JPS636841A - Exposure device - Google Patents

Abstract

PURPOSE:To enable an alignment optical system to be used always in an optimally focused condition independently from variation of thickness of a mask, by removably arranging a glass plate between the mask and the alignment optical system for correcting a optical path length. CONSTITUTION:A holder 21 having a construction equivalent to that of a reticle holder 2 is provided between a reticle R and an alignment optical system so that a transparent glass plate 20 having the similar configurations to those of the reticle R can be arranged for correcting an optical path length. The holder 21 holds the glass plate 20 by sucking it with vacuum. The reticle R and the glass plate 20 are conveyed onto the reticle holder 2 and onto the holder 21, respectively, by a fork-type arm 30. A reticle R is received in each of cases 51, 52 and 53. Cases 54 and 55 similar to the reticle cases 51, 52 and 53 receive glass plates 20 having different thicknesses, respectively. An appropriate glass plate is selected in accordance with a thickness of a mask to be used and the selected glass plate is conveyed automatically by a conveying means 30.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an exposure apparatus used in a photolithography process for manufacturing semiconductor elements, working masks, and the like.

(Prior Art) This type of exposure apparatus includes a projection type in which a pattern on a reticle (synonymous with a mask) is projected onto a semiconductor urchin, etc. at a predetermined magnification via a projection optical system (lens, mirror). A gloximity (contact) type is known in which the mask and the sea urchin are brought into close proximity (or in close contact).

In either device, before the exposure operation, the mask or reticle and the area to be exposed on the wafer are aligned (
alignment).

This alignment is usually performed by simultaneously observing the mark pattern formed on the mask (or reticle) and the mark pattern previously formed on the wafer using an alignment microscope, etc., and making sure that both marks have the desired positional relationship. This is done by relatively moving the mask (or reticle) and wafer. In addition, as another 7 alignment sequence, the reticle is aligned with a microscope installed at a fixed position of the equipment, and the wafer is also aligned with a microscope for wafer observation installed at a fixed position of the equipment. There is also a method of aligning the reticle and wafer.

In either method, the alignment optical system that observes the marks on the mask (or reticle) detects the marks formed on the lower surface (the surface facing the wafer) through the curvature of the mask (or reticle) itself. will be observed.

(Problems to be Solved by the Invention) However, this type of 7-line optical system usually has a high magnification when observing marks and a shallow depth of focus.

For this reason, if the glass thickness of the mask (or reticle) changes, the length of the imaging optical path will substantially change, resulting in the inconvenience that the observed image of the mark will become blurred.

As a method of resolving this inconvenience, it may be possible to provide a focusing mechanism that moves some of the lenses in the alignment optical system in the optical axis direction. However, the thickness of the mask (or reticle) may differ by more than twice based on a certain standard, and if you try to focus on all of these masks (or reticles), the alignment optical The disadvantage is that the system structure becomes complicated.

(Means for Solving the Problems) The present invention provides a mask holding means, a stage, an alignment optical system, a transparent plate holding means, and a conveying means, so that the optical path length determined by the sum of the mask thickness t is approximately constant. The thickness t! A transparent plate is removably placed between the mask and the 7-line optical system.

As a result, the optical path length from the pattern surface of the mask to the alignment optical system is set to a predetermined value. The transparent plate and the mask are then transported to their respective holding means via a common transport means.

(Function) In the above configuration 2, a plurality of transparent plates with different thicknesses t are prepared in response to several changes in the thickness tl of the mask, and the transparent plates are adjusted according to the thickness t of the mask to be used. is selected and automatically transported by the transport means. In this way, the alignment optical system can always detect the pattern in focus even if the thickness of the mask changes.

Furthermore, if you make the transparent plate almost the same shape as the mask,
This prevents dust from falling onto the mask and prevents dust from falling onto the mask.
It is possible to minimize the impact on 'Furthermore, since the transparent plate is removable and replaceable, it can be cleaned freely in case of contamination.

(Embodiment) FIG. 1 shows a schematic structure of an exposure apparatus according to an embodiment of the present invention, and in particular is a diagram showing the structure of a projection type exposure apparatus.

