JP4622482B2 - Method for exposing substrate coated with photosensitive resin - Google Patents

Description

  The present invention relates to a substrate exposure method for transferring a mask pattern to a photosensitive resin.

  Conventionally, a patterning method for transferring a mask pattern to a photosensitive resin by performing exposure that gives light energy to the photosensitive resin through an exposure mask patterns the resist to form an etching mask for forming an electric circuit. This method is widely applied to the case of forming a master structure for making a fine mold for forming a fine structure by electroforming or the like. The usage form of the photosensitive resin includes a form in which a liquid resin whose viscosity is adjusted is uniformly applied to the base material, or a film-like resin is attached to the base material. It is properly used according to the situation. Further, the patterning result, that is, the finish of the pattern shape, is greatly influenced by the conditions during exposure depending on the characteristics of the photosensitive resin.

  For example, in the case of a photosensitive resin having an acrylic group that is cured by applying radical energy to generate crosslinks by radical polymerization, the presence of oxygen during exposure inhibits the crosslinking reaction, resulting in insufficient curing. When the photosensitive resin applied to the substrate and in contact with the air layer is exposed, only the surface becomes uncured. In this case, in the development process that removes the uncured portion, which is the next step of the exposure step, the surface portion of the pattern that should not be removed is removed due to uncured, and the surface layer portion of the pattern is rounded. . If the processing accuracy is required for the three-dimensional shape in the thickness direction of the photosensitive resin in addition to the planar (two-dimensional) pattern accuracy of the portion where the pattern is in contact with the substrate, the pattern surface layer portion The roundness becomes a problem as deterioration of the pattern shape. For example, when an optical waveguide is formed using a light-transmitting photosensitive resin, a highly accurate three-dimensional shape is required because the three-dimensional shape of the pattern is the shape of the optical waveguide and directly affects the optical waveguide characteristics. Is done.

  The above-described curing inhibition by oxygen can be solved by adopting a configuration in which the photosensitive resin does not contact the air layer. For example, there is a so-called contact exposure method in which exposure is performed in a state where an exposure mask is in close contact with the photosensitive resin layer. However, when applying contact exposure, it is necessary to easily separate the photosensitive resin from the exposure mask after exposure, and use a dry photosensitive resin that is in a cured state and has no adhesion to the mask. There are constraints such as having to. Therefore, as a method for exposing a photocurable resin that is supposed to be inhibited by oxygen, a method of lowering the oxygen concentration in the exposure atmosphere by purging air with an inert gas such as nitrogen is generally used (for example, patents). Reference 1).

An example in which exposure is performed by purging with the above-described inert gas will be described with reference to FIG. A substrate 92 coated with a photosensitive resin 93 is placed on a substrate holder 91 placed in an open space, and an exposure mask 94 is disposed above the substrate 92. In this state, nitrogen gas is supplied onto the substrate 92 from the air supply hole 96 provided in the outer peripheral portion of the substrate 92 via the valve V1, and the valve V2 is supplied from the exhaust hole 97 also provided in the outer peripheral portion of the substrate 92. And exhaust air and nitrogen gas. Exposure is performed after a predetermined time.
JP-A-5-335201

  However, in the exposure method as shown in Patent Document 1 and FIG. 9 as described above, there is a possibility of inflow of oxygen in the atmosphere because of the configuration in which nitrogen is blown from the periphery of the substrate in an open space. There is a problem that the quality of the produced product is not stable. Further, due to the presence of inactive gas concentration unevenness due to incomplete purging or air flow accompanying purging, for example, there can be a difference in exposure conditions in the vicinity of the air supply hole 96 and the exhaust hole 97 shown in FIG. As a result of the exposure and development, as shown in FIG. 9, there is a problem that the shape varies depending on the location on the substrate with respect to the three-dimensional shape that should have the same cross-sectional pattern.

The present invention has been made to solve the above problems, that the photosensitive resin highly accurate three-dimensional shape of the exposed pattern can be uniformly realized across the substrate whole surface to provide an exposure method of a substrate coated Objective.

