JPH0654750B2 - Projection optical system characteristic detection method and exposure method using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for detecting the characteristics of a projection optical system and an exposure method using the same, and particularly on a mask or reticle surface in the fabrication of integrated circuits such as ICs and LSIs. The present invention relates to a method for detecting characteristics of a projection optical system, which is suitable when a pattern is projected and exposed on a wafer surface by the projection optical system, and an exposure method using the same.

(Prior Art) In recent years, a large number of reduction projection type exposure apparatuses (so-called steppers) have been used in the production sites of semiconductor devices such as IC and LSI as an apparatus for exposing and transferring a fine circuit pattern. This reduction projection type exposure apparatus reduces an image of a circuit pattern drawn on a reticle (mask) by a projection optical system to expose a layer of photoresist (photosensitive agent) on a semiconductor wafer.

At present, as the resolving power of the projection optical system, 1 micron (μm) can be easily obtained within the exposure area of 15 angles on the wafer. However, even if such a high resolution projection optical system is used,
Overlay exposure of the projected image of the circuit pattern (chip) already formed on the wafer and the circuit pattern of the reticle may not be performed with sufficient accuracy. That is, relative expansion and contraction between one chip and a projected image of a circuit pattern caused by expansion and contraction due to a wafer process (steps such as etching and diffusion), and variation in reduction ratio of the projection optical system itself.

In particular, fluctuations in the reduction magnification of the projection optical system lead to deterioration in overlay accuracy, so the exposure apparatus is adjusted in advance so as to be as small as possible.

However, fluctuations in magnification that occur during operation of the exposure apparatus are
After exposing a pattern of a test reticle having a plurality of marks provided at a predetermined position at a predetermined interval on a wafer and developing a photoresist on the wafer, the arrangement relationship of the plurality of marks formed on the wafer is examined. It is detected by measuring with another measuring device. Therefore, in order to perform superposition exposure of a finer circuit pattern with sufficient accuracy, it is inconvenient because the magnification variation of the projection optical system must be successively measured.

Further, even if the magnification variation occurs during the exposure operation, the variation cannot be measured immediately, and the accurate magnification variation amount cannot be known.

In the projection optical system, not only the magnification change but also the focus change occurs. This focus fluctuation also causes the same problem as the above-mentioned magnification fluctuation. The fluctuations in magnification and focus of the projection optical system are largely caused not only by the projection optical system itself but also by environmental changes such as temperature changes and atmospheric pressure changes in the surrounding air.

On the other hand, in recent years, various steppers have been proposed which use an excimer laser as a light source for narrowing the spectral width by optical means. The oscillation wavelength of this excimer laser varies, though it varies slightly. Therefore, when the excimer laser is used, the refractive index of the glass material forming the projection optical system varies, which causes factors such as magnification variation and focus variation of the projection optical system.

(Problems to be Solved by the Invention) According to the present invention, a pattern formed on a first object plane such as a reticle is formed on a second object plane such as a wafer arranged on a movable stage via a projection optical system. At the time of projection exposure, a writable and erasable recording medium is provided in a part of the second object in order to detect various amounts such as magnification variation and focus variation of the projection optical system, and the image is projected and transferred onto the recording medium. PROBLEM TO BE SOLVED: To provide a method of detecting a characteristic of a projection optical system in which a pattern image of a first object is observed by an observation optical system with high accuracy to align a first object and a second object, and an exposure method using the same. With the goal.

(Means for Solving Problems) A characteristic detecting method for a projection optical system according to the present invention is a method for detecting a characteristic of a projection optical system for projecting a pattern formed on a reticle onto a wafer placed on a movable stage. In the method of detecting the characteristics of the projection optical system for detecting, a step of irradiating a mark formed on the reticle with light; a recording medium provided at a position different from the wafer on the movable stage via the projection optical system. A step of exposing and transferring the image of the mark thereon; a step of observing the mark image with an observation optical system; a projection magnification or a focus position of the projection optical system based on the information of the mark image obtained in the observing step. It is characterized by having a step of detecting.

