WO2006037153A1 - A mask and a method for treating a substrate with a material flux to deposit or remove a layer having a predetermined thickness profile - Google Patents

A mask and a method for treating a substrate with a material flux to deposit or remove a layer having a predetermined thickness profile Download PDF

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Publication number
WO2006037153A1
WO2006037153A1 PCT/AU2005/001503 AU2005001503W WO2006037153A1 WO 2006037153 A1 WO2006037153 A1 WO 2006037153A1 AU 2005001503 W AU2005001503 W AU 2005001503W WO 2006037153 A1 WO2006037153 A1 WO 2006037153A1
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WO
WIPO (PCT)
Prior art keywords
mask
apertures
flux
substrate
aperture
Prior art date
Application number
PCT/AU2005/001503
Other languages
French (fr)
Inventor
John Arkwright
Original Assignee
Commonwealth Scientific And Industrial Research Organisation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from AU2004905710A external-priority patent/AU2004905710A0/en
Application filed by Commonwealth Scientific And Industrial Research Organisation filed Critical Commonwealth Scientific And Industrial Research Organisation
Publication of WO2006037153A1 publication Critical patent/WO2006037153A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/04—Coating on selected surface areas, e.g. using masks
    • C23C16/042—Coating on selected surface areas, e.g. using masks using masks
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/04—Coating on selected surface areas, e.g. using masks
    • C23C14/042—Coating on selected surface areas, e.g. using masks using masks
    • C23C14/044—Coating on selected surface areas, e.g. using masks using masks using masks to redistribute rather than totally prevent coating, e.g. producing thickness gradient
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
    • C23C16/52—Controlling or regulating the coating process

Definitions

  • the present invention broadly relates to a mask and a method for treating a substrate with a material flux to deposit or remove a layer having a predetermined thickness profile.
  • Films having a predetermined thickness profile are used for a variety of applications.
  • films of uniform thickness are often required for fabrication of electronic devices.
  • These films may be composed of insulating materials and may have an insulating function. Alternatively they may be formed from semi-conducting or electrically conductive materials .
  • electronic devices having a very small scale such as a sub-micro or nano-scale, often require such layers.
  • Specific examples include integrated devices having tunnelling junctions in which a tunnelling current critically depends on a thickness of an insulating layer.
  • hard disc devices require layers of uniform thickness and there is a range of other devices which semi-conductor industries produce or plan to produce and for which uniformity of layer thickness is of critical importance.
  • optical applications such as applications in which interference conditions are important, often require films having a uniform film thickness or films having a predetermined thickness profile.
  • extreme UV microlithography which is of great interest for semiconductor and nano- technology, places high demands on the quality of optical surfaces.
  • Thin film deposition systems typically generate a flux of a material which is deposited on a substrate.
  • the thickness profile of the deposited material often is not ideal.
  • Various methods have been employed to improve the uniformity of the deposited films. Examples include methods in which the substrate is rotated during deposition, methods in which a random motion of the substrate during deposition is effected, and/or a shutter is introduced to control the flux as the substrate moves. With these methods it may be possible to achieve thickness profiles that are within approximately 1% of an ideal thickness profile. However, these methods usually require complex vacuum compatible rotation and/or translation stages capable of moving substrates that may weigh many 10's of kg.
  • a mask with apertures may be moved through the flux in a predetermined manner to control the flux.
  • slight misalignments of the apertures in the mask or slight deviations of the mask movement can cause significant imperfections of the thickness profile. Consequently there is a need for technological advancement.
  • the present invention provides in a first aspect a mask for treating a substrate with a material flux to deposit or remove a layer having a predetermined thickness profile, the mask comprising: a plurality of apertures for interfering with a first beam of the material flux in a manner such that a plurality of secondary beams of the material flux are generated which are directed to the surface of the substrate, the apertures being arranged in a plurality of rows and positioned so that portions of apertures of one row are interspaced with portions of apertures of an adjacent row, the interspaced aperture portions having an average width that is smaller than an average width of aperture portions that are not interspaced.
  • the mask is typically arranged so that an oscillatory movement of the mask or the substrate relative to each other results in predetermined distribution of the material flux for depositing or removing the layer having the predetermined thickness profile.
  • the oscillatory movement may be oriented substantially along at least one of the rows of apertures.
  • the rows of the apertures are substantially parallel to each other.
  • the mask according to the first aspect of the present invention has the advantage that small directional errors of the oscillatory movement or small misplacement of the apertures in the mask have a reduced effect on the created surface profile.
  • the interspaced aperture portions typically are sized so that during the oscillatory movement the flux is uniform or changes smoothly in a direction perpendicular to the direction of the movement and across at least one mask region having at least some of the interspaced aperture portions.
  • embodiments of the mask according to the first aspect have the advantage that it may not be necessary to effect large movements of the substrate or the mask.
  • the mask has a fine structure and may comprise a large number of the apertures, such as more than one hundred or more than one thousand.
  • Using such a mask typically only a very small movement, such as a small oscillatory movement, of the mask or the substrate is required to deposit or remove a layer having a predetermined thickness profile.
  • the predetermined thickness profile may be flat and may be the profile of a uniform coating.
  • the predetermined thickness profile may be any other profile including spheric and aspheric profiles.
  • a substrate surface such as the surface for an electronic or optical device, may have an unsatisfactory surface profile that needs correction.
  • the mask may be designed, for example using a suitable computer software routine, having apertures that are shaped, sized and positioned so that a desired material flux is achieved that corrects the surface profile either by depositing or removing a layer having the predetermined thickness profile.
  • the mask typically is designed to take into account a non-uniform flux distribution of the primary beam.
  • the surface is a surface for an optical device that has an unsatisfactory phase property.
  • the mask is designed so that the surface treatment using the mask will correct the phase property either by depositing or removing a layer having the predetermined thickness profile.
  • the mask is designed to deposit a film of uniform thickness for an optical device.
  • the surface may be a surface for an electronic device and the mask may be designed to deposit a film of uniform thickness or to treat the surface, either by depositing material or by removing material, to create a predetermined surface profile such as a flat surface profile or any other surface profile.
  • the apertures may have any suitable shape, including circular, oval and polygonal shapes. Throughout this specification the terms “polygonal” , “triangular” and
  • hexagonal are also used for shapes that approximate that of polygons, triangles, and hexagons, respectively, and that have curved side-portions and/or rounded corners.
  • the apertures typically have interspaced end-portions that have a tapered width.
  • the interspaced end-portions may be tapered to a point .
  • Each aperture typically has two such end-portions that form opposite ends of each aperture.
  • the interspaced end- portions may be the triangular end-portions of the hexagonal shaped aperture.
  • each aperture may also have more than two interspaced end-portions.
