Patent Application
20190121229
The present invention relates to a pellicle film, a pellicle frame, and a pellicle usable for a mask for photolithography, and a method for producing the same. The present invention specifically to a pellicle film which is an extremely thin film for extreme ultraviolet (EUV) lithography, a pellicle frame, a pellicle and a method for producing the same.
In a photolithography process, in order to prevent dust or the like from being attached to a mask or a reticle, a pellicle including a pellicle film extended along one end of a frame having a size appropriate to enclose a mask pattern is used.
A pellicle is used to protect a photomask against foreign substances such as dust or the like. If a produced pellicle has dust or the like attached thereto, it is meaningless to use the pellicle. Therefore, a pellicle decreased in the amount of dust or the like attached thereto and a method for producing the same are currently strongly desired.
So far, the wavelength of light used for lithography has been progressively shortened. As a next-generation lithography technology, EUV lithography is now being developed. “EUV light” refers to light having a wavelength in a soft x-ray range or a vacuum ultraviolet range, more specifically, a light beam having a wavelength of about 13.5 nm±about 0.3 nm. In photolithography, the resolution limit of a pattern is about ½ of the exposure wavelength, and is considered to be about ¼ of the exposure wavelength even if an immersion method is used, and even if an immersion method is used with ArF laser light (wavelength: 193 nm), the exposure wavelength is expected to be about 45 nm at the minimum. In such a situation, EUV lithography is anticipated as a revolutionary technology that realizes significant reduction in the resolution limit as compared with the conventional lithography.
EUV light is easily absorbed by any substance. Therefore, especially, a pellicle for EUV needs to include a pellicle film having a thickness of a nanometer order, which is not provided conventionally.
A pellicle for EUV, which needs to use such an extremely thin film, is generally obtained as follows as described in Japanese Laid-Open Patent Publication No. 2013-004893. A pellicle film is formed on a substrate such as a silicon substrate or the like by CVD, sputtering or any other appropriate film formation method, and then, only the substrate is removed by etching or the like (back-etching) while a peripheral frame-like region of the substrate is left.
In order to achieve an aim of producing a pellicle with little dust, various problems have been investigated and various attempts have been made to solve the problems. For example, Japanese Examined Utility Model (Registration) Application Publication No. S63-39703 describes a pellicle including at least one air hole formed in a pellicle frame and a filter member provided in the air hole. The filter member prevents dust or the like from passing the air hole, and is provided so as not to fall into a space enclosed by a frame member, a mask substrate and a pellicle film. It should be noted that this invention does not relate to a pellicle for EUV, and is not sufficient from the point of view of decreasing the dust.
A pellicle may be contaminated with dust or the like for various reasons during the production thereof. Especially, there is a problem that the risk that the dust or the like is attached is high during trimming, various processes performed on the pellicle film, transportation or the like. The present invention has an object of providing a pellicle film, a pellicle frame and a pellicle for EUV decreased in the amount of dust or the like attached thereto, and a method for producing the same.
Provided in order to achieve the above-described object is a method for producing a pellicle including forming a pellicle film on a substrate; forming a metal mask on a surface of the substrate opposite to a surface having the pellicle film formed thereon; removing a part of the substrate from the side of the metal mask; and removing the metal mask.
In an embodiment according to the present invention, the method may further include forming a surface metal coating layer between the substrate and the pellicle film.
In an embodiment according to the present invention, the metal mask may be formed of chromium. In an embodiment according to the present invention, the surface metal coating layer may be formed of ruthenium.
In an embodiment according to the present invention, a step of the removal of the part of the substrate is performed by a step of wet etching.
In an embodiment according to the present invention, before the part of the substrate is removed, particles attached to at least a surface of the pellicle film may be removed.
In an embodiment, before the part of the substrate is removed, an end portion of the substrate may be chamfered.
In an embodiment, before the particles are removed, a hole may be formed in at least the substrate.
In an embodiment, before the particles are removed, a hole may be formed in at least the pellicle film and the substrate.
In an embodiment, before the particles are removed, a hole may be formed in at least the pellicle film.
In an embodiment, ultra-short pulse laser light may be used to form the hole.
In an embodiment, the removal of the part of the substrate is performed by wet etching, and the hole may be formed by wet etching.
In an embodiment, ultra-short pulse laser light may be used for trimming.
Provided in order to achieve the above-described object is a pellicle frame including a pellicle film; and a first frame. The pellicle film is extended over the first frame; and the first frame includes an eaves-like portion having a length of 0 μm or greater and 0.5 μm or less.
