FR2516911A1 - LOW TEMPERATURE REDUCTION PROCESS FOR PHOTOMASKS - Google Patents

Abstract

GLASS PHOTOMASKS, CARRYING A HIGH RESOLUTION IMPREGNATED DESIGN AND INTENDED TO BE USED IN PHOTOLITHOGRAPHIC MANUFACTURING OPERATIONS, ARE PREPARED BY MIGRATION OF STAIN-FORMING IONS BY IMPREGNATION INTO THE SURFACE OF A GLASS SUBSTRATE AND AGGREGATION AND BY REDUCTION OF THESE STAIN FORMATORS BY IMPREGNATION IN THE PRESENCE OF PURE HYDROGEN UNDER PRESSURE, AT RELATIVELY LOW TEMPERATURES, IN ORDER TO OBTAIN A HIGH RESOLUTION IMPREGNATED DRAWING. LARGE GLASS PHOTOMASKS, BEARING A HIGH RESOLUTION IMPREGNATED DESIGN AND INTENDED TO BE USED IN PHOTOLITHOGRAPHIC MANUFACTURING OPERATIONS, ARE PREPARED BY MIGRATION OF STAIN-FORMING IONS BY IMPREGNATION IN THE SURFACE OF A GLASS SUBSTRUCTION AND SUBSTRUCTION AGGLOMERATION OF THESE STAIN-FORMING IONS BY IMPREGNATION IN THE PRESENCE OF PURE HYDROGEN UNDER PRESSURE, AT RELATIVELY LOW TEMPERATURES, IN ORDER TO OBTAIN A HIGH RESOLUTION IMPREGNATED DESIGN.

Description

The present invention generally relates to the technique for producing

  drawings by impregnation in glass and, more precisely, the conditions to be applied for the reduction and the agglomeration of the cations producing impregnation spots in a photomask drawing at high resolution.

  Photomasks are used in photolithographic processes

  phiques for printing wiring diagrams of electrical circuits

  triques and other high precision items manufactured by.

  photogravure In a typical photolithographic process, a substrate is covered with a layer of photoresist material, on which a photomask is superimposed.

  a drawing of opaque and transparent areas with respect to a rayon-

  actinically, typically ultraviolet light, which is passed through the photomask in order to reproduce the design in the photoresist material The design is developed in the form of an image in relief in the photoresist material, by making use of different solubilities of the exposed parts and

  unexposed photoresist material.

  Having regard to the fact that the preparation of a photomask requires

  a lot of time, manpower and materials, it is often

  It is also desirable that a photomask be sufficiently durable to be able to be used repeatedly in the manufacture of objects produced by photogravure. It is also desirable to obtain a maximum resolution of the design that a photomask carries, in order to improve the accuracy image that this one produced by transfer on

  objects produced by photogravure.

  Photolithographic processes have used

  photomasks constituted by a sheet of glass carrying a coating

  chrome, iron oxide or photographic emulsion corresponding to the drawing to be reproduced Admittedly, chromium and iron oxide films are much more durable than photographic emulsions, but all photomasks produced with a coating layer are subject to scratching and other mechanical damage which shortens their useful life.Also, the acid etching necessary to produce a desired design in chromium or iron oxide films results in loss of resolution. as a consequence of the acid attack factor, i.e. the fact that a groove produced by attack at

  the acid develops more in width than in depth.

  Photomasks of improved durability, formed by an impregnation pattern inside a glass substrate, are described in US Pat. Nos. 3,573,948 (Tarnopol) and 3,732,792 (Tarnopol et al) Admittedly, photomasks of impregnated glass have improved durability, but the phase of formation of a design by acid attack through a layer impregnated with glass in the first case or the phase of acid attack through a coating of tin oxide in the second case results in insufficient resolution for certain applications. US Patent No. 3,561,963 (Riba) describes a photomask of glass formed by impregnation, the desired design being engraved with acid in a copper film on a glass substrate, after which it causes the migration of copper ions in the glass

  by heating Certainly, the design of the photomask formed by

  gnation is more durable than a coating, but the resolution is compromised in this process, as a result of the acid attack of the film and the migration phase which gives rise to a lateral propagation of the impregnated zones in the zones

contiguous impregnated.

