JP4696813B2 - Mold manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a mold in which a portion constituting the mold is made of a resin.

  Transfer technology using UV curable resin is used in many fields. In particular, in recent years, the molded product has been used as an optical element as it is because of its faithful transfer characteristics and chemical stability. In addition, this transfer technique is widely used in fine pattern transfer processes such as optical nanoimprint.

  The mold for transcription is made by various methods. Development is progressing mainly in various fields such as machining, resist exposure with a stepper, and resist drawing with an electron beam. In particular, a technique for creating a shape by exposing and developing a resist with a stepper or electron beam drawing is based on a technique established in a semiconductor process, so that it can be easily implemented in existing equipment.

  Usually, these molds are made by applying a resist on a quartz or Si substrate, exposing the resist pattern using photolithography, and developing the resist, thereby engraving a predetermined pattern into the resist. Include. Then, the resist and the substrate are simultaneously dry-etched to transfer the resist shape onto the substrate to form a mold. Alternatively, there is a method of creating a metal inversion mold by directly electroforming and transferring from a resist surface having a predetermined shape. These are generally used for creating stampers for optical disks and the like.

  Among these mold creation methods, the most common method of creating a mold using resist exposure / development and resist / substrate etching is to start with a resist pattern for forming the final target mold shape. The shape is accurately calculated by simulation or the like. In recent years, the number of items that require strict optical characteristics has increased, and it has become necessary to adjust the shape tolerance of diffraction gratings on the order of several nanometers. For example, when the final diffraction grating is a resin having a refractive index of 1.5 and a depth of 1500 ± 10 nm and an L / S pitch of 5 μm, a mold having a shape obtained by reversely calculating the shrinkage rate of the resin is required for this reversed shape. If the shrinkage rate of the resin is 1%, it is necessary to make the mold at a depth of 1515 nm ± 10 nm.

  On the other hand, it is not usually necessary to consider the shrinkage of the resin in the lateral direction. When a thin UV curable resin is transferred onto a thick substrate, it generally shrinks only in the depth direction and hardly shrinks in the surface direction. This is because the resin is fixed to the substrate.

  Next, the etching selectivity between the resist and the substrate is calculated, and a sufficient amount of resist is applied to a substrate such as quartz. The resist may be pre-baked as necessary. On the other hand, a reticle corresponding to the pattern is created. Using the reticle, the resist is exposed to a pattern and developed. After the development, the state of the resist pattern is confirmed, and if necessary, the resist and the substrate are dry etched after baking. An etching time is set using a selection ratio calculated in advance, and a desired shape is engraved on the substrate. Thereafter, the resist is washed to complete the mold.

  However, the problem here is that the etching amount varies slightly depending on the resist state and the state of the etching apparatus. Therefore, in order to achieve an accurate etching amount, it is necessary to perform dry etching in several steps. Is that there is. In other words, it is necessary to perform etching to a smaller amount than originally required, measure the dimensions, repeat etching further as much as necessary, and pursue accuracy, so this repeat process is especially necessary when depth accuracy is severe Is required.

  Usually, a confirmation pattern is created outside the effective area, etched a little less than the pre-calculated etching amount, and the resist only on the confirmation pattern portion is washed to reduce the depth of the pattern formed on the substrate. measure. The difference from the target depth is etched from the measurement result. The depth accuracy is improved by such a method.

  However, there are several problems with the method of measuring the confirmation pattern by interrupting the etching. First, it is necessary to measure quickly to prevent the resist state from changing. Therefore, the measurement means must be simplified. In other words, it is impossible to use a technique such as a cross-sectional SEM, and an apparatus using a contact-type needle or a system using optical interference must be used. In these cases, in the contact-type needle method, there is a possibility that the tip of the needle does not enter when the aspect ratio of the desired pattern is large. Of course, it is possible to measure by changing the confirmation pattern and the desired diffraction grating pattern (widening the pitch of the confirmation pattern), but it is known that the selectivity changes slightly when the aspect ratio changes due to the etching characteristics. Therefore, the actual dimension of the desired pattern cannot be measured accurately. Even in the case of a measurement method based on optical interference, in-plane resolution is insufficient for an L / S pattern with a pitch of 1 μm or less, and accurate measurement is impossible.

  In either method, since the measurement surface is exposed by a method of cleaning only a part of the same substrate, the resist may not be completely removed by a cleaning method such as wiping. This leads to an error in depth measurement. Furthermore, since the confirmation pattern is provided at the end, the etching depth at the actually used location cannot be accurately measured due to the difference in the etching selection ratio between the actually used location and the end. There is a problem.