Further, in the exposure method of the present invention, in the exposure method of projecting and exposing the pattern formed on the reticle onto the wafer mounted on the movable stage, a step of irradiating the mark formed on the reticle with light A step of exposing and transferring the image of the mark on a recording medium provided at a position different from the wafer on the movable stage via the projection optical system; and a step of observing the mark image by an observation optical system. A step of detecting a projection magnification or a focus position of the projection optical system from information of the mark image obtained in the observing step; and a correction of a projection magnification of the projection optical system based on the detected projection magnification. Alternatively, the detected image plane position is corrected to match the coated light surface of the wafer, and then the pattern of the reticle is projected and exposed onto the wafer surface. It is characterized by having and.

(Embodiment) FIG. 1 is an overall schematic view of a detection method of a projection optical system and an exposure method using the same according to an embodiment of the present invention. In the figure, the light emitted from the irradiation optical system 1 irradiates the reticle 2 as the first object, and the pattern thereof is transferred onto the wafer 4 as the second object by the projection optical system 3. The wafer 4 is fixed on a movable stage 5 arranged on a surface plate 10.

The projection optical system 3 is carried by a lens barrel (not shown), and in some cases, as will be described later, a lens driving means is arranged so that a predetermined lens of a plurality of lenses forming the projection optical system 3 can be moved.

Also, the reticle 2 is held on the reticle stage,
The reticle stage moves the X,
It is moved in the Y, Z, and θ directions.

The movable stage 5 can be moved in X and Y by a drive system 101, and the movement amounts thereof are X and Y, respectively.
It is monitored by a laser length measuring machine for each direction. or,
The movable stage 5 is movable in the X direction, and the position of the movable stage 5 in the Z direction is also monitored by the Z-direction position detecting means (not shown).

In FIG. 1, the laser measuring device 8 for the X direction is shown, but the laser length measuring device for the Y direction is not shown.
The height of the optical axis of the laser measuring device 8 is the same as the surface of the wafer 4 in order to eliminate Abbe's error.

Further, a magneto-optical recording medium 6 as a recording medium is arranged outside the wafer 4 on the movable stage 5, and the height of the surface thereof is substantially matched with the height of the wafer 4. Also, if necessary,
An adjusting mechanism is provided to match the height of the surface of the magneto-optical recording medium 6 with the height of the wafer 4. An electromagnet 7 as a magnetic field applying means is embedded below the magneto-optical recording medium 6 so that a magnetic field can be applied in an arbitrary vertical direction in the optical axis direction of the projection optical system 3.

Further, a magnetic shield 22 is provided in the periphery so that the magnetic field generated by the electromagnet 7 does not adversely affect other members.
Further, the magnetic field is prevented from reaching the magneto-optical recording member 6 from other members. An observation optical system 9 is parallel to the optical axis of the projection optical system 3 and is located away from the optical axis, and includes a lamp 14, a beam splitter 15 for distributing the optical path, an objective lens 16, a television camera 17 for observation, and the like. . The observation optical system may also have a polarization microscope. The image captured by the television camera 17 is sent to the computer 100 and subjected to image processing for position detection and contrast detection.

Numerals 11a and 11b are mark irradiation optical systems for irradiating the marks 18a and 18b for magnification and focus detection on the reticle 2, respectively, and a part of the exposure light of the illumination optical system 1 is extracted to irradiate the slits 12a and 12b. And then slit 12
It has a function of forming images a and 12b on the surface of the reticle 2. Light guiding from the illumination optical system 1 to the mark irradiation optical systems 11a and 11b is turned on / off by shutters 13a and 13b.

As shown in FIG. 2, two marks 18 are arranged outside the area 19 where the actual element pattern on the surface of the reticle 2 is drawn and inside the effective screen 21 of the projection optical system 3.
The distance between the two marks is L. 2 in the figure
Reference numerals 0a and 20b denote irradiation ranges of the mark illumination optical system 11, respectively.

3 to 5 are state explanatory views in the vicinity of the magneto-optical recording medium 6 shown in FIG. FIG. 3 illustrates a method of detecting the magnification and focus of the projection optical system 3 in the apparatus. The magnetic shield 22 is omitted in FIG.

