JPH0812287B2 - How to make a grating - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a diffraction grating (grate
Manufacturing method ) .

[0002]

2. Description of the Related Art As an example of etching using a photoresist, a method of manufacturing a blazed diffraction grating will be described with reference to FIG. (A) A photoresist 21 is applied to the surface of a substrate 20 such as glass or quartz that has been optically polished. (B) Photoresist 2 by holographic exposure method
A latent image of two-beam interference fringes is formed on No. 1 and by development, a parallel-line resist pattern 23 having a half-sine wave shape and a part of the substrate exposed is formed. (C) Substrate 2 perpendicular to the arrangement direction of resist pattern 23
Etching is performed by the ion beam 24 from diagonally above 0. As a result, the exposed portion of the substrate 20 is etched. (D) When the ion beam etching is stopped when the resist pattern 23 disappears, a sawtooth grating 25 is formed on the substrate 20. (E) After cleaning, the reflective film 26 is formed on the surface of the grating 25.
Coating.

[0003]

As the density of the grating grooves increases (that is, the number of grooves per unit length increases), the pitch of the exposure interference fringes becomes smaller during holographic exposure. There is a need to. However, if the distance between the interference fringes is too small, the contrast of the interference fringes deteriorates due to the vibration of the substrate and the fluctuation of the air which are transmitted from the outside, and the contrast of the interference fringes is reduced, as shown in FIG.
As shown in (b), the boundary between the photoresist 43 and the portion of the substrate 40 to be exposed is not a correct straight line, and a part of the photoresist 43 protrudes in a beard shape at the portion where the substrate 40 is to be exposed. 44, or 45 remaining like islands. If etching is performed with such unnecessary portions 44 and 45 remaining, the shape of the grating groove is disturbed, and it becomes impossible to obtain a highly accurate diffraction grating.

The present invention has been made to solve such a problem, and its object is to prepare a resist pattern having an accurate contour by
It is to provide a method capable of producing a highly accurate grating (diffraction grating) .

[0005]

In the method of manufacturing a grating according to the present invention made to solve the above problems, a) a photoresist is applied on a substrate, and b) holographic exposure and development are performed. in the method of the linear portion is covered by the linear portions and photoresist substrate is exposed to form a resist pattern appearing alternately, c) to produce a grating by etching the substrate according to the shape of the resist pattern D) It is characterized in that unnecessary portions of the photoresist are removed by irradiating the substrate only with the radical component of O ₂ plasma after forming the resist pattern and before etching.

[0006]

Since the photoresist is basically a compound of C, H and O, it reacts with O ₂ radicals to produce CO,
It becomes CO ₂ , H ₂ O, O _2, etc., and dissipates. Holographic
And the linear part where the substrate is exposed by quick exposure and development.
The linear parts covered by the photoresist appear alternately.
After forming a resist pattern of the grating to be unnecessary photoresist remaining on the contour portion and the exposed portion of the substrate of the resist pattern is typically because much thinner than the portion of the original resist pattern, and O ₂ radical By properly adjusting the reaction time of, the original resist pattern can be left, and only the unnecessary portion can be vaporized and removed to obtain a correct resist pattern. That
And perform etching using this resist pattern.
By doing so, it is possible to obtain a highly accurate grating.
It

[0007]

EXAMPLES An example in which the method for producing a grating according to the present invention is used for producing a blazed diffraction grating will be described with reference to FIGS. 1, 2 and 4. In this embodiment, the blazed diffraction grating is manufactured by the following steps.

(A) A photoresist 21 is applied to the surface of the quartz substrate 20 that has been optically polished. In this example, Microposit S-1400 (hereinafter, the names of photoresist and developer are trade names) was used as the photoresist 21, and coating was performed by spin coating to a thickness of 300 nm. After coating, bake at 90 ° C for 30 minutes in a fresh air environment,
The photoresist 21 was fixed on the substrate 20.

(B) A latent image of two-beam interference fringes is formed on the photoresist 21 by a holographic exposure method, and by development, a resist pattern 23 having a sinusoidal half-wave shape and a part of the substrate exposed is formed in parallel lines. . The light used in this example is He—Cd laser light with a wavelength λ = 441.6 nm,
The plane waves 22 were incident on the substrate from two directions at an incident angle of about 32 ° and were interfered with each other to form a latent image in a striped pattern of 2400 lines / mm at equal intervals. For the development, 303A developer was used. Here, the exposure time and the development time were adjusted so that the ratio (L & S ratio) of the portion covered with the photoresist and the portion where the substrate was exposed was set to 4: 1.

