JP2008102162A - Method for managing foreign substance of reticle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for detecting generation of a foreign substance on a reticle for manufacturing a semiconductor device. <P>SOLUTION: An inspection portion where a light non-transmitting portion and a light transmitting portion are laid is provided on a pattern face of a reticle substrate. An effective transmittance in a predetermined region including at least a part of the light non-transmitting portion and at least a part of the light transmitting portion is measured. A foreign substance on the reticle is detected based on the effective transmittance. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a reticle foreign matter generation management method for detecting the occurrence of foreign matter in a semiconductor device manufacturing process.

  Currently, when manufacturing a semiconductor device, a light reduction projection exposure apparatus (hereinafter referred to as an exposure apparatus) is used. In this exposure apparatus, a reticle in which a predetermined pattern is provided on a light shielding film made of a chromium film or the like is used on a glass substrate (reticle substrate). The reticle pattern is projected onto the wafer having a resist film formed on the surface by the optical system of the exposure apparatus, and exposure (baking) is performed.

  In order to prevent foreign matter from entering the reticle, a method of mounting a pellicle film on the reticle substrate has become common. This is because the size of the foreign matter allowed on the reticle has been reduced with the progress of the finer half pitch in the semiconductor element, but the pellicle film is a non-imaging region sufficiently separated from the reticle substrate surface. This is because the size of the foreign matter on the pellicle film is acceptable up to a considerably large size.

  The structure of the reticle will be described with reference to FIG. 4A is a plan view of the reticle, FIG. 4B is a cross-sectional view taken along the line AA ′ of FIG. 4A, and FIG. 4C is the back surface of FIG. 4A. Each figure is shown.

  As shown in FIG. 4, the reticle 1 has a glass substrate 10, and an effective exposure area 13 (inside the one-dot chain line) in which a chromium film having a predetermined pattern shape is formed on the back surface of the glass substrate 10. Yes. Further, a pellicle frame 11 and a pellicle film 12 for preventing foreign matter from being mixed are mounted on the front surface (glass surface) and the back surface (chrome surface) of the glass substrate 10. The pellicle film 12 is made of a nitrocellulose-based substance.

  Conventionally, if a state in which no foreign matter is present on the surface of the reticle substrate 10 covered with the pellicle film 12 can be realized, then no foreign matter that would hinder exposure is attached or generated in the imaging area of the reticle 1. It was generally considered that the use of the reticle 1 could be continued until the pellicle film 12 deteriorated.

  However, for example, as shown in Patent Document 1, it is clear that the reticle 1 is likely to generate foreign matter due to the influence of the residual fine cleaning liquid or gas from the use environment.

  Here, since the size of the foreign matter generated on the reticle is finer than the edge step of the chromium film on the reticle, it is very difficult to find the foreign matter by visual inspection of the reticle. For this reason, the presence of foreign matter on the image plane of the reticle is recognized only when the product yield is significantly reduced.

  Thus, since a considerable time is required from the occurrence of foreign matter to the recognition, the product flow cycle is disturbed, and there is a risk of delaying the delivery date of the product.

  Therefore, it is important to detect the possibility that foreign matter may be generated in the reticle that is planned to be used in the exposure process in order to prevent damage and minimize the damage. Technology.

Conventionally, various countermeasures have been proposed as countermeasures against such foreign matters. For example, the method disclosed in Patent Document 1 irradiates the reticle with ultraviolet light, thereby preventing the generation of foreign matter.
JP 2005-191184 A

  However, even if the method of Patent Document 1 is implemented, the generation of foreign matter cannot be completely prevented, and detection of the occurrence of foreign matter is necessary.

  Usually, reticle particle inspection is performed before the reticle is used. This inspection is one of the functions provided in the stepper, and is performed before and after loading the reticle onto the reticle stage for exposure. The principle is that the reticle surface is scanned with an optical laser and foreign matter is detected by the presence or absence of scattering.