  • Each aperture typically is shaped so that during substrate treatment and during the oscillatory movement the apertures interfere with the first beam of material flux in a manner so that the generated secondary beams have a flux profile that creates a predetermined surface profile in a direction substantially perpendicular to a direction along the oscillatory movement and along the substrate surface.
  • the rows of apertures may be parallel and the width of the apertures in a direction along each row may be varied so as to control the amount of the flux.
  • the mask typically is arranged for an oscillatory movement which oscillates the mask or the substrate by a distance that corresponds to the pitch P of the mask. Throughout this specification the term "pitch of the mask" is used for a distance by which the mask is oscillated during the treatment.
  • Dl typically equals D2 and the apertures may form a checkerboard-like arrangement.
  • the total aperture area that allows flux to pass through may be relatively large, such as more than 50%, 60%, 70%, 80%, 90% or even nearly 100% of the mask area.
  • the first beam of material flux may be generated using any suitable method including physical and chemical vapour generation techniques such as thermal evaporation effected by resistive heating or by electron beam evaporation, and chemical vapour deposition.
  • the flux may be the flux of a molecular beam or of an ion beam or the flux may be generated using a sputtering source such as a rf or dc sputtering source.
  • the flux may be generated by introducing the material or a precursor of the material in gaseous form into a vacuum chamber and directing the gaseous material or precursor through the mask by differential pumping.
  • the present invention provides in a second aspect a method of treating a substrate to deposit or remove a layer having a predetermined thickness profile using the above-defined mask.
  • the present invention provides in a third aspect a method of designing a mask for treating a substrate with a material flux to deposit or remove a layer having a predetermined thickness profile, the mask having rows of interspaced apertures and the method comprising: selecting a desired distribution of material flux for treating a substrate surface that deposits or removes the layer having a predetermined thickness profile, selecting sizes and shapes for the apertures so that the apertures of the mask positioned in a first beam of material flux would interfere with the first beam of the material flux in a manner such that a plurality of secondary beams of the material flux are generated which together result in the desired flux distribution.
  • the method typically also comprises the step of fabricating the designed mask.
  • the designed mask typically is a monolithic mask and typically is relatively easy to fabricate for example from a sheet of mask material for example using commercially available laser cutting or chemical etching equipment.
  • a profile of the substrate surface may initially be characterised for example using interferometric methods.
  • the substrate surface may have a profile that deviates from a desired profile.
  • the step of selecting the desired flux distribution may comprise selecting the flux having a distribution so that the selected flux would correct the substrate surface profile by depositing or removing the layer having a predetermined thickness profile.
  • the step of selecting shapes and sizes of the apertures typically is conducted so that an oscillatory movement along the rows of the apertures results in the desired flux distribution.
  • This step typically is computer software implemented. Selecting shapes and sizes of the apertures typically comprises performing an imaginary division of a cross-sectional area of the desired flux into a plurality of linear regions which have a length that substantially corresponds to the pitch of the mask and a width that is smaller than an extension of each aperture in a direction perpendicular to the parallel rows of the apertures.
  • the apertures typically have an extension along the length of the linear region that is dependent on an average of the desired flux intensity within that linear region.
  • the present invention provides in a fourth aspect a method of treating a substrate to deposit or remove a layer having a predetermined thickness profile, the method comprising: generating a first beam of a material flux and interfering with the first beam of the material flux using a mask having a plurality of apertures in a manner such that a plurality of secondary beams of the material flux are generated which are directed to the substrate, the apertures being arranged in a plurality of rows and positioned so that portions of apertures of one row are interspaced with portions of apertures of an adjacent row, the interspaced aperture portions having an average width that is smaller than an average width of aperture portions that are not interspaced and moving the mask or the substrate so that the apertures with interspaced end-portions together generate a flux profile that deposits or removes the layer having a predetermined thickness profile.
  • the step of moving typically includes oscillating the mask or the substrate in a direction along at least one row of the apertures.
  • the movement typically is a relatively small oscillatory movement of the mask and the substrate relative to and over each other.
  • Dl typically equals D2.
  • the oscillation is typically of substantially constant velocity in each direction.
  • the oscillatory movement may be effected by a drive or actuator that is positioned inside a vacuum chamber of a deposition system.
  • the oscillatory movement may be effected by a drive or actuator that is positioned outside the vacuum chamber of a deposition system.
  • the material flux of each secondary beam may remove material from the surface. For example, this may involve ion milling.
  • the material flux of each secondary beam may deposit material on the substrate, such as thin film material.
  • the mask is positioned so that a distance between the substrate and the mask is much larger, such as a few ten times, a few hundred or thousand times larger, than a typical distance across one the apertures. Smoothing of the surface profile owing to non- parallel flux trajectories facilitate formation of smooth surfaces. While a point source may be used for surface treatment, a distributed source having non-parallel trajectories is for the above-described reason particularly advantageous. Further, scattering of flux at edges of the mask typically results in additional smoothing.
  • the step of generating the first beam of material flux may comprise any suitable physical and chemical flux generating technique such as thermal evaporation effected by resistive heating or by electron beam evaporation, and chemical vapour deposition.
  • the flux may be the flux of a molecular beam or of an ion beam or the flux may be generated using a sputtering source such as a rf or dc sputtering source.
  • the flux may be generated by introducing the material in gaseous form into a vacuum chamber and directing the gaseous material through the mask by differential pumping.
  • the method may comprise depositing a layer of uniform thickness.
  • the predetermined thickness profile may be non-uniform.
  • the layer that is deposited or removed may correct a surface profile of the substrate.
  • the flux may comprise the material in a pure form or may comprise a precursor for the material and may also comprise a carrier gas. Further, surface treatment may involve generation of more than one first beam.
  • the present invention provides in a fifth aspect a device having a surface treated by the method according to the fourth aspect of the present invention.
  • the device typically is an electronic or optical device.
  • the surface may form a part of an anti-reflection coating or may be a layer of a filter such as a dielectric filter.
  • the surface may be a surface of an optical device for which a surface was treated to correct an unsatisfactory surface profile.
  • the device may be an electronic device such as a computer hard drive and the film may be a coating of the computer hard drive.
  • the device may be an electronic device in which a thin film of uniform thickness, such as a thin film of an insulating material is deposited onto a substrate.
  • the device may comprise the thin film of an insulating material to control flow of electrons between conductive layers which sandwich the thin film of an insulating material .
  • Figure 1 shows a schematic representation illustrating a mask and a method for treating a substrate with a material flux to deposit or remove a layer having a predetermined thickness profile according to a specific embodiment of the present invention
  • Figure 2 shows (a) a surface profile map of a substrate and (b) a mask for treatment of the substrate with a material flux to deposit or remove a layer having a predetermined thickness profile according to a specific embodiment of the present invention
  • Figure 3 shows plots characterising film uniformities for (a) a horizontal film direction and (b) a vertical film direction;
  • Figures 4 (a) to (c) show apertures of a mask according to specific embodiments of the present invention
  • Figure 5 shows (a) a thickness map of a substrate, (b) a thickness profile of the substrate, and (c) a mask and aperture design according to an embodiment of the present invention
  • Figure 6 shows apertures of a mask according to an embodiment of the present invention
  • Figure 7 shows plots characterising a surface profile of an optical device (a) prior to correction and (b) after correction by deposition of a film having a predetermined thickness profile according to an embodiment of the present invention
  • Figure 8 shows plots characterising the surface roughness of the surfaces of the optical devices characterised by the plots shown in Figures 7 (a) and 7 (b) .
