JPH11143053A - Photomask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the breakage of a photomask produced using a low hardness material such as fluorite in the conveyance or scanning exposure of the photomask. SOLUTION: In a reticle R using fluorite (calcium fluoride (CaF2 )) as the material of the substrate, protective films 42A-42D of chromium(Cr), chromium oxide(CrO) or silicon oxide(SiO2 or SiO) are formed in regions other than the pattern region 40 and coming in contact with other member in the conveyance or exposure of the reticle R.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a photomask used in a lithography process for manufacturing, for example, a semiconductor device, a liquid crystal display device, or a thin-film magnetic head.

[0002]

2. Description of the Related Art When manufacturing a semiconductor device or the like, each shot area on a wafer (or a glass plate or the like) coated with a resist as a substrate through an image projection optical system of a reticle pattern as a photomask is formed. A projection exposure apparatus for transferring is used. Conventionally, as a projection exposure apparatus,
Although a projection exposure apparatus (stepper) of a step-and-repeat type (batch exposure type) has been frequently used, recently, a step-and-repeat in which a reticle and a wafer are synchronously scanned with respect to a projection optical system to perform exposure. Attention has been paid to a scanning exposure type projection exposure apparatus (scanning exposure apparatus) such as a scanning method.

As a photomask for these exposure apparatuses, a reticle in which a pattern to be formed is similarly enlarged to about 4 to 5 times and drawn is used. A conventional reticle is a transparent flat plate made of quartz glass or the like that transmits an exposure light beam. On one surface, a pattern to be transferred is shielded by chrome (Cr), molybdenum silicide (for example, MoSi ₂ ), or the like. It was formed as a nature pattern.

[0004]

With the recent miniaturization of integrated circuits, a further reduction in the wavelength of an exposure light beam is required in order to enable transfer of a finer pattern.
The current exposure wavelength is 24 KrF excimer laser.
Although 8 nm is being used, use of extreme ultraviolet light such as 193 nm of an ArF excimer laser and 157 nm of an F ₂ excimer laser is being studied. Note that the F ₂ excimer laser is also classified as a halogen molecule laser.

However, quartz glass, which is a conventional reticle substrate material, has a large absorption for extreme ultraviolet exposure light and cannot sufficiently transmit extreme ultraviolet exposure light, so that extreme ultraviolet light such as an F ₂ excimer laser (wavelength: 157 nm) is used. Exposure light could not be used for exposure. Fluorite (calcium fluoride (CaF ₂ )) is an optical material that transmits such an extreme ultraviolet exposure light beam and can form a flat plate of a practical size. However, Mohs hardness of fluorite is 4, which is softer than Mohs hardness 7 of quartz (quartz), which is a substrate material of a conventional reticle, and is used as a reticle. Further, even in the case of a batch exposure type projection exposure apparatus, the reticle is likely to be damaged during transport, and dust generated from the damaged portion causes unnecessary foreign substances to adhere to the pattern, making it impossible to expose a desired pattern. There is fear.

In view of the foregoing, the present invention provides a reticle manufactured using a material having a low hardness, such as fluorite, in order to shorten the exposure wavelength and enable transfer of a finer pattern. Another object of the present invention is to provide a reticle that does not break during transport of the reticle or during scanning exposure.

[0007]

A photomask (R) according to the present invention is a photomask (R) on which a pattern (40) for transfer is formed, the photomask (R) being provided on the outer surface of the photomask (R). Patterned area (40)
To protect the substrate of the photomask (R) at the contact surface with the member (20A) holding the photomask (R) and at least a part of the region near the contact surface in the outer region. In which the protective films (42A to 42D) are formed.

[0008] According to the photomask of the present invention, the photomask (R) is formed on the outer surface of the photomask (R) outside the region (40) where the transfer pattern is formed.
A photomask (R) is formed on at least a part of the contact surface with the member (20A) for holding the
In order to form a protective film (42A to 42D) for protecting the substrate, even if the photomask (R) is manufactured using a low hardness material such as fluorite, the photomask (R) Photomask (R) during transport or scanning exposure
No breakage occurs.

