JP2667965B2 - Projection exposure method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure method, and more particularly to a projection exposure method having a so-called autofocus function in the field of semiconductor device manufacturing, in which a reticule circuit pattern is repeatedly reduced and projected on a semiconductor surface. The present invention relates to a projection exposure method for an exposure apparatus.

[0002]

2. Description of the Related Art In recent years, semiconductor devices, LSI devices, super LS
Due to the demand for finer patterns and higher integration of I-elements,
Since an imaging (projection) optical system having a high resolving power is required in a projection exposure apparatus, the NA of the imaging optical system is increasing, and the depth of focus of the imaging optical system is becoming shallower.

[0003] In addition, the wafer has a planar processing technology,
Some thickness variation and bending must be tolerated. Normally, correction of wafer bending is performed by placing a wafer on a wafer chuck processed to assure flatness on the order of sub-cyclones and vacuum-sucking the back surface of the wafer to perform flatness correction. However,
Regarding the variation in the thickness of a single wafer, the deformation of the wafer caused by the suction and the method, and the progress of the process, it is impossible to correct the flatness of the wafer no matter how much it is to be corrected.

For this reason, the effective depth of focus of the optical system is further reduced because the wafer has irregularities in the screen area where the reticle pattern is reduced and exposed.

Therefore, in the reduction projection exposure apparatus, an effective automatic focusing method for matching the wafer surface with the focal plane (the image plane of the projection optical system) is an important theme.

As a method of detecting a wafer surface position in a conventional reduction projection exposure apparatus, a method using an air microsensor,
2. Description of the Related Art There is known a method (optical method) of causing a light beam to enter a wafer surface from an oblique direction without passing through a projection exposure optical system and detecting a positional shift amount of the reflected light.

On the other hand, in this type of projection exposure apparatus, a change in the ambient temperature of the projection optical system, a change in the atmospheric pressure, a temperature rise due to a light beam applied to the projection optical system, or a temperature rise due to heat generation in an apparatus including the projection optical system. Causes the focus position (image plane position) to move, which must be corrected. Therefore, the focus position of the projection optical system is measured by measuring the ambient temperature change and the atmospheric pressure change with a detector, or measuring part of the temperature change and the atmospheric pressure change in the projection optical system with the detector. Calculated and corrected.

[0008]

However, in this method, since the focus position of the projection optical system is not directly measured, the detection error of the detector for measuring the temperature and the atmospheric pressure, the amount of change in the temperature and the change in the atmospheric pressure, When calculating and correcting the focus position of the projection optical system based on the quantity, there is a disadvantage that it is impossible to detect the focus position of the projection optical system with high accuracy due to an error included in a calculation formula that is an approximate formula.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a projection exposure method capable of detecting a focus position (image plane position) of a projection optical system with high accuracy and accurately matching an image plane of the projection optical system with a wafer surface. To provide.

[0010]

One aspect of the projection exposure method of the present invention for achieving the above object is a projection exposure method for projecting and exposing a circuit pattern onto a resist-coated wafer via a projection optical system. Illuminating a pattern located in a detection area within a screen area of the projection optical system, causing light from the pattern to enter a reflection surface via the projection optical system, and projecting reflected light from the reflection surface into the projection area A focus position detecting step of receiving light through the optical system and the pattern and detecting a focus position of the detection area in the projection optical system based on the received light amount, and a focus position obtained from the focus position detecting step. Setting the surface position of the wafer positioned in the detection area in the optical axis direction of the projection optical system to a reference position of a surface position detection unit that detects the surface position; and The offset between the position of the wafer positioned at the reference position and the best printed position of the wafer that is the best printed circuit pattern when actually exposed, based on the resist coating thickness or the step amount of the wafer Determining and storing, and detecting the surface position of the wafer by the surface position detecting means, positioning the wafer at a position determined by the offset and the reference position, and projecting and exposing the circuit pattern and the wafer. And having.

A preferred form of the pattern located in the detection area is a circuit pattern projected and exposed on a wafer.

[0012]

FIG. 1 is a conceptual diagram showing the configuration of a reduction projection exposure apparatus having an automatic focus control device according to one embodiment of the present invention.

