JP4668696B2 - Method for producing chirped grating forming substrate - Google Patents

Description

  The present invention relates to a method for producing a chirped grating in which a concave groove pattern is repeatedly provided on one surface of a transparent substrate, which is provided as a grating, and the pitch of the grating is changed little by little.

Optical fiber has revolutionized global communications and has enabled high-quality, high-capacity transoceanic telephone communications. Conventionally, along this optical fiber, a periodic refractive index profile has been created in the core, which A black diffraction grating is formed inside, and the diffraction grating is used for optical communication by determining the level of reflectance and wavelength characteristics depending on the period and length of the diffraction grating and the size of the refractive index modulation. It is known that it can be used as a wavelength multiplex divider, a narrow-band high-reflecting mirror used in lasers and sensors, a wavelength selection filter that eliminates excess laser wavelengths in fiber amplifiers, and the like.
However, since the attenuation of quartz fiber is minimized and the wavelength suitable for long-distance communication systems is 1.55 μm, in order to use the fiber diffraction grating at this wavelength, it is necessary to set the grating interval to about 500 nm. It is said that making such a fine structure in the core itself is difficult at first, and side polishing, photoresist process, holographic exposure, reactivity are required to create a black diffraction grating in the core of the optical fiber. Many steps of complicated processes such as ion beam etching were employed.
For this reason, the production time was long and the yield was low.

However, recently, a method of making a diffraction grating by irradiating a fiber with ultraviolet light and changing the refractive index directly in the core has been known, and this method of irradiating ultraviolet light does not require a complicated process. It has come to be implemented gradually with the progress of peripheral technology.
In the case of this method using ultraviolet light, since the grating interval is as small as about 500 nm as described above, an interference method in which two light beams interfere with each other (a single diffraction grating surface is formed by condensing a single pulse from an excimer laser). A method using writing for each point, a method using a phase shift mask having a grating, and the like are used.

  The interference method that causes the two light beams to interfere has a problem in the quality of the beam in the lateral direction, that is, spatial coherence, and the method by writing point by point requires precise step control of submicron size, and However, it was required to narrow down the light and write many surfaces, and there was a problem in workability.

For this reason, an irradiation method using a phase shift mask (hereinafter also simply referred to as a phase mask) has been attracting attention as a method that can cope with the above problem. This method is shown in FIG. Using a phase shift mask 21 in which concave grooves are provided on one surface of a quartz substrate at a predetermined pitch and at a predetermined depth, a KrF excimer laser (248 nm) 23 is irradiated to directly apply a refractive index to the core 22A of the optical fiber 22. It brings about a change and produces a grating (grating).
FIGS. 5A and 5B are enlarged views showing the interference fringe pattern 24 in the core 22A in an easy-to-understand manner. FIGS. 5B and 5B and FIG. 5B and FIG. The cross section of the phase shift mask and all or part of the upper surface are shown.
D and P indicate the depth and pitch of the groove 26, respectively.
The depth of the concave groove 26 is selected so as to be modulated by the phase π radians of the excimer laser light (beam) that is the exposure light, and the 0th-order light (beam) 25A is reduced to 2% or less by the phase shift mask 21. The main light (beam) emitted from the phase shift mask 21 is diverged into plus first-order diffracted light 25B and minus first-order diffracted light 25C including 35% or more of diffracted light. For this reason, irradiation with a predetermined pitch is performed with the plus first-order diffracted light 25B to minus first-order diffracted light 25C, and a refractive index change at this pitch is brought into the fiber.

Japanese Patent Laid-Open No. 9-80738 (Patent Document 1) describes a method of manufacturing a phase shift photomask for processing an optical fiber, in which lattice-like grooves can be formed in a predetermined pitch and shape. .
Japanese Patent Laid-Open No. 9-80738

As described above, conventionally, in an optical communication system, a high-purity silica optical fiber is generally used as a transmission medium, and is typically designed to transmit an optical signal using a certain wavelength range. In the system, longer wavelength components experience a slightly longer propagation time delay than shorter wavelength components.
However, this dispersion has not so far deteriorated the information of the optical signal. This is because in the initial system, a single channel was selected from a wavelength region having a small dispersion.