The pellicle frame may further include a surface metal coating layer between the pellicle film and the first frame.
In an embodiment according to the present invention, an end portion of the first frame may be R-chamfered. Namely, the end portion of the first frame may include at least one curved portion.
In an embodiment according to the present invention, the pellicle frame may include a pellicle film and a first frame. The pellicle film may be extended over the first frame; and an end portion of the first frame may be C-chamfered. Namely, the end portion of the first frame may include an inclining surface, and the angle made by a top surface and the inclining surface of the first frame may be 100 degrees or greater and 170 degrees or less.
In an embodiment according to the present invention, the pellicle frame may be connected with a second frame; and an end portion of the second frame may be R-chamfered. Namely, the end portion of the second frame may include a curved portion.
In an embodiment, the present invention provides a pellicle film, a pellicle frame and a pellicle for EUV decreased in the amount of dust or the like attached thereto, and a method for producing the same.
Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like. The present invention may be carried out in various forms and is not to be construed as being limited to any of the following embodiments. In the drawings, components may be shown schematically regarding the width, thickness, shape and the like, instead of being shown in accordance with the actual sizes, for the sake of clearer illustration. The drawings are merely examples and do not limit the interpretations of the present invention in any way. In the specification and the drawings, components that have substantially the same functions as those described before with reference to a previous drawing(s) bear the identical reference signs thereto, and detailed descriptions thereof may be omitted.
In this specification, when a certain member or region is referred to as “above (or below)” another member or region, unless there is a specific limitation, this includes not only the case where it is directly above (or directly below) the certain member or region but also the case where it is above (or below) another member or region, that is, the case when another structural component is included between above (or below) the certain member or region.
In this specification, a “pellicle film” refers to a thin film used for a pellicle. A “pellicle frame” refers to an assembly of a pellicle film and a first frame that are connected with each other. A “pellicle” refers to an assembly of a pellicle frame and a second frame that are connected with each other.
“Trimming” refers to cutting a substrate, or an assembly of the substrate and the pellicle film formed above the substrate, in accordance with a desired pellicle shape. The shape of the pellicle is often rectangular. Therefore, in this specification, an example of cutting the substrate, or an assembly of the substrate and the pellicle film formed above the substrate, into a rectangular shape is shown as a specific example of trimming.
In this specification, “back-etching” refers to a step of removing a part of the substrate while the pellicle film is left. In this specification, etching of the substrate from a rear surface thereof (surface opposite to a surface on which the pellicle film is formed) is shown as an example of back-etching.
In this specification, an “end portion” refers to a side surface, an edge or a corner edge; specifically, refers to a side surface of a substrate (first frame in the case where the substrate is used as the first frame), an edge formed by side surfaces of the substrate (first frame in the case where the substrate is used as the first frame), an edge formed by a top surface of the substrate (surface to be in contact with the pellicle film) and a side surface of the substrate, or a corner edge including a point at which a top surface and two side surfaces of the substrate cross each other.
A pellicle to be produced by a pellicle production method according to the present invention is a pellicle for photolithography. First, above a substrate 100 (
Then, a part of the substrate is removed while an exposure area of the pellicle film 102 is left. The part of the substrate is removed by back-etching. As described above, the “back-etching” refers to etching from a rear surface (surface of the substrate opposite to the surface having the pellicle film formed thereon).
In this step, in order to leave a part of the substrate, namely, to leave a non-exposure area of the silicon wafer in a frame shape, it is conceivable to use a SiN (silicon nitride) mask 104 on the surface opposite to the surface having the pellicle film formed thereon (on the rear surface).
However, the present inventors found the followings (1) to (4). (1) In the case where back-etching is performed on the rear surface of the substrate, an etchant is partially put on a part of the substrate that is present under the mask provided on the surface opposite to the surface having the pellicle film formed thereon (the mask provided on the rear surface); and as a result, the silicon wafer is etched under the SiN mask 104 (portion 110 enclosed by the dashed line in
It is conceivable to remove the eaves-like portion itself by etching. However, especially in the case where, for example, the pellicle film is formed of SiN, it is highly difficult to remove the SiN mask 104 left in the eaves-like shape by etching with no influence on the performance of the pellicle film. Thus, the eaves-like portion could not be removed.