In order to achieve the above object, the invention of claim 1 is a method for exposing a substrate coated with a photosensitive resin, wherein the photosensitive resin is applied and disposed in a sealed space that can be supplied and exhausted. A mask placement step of placing a mask for exposure with a predetermined distance from the main surface of the substrate, and an atmosphere in the sealed space to make an inert gas atmosphere, while exhausting air in the space A purge step of injecting an inert gas, and an exposure step of patterning by irradiating the photosensitive resin applied to the main surface of the substrate with light through the mask,
The substrate is placed on a flat substrate holder, and the sealed space includes the substrate holder, a spacer standing on the substrate holder so as to surround the substrate placed on the substrate holder, A mask, and
The substrate holder has a through hole communicating with an air supply / exhaust path for supplying and exhausting the inside of the sealed space,
The spacer is formed of a material having flexibility, and the height of the spacer is increased by the flexibility of the spacer and the pressure change in the sealed space by exhausting from the through hole and reducing the pressure in the sealed space. there is adjusted distance between the mask and the substrate changes, in the purge step with a large interval so prone to substitution of gas, wherein in the exposure step is shall be adjusted to the interval suitable for exposure .

According to a second aspect of the invention, the exposure method of a substrate according to claim 1, wherein the substrate holder, air supply hole and an exhaust hole respectively communicating with the air supply passage and an exhaust passage for supply and exhaust of the enclosed space is formed The plurality of air supply holes or exhaust holes are formed at substantially equal intervals around the substrate placed on the substrate holder.

According to a third aspect of the present invention, in the substrate exposure method according to the first or second aspect , the purge step starts the injection of the inert gas prior to the exhaust of the air.

According to a fourth aspect of the present invention, in the substrate exposure method according to any one of the first to third aspects, the exposure step is performed after the purge step is completed.

According to the invention of claim 1, when the photosensitive resin is cured by light irradiation through the mask by lowering the oxygen concentration in the sealed space and consequently increasing the concentration of the inert gas, The photosensitive resin surface layer is not hindered by the cross-linking reaction, and deterioration of pattern accuracy can be prevented. In particular, not only two-dimensional pattern accuracy (line and space) on the substrate surface but also three-dimensional accuracy in the cross-sectional direction of the photosensitive resin layer is ensured. In the formation of the optical waveguide, the isotropic shape with respect to the light propagation direction can reduce the propagation loss. When the photosensitive resin layer is formed in the ridge shape as the optical waveguide, the corner is near the surface layer. 3D accuracy is required. Therefore, according to the present invention, the vicinity of the surface layer of the photosensitive resin layer serving as the optical waveguide can be sufficiently photocured during exposure, and the propagation loss can be reduced as the waveguide core shape. When performing the three-dimensional simulation of the design of the optical waveguide, the mask because it is two-dimensional, prone to actual machining three-dimensional shape and differences were, but pre-simulation Mi configuration designed according to the invention Patterning according to the mask can be performed. Further, with respect to general optical waveguide is disposed a uniform shape over the corresponding area (distance) assuming within the substrate plane, the present invention provides a patterning in the region of the substrate whole surface satisfies the premise of its uniform Sex can be obtained. In this way, the space where the photosensitive resin exists between the mask and the substrate is a sealed space, and the inert gas is injected while exhausting the air in the sealed space, thereby comparing the concentration of the inert gas with that of the conventional example. Therefore, it is possible to form a highly accurate pattern shape by preventing inhibition of curing of the photosensitive resin by oxygen.

Further, according to the first aspect of the invention, it is possible to form a closed space in a small area, it is possible to further speed up the purge step.

Further, according to the invention of claim 1, without requiring special control mechanism for adjusting the distance (gap) between the substrate and the mask, closer to the substrate and the mask in conjunction with the purge step in the time of exposure Thus, exposure accuracy can be improved.

