CN100371834C - A Method of Accurately Controlling the Line Density in the Fabrication of Planar Holographic Gratings - Google Patents

Abstract

The invention relates to a method for precisely controlling the groove density of a grating in the manufacture of a plane holographic grating, which belongs to a method related to the field of spectrum technology. The technical problem to be solved is to provide a method for precisely controlling the density of grating lines in the production of planar holographic gratings. Technical solution: first, equip a set of holographic grating exposure device; second, put a standard machine-engraved grating and a half mirror in the light path of the device, and then separate the light path from the collimating mirror light path to make it produce Interference fringes, thirdly, take out the standard machine-engraved grating and the reflector in the branched optical path in the optical path, keep the position of the half mirror unchanged, and adjust the optical path so that the interference fringes on the receiving screen and the interference fringes generated in the second step Consistent, fourth, take out the half mirror in the optical path, place the grating substrate coated with photoresist at the position of the original standard machine-engraved grating, the number of interference fringes recorded by the photoresist is the engraved holographic grating Linear density. The method controls the grating line density with high precision.

Description

A Method of Accurately Controlling the Line Density in the Fabrication of Planar Holographic Gratings

1. Technical field

The invention belongs to the field of spectroscopic technology and relates to a method for precisely controlling the groove density in the manufacture of a plane holographic grating.

2. Technical background

The grating constant is a very important technical index of the diffraction grating. The so-called grating constant refers to the reciprocal of the number of lines per millimeter, which determines the dispersion rate and resolution of the grating. For spectroscopic instruments, the change of the grating constant will inevitably cause the change of the diffraction angle of the grating, which will lead to the shift of the spectral line position of the spectroscopic instrument. Therefore, the accuracy of the grating constant directly affects the wavelength accuracy of the spectroscopic instrument. control.

In the manufacturing process of holographic gratings, a very critical process is to place the grating substrate coated with photoresist in the interference field, and record the interference fringes in the interference field by the photoresist. The density of the interference fringes is is the line density of the grating to be fabricated.

When the exposure wavelength is constant, the density of interference fringes is only determined by the angle between two beams of parallel light. The conventional method of detecting the reticle density is generally to calculate the reticle density of the grating by measuring the angle between the 0th order and the 1st order diffracted light after the grating is manufactured. The measurement error is relatively large, and there is no fixed benchmark for the optical path adjustment process. However, adjustments based on experience often require multiple rounds of grating production, and it is difficult to achieve the required accuracy.

3. Contents of the invention

In order to overcome the above-mentioned defects in the prior art, the object of the present invention is to establish a simple and feasible method capable of accurately controlling the grating line density.

The technical problem to be solved by the present invention is to provide a method for precisely controlling the density of reticle lines in the manufacture of planar holographic gratings. The technical solution to solve the technical problem is as follows: First, a set of holographic grating exposure device is equipped, as shown in Figure 1, including a laser light source 1, a first reflector 2 and a second reflector 3, a beam expander filter 4, a collimator Mirror 5, the first adjustment mirror 6 and the second adjustment mirror 7; the second, as shown in Figure 2, in the holographic grating exposure device shown in Figure 1, the collimation mirror 5 and the second adjustment reflector In the optical path between the mirrors 7, a third reflector 8 is placed at a certain angle with the parallel light, and a machine for standard reticle density is placed in the interference field formed by the reflected light of the first adjustment reflector 6 and the second adjustment reflector 7. Engraving reflective grating 11, the direction of the grating marking line is perpendicular to the laser light source 1, the first reflector 2 and the second reflector 3, the beam expander filter 4, the collimating reflector 5, the first adjustment reflector 6 and the second adjustment The plane formed by optical elements such as mirror 7, the surface of the grating faces away from the first adjustment mirror 6 and the second adjustment mirror 7, and the normal line of the grating is roughly parallel to the reflection of the first adjustment mirror 6 and the second adjustment mirror 7 The bisector of the included angle of light, a half mirror 10 is arranged on the direction perpendicular to the surface of the machine engraved reflective grating 11 with standard groove density, and the projection of the half mirror 10 on the grating is parallel to the grooves of the grating ; Relative to the reflective surface of the third reflector 8, and parallel to the engraving direction of the engraved reflective grating 11 of the standard engraved line density, the fourth reflector 9 is placed at a certain distance from the left end of the half mirror 10, so that it The reflected light is divided into two beams of light after the half mirror 10, one beam is reflected light, and the other beam is transmitted light. The reflector 9 makes the two beams of light incident on the machine-engraved grating 11 at the ±1-order self-alignment diffraction angle of the machine-engraved reflective grating 11 with standard reticle density respectively, and the two beams of light pass through the ±1-order self-alignment of the grating 11 After diffracting, they return in the same way according to their incident directions, and after passing through the half mirror 10, the reflected light of -1 order and the transmitted light of +1 order overlap on the other side of the half mirror 10 and appear on the receiving screen. Form interference fringes on 12, as shown in Figure 3, carefully adjust the elevation and the azimuth angle of half mirror 10, to guarantee that the interference fringes on receiving screen 12 are vertical and clearly visible, record the quantity of interference fringes at this moment; Three, as shown in Figure 4, take off the machine-engraved reflective grating 11 and the third reflector 8 of the standard engraved line density shown in Figure 2, and ensure that the positions of the half mirror 10 and the receiving screen 12 are constant, at this moment After adjusting the reflected light of the first adjusting mirror 6 and the second adjusting mirror 7 through the transmission and reflection of the half-mirror 10 respectively, after being superimposed, interference fringes are formed on the receiving screen 12, and then the first adjusting mirror 6 is adjusted respectively And the pitch and the azimuth angle of the second adjustment reflector 7, make the direction and quantity of the interference fringes on the receiving screen 12 identical with the interference fringes produced by the machine-engraved reflective grating 11 of the standard reticle density respectively, as shown in Figure 5, At this moment, the density of the interference fringes in the interference field is the same as that of the machine-engraved reflective grating 11 of the standard scale density; the 4th, as shown in Figure 6, take out the half-mirror 10 shown in Figure 4, and coat it with light The grating substrate 13 of the photoresist is placed on the position where the machine-engraved reflective grating 11 of the standard line density shown in Figure 2 is originally, and is recorded by the photoresist from the first adjustment reflector 6 and the second adjustment reflector. 7 Interference fringes in the interference field of reflected light, the density of the interference fringes is the line density of the holographic grating to be fabricated.