  U.S. Patents Nos. 2,927,042 (Hall et al) and 3,620,795 (Kiba) describe methods designed to minimize the lateral diffusion of impregnating ions into

  aforementioned processes The Hall patent proposes to deposit a film

  fumes from a metal producing stains by impregnation on

  glass and to remove parts of the film by photoengraving.

  An electric field is then passed through the glass, so that the drawn film migrates into the glass substrate. The Kiba patent proposes to engrave a design in a metal film and to migrate spot-forming ions by impregnation with through openings in the metal film, by heating in an electric field These two methods have the disadvantage of a loss of resolution, due to the etching phase. US Pat. Nos. 2,732,298 and 2,911,749 Stookey) both describe the production of an image impregnated in a glass plate, by heating a photographic emulsion containing silver and developed on glass But the application of relatively high temperatures, 400 to 65020, results in a loss of resolution of the pattern formed by impregnation and the optical density that it is possible

  getting is not as high as it may be necessary.

  U.S. Patent No. 4,155,735 (Ernsberger) describes an improved process for the manufacture of glass photomasks

  impregnated The process comprises the operations of developing

  lopper a photoresist layer drawn on a substrate of

  glass and apply an electric field to accentuate the migra-

  tion of stain-forming ions by impregnation into the surface of the glass substrate, through openings in the drawing of

  photoresist The stain-forming ions by impregnation

  gnation are then reduced and agglomerated to form a design

  impregnated into the glass surface, by heating the glass in advance

  sence of a reducing agent such as tin or copper ions or in a reducing atmosphere such as a molding gas, preferably at a temperature of 400 to 5002 C. In United States patent N 2 4 309 495, Ernsberger describes the making of drawings of photomasks of glass impregnated by exposure and development of a photographic emulsion on a

  glass sheet and migration of silver ions, from emulsion

  sion, in the glass surface, under the influence of an electric field

  at a moderately high temperature These silver ions

  are then reduced and agglomerated to form an imprint pattern.

  generation inside the glass surface, by maintaining the

  glass at a high temperature in the presence of a reducing agent.

  The reducing agent can be constituted by reducing ions, for example copper ions introduced by migration into the glass, or stannous ions which are inherently present

  near the surface of glass produced by the process of.

  float, in which case an optimized speed can be obtained at a temperature of the order of 475 to 5252 C: In another possible embodiment, the reducing agent can be a reducing atmosphere, such as molding gas, in the heating chamber during the reduction and agglomeration heat treatment, in which case practical speeds can be obtained at lower temperatures, of the order of 350 to 4 1000 C. A microscopic examination of drawings obtained by impregnation in glass photomasks prepared according to the processes

  above shows that the edges of the drawing are slightly blurred.

  Exploration with a microdensitometer shows that the optical density profile of such an edge is sloping, the passage from maximum to minimum density extending over a distance as large as 15 microns (about 0.006 inches) This sloping profile is

  known as the "roll-off region".

  The ideal optical density profile of an edge, which could be 8

  deduced as a perfect definition of the edge, would be rectangular

  re For certain applications, such as photomasks

  for use in the silicon integrated circuit industry

  cium, drawing lines of only 5 to 10 microns are required

  Therefore, the definition of the edges must be very good. A rolling region of 1 micron in width can be

the upper tolerable limit.

  A microscope examination of drawings obtained by impregnation in glass photomasks prepared according to the methods

  piecities also shows that when the reduction and agglomeration-

  tion of stain-forming ions by impregnation are carried out in an atmosphere of molding gas at high temperature, the impregnation design contains a large proportion of the impregnation ions reduced in an over-agglomerated form; that is to say in the form of typically spherical particles of size corresponding to the resolving power of the microscope This

  method of making an impregnation design is therefore ineffective

  effective to a certain extent, because impregnation particles having such dimensions contribute very little to the strip

  absorption of ultraviolet rays, which is produced mainly

  palement by the resonance absorption of light by particles of submicroscopic colloidal dimensions We can appreciate the extent of this ineffectiveness by considering that a single spherical particle of one micron in diameter would contain, for example, enough silver to give a million

  particles of the preferred diameter, namely 0.01 microns Thus, a.

  given amount of silver per unit area will provide absorption

  much larger bench * (optical density) in the spec region

  desired amount of ultraviolet radiation, if agglomeration is carried out under conditions which give rise to particles

subai croscopic.

