Method for producing photomask blank

FIELD: electronic engineering; production of photomask blanks.

SUBSTANCE: proposed method for producing photomask blanks includes mechanical and chemical treatment of glass wafers, their placement in vacuum chamber, and coating with masking chromium layer by heating chromium-containing evaporator in nitrogen environment until desired optical density is attained, this being followed by wafer washing, covering with resist, and control. Chromium is cleaned prior to being applied to masking layer by remelting it at temperature of 2000 to 2100°C and residual pressure of 400 - 500 mm of mercury in argon environment; chamber is cooled down to room temperature, evaporator is heated at a rate of 500 - 700°C a minute to 1700 - 1850°C, exposed to this temperature for 25 - 35 minutes, then evaporator is heated to 1860 - 1950°C and chromium is evaporated at a rate of 140 - 160Å a minute until desired optical density is attained.

EFFECT: enhanced quality of varying-reflectance masking layer and environmental friendliness of method.

4 cl, 1 tbl

 

The invention relates to the electronics industry, namely FOTOSALON the blanks (FSS), intended for the formation of the pattern of micro in the manufacture of integrated circuits.

A method of obtaining FSS associated with evaporation and condensation of vapors of chromium vacuum-thermal method by discrete step of heating the evaporation source to the temperature 1100-1500° (ed. St. USSR №688009).

The disadvantage of this method is the high defect layer masking. Modern requirements to FSS increased significantly, and for most microelectronic devices require FSS with low defectivity.

Closest to the present invention is a method (Electronic industry, 1980, VIP-9, p.100, 121) obtain FSS associated with careful preparation of the surface of the glass plate with the use of highly active detergents, ultrasonic treatment and quality deionized water, held additional bactericidal cleaning, and drying in a vapor of isopropyl alcohol or freon. It is noted that on such substrates obtained chromium mask layers with defects to 0.01 cm-2when the control "punctures" size of 1.5 μm or more.

The disadvantage of this method is the increased defect masking layer during the inspection of defects of size 1.0 m is m or more. Modern requirements to FSS for large-scale integrated circuits (LSI) and very large scale IC (VLSI) are characterized by the necessity of the control of defects smaller than 1.5 μm, due to the size of the critical components of these schemes, the size of which does not exceed 1-2 microns, and often lie in the submicron region. When the control micron defects they grow up to 0.5 cm-2.

Another disadvantage is the lack of reflectance characteristics of the surface of chromium.

The use of freon is also unacceptable for environmental reasons.

We propose a method of obtaining FSS devoid of these shortcomings.

This objective is achieved in that, in addition to the deposition of the masking layer are cleaned chromium by melting it at a temperature of 2000-2100°and a residual pressure of 400-450 mm Hg in the atmosphere of argon, cooled to room temperature, heat the evaporator with the speed of 500-700°min until the temperature 1750-1850°C, incubated for 25-35 seconds, heat the evaporator to 1860-1950°and sprayed chrome with speed of 140-160 Å min up to the desired optical density.

The method consists in the repeated treatment of chromium due to the removal of dissolved gases by melting in an inert atmosphere and create conditions resperine and recrystallization x is Ohm due to the heating of the evaporator, and suspend this process, that allows not only to carry out the condensation and resperine crystals of chromium in the evaporator, but also to create conditions recrystallization of atoms of chromium on glass substrates in the initial condensation. The process of deposition of the "optically thick" evaporator contributes to this mechanism.

It is known that ("Technology of thin films", M: "Cofradia", 1977, p.41) the initial formation of thin films of metals is crucial from the point of view of formation of potential defects and their manifestations in the future in the mask layer as a whole. This especially applies for defects of micron and submicron sizes. In the process of "pure" explosive evaporation occurs "masking" of these defects, although this stage is also necessary from the point of view of forming a uniform crystalline film, characterized by uniform properties in the entire area of the plate and from the plate to the plate. Stage of recrystallization and resperine mode provides heating of the evaporator and the extract for 25-35 seconds after heating the evaporator to 1750-1850°and further heating the evaporator to 1860-1950°at constant speed spraying 140-160 Å/min. This technology allows you to form a chromium film with fewer defects not only about 1.5 micron, but subm the crown cap size.

Another requirement VLSI technology is the requirement for the reflectivity of the surface of the masking film, which is explained by the need for precise alignment of a set of templates from 15-20 layers. While disruptions and interference in the optical system combining initiated reflected from the surface of the chromium rays. In the international standard SEMI there are three categories FSS with different reflective surfaces of chromium: 1) more than 40%; 2) 25-40%, and 3) less than 25%.

The process of deposition of chromium in the atmosphere of nitrogen at a residual pressure of (0,5-1,5)·10-4mm Hg and (1,5-2,5)·10-5mm Hg allows you to form a mask layer with a reflectivity of 25-40% and 40%, respectively, and in the presence of an additional layer of chromium oxide with a thickness of 200-300 Å the reflection coefficient is less than 25%.

