JP6408396B2 - Pellicle film manufacturing method, pellicle manufacturing method, and photomask manufacturing method - Google Patents

Description

  The present invention relates to a technique for manufacturing a pellicle film capable of transmitting EUV (Extreme Ultraviolet) light.

  A photomask used in photolithography (sometimes referred to as a reticle) causes a pattern formation defect when dust or the like adheres to the pattern surface. Therefore, the pellicle is arranged on the photomask so that the pellicle film is arranged at a part slightly away from the pattern surface. As a result, even if dust adheres to the pellicle film, it is present at a position shifted from the pattern surface. Therefore, the shape of the attached dust can be prevented from focusing on the exposure surface.

  With the miniaturization of patterns to be formed, there are exposure apparatuses that use EUV light. For EUV light, for example, light with a very short wavelength of about 13.5 nm is used, so that the transmittance to a substance is very low and the refractive index is close to 1, so that a transmission optical system is used. Can not. Therefore, a reflection optical system is used for the exposure apparatus (for example, Patent Document 1).

JP 2014-071208 A

  However, the pellicle film needs to be incorporated in the optical system so that EUV light is transmitted. Therefore, the pellicle film is not used in the technique of Patent Document 1. If the film thickness can be reduced to about 10 nm, the transmittance for EUV light may be improved. However, it is difficult to manufacture a pellicle film that is thin and large in area as the transmittance for EUV light increases. there were.

  One of the objects of the present invention is to provide a method for producing a pellicle film having a high transmittance for EUV light.

  According to one embodiment of the present invention, forming a nitrogen-containing silicon layer and a main layer on a substrate and forming a laminated film that transmits EUV light, and forming the nitrogen-containing silicon layer includes forming the nitrogen-containing silicon layer. Provided is a method for manufacturing a pellicle film, which includes forming a film thicker than a silicon layer containing silicon, and then thinning the nitrogen-containing silicon layer to have a film thickness of 5 nm or less using xenon difluoride gas. .

  The nitrogen-containing silicon layer may be formed on both surfaces of the main layer.

  The nitrogen-containing silicon layer may have a composition ratio of nitrogen to silicon of 1 to 1.5.

  The nitrogen-containing silicon layer may further contain oxygen, and a composition ratio of oxygen to silicon may be greater than 0 and 2 or less.

  The nitrogen-containing silicon layer may be formed to 4 nm to 15 nm and then thinned to 3 nm or less.

  According to an embodiment of the present invention, a pellicle film is formed on the support substrate by the method for manufacturing a pellicle film described above, and the support substrate is etched to expose a part of the pellicle film, A method for manufacturing a pellicle is provided, which includes forming a support portion that supports the periphery of the pellicle membrane and attaching a frame to the support portion.

Further, according to an embodiment of the present invention, on a supporting substrate, the nitrogen-containing silicon layer and forming a multilayer film comprising a main layer, the supporting substrate is etched to expose a portion of the laminated film, Forming a support portion that supports the periphery of the laminated film, and attaching a frame body to the support portion, and after forming the support portion or after attaching the frame body to the support portion, the exposure A pellicle comprising: thinning the nitrogen-containing silicon layer of the laminated film using xenon difluoride gas so as to have a film thickness of 5 nm or less, and imparting EUV light transmission to the laminated film A manufacturing method is provided.

  According to another embodiment of the present invention, there is provided a photomask manufacturing method including bonding a pellicle manufactured by the above-described pellicle manufacturing method to a substrate on which a pattern is formed via the frame. Provided.

  According to an embodiment of the present invention, it is possible to provide a method for manufacturing a pellicle film having a high transmittance for EUV light.

It is the schematic which shows the external appearance of the photomask with a pellicle in one Embodiment of this invention. It is the schematic which shows the cross-section of the photomask with a pellicle in one Embodiment of this invention. It is a figure explaining the manufacturing method of the pellicle film in one embodiment of the present invention. It is a figure explaining the manufacturing method of the pellicle and photomask with a pellicle in one Embodiment of this invention. It is a figure explaining the manufacturing method of the pellicle film in other embodiment of this invention.

