JPH06216009A - X-ray aligner - Google Patents

Abstract

PURPOSE:To provide an X-ray aligner with which a highly precise alignment can be made and a proximity gap can be maintained at a fixed value utilizing an LFZP. CONSTITUTION:A mask mark 12 and a wafer mark 11 are composed of a linear Fresnel zone plate, and light is projected obliquely on the above-mentioned mask mark and the wafer mark. The condensed image formed by the mask mark and the wafer mask is image-formed on a licensor 34 and a secondary sensor 35 by an optical system 33. The first image treatment device 36 detects the position of the condensed image of each mark on the licensor. The second image treatment device 37 detects the focus of the condensed image of each mark on the secondary sensor. Either of the mask stage and the wafer stage is controlled by the output of the first image treatment device, and the focus of the mask stage and the wafer stage is controlled by the output of the second image treatment device.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an improvement of an X-ray exposure apparatus.

[0002]

2. Description of the Related Art Generally, when manufacturing a semiconductor device,
An exposure process using a mask is indispensable, and for this exposure process, position control of a mask stage with a mask and a wafer stage with a wafer is required. FIG. 6a shows a schematic configuration of the X-ray exposure apparatus, and FIG. 6b is a view of a certain exposure field on the semiconductor wafer as seen from above. In this apparatus, a wafer stage (not shown) is passed through a mask 50 mounted on a mask stage (not shown).
When the wafer 60 mounted on the wafer is irradiated with X-rays, a pattern defined by the mask 50 is formed in the pattern formation region 62 defined in the exposure field 61 of the wafer, as shown in FIG. Alignment patterns 63 are formed on both sides of.

[0003]

By the way, the mask 50 is used.
Two optical systems 51 for observing the positional deviation of the alignment pattern 63 (only one of them is shown because they are arranged in the direction perpendicular to the paper surface) are arranged above the optical patterns 51. Since the X-rays are shielded by, the pattern formation area 62 is limited to these inner areas. On the other hand, in order to enlarge the pattern formation area 62, it is necessary not only to retract the optical system 51 to another position outside the X-ray passage area, but also to make alignment control during exposure impossible. turn into.

As a method of solving such a problem,
Linear Fresnel Zone Plate (hereinafter LFZP
However, the alignment method is apt to be affected by the proximity gap between the mask and the wafer and the measurement range is narrow, which hinders its practical use.

Therefore, it is an object of the present invention to provide an X-ray exposure apparatus which utilizes LFZP, enables highly accurate alignment, and can maintain the proximity gap at a constant value.

[0006]

SUMMARY OF THE INVENTION The present invention provides a mask alignment mark (hereinafter referred to as a mask mark) attached to a mask and a pair of wafer alignment marks (hereinafter referred to as a wafer mark) attached to a wafer. In the X-ray exposure apparatus for detecting and controlling the alignment of the wafer, the mask mark and the wafer mark are each formed of LFZP, and means for obliquely irradiating the mask mark and the wafer mark with irradiation light, An optical system for forming a focused image of a mask mark and a wafer mark on a line sensor and a two-dimensional sensor, and a first image processing device for detecting a positional relationship between the focused images of the marks on the line sensor. A second image processing device for detecting a focus of a focused image of each mark in the two-dimensional sensor, the first image Mask stage at the output of the management unit,
One of the wafer stages is controlled, and the focus of the mask stage and the wafer stage is controlled by the output of the second image processing apparatus.

[0007]

In this apparatus, the optical system is arranged at a position in consideration of the incident angle of the irradiation light and the proximity gap between the mask and the wafer, and the mask mark is focused between the focused images of the pair of wafer marks. Position the statue. Due to the depth of focus of the optical system, the focused image becomes the clearest image in the center part, and becomes a blurred image as it deviates from the center. In consideration of this, the central portion of the condensed image is used for detecting the positional deviation, and the portion outside the central portion is used for adjusting the focus. From this point of view, the line sensor takes out the image information of the central area of the focused image of the mask mark and the wafer mark and sends it to the first image processing device, and the two-dimensional sensor uses the central area. The image information on both sides of is extracted and sent to the second image processing device.
The first image processing device detects, based on the image information of the central region, how much the focused image of the mask mark deviates from the intermediate position between the focused images of the pair of wafer marks, and this detection is performed. The value is sent to the mask stage controller or the wafer stage controller as a displacement signal. On the other hand, the second image processing device detects the difference in light amount between the images on both sides of the image information on both sides of the central region and sends this detection signal to the focus control device for the mask stage and the focus control device for the wafer stage. To do.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. In FIG. 1, a wafer mark 11 formed on a wafer (not shown) mounted on the wafer stage
Then, the mask mark 12 formed on the mask (not shown) mounted on the mask stage is irradiated with illumination light such as laser light from an irradiation means (not shown) at an incident angle of 45 degrees. The X-rays are emitted from directly above the mask.
Wafer mark 11 and mask mark 12 are both LFZ
It is composed of P and is formed with a positional relationship as shown in FIG.