Thus, all categories of mask layers in reflectivity can be obtained in accordance with the proposed method of obtaining FSS.

Example. Glass plate 127×127 mm handle on machines simultaneous bilateral treatment. As a polishing powder used powder on the basis of cerium dioxide "Ferropol (TU 334-97) with the contents of the working fraction 0.6 to 6.0 μm 85% and the total content of oxides of neodymium and praseodymium 10% and iron oxide 5%. As p is mirovalev cloth used non-woven material (TU 17-21-40-1-90) based on synthetic fibers with a diameter of 8-10 μm and bulk density of 0.75 g/cm 3. Based polishing powder and deionized water to prepare a polishing slurry with a density of 1.2-1.3 g/cm3. The polishing cloth is glued to the polishing pad waterproof glue. The treatment is carried out in batch process in a special metal device with plastic liners to prevent injury to the glass with periodic flow of suspension in the treatment area. Upon completion of the polishing process define "hooking up" glass surfaces and spend processing in aqueous solutions of organic acids, in deionized water, followed by dehydration and drying in a vapor of isopropyl alcohol. Then the plate was subjected to close monitoring in an intensive beam of light when light 60 thousand Lux at a distance of 15-20 cm from the surface of the glass. A glass plate having no surface defects such as scratches, Latin, points, Neopalimovsky and others, is directed to repeated washing and form a party for applying a masking layer of chromium in compliance with the requirements of the electronic vacuum hygiene by dust, temperature and humidity in the room where the vacuum sputtering installation.

Download glass plates are produced in a clean box on polictial, which is then placed in a vacuum chamber. Preparation of chromium conduct PE is alaway it in a tungsten boat at a temperature of 2000-2100° In an argon atmosphere at a residual pressure of 400 mm Hg In the evaporator of molybdenum is placed purified sample of chromium, and the evaporator is installed in a vacuum chamber. Walls lined with aluminum foil to facilitate subsequent cleaning. Before spraying, hold the vacuum chamber to a residual pressure of 1·10-6mm Hg, heated walls of the chamber up to 80°C and maintained at these conditions for 30 minutes and Then the chamber wall is cooled to room temperature, establish a uniform stream of nitrogen so that the pressure in the chamber was 1·10-4mm Hg, include heating of the evaporator, uniformly increase the temperature of the evaporator to the 1800°C for three minutes, after which the temperature rise is halted for 30 seconds, increase the temperature up to 1900°so that the rate of condensation of chromium on glass plates was constant and equal to 150 Å/min, the process continues until the optical density on the plates of the desired value (typically, 2,5-2,8 UNED). Controlling the rate of condensation of chromium and the increase in optical density is carried out by special devices and sensors installed in the system. Then, without switching off the heater, gradually reduce the temperature of the source within three minutes and turn off the heater, withstand crashes-auto St is t installation for 15 min, spend the depressurization of the vacuum chamber and unload plates. Control plates hold the control defects, and other parameters. Defects in the control punctures size of 1.0 μm or more was 0.08 Def./cm2and the reflection coefficient of the surface chromium - 30%.

Other data in comparison with the prototype shown in the table.

The table shows that the control defects from 1.0 μm, and more defections plate, obtained by the proposed method is less than three times, and the reflection coefficient is fixed in the desired interval: <25% - low, 25-40% - medium, >40% - high.

1. The method of obtaining FOTOSALON workpieces, comprising machining the glass plates, the processing in aqueous solutions of chemicals when exposed to ultrasound treatment in a neutral aqueous medium, dehydration and drying of a vapor of isopropyl alcohol (IPA), placing the glass plate on polictial in the vacuum chamber, the mounting of the evaporator, the vacuum chamber by heating its walls, applying a masking layer of chromium by heating the evaporator with chromium in the atmosphere of nitrogen to achieve the desired optical density, the cooling chamber and razukrashivanie her, cleaning of chrome plates, application of resist and control, characterized in that the additional to the deposition of the masking layer conduct cleanup of chromium by melting it at a temperature of 2000-2100° And a residual pressure of 400-450 mm Hg in the atmosphere of argon, cooled to room temperature, heat the evaporator with the speed of 500-700°min until the temperature 1750-1850°With, maintain within 25-35, heat the evaporator to 1860-1950°and sprayed chrome with speed of 140-160 Å min up to the desired optical density.

2. The method according to claim 1, characterized in that the chromium plating is carried out at a residual pressure of (0,5-1,5)·10-4mm Hg

3. The method according to claim 1, characterized in that the chromium plating is carried out at a residual pressure of (1,5-2,5)·10-5mm Hg

4. The method according to claim 1, characterized in that after reaching the desired optical density of the mask layer is additionally applied a layer of chromium oxide with a thickness of 200-300 Å.



 

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