According to the second aspect of the present invention, since the non-uniformity of the flow in the sealed space can be reduced by injecting the inert gas from the plurality of air supply holes, the concentration unevenness of the inert gas can be reduced, and the pattern has high accuracy. A three-dimensional shape can be realized uniformly over the front surface of the substrate. In addition, since the air supply amount and the exhaust amount of each air supply hole and exhaust hole can be individually adjusted, the concentration unevenness of the inert gas can be further reduced.

According to the invention of claim 3 , since the exhaust gas is started after the inert gas fills the entire enclosed space a little, uneven concentration of the inert gas can be reduced, and a highly accurate three-dimensional shape of the pattern can be obtained. It can be realized uniformly over the front surface of the substrate.

According to the invention of claim 4, since the non-uniformity of the inert gas concentration due to the gas flow in the sealed space is reduced, the exposure non-uniformity is reduced, and a highly accurate three-dimensional shape of the pattern can be realized uniformly over the front surface of the substrate. .

  Hereinafter, an exposure method for a substrate coated with a photosensitive resin according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an exposure apparatus used in the exposure method of the present invention, and FIG. 2 shows a flowchart of the exposure method. In the exposure method of the present invention, a photosensitive resin 3 is applied in a sealed space 11 formed by a sealed container 10 capable of supplying and exhausting air, and the main surface of the substrate 2 disposed on the substrate holder 1 in the space 11 (see FIG. A mask placement step (S1) for placing the exposure mask 4 at a predetermined distance from the upper surface of the air), and the air in the space 11 to make the atmosphere in the sealed space 11 an inert gas atmosphere. A purge process (S2) for injecting an inert gas while exhausting gas, an exposure process (S3) for patterning by irradiating the photosensitive resin 3 applied to the main surface of the substrate 2 with light L through a mask 4, and have. Next, details of each step will be described.

(Mask placement step S1)
The substrate 2 in FIG. 1 is a smooth substrate such as a silicon substrate or glass, and the photosensitive resin 3 on the substrate 2 is applied using a coating method such as spin coating, spray coating, or dipping. It is formed. As a material of the photosensitive resin 3 to be exposed in the present invention, a polymer resin material such as acrylic, epoxy, silicone, and polyimide, or a network of highly transparent inorganic materials such as SiO _{2 is} added thereto. The incorporated composite resin material can be used. Moreover, in order to control the thickness of the photosensitive resin 3, you may adjust a viscosity with a solvent. The substrate 2 coated with such a photosensitive resin 3 is placed on the substrate holder 1, and the substrate 2 and the mask 4 are arranged so as to have a predetermined gap.

(Purge step S2)
Next, an inert gas such as nitrogen gas N ₂ is injected from the piping system provided with the valve V1 through the piping system provided with the valve V2 while exhausting the inside of the sealed space 11 by an exhaust pump (not shown). The oxygen O ₂ concentration causing the curing inhibition of the functional resin 3 is decreased. At this time, by using the flow meter 14 in the exhaust system and the flow meter 12 in the inert gas supply system, the air is replaced with the inert gas while the sealed space 11 is maintained at, for example, substantially atmospheric pressure. The replacement with the inert gas depends on the volume of the space 11. For example, if the diameter is about 150 mm × the height is about 10 mm, the replacement can be sufficiently performed within about 5 minutes. More reliable replacement can be determined by monitoring the oxygen concentration in the exhaust gas using the oxygen concentration meter 13 provided in the exhaust system.

(Exposure step S3)
In the sealed space 11, exposure is performed on the substrate in which oxygen is replaced with an inert gas in the purge step S2. As described above, the space between the mask 4 and the substrate 2 is the sealed space 11, and the inert gas is injected while exhausting the air in the sealed space 11, so that the concentration of the inert gas is higher than that of the conventional example. Therefore, it is possible to carry out exposure by reliably reducing the oxygen concentration and preventing deterioration of pattern accuracy due to inhibition of curing of the photosensitive resin by oxygen.