  • a mask and a method for treating a substrate to deposit or remove a layer having a predetermined thickness profile is now described.
  • a film having the predetermined thickness profile is created on a substrate by depositing material on the substrate.
  • the illustration 10 shows a flux source 12, a substrate 14 and a mask 16.
  • the substrate 14 and the mask 16 are positioned so that a flux 18 originating from the source 12 is directed through apertures of the mask 16 to the substrate 14 so as to deposit a film on.
  • the source 12 may be any suitable source that emits the flux 18.
  • the source 12 may be a source in which flux material is evaporated.
  • the source 12 may be a part of an electron beam evaporator or may comprise a resistively heated heater. Alternatively, the source 12 may be a source of a directional chemical vapour such as a precursor for the film material. Further, the source 12 may also be a source that emits an ion beam or any other type of directional physical or chemical vapour or the flux may be generated using a sputtering source such as a rf or dc sputtering source.
  • the mask 16 has a plurality of apertures that are positioned in rows and form a checkerboard-like arrangement . During the treatment the mask 16 is oscillated along the rows by the pitch of the mask 16.
  • the pattern of the mask 16 comprises a fine structure having a 1600 apertures but in variations of the embodiment the mask may also comprise any other number of apertures such as a few thousand apertures.
  • Each of the apertures is sized and positioned so as to control the flux 18 penetrating through the apertures of the mask 16 in a manner such that a film having a predetermined thickness profile is deposited on substrate 14.
  • the source 12 of the flux 18 typically has a non ⁇ uniform flux density in a direction or directions across the mask 16.
  • the apertures of the mask 16 are distributed and sized so as to correct for the non ⁇ uniform flux. For example, in areas where flux density is lower, the apertures are larger so as to correct for the locally low flux density.
  • the mask 16 is designed for the deposition of a film having a uniform thickness.
  • the distance between the substrate 14 and the mask 16 is large compared with the average distance across one of the apertures of the mask 16.
  • Figure 2 (a) shows a surface profile of an optical device.
  • the light area 20 is higher than the surrounding darker areas. It is now described how a method according to an embodiment of the present invention can be used to correct this surface so that the difference in height is corrected and the surface uniformity is improved.
  • Figure 2 (b) shows a designed pattern having apertures that are sized and distributed to correct the surface profile shown in Figure 2 (a) so that the surface is substantially uniform.
  • the apertures have a slightly smaller size in an area that approximately corresponds to light area 20 in Figure 2 (a) . Consequently, more film material will be deposited in areas that surround the light area 20 so that the surface characterised by the plot shown in Figure 2 (a) can be corrected.
  • a mask was prepared having the aperture distribution as shown in Figure 2 (b) .
  • the mask (not shown) is composed of a stainless steel sheet but may alternatively be composed of another suitable material such as aluminium, glass, silicon, a ceramics material, a plastics material or any other suitable conductive or non- conductive material.
  • the apertures are formed in the stainless steel mask of the present embodiment using commercially available laser cutting equipment.
  • FIG. 3 (a) shows surface profiles for a horizontal direction for the optical film thickness surfaces before and after correction. Prior to correction the surface uniformity was approximately 3% and after correction the surface uniformity is better than 0.5% in a horizontal direction.
  • Figure 3 (b) shows a corresponding profile measurement for a vertical direction. In this case the surface uniformity is better than 0.3% after correction.
  • Figure 4 (a) shows apertures 40 of a mask 41 in more detail.
  • the apertures 40 have a hexagonal shape and are positioned in rows. Triangular end-portions of the apertures are interspaced.
  • the mask 41 is oscillated in a direction along the rows and by a distance that corresponds to the pitch 42 of the mask 41.
  • the interspaced triangular portions of the apertures 40 are of a lower width than portions that are not interspaced, small misalignments of the oscillating movement or alignment errors of the apertures relative to each other are less critical .
  • the width of each aperture is selected to result in a flux distribution required for deposition of the film having the predetermined thickness profiles.
  • the apertures 40 of the mask 41 have positions that are selected for an oscillatory movement which has its origin 43 at the left- hand sides of the apertures 40.
  • Figure 4 (b) shows a variation of the embodiment shown in Figure 4 (a) .
  • the apertures 44 are wider than those shown in Figure 4 (a) and it becomes apparent that apertures may overlap once the aperture area of the mask has reached approximately 40 - 50 % of the mask area and consequently only less than 40 - 50 % throughput can typically be achieved with such a mask.
  • This particular embodiment has the advantage that overlapping of apertures can be largely avoided until the aperture area of the mask is very large such as 80%, 90% or even almost 100 % typically only limited by mechanical requirements of the mask area. Consequently the embodiment illustrated in Figure 4 (c) allows the design of mask for higher flux throughput .
  • Figure 5 illustrates a method of designing a mask for treating a substrate with a material flux to create a predetermined surface profile according to an embodiment of the present invention.
  • Figure 5 (a) shows a thickness map 50 of a substrate. The thickness is increasing from position 128 to position 0 in a first direction and constant in a perpendicular direction.
  • Figure 5 (b) shows a thickness profile of the substrate in the first direction.
  • a computer routine was used to design shapes and sizes of apertures 50 of a mask as shown in Figure 5 (c) .
  • the apertures 50, arranged in rows, were designed for an oscillatory movement of the mask in a direction along rows of the apertures 50.
  • each linear region has a length that corresponds to the pitch of the mask that is designed and a width that is smaller than an extension of each aperture in a perpendicular direction. This is schematically shown in Figure 6.
  • Figure 6 shows the linear regions 60 having a length that corresponds to the pitch 62 of the mask.
  • an average flux required for a predetermined substrate treatment was calculated and apertures 64 were designed that have interspaced aperture portions and that are sized and shaped so that for each linear region during oscillation of the mask along the linear regions the desired flux is achieved.
  • the apertures 64 are shaped and sized so that a uniform flux is generated for example for deposition of film having a uniform thickness.
  • the tapered width of the tapered regions of each aperture are calculated by applying a multiplier varying from 1.0 to 0.0 to the width of an un-tapered region of each aperture as the distance from the un-tapered region increases.
  • the region at which the width is tapered to point is a level at which the un- tapered aperture portions of an adjoining row are positioned.
