JPS6140103B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for correcting white spot defects that occur in photomasks used in the manufacture of ICs, LSIs, etc. White spot defects that occur on photomasks have a fatal negative impact on the production yield of LSIs, etc., and a technology to correct white spot defects is required. Conventionally, this technique has used a lift-off method in which the white spot defect area is selectively exposed to light and then etched. However, such a lift-off method has the disadvantage that, like ordinary pattern etching, it requires many correction steps and a large number of man-hours over a long period of time. A method has also been proposed in which partial vapor deposition is performed on the white spot defect using laser light, but this method has practical problems such as poor accuracy and poor film strength. It is an object of the present invention to eliminate the drawbacks and problems of the prior art as described above, and to correct white spot defects occurring on photomasks with a simpler process and shorter time than before, with fewer man-hours, and with high precision. An object of the present invention is to provide a method and apparatus for correcting white spot defects on a photomask. In order to achieve the above object of the present invention, the method for repairing white spot defects in a photomask of the present invention includes applying a metal complex solution to at least one side of a photomask having a white spot defect, and then selectively applying a metal complex solution to the white spot defect. A method of repairing white spot defects on a photomask by irradiating visible light or ultraviolet light to deposit a metal or metal oxide involves measuring the amount of light transmitted through the photomask by the irradiation light, which changes during the deposition process. , the irradiation is stopped when the amount of light falls below a certain percentage of the amount of light when the irradiation was started. Further, the photomask white spot defect correction apparatus of the present invention applies a metal complex solution to at least one side of a photomask having a white spot defect, and selectively irradiates the white spot defect with visible light or ultraviolet light. The apparatus is configured to correct white spot defects in a photomask by depositing a metal or metal oxide, and further includes a photodetector for measuring the amount of light transmitted through the photomask, and information on the photodetector. The control unit stores the amount of transmitted light at the start of irradiation and uses this as a reference value, and the amount of transmitted light of the photomask detected by the detector is set at a certain percentage with respect to this reference value. The structure is such that the light irradiation is stopped when the light amount falls below the following. The present invention will be explained using the drawings. FIG. 1 is a block diagram of a photomask white spot defect correction apparatus used in the method of the present invention. 1 is an Ar laser generator, 2 is a laser beam with a wavelength of 5145 Å generated from it, and the laser beam 2 reaches a rectangular aperture slit 3 whose width in both the X and Y directions can be set independently, and passes through the rectangular aperture slit. The laser beam is sent to the half mirror 4
The light passes through the objective lens 5, is focused, and is irradiated onto the defective mask 6. The rectangular opening slit 3 is arranged so as to be projected onto the surface of the defect mask 6 in a reduced size using the magnification of the objective lens, and the width of the slit 3 can be freely adjusted. The mask pattern of the photomask 6 is illuminated by light from an illumination light source 7 and can be seen by an observation optical system composed of an objective lens 5 and an eyepiece optical system 8. Further, the projected pattern of the rectangular opening slit 3 can be seen as a reduced image on the defect mask 6 by the light from the slit illumination light source 9 using the observation optical system. A silver complex solution is applied onto the defect mask 6, and the solvent is removed by drying to form a silver complex film 10. The white spot defect portion 11 can be adjusted using the XY table 12 so that it is located in the projection area of the rectangular opening slit 3. 17 is an XY table drive unit that drives the XY table 12. The amount of laser light 2 that passes through the defective part 11 is measured by the photodetector 14 through the interference filter 18, and the information is sent to the control section 15.
