JP2011203565A - Method for suppressing haze of photomask, storage warehouse for photomask, and exposure apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for suppressing the generation of HAZE on a MoSi light-shielding film caused by ArF exposure.SOLUTION: The method for suppressing the HAZE of a photomask comprises decomposing and removing HAZE, which comprises ammonia or an organic substance generated in a light-shielding part of a photomask having a light-shielding film made of MoSi, by irradiation with light from an ArF lamp before and after ArF exposure. Disclose is a storage warehouse for a photomask or an exposure apparatus, which is provided with a mechanism of irradiating the front and the back surfaces of the photomask having a light-shielding film containing MoSi with light from an ArF lamp.

Description

  The present invention relates to a method for suppressing HAZE that occurs when a photomask having a light-shielding film covered with a pellicle is exposed.

  When manufacturing a semiconductor product from a silicon wafer, a projection exposure method is used in which a pattern formed on a photomask is transferred onto a wafer substrate coated with a photoresist by a projection optical system. In recent years, with the miniaturization of the pattern shape, the exposure light used has a tendency to be shortened, and an exposure apparatus using KrF (wavelength 248 nm) or ArF (wavelength 193 nm) has been put into practical use. Dozens of photomasks may be used for one semiconductor circuit.

  To these photomasks, floating dust that floats around the photomask adheres to all of the photomask during exposure, storage, and conveyance, and becomes foreign matter. The foreign matter on the photomask hinders image formation at the time of exposure, so that a defect appears in the semiconductor product. In order to prevent such poor resolution due to foreign matters adhering to the photomask surface, the photomask is equipped with a pellicle as a dust-proof cover having translucency on the surface.

  Even in a photomask with a pellicle mounted, defects have recently occurred depending on the usage environment. This is because, in addition to the foreign matter floating around, the exposure and storage are repeated, and the fogging cause substance generated from the inside of the member constituting the pellicle is changed into a foreign matter, and the foreign matter gradually accumulates on the photomask. It is due to influence.

  If foreign matter accumulates over a certain amount on the photomask, the photomask becomes cloudy and defects appear in the semiconductor product. For this reason, it is necessary to clean the photomask in order to remove fogging. However, the cleaning increases the cost for manufacturing the product and wears the pattern of the photomask.

  Furthermore, in recent years, organic clouding (hereinafter generally referred to as “organic cloudiness”) caused by the deposition of organic matter oxidized by ozone generated by exposure or the oxidation deposition of substances generated from the pellicle member in the space between the pellicle film and the photomask. The occurrence of organic HAZE) is also a concern, and attention is focused on the behavior of the organic gas and the gas generating member in the exposed space inside the pellicle film.

  Conventionally, since the size of the HAZE generated by this exposure operation is very small, the influence on exposure to the wafer is small, and it has not been detected at the time of inspection and has not been regarded as a big problem. However, it has become a problem as the pattern transferred to the wafer is miniaturized, and the inspection technology can detect these HAZE foreign matters.

  For this reason, in order not to generate HAZE in the pellicle, the sulfuric acid type HAZE reduces sulfuric acid residue after washing with sulfuric acid, and the organic type HAZE reduces gas generation of the pellicle member. Improvements have been made.

  By these HAZE suppression measures and photomask cleaning at regular intervals, ammonium sulfate HAZE, ammonium phosphate HAZE mainly generated in the photomask transmission part, organic HAZE, cyanuric acid HAZE mainly generated only in the light shielding part, oxalic acid type HAZE and the like were calmed down.

  However, OMOG (Opaque MoSi on glass), which is a photomask using MoSi as a light-shielding film, is adopted to cope with high definition patterns, thereby reducing sulfuric acid residue and reducing gas generation of pellicle members. A new HAZE mode has occurred that cannot be removed by the conventional measures described above, such as cleaning a photomask at regular intervals. This HAZE is a mode that occurs mainly in the light shielding portion of the MoSi film by exposure and does not disappear even after a long time.

  The following is a list of known documents related to HAZE suppression methods and OMOG.

JP 2009-294432 A

SPIE, Volume 7122, pp. 712209-712209-12 (2008).

  The present invention has been devised in view of the above problems, and provides a suppression means for suppressing generation of HAZE generated on a light-shielding film containing MoSi by ArF exposure.

  In order to solve the above-mentioned problems in the present invention, the invention according to claim 1 is characterized in that HAZE generated in a light-shielding portion of a photomask having a light-shielding film containing MoSi is emitted from an ArF lamp before and after ArF exposure. This is a HAZE suppression method for a photomask characterized by being decomposed and removed by irradiation.