(A) Referring to FIG. 3, first, the medium 6 which is magnetized downward in advance is brought directly below the projection optical system 3 to the position where the marks 18a and 18b on the reticle 2 are imaged. . Next, the shutters 13a and (13b) are opened, and the marks 18a and (18b) are exposed by the mark irradiation optical systems 11a and (11b), so that the images of the marks 18a and (18b) are formed on the medium 6. At this time, when a magnetic field is applied upward by the electromagnet 7, only the light-exposed portion of the medium 6 absorbs the light, and the heat generated thereby reaches the Curie point to reverse the direction of magnetization.

As a result, there are two left and right portions of the mark 18a, (18b) in which the magnetization is reversed. The resolution of the medium 6 is determined by the magnitude of the magnetic field and is about 0.02 μm, which is sufficient for the purpose of this embodiment. Further, ultraviolet rays which are usually used for semiconductor exposure have a high absorptivity in the medium 6 and a high photon energy, which is effective. When the marks 18a and (18b) have been exposed, the shutters 13a and (13b) are closed.

(B) Referring to FIG. 4, next, the movable stage 5 is moved by a vector b which is substantially the same as the vector from the exposure position of the marks 18a, (18b) by the projection optical system 3 to the optical axis of the observation optical system 9. The medium 6 is the objective lens 1 of the observation optical system.
It should be almost under 6.

Here, the magnetization images of the left and right marks on the medium 6 formed in step (a) are observed using the observation optical system 9, and the television camera is determined by the difference in the polarization state of the light from the medium 6 caused by the difference in the magnetization. An image of the mark is formed at 17. Then, the distance 1 between the left and right marks can be measured. In the measurement, first, one mark is positioned below the optical axis of the observation optical system 9 by moving the stage, the shift amount α ₁ is measured, then the stage is moved by about 1, and the other mark is the observation optical system. Then, the shift amount α ₂ is measured so that it is positioned substantially below the optical axis of 9. Stage movement amount 1 ₀ of the second is measured by a laser measuring device 8. Then, this measurement result is input to the computer 100 via a signal line (not shown). The distance between the two marks at this time is represented by 1 = | 1 ₀ + α ₁ −α ₂ |. The magnification β of the projection optical system 3 is represented by β = 1 / L. When the reference magnification is β ₀ , the shift amount is Δβ = β−β ₀ . This calculation processing is performed by the computer 100, and the amount of Δβ is corrected by moving the reticle 2 up and down by the reticle drive means 102 or by moving some lenses in the projection optical system 3 by lens drive means (not shown).

The focusing is performed by detecting the line width of the magnetization image of the mark on the medium 6. The correspondence between the line width and the focus position is based on the defocus vs. line width curve stored in advance in the arithmetic processing (not shown) of the computer 100. Since the line width also changes depending on the exposure amount, the exposure amount at the time of transferring the marks 18a and (18b) to the medium in step (a) is always constant. The wafer stage drive means 101 moves the wafer 4 up and down, and a lens drive means (not shown) moves a part of the lenses in the projection optical system 3 so as to correct the focus shift amount thus detected. .

(C) Referring to FIG. 5, when the movable stage 5 applies a strong downward magnetic field by the electromagnet 7 at an arbitrary position, the medium 6 is entirely magnetized downward, and the mark is erased so that it can be reused.

An example of the above sequence is shown in detail in the flowchart of FIG.

The present invention is not limited to the above-mentioned embodiments and can be implemented by being modified appropriately. Next, the modification is shown.

(1-1) As a writable and erasable recording medium, photochromic glass that is colored by being exposed to light such as ultraviolet light can be used. In addition, information (pattern) can be written optically or by radiation, such as an amorphous recording material which causes a phase change between crystallization and non-crystallization due to temperature change. There are various erasable recording media.

In this case, no magnetic field is required unlike the case of the above-mentioned magneto-optical recording medium, so that an electromagnet is not necessary.

Further, it is not necessary to provide a deflection microscope in the observation optical system.

