JPS642935B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a photomask repair method, and more particularly to a photomask repair method using laser light.

Prior Art There are two types of defects called black defects and white defects in photomasks used for manufacturing ICs (integrated circuits), LSIs (large scale integrated circuits), and the like. A black defect is a defect in which a metal film (usually a chromium film) that serves as a light-shielding film remains in an unnecessary part, whereas a white defect is a defect in which a metal film is missing in a necessary part. Yes, if these defects exist in the photomask,
These defects must be corrected because they cause poor performance of ICs and LSIs and reduce yield.

Currently, black defects can be corrected using a repair device that uses laser light, which is actually used on production lines and is effective in improving yields. An example of the general configuration of this device is shown in FIG. The principle of repairing black defects of the repair device will be explained using this figure.

The beam diameter of the laser light emitted from the laser light source 3 is expanded by a beam expander 8. This expanded laser beam is then shaped into a desired shape by a variable slit 11. This shaped laser beam is introduced into the microscope 37, reflected by the dichroic mirror 38, and focused onto the photomask 25 by the objective lens 39. This focused laser beam can instantly melt and evaporate the metal film on the photomask 25.

In this case, the shape of the evaporated metal film can be determined by appropriately selecting the energy and pulse width of the laser beam.
The shape can be made to match the shape of the variable slit 11. Therefore, the variable slit 11 is irradiated with light from the pilot light source 9, and the photomask 25 is
By forming an image of the shape of the variable slit 11 on the photomask 25 and observing the image on the photomask 25 with the naked eye 40 using a microscope 37, the shape of the variable slit 11 can be modified to any desired shape.

Normally, the laser light source 3 is a YAG laser with a wavelength of 1.06 μm or its harmonic of 0.53 μm.
m is used, in this case the pulse width is 20nsec
The energy is approximately 200 μJ/pulse. Note that it is known that the shorter the pulse width, the more accurate correction can be performed.

On the other hand, white defects were repaired in the past using a lift-off method, but recently, methods using a thermal CVD (chemical vapor deposition) method using laser light and a method using a focused ion beam have been announced.

In the lift-off method, a resist is applied onto the photomask 25, white defect areas are exposed, and then a metal film is formed again through a vapor deposition process to perform correction.

Thermal CVD method using laser light was announced by a manufacturer in the United States, and the device is actually being sold. White defect correction using this device is a so-called heat treatment.
This is an application of the CVD method and uses Ar laser light as the heat source. The modification principle of this method is as follows.

Cr(CO) ₆ (chromium carbonyl) gas is flowed over the surface of the photomask 25, and a laser beam is irradiated from above to heat the photomask substrate. Then, the nearby heated Cr(CO) ₆ gas decomposes into Cr atoms.
The CO molecules are separated, and Cr atoms are adsorbed onto the photomask 25 and grow to form a Cr film. However, in this case, the heating principle uses laser light absorption in the metal film, so the temperature rise sufficient to thermally decompose the Cr(CO) ₆ gas is generated in the Cr pattern that has already been created.
Since this occurs only in the membrane part, the method used to form the Cr film is to extend and expand the Cr film one after another from the original Cr film part. That is, an independent Cr film cannot be formed.

In addition, this device uses second harmonic light (wavelength 0.53 μm)
It is equipped with a YAG laser that can generate YAG laser light, and it is also possible to repair black defects using this laser light.
It is not possible to perform repair work by switching between repairing black defects using second harmonic light of a laser at any time.

A focused ion beam method was also announced in the United States and has been put into practice. There are two methods for correcting white defects using this focused ion beam. One of these methods is to make countless minute scratches on the white defect portion of the photomask substrate surface using a focused ion beam, and to equivalently prevent light from passing through the scratches by scattering the beam. Another method is to flow some type of gaseous organic substance onto the photomask surface and irradiate it with a focused ion beam to form a carbon film on the photomask.

Furthermore, an apparatus using this type of focused ion beam can also correct black defects by sputtering the Cr film with the focused ion beam. The correction time for this type of device is approximately 10 to 30 μm ² /min.