  This invention is made | formed in view of such a situation, and makes it a subject to provide the manufacturing method of the type | mold with exact dimensional accuracy.

  A first means for solving the above problem is that the part constituting the mold is a mold made of resin, and the part constituting the mold surface of the mold has a shape in which a vertical uneven part is formed on a plane. A master mold is formed based on the size of the step in the molded product formed from the mold, the shrinkage rate when the resin is solidified, the base correction value, and the number of scheduled transfers. And taking a mold from the master mold to form a first temporary molded article, using the first temporary molded article as a mold, taking a mold to form a second molded article, and By repeating the above-mentioned process, the temporary molded product up to the m-th (m ≧ 3) is repeatedly created until the size of the step becomes a design value or less, and the m-th temporary molded product or the (m− 1) The temporary molded product of (m-2) is adopted as a final mold. It is the type method of manufacturing.

  In addition, the shape in which the vertical concavo-convex portion is formed on the plane refers to the shape as a whole, and does not indicate only the shape in which the flat portion and the concavo-convex portion are separated. It also includes what is.

  A second means for solving the above-mentioned problem is the first means, characterized in that a base correction value that is a value for correcting a step is changed at least once during the repetitive transfer. Is.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the type | mold with exact dimensional accuracy can be provided.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining a mold manufacturing method as an example of an embodiment of the present invention. The mold to be formed is a mold in which an uneven shape having a vertical cross section is formed on a plane, and the mold material is an ultraviolet curable resin.

  When the aspect ratio of the cured product is large, the ultraviolet curable resin contracts in the depth direction of the mold when irradiated with ultraviolet rays. On the other hand, it hardly shrinks in the planar direction of the mold. This is presumed to be due to receiving a strong restraining force on the side wall of the mold.

  When the mold shape is transferred to form an ultraviolet curable resin molding, it is assumed that the step changes as follows in one transfer.

Here, d ₀ is a mold step (depth of unevenness) α is a shrinkage rate of the ultraviolet curable resin, β is a base correction value, which is a step caused by the influence of a release film, and may be negative. d ₁ is the step of molding of the ultraviolet curable resin.

Now, a mold of UV curable resin is formed from the mold, and a mold of UV curable resin is formed as a new mold, and a mold of UV curable resin is formed as a new mold. When the process was repeated n times that then, from the above equation, the step d _n in the ultraviolet ray curable resin formed on the n-th is

It becomes. From this, α and β are known, and when n is appropriately determined, the step d ₀ in the mother die that is manufactured first is

Is determined. Actually, for the reasons described later, it is preferable to set the value of d ₀ larger than that calculated by the expression (3).

First, a master mold (master mold) made of a quartz substrate having the step d ₀ as described above is manufactured. As shown in FIG. 1A, a resist 2 is applied on a quartz substrate 1, and a pattern formed on a mask 3 is projected onto the resist 2 using an exposure apparatus to be exposed. Next, the resist 2 is developed to form an uneven pattern of the resist 2 as shown in FIG. Subsequently, the resist 2 and the quartz substrate 1 are simultaneously dry etched to transfer the uneven pattern of the resist 2 to the quartz substrate 1 (c). At this time, the thickness of the resist 2 is determined in consideration of the etching rate so that the designed d ₀ can be obtained as the step of the quartz substrate.

  In this way, a molded product of the quartz substrate 1 is formed. In the following steps, this is used as a mother die (master die). That is, the ultraviolet curable resin 6 is sandwiched between the mother die 4 and the surface plate 5 and irradiated with ultraviolet rays to cure the ultraviolet curable resin 6 (d). After curing, the ultraviolet curable resin 6 is used as the mother die. 4 is peeled off. It is preferable to apply a release agent in advance between the matrix 4 and the uncured ultraviolet curable resin 6. A first molded product of the ultraviolet curable resin 6 is thus formed (e), which is used as the first mold 7.

  That is, the ultraviolet curable resin 8 is sandwiched between the first mold 7 and the surface plate 5 and irradiated with ultraviolet rays to cure the ultraviolet curable resin 8 (f). Peel from No. 1 mold 7. It is preferable to apply a release agent in advance between the mold and the uncured ultraviolet curable resin 8. A second molded product of the ultraviolet curable resin 8 is thus formed (g), which is used as the second mold 9. In this way, the ultraviolet curable resin is molded one after another to create the nth mold (n ≧ 3). In any case, it is preferable to apply a release agent between the mold and the uncured ultraviolet curable resin in advance.