  In general, in a reticle equipped with a pellicle film, particle inspection is performed only on the surface of the pellicle film. The reason is that the reticle surface immediately before mounting the pellicle film is usually kept clean enough by cleaning, and after mounting the pellicle film, foreign matter is not present between the pellicle film and the reticle substrate. This is because it is generally difficult to think of newly mixing or growing. Further, as shown in FIG. 6, even if particle inspection on the reticle surface is performed after the pellicle film is mounted, the size is sufficiently smaller than the edge step of the chrome film at the initial stage of foreign material growth. This is because it is difficult to detect by laser scanning.

  As described above, it is extremely difficult to detect the foreign matter on the reticle.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a method for detecting the occurrence of foreign matter generated on a reticle.

In order to achieve the above object, the present invention has the following features.
(1) A method for detecting a foreign substance in a reticle for manufacturing a semiconductor device, wherein an inspection part in which a light non-transmission part and a light transmission part are installed is provided on a pattern surface of a reticle substrate, and at least of the light non-transmission part An effective transmittance of a predetermined region including a part and at least a part of the light transmitting portion is measured, and foreign matter on the reticle is detected based on the effective transmittance.
(2) In the above (1), the representative length of the light transmission part is 1.0 to 1.2 times the wavelength of the inspection light.
(3) In the above (1) or (2), the shape of the light transmission part is substantially circular.
(4) In (1) to (3) above, when the difference between the measured effective transmittance and a predetermined effective transmittance exceeds a predetermined threshold value, an alarm prohibiting the exposure process is issued. It is characterized by emanating.
(5) In the above (1) to (4), when the rate of change over time of the difference between the measured effective transmittance and the predetermined effective transmittance is equal to or greater than a predetermined change rate, An alarm for prohibiting the exposure process is issued.

  ADVANTAGE OF THE INVENTION According to this invention, the method of detecting generation | occurrence | production of the foreign material which generate | occur | produces on a reticle is provided, and it can contribute to the yield improvement of a product by this. Further, it is possible to avoid the risk of product flow cycle disturbance and product delivery delay due to the occurrence of foreign matter.

  Hereinafter, an example of the best mode for carrying out the present invention will be described.

  FIG. 1 shows an example of a foreign object detection method for a reticle according to the present invention. As shown in FIG. 1, the foreign object detection method according to the present invention is implemented using an inspection unit provided on a reticle.

  FIG. 2 shows an example of the inspection unit 3 for detecting the foreign matter 5 according to the present invention, and shows an example of the inspection unit 3 provided outside the effective exposure area 2 of the reticle 1 and the enlarged inspection unit 3. ing. As shown in FIG. 2, the inspection unit 3 includes a portion that transmits light (hereinafter referred to as a light transmission portion 6) and a portion that does not transmit light (hereinafter referred to as a light non-transmission portion 7). A predetermined region in the inspection unit 3, for example, a predetermined region 4 including at least a part of the light non-transmission part 7 and at least a part of the light transmission part 6 is irradiated with a predetermined amount of inspection light. Then, the ratio of the amount of light transmitted through the light transmission unit 6 included in the predetermined region 4 to the amount of inspection light is measured as the effective transmittance of the predetermined region. In addition, as said inspection light, it is desirable to use the exposure light used for exposure, for example.

  The light transmitting portion 6 needs to have a size that significantly reduces the amount of transmitted light when the foreign material 5 is generated on the reticle 1. For example, it is desirable that the dimension of the light transmission part 6 is approximately the same as the dimension of the foreign material 5. In particular, it is desirable that the dimension of the light transmission portion 6 is made equal to or less than the wavelength of the exposure light used for measuring the effective transmittance. In this case, even if the entire light transmission part 6 does not become completely blocked by the foreign substance 5 due to the property as a wave of light, when the part is blocked, the light transmission part 6 Is substantially zero, and the foreign object 5 can be detected with high sensitivity. However, if the representative length of the light transmitting portion 6 is shorter than the wavelength of the light, the exposure light is not transmitted. Therefore, the size is preferably about the same as the wavelength or about 20% longer than the wavelength. .