The photomask (R) has a wavelength of 19
It is desirable to irradiate with illumination light of 0 nm or less. In this case, an extremely fine pattern can be transferred by extreme ultraviolet illumination light having a wavelength of 190 nm or less. The substrate of the photomask (R) is made of calcium fluoride (CaF
₂ ) It is desirable to form it. The representative one is fluorite. In this case, extreme ultraviolet exposure light such as F ₂ excimer laser (wavelength 157 nm) can be used for exposure.

The protective films (42A to 42D) are preferably made of chromium (Cr), chromium oxide (CrO), or silicon oxide (SiO ₂ or SiO). In this case, the cost for forming the protective films (42A to 42D) for preventing the photomask (R) from being damaged can be reduced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a photomask according to the present invention will be described below with reference to FIG. FIG. 1A shows a pattern surface of a reticle R of the present example as a photomask, and FIG. 1B shows a side view thereof. In FIG. 1, reticle R is made of calcium fluoride (CaF).
₂ ) A pattern to be transferred and a predetermined protective film are formed on a flat substrate made of fluorite.
That is, a pattern to be transferred is formed in the central pattern area 40 of the pattern surface (bottom surface) of the reticle R.
On both sides of the pattern area 40, reticle alignment marks 41A and 41B for aligning the reticle R with an exposure apparatus (pattern transfer apparatus) are formed. The protective films 42A to 42 made of the same material as the material forming the pattern to be transferred are formed above and below the reticle alignment marks 41A and 41B.
D is formed.

Normally, when the reticle R is loaded into the exposure apparatus, a predetermined area in the surface of the reticle R on the side of the pattern area 40 is used to prevent the reticle R from being displaced during the exposure operation. Is adsorbed in vacuum. The reticle R of this example has a protective film 42A in the area where the vacuum suction is performed.
To 42D are formed, and the vacuum suction surface of the reticle R is covered with the protective films 42A to 42D. When the reticle R of this example is loaded into a scanning exposure apparatus, the direction parallel to the axis of symmetry of the reticle alignment marks 41A and 41B is the scanning direction.

As described above, since the protective film is formed on the vacuum suction surface of the reticle R of this embodiment, even if the reticle uses a substrate made of a soft material such as fluorite, the reticle R is not in contact with the exposure apparatus. Occasionally, damage or the like does not occur, and it is possible to completely prevent the generation of foreign matter when the damage occurs and the adhesion of the foreign matter to the pattern surface. In addition, not only during exposure, but also when transporting the reticle R to the exposure apparatus,
Even when the reticle is housed in the case, the reticle is generally transported and held while contacting the reticle R in the region where the protective films 42A to 42D are formed with the reticle loader or the case. , Protective film 4
2A-42D also prevents damage and dusting at these stages.

Since the area where the protective films 42A to 42D are formed is located at a position different from the pattern area 40 on which the pattern to be transferred is drawn, the protective film 42A is formed.
The material of ~ 42D may not transmit the exposure light, and for example, diamond grown by chemical vapor deposition (CVD) may be used. Also, when using silicon oxide (Si0 ₂ or Si0) has the advantage of being able reduce the manufacturing cost.

The material of the light-shielding pattern used for the pattern area 40 is the same as that of the pattern to be transferred.
r), chromium oxide (CrO), or molybdenum silicide (for example, MoSi ₂ ), the protective films 42A to 42D can be formed simultaneously with the formation of the pattern region 40. , The film forming process is simplified,
There is an advantage that the manufacturing cost can be reduced.

In this embodiment, fluorite is used as the material of the substrate of the reticle R. However, like fluorite, phosphorus (P) or fluorine (F) having a high transmittance for extreme ultraviolet light is used. ), The hardness of these materials is lower than that of conventional quartz glass. Therefore, by forming the protective films 42A to 42D, breakage may occur during transport of the reticle R or during scanning exposure. Can be prevented.