  The above-described exposure step S3 is preferably performed after a purge step S2 and after that a step of reducing the gap between the substrate 2 and the mask 4 is performed. This is due to the following reason. When the inert gas is replaced in the purge step S2, the gap between the substrate 2 coated with the photosensitive resin 3 and the mask 4 is desirably set to 50 μm or more in order to prevent insufficient gas replacement. On the other hand, the gap between the substrate 2 and the mask 4 is preferably 50 μm or less when a pattern of 10 μm or less is formed using, for example, ultraviolet light having a wavelength λ = 350 to 450 nm. Therefore, by performing the purge process under a large gap and performing the exposure process under a small gap, an efficient purge process and an exposure process that improves pattern accuracy can be performed.

  Next, another example of the exposure method of the present invention will be described with reference to FIGS. In this exposure method, as shown in FIGS. 3A and 3B, the substrate 2 is placed on a flat substrate holder 1, and the sealed space 11 is placed on the substrate holder 1 and the substrate holder 1. The spacer 5 and the mask 4 are provided on the substrate holder 1 so as to surround the periphery of the substrate 2. The inert gas is supplied from the air supply hole 6 provided in the substrate holder 1, and the space 11 is exhausted from the exhaust hole 7. In the mask arrangement step S1 of the exposure method using such an apparatus, the substrate 2 on which the photosensitive resin 3 is formed is set on the substrate holder 1, and the spacer 5 is installed on the substrate holder 1 so as to form a predetermined gap. Then, by placing the mask 4 on the spacer 5, a sealed exposure space 11 is formed. Thereafter, the purge process S2 and the exposure process S3 are performed as described above. When the sealed space 11 is formed with such a configuration, a small sealed space 11 can be formed, and thus the purge process can be speeded up. As shown in FIG. 4, an inert gas supply hole 6 and an exhaust hole 7 may be provided in the spacer 5. Further, the air supply holes 6 and the exhaust holes 7 may be provided in the mask 4.

  Next, another example of the exposure method of the present invention will be described with reference to FIGS. In this exposure method, as shown in FIG. 5A, the substrate holder 1 is formed with through holes (air supply holes 6 and exhaust holes 7) communicating with an air supply / exhaust path for supplying and exhausting air in the sealed space 11. The spacer 5 having a height d1 is formed of a flexible material, and is evacuated from the exhaust hole 7 to depressurize the sealed space 11, whereby the atmospheric pressure is obtained as shown in FIG. The height of the spacer 5 subjected to pressure by P is reduced to a height d2 (d2 <d1), and the distance (gap) between the substrate 2 and the mask 4 is reduced. That is, the gap adjustment is performed by changing the pressure in the sealed space 11.

  In the mask arrangement step S1 of the exposure method using such an apparatus, the substrate 2 on which the photosensitive resin 3 is formed is set on the substrate holder 1, formed of a flexible material, and the spacer 5 is installed. Further, by installing the mask 4 on the spacer 5, a sealed exposure space 11 is formed. By adjusting the supply amount of the inert gas from the air supply hole 6 and the exhaust amount from the exhaust hole 7 with reference to the flow meters 12 and 14 respectively, the pressure in the sealed space 11 is appropriately reduced, and the spacer 5 Is set to d2, and the substrate 2 and the mask 4 are brought close to a predetermined gap. According to such a method, a desired gap in which the substrate 2 and the mask 4 are closer to each other is realized by adjusting the pressure in the space 11 without using a special control mechanism for adjusting the gap, thereby improving the pattern accuracy. Can be made. In this case, a second spacer for fixing the height (not shown) made of a rigid body having a predetermined height d2 may be used at a position adjacent to the spacer 5.