  The present invention relates to making drawings

  high resolution agglomeration in a glass substrate.

  According to the present invention, stain-forming ions by impregnation are electrically caused to migrate in the glass at a relatively low temperature (around 2009 C), as in the case of the previous methods However, instead of reducing and d '' agglomerate the spot-forming ions by impregnation at a relatively high temperature, in the presence of reducing agents such as cuprous or stannous ions or in

  an atmosphere of molding gas as in the previous processes

  laughing - the present invention provides for the reduction and agglomeration

  meration of the spot-forming ions by impregnation in pre-

  sence of pure hydrogen under superatmospheric pressure Temperatures in the same range as the temperatures applied during the electromigration of the stain-forming ions by impregnation, for example from 150 to 200 C, are sufficient to produce impregnation patterns at high resolution in the

  glass, when using pure hydrogen as a reducing agent

  pressure at pressures above atmospheric pressure, for example from 10 to 100 bars, during a compatible duration

with the demands of practice.

  The present invention also relates to the production of high resolution impregnation patterns in a large substrate.

  glass According to the present invention, ta- forming ions

  Ches by impregnation are led elé rically to migrate in the glass at relatively low temperatures (around QC), as in the case of previous processes However, instead of reducing and agglomerating the stain-forming ions by impregnation at a relatively high temperature, in the presence of reducing agents such as cuprous or stannous ions or in

  an atmosphere of molding gas as in the previous processes

  laughing - the present invention provides for the reduction and agglomeration

  meration of the stain-forming ions by impregnation in a pressure-holding container which contains an inert liquid saturated with hydrogen under pressure Temperatures in the same range as the temperatures applied during the electro-migration of the stain-forming ions by impregnation, typically from 150 to 20,000, are sufficient to produce impregnation drawings

  high resolution in the glass, when using hydro-

  gene in an inert liquid as a reducing agent, at pressures above atmospheric pressure, preferably pressures of up to about 10 bars, The cited reference documents illustrate the development of methods for making durable impregnation patterns in glass photomasks However, certain photolithographic processes require drawings with high resolution, formed of lines whose width is only 5 to 10 microns and

  which have a very clear definition of the edges.

  It was discovered that although the drawing of impregnated ions-

  tion injected is very clear initially, the definition of the edges deteriorates during the reduction and the agglomeration at high temperature of the impregnation ions, carried out to produce the design of the photomask It has been discovered that the main reason for this alteration of the definition of the edges of the design is the random diffusion of the stain-forming ions by impregnation during the first stages of the reduction treatment the stain-forming ions by impregnation which are not yet reduced and incorporated into a particle design colloids diffuse in all directions, in particular in lateral direction, that is to say in a plane parallel to the surface Thus, a certain share of the spot-forming ions by impregnation

  diffuse outside the desired limits of the design, before

  counter a reducing agent and be converted to particles of im-

relatively immobile pregnation.

  Another factor that can have a detrimental influence on

  the definition of the edges is the injection of too large a quantity

  tee-forming ion ions by impregnation during the

  electro-migration phase The intense electric field inside

  laughing glass tends to suppress any lateral movement of the stain-forming ions by impregnation, at the moment when these are injected into the glass However, the electric field is not really unidirectional at all times after the injection of Impregnation stain forming ions started, since the region of the glass in which sodium ions have been replaced by impregnation stain forming ions has a significantly higher resistance than the rest, which results in the development of a Parasitic dispersion field diverges at the edges of the design As a result of this parasitic dispersion field, the injection profile of the spot-forming ions

  by impregnation is probably trapezoidal The characteristic angle

  tick of this trapezoid is not known, but it could reach degrees If this is the case, the edge of the design will be displaced by 1 micron for each micron of injection depth Consequently, we can improve the definition of the edges by limiting the injection depth of the spot-forming ions by

  impregnation, preferably less than 1 micron.