In general, photochromic glass is slow in coloring when it is exposed to light and decoloring after it is not exposed to light.
Taking advantage of the property of photochromic glass that the speed becomes higher when the temperature is low, it is advisable to add a cooling mechanism capable of cooling when the mark is exposed and when the mark is erased. If it is still slow, provide multiple positions on the photochromic glass to form the mark image for magnification and focus detection, change the position each time to form the mark image, and after a sufficient time, the first mark formed disappears. It is also possible to adopt a method of returning to the first mark image forming position after the start.

Since the photochromic glass may be exposed to not only exposure light but also observation light and ambient light, in order to maintain the state as much as possible from the mark exposure to the erasing, especially during the observation, On the contrary, it is better to add a heating mechanism for heating. Here, since ultra-precision equipment such as a stepper is very sensitive to temperature changes, when these cooling and / or heating mechanisms are attached, it is desirable to cover the surroundings with heat insulating means so that the temperature is not transmitted to other parts. .

In the above case, in the embodiment shown in FIG. 1, 6 is photochromic glass, 7 is a heating / cooling device 2 for cooling and heating.
2 may be made of a heat insulating material.

(1-2) In addition to arranging the observation optical system parallel to the optical axis of the projection optical system as described above and at a position away from the optical axis, there is also a method of observing from above the projection optical system through the projection optical system. is there. In this case, since the projection optical system and the observation optical system have the same optical axis, there is an advantage that it is not necessary to move the stage to move the medium from under the projection optical system to under the observation optical system. However, since the projection optical system is generally aberration-corrected only to the exposure wavelength, the observation light is limited to the exposure wavelength. Alternatively, there are additional restrictions such as correction of chromatic aberration.

(1-3) A reference mark may be provided inside the observation optical system, and the observation optical system may also be used as an alignment (positioning) optical system by means such as measuring the amount of deviation from the observed mark. Here, the projection optical system as in the first embodiment is arranged at a position parallel to the optical axis and apart from the optical axis,
In the case of the observation optical system, so-called off-axis (Off-Ax)
s) In the case of the observation optical system arranged on the projection optical system as described in the previous section, the so-called TTL (Th
rough-The-Lens) Alignment optical system. In either case, a die-by-die method in which all the shots on the wafer 4 are aligned by the observation optical system, or the wafer alignment mark and the optical system 9 in some shots are used.
The exposure can be performed by selecting the global alignment method in which the stage is sent to the position of the reference grid calculated from the measured value of 1 and the coordinates of the stage at that time.

(1-4) The mark erasing in step (c) may be performed immediately before the mark exposure in step (a). Further, when erasing is performed while irradiating the entire surface of the medium 6 with light, it is possible to erase the mark with a magnetic field of the same strength as the magnetic field applied during the mark exposure without applying a strong magnetic field.

(1-5) Further, the electromagnet 7 may be a vertically-reversible permanent magnet, and the position thereof can be arranged at various positions other than directly below the medium 6. In short, the projection optical system 3 is placed at the position of the medium 6.
Any magnetic field may be applied during the exposure in the direction of, and it may be arranged in any position as long as it has no adverse effect on the other.

(1-6) Some magneto-optical recording media 6 have a limited number of times that they can be used and may change over time. Therefore, if only the medium 6 is unitized, it can be replaced easily. .

(1-7) Irradiation of the mark for magnification focus detection on the reticle may be performed directly using the illumination optical system 1 instead of using the mark irradiation optical systems 11a and 11b. At this time, the entire surface of the reticle 2 may be irradiated. When the mark image formed on the medium 6 may change due to heat or the like due to environmental conditions, a masking mechanism is arranged in the illumination optical system 1 and a part of the reticle 2 is selectively exposed to expose the mark image. Should be formed.

(1-8) It can also be used for reticle positioning by utilizing the mark irradiation optical systems 11a and (11b).

(1-9) The shutters 13a and 13b are not necessary if the exposure light source in the illumination optical system 1 can turn on / off a laser or the like.

(1-10) The light source for irradiating the marks 18a and (18b) may be another light source having substantially the same wavelength without extracting the exposure light from the illumination optical system 1.