  The invention described in claim 2 is the photomask HAZE suppressing method according to claim 1, wherein the HAZE is ammonia or an organic substance.

  According to a third aspect of the present invention, there is provided a photomask storage comprising a mechanism for irradiating light from an ArF lamp on the front and back of a photomask provided with a light-shielding film containing MoSi.

  According to a fourth aspect of the present invention, there is provided an exposure apparatus comprising a mechanism for irradiating light from an ArF lamp on the front and back of a photomask having a light shielding film containing MoSi.

  In the photomask of the present invention, the MoSi light-shielding film of the photomask and its periphery are irradiated with ArF light having a wavelength of 193 nm before and after the ArF main exposure, whereby ammonium sulfate generated in the pellicle, organic mode, etc. In addition to conventional HAZE, the HAZE generated on MoSi can be removed. As a result, the productivity of the semiconductor product is improved and the life of the photomask can be further extended, for example, the number of cleanings can be reduced.

(A) OMOG mask in plan view, (b) AA ′ cross-sectional view. The figure explaining the generation | occurrence | production situation of various HAZE. The figure which shows the ToF-SIMS surface analysis result which shows the behavior of the sulfuric acid of Qz and Cr before and behind exposure. The left side is before exposure, and the right side is after exposure. The figure which shows the sulfuric-acid-residue ratio of Qz and Cr (normalized with the sulfuric-acid-residue amount in Cr). The figure which shows the relationship between the generation number of organic HAZE, and time dependence. The figure which shows the result of MAGICS in exposure experiment. The left side is immediately after exposure, and the right side is one month after exposure. The schematic diagram of generated HAZE. The figure explaining the irradiation timing of the ArF lamp and ArF laser which become this invention. The figure explaining the irradiation timing of the conventional ArF laser.

  Hereinafter, embodiments of the present invention will be described in detail. The conditions described in the present embodiment are merely examples, and are not limited to the conditions described below.

  1A is a schematic top view showing an example of an OMOG mask used in the fog suppression method of the present invention, and FIG. 1B is a cross-sectional view of FIG. 1A taken along line AA ′. The figure is shown.

  A photomask 10 used in the HAZE suppression method shown in FIGS. 1A and 1B includes a synthetic quartz substrate 11 on which a MoSi light-shielding film 12 is patterned, a pellicle film 21 placed on the photomask, a pellicle frame 22, and a mask. It consists of an adhesive 23, a pellicle adhesive 24 and a filter 25.

  The photomask 10 includes a light shielding film 12 made of MoSi on the surface of a synthetic quartz substrate 11. The light-shielding film 12 is referred to as OMOG (Opaque MoSi on glass) because it is a MoSi light-shielding film as the accuracy increases.

  The pellicle is a light-transmitting dustproof cover installed on the photomask 10, a pellicle frame 22 for holding and spreading the pellicle film 21, and a pellicle adhesive for bonding the pellicle frame 22 and the pellicle film 24 and a mask adhesive 23 for bonding the pellicle frame 22 and the photomask 10 together.

The pellicle film 21 is held by the pellicle frame 22 and is provided so as to cover the exposure area of the photomask 10. For this reason, the pellicle film 21 has translucency so as not to cut off energy by exposure. Further, it is stretched so as to receive a uniform force from the pellicle frame 22 so as not to make a shadow on the photomask surface due to wrinkles or the like.
As the pellicle film, a transparent film such as fluorine-based or cellulose acetate, quartz glass, or the like is used.

 The mask adhesive 23 is used for bonding the pellicle frame and the photomask. As the mask adhesive, a silicon resin-based or acrylic resin-based adhesive is suitable.

The pellicle adhesive 24 is used for bonding the pellicle frame and the pellicle film 21. As the pellicle adhesive, a silicon resin-based, polyvinyl acetate resin-based, or acrylic resin-based adhesive is suitable.

  The pellicle film 21 is mounted on the photomask in order to prevent the foreign matter adhering to the photomask from being focused and to prevent poor resolution on the wafer. At this time, the pellicle is mounted so as to cover the exposure area of the photomask.

According to the analysis by the inventors of the OMOG photomask produced in this way, as shown in FIG. 2, in the case of HAZE that occurs in the light shielding portion of the MoSi film, it is known that it also occurs in the Qz portion. The component is ammonium sulfate. However, in OMOG, ArF energy is not applied to the light shielding portion, and therefore, it is expected to exhibit the same behavior as the Cr light shielding body. However, as a result of analysis by the inventors so far, as shown in FIG. 3, even in the case of Cr having a large amount of sulfuric acid residue, there is a tendency that sulfuric acid aggregates do not occur on the light shielding portion.