  Next, the purge process in the present invention will be described with reference to FIGS. If there is a bias in the flow of the inert gas supplied into the sealed space or the gas exhausted from the sealed space in the purge process, the concentration of the inert gas is uneven as shown in region D of FIG. To do. Such concentration unevenness of the inert gas causes a shape defect or shape non-uniformity in the pattern shape formed on the photosensitive resin. In order to reduce such density unevenness, as shown in FIG. 6B, among the air supply holes 6 and the exhaust holes 7 respectively communicating with the air supply path and the exhaust path for supplying and exhausting the sealed space, the air supply holes 6 is formed around the substrate 2 placed on the substrate holder 1 at substantially equal intervals, and an inert gas is injected into the sealed space using the plurality of inert gas supply holes 6. Thereby, density unevenness can be reduced and pattern shape accuracy can be improved.

  Further, by adjusting the air supply flow rate of the air supply holes 6, the concentration unevenness of the inert gas in the sealed space can be further reduced. As a method, a flow meter is installed in each of the air supply holes 6 and the valves are individually opened and closed to individually adjust the flow as needed. In addition, the pipe diameter of the air supply holes 6 is set in advance and the flow rate is thereby adjusted. Adjustments can be made. In this case, it is effective to obtain the flow of the airflow by simulation in advance and refer to the result. These things can be performed in the same way for the exhaust holes 7 to reduce the concentration unevenness of the inert gas.

  Further, in order to make the atmosphere in the sealed space an inert gas atmosphere, as shown on the left side of FIG. 7, while the air in the space is exhausted from the exhaust hole 7, the inert gas is supplied from the supply hole 6, In addition, it is effective to sequentially switch the exhaust hole 7 and the air supply hole 6 as shown on the right side of FIG. In this way, by sequentially switching the positions of the exhaust hole 7 and the air supply hole 6, the deviation of the gas flow in the sealed space can be reduced, and the concentration unevenness of the inert gas can be reduced.

  Next, with regard to the exposure method performed under the configuration of any one of the air supply holes 6 and the exhaust holes 7 described above and the configuration of the sealed space, matters related to a purge process effective for obtaining a highly accurate pattern shape will be described. To do. For example, in the purge process, the inert gas injection is started before the air is exhausted. According to this method, since the exhaust gas is started after the inert gas fills the entire sealed space a little, the concentration unevenness of the inert gas can be reduced. The exposure process is performed after the purge process is completed. When stopping the purge process, it is desirable to stop the exhaust of air before stopping the supply of inert gas. As a result, it is possible to prevent a sudden pressure drop in the sealed space that occurs when the injection of the inert gas is stopped first, and the accompanying contamination from the outside.

  Further, the purge process is performed by supplying an inert gas from a plurality of supply holes while exhausting the air in the space in order to make the atmosphere in the sealed space an inert gas atmosphere. At this time, each air supply hole is connected to a gas reservoir (buffer) having a uniform pipe diameter from each other, and the pipe distance from each air supply hole is substantially equal, and through this gas reservoir Air supply shall be performed. In the purge step by such an air supply method, the flow rate of the inert gas to be supplied can be made uniform between the air supply holes, and therefore the concentration unevenness of the inert gas can be reduced.

  Next, an example in which an optical waveguide is formed using any of the exposure methods of the present invention described above will be described. The optical waveguide plate is formed using a clad substrate made of the clad material itself or a clad substrate in which a clad material is formed on a smooth substrate such as a silicon substrate or a glass substrate. The thickness of the clad material is preferably 10 μm or more in order to reduce polarization dependent loss, although it depends on the refractive index difference with the core material. On the prepared clad substrate, a core layer for forming a core to be a waveguide is formed with a photosensitive resin. In order to propagate light having a wavelength of 1.3 to 1.6 μm through the core in a single mode, the height and width of the core are preferably about 3 to 10 μm. For more stable light propagation, it is desirable that the core shape is isotropic with respect to the central axis of the propagation direction, for example, in the case of a rectangle, the aspect ratio of the core is 1. However, depending on the required optical circuit pattern, Not as long. The clad substrate on which the core layer is formed is set on a substrate holder. Thereafter, a clad substrate having a core layer that is exposed and patterned into the shape of a waveguide core is obtained through the above-described mask placement step (S1), purge step (S2), and exposure step (S3). Thereafter, the soluble portion of the core layer is removed by etching or the like to form a core portion as an optical waveguide, and an optical waveguide plate having a favorable rectangular waveguide core is obtained. FIG. 8 shows an example of a waveguide core cross section in a plane orthogonal to the optical axis of the waveguide core. The rectangular shape in the center of the figure is the core portion, and the substrate below the core portion is a clad material. A waveguide core having a good cross-sectional shape is thus formed at any location on the substrate. For reference, a 6 μ dimension scale is attached. According to the exposure method of the present invention, in addition to the accuracy of the two-dimensional pattern shape without deviation in the substrate plane, the waveguide core is close to the design shape while maintaining the cross-sectional shape of the waveguide core, that is, the three-dimensional shape accuracy. Thus, a good optical waveguide plate with little optical loss can be obtained. The present invention is not limited to the above-described configuration, and various modifications can be made.