However, as seen in wavelength division multiplexing (WDM) systems, which are high-speed transmission technologies using optical fibers, today, in order to carry more information, many channels are used over a wider wavelength region. Accordingly, it has become necessary to compensate for the group velocity dispersion more precisely.
For example, for WDM systems, dispersion compensation becomes an increasingly important issue as the number of channels provided in the WDM system increases.

Accordingly, as a Bragg diffraction grating formed in an optical fiber, a grating (hereinafter referred to as a grating) in which the pitch of the grating increases or decreases linearly or non-linearly in accordance with the position in the direction orthogonal to the grating (repetitive direction of the grating). , Also called chirped grating or chirped grating).
Such a grating is used as, for example, a high reflection mirror having a wide reflection band, a means for adjusting a delay time, and the like.

Thus, a chirped grating is required as a Bragg diffraction grating formed in an optical fiber, and even in the production of a phase shift mask having a grating for forming a Bragg diffraction grating in an optical fiber, a chirp is also required. Fabrication of a phase shift mask having a toggling has been demanded.
As a method of patterning a chirped grating on a phase shift mask, there is a method using two-beam interference, but a drawing exposure method using an electron beam drawing apparatus (also called an electron beam exposure apparatus) has been implemented as a simple method. Yes.
In response to the increase in demand for the chirped grating as described above, the inventor has provided a repetitive pattern of lattice-shaped concave grooves and ridges on one surface of the transparent substrate, and diffracted light by the repetitive pattern is provided. In a manufacturing method of a phase mask for processing an optical fiber that irradiates an optical fiber and produces diffraction gratings in the optical fiber by interference fringes of different orders of diffracted light, a drawing exposure method using an electron beam drawing apparatus, and a plurality of different pitches A method of manufacturing a phase mask for optical fiber processing, in which linear patterns are drawn in parallel and a repetitive pattern of the grid-like concave grooves and convex stripes is produced therefrom, is disclosed in JP-A-11-72631 (Patent Document 2). Is shown.
JP-A-11-72631 In addition, JP-A-2003-75620 (Patent Document 3) prepares the above-described optical fiber processing phase mask with high quality by a drawing exposure method using an electron beam drawing apparatus. A manufacturing method is disclosed. This method uses a pattern data for drawing formed by arranging a plurality of data of repeating patterns of concave grooves and ridges while modulating the pitch repeatedly, and corresponds to the occurrence of connection during drawing. . JP-A-2003-75620

In the drawing exposure method using the electron beam drawing apparatus described above, a pattern having a basic specific pitch representing a grating is arranged by changing the magnification in pattern data processing by drawing exposure using a raster type exposure apparatus. It is something to be made.
However, in order to fabricate a phase mask for optical fiber processing having chirped grating, when the pattern of the basic specific pitch is continuously changed with the magnification on the pattern data processing, the pattern magnification In order to express the above, it is necessary to have an accuracy of 6 digits below the decimal point in units of μm, and in a normal drawing exposure apparatus that does not have such a high-precision magnification in pattern data processing, Therefore, it was said that patterning for forming chirped grating was impossible.

As described above, a drawing exposure method using a raster type exposure apparatus has recently been adopted as a method for forming a chirped grating pattern of a phase mask for optical fiber processing in recent years. In the method, a pattern having a basic specific pitch is arranged by changing the magnification continuously in pattern data processing, and drawing exposure is performed using this pattern. To express the magnification of the pattern, a decimal point is expressed in μm. The precision of the last six digits or less is required for pattern data processing, and it is necessary to perform drawing exposure for forming a chirped grating with a normal drawing exposure apparatus that does not have such a high-precision pattern magnification expression. This response was sought after.
The present invention corresponds to this, and is an ordinary drawing exposure apparatus that does not have a high-precision pattern magnification expression in pattern data processing, and in particular, patterning of a desired chirped grating in a phase mask for optical fiber processing. It is an object of the present invention to provide a method for manufacturing a chirped grating-formed substrate capable of performing the above.
At the same time, an object of the present invention is to provide a chirped grating forming mask manufactured by such a method of manufacturing a chirped grating formed substrate.