Next, a second embodiment of the photomask of the present invention will be described with reference to FIG. FIG. 2 shows a reticle R1 on which protective films 42E, 42F, 42G, and 42H are also formed on the side surfaces. By forming the protective films 42E to 42H on the side surfaces of the reticle R1, the reticle is used at the time of reticle defect inspection or the like. When the side surface of the reticle comes into contact with another member, damage to the reticle can be prevented. As described above, by forming the protective film on all portions where the reticle comes into contact with other members, the reticle can be completely prevented from being damaged.

Next, an example of a method of using the reticle of the above embodiment will be described. Hereinafter, a case in which exposure is performed by a step-and-scan type projection exposure apparatus using the reticle R of the first embodiment will be described with reference to FIG. FIG. 3 shows a schematic configuration of the projection exposure apparatus of the present embodiment. In FIG. 3, an ultraviolet pulse light IL as exposure light narrowed at a wavelength of 157 nm from the F ₂ excimer laser light source 1 is supplied to the exposure apparatus main body. The light passes through a beam matching unit (BMU) 3 including a movable mirror and the like for positionally matching an optical path between the light path and the light path, and enters a variable attenuator 6 as an optical attenuator through a light-shielding pipe 5. An exposure control unit 30 for controlling the amount of exposure of the resist on the wafer controls the start and stop of light emission of the F ₂ excimer laser light source 1, the output determined by the oscillation frequency and pulse energy, and a variable dimmer. 6, the extinction ratio for the ultraviolet pulse light is stepwise,
Or adjust continuously. Note that a wavelength of 193 is used as exposure light.
nm ArF excimer laser light or other wavelength 25
The present invention is also applicable to a case where a laser beam of about 0 nm or less is used.

The ultraviolet pulse light IL that has passed through the variable dimmer 6
Are lens systems 7A and 7B arranged along a predetermined optical axis.
Fly-eye lens 11 through a beam shaping optical system
Incident on. Thus, in this example, the fly-eye lens 1
Although 1 is one stage, in order to improve the uniformity of the illuminance distribution, two stages of fly-eye lenses may be arranged in series as disclosed in, for example, Japanese Patent Application Laid-Open No. 1-235289. An aperture stop system 12 of an illumination system is arranged on the exit surface of the fly-eye lens 11. In the aperture stop system 12, a circular aperture stop for normal illumination, an aperture stop for deformed illumination composed of a plurality of eccentric small apertures, an aperture stop for annular illumination, and the like are arranged to be switchable. The ultraviolet pulse light IL emitted from the fly-eye lens 11 and having passed through a predetermined aperture stop in the aperture stop system 12 enters the beam splitter 8 having a high transmittance and a low reflectance. The ultraviolet pulse light reflected by the beam splitter 8 enters an integrator sensor 9 composed of a photoelectric detector, and a detection signal of the integrator sensor 9 is supplied to an exposure control unit 30.

The transmittance and the reflectance of the beam splitter 8 are measured with high precision in advance and stored in a memory in the exposure control unit 30. The configuration is such that the incident light amount of the ultraviolet pulse light IL to the projection optical system PL and its integral value can be monitored. In order to monitor the amount of light incident on the projection optical system PL,
As shown by a two-dot chain line in FIG. 3, for example, a beam splitter 8A is arranged in front of the lens system 7A, reflected light from the beam splitter 8A is received by a photoelectric detector 9A, and a detection signal of the photoelectric detector 9A is detected. May be supplied to the exposure control unit 30.