  As shown in FIG. 4, it is known that the amount of sulfuric acid contained in the MoSi film is one order of magnitude lower than that of Cr as a feature of the MoSi film. Considering that energy is not applied to the light shielding portion as described above, it is unlikely that ammonium sulfate is generated on the light shielding portion before HAZE is generated on Qz.

  Further, the possibility of organic HAZE is known to be volatile at room temperature as shown in FIG. 5 as a characteristic of conventional organic HAZE, and decreases depending on time. Furthermore, in the case of the ammonium sulfate mode, it is known that both the number and size increase depending on the time as shown in FIG. 6, so that HAZE generated on the entire MoSi light-shielding film is considered from the generation location and its behavior. Even so, the possibility of not falling under the conventional mode was found.

  Based on this, we invented the following mechanism hypothesis and suppression measures. Since OMOG is a total light-shielding film unlike a normal halftone film, exposure energy is not directly applied to the surface of the MoSi film. In the case of a conventional halftone film, organic substances that have been removed by ArF energy during exposure of the photomask remain without being removed by OMOG.

Furthermore, it is known that the MoSi film has a higher ratio of nitrogen contained in the film than the Cr film, and the contained nitrogen reacts with water in the air to generate ammonia.
In conventional MoSi halftone photomasks, even if ammonia is generated, energy is applied by exposure, so ammonia has been decomposed. As for the organic matter, since the energy of ArF is added to the surface of the MoSi halftone film by exposure, the organic matter has been decomposed.

  However, since OMOG is a light shielding film of MoSi, the energy of ArF does not pass through, so the organic matter that was originally decomposed remains on the light shielding part, and further, ammonia adheres to the film, so far The possibility of a different mode of HAZE was found. Further, not only ammonia and organic substances but also water components remaining on the surface of the light-shielding film were found to be possible hydrates in which ammonia reacts with water.

  In order to clarify the cause of these phenomena, irradiation with an ArF lamp was performed from the light shielding film side after exposure of ArF and before exposure, and it was examined whether generation and adsorption of ammonia and organic substances could be suppressed. It turned out to be effective. In order to perform irradiation specifically, it is desirable that the ArF irradiation lamp is installed in an exposure machine or a photomask storage.

  As for the energy to be irradiated, the exposure wavelength may be an energy larger than the bond dissociation energy of NH (about 93 kcal / mol), but the transmittance of the pellicle using CYTOP (made by Asahi Glass Co., Ltd.) as the material In view of the deterioration state, the ArF wavelength is suitable for matching the wavelength with the actual exposure.

  In addition, the wavelength of the organic matter decomposition may be any energy that is larger than the bond dissociation energy of CC and CH (approximately 83 and 100 kcal / mol, respectively), but CYTOP (Asahi Glass Co., Ltd.) was used as the material. In view of the transmittance and deterioration state of the pellicle, the ArF wavelength is suitable for matching the wavelength with the actual exposure.

In view of cost and the like, it is preferable to install a unit such as an ArF lamp in the exposure unit in the exposure machine or in a storage room in a state where the light-shielding unit can be cleaned rather than a laser type apparatus.

  Hereinafter, the present invention will be described in detail by way of examples.

Six blanks using an OMOG film as a light-shielding film were prepared on Qz, a pattern was formed, and a photomask was created. Two sheets were exposed to 50 kJ and inspected. Four sheets were exposed to 10 kJ and then subjected to IC and GC / MS analysis in order to confirm the irradiation effect of the ArF lamp.
Two samples were stored in a polycarbonate case for 72 hours. This case was stored in a clean draft, and the gas flowing into the case was passed through a chemical filter (manufactured by Luminous Guard Entgris) to create an environment in which particles, humidity, organic and acid-alkali were controlled.

An OMOG test plate was irradiated with a predetermined amount of ArF laser (produced by ximer-300 MPB) from the Qz side at a cycle of 50 mW / cm ² and 200 Hz. At this time, there was no energy fluctuation. The exposure atmosphere was such that no environmental contamination was contained, and nitrogen gas and oxygen gas were introduced at a ratio of 4 to 1.

An ArF lamp (manufactured by Ushio Electric Co., Ltd.) installed in the loader section of the exposure machine after the exposure is 100 J within a range of 100 mm × 65 mm so that no energy is applied to the pellicle frame with an output of 1 mW / cm ² from the light shielding part side of the photomask. / Cm ² and stored.