  • a process analogous to that described in the context of Figure 6 was used to calculate sizes and shapes of the apertures 50 shown in Figure 5.
  • the thickness profile of the substrate was non-uniform (see Figure 5 (a) and (b) ) .
  • the substrate thickness increased from position 127 to position 0 (see Figure 5 (b) ) .
  • the amount of material that needs to be deposited decreases from position 127 to position 0.
  • the calculated shapes for the apertures 50 have curved side portions and sizes that allow the deposition of material for correcting the thickness profile of the substrate and creating a substrate having a uniform thickness profile.
  • the substrate thickness may be corrected by removing material, for example by ion milling.
  • the apertures 50 would have a reverse positions and orientations.
  • a mask designed in the above-described manner typically has a large number of such apertures, for example more than 500 or more than 1000.
  • Figure 7 shows film thickness plots for an optical device (a) before and (b) after correction by deposition of a further film using a method according to a specific embodiment of the present invention.
  • Figure 7 (a) shows that the original surface has an area of lower film thickness on the left-hand side.
  • the deposited film material is selected to have a refractive index nominally matched to that of the substrate so that optical continuity of the optic is ensured.
  • a mask having apertures with shapes and sizes chosen to correct that film thickness profile was designed and in this embodiment the mask (not shown) was arranged so that the apertures allow more flux to pass through on the left-hand side so that a film of a varying thickness is deposited on the original surface.
  • Figure 7 (b) shows the resultant total film thickness after correction. As may be seen from the plots, the thickness non-uniformity is largely corrected.
  • Figure 8 shows plots (a) and (b) characterising the surface roughness across the surfaces of the optical devices for which surface profiles are shown in Figures 7 (a) and ,7 (b) respectively.
  • deposition of material was used to create the predetermined surface profile. It will be appreciated, however, that in alternative examples material may be selectively removed from the surface to create the surface having the predetermined profile.
  • the flux of the material may be an ion beam and ion milling may be used in conjunction with the mask to remove material from the surface so as to create the predetermined surface or film thickness profile.
  • the invention has been described with reference to particular examples, it will be appreciated by those skilled in the art that the invention may be embodied in other forms.
  • more than one mask may be employed for the surface treatment either simultaneously or sequentially.
  • the substrate may have any shape including irregular shapes or spherical shapes.
  • the aperture dimensions may be further adjusted to account for the variation in deposited thickness caused by the angle of incidence of the flux on the surface.
  • the substrate may be oscillated relative to the mask to effect the relative movement.

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  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
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Abstract

A mask is providing for treating a substrate with a material flux to deposit or remove a layer having a predetermined thickness profile. The mask comprises a plurality of apertures (45) for interfering upon oscillatory movement with the first beam of flux material in a manner such that a plurality of secondary beams of the material flux are generated which are directed to the surface of the substrate. The apertures (45) are arranged in a plurality of rows and positioned so that portions of apertures of one row are interspaced with portions of apertures of an adjacent row. The interspaced aperture portions have an average width that is smaller than an average width of aperture portions that are not interspaced.

Description

A MASK AND A METHOD FOR TREATING A SUBSTRATE WITH A MATERIAL FLUX TO DEPOSIT OR REMOVE A LAYER HAVING A
PREDETERMINED THICKNESS PROFILE
Field of the Invention
The present invention broadly relates to a mask and a method for treating a substrate with a material flux to deposit or remove a layer having a predetermined thickness profile.
Background of the Invention
Films having a predetermined thickness profile, such as flat or profiled films, are used for a variety of applications. For example films of uniform thickness are often required for fabrication of electronic devices. These films may be composed of insulating materials and may have an insulating function. Alternatively they may be formed from semi-conducting or electrically conductive materials . Especially electronic devices having a very small scale, such as a sub-micro or nano-scale, often require such layers. Specific examples include integrated devices having tunnelling junctions in which a tunnelling current critically depends on a thickness of an insulating layer. Further, hard disc devices require layers of uniform thickness and there is a range of other devices which semi-conductor industries produce or plan to produce and for which uniformity of layer thickness is of critical importance.
In addition, optical applications such as applications in which interference conditions are important, often require films having a uniform film thickness or films having a predetermined thickness profile. For example, extreme UV microlithography, which is of great interest for semiconductor and nano- technology, places high demands on the quality of optical surfaces.
Thin film deposition systems typically generate a flux of a material which is deposited on a substrate. Unfortunately, the thickness profile of the deposited material often is not ideal. Various methods have been employed to improve the uniformity of the deposited films. Examples include methods in which the substrate is rotated during deposition, methods in which a random motion of the substrate during deposition is effected, and/or a shutter is introduced to control the flux as the substrate moves. With these methods it may be possible to achieve thickness profiles that are within approximately 1% of an ideal thickness profile. However, these methods usually require complex vacuum compatible rotation and/or translation stages capable of moving substrates that may weigh many 10's of kg.
Alternatively, a mask with apertures may be moved through the flux in a predetermined manner to control the flux. However, slight misalignments of the apertures in the mask or slight deviations of the mask movement can cause significant imperfections of the thickness profile. Consequently there is a need for technological advancement.
Summary of the Invention
The present invention provides in a first aspect a mask for treating a substrate with a material flux to deposit or remove a layer having a predetermined thickness profile, the mask comprising: a plurality of apertures for interfering with a first beam of the material flux in a manner such that a plurality of secondary beams of the material flux are generated which are directed to the surface of the substrate, the apertures being arranged in a plurality of rows and positioned so that portions of apertures of one row are interspaced with portions of apertures of an adjacent row, the interspaced aperture portions having an average width that is smaller than an average width of aperture portions that are not interspaced.
The mask is typically arranged so that an oscillatory movement of the mask or the substrate relative to each other results in predetermined distribution of the material flux for depositing or removing the layer having the predetermined thickness profile. For example, the oscillatory movement may be oriented substantially along at least one of the rows of apertures. Typically the rows of the apertures are substantially parallel to each other.
As the rows have apertures with interspaced aperture portions which have an average width that is smaller than the average width of aperture portions that are not interspaced, the mask according to the first aspect of the present invention has the advantage that small directional errors of the oscillatory movement or small misplacement of the apertures in the mask have a reduced effect on the created surface profile.
The interspaced aperture portions typically are sized so that during the oscillatory movement the flux is uniform or changes smoothly in a direction perpendicular to the direction of the movement and across at least one mask region having at least some of the interspaced aperture portions.
Further, embodiments of the mask according to the first aspect have the advantage that it may not be necessary to effect large movements of the substrate or the mask. Typically the mask has a fine structure and may comprise a large number of the apertures, such as more than one hundred or more than one thousand. Using such a mask, typically only a very small movement, such as a small oscillatory movement, of the mask or the substrate is required to deposit or remove a layer having a predetermined thickness profile.
The predetermined thickness profile may be flat and may be the profile of a uniform coating. Alternatively, the predetermined thickness profile may be any other profile including spheric and aspheric profiles.