  Hereinafter, a photomask with a pellicle according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition, embodiment shown below is an example of embodiment of this invention, This invention is limited to these embodiment, and is not interpreted. Note that in the drawings referred to in the present embodiment, the same portion or a portion having a similar function is denoted by the same reference symbol or a similar reference symbol (a reference symbol simply including A, B, etc. after a number) and repeated. The description of may be omitted. In addition, the dimensional ratios of the drawings (the ratios between the components, the ratios in the vertical and horizontal height directions, etc.) may be different from the actual ratios for convenience of explanation, or some of the configurations may be omitted from the drawings.

[overall structure]
FIG. 1 is a schematic diagram showing the appearance of a pellicle-equipped photomask 1 according to an embodiment of the present invention. FIG. 2 is a schematic view showing a cross-sectional structure of the photomask with pellicle 1 in one embodiment of the present invention. This cross-sectional structure corresponds to the cross section along the cross-sectional line AA ′. In FIG. 2, it is represented as an end view.

  The photomask with pellicle 1 includes a pellicle 10 and a photomask 50. The pellicle 10 is attached to the surface 55 side on which the pattern of the photomask 50 is formed. The pellicle 10 includes a pellicle film 100, a support part 200, and a frame body 30.

  Although the pellicle film 100 is shown as a single layer in FIG. 2, it is actually a laminated film in which a main layer and protective layers are formed on both sides thereof. Details of the pellicle film 100 will be described later. The support part 200 is about 0.7 mm of silicon and supports the periphery of the pellicle film 100.

  The frame body 30 is disposed between the photomask 50 and the support portion 200. In this example, the thickness of the frame is determined so that the pellicle film 100 and the photomask 50 have an interval of about 2 mm. The frame 30 is joined to the photomask 50 and the support part 200 via an adhesive layer. Note that a vent hole for connecting the space formed between the photomask 50 and the pellicle film 100 and the external space may be formed in the frame 30 or the support portion 200.

[Configuration of Pellicle Film 100]
As described above, the pellicle film 100 is a laminated film of a main layer and a protective layer. In this example, the main layer is a polysilicon (p-Si) film, and the protective layer is a silicon nitride (Si ₃ N ₄ ) film. Here, the role of the protective layer will be described. In FIG. 3F described later, the laminated film constituting the pellicle film 100 is represented as a main layer 130 and protective layers 110 and 150.

  In the EUV exposure process, impurities (for example, carbon-derived components) adhere to the photomask 1 with a pellicle during EUV exposure. Therefore, hydrogen gas flows near the stage where the pellicle-equipped photomask 1 is installed. When hydrogen gas absorbs EUV light, it changes into hydrogen radicals or hydrogen ions. Therefore, the outermost surface is required to have reduction resistance so that the pellicle film 100 is not reduced.

  In this example, a silicon nitride film is used as one of the reduction resistant films. However, the silicon nitride film has a higher EUV light absorption rate than a silicon film, a carbon film, or the like. Therefore, in order to use the silicon nitride film as a self-supporting film, it is difficult to transmit EUV light when it is attempted to obtain a film strength by increasing the film thickness.

  Therefore, a film having a high transmittance with respect to EUV light is used as a main layer, and the main layer is made thick enough to obtain a film strength necessary for self-supporting. Then, a protective layer (silicon nitride film) having higher reduction resistance than the main layer is thinly laminated on the surface of the main layer. The surface of the main layer may be only one side or both sides. Thereby, reduction resistance is improved while obtaining film strength as a whole laminated film constituting the pellicle film 100.

  As described above, in consideration of the EUV light absorption rate, the silicon nitride film needs to be formed as thin as possible while leaving a protective function having resistance to reduction. In this case, the thickness of the silicon nitride film is desirably 5 nm or less, more desirably 2 nm or less. In addition, it is necessary to make the film thickness distribution as uniform as possible in order to suppress variation in transmittance. A method of manufacturing the pellicle film 100 that satisfies such conditions and has high transparency to EUV light as a whole film will be described below.

[Method of Manufacturing Pellicle Film 100]
FIG. 3 is a diagram illustrating a method for manufacturing a pellicle film according to an embodiment of the present invention. First, a support substrate 250 that finally becomes the support portion 200 is prepared (FIG. 3A). The support substrate 250 is a silicon substrate in this example. The support substrate 250 may not be a silicon substrate. However, as will be described with reference to FIG. 4B, when the support substrate 250 is etched, the selectivity with respect to the pellicle film 100 (particularly, the protective layer 110). Therefore, it is necessary to be able to take an etching method that can sufficiently ensure (the extent that the protective layer 110 remains).