In FIG. 1, reference numeral 7 denotes a reticle, which is held by a reticle stage 70. The circuit pattern on the reticle 7 is reduced to 1/5 by the reduction projection lens 8 to form an image on the wafer 9 on the xyz stage 10, and exposure is performed. In FIG. 1, at a position adjacent to the wafer 9,
A reference plane mirror 17 whose mirror surface almost coincides with the upper surface of the wafer 9 is provided. The reason for using the reference plane mirror 17 instead of using the wafer coated with the actual resist is as described above.

The xyz stage 10 is movable in the optical axis direction (z) of the projection lens 8 and in a plane perpendicular to this direction, and can be rotated around the optical axis.

The reticle 7 is illuminated in the screen area where the circuit pattern is transferred by the illumination optical system shown by 1 to 6 in FIG.

A light-emitting portion of a mercury lamp 1 as a light source for exposure is located at a first focal point of an elliptical mirror 2, and light emitted from the mercury lamp 1 is focused at a second focal point of the elliptical mirror 2. doing. An optical integrator 3 having its light incident surface positioned at the second focal position of the elliptical mirror 2 is provided, and the light exit surface of the optical integrator 3 forms a secondary light source. The light emitted from the optical integrator 3 as a secondary light source passes through the condenser lens 4 and has an optical axis (optical path) of 90 by the mirror 5.
° can be bent. Reference numeral 55 denotes a filter for selectively extracting light having an exposure wavelength, and reference numeral 56 denotes a shutter for controlling exposure. The exposure light reflected by the mirror 5 illuminates, via a field lens 6, a screen area on the reticle 7 where a circuit pattern is transferred. In this embodiment, the mirror 5 changes the exposure light to, for example, 5 to 5.
It is configured to partially transmit light such as 10%.
The light that has passed through the mirror 5 reaches a photodetector 50 for monitoring the fluctuation of the light source through a lens 52 and a filter 51 that transmits an exposure wavelength and cuts off extra light for photoelectric detection.

In FIG. 1, reference numerals 11 to 12 form a well-known off-axis autofocus optical system. 11
Denotes a light projecting optical system, and a light beam as non-exposure light emitted from the light projecting optical system 11 intersects the optical axis of the reduction projection lens 8. It is assumed that the light is condensed and reflected on a point on the reference plane mirror 17 (or the upper surface of the wafer 9). The light beam reflected by the reference plane mirror 17 enters the detection optical system 12. Although not shown, a light receiving element for position detection is arranged in the detection optical system 12, and the light receiving element for position detection and the reflection point of the light beam on the reference plane mirror 17 are arranged to be conjugate. The displacement of the reference plane mirror 17 in the optical axis direction of the reduction projection lens 8 is measured as the displacement of the incident light beam on the position detecting light receiving element in the detection optical system 12.

The positional deviation of the reference plane mirror 17 from the predetermined reference plane measured by the detection optical system 12 is transmitted to an autofocus control system 19. The auto focus control system 19 includes an xy with the reference plane mirror 17 fixed.
A command is given to a drive system 20 for driving the z stage 10. When detecting the focus position by TTL, the autofocus control system 19 drives the reference mirror 17 up and down in the optical axis direction (z direction) of the projection lens 8 near a predetermined reference position. In addition, the position control of the wafer 9 at the time of exposure (the wafer 9 is arranged at the position of the reference plane mirror 17 in FIG. 1) is also performed by the autofocus control system 19.

Next, a reduction projection lens 8 according to the present invention.
Will be described.

In FIGS. 2 and 3, reference numeral 7 denotes a reticle, and reference numeral 21 denotes a pattern portion formed on the reticle and has a light shielding property. Reference numeral 22 denotes a light shielding portion sandwiched between the pattern portions 21. Here, when the focus position (image plane position) of the reduction projection lens 8 is detected, the xyz stage 10 moves in the optical axis direction of the reduction projection lens 8.

The reference plane mirror 17 is located on the optical axis of the reduction projection lens 8, and the reticle 7 is
6 is illuminated.

