JP2005070490A - Photomask substrate with identification tag, photomask and identification method thereof - Google Patents

Abstract

A photomask substrate can be directly processed in a short time without affecting the processing process and the quality of the mask for manufacturing management of the photomask. To provide a method for efficiently identifying a photomask substrate and a photomask and information written therein.
In a photomask substrate having an identification tag composed of an information pattern used for identification and management of the photomask substrate in the process of manufacturing the photomask, the identification tag is an internal region other than the surface of the photomask substrate. In addition, a photomask substrate with an identification tag on which an identification tag made of a diffraction grating is written by direct processing using two-beam interference exposure of an ultrashort pulse laser.
[Selection] Figure 1

Description

  The present invention relates to a photomask substrate with an identification tag, a photomask, and a method for identifying the same for manufacturing a photomask for exposure transfer used in a photolithography process during a semiconductor processing process.

  The photomask is manufactured by a process such as a light-shielding film forming process, a resist patterning process, a light-shielding film etching process, and a resist stripping process. In recent years, a large number of photomasks are used in a process of manufacturing a semiconductor device, and there are many types of conditions required for each photomask. Therefore, in manufacturing photomasks, it is necessary to manage a large variety of products.

  Since the conditions required for photomasks vary depending on the product, there are various types of photomask substrates for photomasks (hereinafter referred to as substrates), which are materials, and information on required processing processes. This is done by attaching an instruction sheet consisting of information such as a corner cut of the substrate and a processing process to the storage case for storing the substrate. The corner cut is made so that the corners of the substrate are polished so that the material type of the substrate and the front and back of the substrate can be distinguished at a glance. However, in recent years, the combination of corner cuts of only four corners (up to six) has a problem that it is difficult to cope with the increase in the types of substrates and the types of information.

  The instructions are attached to a storage case for storing the substrate during the process, and are used for managing the substrate identification and the process conditions during the process. However, the instructions themselves may be a source of dust generation, and it is necessary to manage the instructions and the substrate on a one-on-one basis. Therefore, there is a risk of producing a photomask under wrong conditions. In order to improve such problems, it was necessary to provide a lot of information that was easy to identify on the board itself.

  Therefore, in the prior art, the type and information of the substrate are written together when drawing the mask pattern, and a method of finally giving the type and information to the light shielding film is currently used. However, since the information cannot be visually recognized until the light-shielding film is etched during the above-described process, it is not suitable for the management of the photomask manufacturing process. It has also been proposed to attach information by attaching a light-shielding film that has been subjected to surface processing or patterning processing using a laser marker on the periphery of a photomask substrate. However, it is conceivable that by forming irregularities on the surface of the substrate, not only dust is generated by processing, but also dirt is more likely to accumulate than in an untreated surface in a resist coating process in the subsequent processing. In addition, there is a possibility that contamination may occur in the process of etching or the like by applying another material such as a patterned light shielding film. Therefore, it can be considered that such a method adversely affects the process of manufacturing the photomask.

  Therefore, it is necessary to attach an identification tag to the photomask substrate itself that enables process management without affecting the processing process.

On the other hand, processing of a transparent material inner region using an ultrashort pulse laser beam has been studied. By directly irradiating the internal region of the transparent material with a laser pulse with a pulse width as short as a femtosecond order, direct processing is performed only on the internal region where the laser is focused without affecting the surface of the transparent material. Can do. Further, since the direct processing is not thermal, but directly induces a structural change of the material, processing with very high accuracy can be performed only on the irradiated portion. Such a direct processing method is only possible by using an ultrashort pulse laser. There have been many methods for marking inside thin glass substrates using this technique. For example, in Patent Document 1, a linear mark pattern is written on a soda-lime glass substrate by multiple exposure of 1000 pulses by combining a laser having a pulse width of 100 femtoseconds (fs) and a lens having an aperture ratio of 0.28. The method is shown.

  However, in direct processing using an ultrashort pulse laser of about 100 fs, energy is concentrated in an extremely short time, so that the incident surface of the sample is easily damaged. Therefore, it is necessary to abruptly condense light of low energy on the entrance surface using performance near the focal point of the objective lens. For this reason, the area where direct processing is possible in the internal region is limited to the depth of the working distance of the lens (near the range of the focal depth of the objective lens), and since the energy is low, multiple exposure is required for processing at one location. It took a long time.