  Specific dimensions of the light transmitting portion 6 are generally as follows according to the form. When the wavelength of the exposure light used as the light source is i-line (365 nm), if the light transmission part 6 is circular, its diameter is about 365 nm to 438 nm (= 365 nm × 1.2), and if the light transmission part 6 is square. The one side is preferably about 258 nm (= 365 nm / √2) to 310 nm (= 365 / √2 × 1.2). In addition, when the shape of the light transmitting portion 6 is substantially elliptical, the major axis is used. When the shape of the light transmitting portion 6 is polygonal, the length of the longest diagonal line is set. When the “representative length” of the light transmitting portion 6 is used, the representative length is approximately the same as the wavelength of the exposure light for measuring the effective transmittance. Specifically, for example, 1.0 to 1 times the wavelength. It is preferable to make it about twice.

  In order to irradiate the predetermined region 4 including at least part of the light non-transmissive part 7 and at least part of the light transmissive part 6 in the inspection part 3 on the reticle substrate 10, for example, as shown in FIG. As described above, by setting the stop 111 at substantially the same height level as the reticle blind 110, a part of the exposure light 120 from the upper part is irradiated. The light irradiated to the predetermined region 4 by the diaphragm 111 passes through the inspection unit 3 on the reticle substrate 10, and the amount of light is measured by the sensor 201. The diaphragm 111 does not necessarily have to be installed at substantially the same height level as the reticle blind 110, and may be installed at a height level directly above the sensor 201.

  First, the effective transmittance of the predetermined region 4 of the inspection unit 3 provided on the pattern surface of the reticle substrate 10 is measured every predetermined exposure time, every predetermined number of exposures, or every exposure opportunity.

  Next, the measured effective transmittance is compared with a predetermined effective transmittance. Here, the “predetermined effective transmittance” is an effective transmittance when no foreign material 5 is generated.

  The predetermined effective transmittance is calculated as follows, for example. As shown in FIG. 8, when the shape of the light transmission part 6 in the inspection part 3 is square, when the four light transmission parts A to D are not blocked by the foreign matter 5, the area of the predetermined region 4 is set. On the other hand, the calculation is based on the ratio of the area of the light transmitting portion. Specifically, since light is transmitted from four light transmitting portions of 25 squares, the predetermined effective transmittance is 16%. On the other hand, for example, when only the D light transmission portion is blocked by the foreign material 5, light is transmitted through only three of the 25 squares, so the transmittance is 12%. Therefore, 4% which is the difference between the measured effective transmittance of 12% and the predetermined effective transmittance of 16% is a threshold for detecting the occurrence of the foreign material 5.

  As a result of the above comparison, if the difference between the measured effective transmittance and the predetermined effective transmittance is less than the threshold value of 4%, it is determined that the reticle can be used continuously, and exposure processing is performed. On the other hand, if the threshold is 4% or more, it is determined that the reticle cannot be used continuously, and an alarm for stopping the exposure process is issued. The worker who has recognized the alarm inspects the reticle 1 in detail. Thereby, problems such as a decrease in product yield caused by the foreign matter 5 can be avoided in advance.

  In addition, by setting the representative length of the light transmission portion according to a half pitch (also referred to as a minimum line width or a design rule) in the design of a semiconductor device, foreign matter according to the level of the design rule is detected. It is also possible.

  Furthermore, when the shape of the light transmission part is a circle, foreign objects can be detected and managed more strictly than when the shape of the light transmission part is a rectangle including the square. Is possible.

  Further, instead of the above-described predetermined effective transmittance, when the change rate with time of the measured effective transmittance is equal to or higher than the predetermined change rate, a reference for issuing an alarm for stopping the exposure process may be used. In this case, the measured effective transmittance is stored and made into a database, and the change tendency of the effective transmittance with time is analyzed. When the change over time reaches a predetermined change rate that is a management value, an alarm for stopping the exposure process is issued.

  In order to manufacture a semiconductor product, a plurality of reticles are necessary, but it is necessary to measure the effective transmittance for each of the reticles. Therefore, the procedure of FIG. 1 is performed for each reticle.