First, the case where the reference plane mirror 17 is on the focus surface of the reduction projection lens 8 will be described with reference to 1 in FIG. Exposure light passing through the transmission portion 22 on the reticle 7 is condensed and reflected on the reference plane mirror 17 via the reduction projection lens 8. The reflected exposure light follows the same optical path as the outward path, is condensed on the reticle 7 via the reduction projection lens 8, and is transmitted through the light transmitting section 22 between the pattern sections 21 on the reticle 7.
Pass through. At this time, the entire light flux of the exposure light passes through the transmission part of the pattern part 21 without vignetting on the pattern part 21 on the reticle 7.

Next, FIG. 3 shows a case where the reference plane mirror 17 is at a position shifted from the focal plane of the reduction projection lens 8.
This will be described with reference to FIG. Exposure light passing through the transmission part of the pattern part 21 on the reticle 7 reaches the reference plane mirror 17 via the reduction projection lens 8, and the reference plane mirror 17
Since the exposure light is not on the focus surface of the reduction projection lens 8, the exposure light is reflected by the reference plane mirror 17 as a spread light flux. That is, the reflected exposure light follows an optical path different from the outward path, passes through the reduction projection lens 8, and does not converge on the reticle 7, and corresponds to the amount of displacement of the reference plane mirror 17 from the focus surface of the reduction projection lens 8. The luminous flux having a widened spread reaches the reticle 7. At this time, part of the exposure light is vignetted by the pattern portion 21 on the reticle 7, and all the light beams cannot pass through the light transmitting portion 22. That is, a difference occurs between the amount of light reflected through the reticle and the amount of light reflected through the reticle when the focal plane coincides with the focal plane.

The optical path after the light beam of the exposure light reflected by the reference plane mirror 17 has passed through the reticle 7 described with reference to FIGS. 2 and 3 will be described with reference to FIG.

The exposure light transmitted through the reticle 7 passes through the field lens 6 and reaches the mirror 5. Since the mirror 5 has a transmittance of about 5 to 10% with respect to the exposure light as described above, a part of the exposure light that has reached the mirror 5 passes through the mirror 5 and passes through the imaging lens 13 to form a field stop 14. Focus on the surface of. At this time, the surface of the reticle 7 where the pattern exists and the field stop 14 are at conjugate positions via the imaging lens 13.

The exposure light that has passed through the opening of the field stop 14 enters the light receiving element 16 through the condenser lens 15.

If necessary, a filter 51 for selectively transmitting only the exposure light is provided on the front surface of the light receiving element 16, and an electric signal corresponding to the amount of the incident exposure light is output.

Here, the operation of the field stop 14 will be described. The field stop serves to limit the detection area detected by the light receiving element 16. The detection area is configured so as to correspond to that based on the off-axis focus optical system basically constituted by 11 to 12, that is, to detect in the same area. However, when a coarse pattern such as a scribe line is included in the detection area and its influence is dominant and there is a problem in detection sensitivity, the position of the diaphragm 14 is shifted to make the influence of a signal from a fine pattern dominant. Various things can be considered. In such a case, the field stop 14 is controlled so that any or all of the position in the direction orthogonal to the optical axis direction, the size of the opening, the shape of the opening, and the like can be controlled as shown in FIG. Good to put. In addition, 1
Although the movement of the entire optical system up to 5 to 16 is also conceivable, they are all off-axis autofocus optical system 1
It is kept within a range where the positions correspond to the detection areas 1 and 12. When the detection area is limited by the shape of the light receiving element 16, the field stop 14 is not always necessary. At this time, the light receiving element 16 is arranged at a position conjugate with the reticle 7, for example, at the position of the field stop 14 in FIG.

A method for detecting the focus position (image plane position) of the reduction projection lens 8 using the signal output of the light receiving element 16 will be described below.

The xyz stage 10 on which the reference plane mirror 17 is mounted is driven by the drive system 20 in the optical axis direction of the reduction projection lens 8 around the zero point of measurement preset by the off-axis autofocus detection system 12. And At this time, a position signal (autofocus measurement value z) in the optical axis direction of the reference plane mirror 17 measured by the autofocus detection system 12 at each position and the exposure light reflected by the reference plane mirror 17 are received by the light receiving element 16. The relationship between the outputs obtained from the focal plane (image plane) detection system 18 by receiving the light and converting it into an electric signal is as shown in FIG. At this time, the signal of the detection system 18 is used to remove the influence of the fluctuation of the light source 1.
It is assumed that the signal of No. 8 is normalized by the signal of the detection system 53 to be corrected by the signal from the reference light amount detection system 53.