Further, a substrate surface, such as the surface for an electronic or optical device, may have an unsatisfactory surface profile that needs correction. In this case the mask may be designed, for example using a suitable computer software routine, having apertures that are shaped, sized and positioned so that a desired material flux is achieved that corrects the surface profile either by depositing or removing a layer having the predetermined thickness profile. The mask typically is designed to take into account a non-uniform flux distribution of the primary beam.
In one particular example the surface is a surface for an optical device that has an unsatisfactory phase property. In this example the mask is designed so that the surface treatment using the mask will correct the phase property either by depositing or removing a layer having the predetermined thickness profile.
In another example the mask is designed to deposit a film of uniform thickness for an optical device.
Alternatively the surface may be a surface for an electronic device and the mask may be designed to deposit a film of uniform thickness or to treat the surface, either by depositing material or by removing material, to create a predetermined surface profile such as a flat surface profile or any other surface profile.
The apertures may have any suitable shape, including circular, oval and polygonal shapes. Throughout this specification the terms "polygonal" , "triangular" and
"hexagonal" are also used for shapes that approximate that of polygons, triangles, and hexagons, respectively, and that have curved side-portions and/or rounded corners.
The apertures typically have interspaced end-portions that have a tapered width. For example, the interspaced end-portions may be tapered to a point . Each aperture typically has two such end-portions that form opposite ends of each aperture. For example, the interspaced end- portions may be the triangular end-portions of the hexagonal shaped aperture. In a variation of this embodiment each aperture may also have more than two interspaced end-portions.
Each aperture typically is shaped so that during substrate treatment and during the oscillatory movement the apertures interfere with the first beam of material flux in a manner so that the generated secondary beams have a flux profile that creates a predetermined surface profile in a direction substantially perpendicular to a direction along the oscillatory movement and along the substrate surface. For example, the rows of apertures may be parallel and the width of the apertures in a direction along each row may be varied so as to control the amount of the flux. The mask typically is arranged for an oscillatory movement which oscillates the mask or the substrate by a distance that corresponds to the pitch P of the mask. Throughout this specification the term "pitch of the mask" is used for a distance by which the mask is oscillated during the treatment.
The apertures may be positioned so that an oscillatory movement that moves each aperture by a distance Dl in a first direction from an origin and back to the origin (with P = Dl) results in the desired flux distribution for creating the predetermined thickness profile.
In one specific embodiment the apertures are positioned so that an oscillatory movement that moves the mask by a distance of Dl in a first direction from an origin and back to the origin, and by a distance D2 from the origin in an opposite second direction and back to the origin (P = Dl + D2) results in the desired flux distribution for creating the predetermined thickness profile. In this case Dl typically equals D2 and the apertures may form a checkerboard-like arrangement. This specific embodiment has the advantage that the ratio of the aperture area and an area of the mask that blanks flux off can be maximised and the total aperture area of the mask typically is only limited by structural requirements of the mask.
The total aperture area that allows flux to pass through may be relatively large, such as more than 50%, 60%, 70%, 80%, 90% or even nearly 100% of the mask area. The first beam of material flux may be generated using any suitable method including physical and chemical vapour generation techniques such as thermal evaporation effected by resistive heating or by electron beam evaporation, and chemical vapour deposition. Alternatively, the flux may be the flux of a molecular beam or of an ion beam or the flux may be generated using a sputtering source such as a rf or dc sputtering source. Further, the flux may be generated by introducing the material or a precursor of the material in gaseous form into a vacuum chamber and directing the gaseous material or precursor through the mask by differential pumping.
The present invention provides in a second aspect a method of treating a substrate to deposit or remove a layer having a predetermined thickness profile using the above-defined mask.
The present invention provides in a third aspect a method of designing a mask for treating a substrate with a material flux to deposit or remove a layer having a predetermined thickness profile, the mask having rows of interspaced apertures and the method comprising: selecting a desired distribution of material flux for treating a substrate surface that deposits or removes the layer having a predetermined thickness profile, selecting sizes and shapes for the apertures so that the apertures of the mask positioned in a first beam of material flux would interfere with the first beam of the material flux in a manner such that a plurality of secondary beams of the material flux are generated which together result in the desired flux distribution.
The method typically also comprises the step of fabricating the designed mask. The designed mask typically is a monolithic mask and typically is relatively easy to fabricate for example from a sheet of mask material for example using commercially available laser cutting or chemical etching equipment. A profile of the substrate surface may initially be characterised for example using interferometric methods. The substrate surface may have a profile that deviates from a desired profile. The step of selecting the desired flux distribution may comprise selecting the flux having a distribution so that the selected flux would correct the substrate surface profile by depositing or removing the layer having a predetermined thickness profile.
The step of selecting shapes and sizes of the apertures typically is conducted so that an oscillatory movement along the rows of the apertures results in the desired flux distribution. This step typically is computer software implemented. Selecting shapes and sizes of the apertures typically comprises performing an imaginary division of a cross-sectional area of the desired flux into a plurality of linear regions which have a length that substantially corresponds to the pitch of the mask and a width that is smaller than an extension of each aperture in a direction perpendicular to the parallel rows of the apertures.
The apertures typically have an extension along the length of the linear region that is dependent on an average of the desired flux intensity within that linear region.
The present invention provides in a fourth aspect a method of treating a substrate to deposit or remove a layer having a predetermined thickness profile, the method comprising: generating a first beam of a material flux and interfering with the first beam of the material flux using a mask having a plurality of apertures in a manner such that a plurality of secondary beams of the material flux are generated which are directed to the substrate, the apertures being arranged in a plurality of rows and positioned so that portions of apertures of one row are interspaced with portions of apertures of an adjacent row, the interspaced aperture portions having an average width that is smaller than an average width of aperture portions that are not interspaced and moving the mask or the substrate so that the apertures with interspaced end-portions together generate a flux profile that deposits or removes the layer having a predetermined thickness profile.
The step of moving typically includes oscillating the mask or the substrate in a direction along at least one row of the apertures.
The movement typically is a relatively small oscillatory movement of the mask and the substrate relative to and over each other. For example, the oscillatory movement may oscillate the mask in a manner such that each aperture is moved by a distance Dl from an origin in a first direction and back to the origin (with P = Dl) . In one specific embodiment the oscillatory movement oscillates the mask in a manner such that each aperture is moved by a distance of Dl in a first direction from an origin and back and thereafter by a distance D2 in an opposite second direction from the origin and back to the origin (with P = Dl + D2) . In this case Dl typically equals D2. The oscillation is typically of substantially constant velocity in each direction.
The oscillatory movement may be effected by a drive or actuator that is positioned inside a vacuum chamber of a deposition system. Alternatively, the oscillatory movement may be effected by a drive or actuator that is positioned outside the vacuum chamber of a deposition system. The material flux of each secondary beam may remove material from the surface. For example, this may involve ion milling.
