of the projection optical system 7.
XY stage for two-dimensionally positioning the projection optical system 7
A Z stage for positioning the wafer 8 in a direction parallel to the optical axis (Z direction), a stage for slightly rotating the wafer 8, and the like.

A movable mirror 1 is provided on the upper surface of the wafer stage 10.
1 is arranged, and a laser interferometer 12 is arranged so as to face the moving mirror 11. Although shown in a simplified manner in FIG. 1, the movable mirror 11 is a plane mirror having a reflecting surface perpendicular to the X axis, with the orthogonal coordinate system in the plane perpendicular to the optical axis of the projection optical system 7 as the X axis and the Y axis. And a plane mirror having a reflecting surface perpendicular to the Y axis. In addition, the laser interferometer 12
Are two laser interferometers for the X axis that irradiate the movable mirror 11 with a laser beam along the X axis and the movable mirror 1 along the Y axis.
1 is composed of a laser interferometer for Y-axis for irradiating a laser beam to two laser interferometers for X-axis and one for Y-axis.
The X and Y coordinates of the wafer stage 10 are measured by the laser interferometers. The coordinate system (X, Y) composed of the X coordinate and the Y coordinate measured in this way is hereinafter referred to as a stage coordinate system or a stationary coordinate system.

The rotation angle of the wafer stage 10 is measured based on the difference between the measured values of the two X-axis laser interferometers. The information of the X coordinate, the Y coordinate, and the rotation angle measured by the laser interferometer 12 is stored in the coordinate measuring circuit 12a and the main control system 6.
The main control system 6 controls the positioning operation of the wafer stage 10 via the driving device 13 while monitoring the supplied coordinates. Although not shown in FIG. 1, the same interferometer system as that on the wafer side is provided on the reticle side.

The projection optical system 7 of this embodiment is provided with an imaging characteristic control device 14. Imaging characteristic control device 1
4 is, for example, by adjusting the interval between predetermined lens groups of the lens groups constituting the projection optical system 7, or by adjusting the pressure of gas in the lens chamber between the predetermined lens groups.
The projection magnification and distortion of the projection optical system 7 are adjusted. The operation of the imaging characteristic control device 14 is also controlled by the main control system 6.

In the present embodiment, an off-axis alignment system 15 is arranged on the side of the projection optical system 7, and in this alignment system 15, illumination light from a light source 16 is collimated by a collimator lens 17, a beam splitter 18, and a mirror 19. Then, the light is irradiated to the vicinity of the alignment mark 29 on the wafer 8 via the objective lens 20. In this case, the baseline amount, which is the distance between the detection center 20a of the objective lens 20 and the center of the reticle via the projection optical system 7, is measured in advance. Then, the reflected light from the alignment mark 29 is transmitted to the objective lens 20, the mirror 19, the beam splitter 1
The light is irradiated onto the index plate 22 via the focusing lens 8 and the condenser lens 21, and an image of the alignment mark 29 is formed on the index plate 22.

The light transmitted through the index plate 22 is directed to the beam splitter 24 via the first relay lens 23, and the light transmitted through the beam splitter 24 is converted by the second relay lens 25X for X-axis into an X-axis formed by a two-dimensional CCD. Image sensor 2
The light converged on the 6X imaging surface and reflected by the beam splitter 24 is reflected by the second relay lens 25Y for Y-axis.
It is focused on the imaging surface of a Y-axis imaging device 26Y composed of a dimensional CCD. On the imaging surfaces of the imaging elements 26X and 26Y, an image of the alignment mark 19 and an image of the index mark on the index plate 22 are formed so as to overlap each other. Image sensor 26X
26Y are supplied to the coordinate position measuring circuit 12a.

FIG. 2 shows a pattern on the index plate 22 shown in FIG. 1. In FIG. 2, an image 29P of a cross-shaped alignment mark 29 is formed at the center, and an orthogonal linear pattern image 29XP of this image 29P is formed. And XP perpendicular to 29YP
Direction and the YP direction are respectively the wafer stage 1 of FIG.
0 is conjugate to the X and Y directions of the stage coordinate system. Then, two index marks 31A and 31B are formed so as to sandwich the alignment mark image 29P in the XP direction, and two index marks 32A and 32B are formed so as to sandwich the alignment mark image 29P in the YP direction.

In this case, in the XP direction, the index marks 31A,
Detection area 33 surrounding 31B and linear pattern image 29XP
The image in X is picked up by the X-axis image sensor 26X in FIG.
An image in the detection area 33Y surrounding the index marks 32A and 32B and the linear pattern image 29YP in the P direction is picked up by the Y-axis image sensor 26Y in FIG. Further, the scanning direction when reading the photoelectric conversion signal from each pixel of the imaging elements 26X and 26Y is set to the XP direction and the YP direction, respectively, and by processing the imaging signals of the imaging elements 26 and 26Y, the alignment mark image 29P and Index marks 31A, 31B
, 32A, and 32B in the XP direction and the YP direction. Therefore, in FIG. 1, the coordinate measuring circuit 12a determines the alignment mark 29 based on the positional relationship between the image of the alignment mark 29 on the wafer 8 and the index mark on the index plate 22 and the measurement result of the laser interferometer 12 at that time. Are determined on the stage coordinate system (X, Y), and the coordinate values measured in this way are
To supply.