The method for producing a chirped grating-formed substrate according to the present invention is such that a rectilinear groove is repeatedly formed on one surface of a transparent substrate in a lattice pattern to form a repeating pattern of grooves and ridges, and the width of the groove. And the ratio of the width of the ridges is kept constant, the pitch of the repetitive pattern is changed little by little, and this is arranged as a chirped grating, which is a chirped grating forming substrate of a phase mask for optical fiber processing The patterning method for forming the groove is a resist disposed on one side of the transparent substrate, and the resist is exposed to drawing by a drawing apparatus to correspond to the groove forming region. the areas of the resist selectively drawn exposed to, the resist film intended to be done by developing treatment, in the drawing apparatus variable-shaped EB drawing apparatus, control the drawing operation of the drawing device In the drawing operation control data for performing the drawing exposure, the position coordinates and the opening width are designated for each shot exposure for exposing each line-shaped rectangular area, and the drawing operation control data The position coordinates of each shot exposure in are created by performing magnification calculation on the pattern data of the drawing unit in a sufficiently small unit relative to the grid of the drawing coordinate system unit on the data, The line-shaped rectangular area drawing data is characterized in that the drawing data for each shot exposure for exposing each line-shaped rectangular area is created with a numerical value rounded to the grid of the drawing coordinate system. is there.

(Function)
The manufacturing method of the chirped grating forming substrate of the present invention is a normal drawing exposure apparatus that does not have a high-precision pattern magnification expression in pattern data processing, particularly for optical fiber processing. It is possible to provide a method for manufacturing a chirped grating-formed substrate capable of patterning the intended chirped grating in the phase mask.
Specifically, for patterning to form the groove, a resist is provided on one surface side of the transparent substrate, and the resist is exposed by drawing with a drawing apparatus to correspond to the region where the groove is formed. The drawing apparatus is a variable-forming type EB drawing apparatus , and the drawing operation control data for controlling the drawing operation of the drawing apparatus is used. In each of the shot exposures for exposing each linear rectangular region, the position coordinates and the aperture width are designated for drawing exposure, and the position coordinates of each shot exposure on the drawing operation control data are set. Create all line-shaped rectangular areas to be drawn by performing magnification calculation on the pattern data of the drawing unit in a sufficiently small unit relative to the grid of the drawing coordinate system unit on the data For drawing data, the drawing data for each shot exposure that exposes each line-shaped rectangular area is rounded to the drawing coordinate system grid, that is, rounded up on the drawing coordinate system grid. This is achieved by creating something with no numerical value.
Specifically, although the pitch Px of the concave groove and ridge repetitive pattern changes little by little, drawing exposure is performed in accordance with the instruction of the drawing operation control data in the numerical display on the drawing system grid as described above. Therefore, the variation in the pitch Px, that is, the error with respect to the design data can be set to 1 or less in the grid unit of the drawing system.
As a result, a highly accurate phase shift mask provided with a chirped grating can be formed.
More specifically, the drawing apparatus may be an EB drawing apparatus (also referred to as an electron beam drawing apparatus).
In this case, of course, the resist film is an electron beam resist.
In particular, the transparent substrate on which the chirped grating is manufactured is effective when it is a phase mask for processing an optical fiber in which a diffraction grating is formed in the optical fiber.