FIG. 2a shows the mask mark 12 and FIG.
Indicates a pair of wafer marks 11a and 11b. As shown in FIG. 2c, the positional relationship is such that the mask mark 12 is located between the pair of wafer marks 11a and 11b, and the incident angle of the illumination light is 45 degrees and the proximity gap Pg (see FIG. 1). Can be decided in consideration.
That is, since the incident illumination light forms a single linearly focused image on the focal lengths of the wafer marks 11a and 11b and the mask mark 12 by LFZP, these focused images are formed on the same surface. The focal length of each mark is set so as to form an image, and the positional relationship of each mark is set so as to be aligned in a line as shown in FIG. 2d. 21 in FIG. 2d
Reference numerals a and 21b denote focused images by the wafer marks 11a and 11b, respectively, and 22 denotes a focused image by the mask mark 12, and these focused images are formed to be bright against a dark background.

In order to satisfy the above setting conditions, the focal length F of the wafer mark 11 in FIG.
₁₁ is ΔF = P in consideration of the proximity gap Pg and the incident angle θ (angle with respect to the normal line of the mask, which is 45 degrees in this case) compared with the focal length F ₁₂ of the mask mark 12.
It is set to be longer by g / sin θ. As a result, three focused images (only one is shown for convenience) are formed as shown in FIG. 2d in the area AR of FIG. These three condensed images are collected by the optical system 33 including the objective lens 31 and the half mirror 32 and the line sensor 34 and the two-dimensional sensor 3.
It is divided into 5 and.

By the way, the optical system 33 includes an objective lens 31.
Is placed so that the focal point of is aligned with the center of the condensed image in the longitudinal direction. Therefore, the condensed image of the area AR is imaged on the line sensor 34 and the two-dimensional sensor 35 by the optical system 33, but the imaged state is clear at the central portion in the longitudinal direction of the image as shown in FIG. , It becomes a blurry image as it gets away from this central part. 3 shows the condensed image 22 and the line sensor 3.
Although the case of 4 is shown, the other condensed images 21a, 2
The same applies to the case of 1b and the two-dimensional sensor 35.

The line sensor 34 is used to detect the position shift of the focused image 22 of the mask mark with respect to the intermediate position between the focused images 21a and 21b of the pair of wafer marks and to control the alignment of the mask stage or the wafer stage. Therefore, it is necessary to use a clear portion of the image formed by each collected image. For this reason,
The line sensor 34, as shown in FIG.
Imaging 21a ', 21b', 2 by 1a, 21b, 22
In order to detect the positional relationship in the central part of 2 ',
An image in an area A1 shown by hatching in the figure is converted into an image signal.

On the other hand, the two-dimensional sensor 35 is used for focus control of the mask stage and the wafer stage, and therefore it is convenient to use the blurred portion of the image formed by each condensed image. Therefore, the two-dimensional sensor 35, as shown in FIG.
In order to be able to detect the relationship of the light amount outside the central portion in the images 21a ', 21b', 22 'formed by 1b, 22, the images in the two areas B1, B2 shown by the diagonal lines in the figure are converted into image signals. .

Returning to FIG. 1, the image signal from the line sensor 34 is output to the first image processing device 36, and the image signal from the two-dimensional sensor 35 is output to the second image processing device 37. In the first image processing device 36, the image signal from the line sensor 34 is processed to detect the positional deviation of the condensed image 22 from the intermediate position between the condensed images 21a and 21b. Then, the wafer stage controller 38
Output to. The wafer stage control device 38 controls the position correction of the wafer stage based on the signal indicating the positional deviation, and the positional deviation is 0, that is, the focused image 22 is the focused image 21.
Set it to the exact middle position between a and 21b. Of course, the signal of the first image processing device 36 may be supplied to a mask stage control device (not shown) to control the position correction of the mask stage.