  In addition to the above method, when marking is performed using a simple condensing irradiation method using a single beam of femtosecond laser, the direct processing at one place is poor in visibility, and a plurality of processing sites are combined. It is necessary to have one pattern. Further, in a larger processing range, multiple exposure with weak energy is required for processing at one place in order to perform without generating cracks. In this respect, this method is inefficient in terms of processing time and its visibility.

  Up until now, it was possible to write the grating structure by periodically arranging the processing parts by multiple exposure of one light beam, but it is necessary to keep the distance between the processing parts several tens of μm in order to prevent cracks inside the substrate. Therefore, it was impossible to write a grating structure with a narrower pitch width corresponding to the grating structure requested to be finer and higher diffraction efficiency. In addition, the accuracy of the structure depends on the accuracy of the sample stage, and it takes an enormous amount of time to obtain the number of periodic structures enough to obtain a diffraction grating by repeating processing.

  Next, as a method of reading the information attached to the substrate, the reflection from the light shielding film is used for a barcode pattern or the like disclosed by Patent Document 2 or the like based on the contrast between the light shielding film written on the mask surface and the substrate. There is a reading method. Patent Document 3 and the like show a method of reading information as a two-dimensional bright field image using a CCD camera. However, in the identification tag written inside by the usual method using a single light beam, a clear reflection or transmission image cannot be obtained because it is due to a local refractive index change of the substrate. Further, although the image is made up of a collection of minute dots, the dots cannot be written at a high density because the generation of cracks inside the substrate is prevented and the processing time is enormous. Therefore, it is difficult for the dots to obtain a contrast ratio comparable to that of the light shielding film to glass and to process a two-dimensional image.

The known literature is shown below.
JP-A-11-267861 JP-A-2-125605 JP 2000-99619 A

An object of the present invention is to perform manufacturing management of a photomask, so that the photomask substrate can be directly processed in a short time without affecting the processing process and the quality of the mask, and the produced high visibility. It is an object of the present invention to provide a photomask substrate with an identification tag and a photomask and a method for efficiently identifying information written therein.

  According to a first aspect of the present invention, in the photomask substrate having an identification tag composed of an information pattern used for identification and management of the photomask substrate in the process of manufacturing the photomask, the identification tag is a photomask. A photomask substrate with an identification tag, wherein a diffraction grating is written directly into an internal region other than the surface of the substrate by processing.

  The invention according to claim 2 of the present invention is characterized in that the direct processing uses a two-beam interference exposure of an ultrashort pulse laser to write an identification tag made of a diffraction grating. It is a photomask substrate with a vote.

  The invention according to claim 3 of the present invention uses the photomask substrate with the identification tag in a photomask in which a mask pattern is formed on the photomask substrate. This is a photomask using a photomask substrate.

  The photomask substrate of the present invention is characterized by being directly processed by an ultrashort pulse laser. Since the substrate is directly processed in the atmosphere, no special processing process or processing environment for marking is required. Moreover, if the timing which performs marking is after grinding | polishing of the base material for board | substrates, it can carry out at any time in the subsequent process, and an additional process is also possible.

  In addition, in the above, an identification tag is formed by locally forming a refractive index change region inside a transparent substrate. In general surface processing, fine debris and the like are generated, and this becomes a dust generation source, so new cleaning is necessary, or the substrate surface shape changes, increasing the surface area of the substrate and collecting dirt. There was a risk of problems in the processing process, such as easy. On the other hand, in the method of the present invention, since the identification tag is written only inside the transparent substrate, the substrate surface is not affected at all in this processing. In addition, the written information is stored semi-permanently even after processing such as repolishing the substrate surface and etching the surface layer.

  The invention according to claim 4 of the present invention is used for identifying and managing the photomask substrate or the photomask by visually recognizing the identification tag from the photomask substrate with the identification tag or the photomask in the process of manufacturing the photomask. In the identification tag identification method, the identification tag of the diffraction grating written in the inner region irradiates the illumination light beam and uses the visibility of the diffraction grating for identification. This is a method for identifying the attached photomask substrate or photomask.

  In the invention according to claim 5 of the present invention, the identification method irradiates an illumination light beam, and from the intensity of transmitted light due to scattering and a change in the refractive index of the diffraction grating, as a pattern for image processing or a visual pattern, 5. The method for identifying a photomask substrate or photomask with an identification tag according to claim 4, wherein the visibility is identified by using one of the front surface, back surface, and side end surface of the mask substrate or photomask. is there.

  In the invention according to claim 6 of the present invention, the method for identifying the identification tag of the diffraction grating optically identifies the transmitted light that is diffracted by irradiating the illumination light beam and diffracting the light diffraction ability of the diffraction grating. The photomask substrate or photomask identification method with an identification tag according to claim 4.

In the invention according to claim 7 of the present invention, the identification method irradiates an illumination light beam, and optically identifies a change in the intensity of transmitted light to be diffracted by a binarization process with a light diffraction ability of a diffraction grating. The photomask substrate or photomask identification method with an identification tag according to claim 6.

  The invention according to claim 8 of the present invention is characterized in that the identification method irradiates an illumination light beam and optically identifies the transmitted light that is diffracted in a specific angle direction by the light diffraction ability of the diffraction grating. A photomask substrate or photomask identification method with an identification tag according to claim 6.

  In the invention according to claim 9 of the present invention, the identification method irradiates an illumination light beam, and transmits the transmitted light diffracted in one direction by the light diffraction ability of the diffraction grating and the other one direction. 7. The photomask substrate or photomask identification method with an identification tag according to claim 6, wherein the identification is performed optically by transmitted light diffracted in two directions.

  The invention according to claim 10 of the present invention is characterized in that the identification method irradiates the illumination light beam with the incident angle of the illumination light beam and / or the wavelength of the illumination light beam being changed, so that the diffraction is performed with the light diffraction ability of the diffraction grating. 7. The photomask substrate or photomask identification method according to claim 6, wherein a difference in diffraction characteristics that changes depending on the pitch width of the grating is optically identified by transmitted light that is diffracted.

  In writing, in addition to scanning the condensing part in a direction parallel to the surface of the substrate where the laser is focused and irradiated, writing an identifiable image on this surface, in addition to the surface in the parallel direction On the other hand, the condensing part is scanned in the vertical direction, and an identifiable image can be written on this surface. That is, it is possible to write an identifiable image on the parallel plane parallel to the substrate surface and a vertical plane in the vertical direction (depth direction). By combining these, it is possible to write the identification table three-dimensionally in the intended area outside the circuit pattern area in the internal area of the board, so that information can be written and read from any surface of the board. It becomes possible.

  The identification tag in the present invention is a diffraction grating using two-beam interference exposure of femtosecond laser pulses. Unlike a structure created by simple single-beam multiple exposure, writing a structure with high visibility at one location with only one pulse of irradiation eliminates the need for multiple exposure and greatly reduces the time required for direct processing. . In addition, the optically written information can be read using the diffracted light transmitted and reflected.

  The photomask substrate shown in the present invention has an identification tag written directly to a three-dimensionally intended location inside the substrate using an ultrashort pulse laser. Further, since this identification tag is a volume type diffraction grating by two-beam interference exposure, it has higher visibility than processing by one beam, and can be identified from any surface of the substrate not only by visual observation but also by an optical method. In addition, since the periodic structure can be processed with only one pulse of irradiation, the efficiency is good. Therefore, there is an effect that efficient substrate management can be performed without the influence of particles, contamination and the like in the process of manufacturing the mask.

  The present invention will be described with reference to the drawings. FIG. 1 shows the writing of the diffraction grating into the transparent material by the two-beam interference method used in this method. A femtosecond laser 2 in which one beam of laser light is once divided into two optical paths is condensed at one point inside the transparent material using a lens 3 or the like. At this time, the two pulses coincide with each other both in terms of time and space, so that the pulses can interfere with each other, and the diffraction grating 4 can be written at the internal condensing point. At this time, the laser incident surface A on the surface of the sample is not affected by the processing.

  The wavelength of the laser used for processing in the present method needs to be a wavelength that can pass through the material irradiated when not condensed. In order to process only the inside, the energy density is below the processing threshold on the sample surface, and it is only necessary to increase the spatial energy density near the focal point by condensing, so that the laser will exceed the processing threshold of the material. Adjust the strength of the.

  Further, the pulse width of the laser is used by chirping a 100 fs pulse to widen the time width. The shorter the pulse width, the less the possibility of cracking and the like, and processing can be performed with low power. However, since the peak value is high, in order to avoid damage on the incident surface, it is necessary to perform condensing with an objective lens or the like. In this case, since the working distance, which is the depth range in which the condensing point is variable, becomes short, it is impossible to perform processing by condensing deep inside the sample. By expanding the pulse width, it becomes possible to enlarge the working distance using a convex lens having a focal length of 50 mm or more and to process it deeply, so adjustment is performed according to the processing conditions.

  The diffraction grating can be written in the transparent material by the method described above. The size of the diffraction grating that can be written by irradiation with one pulse is about 20 μm in diameter. This can be changed depending on the intensity of the laser to be irradiated. The pitch width of the diffraction grating formed in the beam spot is variable depending on the interference conditions such as the light source wavelength and the crossing angle of the two light beams in the sample, and a minimum periodicity close to the diffraction limit of the light source wavelength can be obtained. For example, when a laser having a wavelength of 800 nm is used as a light source and two light beams intersect with each other at an angle of 60 degrees in a sample and a diffraction grating is written, a diffraction grating having a periodicity with a pitch width of 800 nm can be written.

  Even if the written diffraction grating is only one place, the visibility is higher than that of a processed part obtained by condensing one beam of the same size. In the conventional method, light is scattered by a processing site and identification is performed. In this method, in addition to the scattering by the processing site, the diffraction grating formed in the spot is several hundred nm to several μm. This is because light diffraction due to the periodic structure can be recognized. In processing, not only the marking at only one place but also several patterns arranged in close proximity can be combined into one symbol.

  In this case, as shown in FIG. 2, the condensing point is scanned in parallel to the incident surface A, for example, in the right direction from the left side of the drawing to directly process the plurality of diffraction gratings. In FIG. 2, the two light beams intersect with each other at a different angle from the laser incident surface A of the substrate through the lens 2 or the like, and are gathered from the left side of the drawing to the right and from the front side without changing the depth in the vertical direction of the drawing. The light spot is scanned and the diffraction grating 4 is continuously written.

  3A and 3B are diagrams illustrating the diffraction grating of FIG. 2, where FIG. 3A is a plan view, FIG. 3B is a side cross-section of the XX plane, and FIG. 3C is a side of the YY plane. It is a cross section. FIG. 3A is a plan view seen from the surface of the substrate, that is, the beam incident surface A. FIG. In (b), the periodic direction of the diffraction grating can be determined by a side sectional view taken along the plane XX, that is, a side sectional view viewed from a plane B parallel to the scanning direction of the beam incident surface A. (C) is a side cross-sectional view in the YY plane, that is, a side cross-sectional view as viewed from a plane C perpendicular to the direction in which the beam incident surface A is scanned, and has a periodic layered structure, and is diffracted. The periodic direction of the grating cannot be determined. Moreover, it is a condensing point of one depth, and the scanning direction is only the direction parallel to the substrate surface.

  In addition to this, as shown in FIG. 4, the condensing unit is scanned in the depth direction of the incident surface, and information can be identified from the surface B perpendicular to the incident surface. Therefore, when writing the identification tag on the photomask substrate, writing can be performed not only from the film surface before the light-shielding film is formed, but also from the back surface thereof, from the end face regardless of before and after the film formation.

5A and 5B are diagrams for explaining the diffraction grating of FIG. 4, in which FIG. 5A is a plan view, FIG. 5B is a side cross section of the XX plane, and FIG. 5C is a YY plane. FIG. FIG. 5A is a plan view seen from the surface of the substrate, that is, the beam incident surface A. FIG. In (b), the periodic direction of the diffraction grating can be determined by a side sectional view taken along the plane XX, that is, a side sectional view viewed from a plane B parallel to the scanning direction of the beam incident surface A. Since scanning is performed in the vertical direction, there are three stages of light condensing points in the depth direction. (C) is a side sectional view taken along the YY plane, that is, a side sectional view seen from a plane C perpendicular to the direction in which the beam incident surface A is scanned, and has a periodic layered structure. The direction of the period cannot be determined. It is a condensing point of three depths, and the scanning direction is processed into a direction parallel to and perpendicular to the substrate surface.

  A method for identifying the information when the material processing shown in FIGS. 1, 2, 3, 4, and 5 is applied to a photomask will be described. The identification methods are summarized in Table 1 below.

１箇所に書きこまれたマーキング、または数カ所のパターンをまとめてガラス基板の内部に書きこまれた文字・記号はその屈折率変化領域を像として基板の面、端面から目視またはＣＣＤカメラ等の画像認識によって識別可能である（表１参照）。

The markings written in one place, or the letters and symbols written in the glass substrate by putting together several patterns are images of the refractive index change area as an image or images from the surface of the substrate or from the end face It can be identified by recognition (see Table 1).

  Further, as shown in FIG. 6, the region processed by the ultrashort pulse laser diffracts and scatters the incident illumination light 5, so that the intensity of transmitted light (0th order diffracted light) is lower than that of the unprocessed region. The spot 7 of the laser transmitted light that passes through the unprocessed area and the scattered laser beam spot 8 in the processed area are identified by the screen 60. By using this intensity difference as 0/1 information, it is possible to optically identify barcodes, area codes, etc. written inside.

  In addition to simple refractive index changes, it is also possible to read information that has been optically written using the diffraction power of the diffraction grating. As shown in FIG. 7, only when the diffraction grating portion is irradiated, it is possible to identify optically written information using the diffracted light 11 of the illumination light emitted at a specific angle. In FIG. 7A, the laser transmitted light spot 7 that passes through the unprocessed area of the substrate 1 is not identified by the light receiving unit 6. In (b), the light is diffracted by the diffraction grating, and the laser diffracted light 11 is identified by the light receiving unit 6.

  Further, the periodic direction of the diffraction grating written in one pulse is one-dimensional. As shown in FIG. 8, the sample is written by rotating it 90 degrees counterclockwise during processing, and the direction in which the diffracted light is strongly generated can be changed by changing the periodic direction of the diffraction grating. Further, at this time, a two-dimensional periodic structure in a lattice shape can be written by rotating the sample and performing double exposure on the same portion. At this time, the direction in which the diffracted light is generated can be expanded in a two-dimensional direction. In FIG. 8A, the laser illumination light incident on the processing area is identified by the screen 60 on the same plane together with the transmitted light spot 7 and the diffracted light spot 11. FIG. 8 (b) shows that the transmitted light spot 7 is identified by the screen 60 in the same way as in (a) above for the laser illumination light incident from the same direction by rotating the periodic direction of the diffraction grating by 90 degrees. Spot 11 is identified by another screen 61.

  In addition, in the writing of the diffraction grating, it is possible to write by changing the pitch width in the period direction. In this case, as shown in FIG. 9, a difference is identified in the diffraction characteristics such that the place where the diffracted light appears strongly differs depending on the pitch width of the written diffraction grating. Further, by changing the incident angle of the illumination light or the wavelength of the illumination light, there is a possibility that more multi-dimensional information can be written using this feature and used for substrate management. 9A and 9B, when two diffraction gratings having different pitch widths are irradiated with the laser illumination light 12 and 13 and the incident angle changed, the spot 11 of the laser diffracted light identified by the screen 60 is used. Shows the difference. The difference was defined as diffraction characteristics.

Explanatory drawing of the writing method of the diffraction grating by the ultrashort pulse laser inside the photomask substrate used by this invention. Explanatory drawing of the method of writing the identification tag which can be recognized from a laser incident surface or a back surface by scanning the laser condensing part of this invention in parallel with respect to an incident surface. FIG. 3 is an explanatory drawing of the identification tag of FIG. 2 according to the present invention, where (a) is a plan view, (b) is a side sectional view of the XX plane, and (c) is a side sectional view of the YY plane. Explanatory drawing of the method of writing the identification tag which can be recognized from the surface which scans the laser condensing part of this invention perpendicularly | vertically with respect to an incident surface, and is orthogonal to an incident surface. 4 is an explanatory drawing of the identification tag of FIG. 4 according to the present invention, where (a) is a plan view, (b) is a side sectional view of the XX plane, and (c) is a side sectional view of the YY plane. Explanatory drawing of the identification method which shows the difference in the transmission intensity | strength of the illumination light in the part which performed the process of this invention, and the unprocessed part. Explanatory drawing of the identification method which shows the difference in the diffraction characteristic of the illumination light in the part which wrote in the diffraction grating of this invention, and an unprocessed part. Explanatory drawing of the identification method which shows that the diffraction direction of the light which injected into the board | substrate from the same direction differs by the difference in the pitch direction of the diffraction grating of this invention. Explanatory drawing of the identification method which shows that the incident angle of the light of the same wavelength in which diffraction arises differs by the difference in the pitch width of the diffraction grating of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... (Glass) substrate 2 ... Femtosecond laser 3 ... Lens etc. 4 ... Diffraction grating 5 written in the inside of substrate ... Illumination light laser 6 ... Light receiving part 7 ... Laser transmitted light spot 8 ... Scattered laser Spot of light 9 ... Incident direction 10 of illumination light beam ... Enlarged image 11 of diffraction grating written inside glass ... Spot 12 of laser diffracted light ... Laser illumination light incident at an angle to the sample (incident angle) small)
13 ... Laser illumination light incident at an angle to the sample (large incident angle)
14 ... Diffraction grating written inside glass substrate (wide pitch)
15 ... Diffraction grating written inside glass substrate (narrow pitch)
30 ... Beam splitter etc. 31 ... Mirror etc. 60 ... Screen A ... Incident surface A of femtosecond laser
B: Surface B perpendicular to the incident surface A
C: plane C perpendicular to incident plane A and plane B

Claims (10)

  In a photomask substrate having an identification tag composed of an information pattern used for identification and management of the photomask substrate in the process of manufacturing the photomask, the identification tag is directly processed in an internal region other than the surface of the photomask substrate. A photomask substrate with an identification tag characterized by writing a diffraction grating.   2. The photomask substrate with an identification tag according to claim 1, wherein the direct processing uses a two-beam interference exposure of an ultrashort pulse laser to write an identification tag made of a diffraction grating.   3. A photomask using a photomask substrate with an identification tag according to claim 1, wherein the photomask substrate with an identification tag is used in a photomask having a mask pattern formed on the photomask substrate.   In the photomask manufacturing process, the identification tag is visually recognized from the photomask substrate with the identification tag or the photomask, and written in the inner area in the identification tag identification method used for identification and management of the photomask substrate or the photomask. A method for identifying a photomask substrate or a photomask with an identification tag, characterized in that the identification method for an identification tag of an embedded diffraction grating irradiates an illumination light beam and uses the visibility of the diffraction grating.   The identification method irradiates an illumination light beam, and from the intensity of transmitted light due to scattering and refractive index change of the diffraction grating, as an image processing pattern or a visual pattern, a photomask substrate or a photomask surface, back surface, side 5. The method of identifying a photomask substrate or photomask with an identification tag according to claim 4, wherein the visibility is identified by using one of the end faces.   5. The identification tag according to claim 4, wherein the identification tag of the diffraction grating is discriminated optically by transmitted light that is irradiated with an illumination light beam and diffracts using the light diffraction ability of the diffraction grating. A method for identifying the attached photomask substrate or photomask.   7. The identification method according to claim 6, wherein the identifying method irradiates an illumination light beam and optically identifies a change in intensity of transmitted light diffracted by a light diffraction ability of a diffraction grating by binarization processing. Photomask substrate or photomask identification method with identification tag.   7. The photo with an identification tag according to claim 6, wherein the identification method irradiates an illumination light beam and optically identifies the transmitted light that is diffracted in a specific angle direction by the light diffraction ability of the diffraction grating. A method for identifying a mask substrate or a photomask.   In the identification method, an illumination light beam is irradiated and optically diffracted in two directions, that is, transmitted light diffracted in one direction and the other one direction by the light diffractive power of the diffraction grating. The method for identifying a photomask substrate or a photomask with an identification tag according to claim 6, wherein identification is performed.   When the identification method irradiates the illumination light beam with the illumination light beam incident angle and / or its wavelength changed, the difference in diffraction characteristics that changes depending on the pitch width of the diffraction grating due to the light diffraction ability of the diffraction grating. 7. The method of identifying a photomask substrate or a photomask with an identification tag according to claim 6, wherein the optical mask is optically identified by transmitted light that diffracts.

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