  The propagation by diffusion of the form ions can be reduced

  stain matters by impregnation by performing the operations

  reduction and agglomeration at lower temperatures.

  However, the reduction speed would be reduced proportionately.

  The compensatory increase in the time required for the reduction-

  tion would give more time for propagation by diffusion,

  which would negate the benefits of lowering the temperature.

  re In fact, it has been found that this logical consequence manifests itself in practice when the stain-forming ions by impregnation are reduced by reducing ions such as

  than tin or copper in the surface layer of glass.

  On the other hand, it has been discovered, according to the present invention, that if the reducing agent is pure hydrogen, there is an appreciable net benefit from the lowering of the treatment temperature,

  especially if the pressure is high.

  This benefit, derived from the use of pure hydrogen as a reducing agent at low temperature, can be explained by the nature of the diffusion of hydrogen in the glass. The activation energy for the penetration of hydrogen into glassy silica is, as we know, from 7 to 8 kcal (29 to 33.5 k J) per atrore gram, while the activation energy for silver ions for example is at least 35 kcal per atom -gram According to a principle of

  physico-chemistry, the temperature coefficient of an active process

  vé is in exponential relation with the energy of activation of this process Consequently, the speed of diffusion of the money

  drops rapidly as the temperature drops,

  almost negligible at 15020, while the diffusion of hy-

drogen declines relatively little.

  In spite of the low activation energy, the transport of hydrogen in the glass is inherently slow, due to

  the low solubility of hydrogen in glass We can increase

  ter the concentration of dissolved hydrogen, at levels valid for the reduction of spot-forming ions by impregnation with a view to the formation of photomask patterns according to the

  present invention, using pure hydrogen at pressures

  above atmospheric pressure In addition, the use of

  sation of spot-forming ions by impregnation according to the

  present invention is sufficiently effective that the depth

  injection time of these ions can be limited to 1 micron or

  less There is a great deal of latitude in the choice of

  operating whites which will give high resolution photomask designs in glass substrates according to the present

  invention, but one can indicate, among other conditions

  rees, temperatures below 3002 C, preferably below

  lower than 20020, and pressures significantly higher than atmospheric pressure, preferably greater than 10 bars and

  notably more than 7 Obars (1000 p s i approximately).

  There is a great deal of latitude in the choice of variables

  which will give drawings of photomasks to be resolved

  high tion in large glass substrates according to the present

  INVENTION The preferred conditions are in particular temperatures

  res less than 3002 C, preferably less than 20020, and

  pressures well above atmospheric pressure.

  While pressures from 10 to 100 bar can be reached easily and safely for relatively small substrates, the problems of building a large autoclave capable of withstanding such pressures, as well as the safe handling of large ones quantities of hydrogen under such pressure are not negligible The present invention eliminates these problems, while still achieving effective reduction and agglomeration of staining ions by impregnation using hydrogen under pressure

  as a reducing agent According to the process of the present invention

  Note, large substrates are placed in a large pressure-holding container which is filled with an inert liquid saturated with hydrogen under pressure. Reduction and agglomeration of stain-forming ions by impregnation can be carried out effectively at temperatures moderate, below 3002 C and preferably below 2009 C and under pressures which

can reach the Obars approximately.

  The glass compositions which are suitable for photomask substrates according to the present invention are those which

  contain mobile cations capable of being brought electrically

  only to migrate at moderate voltages, to create sites in which the stain-forming cations by impregnation can be injected the ions of alkali metals, such as sodium, potassium and lithium, have a relatively large mobility in the glass. therefore particularly the glasses which comprise at least minimal proportions of alkali metal oxides For example, the conventional compositions of soda-lime-silica glass typically contain 10 to 13% in

  weight approximately sodium dioxide and traces of potassium oxide, -

  which represents a more than sufficient source of mobile cations

  Other glass compositions, having lower concentrations

  alkali metal oxides, can also be used

  in the context of the present invention, the only limitation being the ability to create an impregnation pattern having a density sufficient to mask the actinic radiation which

  will be used in a later photolithography operation.

  photoresist materials which are suitable according to the

  present invention can be defined as poly-

  mothers who, exposed to actinic radiation, typically ultraviolet light, develop areas that are soluble

  in a particular solvent and other areas that are insoluble.