According to the present invention, the mask for back-etching is formed of a metal material (e.g., chromium (Cr) or the like) instead of the SiN mask 104, and a metal mask 204 is removed after the back-etching. According to the present invention, a mask having a significantly different etching rate from that of a material of a pellicle film 202 is used instead of the SiN mask 104, so that the mask is removed with no influence on a substrate 200 or the pellicle film 202. Thus, the mask is not left in the eaves-like shape, and the eaves-like portion is not formed. As a result, dust, which would be generated as a result of the SiN mask 104 left in the eaves-like shape being broken, is not generated.
First, the substrate 200 does not need to be a silicon wafer substrate. The shape of the substrate is not limited to a true circle, and the substrate may have an orientation flat, a notch or the like formed therein. The pellicle film does not need to be formed above the entire surface of the substrate.
It is preferred that the substrate 200, the pellicle film is to be formed, is formed of a material containing at least one of silicon, sapphire and silicon carbide. It is more preferred that the substrate 200 is formed of a material containing silicon, with which the substrate 200 may easily have a large area size.
There is no specific limitation on materials of the pellicle film, although there is an issue of compatibility between the substrate and the pellicle film to be stacked above the substrate, such that in the case where the pellicle film 202 formed of a silicon-based material is to be stacked above the substrate, it is preferred that the substrate is a silicon wafer substrate because of ease of stacking. For example, it is preferred that the pellicle film 202 is formed of a SiN film, a carbon-based film (e.g., graphene film, carbon nanotube film formed by spin coating, carbon nanosheet, or the like), a polycrystalline silicon film, or a stack structure including a plurality of layers of such materials. Among these materials, it is preferred that the pellicle film 202 is formed of a stack structure including three layers of a first SiN (silicon nitride) layer, a polycrystalline layer and a second SiN (silicon nitride) layer, or formed of a carbon-based film.
The pellicle film 202 has a thickness of about 10 nm or greater and about 100 nm or less, preferably 20 nm or greater and 60 nm or less because the pellicle film 202 needs to transmit EUV. In the case where the pellicle film has a stack structure including three layers of a first silicon nitride layer, a polycrystalline silicon layer and a second silicon nitride layer (not shown), the first silicon nitride layer may have a thickness of 1 nm or greater and 5 nm or less, the polycrystalline silicon layer may have a thickness of 30 nm or greater and 60 nm or less, and the second silicon nitride layer may have a thickness of 1 nm or greater and 5 nm or less. More preferably, the first silicon nitride layer may have a thickness of 1.5 nm or greater and 3 nm or less, the polycrystalline silicon layer may have a thickness of 30 nm or greater and 50 nm or less, and the second silicon nitride layer may have a thickness of 1.5 nm or greater and 3 nm or less. In the above step (S103), the metal mask 204 (e.g., chromium (Cr), titanium (Ti), nickel (Ni), copper (Cu), gold (Au), tungsten (W), molybdenum (Mo), iron (Fe), stainless steel, or the like) is provided on the surface opposite to the surface having the pellicle film formed thereon (
Next, (2) a part of the substrate is removed from the rear surface thereof, namely, from the side of the metal mask, (the part of the substrate is back-etched) until the pellicle 202 is exposed (S105;
The back-etching is performed by use of an etchant (first etching agent) that does not easily dissolve the pellicle film or the metal mask but dissolves the substrate. The material to be used as the etchant (first etching agent) is selected in accordance with the materials of the substrate, the pellicle film and the metal mask. The first etching agent may be formed of, for example, potassium hydroxide (KOH), tetramethylammonium hydroxide (TMAH) or the like, but is not limited to being formed of any of these materials.
There is no specific limitation on the shape of the frame. A relatively large region of the substrate may be left as the frame from the point of view of increasing the strength. Etching may be performed in a state that a different frame is attached to a portion to be a frame before the etching. By attaching the different frame, the frame can be reinforced. As the different frame, for example, a second frame 208 may be used. In a later step, the second frame 208 may be connected with the pellicle frame, in addition to the first frame 207. It should be noted that since the pellicle for EUV is limited in the height thereof, it is preferred that the pellicle film and the frame have a total height of 2 mm or less. The second frame 208 to be connected with the pellicle frame may have a jig hole formed therein.