Sectional drawing of the exposure apparatus used for the exposure method of the board | substrate which concerns on this invention. The flowchart which shows an exposure method same as the above. (A) is a top view of the state which removed the mask of the exposure apparatus used for the other example of the exposure method of this invention, (b) is AA sectional drawing of (a). Sectional drawing of the exposure apparatus used for the further another example of the exposure method of this invention. (A) is sectional drawing of the state before the purge process of the exposure apparatus used for the further another example of the exposure method of this invention, (b) is sectional drawing after the purge process of the exposure apparatus. (A) is an internal top view of the exposure apparatus explaining the purge process in the further another example of the exposure method of this invention, (b) is an internal top view of the exposure apparatus explaining the malfunction of a purge process. The internal top view of the exposure apparatus which showed the purge process in the further another example of the exposure method of this invention in time series. The figure which expanded and imaged and showed the cross section of the photosensitive resin exposed and developed by the exposure method of this invention. Sectional drawing of the exposure apparatus which shows the conventional exposure method, and the figure which expanded and imaged and showed the cross section of the photosensitive resin exposed and developed by the exposure method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Board | substrate holder 2 Board | substrate 3 Photosensitive resin 4 Mask 5 Spacer 6, 6a Air supply hole 7, 7a Exhaust hole 11 Sealed space

Claims (4)

An exposure method for a substrate coated with a photosensitive resin,
In a sealed space where air can be supplied and exhausted, a mask placement step of placing a mask for exposure with a predetermined distance from the main surface of a substrate coated with a photosensitive resin and placed in the space;
In order to make the atmosphere in the sealed space an inert gas atmosphere, a purge step of injecting an inert gas while exhausting air in the space;
An exposure step of patterning by irradiating light to the photosensitive resin applied to the main surface of the substrate through the mask, and
The substrate is placed on a flat substrate holder, and the sealed space includes the substrate holder, a spacer standing on the substrate holder so as to surround the substrate placed on the substrate holder, A mask, and
The substrate holder has a through hole communicating with an air supply / exhaust path for supplying and exhausting the inside of the sealed space,
The spacer is formed of a material having flexibility, and the height of the spacer is increased by the flexibility of the spacer and the pressure change in the sealed space by exhausting from the through hole and reducing the pressure in the sealed space. features There is adjusted distance between the mask and the substrate change, with a large interval so prone to substitution gas in the purge step, that you adjust the spacing suitable for exposing the said exposure step A substrate exposure method.   The substrate holder has an air supply hole and an exhaust hole communicating with an air supply path and an exhaust path for supplying and exhausting the sealed space, respectively, and the air supply hole or the exhaust hole is a substrate placed on the substrate holder. The substrate exposure method according to claim 1, wherein a plurality of wafers are formed at substantially equal intervals around the substrate.   3. The substrate exposure method according to claim 1, wherein the purging step starts injection of an inert gas before exhausting air. 4.   4. The substrate exposure method according to claim 1, wherein the exposure step is performed after the purge step is completed. 5.

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