In FIG. 1, light from an exposure illumination light source illuminates a reticle Ri with uniform light t through a condenser lens 1t. Reticle RK is circuit turn CP and mark R
A circuit pattern CP and a mark RM are vacuum-adsorbed to the reticle holder 2 so that the circuit pattern CP and the mark RM are not blocked from light. The circuit pattern CP (or mark RM l) of the reticle R is imaged onto the wafer W via the projection optical system 3 composed of lenses L, L, etc. The wafer W is placed on a stage 4 that moves two-dimensionally.

The stage 4 is provided with a reference mark FM that serves as the next reference for alignment. Above the reticle R is a mark detection optical system for alignment (alignment optical system).
is provided.

This consists of an illumination light source (including fibers, etc.), a 10° beam splitter, and a 11. Objective lens 12. Mirror 13, focus plate 1
4. and an imaging device (such as a television camera) 15, and this system itself is well known. This alignment optical system has the same configuration as a microscope with coaxial epi-illumination, and can simultaneously detect the mark RM on the reticle R and the mark WM on the wafer W by the image pickup element 15. Alternatively, if the surface of the member on which the fiducial mark FM is formed is a mirror surface and this is positioned at the projection point of the mark RM, the reticle R
It is possible to detect only the mark RM. Note that when using this alignment optical system for the purpose of detecting only the mark RM and aligning it with the reticle R1 device, it is possible to simultaneously observe the next index mark formed on the reticle 14 and the mark RM. Line up the mark RM 7 times against the mark. On the other hand, when this alignment optical system is used for the purpose of detecting the alignment state between the marks RM and WM, the focus plate 14 is not particularly necessary and can be removed from the optical path. Further, the gR element 15 may be a photoelectric detector that combines a vibrating slit and a photomultiple, or may be a simple photomultiplier that is a combination of the light source 1 (l laser beam generation source and a scanner).

In this embodiment, a holder 21 having the same structure as the reticle holder 2 is provided between the reticle R and the 7-line optical system so that a transparent glass plate 20 having the same shape as the reticle R can be placed for optical path length correction. establish.

The reticle holder 2 is designed to be movable during reticle alignment, whereas the holder 21 only needs to hold the glass plate 21 parallel to the reticle R.
No moving mechanism is required. The holder 21 is a glass plate 201
Hold by vacuum suction. These reticle R and glass plate 2
0 and 7 are conveyed onto the reticle holder 2 or onto the holder 21 by the oak-shaped arm 30, respectively. The structure of this conveying arm 30 is disclosed in, for example, Japanese Patent Application Laid-Open No. 57-64928, so a detailed explanation will be omitted. The arm 30 is moved in the direction of arrow Y by a linear drive section 31. The arm 30 and the linear drive section 31 are rotated in the direction of arrow θ by the rotation drive section 32.

Furthermore, arm 30. The linear drive section 311 and the rotation drive section 32 are linearly moved in the two directions of arrows by the vertical drive section 33. still,
The arm 30 is originally the next one to transport the reticle R, but if the glass plates 20 have the same shape, the glass plates 20
It can also be shared for transportation.

Now, in this embodiment, a foreign object (
A dust inspection device 40 for inspecting dust etc. is installed. This dust inspection device uses a scanned laser beam 40a.
This is a system in which the surface to be inspected of the i-reticle (or pellicle) is irradiated and the scattered light generated from foreign objects is received by a 7-photodetector 40b.
This is as disclosed in Japanese Patent Application Laid-Open No. 58-62544, and the like. Furthermore, the reticles R are stored one by one in cases 51, 52, and 53. The structure of this case and the interlocking relationship with the arm 30 are also discussed in Japanese Patent Application Laid-Open No. 57-64.
It is disclosed in Japanese Patent No. 928.

The reticle cases 51, 52, 53 and the same case 54, 55 each have glass plates 20 of different thickness.
is stored. Therefore, the Y direction, θ direction of arm 30, 2
Due to the movement in the direction, the reticle R moves to the reticle holder 2.
Garbage inspection equipment [! [40, and one of the cases 51, 52, 53, and the glass plate 20
Holder 21° Dust inspection device 40. and case 54.
55 cases.