It is recorded on a recorder 16 directly connected to. The interference filter 18 has a function of passing only the light to be measured. Next, one aspect of a method for correcting white dot defects on a photomask using the white dot defect correction apparatus shown in FIG. 1 will be described. As will be explained in detail later, a silver complex solution in which silver nitrate and carboxylic acid are added to an organic solvent (for example, dimethyl sulfoxide) is prepared as a metal complex solution, and this solution is spin-coated on the upper surface of a photomask having white spot defects 11. The organic solvent is evaporated to form a silver complex film 10. At this time, the normal pattern 13 is arranged so as to surround the white spot defective portion 11. Then, while viewing with the observation optical system, the width of the rectangular opening slit 3 is adjusted so that the slit projected image is connected to the normal pattern 13. Next, Ar laser light 2 is generated by an Ar laser generator and irradiated onto the white spot defect portion 11 . A photodetector 14 measures the amount of laser light 2 passing through the photomask 6 at the start of irradiation and during subsequent irradiation, and sends information at that time to a control unit 15 . The control unit 15 stores the amount of transmitted light at the start of irradiation, uses this as a reference value, and when the amount of light falls below a certain percentage (for example, 10%) of this reference value, the Ar
Stop the laser beam irradiation. In this way, silver is precipitated by the laser beam, and when the light-shielding property becomes sufficient, the laser beam is automatically shut off and the process ends.
If irradiation is continued, the silver deposited film will be damaged, and the amount of transmitted light will begin to increase after reaching the lower limit, and the light-shielding property will begin to deteriorate. For this reason, it is essential to stop irradiation once the reference value is reached. Information on the amount of transmitted light is recorded by a recorder 16 connected to the control unit 15.
The data can be extracted as data and used for quality control of correction work. By doing so, there is no need to inspect the repaired portion again. When the laser beam is automatically turned off and the correction is completed, this signal is sent to the XY table drive unit 17,
The table is moved to the address of the next white spot defect. By doing so, the number of man-hours required for correction can be reduced. When the irradiation of the defective area is completed, the photomask 6
Wash with water and remove the silver complex film 1 in the area where silver is not deposited.
Remove 0. The unprecipitated silver complex, ie, carboxylic acid silver salt, is soluble in water and can be easily removed. When silver is deposited, it has a light-shielding property against green light of 5145 Å, and at the same time has a similar light-shielding property against light of up to 4000 Å. Therefore, instead of directly measuring the transmittance of G-line (4358 Å), H-line (4047 Å), etc. used for wafer exposure, the purpose can be sufficiently achieved by measuring the light shielding property of 5145 Å green light. Even if silver is precipitated by irradiation using ultraviolet output light (for example, 3638 Å) of an Ar laser and the ultraviolet light is monitored, the purpose of correcting white spot defects by optimal precipitation according to the present invention can be similarly achieved. Instead of Ar laser as the irradiation light source for silver deposition, other lasers emitting light of similar wavelength (e.g.
The object of the present invention can also be achieved using monochromatic light in the range from green to near ultraviolet (second harmonic of YAG laser: 5300 Å, dye laser: 5500 to 4000 Å, etc.) or ordinary green light to near ultraviolet light. FIG. 2 shows an example of a change in the amount of laser light transmitted during correction by the method of the present invention. The horizontal axis represents the relative value of the laser irradiation time, and the vertical axis represents the amount of laser light transmitted through the white spot defect at the start of irradiation.