As described above, the present invention is an ordinary drawing exposure apparatus that does not have a high-precision pattern magnification expression in pattern data processing, and in particular, performs the intended chirped grating patterning in a phase mask for optical fiber processing. It is possible to provide a method for manufacturing a chirped grating-formed substrate that can be performed.
As a result, it is possible to provide a chirped grating forming mask in which a target chirped grating patterning is provided in a fiber processing phase mask.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a processing flow of an example of an embodiment of a method for manufacturing a chirped grating forming substrate according to the present invention, FIG. 2 is a sectional view of a phase mask having a chirped grating, and FIG. 3 is a drawing operation. FIG. 4 is a process cross-sectional view showing process processes corresponding to the process flows S14 and S7 to S10 shown in FIG. 1.
2 to 4, 110 is a transparent substrate, 111 is a groove (also referred to as a groove pattern), 112 is a protrusion, 120 is a Cr film, 121 is a Cr opening, 130 is a resist (also referred to as a resist film), 131. Is a resist opening, 140 is an electron beam, 210 is a unit pattern data (also simply referred to as a unit pattern), 211 is a line pattern, 220 and 230 are pattern data obtained by multiplying unit pattern data by a magnification, and W0 is The width of the groove, W1 is the width of the ridge, H0 is the depth of the groove (also referred to as the height of the ridge), Gx is a grid in the x direction, and Gy is a grid in the y direction.

First, an example of an embodiment of a method for producing a chirped grating forming substrate of the present invention will be described with reference to FIGS.
The method for producing the chirped grating forming substrate of this example is to form a repeating pattern of concave grooves 111 and ridges 112 by providing linear concave grooves 111 in a lattice pattern on one surface of a transparent substrate 110 made of quartz. Further, the ratio of the width W0 of the groove 111 to the width W1 of the ridge 112 (W1 / W0) is kept constant, and the pitch of the repetitive pattern is changed little by little, and this is arranged as a chirped grating. A method for producing a chirped grating-formed substrate, wherein patterning for forming the concave groove 111 is performed by arranging a resist on one surface side of the transparent substrate, and using the resist for drawing exposure by a drawing apparatus. Then, the resist region corresponding to the concave groove pattern forming region is selectively drawn and exposed, and the resist film is developed.
In particular, a chirped grating forming substrate used as a phase mask for optical fiber processing for producing a diffraction grating in an optical fiber is produced.
In this example, the drawing apparatus is a variable shaping type EB drawing apparatus (also referred to as an electron beam drawing apparatus) exposure apparatus, and each line shape is drawn on drawing operation control data (JOB data) for controlling the drawing operation of the drawing apparatus. For each shot exposure for exposing the rectangular area, the position coordinates and the aperture width are designated and the drawing exposure is performed. This is also called a vector-type EB drawing apparatus.
Then, the position coordinates of each shot exposure on the drawing operation control data (JOB data) are created in pattern data of drawing units in a sufficiently small unit with respect to the grid of drawing coordinate system units on the data. For all the line-shaped rectangular area drawing data to be drawn, the drawing data for each shot exposure that exposes each line-shaped rectangular area is rounded to the grid of the drawing coordinate system. create.

Furthermore, an example of the processing flow of this example will be described with reference to FIG.
Based on the target chirped grating design data (S 1), unit pattern data (S 2) and magnification data (S 3) are prepared for producing the design data.
Here, the magnification is calculated for the pattern data of the drawing unit in a sufficiently small unit with respect to the grid of the drawing coordinate system unit, and each line is drawn for all the line-shaped rectangular area drawing data to be drawn. The drawing data for each shot exposure for exposing the rectangular area is created with numerical values that do not cause rounding on the grid of the drawing coordinate system. (S4-S5)
For example, such data is created on Excel (commercially available spreadsheet software).
Then, drawing operation control data (JOB data) is created using the created data. (S6)
Here, the drawing operation control data (JOB data) is expressed by the coordinate position on the drawing grid.