  The organic, acid, and alkali were stored in a storage room equipped with chemical filters, and the shipping case was used by introducing dry nitrogen into a PC case that generates less gas.

Next, for the purpose of removing organic matter accumulated before exposure after storage for a certain period, within a range of 100 mm × 65 mm so that energy is not applied to the pellicle frame with an output of 1 mW / cm ² from the light shielding part side of the photomask. Irradiated with 100 J / cm ² and introduced into an exposure machine.

  As a result of repeating exposure and storage under the above conditions, as a result of inspection after exposure of 50 kJ in total, generation of HAZE was not confirmed.

  Next, in order to evaluate whether the amount of ammonia remaining on the photomask exposed with the ArF laser differs depending on the presence or absence of irradiation, one of the two masks exposed with the same amount of ArF laser is irradiated with a light shielding portion with an ArF lamp. The other was stored in the storage.

  Subsequently, it was placed in 100 ml of pure water and heated to a certain temperature which is an oven. The extract was analyzed with an ion chromatograph (DX-320, manufactured by Dionex Co., Ltd.). The amount of NH4 extracted was 1.2 ng / sheet for the sample irradiated with the ArF lamp and 3.6 ng / sheet for the sample not irradiated.

  Next, in order to evaluate whether the organic matter remaining on the photomask after storage for a certain period of time can be decomposed by irradiation with an ArF lamp, one of the two photomasks exposed by the same amount is irradiated with a light shielding portion with an ArF lamp. The other was stored in a storage.

The amount of TOC (total amount of organic substances) remaining on the photomask was analyzed using MSTD-GC / MS (MSTD258 manufactured by GL Sciences Inc./6890/5973 MSD manufactured by Agilent Technologies Inc.). As a result of measuring the TOC amount in terms of C16, the TOC amount of the photomask exposed with the ArF lamp was 15 ng / sheet, and the TOC amount of the stored photomask was 900 ng / sheet. (However, a large amount of phthalates were detected from a photomask that was not irradiated with an ArF lamp, and it was 118 ng / sheet excluding phthalates (DBP, DEP, DOP) that are considered to be present on the Qz substrate. )
(Comparative Example 1)
As in Example 1, three OMOG photomasks were prepared, and a predetermined amount of ArF laser (made by ximer-300 MPB) was exposed on the patterned OMOG test plate at a cycle of 50 mW / cm ² and 200 Hz. . At this time, there was no energy fluctuation. The exposure atmosphere was such that no environmental contamination was contained, and nitrogen gas and oxygen gas were introduced at a ratio of 4 to 1.

  After exposure, it is stored in a storage room with chemical filters for organic, acid, and alkali as in Example 1 without irradiation with an ArF lamp. The shipping case is made of dry nitrogen in a PC case that generates less gas. Introduced and used.

  Next, ArF laser exposure was performed without storage with an ArF lamp in advance after storage for the same period as in Example 1.

  Exposure and storage were repeated under the above conditions. As a result of inspection after exposure of 50 kJ, generation of HAZE as shown in FIG. 7 was confirmed. The description of Example 1 and Comparative Example 1 is shown in FIG.

For each analysis, the use of an ArF lamp confirmed that the ammonia residue amount was reduced by 90%, and the TOC amount was also reduced by 90%, confirming the effect of this method.
Moreover, since the ArF lamp having the same wavelength as that of the ArF exposure apparatus was used for deterioration of the pellicle, neither film deterioration nor phase difference transmittance fluctuation was observed.

  With respect to an OMOG photomask using an ArF laser, HAZE can be suppressed and a stable photomask can be used.

DESCRIPTION OF SYMBOLS 10 ... Photomask 11 ... Synthetic quartz glass 12 ... Light-shielding film 13 ... HAZE
20 ... Pellicle 21 ... Pellicle film 22 ... Pellicle frame 23 ... Mask adhesive 24 ... Pellicle film adhesive 25 ... Filter

Claims (4)

  A HAZE suppression method for a photomask, characterized in that HAZE generated in a light-shielding portion of a photomask having a light-shielding film containing MoSi is decomposed and removed by irradiating light from an ArF lamp before and after ArF exposure.   2. The method of suppressing HAZE of a photomask according to claim 1, wherein the HAZE is ammonia or an organic substance.   A photomask storage comprising a mechanism for irradiating light from an ArF lamp on the front and back of a photomask having a light-shielding film containing MoSi.   An exposure apparatus comprising a mechanism for irradiating light from an ArF lamp on the front and back of a photomask having a light-shielding film containing MoSi.