By the way, a plurality (three or more) on the wafer 8
If the position of the alignment mark 29 can be measured, EG
By the A method, the attitude of the wafer can be obtained, and the attitude (position) of all the circuit patterns on the wafer 8 can be accurately estimated based on the attitude. Such EG
The method A is disclosed in detail in, for example, Japanese Patent Application Laid-Open No. 6-275496, and the description thereof is omitted.

Here, in order to apply the EGA system,
It is necessary to detect the positions of the plurality of alignment marks 29. FIG. 3 is a flowchart showing the position measurement of the plurality of alignment marks 29 according to the present embodiment.

First, it is assumed that the processing has been set in advance so that the position calculation of the alignment mark 29 and the stage movement are performed in parallel. In FIG. 3, step S101
First, the position of the first alignment mark is measured. More specifically, the alignment system 1 shown in FIG.
5 irradiates the alignment mark 29 with detection light,
The reflected light is received, and the calculation of the mark position is started based on the reflected light. Then, the wafer stage 10 is immediately moved without waiting for the calculation result of the mark position, so that the next alignment mark 29 is irradiated with the detection light.

Further, in step S102, it is determined whether or not the calculation result of the mark position is appropriate. If an error occurs in the calculation of the mark position and the result is not appropriate, the number is counted in step S103. In the following step S104, it is determined whether or not the count number N has exceeded the threshold value S.

The threshold value S is determined based on experimental results or experience assuming that if errors occur S times, a considerable number of errors are predicted in subsequent calculations.

If it is determined in step S104 that the error count number N has exceeded the threshold value S, in step S105, after the position calculation of the alignment mark 29 is completed, the stage is moved (moved between marks). Change the content. Further, in step S106, the number of errors N is set to -999. By doing so, after once passing through step S105, it does not substantially pass through step S105 again.

On the other hand, if it is determined that the error count number N does not exceed the threshold value S after step S106 or in step S104, the process proceeds to step S104.
Subsequently, in step S107, the wafer stage 10 is moved so that the calculation result of the mark position returns to the position of the invalid alignment mark.

It is considered that many of the causes of errors in the mark calculation are due to inappropriate detection light reflected light. Therefore, if the detection condition of the alignment mark is changed by increasing the light amount of the detection light or expanding the scanning range of the detection light, the possibility of receiving appropriate reflected light increases. After changing the detection conditions in this way, the process returns to step S101 again, and the position of the mark is measured again.

If the mark position can be calculated in step S102, it is determined in step S108 whether the position measurement of all marks has been completed. Here, if it is determined that the position measurement of all the marks has not been completed, the position measurement of the next mark is performed in step S109, and a series of processing flow starting from the subsequent step S102 is similarly executed. . On the other hand, if it is determined in step S108 that the position measurements of all the marks have not been completed, the process ends.

As described above, according to the present embodiment, when an error occurs in the alignment mark position calculation,
Since the processing content is changed based on the number of errors as shown in step S105, when there are many errors, the stage is moved after the calculation of the mark position is completed, and the number of stages of the stage required for measurement is reduced. Can be done. On the other hand, when the number of errors is small, the calculation of the mark position and the movement of the stage can be performed in parallel, thereby speeding up the wafer alignment.

[0035]

As described above, according to the alignment method of the present invention, when the calculation step is repeated, the step of counting the number of calculation steps in which the position of the alignment mark could not be calculated, When the counted number exceeds a predetermined number, the relative movement step performed in parallel with the calculation step is changed to be performed after the calculation step. When the predetermined number of times has occurred, it is determined that there is a high possibility that an error will occur in the future, so that the calculation step and the relative movement step are stopped in parallel, and the relative movement step is performed after the calculation step is completed. Can be performed without waste.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an exposure apparatus according to the present embodiment.

FIG. 2 is a view showing a pattern on an index plate 22 of FIG. 1;

FIG. 3 is a flowchart showing position measurement of a plurality of alignment marks 29 according to the embodiment.

[Explanation of symbols]

 7 Projection optical system 8 Wafer 10 Wafer stage 11 Moving mirror 12 Laser interferometer 12a Coordinate measurement circuit 14 Image forming characteristic control device 15 Alignment system 16 Light source 17 Collimator lens 18 Beam splitter 19 Mirror 20 Objective lens 22 Index plate 29 Alignment mark

Claims (4)

[Claims] 1. An alignment method for aligning a substrate based on sequentially and optically detecting the positions of a plurality of alignment marks formed on a substrate, wherein: Irradiating detection light reflected from the alignment mark, receiving the detection light reflected from the alignment mark, calculating the position of the alignment mark based on the received detection light, And causing the detection light to irradiate another alignment mark with the detection light by moving the detection light and the substrate relative to each other. A step of counting the number of calculation steps in which the position could not be calculated; and when the counted number exceeds a predetermined number, Changing the relative movement step performed in parallel with the calculation step to be performed after the calculation step ends. 2. The method according to claim 1, wherein, in the calculating step, when the position of the alignment mark cannot be calculated, the detection light and the substrate are irradiated again so that the detection light is irradiated onto the alignment mark whose position could not be calculated. Relative detecting the position, changing the detection conditions, irradiating the alignment mark whose position could not be calculated with detection light, and detecting the detection light reflected from the alignment mark whose position could not be calculated. 2. The method according to claim 1, further comprising the step of receiving light again, and calculating the position of the alignment mark again based on the received detection light. 3. The alignment method according to claim 2, wherein the detection condition is changed by increasing a light amount of the detection light. 4. The alignment method according to claim 2, wherein the detection condition is changed by expanding an irradiation range of the detection light.