  When exposed to this particular solvent, the soluble areas are eliminated, leaving a pattern of openings in the photoresist layer, through which the stain-forming ions by impregnation can migrate. Among other particular examples of photoresist materials available commercially available for the present invention, the LSI-195 Photoresist sold by the Philip

  At Hunt Company, the KPR and EFTR Photoresists sold by the East-

  man Kodak Company and the AZ-ll and AZ-1350 J sold by the

Shipley Company.

  It The layer of stain-forming ion by impregnation can be applied as a compound of one or more stain-forming cations by impregnation, having a relatively low electrical conductivity, or in the form of a metallic film, by application of classic coating techniques

  such as evaporation, spraying, chemical deposit

  wet mique and other known techniques.

  Preferably, the migration of the spot-forming ions by impregnation in the surface of the glass is carried out by the application of electrically conductive layers on the two faces of the substrate and the application of an electrical potential therebetween. The electrically conductive layers are preferably made of colloidal graphite which can be applied to the substrate in the form of an aqueous or alcoholic slurry or by

  spray as an aerosol.

  The application of an electric field between the electric layers

  trodes cause the mobile alkali metal cations to penetrate deeper into the glass substrate, while causing the injection of stain-forming ions by impregnation into the glass, into the spaces left empty by the displacement of the alkali metal cations The speed of ion migration is determined by the applied voltage and the temperature At the

  ambient temperature, the ion migration speed is relatively

  tively slow; for this reason, high temperatures, preferably higher than about 1002 C, are preferred, in order to obtain reasonable times for migration of the ions to a potential.

  several hundred volts.

  After the stain-forming ions by impregnation

  have been caused to migrate electrically into the glass

  desired size, preferably 1 micron or less, the development of the optical density in the ion migration zones is obtained by heating the glass substrate in the presence of a reducing agent, in order to reduce the stain-forming ions by impregnation in their elementary state and then agglomerate the

  metal atoms in a submicroscopic crystal form.

  With small substrates, these operations are carried out, according to the present invention, in an atmosphere of pure hydrogen at a relatively low temperature, preferably below 30020 and especially below 20020, at a pressure above atmospheric pressure, preferably of the order of 10 to 100 atm. With large substrates, these operations are carried out, according to the present invention, in the presence of an inert liquid saturated with hydrogen, at a relatively low temperature, preferably less than 30,000 and in particular less than 200 OC, at a pressure higher than atmospheric pressure, preferably around

from 2 to 10 bars.

  Numerous ion-forming spot systems by impregnation

  generation and photoresist materials suitable for

  of the present invention For example, direct-

  a photoresist on the glass substrate, create a pattern in this photoresist, then apply a layer of stain-forming ions by impregnation on the photoresist. In another possible embodiment, a layer of stain-forming ions by impregnation can be

  deposited on the surface of the glass and a drawing of photo material

  resistant can be created over different systems are

  discussed in detail in U.S. Patent No. 2,455,735.

  In the preferred embodiment of the present invention, a high resolution impregnated glass photomask is prepared by developing a photographic emulsion containing silver on a glass substrate and by migrating silver into the glass from the developed photographic emulsion Silver ions migrate into the glass, displacing mobile cations which migrate deeper into the glass substrate The silver ions which have migrated are then reduced to the elementary state and agglomerated into submicroscopic crystals inside the glass, to give an impregnation pattern, by heating in the presence

  of hydrogen under pressure according to the present invention.

  photographic sions which are suitable for the production of

  drawings of photomasks of glass impregnated in this embodiment

  sation of the invention are those which it is possible to develop

  to form a residual layer of emulsion and silver or ha-

  silver housing, having sufficient electrical conductivity to allow electro-migration of silver ions into the glass substrate from the emulsion The emulsion must also have

  a high resolution capacity, so that one gets a

  sin of high resolution photomask.