Here, when the unit pattern data (corresponding to 210 in FIG. 3A) is, for example, pattern data having three line-shaped patterns 211 as shown in FIG. Such processing on data will be described.
In this case, the ratio between the line width and the inter-line width is constant, and the line width and the inter-line width are the same size as the basic data part that is not scaled on the design data.
As shown in FIG. 3B, according to the design data specifications, unit pattern data 210 and pattern data 220 and 230 each multiplied by a predetermined magnification are arranged, and each line-shaped pattern data 210 is arranged. For each pattern, its position coordinates, width and height are calculated.
Here, the magnification is calculated for the pattern data of the drawing unit in a sufficiently small unit with respect to the grid of the drawing coordinate system unit.
Then, as shown in FIG. 3C, the data is rounded so that the position coordinates of each line-shaped pattern are on the drawing grid.
In this way, drawing operation control data (JOB data) is created using the data in which the position coordinates of each line pattern are placed on the drawing grid.

On the other hand, a transparent substrate made of quartz, which is a material for forming a target optical fiber processing phase mask, is prepared (S11). A Cr film to be an etching film is formed by sputtering or the like (S12), and a resist film sensitive to an electron beam is disposed on the Cr film (S13), and a processing substrate for drawing exposure processing is prepared. deep. (S14)
Next, in a state where the processing substrate (S14) is placed on the drawing stage (not shown) of the electron beam drawing apparatus, under the instruction of the previously created drawing operation control data (JOB data). Then, drawing exposure is performed. (S7)
When performing the drawing exposure according to the instruction of the drawing operation control data (JOB data), the electron beam drawing apparatus uses the coordinates of the drawing system corresponding to the instruction of the drawing operation control data (JOB data), that is, coordinates with high accuracy. Drawing is performed at the coordinate position of the grid in the drawing system in which position management is performed.
After all the drawing exposure is completed, the exposed processing substrate is developed (S8), and the Cr film exposed from the resist opening is removed by etching to form a Cr opening in the resist opening. Further, the transparent substrate exposed from the Cr opening is etched to form a recess having a predetermined depth (S9), and a phase mask provided with a chirped grating is formed. (S10)
Here, the pitch Px of the repeating pattern of the groove and the ridge changes little by little, but the variation of the change, that is, the error with respect to the design data is a numerical value placed on the drawing system grid as described above. In the display, since drawing exposure is performed in accordance with an instruction of drawing operation control data (JOB data), the number of grids in the drawing system is 1 or less.
In this way, a highly accurate phase shift mask provided with a chirped grating can be formed.

In the process flow shown in FIG. 1, for example, a phase mask having a chirped grating as shown in FIG. 2 is created.
In the method disclosed in Japanese Patent Application Laid-Open No. 11-72631 (Patent Document 2) and Japanese Patent Application Laid-Open No. 2003-75620 (Patent Document 3) described above, the pitch is similarly changed on the data, When this is expressed by drawing system coordinates and used as drawing operation control data (JOB data), the rounding error due to the minimum unit (also called increment) on the data is larger than the grid unit of the drawing system coordinates. Although the phase mask for optical fiber processing for producing a diffraction grating in an optical fiber was not negligible in quality, the phase mask for optical fiber processing for producing a diffraction grating in the optical fiber manufactured in this example is As described above, the error with respect to the design data of the pitch Px of the repetitive pattern of the concave grooves and the convex stripes is 1 or less per grid unit of the drawing system. , And therefore, the quality to cope.

