JP2014211572A - Method for examining photomask cleanliness and photomask management system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an examination method capable of easily confirming the cleanliness of a photomask stored after final cleaning, and a photomask management system using the same.SOLUTION: A method for examining photomask cleanliness is provided which can determine cleanliness of a photomask by storing a substrate having a metal film with a catalytic action in the same environment as the photomask and thereafter irradiating the metal film of the substrate with UV light, and confirming whether or not precipitation of a crystal component is present, or an examination method for determining cleanliness of a photomask stored in the same environment by irradiating a photomask to be managed with UV light and confirming whether or not precipitation of a crystal component is present. Also, a photomask management system using these examination methods is provided. By using these methods, cleanliness of a photomask stored for a certain period of time after being finally cleaned can be easily confirmed. By carrying out a cleaning treatment again if necessary, defects due to haze can be prevented during transfer at a shipping destination.

Description

  The present invention relates to a photomask cleanliness inspection method and a photomask management system used when, for example, an ultrafine circuit pattern is transferred using an ArF excimer laser (wavelength 193 nm) or the like in a manufacturing process of a semiconductor integrated circuit.

Lithography technology using light is used for nano-level microfabrication such as LSI circuit patterns. Along with higher integration, in order to produce a finer pattern, the wavelength of the exposure light source is being shortened. For example, the exposure light source is shifted to a KrF excimer laser (wavelength 248 nm) and an ArF excimer laser and put into practical use.
When a photomask transfers a pattern, for example, while ArF excimer laser is repeatedly irradiated for a long time, a small amount of adhering components on the surface of the photomask is called “haze” due to a photo-CVD (chemical vapor deposition) reaction by laser energy. Changes to precipitates such as ammonium sulfate. Haze is a problem because it becomes a foreign matter defect which is one of the causes of pattern transfer failure.

  Examples of components adhering to the photomask surface include sulfuric acid / hydrogen peroxide (mixed solution of sulfuric acid and hydrogen peroxide) and ammonia hydrogen peroxide (mixed solution of ammonia water and hydrogen peroxide solution) used in the cleaning process. And sulfate ions and ammonium ions derived from chemicals such as For these cleaning residues, as shown in Patent Document 1, measures are taken such as introduction of rinsing with warm water and switching to treatment with ozone gas-dissolved water or the like without using sulfuric acid.

Moreover, not only cleaning residues but also organic components present in the clean room environment cause haze. For example, butylbenzenesulfonamide, which is a plasticizer for nylon, can be cited as one component that exists in a general clean room environment. When this component is decomposed and oxidized, sulfate ions and ammonium ions are generated.
As a method for reducing the organic components in the clean room environment, the use of a chemical filter is conceivable, but there are drawbacks that low boiling point components and the like are difficult to remove and the timing of deterioration is difficult to detect. Therefore, it is difficult to completely eliminate organic components even in an environment under a chemical filter.

Photomasks are stored in a clean room environment after final cleaning, but the storage period varies depending on the product. Even if the photomask is cleaned by a method for preventing cleaning residues as in Patent Document 1, if a component in the clean room environment adheres during subsequent storage, haze generation is prevented during transfer at the shipping destination. Can not do it.
Therefore, it is necessary to construct a management system for preventing the occurrence of haze, such as confirming the cleanliness of the surface of the photomask stored for a certain period after the final cleaning, and shipping only the products determined to be clean.
As means for confirming the cleanliness of the surface of the photomask, a method using an ion chromatograph as proposed in Patent Document 2 has been conventionally used.

Japanese Patent No. 40000247 JP 2012-133343 A

However, the above method performs analysis by extracting ion components adhering to the photomask surface into ultrapure water. Since the amount of ionic components on the photomask surface is very small, it is necessary to immerse it in ultra-pure water as little as possible for several hours. In addition, since slight elution components from the container to be used affect the measurement result, it is necessary to give due consideration to the tools to be used, which takes time and labor.
Therefore, an object of the present invention is to provide an inspection method capable of easily confirming the cleanliness of a photomask stored after the final cleaning, and a photomask management system using the inspection method.

One aspect of the present invention is to store a substrate having a catalytic metal film in the same environment as a photomask, and then irradiate the metal film with UV light to confirm the presence or absence of a crystal component to be precipitated. It is a photomask cleanliness inspection method characterized by determining the cleanliness of a photomask.
In the photomask cleanliness inspection method, the metal film may be a thin film made of Pt, Pd, or an alloy thereof.
In the photomask cleanliness inspection method, the UV light source may be an excimer lamp having a wavelength of 172 nm.
In the above-described photomask cleanliness inspection method, the crystal component may be ammonium sulfate.