When the reference plane mirror 17 is located on the focus plane of the reduction projection optical system 8, the output of the focal plane detection system 18 shows a peak value. This time to have an auto-focus measurement value z _0, using a reduction projection lens 8, the focus position of the projection optical system 8 for performing an exposure on the wafer 9. (Or corrects the focus position set in advance based on the measurement values z _0).

The focus position of the projection lens 8 determined in this manner becomes a reference position of the off-axis automatic focus detection system. The actual best printing position of the wafer is a value obtained by giving an offset from the reference position by an amount in consideration of the values such as the coating thickness of the wafer and the step amount. For example, when exposing a wafer using a multi-layer resist process, only the uppermost portion of the multi-layer needs to be burned, so that the resist surface of the wafer and the reference position substantially coincide. On the other hand, when the exposure light sufficiently reaches the substrate with a single-layer resist, the focus of the wafer coincides with the substrate surface instead of the resist surface. In this case, an offset of 1 μm or more exists between the resist surface and the reference position. Things are not uncommon. Such an offset amount is specific to the process and is given as an offset different from that of the projection exposure apparatus. It is sufficient for the apparatus itself that the focus position of the projection lens 8 itself can be accurately obtained by the method as in the present invention. What is necessary is just to input in advance via a system controller (not shown) of the projection exposure apparatus.

The detection of the focus position z ₀ may be determined based on the peak of the output of the focal plane detection system 18, but various other methods can be considered. For example, in order to further increase the detection sensitivity, a certain level of the slice level 220 with respect to the peak output is set.
Autofocus measurement values z ₁ and z ₂ when indicating the output of 20
Knowing the focus position

[0034]

[Outside 1] Alternatively, a method of finding the peak position using a differential method may be considered.

Further, in order to increase the detection resolution of the focus position z ₀ , as shown in FIG. 4, the position of the field stop 14 (in some cases, together with the condenser lens 15 and the light receiving element 16) is moved. By doing so, it is conceivable to make the exposure light incident on the light receiving element 16 correspond to the light that has passed through the light transmitting portion 22 closer to the limit resolution line width of the reduction projection lens 8.

FIG. 6 is a flow chart showing the process of detecting the focus position of the reduction projection optical system 8 and exposing the wafer 9 according to the present invention.
FIG.

FIG. 6 shows a flowchart for detecting the focus position of the reduction projection optical system 8 for each wafer, but the focus position may be detected for each shot, every few shots, or every several wafers. It goes without saying that you can't use it.

Accordingly, the reticle used for the actual pattern transfer and the exposure light passing through the projection lens are used as the detection light.
In addition, the position of the wafer to which the pattern is to be transferred is detected, and the focus position of the projection lens is directly measured using an off-axis autofocus system. It is possible to position.

Therefore, conventionally, a change in the focus position with time due to a change in temperature around the projection exposure optical system, a change in atmospheric pressure, or a rise in temperature due to an irradiated light beam, or a rise in temperature due to heat generation in an apparatus including the projection optical system. It has the advantage that it is not affected in principle.

Further, the mounting advantage that the focal plane (image plane) detection system of the projection optical system can be configured by simply adding a simple and inexpensive imaging optical system, a condenser lens, and a light receiving element to the conventional illumination system. There is.

The focus position measurement according to the present invention can be inserted at any time during the exposure cycle.
It also has the advantage that the time difference between measurement and exposure can be minimized.

FIG. 7 shows another embodiment of the present invention.

Reticle 7 for transferring a pattern to wafer 9
In the actual projection exposure apparatus, only a certain range of the exposure area is illuminated on the reticle 7 because, for example, the exposure area where the pattern transfer is performed may differ depending on each process. In many cases, a so-called mass mangling mechanism as shown in Japanese Patent Application Laid-Open No. 45252 is mounted.