Such conventional photomask repair equipment can only repair black defects, and the lift-off method has the disadvantage that the repair process is complicated and takes a long time, and new defects are generated in the repair process. In addition, equipment using the thermal CVD method cannot repair independent white defects, and has the drawback of not being able to perform high-precision correction due to thermal spread. This method has drawbacks such as the need for two laser devices to repair both black and white defects. The method using a focused ion beam can repair both black defects and white defects, but the photomask substrate is damaged when repairing white defects, and the film formed is not a Cr film.
This method has drawbacks such as a long correction time.

Purpose of the Invention The present invention has been made to eliminate the drawbacks of the conventional methods as described above, and an object of the present invention is to provide a photomask repair method that can quickly repair white defects without producing secondary defects. purpose.

Another object of the present invention is to provide a photomask repair method that can repair white defects and black defects in a timely and continuous manner.

Structure of the Invention The photomask repair method according to the present invention is a photomask repair method in which a white defect of the photomask is corrected by condensing laser light onto the photomask, and comprises:
A holding means is provided for gasifying a compound containing chromium and holding the photomask in the gas when repairing the white defect; The present invention is characterized in that the white defect is corrected by condensing light irradiation onto the photomask held in the gas by a holding means.

Another photomask repair method according to the present invention is a photomask repair method in which white and black defects on the photomask are repaired by condensing laser light onto the photomask, and in which a compound containing chromium is gasified to correct the white defects. A holding means for holding the photomask in the gas during correction and a selection means for selecting one of ultraviolet laser light and visible laser light are provided, and the selection means selects the laser light during correction of the white defect. The selected ultraviolet laser beam is used, and the ultraviolet laser beam is condensed and irradiated onto the photomask held in the gas by the holding means to correct the white defect, and when the black defect is corrected. The laser beam is the visible laser beam selected by the selection means, and the visible laser beam is focused and irradiated onto the photomask to correct the black defect.

Embodiment Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, a laser light source 3 that generates a laser beam with a wavelength of 1.06 μm uses power supplied from a laser power source 2 to generate a CW (connected wave) laser beam or a single pulsed laser beam with an arbitrary repetition frequency according to a signal from a control circuit 1. can occur. Second
The harmonic generation unit 4 receives the energy from the laser light source 3.
It works to convert 1.06μm laser light into 0.53μm laser light. Optical crystals commonly used in this second harmonic generation unit 4 are CD ^* A and KTP, and the exchange efficiency in this case is normally 10 to 30%.

The fourth harmonic generation unit 5 converts the 0.53 μm laser beam from the second harmonic generation unit 4 into 0.266 μm.
It functions to convert into laser light. The optical crystal commonly used in this fourth harmonic generation unit 5 is KDP, and the exchange efficiency in this case is also 10.
~30 is normal.

The attenuator 6 is a fourth harmonic generation unit 5.
The energy of the ultraviolet laser light from can be adjusted to a desired value. The ultraviolet laser beam adjusted by the attenuator 6 is reflected by the fixed mirror 7 and the beam diameter is expanded by the beam expander 8. This expanded laser beam is reflected by a dichroic mirror 10, enters a variable slit 11, and is shaped into a desired shape. Next, this laser beam is reflected by a dichroic mirror 12, passes through a laser optical axis A that is reflected by a fixed mirror 13, is reflected by dichroic mirrors 14 and 20, and enters an objective lens 21.

On the other hand, visible light emitted from the pilot light source 9 used to confirm the shape of the variable slit 11 passes through the variable slit 11 via the dichroic mirror 10, passes through the correction lens system 15, and is reflected by the fixed mirror 16. The light enters the objective lens 21 through the pilot optical axis B. This correction lens system 15 is a lens system for correcting the shift in the imaging position of the variable slit 11 due to the wavelength difference between the ultraviolet laser beam and the visible light.

In this way, the image of the variable slit 11 created by the ultraviolet laser beam and the pilot beam is transmitted to the objective lens 21.
An image is formed on the photomask 25 by this. In this case, since the objective lens 21 needs to pass the ultraviolet laser light well, a combination lens using quartz or fluorite is usually used. The shape of the photomask 25 and the pilot light can be observed by the observation optical system 17 through the dichroic mirror 19 using the epi-illumination light source 18 and the transmitted-illumination light source 28.

