JP2797053B2 - X-ray exposure equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an X-ray exposure apparatus.

[0002]

2. Description of the Related Art Generally, in manufacturing a semiconductor device,
An exposure process using a mask is indispensable, and the exposure process requires position control of a mask stage on which a mask is mounted and a wafer stage on which a wafer is mounted. FIG. 6a shows a schematic configuration of an X-ray exposure apparatus, and FIG. 6b is a view showing a certain exposure field on a semiconductor wafer as viewed from above. In this apparatus, a wafer stage (not shown) passes through a mask 50 mounted on a mask stage (not shown).
When a wafer 60 mounted on the wafer is irradiated with X-rays, a pattern defined by the mask 50 is formed in a pattern forming area 62 defined in an exposure field 61 of the wafer, as shown in FIG. Are formed on both sides of the substrate.

[0003]

By the way, the mask 50
Above this, two optical systems 51 (only one is shown because they are arranged in a direction perpendicular to the paper surface) for observing the positional shift of the alignment pattern 63 are arranged. Therefore, the X-rays are shielded, so that the pattern forming region 62 is limited to these inner regions. On the other hand, in order to enlarge the pattern formation region 62, it is necessary not only to retreat the optical system 51 to another position outside the X-ray passage area, but also to make alignment control during exposure impossible. turn into.

[0004] As a method of solving such a problem,
Linear Fresnel Zone Plate (hereinafter LFZP)
This method is susceptible to the proximity gap between the mask and the wafer and has a narrow measurement range, which hinders practical application.

It is therefore an object of the present invention to provide an X-ray exposure apparatus that utilizes LFZP, enables high-precision alignment, and maintains a constant proximity gap.

[0006]

According to the present invention, a mask alignment mark (hereinafter, referred to as a mask mark) provided on a mask and a pair of wafer alignment marks (hereinafter, referred to as a wafer mark) provided on a wafer are provided. In an X-ray exposure apparatus for detecting and controlling the alignment of a wafer, the mask mark and the wafer mark are each composed of LFZP, and a means for irradiating the mask mark and the wafer mark with irradiation light obliquely; An optical system for forming a condensed image by a mask mark and a wafer mark on a line sensor and a two-dimensional sensor, and a first image processing apparatus for detecting a positional relationship between the condensed images of each mark in the line sensor. A second image processing device for detecting a focus of a condensed image of each mark in the two-dimensional sensor, wherein the first image Mask stage at the output of the management unit,
One of the wafer stages is controlled, and the focus control of the mask stage and the wafer stage is performed by the output of the second image processing apparatus.

[0007]

In this apparatus, the optical system is disposed 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 light of the mask mark is condensed between the condensed images of the pair of wafer marks. Position the image. Due to the depth of focus of the optical system, the condensed image becomes the clearest image at the center and becomes blurred as the distance from the center increases. In consideration of this, the central portion of the condensed image is used for detecting the positional deviation, and a portion outside the central portion is used for adjusting the focus. From such a viewpoint, the line sensor extracts the image information of the central area with respect to the condensed image of the mask mark and the wafer mark and sends it to the first image processing apparatus. And extracts the image information on both sides of the image processing apparatus and sends it to the second image processing apparatus.
The first image processing apparatus detects, based on the image information of the central area, how much the focused image of the mask mark is deviated from an intermediate position between the focused images of the pair of wafer marks. The value is sent as a position shift signal to the control device of the mask stage or the control device of the wafer stage. On the other hand, the second image processing device detects a difference in light amount between the images on both sides from 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. I do.

[0008]

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 (both not shown) mounted on a wafer stage
Then, the mask mark 12 formed on the mask (neither is shown) mounted on the mask stage is irradiated with illumination light such as laser light at an incident angle of 45 degrees from an irradiation means (not shown). Note that X-rays are emitted from directly above the mask.
Both wafer mark 11 and mask mark 12 are LFZ
P and are 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, the incident angle of the illumination light is 45 degrees, and the proximity gap Pg (see FIG. 1). It is decided in consideration of.
That is, the incident illumination light becomes one linear condensed image on the focal length of the wafer marks 11a and 11b and the mask mark 12 by LFZP, and these condensed images are formed on the same plane. The focal length of each mark is set so as to form an image, and the positional relationship between the marks is set so as to be arranged in a line as shown in FIG. 2D. In FIG.
Reference numerals a and 21b denote condensed images by the wafer marks 11a and 11b, respectively, and reference numeral 22 denotes a condensed image by the mask mark 12, and these condensed images are formed so as to be brighter against a dark background.