Next, an example of processing of the processing substrate (S14 in FIG. 1) will be described more specifically based on FIG.
In the embodiment, the phase mask shown in FIG. 2 is produced by the method of manufacturing the phase mask shown in FIG.
A concave groove pattern (diffraction grating pattern) with a pitch of 1.06 μm was produced to a length of 10 mm.
A commercially available chemical amplification that is a positive electron beam resist on the light-shielding film 120 of the substrate (FIG. 4A) in which a light-shielding film made of chromium is disposed on the transparent substrate 110 made of a quartz substrate to a thickness of 1100 mm. The mold resist was applied to a thickness of 400 nm and dried. (Fig. 4 (b))
Next, the electron beam drawing apparatus EBM3000 (manufactured by Toshiba Machine Co., Ltd.) performs exposure for exposing the groove forming portion at a predetermined exposure amount (also referred to as a dose amount) of 5.4 μC / cm ² . (FIG. 4 (c)) After the exposure, development processing is performed to provide a resist opening 131 at a groove forming portion, and further, a chromium film (light shielding film 120) exposed from the opening 131 of the resist 130 is replaced with CH ₂ Cl _2. An opening 121 was provided by dry etching using a gas. (Fig. 4 (d))
Next, using the chromium (light-shielding film 120) as a mask, the transparent substrate 110 exposed from the opening 131 of the resist 130 and the opening 121 of the chromium (light-shielding film 120) is dry-etched using CF4 gas, and an exposure wavelength of 248 nm in optical fiber fabrication. It was formed at a depth of 250 nm, which is a half wavelength. (Fig. 4 (e))
Thereafter, the remaining resist 130 is removed with sulfuric acid at 70 ° C., and the light-shielding film 120 is removed by etching with a ceric ammonium nitrate solution, followed by a cleaning process, so that a groove pattern having a pitch of 1.06 μm is obtained. It was manufactured by changing the width to 10 mm depending on the coordinate position. (Fig. 4 (f))
In this way, the phase mask shown in FIG. 2 was produced.

It is the figure which showed the processing flow of one example of embodiment of the manufacturing method of the chirped grating formation board | substrate of this invention. It is sectional drawing of the phase mask which has a chirped grating. It is a figure for demonstrating the process on data at the time of producing drawing operation control data. It is process sectional drawing which showed the process process corresponding to process flow S14, S7-S10 shown in FIG. It is a figure for demonstrating formation of the diffraction grating to the optical fiber by a phase mask, and a phase mask.

Explanation of symbols

110 Transparent substrate 111 Groove (also called groove pattern)
112 ridge 120 Cr film 121 Cr opening 130 resist (also referred to as resist film)
131 resist opening 140 electron beam 210 unit pattern data (also simply referred to as unit pattern)
211 Line data 220, 230 Pattern data obtained by multiplying unit pattern data W0 Groove width W1 Convex width H0 Convex groove depth (also referred to as convex height)
Gx Grid in the x direction Gy Grid in the y direction 21 Phase mask 22 Optical fiber 22A Core 22B Cladding 23 KrF excimer laser light 24 Interference fringe pattern 25A Zero order light (beam)
25B plus first-order diffracted light 25C minus first-order diffracted light 26 concave groove D (of concave groove 26) depth P (of concave groove 26) pitch

Claims (1)

A linear groove is repeatedly formed on one surface of the transparent substrate in a lattice pattern to form a repeating pattern of the groove and the ridge, and the ratio of the width of the groove to the width of the ridge is kept constant. Then, the pitch of the repetitive pattern is changed little by little, and this is disposed as a chirped grating, which is a method for producing a chirped grating forming substrate of a phase mask for optical fiber processing , wherein the concave groove is formed For the patterning, a resist is provided on one surface side of the transparent substrate, and the resist is selectively drawn and exposed in a resist region corresponding to the formation region of the concave groove by drawing exposure by a drawing device, resist film intended to be done by developing, the drawing device is a variable-shaped EB drawing device, on the drawing operation control data for controlling the drawing operation of the drawing apparatus, each linear For each shot exposure that exposes the shape area, the position coordinates and the aperture width are specified and drawing exposure is performed, and the position coordinates of each shot exposure on the drawing operation control data are created on the data. The magnification calculation is performed on the pattern data of the drawing unit in a sufficiently small unit with respect to the grid of the drawing coordinate system unit, and for each line-shaped rectangular area drawing data to be drawn, A method for producing a chirped grating forming substrate, wherein drawing data for each shot exposure for exposing a rectangular region is created by rounding a drawing coordinate system to a grid value.

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