  Further, the position where the inspection unit 3 is arranged on the reticle 1 is not subjected to the cleaning effect by the exposure light, is a place where the growth of the foreign matter 5 is remarkable, and the effective exposure area 13 which is a source of heat energy. It is desirable to arrange it outside the effective exposure area 2 in the vicinity. However, if it is not preferable in design to install the inspection unit 3 in the vicinity of the effective exposure area 13, it may be arranged at a location away from the effective exposure area 13 as shown in FIG.

  However, the position where the inspection unit 3 is arranged is not necessarily limited to the outside 2 of the effective exposure area. As shown in FIG. 5, the region where the foreign material 5 frequently occurs extends not only outside the effective exposure area 2 but also inside the effective exposure area 13. Since the inside of the effective exposure area 13 is irradiated with ultraviolet rays as exposure light, it is generally considered that no foreign material 5 is generated. However, depending on the thermal energy of the exposure light irradiated to the effective exposure area 13, effective exposure is possible. This is because the thermal environment of the area 13 may be suitable for the growth of foreign matter. Therefore, it is preferable to arrange the inspection unit 3 not only in the effective exposure area 2 but also in the effective exposure area 13.

  In this invention, it becomes the structure which can detect generation | occurrence | production of the foreign material 5 by setting it as the said structure, Thereby, the fall avoidance of a yield, etc. can be achieved.

It is a figure which shows an example of the method of detecting a foreign material and issuing an alarm based on the transmittance | permeability measurement of the reticle which concerns on this invention. It is a figure which shows the example of the form of an inspection part which concerns on this invention, and an installation place. It is a figure which shows the other example of the installation place of the test | inspection part which concerns on this invention. It is a figure which shows the structure of the reticle which concerns on a prior art, (a) is a top view, (b) is sectional drawing, (c) shows a back view, respectively. It is a figure which shows the area | region where a foreign material generate | occur | produces frequently on a reticle. It is a figure which shows the condition where a foreign material generate | occur | produces in the chromium film vicinity on a reticle. It is a figure at the time of applying the detection method of the foreign material which concerns on this invention to exposure apparatus. It is a figure which shows another example of the test | inspection part which concerns on this invention. It is a figure which shows another example of the test | inspection part which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reticle 2 Outside effective exposure area 3 Inspection part 4 Predetermined area 5 Foreign substance 6 Light transmission part 7 Light non-transmission part 10 Glass substrate 11 Pellicle frame 12 Pellicle film 13 Effective exposure area (inside the one-dot chain line)
DESCRIPTION OF SYMBOLS 14 Main generation | occurrence | production location of a foreign material 15 Chromium film | membrane 100 Illumination system 110 Reticle blind 111 Aperture 120 Exposure light 130 Wafer 200 Projection lens system 201 Sensor

Claims (5)

An inspection part in which a light non-transmission part and a light transmission part are provided is provided on the pattern surface of the reticle substrate, and includes a predetermined part including at least a part of the light non-transmission part and at least a part of the light transmission part Measure the effective transmittance of the area,
A method for detecting foreign matter in a reticle for manufacturing a semiconductor device, wherein foreign matter in a reticle is detected based on the effective transmittance.   2. The method for detecting foreign matter in a reticle for manufacturing a semiconductor device according to claim 1, wherein a representative length of the light transmitting portion is 1.0 to 1.2 times the wavelength of the inspection light.   The method for detecting foreign matter in a reticle for manufacturing a semiconductor device according to claim 1, wherein the light transmitting portion has a substantially circular shape.   4. An alarm for prohibiting exposure processing is issued when a difference between the measured effective transmittance and a predetermined effective transmittance exceeds a predetermined threshold value. A method for detecting foreign matter in a reticle for manufacturing a semiconductor device according to claim 1.   An alarm for prohibiting exposure processing is issued when a change rate with time of a difference between the measured effective transmittance and a predetermined effective transmittance exceeds a predetermined change rate. A method for detecting foreign matter in a reticle for manufacturing a semiconductor device according to claim 1.

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