In order to satisfy the above set 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 (the angle with respect to the normal line of the mask, 45 degrees here) as 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 condensed images (only one is shown for convenience) as shown in FIG. 2D are formed in the area AR of FIG. These three condensed images are converted into a line sensor 34 and a two-dimensional sensor 3 by an optical system 33 including an objective lens 31 and a half mirror 32.
It is split into five.

Incidentally, the optical system 33 includes the objective lens 31.
Is installed so that the focal point of the image is focused on the center in the longitudinal direction of the converged image. Therefore, the condensed image of the area AR is formed on the line sensor 34 and the two-dimensional sensor 35 by the optical system 33. The image formation state is such that the central portion in the longitudinal direction of the image is clear as shown in FIG. As the distance from the center increases, the image becomes blurred. FIG. 3 shows the converged image 22 and the line sensor 3.
4, the other condensed images 21a, 21a
The same applies to the case of the 1b and the two-dimensional sensor 35.

The line sensor 34 is used to detect a positional shift of the condensed image 22 of the mask mark with respect to the intermediate position between the condensed images 21a and 21b formed by 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 sharp part of the image formed by each condensed 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 at the center of 2 ',
An image falling within the area A1 indicated by oblique lines 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. Therefore, it is more 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 detect the relationship between the light amounts outside the central portion in the images 21a ', 21b', and 22 'formed by 1b and 22, the images entering the two regions B1 and B2 indicated by oblique lines in the drawing are converted into image signals. .

Returning to FIG. 1, the image signal from the line sensor 34 is output to a first image processing device 36, and the image signal from the two-dimensional sensor 35 is output to a second image processing device 37. The first image processing device 36 processes an image signal from the line sensor 34 to detect a position shift of the condensed image 22 from an intermediate position between the condensed images 21a and 21b, and outputs a signal indicating the position shift here. Then, the wafer stage control device 38
Output to The wafer stage control device 38 performs position correction control of the wafer stage based on the signal indicating the position shift, and the position shift is 0, that is, the condensed image 22 is
a, 21b. Of course, the signal of the first image processing device 36 may be supplied to a mask stage control device (not shown) to perform the position correction control of the mask stage.

The second image processing device 37 processes an image signal from the two-dimensional sensor 35 and outputs a signal representing focus data. This will be described in the case of the condensed image 22 of the mask mark. For the image 22 'of the condensed image 22 of the mask mark in FIG. 4B, the light intensity at the central point in the region B1 and the light intensity at the central point in the region B2 ( In the figure, a value integrated in the Y direction may be detected), and these difference values are obtained. The light intensity in the region B1 and the light intensity in the region B2 each differ in the brightness of the image depending on the direction in which the focus point is deviated from the focus point, and as a result, change as shown in FIG. 5B. Then, the difference value between the two light intensities becomes 0 when it is at the focus point, as shown in FIG. 5A. The second image processing device 37 outputs a signal representing the difference value to the focus control device 39 of the mask stage. The focus control device 39 controls the focus of the mask stage based on the signal representing the difference value so that the difference value becomes zero.

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

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

[0018]

As described above, the present invention has been described with respect to one embodiment. According to the present invention, the following effects can be obtained.

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

(2) Since a converged image by LFZP is used, the brightness (S / N ratio of light intensity) of the image is much higher than that of a normal non-condensed image, thereby improving the detection accuracy. it can.

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

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

[Brief description of the 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 positional relationship between a mask mark and a wafer mark used in the present invention and a condensed image formed thereby.

FIG. 3 is a diagram for explaining an image forming state in the optical system shown in FIG. 1;

FIG. 4 is a diagram for explaining an image forming state in the line sensor and the two-dimensional sensor shown in FIG. 1;

FIG. 5 is a diagram for explaining the operation principle of the second image processing apparatus shown in FIG. 1;

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

[Explanation of symbols]

 11, 11a, 11b Wafer mark 12 Mask mark 21a, 21b Condensed image by wafer mark 22 Condensed 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)

(57) [Claims] An alignment control of a wafer 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 constituted by a linear Fresnel zone plate, and means for irradiating the mask mark and the wafer mark with irradiation light obliquely; Optical system for forming a condensed image by a line sensor and a two-dimensional sensor on the line sensor, a first image processing device for detecting a positional relationship between the condensed images of the respective marks in the line sensor, and the two-dimensional sensor A second image processing device that detects the focus of the condensed image of each mark in the above, wherein a mask stage is output from the first image processing device,
An X-ray exposure apparatus, wherein one of the wafer stages is controlled, and focus control of the mask stage and the wafer stage is performed by an output of the second image processing apparatus.