Description of the working principle of the present invention: with the standard machine-engraved grating as a reference, the nominal value of the reticle density of the holographic grating to be produced is consistent with the reticle density of the machine-engraved grating. Step 1, adjust the fourth reflecting mirror 9 so that its reflected light is divided into two beams of light after passing through the half mirror 10, one beam is reflected light, and the other beam is transmitted light. The reflected light is incident on the machine-engraved reflective grating 11 of the standard standard reticle density in the +1 self-collimation direction of the standard reticle density machine-engraved reflective grating 11. According to the principle of self-collimation, the diffracted light The path returns to the half-mirror 10, and as a result, half of it passes through the half-mirror 10 and reaches the receiving screen 12; the transmitted light is incident on the standard reticle in the self-collimation direction of the -1 order of the machine-engraved reflective grating 11 of the standard reticle density On the machine-engraved reflective grating 11 of density, according to the principle of self-collimation, the diffracted light returns to the half-mirror 10 according to the original path of its incident direction, and half of it is reflected by the half-mirror 10 to reach the receiving screen 12 as a result. The above two beams of coherent light are superimposed to form interference fringes on the receiving screen 12 . The specific optical path is shown in Figure 7(a), and the interference fringes are shown in Figure 3. Step 2, remove the reference engraved grating 11 and the third mirror 8, and use the reflected light of the first adjustment mirror 6 and the second adjustment mirror 7 to replace +1 in the self-collimation state of the reference engraved grating 11 order and -1 order diffracted light. The following process is the same as step one method: the reflected light from the first adjustment mirror 6 is incident on the half mirror 10, and half of it reaches the receiving screen 12 through the half mirror 10; from the second adjustment mirror 7 The reflected light is incident on the half-mirror 10 , half of which is reflected by the half-mirror 10 to reach the receiving screen 12 . The above two beams of coherent light are superimposed to form interference fringes on the receiving screen 12 , the specific optical path is shown in FIG. 7( b ), and the interference fringes are shown in FIG. 5 . Since the coherent light obtained by step 1 and step 2 has the same propagation direction and optical path difference, it must have the same interference fringes (including fringe density and fringe direction).

The positive effect of the present invention is that not only the density of interference fringes in the interference field of the holographic grating exposure device can be quickly detected, but also the accuracy of the reticle density can be controlled at about 0.01%, which is an order of magnitude higher than the traditional method.

4. Description of drawings

Fig. 1 is a schematic diagram of the optical path structure of the holographic grating exposure device, and Fig. 2 is a machine-engraved reflective grating 11 with a third reflector 8 and a fourth reflector 9, a half mirror 10 and a standard reticle density added to the optical path of the holographic exposure device The interference light path schematic diagram that forms, Fig. 3 is the interference fringe schematic diagram that shows on the receiving screen 12 in the interference light path shown in Fig. 2, Fig. 4 removes the 3rd mirror 8 and the 4th mirror 9 and The schematic diagram of the interference light path formed by the machine-engraved reflective grating 11 of the standard line density, Fig. 5 is a schematic diagram of the interference fringes displayed on the receiving screen 12 in the interference light path shown in Fig. A schematic diagram of the optical path of the anti-half mirror 10 and the holographic grating added with the grating substrate 13 coated with photoresist. FIG. 7 is a schematic diagram of the working principle of the present invention and a comparison of interference fringes.

