JPH04448A - Method for correcting photomask - Google Patents

Abstract

PURPOSE:To recover the resolution of deteriorated pattern images and to improve accuracy of correction by providing a process of holding a photomask in high vacuum following the process of recognizing the pattern with second ions. CONSTITUTION:The photomask 2 is fixed on a stage 1 and irradiated with an ion beam from an ion source 3, and second ions generating from the pattern are counted by a detector 4 for image processing to display the pattern image on a CRT 6. Then black defects or white defects are corrected by visual check of the pattern image. When the resolution of the pattern image is degraded because of repeated irradiation of ion beams, the mask 2 is held in high vacuum (e.g. higher vacuum than 10<-6> Torr) for a certain period to recover the resolu tion, and then corrected. Or, instead of holding the mask in high vacuum, it is also preferable to treat the mask with oxygen plasma or far-UV ray.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for modifying a photomask used in a photolithography process for forming fine two-dimensional patterns on a semiconductor substrate.

Conventional technology Photomasks for manufacturing semiconductor devices generally have a light-shielding pattern formed on a transparent glass substrate, but there are two types of pattern-forming materials: emulsion masks using silver salt dry plates and hard masks using inorganic materials. It is roughly divided into two types (see Semiconductor Handbook Editorial Committee: Semiconductor Handbook 2nd edition, published by Ohmsha, 1989, p. 307).

A chromium film or a chromium oxide film is often used as an inorganic thin film material, and gas plasma etching is also used as a pattern forming method (Japanese Patent Laid-Open No. 50-119
(See Publication No. 575).

These hard masks are said to be able to be used many times due to their high surface strength, but in reality they are often damaged by foreign matter or deposits on the wafer, and in such cases the mask must be disposed of. Correction is required.

Conventionally, this type of photomask repair work was often performed using an ion beam. In other words, the ion source directly irradiates the photomask with an ion beam, detects the various secondary ions generated on the photomask, recognizes the current state of the pattern, identifies the areas to be corrected, and then irradiates the ion beam. Correcting work has been carried out by removing unnecessary portions of the pattern or depositing separately supplied pattern forming material in the missing portions.

Problems to be Solved by the Invention However, in the conventional method described above, the ion beam is first irradiated once to obtain a pattern image of the repaired part, but there are cases where the repaired part cannot be recognized at this time, or there are cases where the repaired part is displayed on one screen. If the ion beam does not fully enter, the peripheral area will be irradiated with the ion beam many times. In the case of a photomask using a single layer of chromium, the resolution of a pattern image created by secondary ions deteriorates when ion sealing is performed two or more times. Further, when the degree correction is performed, the yield of secondary ions from the pattern forming material in the vicinity decreases, and the sharpness of the obtained pattern image also deteriorates significantly. If correction is performed in this state, the correction accuracy will be significantly reduced.

The present invention is intended to solve the above-mentioned conventional problems, and aims to provide a highly accurate correction method by restoring the once degraded resolution of a pattern image caused by secondary ions.

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention modifies the photomask process of holding the process at a high altitude or in the air for a certain period of time, oxygen plasma treatment, treatment with deep ultraviolet light, or treatment with high concentration ozone. It is something that is inserted during the process.

Effect of the Invention With the above configuration, the present invention can increase the secondary ion yield of the light-shielding thin film material which has been degraded by -degrees, and can restore the resolution of the secondary ion pattern image which has deteriorated by -degrees.

EXAMPLES Examples of the present invention will be described below with reference to FIGS. 1 to 3.

(Example 1) In FIG. 1, 1 is a stage, 2 is a photomask, and 3 is a stage.
is an ion source, 4 is a secondary ion detector, 5 is a gas gun, and 6 is a CRT (cathode ray tube). Stage 1 to gas gun 5 are all kept in a vacuum. First, a photo is placed on stage 1. The mask 2 is fixed, and an ion beam is irradiated onto the photomask 2 from the ion source 3 directly above the photomask 2. As a result, secondary ions such as chromium, silicon, oxygen, etc. are generated, and these are converted into secondary ions. It is counted through the detector 4. Then, image processing is performed based on this data.
A pattern image is displayed on the CRT 6 as a secondary ion image of chromium, silicon, or chromium and silicon. CRT
When a black defect is to be corrected while viewing the pattern image displayed on the screen 6, an ion beam is irradiated only to the defective part to perform ion sealing. In the case of a white defect, a hydrocarbon-based organic gas is sprayed from the gas gun 5 around the defect and an ion beam is irradiated thereto, thereby depositing a carbon film and repairing the defect.

In this case, when recognizing defects in the photomask 2, the same location may be irradiated with the ion beam several times. In that case, the intensity of secondary ions from chromium, which is a film-forming substance, is significantly reduced, and as schematically shown in FIG. 2, the pattern image becomes weak and the resolution of the image is significantly reduced.