When , it represents the amount of light transmission. As can be seen from the figure, as the irradiation continues, the amount of transmission gradually decreases, reaching the minimum amount of transmission after 1.7 relative time, and as the laser beam continues to be irradiated, the amount of transmission begins to increase, and finally approaches 50%. I'm getting used to it. Because of this tendency, when using a silver complex solution to correct white spot defects, if a method is used in which the deposition is performed without monitoring, the film thickness, irradiation light amount and its fluctuation amount, amount of out-of-focus during irradiation, aperture There are many factors that affect the amount of precipitation, such as changes in power density due to the influence of diffraction due to size, and it is quite difficult to always keep the amount of transmission below a predetermined value. In contrast, the embodiment of the present invention uses a monitoring system that measures the transmitted laser light and automatically stops irradiation when a predetermined amount of transmitted light is reached. Since it is possible to confirm that the amount of light is correct, the repair is always highly reliable, and the light-shielding property of the repaired area can also be inspected at the same time, so there is no need to measure the transmittance again. In the present invention, a metal complex solution is applied to one side of a photomask. Various metal complex solutions can be used as long as the metal in the solution or the oxide of the metal precipitates when irradiated with visible light or ultraviolet light. A metal complex is defined here as a metal complex in the narrow sense, that is, one or more metals as a central atom, and other atoms or atomic groups, i.e., ligands, bonded to it to form one atomic group. This concept includes not only the atomic group when it is present, but also metal salts produced in normal solution reactions. In one embodiment of the present invention, as the metal complex,
A solution prepared by adding silver nitrate and carboxylic acid to an organic solvent (hereinafter referred to as a silver complex solution) is used. At this time, carboxylic acid silver salt is formed in a dissolved state in the solution. Among the silver salts, carboxylic acid silver salts are preferably used. This is because silver salts other than carboxylic acid silver salts, such as silver chloride, silver bromide, and silver iodide, are hardly soluble in water or organic solvents, and silver nitrate is highly soluble in water, but when this aqueous solution is applied, This is because even if water is evaporated, a film does not form, and crystal particles precipitate. Various types of carboxylic acids can be used to form carboxylic acid silver salts, but a carboxylic acid with two carboxylic acid groups (-COOH) is preferred because it has good film-forming properties during coating. Dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid,
These include azelaic acid, sebacic acid, fumaric acid, maleic acid, and citraconic acid. Among these,
Citraconic acid has particularly excellent film-forming properties. Carboxylic acids other than dicarboxylic acids that have good film-forming properties in practical terms include carboxyl groups (-COOH) and alcoholic hydroxyl groups (-
There are hydroxy acids with OH). Examples of this include lactic acid, malic acid, citric acid, tartaric acid, culutronic acid, hydroacrylic acid, glycolic acid,
Glyceric acid, β-hydroxypropionic acid, α
-Hydroxy-n-butyric acid, α-hydroxy-isobutyric acid, etc. In addition, as organic solvents, alcohol-based, cellosolve-based, carbitol-based, glycol-based organic solvents,
dimethyl sulfoxide, dimethyl acetamide,
Examples include dimethylformamide. The silver complex solution is spin coated onto a photomask. The rotational speed of spin coating is adjusted so that the coating thickness is 1 μm or less. Then, by drying, the organic solvent is evaporated and a coating film of carboxylic acid silver salt is formed on the photomask surface. When this coating film is irradiated with visible light or ultraviolet light, silver is precipitated. Although silver can be precipitated by the method described above, if it is necessary to increase the adhesion strength of the deposited silver film to the substrate, the purpose can be achieved by adding titanium alcoholate to the silver complex solution. For example, silver nitrate (1.7g), citraconic acid (1.3g), titanium tetrabutyrate (Ti(O-n _{- C4H9} ) ₄ )
(5.13 g) and ethyl cellosolve (10 g) as a coating liquid, the silver titanium oxide film deposited by the method described above has significantly stronger adhesive strength with the substrate. The transmittance of the silver titanium oxide film deposited in this way for visible light is 4000.
It is 5 to 18% for visible light of Å to 5000 Å.
Other titanium alcoholates that can be used for this purpose include Ti(O-iso-C ₃ H ₇ ) ₄ , Ti
[OCH ₂ CH (C ₂ H ₅ ) C ₄ H ₉ ] ₄ , Ti (OC ₁₇ H ₃₅ ) ₄ ,
Ti(O-iso-C ₃ H ₇ ) ₂ [OC(CH ₃ )
CHCOCH ₃ 〕 ₂ , Ti(O-n-C ₄ H ₉ ) ₂ 〔OC ₂ H ₄ N
(C ₂ H ₄ OH) ₂ 〕 ₂ , Ti〔OCH ₂ CH (C ₂ H ₅ ) CH
(OH) _{C3H7 〕 4} ,Ti(O- _n - _C4H9 ) ₃
(OCOC _{17H35 )} Ti(iso−C ₃ H ₇ ) (OCOC ₁₇ H ₃₅ ) ₃ , Ti(iso−
C ₃ H ₇ ) [OCOC(CH ₃ )=CH ₂ ] ₂ (OCOC ₁₇ H ₃₅ ),
Examples include Ti(O-iso-C ₃ H ₇ )(OCOCH=CH ₂ ) ₃ . In addition to the silver complex solution described above, a cobalt complex solution or a copper complex solution can be used as the metal complex solution of the present invention. Here, the cobalt complex solution is cobalt nitrate (Co(NO ₃ ) ₂・nH ₂ O) in an organic solvent.