  Ordinary photographic techniques are used to expose and develop the photographic emulsion. The glass substrate carrying a photographic emulsion film is exposed to actinic radiation through a master image to form a latent image, which is then developed in

  the photographic emulsion by exposure to developed solutions

  appropriate patrices One can develop on the substrate, either a positive image, or a negative image, according to the type of

  the photographic emulsion used in the development operation

  is lying. The electric field used to cause the migration of silver ions, from the developed photographic emulsion,

  in the underlying surface of the glass is preferably sufficient

  intense enough to produce the migration of the quantity necessary

  silver ion within a reasonable time, but weak enough to avoid arcing around the

  edges of the glass substrate, between the anode and cathode layers

  Typically, voltages from 50 to 1000 volts, preferably from 200 to 700 volts, are sufficient at temperatures of approximately 100 to 30020 In order to obtain maximum resolution of the design according to the present invention, the depth of migration of the ions silver is preferably limited to 1 micron or less, which is

  sufficient, having regard to the reduction and agglomeration efficiency

  tion of the spot-forming ions by impregnation, in the presence of pure hydrogen or of an inert liquid saturated with hydrogen under

  pressure according to the present invention The inert liquid, that is

  that is to say chemically inert with respect to molecular hydrogen under the temperature and pressure conditions of the present invention, is preferably a hydrocarbon or a fluorinated carbide having a vapor pressure of less than 1 bar at temperature

  reduction and agglomeration of the present invention.

  Once a sufficient amount of ionic silver has been caused to migrate through the glass substrate to the desired depth, the impregnation pattern is created by

  reduction of silver ions in elementary state and by agglomeration-

  tion in submicroscopic crystals, by heating in the presence

  pure hydrogen under pressure While temperatures above

  about 4000 C are generally necessary for the reduction and agglomeration processes to take place in an ambient atmosphere, and that temperatures on the order of 550 to 40020 are necessary for the reduction and agglomeration processes to take place. take place in an atmosphere of molding gas, the use of pure hydrogen under pressure as a reducing agent according to the present invention allows the reduction and agglomeration of the silver to take place at temperatures below 3002 C and, preferably , lower than 2000 C, in order to obtain a maximum resolution of the design of photomask formed by impregnation At temperatures and pressures according to the present invention, it is possible to obtain a density of at least 2.0 with respect to ultra rays - violets in a period from 2 to 12

  hours approx. For large substrates, the presence of a liquid

  inert saturated hydrogen under pressure as a reducing agent

  according to the present invention allows that the reduction and the agglo-

  silver transfer take place at temperatures below 30020 and, preferably, below 20090, in order to obtain a

  the maximum resolution of the photomask design formed by impregnating

  at temperatures and pressures according to this in-

  vention, we can obtain a density of at least 2.0 with respect to

  ultraviolet rays in about 4 to 6 hours.

  The present invention will be better understood using the

  description which follows of specific examples.

Example I

  A commercial production photomask, formed on a Kodak high resolution emulsion plate in square shape, measuring 2.5 inches (6.35 cm approximately) by side and 0.060 inches (1.5 mm approximately) thick, was coated by immersion in a

  Acheson DAG R 115 7% solids suspension (graphi-

  te colloïdal in 1,1,1-trichloroethane) and baked for 5 h at 2602 C The front and rear coating layers were separated electrically by elimination on all four edges, then the plate was placed in a forced circulation oven of air at 1812 C. The coating layer on the surface bearing the design being connected as an anode and the coating layer of the opposite surface being connected as a cathode, the electrical treatment was carried out, the applied voltage starting at 200 volts, then rising at a constant speed to reach 290 volts at the end of the treatment, 70 minutes later The coating layers were detached from the plate by means

  of a dilute aqueous solution of hot alkali.

  was created by processing the plaque in a container

  holding pressure, filled to 600 p s i (42 bars) (at room temperature

  ambient temperature) of pure hydrogen, for 14 hours at 1822 C La

  optical density of the resulting design, measured with a microdensi-

  Macbeth TD 504 tometer using an ultraviolet filter M 18 (Corning Glass Works), was 2.84 to 2.94 The sharpness of the edges was such that the smallest elements of the drawing, lines and spaces 8 microns wide, were resolved without region

  of rotation perceptible at 200 X optical magnification (resolved

approximately 1 micron).