FIG. 7 is the same as the embodiment described in FIG. 1 except for the illumination optical system. Hereinafter, the illumination optical system will be described.

The light emitting portion of one mercury lamp, which is a light source for exposure, is located at the first focal point of the two elliptical mirrors, and the light emitted from the mercury lamp 1 is focused at the second focal position of the elliptical mirror 2. It is shining. At the second focal position of the elliptical mirror 2, three optical integrators having the incident surface are placed, and the light exit surface of the optical integrator 3 is
The light emitted from the optical integrator 3 serving as the next light source passes through the beam splitter 24 via the condenser lens 23 and then illuminates the surface on which the illumination area variable mechanism 25 exists. Reference numeral 56 denotes a shutter, and 55 denotes a filter for limiting the exposure wavelength range as in FIG.

The illumination area variable mechanism 25 is formed by a stop having a variable aperture, and has a function of passing only a partial area of the light beam illuminating the surface on which the illumination area variable mechanism 25 is present. .

The beam splitter 24 has a property of transmitting exposure light by about 90 to 95%.

The exposure light that has passed through the illumination area variable mechanism 25 passes through the imaging lens 26, is bent by 90 ° in the optical axis by the mirror 27, passes through the field lens 6, and reaches the reticle 7. At this time, the imaging lens 26,
And illumination field variable mechanism 24 via field lens 6
And the surface where the circuit pattern of the reticle 7 exists are conjugated. Furthermore,
The entrance pupil of the reduction projection lens 8 interposed between the reticle 7 and the wafer 9 to be exposed is set to be conjugate with the exit surface of the optical integrator 4, as shown in FIGS.
The illumination optical system denoted by 3 to 27, 6 is configured so that the circuit pattern surface of the reticle 7 is Koehler-illuminated.

Exposure light used for the focal plane detection passes through the pattern portion of the reticle 7, passes through the reduction projection lens 8, is reflected by the reference reflection mirror 17, and again passes through the reduction projection lens 8.
The state of transmission through the pattern portion of the reticle 7 is as described with reference to FIGS.

The exposure light transmitted again through the light transmitting portion 22 of the reticle 7 passes through the field lens 6 and passes through the mirror 2.
7, the light passes through the aperture of the illumination area variable mechanism 25 via the imaging lens 26. Thereafter, the exposure light is increased to 5 to 1
After being reflected by the beam splitter 24 that reflects 0%, the light enters the light receiving element 16 by the condenser lens 28.

The method of detecting the focal plane thereafter is the same as that described in the embodiment of FIG.

FIG. 7 is different from the first embodiment in that the beam splitter 24 replaces the mirror 5 shown in FIG. In this case, there is an advantage that the entire apparatus can be made compact by attaching a variable illumination area mechanism. or,
The beam splitter 24 also serves as a light guide to a photodetector 50 for monitoring the amount of exposure light. Also, the photodetector 50
Is also used as a photodetector for detecting the integrated light amount at the time of circuit pattern projection exposure, and is used for exposure amount control.

In the embodiment described above, the xyz stage 10
Is movable, and the xyz stage 10 is moved in the optical axis direction of the reduction projection lens 8 to measure the focus position (that is, the image plane position) of the projection lens 8 and to position the wafer 9. It would also be possible to perform measurement and positioning by attaching a drive mechanism to the lens 8 and making the projection lens 8 movable in the optical axis direction.

At this time, the projection lens 8 and the reticle 7 (and the reticle stage 70) are moved integrally.

Also, instead of monitoring the amount of reflected exposure light transmitted from the reference reflection mirror 17 provided on the xyz stage 10 through the reticle 7 to detect the focus position, the reference reflection mirror and another TTL autofocus system ( For example, the focus position may be detected using the method disclosed in Japanese Patent Application Laid-Open No. 56-130707 by the present applicant.

In each of the above embodiments, a part of the circuit pattern of the reticle 7 is used to guide predetermined light to the reference reflection mirror 17, but a pattern (window) for detecting a focus position is used.
May be separately formed on the reticle 7 and used.