Another aspect of the present invention is a photomask cleanliness inspection method characterized in that the photomask cleanliness is determined by irradiating the photomask with UV light and confirming the presence or absence of precipitated crystal components. is there.
In the photomask cleanliness inspection method, the UV light source may be an excimer lamp having a wavelength of 172 nm.
In the above-described photomask cleanliness inspection method, the crystal component may be ammonium sulfate.
Another aspect of the present invention is a photomask management system that determines the cleanliness of a photomask using the photomask cleanliness inspection method described above, and determines whether or not shipment is possible.

  According to one embodiment of the present invention, after a substrate having a catalytic metal film is stored in the same environment as a photomask, the metal film of the substrate is irradiated with UV light, and the presence or absence of a deposited crystal component is confirmed. In this environment, the photomask cleanliness inspection method for determining the cleanliness of the photomask, or the photomask itself to be managed is irradiated with UV light and the presence or absence of precipitated crystal components is confirmed. It is possible to provide a photomask cleanliness inspection method for determining the cleanliness of a stored photomask. In addition, a photomask management system using these inspection methods can be provided. By using this method, the cleanliness of the photomask stored for a certain period of time after the final cleaning can be easily checked. If necessary, the cleaning process is performed again, so that the haze can be transferred at the shipping destination. It becomes possible to prevent the failure due to.

It is a figure which shows the process of the cleanliness inspection method of the board | substrate which has a metal film which concerns on embodiment of this invention. It is a figure which shows the process of the cleanliness inspection method of the photomask which concerns on embodiment of this invention. It is a flowchart of the photomask management system which concerns on embodiment of this invention.

Hereinafter, a photomask cleanliness inspection method and a photomask management system according to embodiments of the present invention will be described with reference to the drawings. In the present embodiment, the same constituent elements are denoted by the same reference numerals, and description of overlapping parts is omitted.
First, a substrate 20 having a catalytic metal film according to the present embodiment will be described with reference to FIG. As shown in FIG. 1A, the substrate 20 according to this embodiment includes a base material 10 and a thin film 11 formed on the base material 10.

  The base material 10 is a material that allows the thin film 11 to be uniformly formed on the base material 10 with good adhesion, and if the shape does not change greatly even if the cleaning process similar to that of the photomask to be managed is performed. Any material can be used. Examples include Si and synthetic quartz glass. The size of the substrate 10 can be cleaned using the same cleaning apparatus as the photomask to be managed, and can be installed in a foreign matter inspection apparatus or the like used for confirming the crystal component to be deposited. What is necessary is just 6 inches square and 5 inches square, for example.

The shape of the thin film 11 does not change greatly even when the cleaning process similar to that of the photomask is performed, and the formation reaction of the precipitate 40 is accelerated when the UV light 100 is irradiated from the storage environment to the adhesion component 30 on the surface. This is a metal film having such a catalytic action (see FIGS. 1B and 1C). Examples of such a metal include Pt, Pd, and alloys thereof (for example, PtPd).
The thickness of the thin film 11 is not particularly limited, but is about 10 nm to 200 nm. Further, the thin film 11 can be produced by using a sputtering method, a chemical vapor deposition method, a vacuum vapor deposition method, or the like. Among these methods, since the kinetic energy of the target atom is large, it is preferable to use a sputtering method that can form a strong and difficult-to-peel film.

Next, the photomask 21 according to the present embodiment will be described with reference to FIG. As shown in FIG. 2A, the photomask 21 is a structure having a pattern formed on a general Cr or MoSi film.
The photomask 21 having the MoSi surface and the above-described substrate 20 having the PtPd surface were cleaned at the same time, and then stored together in a clean room environment for about 3 weeks. Thereafter, UV light 100 having a wavelength of 172 nm was irradiated on the surface of the photomask 21 and the substrate 20 for 20 minutes. Then, as a result of observing the surface irradiated with the UV light 100 with an SEM (electron microscope), the precipitate 40 was not confirmed on the MoSi surface, but the precipitate 40 of about several μm was confirmed on the PtPd surface. . Moreover, as a result of further irradiating the surface of MoSi with UV light 100 for 120 hours, a precipitate 40 of about 0.5 to 0.9 μm was confirmed. As a result of analyzing the precipitate 40 on the surface of PtPd using an EDX (energy dispersive X-ray fluorescence spectrometer), the elements of S, N, and O are specifically detected as compared with the portion where the precipitate 40 is not generated. It was. Furthermore, since this deposit 40 is a component which melt | dissolves in water, it estimated that the deposit 40 was ammonium sulfate.