Alternatively, the material flux of each secondary beam may deposit material on the substrate, such as thin film material.
In one embodiment the mask is positioned so that a distance between the substrate and the mask is much larger, such as a few ten times, a few hundred or thousand times larger, than a typical distance across one the apertures. Smoothing of the surface profile owing to non- parallel flux trajectories facilitate formation of smooth surfaces. While a point source may be used for surface treatment, a distributed source having non-parallel trajectories is for the above-described reason particularly advantageous. Further, scattering of flux at edges of the mask typically results in additional smoothing.
The step of generating the first beam of material flux may comprise any suitable physical and chemical flux generating technique such as thermal evaporation effected by resistive heating or by electron beam evaporation, and chemical vapour deposition. Alternatively, the flux may be the flux of a molecular beam or of an ion beam or the flux may be generated using a sputtering source such as a rf or dc sputtering source. Further, the flux may be generated by introducing the material in gaseous form into a vacuum chamber and directing the gaseous material through the mask by differential pumping. _ 1 :L_
The method may comprise depositing a layer of uniform thickness. Alternatively, the predetermined thickness profile may be non-uniform. For example, the layer that is deposited or removed may correct a surface profile of the substrate.
If material is deposited on the surface, the flux may comprise the material in a pure form or may comprise a precursor for the material and may also comprise a carrier gas. Further, surface treatment may involve generation of more than one first beam.
The present invention provides in a fifth aspect a device having a surface treated by the method according to the fourth aspect of the present invention.
The device typically is an electronic or optical device. For example, the surface may form a part of an anti-reflection coating or may be a layer of a filter such as a dielectric filter. Further, the surface may be a surface of an optical device for which a surface was treated to correct an unsatisfactory surface profile.
Alternatively, the device may be an electronic device such as a computer hard drive and the film may be a coating of the computer hard drive. Further, the device may be an electronic device in which a thin film of uniform thickness, such as a thin film of an insulating material is deposited onto a substrate. For example, the device may comprise the thin film of an insulating material to control flow of electrons between conductive layers which sandwich the thin film of an insulating material .
The invention will be more fully understood from the following description of specific embodiments of the invention. The description is provided with reference to the accompanying drawings.
Brief Description of the Drawings
Figure 1 shows a schematic representation illustrating a mask and a method for treating a substrate with a material flux to deposit or remove a layer having a predetermined thickness profile according to a specific embodiment of the present invention;
Figure 2 shows (a) a surface profile map of a substrate and (b) a mask for treatment of the substrate with a material flux to deposit or remove a layer having a predetermined thickness profile according to a specific embodiment of the present invention;
Figure 3 shows plots characterising film uniformities for (a) a horizontal film direction and (b) a vertical film direction;
Figures 4 (a) to (c) show apertures of a mask according to specific embodiments of the present invention;
Figure 5 shows (a) a thickness map of a substrate, (b) a thickness profile of the substrate, and (c) a mask and aperture design according to an embodiment of the present invention;
Figure 6 shows apertures of a mask according to an embodiment of the present invention;
Figure 7 shows plots characterising a surface profile of an optical device (a) prior to correction and (b) after correction by deposition of a film having a predetermined thickness profile according to an embodiment of the present invention; and Figure 8 (a) and (b) shows plots characterising the surface roughness of the surfaces of the optical devices characterised by the plots shown in Figures 7 (a) and 7 (b) .
Detailed Description of Specific Embodiments
Referring initially to Figure 1, a mask and a method for treating a substrate to deposit or remove a layer having a predetermined thickness profile according to a specific embodiment of the present invention is now described. In this example, a film having the predetermined thickness profile is created on a substrate by depositing material on the substrate. The illustration 10 shows a flux source 12, a substrate 14 and a mask 16. The substrate 14 and the mask 16 are positioned so that a flux 18 originating from the source 12 is directed through apertures of the mask 16 to the substrate 14 so as to deposit a film on. the substrate 14. The source 12 may be any suitable source that emits the flux 18. For example, the source 12 may be a source in which flux material is evaporated. The source 12 may be a part of an electron beam evaporator or may comprise a resistively heated heater. Alternatively, the source 12 may be a source of a directional chemical vapour such as a precursor for the film material. Further, the source 12 may also be a source that emits an ion beam or any other type of directional physical or chemical vapour or the flux may be generated using a sputtering source such as a rf or dc sputtering source.
The mask 16 has a plurality of apertures that are positioned in rows and form a checkerboard-like arrangement . During the treatment the mask 16 is oscillated along the rows by the pitch of the mask 16. In this example the pattern of the mask 16 comprises a fine structure having a 1600 apertures but in variations of the embodiment the mask may also comprise any other number of apertures such as a few thousand apertures. Each of the apertures is sized and positioned so as to control the flux 18 penetrating through the apertures of the mask 16 in a manner such that a film having a predetermined thickness profile is deposited on substrate 14. The source 12 of the flux 18 typically has a non¬ uniform flux density in a direction or directions across the mask 16. In this embodiment the apertures of the mask 16 are distributed and sized so as to correct for the non¬ uniform flux. For example, in areas where flux density is lower, the apertures are larger so as to correct for the locally low flux density. In this example the mask 16 is designed for the deposition of a film having a uniform thickness.
In this embodiment the distance between the substrate 14 and the mask 16 is large compared with the average distance across one of the apertures of the mask 16.
Figure 2 (a) shows a surface profile of an optical device. The light area 20 is higher than the surrounding darker areas. It is now described how a method according to an embodiment of the present invention can be used to correct this surface so that the difference in height is corrected and the surface uniformity is improved.
In this embodiment a computer routine is used to analyse the surface profile and design the mask. Figure 2 (b) shows a designed pattern having apertures that are sized and distributed to correct the surface profile shown in Figure 2 (a) so that the surface is substantially uniform. As may be seen from Figure 2 (b) the apertures have a slightly smaller size in an area that approximately corresponds to light area 20 in Figure 2 (a) . Consequently, more film material will be deposited in areas that surround the light area 20 so that the surface characterised by the plot shown in Figure 2 (a) can be corrected.
For film growth a mask was prepared having the aperture distribution as shown in Figure 2 (b) . The mask (not shown) is composed of a stainless steel sheet but may alternatively be composed of another suitable material such as aluminium, glass, silicon, a ceramics material, a plastics material or any other suitable conductive or non- conductive material. The apertures are formed in the stainless steel mask of the present embodiment using commercially available laser cutting equipment. Figure
3 (a) shows surface profiles for a horizontal direction for the optical film thickness surfaces before and after correction. Prior to correction the surface uniformity was approximately 3% and after correction the surface uniformity is better than 0.5% in a horizontal direction. Figure 3 (b) shows a corresponding profile measurement for a vertical direction. In this case the surface uniformity is better than 0.3% after correction.