Further, in each of the above embodiments, a reference reflection mirror (surface) 19 different from the wafer 9 is provided on the xyz stage 10 in order to cope with a process of a multilayer resist or the like. If not provided, a dummy wafer not coated with a resist is mounted on the xyz stage 10 instead of the wafer 9 coated with the resist,
The focus position of the projection optical system can be detected by the method described above.

Various forms of the projection exposure apparatus other than those described in the above embodiment are conceivable.
The present invention is applicable to various devices such as a device using a laser such as an F excimer laser and a device having a projection optical system including a reflecting mirror.

[0059]

As described above, according to the present invention, the focus position of the projection optical system is detected by the TTL autofocus system, and the focus position is used as the reference position of the off-axis autofocus system. When the wafer is positioned with the off-axis autofocus system, the offset is used using the reference position and the offset, so the focus change of the projection optical system that changes with time and the best printing position due to the resist thickness and wafer level difference The wafer can be positioned at the best position for baking without being affected by both of the changes. As a result, a high-resolution pattern can be formed on the wafer, and there is an excellent effect that a circuit with a higher degree of integration can be created.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a projection exposure apparatus having an automatic focus control device according to one embodiment of the present invention.

FIG. 2 is a diagram showing the state of reflected exposure light from the reference plane mirror when the focus plane of the reference plane mirror and the focus plane of the reduction projection lens coincide with each other and when the focus plane is shifted from the focus plane.

FIG. 3 is a diagram showing a state of reflected exposure light from the reference plane mirror when the focus plane of the reference plane mirror and the focus plane of the reduction projection lens coincide with each other and when the focus plane is shifted from the focus plane.

FIG. 4 is a diagram in which the pattern area used for focus detection is shifted by shifting the position of the aperture stop in FIG.

FIG. 5 is a diagram illustrating a relationship between an output of a focal plane detection system and an autofocus measurement value.

FIG. 6 is a flowchart showing a sequence from detection of a focal plane to exposure.

FIG. 7 is a configuration diagram when the present invention is applied to a projection exposure apparatus having an illumination area variable mechanism.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mercury lamp 2 Elliptical mirror 3 Optical integrator 4 Condenser lens 5 Mirror 6 Field lens 7 Reticle 8 Reduction photographing lens 9 Wafer 10 Xyz stage 11 Autofocus light projection system 12 Autofocus detection system 13 Imaging lens 14 Aperture stop 15 Condensing lens Reference Signs List 16 light receiving element 17 reference plane mirror 18 focal plane detection system 19 autofocus control system 20 drive system 21 light shielding pattern 22 light transmitting section 23 condenser lens 24 beam splitter 25 illumination area variable mechanism 26 imaging lens 27 mirror 28 condenser lens 50 photoelectric Detector 51 Filter 52 Condenser lens 55 Filter 56 Shutter 220 Slice level

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-212406 (JP, A) JP-A-61-19129 (JP, A) JP-A-61-152013 (JP, A) JP-A-61-2013 183928 (JP, A) JP-A-58-93233 (JP, A) JP-A-63-55430 (JP, U)

Claims (2)

(57) [Claims] 1. A projection exposure method for projecting and exposing a circuit pattern on a wafer coated with a resist through a projection optical system, the method comprising: illuminating a pattern located in a detection area within a screen area of the projection optical system; From the reflecting surface through the projection optical system, receives the reflected light from the reflecting surface via the projection optical system and the pattern, and based on the received light amount, the projection optical system A focus position detecting step of detecting a focus position of the detection area in; a surface for detecting a surface position of the wafer positioned in the detection area in the optical axis direction of the projection optical system, the focus position obtained from the focus position detecting step; Setting the reference position of the position detecting means; and the position of the wafer positioned at the reference position by the surface position detecting means, and printing when the wafer is actually exposed. Determining and storing the offset from the best printing position of the wafer where the path pattern is best, based on the resist coating thickness or the step amount of the wafer; and detecting the surface position of the wafer by the surface position detecting means. hand,
Projecting the circuit pattern onto the wafer by positioning the wafer at a position determined by the offset and the reference position. 2. The projection exposure method according to claim 1, wherein the pattern located in the detection area is a circuit pattern projected and exposed on a wafer.