Next, the operation of this embodiment will be further explained with reference to FIG. - As a general standard, reticles can be roughly divided into those with a thickness of 0.09 inches and those with a thickness of 0.18 inches.

In this embodiment, as an example, a 0.09 inch thick reticle is stored in the case 51, and a 0.18 inch thick reticle is stored in the case 52.

Further, as the glass plate 20, a thick glass plate corresponding to a 0.09 inch thick reticle is stored in a case 54, and a thin glass plate corresponding to a 0.18 inch thick reticle is stored in a case 55.

The arm 30 is, for example, 0, 09 housed in a case 51.
An inch-thick reticle Ri is taken out and conveyed to the dust inspection device 40. Inside the dust inspection device 40, the focused laser beam 40& scans the top and bottom surfaces of the reticle, but even if the thickness of the reticle R changes, the laser beam 40&
The position of the reticle R in the height direction within the dust inspection device 40 can be automatically adjusted so that the light is condensed (focused) at a predetermined spot size. When the inspection by the dust inspection device 1140 is completed and it is determined that no dust is found or that the dust does not affect the resolution during exposure, the arm 30 detects the reticle R=i dust. It is taken out from the inspection device 40 and transported to the reticle holder 2. Note that the reticle R on the arm 30 is preliminarily positioned with respect to the reticle holder 2 at a pre-alignment section (not shown).

Therefore, the next reticle R placed on the reticle holder 2 is approximately aligned with the apparatus and enters the next state. Here, the reticle holder 2 vacuum-chucks the reticle R.

Next, the arm 30 is housed in the case 54, takes out nine thick glass plates 20t, and conveys them to the dust inspection device 40. In this dust inspection, since the glass plate 20 is placed far away from the reticle R, the size of the dust on the glass plate 20 is allowed to be much larger than that on the reticle R.

For this reason, the dust inspection for the glass plate 20 can be set lower than the inspection standard for the reticle, and instead can be inspected in a high speed mode in a short time. glass plate 2
0 dust inspection can be performed in exactly the same way as the reticle R inspection, as shown at 20' in FIG. glass plate 2
After the inspection of the glass plate 20 is completed, the arm 30
It is taken out from the dust inspection device 40 and transported to the holder 21. The holder 21 vacuum-chucks the pre-aligned glass plate 20, but the pre-alignment accuracy is sufficient for positioning the glass plate 20 on the holder 21, and in some cases, pre-alignment is not necessary.

Next, the alignment optical system is used to align the reticle R. At this time, as shown in FIG. Observe RM. In Fig. 2, if the thickness of the reticle R is t" tt + the thickness of the glass plate 20 is kit, and if the reticle R and the glass plate 20 are made of the same material, the sum of tl and t2 is , is predetermined and set to a constant value. In this state, the conjugate plane with the plane Po formed by the objective lens 12 is Pl. As long as the plane P0 is held at the lower surface of the reticle R=i, the device The working distance from the objective lens 12 to the plane P.t is normally set to a constant value. Next, the conjugate with the plane P0 when the reticle R and the glass plate 20 are not present. The surface is P.The alignment optical system takes into account a certain optical path length difference (difference between surfaces P and P) due to the sum of the thickness 1 of the reticle R and the thickness t of the glass plate 20. , surface P
1 so that the mark RM is imaged.

Therefore, the materials of the reticle R and the glass plate 20 are the same, and t
If the optical path length difference determined by the sum of , and t corresponds to the difference between the planes PI and P, the mark RM can be imaged onto the image pickup element 15 (or focusing plate 14) without being out of focus.

Now, in the case of reticle alignment, the fiducial mark FMi
Next, the stage 4 is positioned so that the reflecting surface is located at the projection point of the mark RM, and the light source 10 is turned on. The image sensor 15 observes the overlapping state of the mark RM and the index mark on the focus plate 14 .

Then, the reticle holder 2 is moved based on the image signal, and the reticle R is aligned. Similarly, the mark RM on the reticle R and the mark WM on the wafer W
Alignment with the image sensor 15 can also be performed based on the image signal from the image sensor 15. In this case, reticle holder 2. It is sufficient to move either one of the stages 4.