A silver complex solution is a solution in which copper nitrate (Cu(NO ₃ ) ₂ .
nH ₂ O) and a carboxylic acid. Further, the organic solvent and carboxylic acid used are the same as those for the silver complex solution. In the case of a silver complex solution, silver precipitates, but in the case of a cobalt complex solution and a copper complex solution, it precipitates as a black oxide. Cobalt oxide has a transmittance of 2 to 4 for visible light with a wavelength of 4000 to 5000 Å. %, copper oxide content is 3 to 9%, and the light shielding properties are quite excellent.
It's quite practical. However, in this case, cobalt,
Copper chelate requires the use of a surfactant in order to improve film formability. As the surfactant, nonionic surfactants are particularly excellent. As a nonionic surfactant, for example, polyethylene glycol alkyl ether R
(OCH ₂ CH ₂ ) nOH, polyethylene glycol fatty acid ester RCO (OCH ₂ CH ₂ ) nOH, fatty acid monoglyceride

[Formula] is used. The present invention has made it possible to correct white spot defects on photomasks, which have a major impact on LSI production yields, in about 1/10 the number of steps compared to the conventional lift-off method. In addition, since the amount of transmitted light can be monitored at the same time during correction, optimal correction is always possible.
Also, since correction data can be retrieved at the same time, it has become easier to manage correction quality. The present invention thus has various practical advantages.

[Brief explanation of the drawing]

FIG. 1 is a diagram of a configuration example of a white spot defect correction device used in the method of the present invention, and FIG. 2 is an example of a change in the amount of light transmission when a white spot defect is repaired by the method of the present invention. FIG. 2... Laser light, 3... Rectangular opening slit, 5
... Objective lens, 6 ... Defect mask, 11 ... White spot defect, 12 ... Photodetector, 15 ... Control unit, 1
6...Recorder.

Claims (1)

[Claims] 1. After applying a metal complex solution to at least one side of a photomask having white spot defects, the white spot defects are selectively irradiated with visible light or ultraviolet light to form a metal or metal oxide. A method of repairing white spot defects on a photomask by depositing irradiation light, which measures the amount of light transmitted through the photomask by the irradiation light that changes during the deposition process, and determines whether the amount of light is relative to the amount of light when irradiation starts. A method for correcting white spot defects on a photomask, characterized in that irradiation is stopped when the value falls below a certain percentage. 2. The method for correcting white spot defects on a photomask according to claim 1, wherein the metal complex solution is a solution prepared by adding at least silver nitrate and carboxylic acid to an organic solvent. 3. The method for correcting white spot defects on a photomask according to claim 1, wherein the metal complex solution is a solution prepared by adding at least silver nitrate, carboxylic acid, and titanium alcoholate to an organic solvent. 4. The method for correcting white spot defects on a photomask according to claim 1, wherein the metal complex solution is a solution prepared by adding at least a carboxylic acid, a surfactant, and cobalt nitrate or copper nitrate to an organic solvent. . 5. The method for correcting white spot defects on a photomask according to claim 4, wherein the surfactant is a nonionic surfactant. 6. The method for correcting white spot defects on a photomask according to claims 2 to 5, wherein the carboxylic acid is a dicarboxylic acid or a hydroxy acid. 7. The method for correcting white spot defects on a photomask according to claim 6, wherein the dicarboxylic acid is citraconic acid. 8. Applying a metal complex solution to at least one side of a photomask having white dot defects and selectively irradiating the white dot defect with visible light or ultraviolet light to precipitate metals or metal oxides. A photomask white spot defect correction device for correcting white spot defects, comprising: a photodetector that measures the amount of light transmitted through the photomask; and a control unit to which information from the photodetector is sent. Then, the amount of transmitted light at the start of irradiation is memorized and used as a reference value, and when the amount of transmitted light of the photomask detected by the detector falls below a certain percentage of this reference value, light irradiation is stopped. A white spot defect correction device for a photomask, characterized in that it has a configuration in which: