JPH04110944A - Marking method for transparent material - Google Patents

Abstract

PURPOSE:To prevent the sticking of dust to a marking part and to obviate the exertion of an adverse influence on a film forming stage and a lithography stage by focusing a high-energy beam to the inside of a transparent material via an optical system and irradiating the inside of the transparent material. CONSTITUTION:The high-energy beam which is not absorbed by the transparent material, such as photmask substrate, is focused to the inside of the transparent material to irradiate the material, by which microcracks or microcrystals are generated in the transparent material. For example, inorg. glass, such as optical glass and quartz glass, transparent resin, such as acrylic resin, etc., are used as the transparent material. The time for irradiation of the high-energy beam is specified to several pulses to several tens pulses depending upon its power. The adhesion of the dust to the marking part is prevented in this way and the marking is executed without the influence on the stage.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method for distinguishing various transparent materials such as photomask substrates from other transparent materials, and for recording the history and characteristics of the transparent materials. Regarding the marking method for

[Prior Art] Conventionally, methods for marking photomasks and the like include cutting out corners of the substrate and recording identification symbols outside the pattern area of the substrate using a laser or the like (Japanese Patent Laid-Open No. 6
2-75532) JP-A-58-56315, JP-A-57
-104934) Similarly, there was a method of providing a bar code or magnetic recording area outside the area.

Furthermore, a reflective surface and a rough surface are provided on the side of the board.

There was a method of using it as an identification mark (Japanese Patent Publication No. 62-40700).

However, all of these methods involve marking the surface of a transparent material in some way. [Problem to be solved by the invention] Transparent materials such as photomask substrates are susceptible to sputtering and erosive materials. Conventional methods for marking the surface of transparent materials have the drawback that the marks are easily damaged by exposure to chemicals during etching.

In addition, as LSIs become more highly integrated, dust-free is required, and when marking the surface, dust tends to adhere to the marking area, and when cleaned, it contaminates the cleaning solution and there is a risk of re-adhesion, so it is difficult to completely remove this dust. becomes difficult.

Furthermore, the quartz glass mask is disclosed in Japanese Unexamined Patent Publication No. 59-20023.
8, JP-A-59-83950 and JP-A-59-883
As shown in 32, etc., recycling is done by polishing, etc. However, when it comes to markings on the surface, polishing etc. scratches the marks and erases them, making them illegible.

Even when marking is done on the side of the board.

Markings on the sides tend to disappear due to abrasives entering between the carrier and the workpiece during recycling.

Another drawback is that the chromium film on the marking part is easily peeled off.

By marking the inside of the transparent material, the present invention prevents dust from adhering to the marking area, does not adversely affect the film forming process or the lithography process, and prevents the surface of the transparent material from being exposed to harsh environments. The purpose is to provide a marking method that will never disappear.

[Means for Solving the Problems] Therefore, the present invention focuses and irradiates the inside of the transparent material with a high-energy beam that is not absorbed by the transparent material such as a photomask substrate, thereby creating minute racks or fine particles inside the transparent material. It marks transparent materials by generating crystals.

For marking, characters such as numbers and alphabets may be imaged through a mask, similar to conventional laser marking methods, or cracks or microcrystals are generated in the form of dots, and the dots are combined to form characters. , may also form numbers.

Furthermore, it is also possible to make the dot rows correspond to letters, numbers, etc., similar to CDs. Alternatively, the symbol may be created in the form of a barcode.

Examples of the transparent material include optical glass, inorganic glass such as quartz glass, and transparent resin such as acrylic resin.

As a high energy beam, Xe F (351 nm
), XeC1 (308nm), KrF (248nm
), A r F (193 nm) and other excimer lasers, YAG lasers and their harmonics, etc. 6 It is necessary to select an appropriate high-energy beam depending on the absorption characteristics of the transparent material for the high-energy beam. be.

The irradiation time of the high-energy beam may be from several pulses to several tens of pulses, depending on its power.

[Operation] The high-energy beam that is not absorbed by the transparent material is focused inside the transparent material through an optical system consisting of lenses and mirrors, and the high-energy beam is irradiated inside the transparent material. Then, microscopic racks or microcrystals are generated at the location irradiated with the high-energy beam. By forming these cracks or microcrystals into a character shape or a barcode shape, a marking is applied to the inside of the transparent material.

The generation of cracks or microcrystals will be explained in more detail.

In a solid, the energy level of valence electrons has a so-called band structure. Insulators do not absorb photons with photon energy below the band gap, that is, long wavelength light.

However, even light with energy lower than the band gap
When the photon density is extremely high, such as by concentrating light with a lens, two or more photons are absorbed simultaneously, causing electrons to move from the charge band (energy band lower in energy than the energy gap) to the conduction band (energy band). It has a higher energy than the gap and is excited to an energy band (an energy band in which no electrons exist under normal conditions).

The simultaneous absorption of two photons in this way is called two-photon absorption, and the absorption of a plurality of photons is called multiphoton absorption.

In this invention, multiphoton absorption is used to cause the transparent material to absorb light at a wavelength that is lower in energy than the band gap and which would normally not cause absorption, thereby cutting the bond in the transparent material.

Alternatively, heat generation is used to generate microscopic racks or microcrystals inside the transparent material.

In silica glass, this bandgap is approximately 9 eV (14
0 nm). Unless there are impurities or defective structures in quartz glass, light with energy lower than the bandgap, that is, with a longer wavelength, is usually not absorbed.

Here, the wavelength and photon energy of the excimer laser are shown below.

Type Wavelength (n+=) ArF 193 KrF 248 XeC1308 XeF 351 Photon energy (eV) 6.4 5.0 4.0 3.5 Number of photons required for excitation Therefore, all excimer lasers have a wavelength of 140 nm
Since it is longer, 1 normally no absorption should occur. However, absorption occurs due to the aforementioned multiphoton absorption, which causes cleavage of the bond or exothermic effect, and the generation of microscopic racks or crystallites inside.

The number of photons required to excite valence electrons from the charge band to the conduction band is the number required to exceed the band gap of 9 eV of silica glass.

[Example] Next, the present invention will be explained in more detail by way of examples.

Example 1 Synthetic quartz glass (OH1) polished on both sides as a transparent material
300 ppm content: 5 mm thick), and as a high energy beam, an excimer laser (KrF 248 nm) using an unstable resonator was used, energy density 50 mJ/cm2 pulse, repetition frequency 1
The excimer laser beam was oscillated at 0 Hz, the excimer laser beam was focused near the center inside the synthetic silica glass using a lens system with a focal length of 2 cm, and each dot was irradiated with the excimer laser for 0.5 seconds. Then, the cracks generated inside the synthetic quartz glass were formed into dots in the shape of the number 1.

As a result, a pattern visible to the naked eye was formed inside the synthetic quartz glass.

Example 2 A photomask quartz glass substrate (5”
25'/100. Made of synthetic quartz glass: OH1300p
pm-containing), and the high-energy beam is an excimer laser (K r F 2
48 nm) with an energy density of 50 mJ
/cm” pulse was oscillated at a repetition frequency of 10 Hz.

At a 5 mm square corner of the photomask substrate, focus the excimer laser near the center of the inside of the quartz glass substrate using a lens system with a focal length of 2 cm, and irradiate the excimer laser to generate a crack inside the quartz glass. to form dots. The diameter of this dot is approximately 0.1 mm, and by shifting the formation position of the dot,
I drew it as G.

Example 3 A photomask quartz glass substrate (5” x
25' /100, made of synthetic quartz glass; OH1300p
pm-containing), and the high-energy beam is an excimer laser (KrF 248
nm) with an energy density of 50 mJ/cm”・pulse,
It was used at a repetition frequency of 150Hz.

Using a mask with holes in the shape of the letters NSG as a marking mask, focus a lens system with a focal length of 21 around the center of a 5 mm square corner of the photomask substrate, and use an excimer laser beam of 2 It was irradiated for seconds to generate cracks inside the quartz glass, and alphabet letters NSG were formed inside the substrate.

Example 4 A fused silica glass plate (100×5×:O
The high-energy beam is an excimer laser (X e
CL 308 nm, energy density 100m
J/cm" pulse, repetition frequency 150 Hz) was used.

Using a mask with a hole in the shape of an alphabet ○X as a marking mask, focus the excimer laser on the inside center of the 5 mm square corner of the fused silica glass plate using a lens system with a focal length of 2 am. was irradiated to generate cracks inside the quartz glass, and alphabet letters ○X were formed inside the substrate.

Fused silica glass absorbs KrF excimer laser and does not generate cracks even when irradiated with it, so XeCl excimer laser was used.

[Effects] As mentioned above, when a high-energy beam that does not absorb into the transparent material is focused on the inside of the transparent material, for example, 1 quartz glass is irradiated with an excimer laser,
Fine lacs or crystallites occur inside the transparent material. This can be used as an identification mark by converting it into letters, dots, or barcodes.

Since this mark is formed inside the transparent material, it is hardly affected by external influences, and since the surface of the transparent material is not damaged in any way, it can be said that it is permanent.

Furthermore, since it is formed inside a transparent material, there is no dust attached to the marking portion, and marking can be performed without affecting the process.

Patent applicant: Nippon Quartz Glass Co., Ltd. Yamaguchi Nippon Quartz Co., Ltd.

Claims (4)

[Claims] (1) A method for marking a transparent material, which comprises irradiating a high-energy beam that is not absorbed by the transparent material with a focus on the inside of the transparent material. (2) The method for marking a transparent material according to claim 1, wherein the transparent material is quartz glass. (3) A method for marking a transparent material according to claim 1, wherein the transparent material is a photomask quartz glass substrate. (4) A method for marking a transparent material according to any one of claims 1 to 3, wherein the high-energy beam is an excimer laser.