  A silicon nitride film 115 that will eventually become the protective layer 110 is formed on the support substrate 250 (FIG. 3B). The silicon nitride film 115 is preferably formed by LPCVD, but other formation methods such as PECVD and sputtering may be employed. The film thickness is 8 nm. This film thickness is preferably 4 nm or more and 15 nm or less, and more preferably 5 nm or more and 10 nm or less. Note that, depending on LPCVD, silicon nitride films may be formed on both surfaces of the support substrate 250, but the description of the back surface side (the lower surface in the figure) of the support substrate 250 is omitted in each drawing. The same applies to the following drawings.

Subsequently, the silicon nitride film 115 is etched to a thickness of 2 nm (FIG. 3C). The thinned film becomes the protective layer 110 described above. Note that the film thickness after being thinned is desirably 1 nm or more and 3 nm or less. Etching is performed by a method in which the silicon nitride film 115 is exposed to xenon difluoride (XeF ₂ ) gas. Hereinafter, the etching for thinning will be described in detail.

An example of the etching method is as follows. First, the substrate shown in FIG. 3B is placed in the chamber. after that,
(1) After the chamber is evacuated (0.3 Torr (40 Pa)), the xenon difluoride crystal is sublimated, and the gasified xenon difluoride is introduced into the etching chamber.
(2) The chamber temperature is maintained at 40 ° C., and the chamber gas pressure is maintained at 3.8 to 4.0 Torr (507 to 533 Pa). Then hold for 60 seconds. During this time, the silicon nitride film 115 is exposed to xenon difluoride and etched.
(3) The chamber is evacuated to 0.03 Torr (4 Pa).
The cycles (1) to (3) are repeated until the thickness of the silicon nitride film 115 reaches the target value. The etching amount in (2) is 0.3 nm per cycle. In this example, 20 cycles are performed to reduce the film thickness from 8 nm to 2 nm. In addition, the time of (2) may be lengthened and the number of cycles may be reduced. On the contrary, the number of cycles may be increased by shortening the time (2). By such treatment, the silicon nitride film 115 is thinned and the protective layer 110 is formed.

  Thus, by forming the silicon nitride film 115 with a thicker film, the film quality can be stabilized than when it is formed with a thin film from the beginning. In addition, xenon difluoride, which is generally not used as an etching gas for a silicon nitride film, is gasified and etched. As a result, the etching rate can be reduced (0.3 nm / min), and the film thickness controllability at the time of thinning can be improved. Further, since the gas is not turned into plasma, physical damage to the protective layer 110 is small.

As the etching of the silicon nitride film 115, the following examples can be considered in addition to the vapor etching using xenon difluoride. However, there is a problem in both cases and it cannot be adopted.
(1) Wet etching with buffered hydrofluoric acid (BHF) The etching rate for the silicon nitride film is about 33.0 nm / min. Therefore, the etching rate is too fast to etch several nm.
(2) RIE plasma etching with CF ₄ + O _{2 The} etching rate for the silicon nitride film is about 250.0 nm / min. Therefore, the etching rate is too fast to etch several nm. In addition, damage to the film due to plasma is large.
(3) Wet etching with alkali (KOH or TMAH (Tetramethylammonium hydroxide)) The etching rate for the silicon nitride film is 0.01 nm / min or less. Therefore, the etching rate is too slow to etch several nm.
(4) Steam etching of hydrofluoric acid Etch pits are generated.

  Subsequently, a polysilicon film which is the main layer 130 is formed on the protective layer 110 (FIG. 3D). This polysilicon film is formed by LPCVD. The film thickness is 40 nm. This film thickness is desirably 30 nm to 50 nm. Note that, similarly to the step of forming the protective layer 110 described above, a slightly thicker polysilicon film may be formed and then thinned.

  A silicon nitride film 155 that will eventually become the protective layer 150 is formed on the main layer 130 (FIG. 3E). In this example, the method for forming the silicon nitride film 155, the film thickness, and the like are the same as the method for forming the silicon nitride film 115, but may be different. Subsequently, the silicon nitride film 155 is etched to a thickness of 2 nm (FIG. 3F). The thinned film becomes the protective layer 150 described above.