The ultraviolet pulse light IL transmitted through the beam splitter 8 enters the fixed illumination field stop (fixed blind) 15A in the reticle blind mechanism 16 via the condenser lens system 14. As disclosed in, for example, Japanese Patent Application Laid-Open No. 4-196513, the fixed blind 15A has a linear slit shape or a rectangular shape (hereinafter, referred to as a direction perpendicular to the scanning exposure direction at the center of the circular visual field of the projection optical system PL).
(Referred to collectively as "slit shape"). Furthermore, reticle blind mechanism 1
A movable blind 15B for varying the width of the illumination visual field in the scanning exposure direction is provided separately from the fixed blind 15A inside the fixed blind 15A. This movable blind 15B reduces the scanning movement stroke of the reticle stage and reduces the reticle R. The width of the light-shielding band is reduced. The information on the aperture ratio of the movable blind 15B is also supplied to the exposure control unit 30, and the value obtained by multiplying the amount of incident light obtained from the detection signal of the integrator sensor 9 by the aperture ratio is the projection optical system PL.
Is the actual amount of incident light.

The ultraviolet pulse light IL shaped like a slit by the fixed blind 15A of the reticle blind mechanism 16
A uniform illumination area similar to the slit-shaped opening of the fixed blind 15A is formed on the circuit pattern area of the reticle R via the imaging lens system 17, the reflection mirror 18, and the main condenser lens system 19. Irradiate in distribution. That is,
Opening of fixed blind 15A or movable blind 1
The arrangement surface of the opening of 5B is substantially conjugate with the pattern surface of the reticle R by the combined system of the imaging lens system 17 and the main condenser lens system 19.

Under the ultraviolet pulse light IL, an image of the circuit pattern in the illumination area of the reticle R is converted into a predetermined projection magnification β (β is, for example, 1/4, 1/5) through a bi-telecentric projection optical system PL. Etc.), the image is transferred to the slit-shaped exposure area of the resist layer on the wafer W arranged on the image plane of the projection optical system PL. The exposure area is located on one of the plurality of shot areas on the wafer. The projection optical system PL of this example is a dioptric system (refractive system), but it goes without saying that a catadioptric system (catadioptric system) can also be used. Hereinafter, the projection optical system P
The Z axis is taken parallel to the optical axis AX of L, the X axis is taken in the scanning direction (here, the direction parallel to the plane of FIG. 3) in a plane perpendicular to the Z axis, and the non-scanning direction ( Here, FIG.
In the following description, the Y axis is taken in the direction perpendicular to the paper surface of FIG.

At this time, the reticle R includes the protective films 42A to 42A.
The area where 42D is formed is the reticle stage 20A.
The wafer is vacuum-absorbed and held on the reticle stage 20A. The reticle stage 20A is a reticle base 20
It is mounted on B so that it can move at a constant speed in the X direction and can finely move in the X direction, the Y direction, and the rotation direction. Two-dimensional position of reticle stage 20A (reticle R),
The rotation angle is measured in real time by a laser interferometer in the drive control unit 22. As a result of this measurement,
And a drive motor (such as a linear motor or a voice coil motor) in the drive control unit 22 based on control information from a main control system 27 including a computer that supervises and controls the entire operation of the apparatus.
And position control.

When aligning the reticle R, the reticle alignment marks 41A, 41B are set with the centers of the reticle alignment marks 41A, 41B substantially at the centers of the exposure fields of the projection optical system PL.
1B is illuminated from the bottom side with illumination light in the same wavelength range as the exposure light IL. Reticle alignment marks 41A, 41B
Is formed near the alignment mark (not shown) on the wafer stage 24, and the reticle alignment marks 41A and 41A are formed by a reticle alignment microscope (not shown).
By detecting the amount of misalignment of the alignment mark on the wafer stage 24 with respect to the image of B and positioning the reticle stage 20A so as to correct these amounts of misalignment, the reticle R is aligned with the wafer W. At this time, by observing the corresponding reference mark with an alignment sensor (not shown), an interval (baseline amount) from the detection center of the alignment sensor to the center of the pattern image of the reticle R is calculated. When performing the overlay exposure on the wafer W, the wafer stage 24 is driven based on the position obtained by correcting the detection result of the alignment sensor by the baseline amount, so that the reticle R A pattern image can be scanned and exposed with high overlay accuracy.