  As described above, the level difference of the mold (the depth of the unevenness) decreases according to the expression (1) for each transfer molding, but does not decrease as theoretically. Therefore, when the target number is close to the number, the step is measured. The advantage of this method is that it allows destructive inspection. That is, it is possible to form two molded articles from one mold, use one of them as the next mold, destroy the other, and accurately measure the step by SEM or the like.

  Thus, when a molded product having a step smaller than the target step appears for the first time, it is preferable to finally adopt the die used to make it as a die. In this way, it is possible to make a mold for forming a molded product having a step slightly smaller than the target step but having a step close to the target step.

  However, in the process as described above, the unevenness of the mold is reversed every time the mold is taken. Therefore, when the target unevenness is reversed by the above-described method of using the mold, when a molded product having a step smaller than the target step appears for the first time, it was used to make the molded product. It is preferable to finally adopt a mold two generations before as a mold. In this case, the molded product molded from the final mold has a step slightly larger than the target step, but has a step close to the target step.

  In addition, when it is not allowed to make a molded product having a step smaller than the target step, and in the above-described method, when the mold shape is reversed, a molded product having a step smaller than the target step is not used for the first time. When it appears, the 3rd generation mold used to make the molded product will eventually be adopted as the mold.

  In this method, if it is determined what number is to be adopted as a mold, it is possible to make a number of molds from the previous mold by molding, which is an excellent manufacturing method. In the figure, the surface plate 5 is peeled off, but it may be made of, for example, a glass plate and kept in close contact with the cured ultraviolet curable resin. This is an effective means for imparting strength when the thickness of the ultraviolet curable resin is thin. At this time, if the surface of a surface plate such as glass is subjected to a silane coupling treatment, the adhesion between the surface plate and the ultraviolet curable resin is improved.

  Furthermore, by deliberately changing α and β in the above formula, the width of one-time resin transfer depth adjustment can be changed. The shrinkage rate is variable by changing the resin material. The base correction value can be obtained by changing the uneven part coating thickness by changing the release agent coating condition. Alternatively, Ni or the like is sputtered as a release film together with the release agent. Particularly, an object having a large aspect ratio (an object whose opening is small with respect to the depth) tends to change the film thickness of the uneven portion. You can change the parameters by using this property well.

  Hereinafter, the base correction value will be described in detail. First, the reason why the shape changes by resin transfer will be described. In general, not only ultraviolet curable resins, but also most resins, such as thermosetting resins and injection molding resins, undergo curing shrinkage. Although the value varies depending on the type of resin, the volume is generally reduced by several to 10%. However, when a very shallow surface shape as in the present embodiment, for example, an uneven surface with a size of several hundred μm or less is transferred, the uneven surface shape does not shrink with the curing shrinkage rate at the time of bulk. The underlying resin layer shrinks due to volume change, leaving the surface intact. The resin cures in a chain and wrinkles where it lasts. It also depends on the thickness of the resin layer and how the ultraviolet rays are applied during initial curing. For example, when curing with a low irradiation power for a long time or when curing with a high irradiation power, the latter causes transfer unevenness due to lack of resin called “sink”. It has been. Of course, it is fully conceivable that a minute shape change occurs due to the power of ultraviolet rays. What is important is to grasp the tendency of deformation by irradiating with ultraviolet rays under the same conditions. When the inventors actually conducted an experiment and confirmed the deformation tendency of the fine shape, it was not only a simple shrinkage rate. One of the reasons is the influence of a release agent and a release film accompanying each transfer. The liquid release agent is likely to accumulate in the concave and convex portions, and is difficult to accumulate in the convex portion. That is, it works in the direction in which the uneven step becomes smaller. Of course, this difference can be made sufficiently small by devising the application method of the release agent, but it is also possible to reverse it. For example, if it becomes considerably deeper than the planned unevenness, the release agent (in this case, the correction layer rather than calling it a release agent) is formed so as to be thickly recessed, so that the number of transfers Can be further reduced. This is to increase the base correction value β in the expression (3). On the other hand, if the release agent or the metal / oxide film can be formed thicker on the convex portion than the concave portion, the value of β has a negative value. In film formation by sputtering or steaming, the convex portion of the substrate tends to be thick and the concave portion tends to be thin. This tendency is particularly noticeable in patterns with a large aspect ratio. If the Ar gas pressure introduced when the release film is formed by sputtering is increased, the mean free path of atoms jumping out of the target is shortened and it is difficult to reach the bottom surface of the recess where the entry is narrow. In this way, by forming the release agent, the release film, or the correction layer intentionally, it is possible to control the base correction value β and bring the molded product closer to a desired shape. This process may be performed at the time of all the transfer, may be performed in the middle, or at the first and last time, or may be performed a plurality of times at an arbitrary stage.