Next, immediately after cleaning the photomask 21 having the MoSi surface and the substrate 20 having the PtPd surface described above, UV light 100 having a wavelength of 172 nm was irradiated on the surfaces of the photomask 21 and the substrate 20 for 20 minutes. . Then, as a result of observing the surface irradiated with the UV light 100 with the SEM, the precipitate 40 was not confirmed on either surface.
A surface made of a metal having a catalytic action such as Pt or Pd is more likely to generate precipitates 40 from the adhesion component 30 than a general photomask surface. Therefore, a substrate having the surface and a photomask 21 to be managed Are stored at the same time, the cleanliness of the photomask 21 can be determined with high sensitivity and simplicity.

  The adhering component 30 is a component that easily adheres to the surface of the photomask 21 and the like among organic components existing in a clean room environment for manufacturing the photomask 21 and changes into a causative substance such as sulfate ion or ammonium ion. is there. For example, the component contained in the additive of the resin etc. which are used for members, such as building materials, apparatus, a mask case, etc., such as butylbenzenesulfonamide, is mentioned.

The precipitate 40 is a haze-causing substance, and an example thereof is ammonium sulfate.
As the UV light 100, a means capable of generating spiders by irradiating the surface of the photomask 21 with a low cleanliness was selected. The wavelength of the ArF laser used in the exposure apparatus for performing the transfer is 193 nm, and the photon energy is about 148 kcal / mol. An excimer UV lamp with a wavelength of 172 nm is smaller and easier than a laser, but has a photon energy close to about 167 kcal / mol, and thus can break a molecular bond similar to an ArF laser. Therefore, since it is assumed that the mechanism for generating haze is almost the same, an excimer lamp having a wavelength of 172 nm was used as the UV light 100.

Next, a photomask cleanliness inspection method and a photomask management system implemented using the substrate 20 shown in FIG. 1 will be described with reference to the flowchart shown in FIG.
First, the substrate 20 and the photomask 21 to be managed are cleaned by chemical-less cleaning using functional water (S2). Thereafter, the foreign matter on the surface of the substrate 20 is measured by the foreign matter inspection apparatus (S3), and the number of foreign matters at that time is set to “P1”. The foreign substance inspection apparatus used here may be any apparatus that can easily detect foreign substances of submicron to several μm. Next, the substrate 20 is stored together with the photomask 21 to be managed in the same environment in a clean room for a certain period (S4), and the surface of the substrate 20 is irradiated with UV light having a wavelength of 172 nm for 20 minutes before shipment (S5). Subsequently, the foreign matter on the surface of the substrate 20 is measured by the foreign matter inspection apparatus (S6), and the number of foreign matters at that time is set to “P2”.

If the inspection result of S6 is “P1 ≧ P2,” the precipitate 40 is not generated, and it is determined that the surface of the photomask 21 stored for the same period in the same environment as the substrate 20 is sufficiently clean. Can be shipped (S7). Thus, the photomask management system is terminated (S8).
If the inspection result of S6 is “P1 <P2,” a precipitate 40 is generated, and it is determined that the surface of the photomask 21 stored in the same environment as the substrate 20 for the same period is not clean and is not shipped. (S7 '). Thus, the photomask management system is terminated (S8 ′).
The photomask management system according to the present embodiment is a system that inspects and manages the cleanliness of the photomask 21 as described above.

Next, a photomask cleanliness inspection method and a photomask management system implemented using the photomask 21 shown in FIG. 2 will be described with reference to the flowchart shown in FIG.
First, the photomask 21 is cleaned by chemical solution-free cleaning using functional water (S2). Thereafter, the foreign matter on the surface of the photomask 21 is measured by a foreign matter inspection apparatus (S3), and the number of foreign matters at that time is set to “P1”. The foreign substance inspection apparatus used here may be any apparatus that can easily detect foreign substances of submicron to several μm. Next, the photomask 21 is stored in a clean room for a certain period (S4), and before shipping, the surface of the photomask 21 is irradiated with UV light having a wavelength of 172 nm for 20 minutes (S5). Subsequently, the foreign matter on the surface of the photomask 21 is measured by the foreign matter inspection apparatus (S6), and the number of foreign matters at that time is set to “P2”.

If the inspection result in S6 is “P1 ≧ P2,” the precipitate 40 is not generated, and the surface of the photomask 21 is determined to be sufficiently clean and can be shipped (S7). Thus, the photomask management system is terminated (S8).
If the inspection result in S6 is “P1 <P2,” the precipitate 40 is generated, and it is determined that the surface of the photomask 21 is not clean and is not shipped (S7 ′). Thus, the photomask management system is terminated (S8 ′).
The photomask management system according to the present embodiment is a system that inspects and manages the cleanliness of the photomask 21 as described above.

[Example 1]
An embodiment of the photomask cleanliness inspection method and photomask management system of the present invention will be described below. However, the present invention is not limited to the present embodiment.
A 6-inch square synthetic quartz glass was prepared as the substrate 10, and a thin film 11 made of an alloy of PtPd was formed thereon with a thickness of 40 nm to obtain a substrate 20. A sputtering method was used to form the thin film 11.
(S2) The substrate 20 was cleaned simultaneously with the photomask 21 to be managed. The photomask 21 to be managed was a halftone mask having a MoSi surface. For the cleaning treatment, functional water such as ozone water or hydrogen water was used without using sulfuric acid or ammonia water.