Example II

  A pattern is developed in a layer of photoresist-W material resistant on a glass substrate The surface of the glass substrate coated with photoresistive material is brought into contact, at a temperature of about 1602 C, with a bath of molten salt which is a eutectic mixture of silver nitrate and potassium nitrate approximately 0.04 mg of silver ion per cm 2 of surface of the

  glass are injected to a depth of about 0.4 microns

  ron by electro-migration The silver ions are reduced and agglomerated to form an impregnation pattern in the surface

  glass, by treatment in pure hydrogen at 800 p s i.

  (56 bars approx.) For 4 hours at 1600 C The imprint drawing

  generation has an optical density of about 2.5 with respect to a ray-

  ultra-violet nemenit of approximately 400 nm wavelength The impregnation pattern has a reddish amber shade, color

  characteristic of a narrow absorption band linked to small

  your silver particles (less than 10 nm) -

Example III

  A test sample, cut from a photomask of pro-

  duction measuring 22 x 28 x 0.190 inches (56 x 71 x 0.5 cm approximately) after electro-migration treatment, but before reduction, is placed in a 4 ounce (113 cm 3) wide-mouth glass bottle and add Gulf DXE R fluid (transfer fluid from

  commercial heat, di-orthoxylyl-ethane) Until me-

* half the length of the sample is immersed in the liquid.

  The open bottle, containing the sample and the liquid, is

  placed in a container holding the pressure of 1 liter (Parr Ins-

  trument Company, No 4611) The container is purged of air by filling twice with molding gases up to 500

  p.s i (35 bars) and expansion twice at am pressure

  biante; then the container is put under a pressure of 360 p s i <

  (About 25 bars) with pure hydrogen and it is closed, her-

  The container is then heated to 1800 C for 14

  hours The pressure inside the container is 460 p s i.

  (32 bars approximately) as a result of heating The measurements carried out on the sample after the completion of this treatment give an optical density to the ultraviolet of 3.21 in the part of the surface which was submerged in the oil , and 3.05

  in the part put only in contact with hydrogen gas.

  The optical density in the visible region of the spectrum (defined by a Wratten 106 filter) is 0.95 in the submerged part and

  0.90 in the rest of the sample The shade is amber red 2-

  be dark Examination with a microscope of the impregnation pattern at x, with a resolution of approximately i micron, does not reveal any observable "rolling" region The properties of the fluid are unchanged An identical sample, treated in molding gases for 3 hours at 34320 C, has an optical density at ultra-

  tra-violet of only 2.30 and an olive-green appearance at sight.

  An examination of the complete absorption spectra for the two impregnation drawings shows that they both have a maximum absorption in the region around 400 nm, but that

  the absorption band of the design produced at a higher temperature

  is larger, which is linked to the fact that a large

  variety of silver particle sizes is present.

Example IV

  Glass substrates, having a latent image formed

  by electro-migration of silver ions, are placed in an autoclave

  ve welded in ordinary mild steel Most of the space

  remaining in the autoclave is filled with paraffin oil.

  Hydrogen is introduced to establish a pressure of approximately bars at 18020 After 12 hours, the glass photomask bears an impregnated bore, having a density of approximately 2.0 with respect to ultraviolet radiation This dersity is comparable

  to that obtained after 3 hours of reduction and agglomeration

  meration in molding gases at 4000 C, temperature at which edge definition is compromised by lateral diffusion

  silver ions forming stains by impregnation.