Figure 4 (a) shows apertures 40 of a mask 41 in more detail. In this embodiment the apertures 40 have a hexagonal shape and are positioned in rows. Triangular end-portions of the apertures are interspaced. During film growth the mask 41 is oscillated in a direction along the rows and by a distance that corresponds to the pitch 42 of the mask 41. As the interspaced triangular portions of the apertures 40 are of a lower width than portions that are not interspaced, small misalignments of the oscillating movement or alignment errors of the apertures relative to each other are less critical . The width of each aperture is selected to result in a flux distribution required for deposition of the film having the predetermined thickness profiles. In the embodiment shown in Figure 4 (a) the apertures 40 of the mask 41 have positions that are selected for an oscillatory movement which has its origin 43 at the left- hand sides of the apertures 40. In this case the mask is arranged for an oscillatory movement that moves the mask in a direction Dl to the right an back (Dl = P) .
Figure 4 (b) shows a variation of the embodiment shown in Figure 4 (a) . In this variation the apertures 44 are wider than those shown in Figure 4 (a) and it becomes apparent that apertures may overlap once the aperture area of the mask has reached approximately 40 - 50 % of the mask area and consequently only less than 40 - 50 % throughput can typically be achieved with such a mask.
Figure 4 (c) shows a mask having apertures 45 which are positioned for an oscillatory movement that moves the apertures by a distance Dl to the right (and back) and by a distance D2 to the left and back (Dl + D2 = P) This particular embodiment has the advantage that overlapping of apertures can be largely avoided until the aperture area of the mask is very large such as 80%, 90% or even almost 100 % typically only limited by mechanical requirements of the mask area. Consequently the embodiment illustrated in Figure 4 (c) allows the design of mask for higher flux throughput .
It is to be appreciated that the apertures may have any other suitable shapes such as round or rounded shapes, oval shapes or other suitable shapes having corners. Further, it is to be appreciated that each aperture may have any number of interspaced aperture portions. Figure 5 illustrates a method of designing a mask for treating a substrate with a material flux to create a predetermined surface profile according to an embodiment of the present invention. Figure 5 (a) shows a thickness map 50 of a substrate. The thickness is increasing from position 128 to position 0 in a first direction and constant in a perpendicular direction. Figure 5 (b) shows a thickness profile of the substrate in the first direction. In this embodiment a computer routine was used to design shapes and sizes of apertures 50 of a mask as shown in Figure 5 (c) . The apertures 50, arranged in rows, were designed for an oscillatory movement of the mask in a direction along rows of the apertures 50.
For selecting shapes and sizes of the apertures an imaginary division of a cross-sectional area of the desired flux into a plurality of linear regions was performed. Each linear region has a length that corresponds to the pitch of the mask that is designed and a width that is smaller than an extension of each aperture in a perpendicular direction. This is schematically shown in Figure 6.
Figure 6 shows the linear regions 60 having a length that corresponds to the pitch 62 of the mask. For each linear region 60 an average flux required for a predetermined substrate treatment was calculated and apertures 64 were designed that have interspaced aperture portions and that are sized and shaped so that for each linear region during oscillation of the mask along the linear regions the desired flux is achieved. In the example shown in Figure 6 the apertures 64 are shaped and sized so that a uniform flux is generated for example for deposition of film having a uniform thickness. The tapered width of the tapered regions of each aperture are calculated by applying a multiplier varying from 1.0 to 0.0 to the width of an un-tapered region of each aperture as the distance from the un-tapered region increases. In this embodiment the region at which the width is tapered to point is a level at which the un- tapered aperture portions of an adjoining row are positioned.
A process analogous to that described in the context of Figure 6 was used to calculate sizes and shapes of the apertures 50 shown in Figure 5. In the example shown in Figure 5, however, the thickness profile of the substrate was non-uniform (see Figure 5 (a) and (b) ) . The substrate thickness increased from position 127 to position 0 (see Figure 5 (b) ) . To correct for the non-uniform thickness profile and create a substrate having a uniform thickness, the amount of material that needs to be deposited decreases from position 127 to position 0. The calculated shapes for the apertures 50 have curved side portions and sizes that allow the deposition of material for correcting the thickness profile of the substrate and creating a substrate having a uniform thickness profile.
In a variation of this embodiment the substrate thickness may be corrected by removing material, for example by ion milling. In this case the apertures 50 would have a reverse positions and orientations. A mask designed in the above-described manner typically has a large number of such apertures, for example more than 500 or more than 1000.
Figure 7 shows film thickness plots for an optical device (a) before and (b) after correction by deposition of a further film using a method according to a specific embodiment of the present invention. Figure 7 (a) shows that the original surface has an area of lower film thickness on the left-hand side. In this embodiment the deposited film material is selected to have a refractive index nominally matched to that of the substrate so that optical continuity of the optic is ensured. A mask having apertures with shapes and sizes chosen to correct that film thickness profile was designed and in this embodiment the mask (not shown) was arranged so that the apertures allow more flux to pass through on the left-hand side so that a film of a varying thickness is deposited on the original surface. Figure 7 (b) shows the resultant total film thickness after correction. As may be seen from the plots, the thickness non-uniformity is largely corrected.
Figure 8 shows plots (a) and (b) characterising the surface roughness across the surfaces of the optical devices for which surface profiles are shown in Figures 7 (a) and ,7 (b) respectively.
In this embodiment deposition of material was used to create the predetermined surface profile. It will be appreciated, however, that in alternative examples material may be selectively removed from the surface to create the surface having the predetermined profile. For example, the flux of the material may be an ion beam and ion milling may be used in conjunction with the mask to remove material from the surface so as to create the predetermined surface or film thickness profile.
Although the invention has been described with reference to particular examples, it will be appreciated by those skilled in the art that the invention may be embodied in other forms. For example, more than one mask may be employed for the surface treatment either simultaneously or sequentially. Further, the substrate may have any shape including irregular shapes or spherical shapes. In the case of non-planar substrate surfaces, the aperture dimensions may be further adjusted to account for the variation in deposited thickness caused by the angle of incidence of the flux on the surface. Further, it will be appreciated that alternatively the substrate may be oscillated relative to the mask to effect the relative movement.

Claims

The Claims :
1. A mask for treating a substrate with a material flux to deposit or remove a layer having a predetermined thickness profile, the mask comprising: a plurality of apertures for interfering with a first beam of the material flux in a manner such that a plurality of secondary beams of the material flux are generated which are directed to the surface of the substrate, the apertures being arranged in a plurality of rows and positioned so that portions of apertures of one row are interspaced with portions of apertures of an adjacent row, the interspaced aperture portions having an average width that is smaller than an average width of aperture portions that are not interspaced.