  A mold was manufactured by the method shown in FIG. The target mold was a diffraction grating mold made of L / S, the groove depth was 1500 ± 10 nm, and the L / S pitch was 5 μm. The shrinkage of the resin used was 0.3%. The base correction value was set to 1 nm in consideration of the thickness of the release film applied to the mold surface being about 1 nm.

In the above-described method in which a mother die is formed on a quartz substrate, and the die is formed by repeating a plurality of times of transfer from this mother die, the number of times of transfer from the mother die is four. As a result, the depths of the master mold and the nth mold groove were calculated as shown in Table 1 by the equation (3).
(Table 1)

  Actually, it is preferable that the depth of the master groove is larger than the calculated value in consideration of the dry etching accuracy when forming the master die and the film formation accuracy of the resist. In the example, 1530 nm, which is an increase of 1% of the design value, was used as a target for the depth of the matrix.

  First, the etching selectivity is calculated, and a sufficient amount of resist is applied to the quartz substrate. Here, the resist was applied by a spin method of about 1 μm. Thereafter, pre-baking was performed, the prepared reticle was set, and the pattern was exposed with an i-line stepper. Thereafter, development was performed, and it was confirmed that the L / S ratio of the pattern was optimum. Post-baking was performed and quartz etching was performed. Etching time was set using the selectivity calculated in advance, and the quartz substrate was etched with a depth of 1530 nm. Thereafter, the resist was washed to obtain a quartz master (quartz master).

  A fluorine mold release agent was applied to the surface of the quartz master disk, an ultraviolet curable resin was applied, and then transferred to a 1 mm thick glass plate to make a replica. This glass plate is lightly polished and then subjected to silane treatment so that the ultraviolet curable resin is firmly adhered.

  As a result of measuring the cross section of the replica from the quartz master disk thus prepared with a length measuring SEM, it was found to be about 1519.2 nm. In reverse calculation, the groove depth of the quartz master was created at a depth of approximately 1524.8 nm.

From the quartz master, which is the mother mold, the transfer was performed five times by the method shown in FIG. 1 to form a molded product of an ultraviolet curable resin. Table 2 shows the groove depth of each molded product.
(Table 2)

  Among these, the one corresponding to the model number 1 is an actual measurement value by nondestructive inspection, and the remaining value is calculated using the equation (1). In this case, the previous fourth mold whose groove depth was equal to or less than the target value was adopted as the final mold because the direction of the unevenness coincided with the target mold. The groove depth of the molded product produced using this mold was measured by nondestructive inspection and found to be 1498.8 nm. The deviation from the calculated values in Table 2 is very small although it seems to be due to the measurement error at each time point and a slight deviation in measurement conditions. It can also be said that the error from the target value of 1500 nm is very small.

  When the direction of the unevenness does not match the target mold, the fifth mold or the third mold is used. If the groove depth is not allowed to be less than 1500 nm, the third mold is used. In this way, an optimal mold is appropriately selected and used according to the purpose.

  In this example, a 3-5 mm glass plate was used as the surface plate 5 in FIG. 1, and after curing of the ultraviolet curable resin, it was used as a substrate without being peeled off.

It is a figure for demonstrating the manufacturing method of the type | mold which is an example of embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Quartz substrate, 2 ... Resist, 3 ... Mask, 4 ... Master mold, 5 ... Surface plate, 6 ... Ultraviolet curable resin, 7 ... 1st type, 8 ... Ultraviolet curable resin, 9 ... 2nd type

Claims (2)

The mold is a mold made of resin, and the mold surface of the mold is a method for manufacturing a mold having a shape in which a vertical concavo-convex portion is formed on a plane, from the mold Based on the size of the step in the formed product, the shrinkage rate when the resin solidifies, the base correction value, and the expected number of transfers, a master mold is formed, and the first mold is formed from the master mold. A temporary molded product is formed, and the first temporary molded product is used as a mold, and a mold is formed to form a second molded product. ) Until the step size is less than the design value, the m-th temporary molded product, or the (m-1) and (m-2) temporary molded products. Is used as a final mold. The mold manufacturing method according to claim 1, wherein a base correction value that is a value for correcting a step is changed at least once during the repetitive transfer.

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