After the alignment between reticle R and wafer W is completed,
Illumination light tt is irradiated onto the reticle R through the glass plate 20 to perform desired exposure. At this time, in order to illuminate only the circuit pattern CP of the reticle R, if an illumination field stop is placed at a position conjugate with the reticle R in the illumination optical path, the illumination optical system will The edge image of the illumination field diaphragm is designed to be accurately focused within the plane P0, taking into account the sum of . If the mirror 13 (or objective lens 12) of the alignment optical system blocks light from the circuit pattern CP during alignment, it is necessary to move the mirror 13 (or objective lens 12) out of the exposure optical path during exposure. For this reason, if the mirror 13 is kept movable, minute dust may be generated from the sliding parts etc. every time it is retracted or extended.
Since the reticle R is shaped to cover the entire surface of the reticle R, generated dust will not adhere to the reticle R.

Incidentally, in recent years, the wavelength of illumination light t has been shortened in exposure equipment in recent years, and exposure using ultraviolet rays (for example, wavelengths of 308 and 249 nm I) is now being performed. etc. Tag glass plate 2
It is desirable to create 0. Also, it would be easier to manage the thickness if the glass plate 20 and the reticle R are made of the same material.
They do not necessarily have to be the same.

Furthermore, the glass plate 20 does not have to have the same shape and size as the reticle R, and may be provided only in the alignment optical path between the alignment optical system and the reticle R.

In this case, the frame 2 that does not shield the circuit pattern CP shown in FIG.
A glass plate 201e is fixed to a part of 00. frame 20
0 has substantially the same shape as the reticle R and can be transported by the arm 30, and the glass plate 201 is positioned in the alignment optical path when mounted on the holder 21.

Furthermore, although the present embodiment uses a projection type exposure apparatus, a proximity type exposure apparatus can be similarly applied.

(Effects of the Invention) According to the present invention, since the glass plate for optical path length correction is removably disposed between the mask and the alignment optical system, the optimal The alignment optical system can be used in the focused state. Moreover, since it is removable, by taking it out from the device and inspecting it, it is possible to estimate the state of foreign matter adhering to the mask, and to check the contamination state of the device.

Furthermore, by making the glass plate the same shape as the reticle as in the embodiment, the glass plate can be transported in common with the reticle without any change in the transport means, and moreover, it can be stored in a case with the same shape. Can be done.

Another advantage is that by making the glass plate the same shape as the reticle, the same dust inspection device can be used to inspect for foreign matter, and if the glass plate is contaminated, it can be cleaned directly using an automatic reticle cleaning device. There is also.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic configuration of a projection exposure apparatus according to an embodiment of the present invention, FIG. 2 is an optical path diagram illustrating how optical path length is corrected, and FIG. 3 is a diagram showing another configuration of a glass plate. FIG. [Explanation of symbols of main parts] R...Reticle, W...Wafer, CP...Circuit pattern, RM, WM...Mark, 2...Reticle halter-13...Projection lens, 4 ...Stage, 12
...Objective lens, 15...Imaging element, 20...Glass plate, 21...Holder, 30...Arm, 40
... Garbage inspection device, 51.52, 53, 54.55.
··Case. Figure j

Claims (2)

[Claims] (1) A mask holding means for detachably holding a mask on which a pattern to be transferred is formed on a transparent glass having a predetermined thickness t_1; a stage for placing a transfer target substrate to which the pattern is transferred; an alignment optical system that optically detects the formed predetermined pattern; a transparent plate having a thickness t_2 determined by the sum of the thickness and t_1 so that the optical path length is approximately constant; a transparent plate holding means that is detachably held between the system and the transparent plate holding means; and a conveying means that carries out both the conveyance of the mask to the mask holding means and the conveyance of the transparent plate to the transparent plate holding means. An exposure device characterized by comprising: (2) The transparent plate has an outer shape that covers the mask, the exposure device further includes an inspection section for detecting foreign matter or pattern defects attached to the mask, and the conveying means connects the mask to the transparent plate. The patent is characterized in that the plate is configured to be able to selectively transport the plate to the inspection section, and by inspecting the transparent plate at the inspection section, foreign matter contamination within the exposure apparatus is detected. An apparatus according to claim 1.