  The above examples are given to illustrate the

  present invention Various spot-forming ions by impregnation

  gration, various photoresists, various temperature and pressure conditions can be used Different other inert liquids can be used, including

  l, l-di- (orthoxylyl) -ethane, mineral oil and fluoro carbs

  res Other stain-forming ions by impregnation and a wide range of treatment times, temperature and pressure

  can be chosen, the only limit being set by the resis-

  tance of the container holding the pressure and by the necessary resolution of the impregnation drawing The scope of this

  invention is defined by the claims which follow.

Claims (16)

CLAIMS O NS   1 Method for producing a design by impregnation in a glass substrate, comprising the operations consisting in injecting stain-forming cations by impregnation into a surface of a glass substrate and in heating the glass in the presence of an agent reducer for reducing and agglomerating the stain-forming cations by impregnation and thus producing a design by impregnation inside the glass surface, characterized in that pure hydrogen is used under pressure in as a reducing agent.   2 Method according to claim 1, characterized in that the stain-forming cations by impregnation are chosen from   the group consisting of silver, copper, gold and thallium.   3 Method according to claim 1, characterized in that   the operation of injecting spot-forming ions by impregnation   generation in the glass surface is performed at a temperature   from 100 to 200-C in the presence of an electric field.   4 Method according to claim 1, characterized in that the stain-forming ions by impregnation are injected into the   glass surface to a depth not exceeding 1 micron.   î Process according to claim 1, characterized in that the reduction and agglomeration operation of the stain-forming ions by impregnation is carried out in the presence of pure hydrogen under a pressure higher than 10 bars and at a temperature lower than 3002 C . 6. Method according to claim 5, characterized in that the operation of reduction and agglomeration of the stain-forming ions by impregnation is carried out in the presence of pure hydrogen at a pressure greater than 1000 psi (approximately 70 bars) at a temperature below 2000 C.   7 Manufactured object prepared according to the process of the resale   cation 1, characterized in that the impregnation pattern has a   optical density of at least 2.0 with respect to ultra- purple.   8 Manufactured object, comprising a transparent glass substrate   rent and, inside this glass substrate, a pattern of stain-forming metal by impregnation, characterized in that the transition ("rolling") region of the edges of the pattern does not no more than 1 micron in width.   9 Object according to claim 8, characterized in that the stain-forming metal by impregnation is silver and in this   that the penetration depth of silver from the over-   side closest to the glass is not more than 1 micron.   10 Object according to claim 9, characterized in that the optical density of silver is at least 2.0 with respect to the ultraviolet radiation.   11 A method for producing a pattern by impregnation in a glass substrate, comprising the steps of injecting stain-forming cations by impregnation into a surface of a glass substrate and heating the glass in a present reducing agent for reducing and agglomerating stain-forming cations by impregnation and thereby producing a pattern by impregnation inside the glass surface, characterized by the improvement of heating the glass in a pressure-holding container which contains a liquid   inert saturated with hydrogen under pressure.   12 Method according to claim 11, characterized in that the stain-forming cations by impregnation are chosen from   the group consisting of silver, copper, gold and thallium.   13 Method according to claim 11, characterized in that   the operation of injecting spot-forming ions by impregnating   tion in the glass surface is performed by applying an electric field at a temperature between 100 and 200 QC about.   14 Method according to claim 11, characterized in that the stain-forming ions by impregnation are injected into the surface of the glass to a depth which does not exceed l micron.   IL Method according to claim 11, characterized in that the reduction and agglomeration of the forming ions   of stains by impregnation is carried out at a lower temperature   less than 30090 and under a pressure of 2 to 10 atm approximately.   16 Method according to claim 11, characterized in that the inert liquid is chosen from the group consisting of hydrocarbons and fluorinated carbides having a pressure of   steam of less than lbar at temperatures up to approximately 3000.   17 Manufactured object prepared according to the process of the resale cation 11.   18 Manufactured object prepared according to the process of the claim cation 14.   19 Object according to claim 18, characterized in that the ion   impregnator of stains is silver.   Object according to claim 19, characterized in that the impregnation pattern has an optical density of at least 2.0 to   respect for ultraviolet radiation.