The photomask 25 is fixed to a mask holder 26 with a heating mechanism, and this mask holder 26 is
It is placed on an XY stage 27. The XY stage 27 is housed in a sealed chamber 22.

This chamber 22 has Cr on the photomask 25.
It has a nozzle that supplies (CO) ₆ gas and a nozzle that exhausts it. Cr(CO) ₆ is a powdered metal, but when heated, it evaporates and becomes a gas, with an upper pressure of approximately 1 Torr at 45°C. This Cr
(CO) ₆ is produced in a raw material chamber 29 equipped with a heating mechanism, and is supplied onto the photomask 25 in the chamber 22 by a carrier gas supply device 30.

Further, in order to keep the concentration of Cr(CO) ₆ gas on the photomask 25 constant and eliminate stagnation, the Cr(CO) ₆ gas is exhausted from the exhaust nozzle by the exhaust device 32. Note that this Cr(CO) ₆ gas is toxic to the human body, so it is collected by the trap 31 before being discharged to the exhaust duct. As the trap 31, a cooling trap or a thermal decomposition trap is used. In addition, Chamber 2
2 is provided with a window 23 for introducing laser light, and the window 23 is made of quartz glass that can transmit ultraviolet laser light.

When ultraviolet laser light is irradiated for several tens of seconds with Cr(CO) ₆ gas present on the photomask 25 in this way, a Cr film is formed only on the portions irradiated with the ultraviolet laser light. The principle of forming this Cr film is based on a film forming method called the so-called laser CVD method.

Therefore, by changing the shape of the variable slit 11 and changing the irradiation shape of the ultraviolet laser beam, a Cr film having an arbitrary shape can be formed on the photomask 25, and white defects on the photomask 25 can be corrected. can.

In this case, the conditions for forming an optimal Cr film in the range of 1 to 100 μm square are that the laser power is 5 to 200 mW and the irradiation time is 5 to 200 mW using a Q-switch ultraviolet laser beam with a repetition frequency of 400 Hz to 10 kHz.
It is experimentally known that irradiation for seconds is good. Regarding the conditions for forming this Cr film, please refer to "Cr
CVD” (December 4, 1984, Semiconductor Integrated Circuit Technology No. 27
Published in Proceedings of the 2017 Symposium, pp. 6-11).

The above is a case of correcting white defects, but in one embodiment of the present invention, black defects can also be corrected.
This will be explained next.

As mentioned above, when repairing white defects, the irradiation time of ultraviolet laser light is long, ranging from several seconds to hundreds of seconds.On the other hand, when repairing black defects, the pulse width is This is possible with a single irradiation of pulsed laser light of several nanoseconds. Therefore, if the irradiation time is as short as this number + nsec, Cr
Even if ultraviolet laser light is irradiated in (CO) ₆ gas, no Cr film is formed, and if there is sufficient energy, the Cr film on the photomask 25 can be evaporated and black defects can be repaired.

In this case, the conditions for evaporating the Cr film on the photomask 25 are that the pulsed ultraviolet laser beam has a pulse width of 50 nsec or less, an energy of 5 to 500 μJ/pulse, and a repetition frequency of 1 to 10 pps. It is experimentally known that defects can be corrected. Regarding the evaporation conditions of this Cr film,
Published in "Processing technology for photomask correction" (technical magazine "Electronic Materials" March 1978, pp. 45-53).

FIG. 2 is a block diagram illustrating an embodiment of another photomask repair method according to the present invention. In the figure, one embodiment of another photomask correction method according to the present invention is shown in FIG.
3, 36, fixed mirror 34, and beam shaper 3
5. Also, a beam expander 8 and dichroic mirrors 10 and 20
, the objective lens 21 and the window 23 are equipped with ultraviolet laser light (wavelength: 0.266 μm) and visible laser light (wavelength: 0.266 μm).
A surface coating is applied to improve the transmittance or reflectance for both 0.53 μm).