(S3) Foreign matter on the surface of the substrate 20 after cleaning was measured by a foreign matter inspection apparatus WM-1500 (manufactured by Topcon). At this time, the number of foreign matters (P1) of 0.5 μm or more was “0”.
(S4) Subsequently, the substrate 20 was stored in the same environment as the photomask 21 to be managed for a period before shipment. Specifically, it was put in the same polycarbonate mask case on the same shelf in the clean room and stored for 3 weeks.
(S5) After 3 weeks, as a pre-shipment inspection, UV light 100 is applied to the surface of the substrate 20 stored in the same environment, during the same period as the photomask 21 to be managed, using an excimer lamp (manufactured by USHIO INC.) Having a wavelength of 172 nm. Irradiated for 20 minutes.

(S6) Foreign matter on the surface of the substrate 20 after UV light irradiation was measured by a foreign matter inspection apparatus WM-1500. As a result, the number of foreign matters (P2) of 0.5 μm or more is “0” and “P1 ≧ P2”. Therefore, no precipitate 40 is generated, and the photomask 21 to be managed is clean. Since it was determined, it was shipped (S7).
The shipped photomask 21 did not cause haze even when 500,000 8-inch wafers were processed using an ArF excimer laser with an average output of 20 W and an oscillation frequency of 4000 Hz, and could be transferred without problems.

[Example 2]
An embodiment of the photomask cleanliness inspection method and photomask management system of the present invention will be described below. However, the present invention is not limited to the present embodiment.
(S2) The photomask 21 was washed. This photomask 21 was a halftone mask having a MoSi surface. For the cleaning treatment, functional water such as ozone water or hydrogen water was used without using sulfuric acid or ammonia water.
(S3) The foreign matter on the surface of the photomask 21 after cleaning was measured by a foreign matter inspection apparatus WM-1500 (manufactured by Topcon). At this time, the number of foreign matters (P1) of 0.5 μm or more was “0”.

(S4) Subsequently, the photomask 21 was stored for a period before shipment. Specifically, it was put in a polycarbonate mask case in a clean room and stored for 3 weeks.
(S5) Three weeks later, as an inspection before shipment, the surface of the photomask 21 was irradiated with UV light 100 for 20 minutes using an excimer lamp (manufactured by USHIO INC.) Having a wavelength of 172 nm.
(S6) The foreign matter on the surface of the photomask 21 after UV light irradiation was measured by the foreign matter inspection apparatus WM-1500. As a result, the number of foreign matters (P2) of 0.5 μm or more was “0”, and “P1 ≧ P2”, so that the precipitate 40 was not generated and the photomask 21 was determined to be clean. Shipped (S7).
The shipped photomask 21 did not cause haze even when 500,000 8-inch wafers were processed using an ArF excimer laser with an average output of 20 W and an oscillation frequency of 4000 Hz, and could be transferred without problems.

  The present invention is preferably used as a photomask cleanliness inspection method and a photomask management system used when transferring an ultrafine circuit pattern using an ArF laser or the like in a manufacturing process of a semiconductor integrated circuit, for example. Can do.

10 ... Base material 11 ... Thin film 20 ... Substrate 21 ... Photomask 30 ... Adhesive component 40 ... Precipitate 100 ... UV light

Claims (8)

  After storing a substrate with a catalytic metal film in the same environment as the photomask, the metal film is irradiated with UV light, and the presence or absence of crystal components to be deposited is checked to determine the cleanliness of the photomask. A method for inspecting the cleanliness of a photomask.   2. The photomask cleanliness inspection method according to claim 1, wherein the metal film is a thin film made of Pt or Pd or an alloy thereof.   The photomask cleanliness inspection method according to claim 1 or 2, wherein the UV light source is an excimer lamp having a wavelength of 172 nm.   4. The photomask cleanliness inspection method according to any one of claims 1 to 3, wherein the crystal component is ammonium sulfate.   A photomask cleanliness inspection method, wherein the photomask cleanliness is determined by irradiating the photomask with UV light and confirming the presence or absence of precipitated crystal components.   6. The photomask cleanliness inspection method according to claim 5, wherein the UV light source is an excimer lamp having a wavelength of 172 nm.   7. The photomask cleanliness inspection method according to claim 5, wherein the crystal component is ammonium sulfate.   8. A photomask management system that determines the cleanliness of a photomask using the photomask cleanliness inspection method according to any one of claims 1 to 7, and determines whether or not shipment is possible. .

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