On the other hand, the wafer W is held by suction on a Z-tilt stage 24Z via a wafer holder WH, and the Z-tilt stage 24Z is an X-axis parallel to the image plane of the projection optical system PL.
The wafer stage 24 is fixed on an XY stage 24XY that moves two-dimensionally along the Y plane, and includes a Z tilt stage 24Z and an XY stage 24XY. Z
The tilt stage 24Z controls the focus position (position in the Z direction) and the tilt angle of the wafer W to adjust the surface of the wafer W to the image plane of the projection optical system PL by the autofocus method and the autoleveling method. Stage 2
4XY is a constant velocity scan of the wafer W in the X direction,
Stepping in the Y direction is performed. Z tilt stage 24
The two-dimensional position and rotation angle of Z (wafer W) are measured in real time by a laser interferometer in drive control unit 25. Based on the measurement result and the control information from the main control system 27, the drive motor (such as a linear motor) in the drive control unit 25 controls the scanning speed and position of the XY stage 24XY. The rotation error of the wafer W is corrected by rotating the reticle stage 20A via the main control system 27 and the drive control unit 22.

The main control system 27 includes the reticle stage 20
A, and the respective movement positions of the XY stage 24XY,
Various kinds of information such as the moving speed, the moving acceleration, and the position offset are sent to the drive control units 22 and 25. At the time of scanning exposure, the reticle R is scanned in the + X direction (or -X direction) at a speed Vr in the + X direction (or -X direction) via the reticle stage 20A in synchronization with the XY plane.
The wafer W is scanned through the stage 24XY with respect to the exposure area of the pattern image of the reticle R in the -X direction (or + X direction) at a speed β · Vr (β is a projection magnification from the reticle R to the wafer W).

The main control system 27 includes a movable blind 1 provided in the reticle blind mechanism 16 described above.
Control for synchronizing the movement of each blade 6B with the movement of the reticle stage 20A during scanning exposure is performed. Further, the main control system 27 sets various exposure conditions for scanning and exposing the resist in each shot area on the wafer W with an appropriate exposure amount, and executes an optimal exposure sequence in cooperation with the exposure control unit 30. That is, when a command to start scanning exposure to one shot area on the wafer W is issued from the main control system 27 to the exposure control unit 30, the exposure control unit 30
Starts emission of the F ₂ excimer laser light source 1 and
The integral value of the amount of light incident on the projection optical system PL via the integrator sensor 9 is calculated. The integrated value is reset to 0 at the start of the scanning exposure. Then, the exposure control unit 30 sequentially calculates the transmittance of the projection optical system PL from the integrated value of the amount of incident light, and according to the transmittance, sets the appropriate exposure amount at each point of the resist on the wafer W after the scanning exposure. Is controlled, the output (oscillation frequency and pulse energy) of the F ₂ excimer laser light source 1 and the dimming rate of the variable dimmer 6 are controlled. Then, at the end of the scanning exposure on the shot area, the emission of the F ₂ excimer laser light source 1 is stopped.

In addition, an irradiation amount monitor 32 composed of a photoelectric detector is provided near the wafer holder WH on the Z tilt stage 24Z in this embodiment, and a detection signal of the irradiation amount monitor 32 is also supplied to the exposure control unit 30. . The irradiation amount monitor 32 has a light receiving surface large enough to cover the entire exposure region of the projection optical system PL, and drives the XY stage 24XY to set the light reception surface at a position covering the exposure region of the projection optical system PL. Thus, the amount of the ultraviolet pulse light IL that has passed through the projection optical system PL can be measured. In this example, the transmittance of the projection optical system PL is measured using the detection signals of the integrator sensor 9 and the irradiation amount monitor 32. The irradiation amount monitor 32
Instead, a non-uniform illuminance sensor having a pinhole-shaped light receiving unit for measuring the light amount distribution in the exposure area may be used.

In this embodiment, since the F ₂ excimer laser light source 1 is used, the variable dimmer 6 and the lens system 7
A, 7B, and a sub-chamber 35 for blocking each illumination optical path from the fly-eye lens 11 to the main condenser lens system 19 from the outside air are provided. A suppressed helium gas (He) is supplied. Similarly, helium gas is supplied to the entire space inside the lens barrel of the projection optical system PL (space between a plurality of lens elements) via the pipe 37.