When a white defect is corrected, the movable mirrors 33 and 36 are at the positions indicated by the solid lines, and the ultraviolet laser beam reaches the photomask 25, allowing the formation of a Cr film as described above. When correcting black defects, move the movable mirror 3
Move 3 and 36 to the position of the broken line, and set the wavelength to 0.53 μm.
visible laser light enters the beam expander 8 through a fixed mirror 34 and a beam shaper 35. Then, this visible laser light passes through the variable slit 11 and then passes through the pilot optical axis B and is condensed onto the photomask 25 to correct the black defect. In this case, since the visible laser light is visible light, the black defect can be repaired without being affected by the CVD reaction involved in forming the Cr film. However, although movable mirrors 33 and 36 are used in this embodiment, if the optical axis rotates, good correction may not be possible or the corrected shape may vary, so it is necessary to have a structure that allows movement with sufficient reproducibility.

In this way, the photomask 25 is held in Cr(CO) ₆ gas (a gas obtained by gasifying a compound containing chromium), and the white defects are corrected by condensing and irradiating ultraviolet laser light onto the photomask 25. By doing so, not only can black defects and white defects of the photomask 25 be repaired continuously in a timely manner with one device, but also the black defect repair using a conventional laser beam can be performed. It has the same performance as the equipment,
White defects can be corrected faster than conventional methods and without the risk of causing secondary defects.

Further, by using ultraviolet laser light and visible laser light for correcting white defects and correcting black defects, it is possible to more reliably correct white defects and correct black defects.

Effects of the Invention As explained above, according to the present invention, a photomask is held in a gas of a compound containing chromium,
By irradiating focused ultraviolet laser light onto this photomask, white defects can be repaired quickly without causing secondary defects, and white and black defects can be repaired in a timely and continuous manner. It has the effect of being able to

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is a block diagram showing an embodiment of another photomask repair method according to the present invention, and FIG. 3 is a block diagram showing a conventional example. Explanation of symbols of main parts, 3... Laser light source, 4
...Second harmonic generation unit, 5...Fourth harmonic generation unit, 6...Attenuator, 15...Correction lens system, 22...Chamber, 23...Window, 24...Cr(CO) ₆ ( chromium carbonyl) gas,
25...Photomask, 29...Material room, 30...
Carrier gas supply device, 31... Trap, 32
...Exhaust system, 33, 36...Movable mirror, 35
...beam shaper.

Claims (1)

[Scope of Claims] 1. A photomask repair method in which white defects and black defects of the photomask are repaired by condensing and irradiating the photomask with a laser beam, wherein a compound containing chromium is gasified to correct the white defects and black defects. a holding means for holding the photomask in the gas during correction; a laser light source that switches and emits a repeated Q switch laser beam and a single pulsed laser beam according to a control signal;
A conversion means for repeatedly converting the switch laser beam and the single pulsed laser beam into a Q-switch ultraviolet laser beam and a single pulsed ultraviolet laser beam is provided, and when the white defect is corrected, the white defect is held in the gas by the holding means. The white defect is corrected by repeatedly irradiating the photomask with the Q-switched ultraviolet laser beam in a condensed manner, and when the black defect is corrected, the single pulsed ultraviolet laser beam is applied to the photomask held in the gas by the holding means. A photomask repair method characterized in that the black defect is repaired by condensing and irradiating light. 2. A photomask repair method in which white defects and black defects on the photomask are repaired by condensing laser light irradiation onto the photomask, wherein a compound containing chromium is gasified, and when the white defects and black defects are repaired, the photomask repair method a holding means for holding the photomask; a laser light source for switching and emitting a repetitive Q-switch laser beam and a single pulsed laser beam according to a control signal; A first converting means for converting into a switched ultraviolet laser beam, and a second converting means for converting the single pulsed laser beam from the laser light source into a single pulsed visible laser beam are provided. The photomask held in the gas by the holding means is repeatedly irradiated with the Q-switch ultraviolet laser beam in a focused manner to repair the white defects, and when the black defects are repaired, the photomask is held in the gas by the holding means. A method for repairing a photomask, characterized in that the black defect is repaired by condensing and irradiating the single pulsed visible laser beam onto the photomask.