The pellicle frame (assembly of the pellicle film and the first frame connected with the pellicle film) is connected with the second frame, and as a result, the pellicle is produced (
The present invention may include a step of removing particles. Examples of a method for removing the particles may include, for example, a wet cleaning method, a mechanical cleaning method, a dry cleaning method, and the like. The method for removing the particles is not limited to any of these methods. The wet cleaning method may be RCA cleaning such as SC1 cleaning or SC2 cleaning. The SC1 cleaning has a function of cleaning particles with ammonia and hydrogen peroxide. The SC2 cleaning has a function of cleaning heavy metal with hydrochloric acid and hydrogen peroxide. Other examples of the wet cleaning include cleaning with pure water and cleaning with an organic solvent. Examples of the wet cleaning also include cleaning sulfuric acid-hydrogen peroxide washing (mixture of sulfuric acid and hydrogen peroxide), cleaning with buffered hydrofluoric acid (mixture of hydrofluoric acid and ammonium fluoride), cleaning with hydrofluoric acid, and the like. These types of cleaning may be combined and performed in any order. Examples of the mechanical cleaning include brush cleaning, swing cleaning, ultrasonic cleaning, and high pressure spraying of aerosol such as argon or the like. Examples of the dry cleaning include ashing cleaning with O2 plasma, argon sputtering, and the like.
Then, (3) the metal mask left on the rear surface is removed (S107). In this step (S107), the metal mask is removed by use of a material that does not easily dissolve the substrate 200 or the pellicle film 202 but dissolves only the metal mask 204.
The material usable as a remover (second etching agent) for the metal mask is selected in accordance with the materials of the substrate, the pellicle film and the metal mask. Preferred combinations of materials are as follows. In the case where the substrate is formed of silicon wafer, the pellicle film is formed of SiN and the metal mask is formed of chromium, it is preferred to use ceric ammonium nitrate as the remover (second etching agent) for the metal mask. The following table shows preferred combinations of materials of the pellicle film 202, the metal mask 204, the etchant (first etching agent) and the remover (second etching agent).
With the above-described production method, a pellicle film and a pellicle frame provided with a mask having a length of the eaves-like portion of 0.5 μm or less, preferably 0.01 μm or less, more preferably 0 μm (no eaves-like portion) may be produced. Thus, a pellicle film, a pellicle frame and a pellicle with a decreased amount of dust are provided. As long as having a length within the above-described numerical range, the eaves-like portion has no influence on the drawings performed by photolithography when the pellicle is used as a pellicle for EUV.
According to the present invention, the substrate, the first frame or the second frame may be chamfered in at least one position. In this specification, “chamfering” refers to a concept encompassing R-chamfering and C-chamfering. “R-chamfering” refers to forming a curved portion by processing at least one end portion (side surface, edge, corner edge, etc.) of the substrate, the first frame (encompassing the first frame obtained as a result of the substrate being back-etched), or the second frame. In this specification, “C-chamfering” refers to shaving the at least one end portion obliquely (at an angle of 100 degrees or higher and 170 degrees or less). Such processing removes a cusp (acute angle portion) and thus chipped-off pieces are not easily generated even if the pellicle collides against some member during the transportation or handling after the production.
According to the present invention, at least one hole may be formed in the substrate 200 (
The holes 230 are formed by use of ultra-short pulse laser light or any other type of laser light, by etching, or the like. In the case where the holes 230 are formed by laser light, it is preferred to use ultra-short pulse laser light (e.g., picosecond laser light or nanosecond laser light), by which hole formation is performed with less debris, in order to form a high quality pellicle film with little dust or the like. It should be noted that the holes do not need to be formed in this step. Alternatively, the holes 230 may be formed by etching at the time of back-etching performed on the substrate as described below. In this manner, the production process may be simplified. In this case, after the trimming is performed, the hole formation and the etching are performed at the same time. In the case where the holes 230 are formed before the back-etching of the substrate, it is preferred to provide a step of protecting the holes 230 because the holes are expanded by the etching. In the step of protecting the holes 230, it is further preferred to form a metal mask according to the present disclosure also on inner walls of the holes 230.
As shown in
It is conceivable to perform trimming such that the substrate becomes, for example, rectangular. There is no specific limitation on the shape of the post-trimming shape of the substrate. The post-trimming substrate may have any shape. There is no specific limitation on the method of trimming. For example, there is a method of mechanically applying force to cut the pellicle film and the substrate, and it is also possible to cut the pellicle film and the substrate by laser cutting, laser half-cutting (stealth dicing), blade dicing, sandblasting, crystal anisotropic etching or dry etching. A technique that does not generate much dust of foreign substance particles at the time of trimming is preferred. After the back-etching, cleaning cannot be performed because the pellicle film is extremely thin. However, in the case where a step resulting in generating dust, such as a trimming step or the like, is performed before the back-etching, cleaning may be performed before the back-etching. Thus, a pellicle film, a pellicle frame and a pellicle with little dust may be produced.