When the airtightness of the sub-chamber 35 and the lens barrel of the projection optical system PL is high, the supply of the helium gas does not need to be performed so frequently after the air has been completely replaced once. However, the fluctuation of transmittance caused by water molecules and hydrocarbon molecules generated from various substances (glass materials, coating materials, adhesives, paints, metals, ceramics, etc.) existing in the optical path adhere to the surface of the optical element. Then, it is necessary to remove the impurity molecules by a chemical filter or an electrostatic filter while forcibly flowing the temperature-controlled helium gas in the optical path.

As described above, the reticle R of the present embodiment is formed of F ₂
Can be used in a scanning type exposure apparatus using an excimer laser light source. In addition, a protective film is formed at the place where the reticle comes in contact with other members due to vacuum suction, etc., causing damage to the reticle during scanning exposure There is an advantage that the scanning speed can be increased without any occurrence. Also, when used in a batch exposure type projection exposure apparatus, there is an advantage that the protective film prevents damages during transport of the reticle and the like.

It should be noted that the present invention is not limited to the above-described embodiment, but can take various configurations without departing from the spirit of the present invention.

[0034]

According to the photomask of the present invention, even if the photomask is manufactured using a material having a low hardness such as fluorite, the photomask is damaged when the photomask is transported or scanned and exposed. Does not occur, fluorite that can transmit extreme ultraviolet exposure light such as F ₂ excimer laser can be used as the material of the photomask, and the exposure wavelength used in the exposure apparatus can be shortened. A fine pattern can be transferred. In particular, when the photomask of the present invention is used in a scanning exposure apparatus, there is an advantage that the scanning speed can be increased to improve the throughput.

The photomask has a wavelength of 190 nm.
When irradiated with the following illumination light, an extremely fine pattern can be transferred and formed by the extreme ultraviolet illumination light. When the substrate of the photomask is formed of calcium fluoride (CaF ₂ ), extreme ultraviolet exposure light such as an F ₂ excimer laser (wavelength: 157 nm) can be used for exposure.

When the protective film is made of chromium (Cr) or chromium oxide (CrO), the material of the light-shielding pattern and the protective film can be made common, and the formation of the protective film is performed simultaneously with the formation of the light-shielding pattern. Can also be performed, so that the film forming process is simplified and economical. In addition, when the protective film is made of silicon oxide (SiO ₂ or SiO), there is an advantage that the cost for forming the protective film can be suppressed because silicon oxide is easily available.

[Brief description of the drawings]

FIG. 1A is a bottom view showing a pattern surface of a photomask according to a first embodiment of the present invention, and FIG. 1B is a side view of FIG. 1A.

FIG. 2A is a bottom view showing a pattern surface of a photomask according to a second embodiment of the present invention, and FIG. 2B is a side view of FIG. 2A.

FIG. 3 is a schematic configuration diagram showing a projection exposure apparatus using the reticle according to the first embodiment of the present invention.

[Explanation of symbols]

R reticle PL projection optical system W wafer 1 F ₂ excimer laser light source 20A reticle stage 42A~42D protective film

Claims (4)

[Claims] 1. A photomask on which a pattern for transfer is formed, wherein a contact surface with a member holding the photomask is formed in a region on an outer surface of the photomask other than a region on which the pattern for transfer is formed. And a protective film for protecting a substrate of the photomask is formed on at least a part of a region near the contact surface. 2. The photomask has a wavelength of 190 nm.
The photomask according to claim 1, wherein the photomask is irradiated with the following illumination light. 3. The photomask substrate according to claim 1, wherein the substrate is formed of calcium fluoride.
Or the photomask of 2. 4. The method according to claim 1, wherein the protective film is made of chromium, chromium oxide, or silicon oxide.
Or the photomask according to 3.