The second image processing device 37 processes the image signal from the two-dimensional sensor 35 and outputs a signal representing focus data. This will be described for the case of the focused image 22 of the mask mark. Regarding the image formation 22 'of the focused image 22 of the mask mark in FIG. 4b, the light intensity at the center point in the region B1 and the light intensity at the center point in the region B2 ( In the figure, it may be a value integrated in the Y direction), and a difference value between them is obtained. The light intensity in the region B1 and the light intensity in the region B2 each differ in brightness and darkness of the image depending on the direction deviating from the focus point with the focus point as a reference value, and as a result, change as shown in FIG. Then, the difference value between the two light intensities is 0 at the focus point as shown in FIG. 5a. The second image processing device 37 outputs a signal representing this difference value to the focus control device 39 of the mask stage. The focus control device 39 controls the focus of the mask stage so that the difference value becomes 0 based on the signal representing the difference value.

In the case of the condensed images 21a and 21b of the wafer mark, the light intensity at the center point in the area B1 and the area B are related to at least one of the images 21a 'and 21b'.
The difference value of the light intensity of the central point in 2 is detected. A signal representing the detected difference value is supplied to the focus control device 40 of the wafer stage. Focus control device 40
Performs focus control of the wafer stage based on the signal indicating the difference value so that the difference value becomes zero.

In the above description, the alignment control of the mask stage or wafer stage is performed in X, Y, θ.
Regarding the X direction of the directions. Since the LFZP can detect only the displacement in one direction, the alignment of X, Y, and θ can be performed by detecting the distances Y1 and Y2 in the Y direction of two points in the Y direction in addition to the X direction, for example. Therefore, similar operation control is performed in the Y1 and Y2 directions by using different mask marks, wafer marks and line sensors. As for the line sensor and the two-dimensional sensor, since the line sensor can collect data in a short time, it is used as an alignment feedback sensor, and the two-dimensional sensor is used as a focus sensor because it takes time to collect data. If the data of the two-dimensional sensor is directly connected to the image processing circuit board capable of hardware processing, the function of alignment processing can be added to the two-dimensional image processing, and the line sensor can be omitted.

[0018]

Although the present invention has been described with reference to the embodiment, the following effects can be obtained according to the present invention.

(1) The alignment detection range is widened by detecting the positional deviation of the mask mark by setting the focused image of the mask mark between the focused images of the pair of wafer marks.

(2) Since the condensed image by LFZP is used, the brightness of the image (S / N ratio of the light intensity) becomes much higher than that of a normal image without condensing, and thereby the detection accuracy can be improved. it can.

(3) The function of the focus sensor can be provided by using the outer portion of the condensed image.

(4) Since the irradiation light is obliquely incident and is received from an oblique position, there is no shield in the X-ray irradiation area,
There is no restriction on the pattern formation area of the wafer.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment of the present invention.

FIG. 2 is a diagram for explaining a mask mark and a wafer mark used in the present invention, and a positional relationship of a focused image by these.

FIG. 3 is a diagram for explaining an imaging state in the optical system shown in FIG.

FIG. 4 is a diagram for explaining an imaging state in the line sensor and the two-dimensional sensor shown in FIG.

FIG. 5 is a diagram for explaining the operation principle of the second image processing apparatus shown in FIG.

FIG. 6 is a diagram for explaining a conventional alignment method.

[Explanation of symbols]

 11, 11a, 11b Wafer mark 12 Mask mark 21a, 21b Focused image by wafer mark 22 Focused image by mask mark 33 Optical system 34 Line sensor 35 Two-dimensional sensor 50 Mask 51 Optical system 60 Wafer 61 Exposure field 62 Pattern formation area

Claims (1)

[Claims] 1. A wafer alignment control by detecting a mask alignment mark (hereinafter referred to as a mask mark) attached to a mask and a pair of wafer alignment marks (hereinafter referred to as a wafer mark) attached to a wafer. Do X
In the line exposure apparatus, the mask mark and the wafer mark are each formed of a linear Fresnel zone plate, and means for obliquely irradiating the mask mark and the wafer mark with irradiation light, and the mask mark and the wafer mark Optical system for forming a focused image by the line sensor and the two-dimensional sensor, a first image processing device for detecting the positional relationship of the focused image of each mark in the line sensor, and the two-dimensional sensor And a second image processing device for detecting the focus of the focused image of each mark in, and a mask stage at the output of the first image processing device,
An X-ray exposure apparatus, wherein one of the wafer stage is controlled and focus control of the mask stage and the wafer stage is performed by an output of the second image processing apparatus.