5. Specific implementation

The present invention is implemented according to the optical path structure shown in Fig. 1, 2, 4, 6 and by the above-mentioned first, second, third, and fourth method steps. And the second reflector 3 is a glass substrate aluminum-coated reflector, the beam expander filter 4 is made up of a microscope objective lens and a pinhole, the aperture of the collimating reflector 5 is φ320mm, the focal length f is 1.2m, and the first adjusting reflector 6 And the second adjustment reflector 7 is a glass base aluminum-coated reflector, the third reflector 8 and the fourth reflector 9 are glass base aluminized reflectors, and the half mirror 10 is made up of two thin glass sheets glued together , the engraved reflective grating 11 with standard reticle density can be selected according to the needs, the receiving screen 12 is made of ordinary white frosted glass, the base of the holographic grating is made of K9 optical glass, and the photoresist coated on the K9 optical glass The photoresist used was Shipley 1805 type photoresist produced in Japan.

Claims (1)

1. A method for accurately controlling the density of reticle lines in the production of a planar holographic grating, which is realized by a holographic grating exposure device, is characterized in that the method for accurately controlling the density of reticle lines in the production of a planar holographic grating is as follows: first, a set of holographic gratings is equipped. The grating exposure device includes a laser light source (1), a first reflector (2) and a second reflector (3), a beam expander filter (4), a collimating reflector (5), a first adjustment reflector (6 ) and the second adjustment mirror (7); the second, in the holographic grating exposure device, in the optical path formed by the collimation mirror (5) and the second adjustment mirror (7), it is placed at a certain angle with the parallel light There is a third reflector (8), and in the interference field formed by the reflected light of the first adjust reflector (6) and the second adjust reflector (7), a machine-engraved reflective grating (11) with a standard reticle density is placed, and the grating The direction of the marking line is perpendicular to the laser light source (1), the first reflector (2) and the second reflector (3), the beam expander filter (4), the collimating reflector (5), the first adjusting reflector ( 6) and the plane formed by optical elements such as the second adjusting mirror (7), the surface of the grating faces away from the first adjusting mirror (6) and the second adjusting mirror (7), and the normal line of the grating is roughly parallel to the first adjusting mirror (7). Adjust the bisector of the reflected light angle between the reflector (6) and the second adjust reflector (7), and place a piece of half mirror (10) on the direction perpendicular to the surface of the engraved reflective grating (11) of the standard groove density ), while making the projection of the half mirror (10) on the grating parallel to the reticle of the grating; opposite to the reflective surface of the third reflector (8), and with the machine-engraved reflective grating (11) of the standard reticle density ) is parallel to the direction of the scribed lines, and a fourth reflector (9) is placed at a certain distance from the left end of the half mirror (10), so that its reflected light is divided into two beams of light after the half mirror (10). is reflected light, and the other beam is transmitted light, both beams of light can reach the machine-engraved reflective grating (11) of standard reticle density, adjust the fourth reflector (9), so that the two beams of light can reach the standard reticle density The ±1-order self-alignment diffraction angle of the machine-engraved reflection grating (11) is incident on the machine-engraved grating (11). The direction goes back the same way, and then through the half mirror (10), the reflected light of -1 level and the transmitted light of +1 level overlap on the other side of the half mirror (10), on the receiving screen (12) Form interference fringes, carefully adjust the pitch and azimuth of the half mirror (10), to ensure that the interference fringes on the receiving screen (12) are vertical and clearly visible, and record the number of interference fringes at this time; the third, remove the Machine-engraved reflective grating (11) and the third reflector (8) of the standard reticle density in the optical path, and ensure that the positions of the half-mirror (10) and the receiving screen (12) are constant, at this time adjust the first adjustment The reflected light of the reflector (6) and the second adjustment reflector (7) is respectively transmitted and reflected by the half-mirror (10), and after being superimposed, interference fringes are formed on the receiving screen (12), and then the first adjustment is adjusted respectively. The pitch angle and the azimuth angle of reflector (6) and the second adjustment reflector (7) make the direction and quantity of the interference fringe on the receiving screen (12) be the same as the machine-engraved reflective grating (11) of standard reticle line density respectively. The interference fringes that produce are identical, and at this moment the density of the interference fringes in the interference field is identical to the engraved reflection grating (11) of the standard reticle density; the 4th, take out the half mirror (10) in the light path, The grating substrate (13) that is coated with photoresist is placed on the position of the engraved reflective grating (11) of the standard line density in the original optical path, and is recorded by the photoresist from the first adjusting reflector (6) and The second adjusts the interference fringes in the interference field of the light reflected by the reflecting mirror (7), and the density of the interference fringes is the density of the ruled lines of the holographic grating to be fabricated.

Images