(1-11) Since the change in the magnification of the projection optical system does not always change linearly on the screen, two or more magnification detection marks are provided and the least square magnification is interpolated from each detected position. It may be calculated.

(1-12) As a focus detection method, particularly when a photochromic glass is used for the medium 6, the focus may be detected by detecting the contrast of the mark image.

(1-13) If the observation optical system 9 measures the deviation in the direction perpendicular to the straight line connecting the two images on the medium 6, γ ₁ and γ ₂ , the deviation in the plane of the reticle (so-called reticle rotation) is detected. It can be detected as θ = (γ ₁ −γ ₂ ) / 1. At this time, the correction may be performed by providing a rotary stage on the reticle or the wafer so that the reticle or the wafer can be rotated in either plane.

(1-14) When measuring the distance 1 between two marks at the time of magnification detection, the two marks may be observed simultaneously.
According to this method, since the stage does not have to be moved, the length can be measured at high speed.

(Effect of the Invention) According to the present invention, a writable / erasable recording medium is arranged outside the second object of a movable stage on which a second object (exposed object) is mounted and moves, and the observation optical Since it has a system, the magnification of the projection optical system when the pattern on the first object is exposed and transferred onto the second object by the projection optical system by the method described above,
It is possible to achieve a method of detecting a characteristic of a projection optical system capable of detecting a variation in focus and performing highly accurate alignment with good correction, and an exposure method using the same.

[Brief description of drawings]

FIG. 1 is a schematic view of an embodiment of the present invention, FIG. 2 is an explanatory view of a magnification on a reticle surface of FIG. 1, a mark for focus detection,
3 to 5 are explanatory views of the operating state in the vicinity of the magneto-optical recording medium in the apparatus of FIG. 1, and FIG. 6 is a flow chart showing the magnification and focus detection method of the apparatus of FIG. In the figure, 1 is an illumination optical system, 2 is a reticle (first object),
3 is a projection optical system, 4 is a wafer (second object), 5 is a stage, 6 is a magneto-optical recording medium, 7 is an electromagnet, 8 is a laser measuring instrument, 9 is a positioning optical system, and 11 is for mark irradiation. It is an optical system.

Claims (8)

[Claims] 1. A characteristic detecting method of a projection optical system for detecting a characteristic of a projection optical system for projecting a pattern formed on a reticle onto a wafer mounted on a movable stage, the method being formed on a reticle. Irradiating the mark with light; exposing and transferring the image of the mark onto a recording medium provided at a position different from the wafer on the movable stage via the projection optical system; A step of observing with an observing optical system; and a step of detecting a projection magnification or a focus position of the projection optical system from information of the mark image obtained from the observing step, characteristic detection of the projection optical system. Method. 2. The projection optical system according to claim 1, wherein the step of observing the mark images includes a step of measuring intervals between the mark images corresponding to different image heights. Characteristic detection method. 3. The characteristic detecting method for a projection optical system according to claim 1, wherein the step of observing the mark image includes a step of measuring the shape of the mark image. 4. The characteristic detecting method for a projection optical system according to claim 3, wherein the shape of the mark image is a line width of the mark image. 5. The mark image according to claim 3, wherein the shape of the mark image is a contrast of the mark image.
A method for detecting characteristics of a projection optical system according to the item. 6. The characteristic detecting method for a projection optical system according to claim 1, wherein the recording medium is a magneto-optical recording medium. 7. The characteristic detecting method for a projection optical system according to claim 1, wherein the recording medium is a photochromic material. 8. An exposure method of projecting and exposing a pattern formed on a reticle onto a wafer mounted on a movable stage, the step of irradiating a mark formed on the reticle with light; Exposing and transferring the image of the mark onto a recording medium provided at a position different from the wafer on the movable stage via a system; observing the mark image with an observing optical system; A step of detecting a projection magnification or a focus position of the projection optical system based on the information of the obtained mark image; a projection magnification of the projection optical system is corrected or detected based on the detected projection magnification. And the exposure surface of the wafer is corrected so that the image surface position and the exposed surface of the wafer coincide with each other, and then the pattern of the reticle is projected and exposed on the wafer surface. Exposure method according to claim.