2. The mask as claimed in claim 1 being arranged so that an oscillatory movement of the mask or the substrate relative to each other results in predetermined distribution of the material flux for depositing or removing the layer having the predetermined thickness profile.
3. The mask as claimed in claim 2 wherein the rows of the apertures are substantially parallel to each other and the oscillatory movement is oriented substantially along the rows of apertures.
4. The mask as claimed in any one of the preceding claims being designed for correcting a phase property of an optical device.
5. The mask as claimed in any one of the preceding claims being designed for depositing a film of uniform thickness for an optical device.
6. The mask as claimed in any one of claims 1 to 3 being designed for treating a surface of an electronic device.
7. The mask as claimed in any one of the preceding claims wherein the interspaced end-portions of the apertures have a tapered width.
8. The mask as claimed in claim 7 wherein each aperture has two such end-Dortions that form ODOOsite ends of each aperture.
9. The mask as claimed in claim 8 wherein the interspaced end-portions are the triangular end-portions of hexagonal shaped aperture.
10. The mask as claimed in any one of the preceding claims wherein each aperture is shaped so that during substrate treatment and during the oscillatory movement the apertures interfere with the first beam of material flux in a manner so that the generated secondary beams have a flux profile that creates a predetermined surface profile in a direction substantially perpendicular to a direction along the oscillatory movement and along the substrate surface.
11. The mask as claimed in claim 10 wherein the rows of apertures are parallel and the width of the apertures in a direction along each row is varied so as to control the amount of the flux.
12. The mask as claimed in any one of the preceding claitns being arranged for an oscillatory movement which oscillates the mask or the substrate by a distance that corresponds to the pitch of the mask.
13. The mask as claimed in claim 12 wherein the apertures are positioned so that an oscillatory movement that moves each aperture by a distance Dl in a first direction from an origin and back to the origin (with P = Dl) results in a desired flux distribution for creating the predetermined thickness profile.
14. The mask as claimed in any one of claims 1 to 11 wherein the apertures are positioned so that an oscillatory movement that moves the mask by a distance of Dl in a first direction from an origin and back to the origin, and by a distance D2 from the origin in an opposite second direction and back to the origin (P = Dl + D2) results in a desired flux distribution for creating the predetermined thickness profile.
15. The mask as claimed in claim 14 wherein Dl substantially equals D2.
16. The mask as claimed in claim 14 or 15 wherein the total aperture area that allows flux to pass through is one of more than 50%, 60%, 70%, 80%, or more than 90% of the mask area.
17. A method of treating a substrate to deposit or remove a layer having a predetermined thickness profile using the mask as claimed in any one of claims 1 to 16.
18. A method of designing a mask for treating a substrate with a material flux to deposit or remove a layer having a predetermined thickness profile, the mask having rows of interspaced apertures and the method comprising: selecting a desired distribution of material flux for treating a substrate surface that deposits or removes the layer having a predetermined thickness profile, selecting sizes and shapes for the apertures so that the apertures of the mask positioned in a first beam of material flux would interfere with the first beam of the material flux in a manner such that a plurality of secondary beams of the material flux are generated which together result in the desired flux distribution.
19. The method as claimed in claim 18 also comprising the step of fabricating the designed mask.
20. The method as claimed in claim 19 wherein the fabricated mask is a monolithic mask.
21. The method as claimed in any one of claims 18 to 20 comprising the step of characterising a substrate surface.
22. The method as claimed in claim 21 wherein the substrate surface is characterised using an interferometric method.
23. The method as claimed in any one of claims 18 to 22 wherein the step of selecting the desired flux distribution comprises selecting a flux distribution that would correct a substrate surface profile by depositing or removing the layer having a predetermined thickness profile.
24. The method as claimed in any one of claims 18 to 23 wherein the rows of the apertures are parallel and wherein the step of selecting shapes and sizes of the apertures is conducted so that an oscillatory movement along the parallel rows of the apertures results in the desired flux distribution.
25. The method as claimed in any one of the claims 18 to 24 wherein the step of selecting shapes and sizes of the apertures is computer software implemented.
26. The method as claimed in any one of claims 18 to 25 wherein selecting shapes and sizes of the apertures comprises performing an imaginary division of a cross- sectional area of the desired flux into a plurality of linear regions which have a length that substantially corresponds to the pitch of the mask and a width that is smaller than an extension of each aperture in a direction perpendicular to the rows of the apertures.
27. The method as claimed in claim 26 wherein the apertures have an extension along the length of the linear region that is dependent on an average of the desired flux intensity within that linear region.
28. A method of treating a substrate to deposit or remove a layer having a predetermined thickness profile, the method comprising: generating a first beam of a material flux and interfering with the first beam of the material flux using a mask having a plurality of apertures in a manner such that a plurality of secondary beams of the material flux are generated which are directed to the substrate, the apertures being arranged in a plurality of rows and positioned so that portions of apertures of one row are interspaced with portions of apertures of an adjacent row, the interspaced aperture portions having an average width that is smaller than an average width of aperture portions that are not interspaced and moving the mask or the substrate so that the apertures with interspaced end-portions together generate a flux profile that deposits or removes the layer having a predetermined thickness profile.
29. The method as claimed in claim 28 wherein the step of moving includes oscillating the mask or the substrate in a direction along at least one row of the apertures.
30. The method as claimed in claim 29 wherein the oscillatory movement oscillates the mask in a manner such that each aperture is moved by a distance Dl from an origin in a first direction and back to the origin (with P = Dl) .
31. The method as claimed in claim 29 wherein the oscillatory movement oscillates the mask in a manner such that each aperture is moved by a distance Dl in a first direction from an origin and back and thereafter by a distance D2 in an opposite second direction from the origin and back to the origin (with P = Dl + D2) .
32. The method as claimed in claim 31 wherein Dl equals D2.
33. The method as claimed in any one of claims 30 to 32 wherein the oscillatory movement oscillates the mask at a substantially constant velocity in each direction.
34. The method as claimed in any one of claims 28 to 33 wherein the material flux of each secondary beam removes material from the surface.
35. The method as claimed in claim 34 wherein removing the material from the surface involves ion milling.
36. The method as claimed in any one of claims 29 to 33 wherein the material flux of each secondary beam deposits material on the substrate.
37. The method as claimed in any one of claims 29 to 36 wherein a layer of uniform thickness is deposited.
38. The method as claimed in any one of claims 29 to 37 wherein the predetermined thickness profile is non¬ uniform.
39. The method as claimed in claim 38 wherein the layer that is deposited or removed corrects a surface profile of the substrate.
40. A device having a surface treated by the method as claimed in any one of claims 28 to 39.
41. The device as claimed in claim 40 being an optical device.
42. The device as claimed in claim 40 being an electronic device.
PCT/AU2005/001503 2004-10-01 2005-09-29 A mask and a method for treating a substrate with a material flux to deposit or remove a layer having a predetermined thickness profile WO2006037153A1 (en)

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