In FIG. 2, 7 is a pattern image created by secondary ions when the ion beam is first irradiated, and 8 is the same pattern image after several irradiations. If the photomask 2 is kept in a high vacuum (higher vacuum than 10<-6 >Torr) for about 10 minutes, the pattern image formed by the secondary ions will recover to a state close to 7. Expressing this in terms of the intensity of secondary ions, if the initial value is 100, then after irradiating the ion beam several times,
It decreases to about 20-30. If this is kept in a high vacuum, it will recover to about 70-80. The presence of oxygen influences the generation of secondary chromium ions. In the case of single-layer chromium, oxygen is initially thought to be adsorbed or oxidized on the surface, but the oxygen is removed by ion beam irradiation. Therefore, the generation efficiency of secondary ions of chromium alone decreases. Regarding the mechanism by which the secondary ion yield increases by holding in a high vacuum, it is thought that some substance that suppresses the generation of secondary ions attached to the chromium surface is removed in a high vacuum. , the details are unknown. However, it has been experimentally confirmed that the yield of secondary ions is increased by maintaining the material in a high vacuum as described above.

As described above, a pattern image that has once deteriorated becomes clear again, and the resolution of the image is restored, allowing for highly accurate correction.

(Example 2) If there is a large defect that cannot be corrected at once, or if the defects are concentrated, it is necessary to perform the correction work in several parts. In this case, the resolution of the peripheral secondary electron pattern image after the previous correction work has been significantly degraded, and the next correction is almost impossible. FIG. 3 shows a pattern image of a white defect portion in such a case. In the figure, numeral 9 indicates a secondary electron pattern image of the photomask before modification. 10 shows the pattern image after the first correction. 11 is the film deposited in the first modification. After the first correction, the ion beam is irradiated several times as shown in Example 1 to confirm the next pattern. The photomask 2 also adsorbs the gas blown from the gas gun 5, and the pattern image 8 is even more deteriorated than the pattern image 8 shown in FIG. 2 after being irradiated with the ion beam several times.

In this embodiment, oxygen plasma is irradiated here to supply oxygen to the chromium surface and to remove gases adsorbed during the previous modification. The equipment used this time was a general parallel plate type RF (high frequency) plasma equipment, and the conditions were: oxygen flow rate of 10
0cc/sin (converted to standard state), processing pressure 200
mTorr, RF power of 350 W, and time of 20 seconds. When the intensity of the secondary ions was initially set at 100, it recovered to about 60 to 70 after the oxygen plasma treatment, making it possible to perform corrections with sufficiently high precision.

(Example 3) As in Example 2, since oxygen plasma may cause some pattern damage to the photomask, irradiation with deep ultraviolet light of 184.9 nm is performed. A normal far ultraviolet lamp was used, the atmosphere was air, and the temperature was 130° C. for 2 hours and 10 minutes. The results were also almost the same as in the above example.

In this case, instead of oxygen plasma, ozone induced by deep ultraviolet light supplies oxygen to the photomask surface.
Also, the adsorbed organic gas molecules are removed. As a result, the secondary ion yield is restored, the pattern image becomes clearer, and the photomask correction accuracy becomes higher.

(Example 4) In the case of the above example, the processing time is long at 10 minutes, and there is a problem with the processing time in actual repair work, so a high concentration ozone generator is used and the photomask 2 is placed directly in an ozone atmosphere. . The conditions were an ozone concentration of 150g/11. temperature 10
The temperature was 0 to 150°C for 2 hours and 1 to 2 minutes. The results were almost the same as in the above example. In this case, the reaction rate is improved because ozone is directly exposed to the photomask surface.

By performing the above-described processing, the secondary ion emission from the photomask, which has decreased due to ion irradiation during correction work, can be increased again, and the clarity of the pattern image caused by the secondary ions, which has deteriorated in appearance, can be restored. I can do it.

Effects of the Invention As is clear from the above examples, according to the present invention, by performing a step of increasing the amount of oxygen attached to the surface, such as high vacuum treatment, oxygen plasma treatment, deep ultraviolet light irradiation, or high concentration ozone treatment, Since the resolution of the secondary ion pattern image degraded during correction is restored, the photomask correction work can be performed with high dimensional accuracy while always recognizing a clear pattern image.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of a repairing device for carrying out the photomask repair method of the present invention, Fig. 2 is a screen shot on a CRT showing deterioration in resolution of a secondary electron pattern image, and Fig. 3 is a repeating FIG. 6 is a screen diagram on a CRT when the resolution of a secondary electron pattern image is further degraded by ion irradiation. 1... Stage, 2... Photomask, 3... Ion source, 4... Secondary ion detector, 5... Gas gun, 6...CRT
(Cathode ray tube). J ion 5 nose

Claims (4)

[Claims] (1) A step of irradiating the defective portion of the photomask with an ion beam multiple times and recognizing a pattern by secondary ions emitted from the photomask, and a step of holding the photomask in a high vacuum for a certain period of time; A method for repairing a photomask, comprising the step of irradiating the defective portion of the photomask with an ion beam. (2) A step of irradiating defective portions of the photomask with an ion beam multiple times and recognizing a pattern using secondary ions emitted from the photomask; a step of treating the photomask with oxygen plasma; A photomask repair method comprising the step of irradiating a defective portion with an ion beam. (3) A step of irradiating defective portions of the photomask with an ion beam multiple times and recognizing a pattern using secondary ions emitted from the photomask, a step of irradiating the photomask with far ultraviolet light, and a step of irradiating the photomask with deep ultraviolet light; A photomask repair method comprising the step of irradiating the defective portion with an ion beam. (4) A step of irradiating the defective portion of the photomask with an ion beam multiple times and recognizing a pattern by secondary ions emitted from the photomask, a step of leaving the photomask in high concentration ozone, and a step of leaving the photomask in high concentration ozone; A method for repairing a photomask, comprising the step of irradiating the defective portion of the mask with an ion beam.