Usually, the emissivity of a substance (ratio of the energy of light released by the substance by heat radiation with respect to the energy of light released by a black body having the same temperature as that of the substance (ratio of the radiance with respect to the black body radiance)) is generally in proportion to the thickness of the layer of the substance. Therefore, in the case where the layer is thin, the emissivity is low, in general. However, there are some metal materials having a locally improved emissivity in an area of the layer that is very thin. For example, ruthenium (Ru) and gold (Au) each have a locally improved emissivity in an area of the layer that is very thin. Since ruthenium (Ru) and gold (Au) have different values of emissivity, an appropriate material may be selected in accordance with the performance required of heat release.
In one embodiment according to the present invention, a surface metal coating layer 309 may be provided between the substrate 200 and the pellicle film 202 (
First, the material needs to have a high radiance even in the case where the layer of the material is thin, to have a high EUV transmittance, and not to be easily etched away by a remover (second etching agent) as a material removing the mask material. For example, ruthenium (Ru) is preferred. Since ruthenium (Ru) is not easily etched away by a remover (second etching agent) as a material removing the mask material, the mask is not left in an eaves-like shape even in the case of being used for the production method described in embodiment 1.
A preferable combination of a pellicle film, the mask and the etching agent including the surface metal coating layer 309: the surface metal coating layer 309 is formed of ruthenium (Ru); the pellicle film is formed of silicon nitride (SiN) layer, is formed of a stack structure including three layers of a first SiN layer, a polycrystalline silicon layer and a second SiN layer, or is formed of a carbon-based film; the mask is formed of chromium (Cr); and the remover (second etching agent) as a material removing Cr used to form the metal mask is formed of cerium diammonium nitrate, hydrochloric acid, or hydrochloric acid and nitric acid. The carbon-based film is usable because the carbon-based film is not easily etched away by a material removing the metal mask, for example, cerium diammonium nitrate or the like, like silicon nitride (SiN).
First, an 8-inch silicon wafer having a thickness of 725 μm was prepared as a substrate.
Next, silicon nitride was deposited to have a thickness of 5 nm on both of two surfaces of the silicon wafer by CVD, polysilicon was deposited thereon to have a thickness of 60 nm, and silicon nitride was deposited thereon to have a thickness of 5 nm. As a result, a pellicle film was formed. As a protective layer, a polycrystalline silicon film was formed to have a thickness of 400 nm.
Next, the film on one of the surfaces of the silicon wafer was removed by dry etching, and a Cr film was formed as a metal mask on this surface (surface of the silicon wafer opposite to the surface having the pellicle film formed thereon) by sputtering.
Next, the Cr film as the metal mask was patterned to have a predetermined shape for the purpose of removing a region of the metal mask corresponding to a region of the substrate that would be subjected to back-etching. As a result, the region of the metal mask corresponding to the region of the substrate that would be subjected to back-etching was removed.
Next, the silicon wafer was trimmed into a rectangular shape having a size of the pellicle. The side surfaces of the trimmed silicon wafer were chamfered (beveled), so that the edges of the silicon wafer were rounded off.
Next, the substrate was cleaned. For the cleaning, physical cleaning (rubbing cleaning) and chemical cleaning (oxidation and oxide layer removal) were used.
Next, a region of the silicon wafer where the pellicle film was to be formed was removed by back-etching. In this step, the silicon wafer was not entirely removed but was partially left such that the left part would be used as a frame. As a result of this step, the Cr film used as the etching mask included an eaves-like portion.
Next, the Cr mask was removed by etching. As a result, the eaves-like portion was removed. Thus, the problem to be solved by the present invention is solved.
The method for producing a pellicle film in preferred embodiments according to the present invention has been described. The above-described embodiments are merely examples, and the technological scope of the present invention is not limited to the above. A person of ordinary skill in the art would make various modifications without departing from the gist of the present invention defined by the claims. Therefore, such modifications are to be duly interpreted as being encompassed in the technological scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-127535 | Jun 2016 | JP | national |
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2016-127535 filed on Jun. 28, 2016, and PCT Application No. PCT/JP2017/022688, filed on Jun. 20, 2017, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2017/022688 | Jun 2017 | US |
| Child | 16222272 | US |