  Note that, in this thinning process, the silicon nitride film 155 is thinned by using xenon difluoride gas in the same manner as the thinning process of the silicon nitride film 115 (FIG. 3C). Is done. In this way, the protective layer 150 is formed in the same manner as the protective layer 110. Then, the pellicle film 100 is formed as a laminated film of the protective layer 110, the main layer 130, and the protective layer 150.

[Method for Manufacturing Pellicle 10]
FIG. 4 is a diagram illustrating a method for manufacturing a pellicle and a photomask with a pellicle according to an embodiment of the present invention. Region A shown in FIG. 4A corresponds to FIG. Although the pellicle film 100 is described as a single layer film in FIG. 4, it is a laminated film as described above.

  In the state of FIG. 3F, the mask 260 is formed only around the back surface side (the surface opposite to the surface on which the pellicle film 100 is formed, the surface on the lower side of the figure) of the support substrate 250 (FIG. 4 ( a)). The mask 260 may be a silicon oxide film, for example. Further, if a silicon nitride film or the like is formed on the back side by LPCVD as described above, the silicon nitride film or the like may be used. The step of forming the mask 260 may be after the step shown in FIG. 3E, that is, after the silicon nitride film 155 is formed and before the silicon nitride film 155 is thinned.

  When wet etching (anisotropic etching) with TMAH or KOH is performed on the substrate in FIG. 4A on which the mask is formed, the support substrate 250 in the unmasked region is etched to form an opening OP, The support part 200 remains around (FIG. 4B). In the portion of the opening OP, the pellicle film 100 supported by the support unit 200 remains as a self-supporting film. The pellicle film 100 has a main layer 130 formed of a polysilicon film, but remains protected without being etched from TMAH or KOH by the protective layers 110 and 150 formed on both sides thereof. Note that thinning of the nitrogen-containing silicon layer with xenon difluoride may be performed after FIG. In this case, the nitrogen-containing silicon layer on the front surface and the back surface of the main layer can be simultaneously thinned, and the process can be simplified. A specific processing method will be described later. Further, since the xenon difluoride gas is not converted into plasma, physical damage to the pellicle film is small.

  Then, the support part 200 and the frame 30 are joined through an adhesive layer (FIG. 4C). Thereby, the pellicle 10 is formed. When the pellicle 10 is bonded to the photomask 50, the frame 30 and the photomask 50 are bonded via an adhesive layer (FIG. 4D). The adhesive layer in this portion may be provided with a release liner, and may be peeled off when bonded to the photomask 50. In this way, the photomask with pellicle 1 is formed.

[Other examples of main layer 130]
The main layer 130 described above is a polysilicon film, but may be another film as long as it is highly permeable to EUV light. For example, the main layer 130 may be a graphene film or a resin film such as a PI (polyimide) film. In the case of a graphene film, a main layer 130 is obtained by forming a film on a predetermined substrate with a thickness of, for example, 8 nm or more and 15 nm or less by thermal CVD, etching the substrate, and transferring it onto the protective layer 110. It is done. In the case of a PI film, it is desirable that the film be formed to a thickness of 8 nm to 15 nm using spin coating.

Here, a combination of the main layer 130 and the protective layers 110 and 150 for obtaining the pellicle film 100 having a transmittance of 90% or more with respect to EUV light (here, the wavelength is 13.5 nm) is illustrated.
(1) When the main layer 130 is a polysilicon film having a thickness of 45 nm, the protective layers 110 and 150 each have a thickness of 1.5 nm.
(2) When the main layer 130 is a polysilicon film having a thickness of 35 nm, the protective layers 110 and 150 each have a thickness of 2.5 nm.
(3) When the main layer 130 is a PI film having a thickness of 10 nm, the protective layers 110 and 150 each have a thickness of 1.5 nm.
(4) When the main layer 130 is a PI film having a thickness of 13 nm, the protective layers 110 and 150 each have a thickness of 2.5 nm.
(5) When the main layer 130 is a graphene film having a thickness of 12 nm, the protective layers 110 and 150 each have a thickness of 1.5 nm.
(6) When the main layer 130 is a 9 nm-thick graphene film, the protective layers 110 and 150 each have a thickness of 2.5 nm.
With the combination of film type and film thickness as described above, a transmittance of 90% or more can be obtained for EUV light.

[Other examples of protective layers 110 and 150]
The protective layers 110 and 150 described above are formed of a silicon nitride film, but may further contain oxygen. That is, the protective layers 110 and 150 may be nitrogen-containing silicon films. When the composition is expressed as Si _x N _y O _z , the composition ratio y / x of nitrogen to silicon is 1 or more and 1.5 or less. The composition ratio z / x of oxygen to silicon is preferably 0 or more and 2 or less.

[Other configurations]
As described above, the silicon nitride films (protective layers 110 and 150) are formed on both surfaces of the main layer 130, but the silicon nitride film may be formed only on one surface. For example, when the space where the photomask 50 and the pellicle film 100 are separated from the external space is the only surface that needs to have reduction resistance, the silicon nitride film is formed only on that surface. It may be.

[Other examples of thinning process of silicon nitride film]
In the embodiment described above, the silicon nitride films 115 and 155 are thinned in the steps of FIGS. On the other hand, the silicon nitride films 115 and 155 may be thinned after the process is performed without forming the thin film and the opening OP is formed as shown in FIG.

  FIG. 5 is a diagram for explaining a method of manufacturing a pellicle film according to another embodiment of the present invention. FIG. 5A corresponds to FIG. 4B, and shows a state where the laminated film 100 </ b> A in which the silicon nitride films 115 and 155 are not thinned is supported by the support portion 200. FIG. 5B is an enlarged view of the vicinity of the support portion 200 (a region surrounded by a broken line) in FIG.

In this state, when the silicon nitride films 115 and 155 are exposed to xenon difluoride (XeF ₂ ) gas, the exposed portions of the silicon nitride films 115 and 155 are thin as shown in FIG. 5B. It becomes. The silicon nitride film 150A is a protective layer obtained by thinning the entire silicon nitride film 155. On the other hand, the silicon nitride film 110A is a protective layer obtained by thinning the silicon nitride film 115 in the region exposed by the opening OP. In this way, the protective layer of the pellicle film may be thinned.

DESCRIPTION OF SYMBOLS 1 ... Photomask with pellicle, 10 ... Pellicle, 30 ... Frame, 50 ... Photomask, 100 ... Pellicle film, 110, 150 ... Protective layer, 130 ... Main layer, 200 ... Support part

Claims (8)

Forming a laminated film that includes a nitrogen-containing silicon layer and a main layer and transmits EUV light on a substrate;
The nitrogen-containing silicon layer is formed by forming a film thicker than the nitrogen-containing silicon layer and then thinning the nitrogen-containing silicon layer to a thickness of 5 nm or less using xenon difluoride gas. A method for manufacturing a pellicle film.   The method for producing a pellicle film according to claim 1, wherein the nitrogen-containing silicon layer is formed on both surfaces of the main layer.   2. The method for producing a pellicle film according to claim 1, wherein the nitrogen-containing silicon layer has a composition ratio of nitrogen to silicon of 1 to 1.5.   4. The method for producing a pellicle film according to claim 3, wherein the nitrogen-containing silicon layer further contains oxygen, and a composition ratio of oxygen to silicon is greater than 0 and 2 or less. 5.   2. The method for producing a pellicle film according to claim 1, wherein the nitrogen-containing silicon layer is formed to have a thickness of 4 nm or more and 15 nm or less and then thinned to 3 nm or less. A pellicle film is formed on a support substrate by the method for producing a pellicle film according to any one of claims 1 to 5,
Etching the support substrate to expose a portion of the pellicle film to form a support portion for supporting the periphery of the pellicle film;
A method for manufacturing a pellicle, comprising attaching a frame to the support portion. A laminated film including a nitrogen-containing silicon layer and a main layer is formed on the support substrate,
Etching the support substrate to expose a part of the laminated film to form a support part for supporting the periphery of the laminated film;
Including attaching a frame to the support,
After forming the support part or attaching the frame body to the support part, the exposed nitrogen-containing silicon layer of the stacked film has a film thickness of 5 nm or less using xenon difluoride gas. A method for producing a pellicle, comprising: forming a thin film so that the laminated film has EUV light transmittance.   A method for manufacturing a photomask, comprising: bonding a pellicle manufactured by the method for manufacturing a pellicle according to claim 6 or 7 to a substrate on which a pattern is formed via the frame.

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