(C) Irradiating the substrate with O ₂ radicals removes unnecessary portions of the photoresist. In the step (b), the contour of the resist pattern is not always a straight line due to vibration of the substrate, fluctuation of air, etc. Unwanted portions 44 and 45 of the photoresist as shown remain. Therefore, as shown in FIG. 1, the substrate 13 (the substrate 20 covered with the resist pattern 23) is loaded inside the etching tunnel 12 arranged inside the barrel type plasma etching apparatus 10, and the O ₂ plasma treatment is performed. Was done. The atmosphere inside the apparatus 10 is 1 torr of O ₂ gas.
The plasma treatment was performed for 1 minute at an output of 450W. Of the generated O ₂ plasma, O ₂ ⁺ ions are blocked by the etching tunnel 12, and only neutral O ₂ radicals pass through the etching tunnel 12 and are applied to the substrate 13. This O ₂ radical is unnecessary Photoresist 4
4, 45 (and the surface layer portion of the original resist pattern 23) are reacted with each other to be vaporized and removed. As a result, as shown in FIG. 4C, the unnecessary residual portions 44 and 45 of the photoresist are removed, and only the originally correct resist pattern 23 remains on the substrate 20.

(D) Etching is performed with the ion beam 24 from diagonally above the substrate 20 perpendicular to the direction of arrangement of the resist patterns 23. In this embodiment, CF ₄ : Ar =
Ion beam etching was performed using a mixed gas of 1: 1. CHF ₃ may be used instead of CF ₄ . In any case, by mixing not only the gas reactive with the quartz substrate 20 but also the inert gas in this way, the etching selectivity of the substrate 20 (the etching rate of the substrate 20 with respect to the etching rate of the photoresist is Ratio is improved, and an accurate grating cross-sectional shape of the blazed diffraction grating can be obtained in a short time.

(E) When the irradiation of the ion beam 24 is stopped when the resist pattern 23 disappears, the grating 25 having a sawtooth-shaped cross section is formed on the substrate 20 accurately.

(F) After cleaning the substrate 20, the surface of the grating 25 is coated with an Al reflection film 26 having a thickness of 150 nm.

Next, an example used for manufacturing a laminar type diffraction grating will be described with reference to FIGS. 1, 3 and 4.

(A) A photoresist 31 is applied to the surface of the quartz substrate 30 that has been optically polished. In this example, unlike the above example, OFPR5000 was used. After coating to a thickness of 300 nm by spin coating,
The photoresist 31 was fixed on the substrate 30 by baking at 90 ° C. for 30 minutes in a fresh air environment.

(B) A latent image of two-beam interference fringes is formed on the photoresist 31 by a holographic exposure method, and a parallel linear resist pattern 33 having a half sinusoidal shape and a part of the substrate exposed is formed by development. . Similar to the above embodiment, the He—Cd laser light plane wave 32 having the wavelength λ = 441.6 nm is used.
Was incident on the substrate from two directions at an incident angle of about 32 °, and interference was caused to form striped latent images of 2400 lines / mm at equal intervals. However, NMD-3 was used as the developing solution in this example depending on the change of the photoresist 31. Further, the exposure time and the development time were adjusted so that the L & S ratio was 1: 1.

(C) The unnecessary portion of the photoresist is removed by irradiating the substrate with O ₂ radicals. The conditions of this step are the same as those in the above embodiment. As a result, FIG.
As shown in (c), the unnecessary residual portions 44 and 45 of the photoresist were removed, and only the original accurate resist pattern 33 remained on the substrate 30.

(D) From the direction perpendicular to the surface of the substrate 30,
Etching is performed by the ion beam 34. In this example, ion beam etching was performed using a mixed gas of CHF ₃ : Ar = 2: 1. Here, the groove depth is 20
The etching time was adjusted to be nm.

(E) The resist pattern 33 remaining on the substrate 30 is ashed and removed by O ₂ plasma.

(F) After cleaning the surface of the substrate 30, a Ni-Cr film having a thickness of 2 nm and an Au film having a thickness of 20 nm are coated as a reflective film 36 by vacuum evaporation. The Ni—Cr layer is an undercoat for increasing the adhesion between Au and the substrate 30.

[0021]

In the method for producing a grating according to the present invention , the substrate is exposed by holographic exposure and development.
Line part and line part covered with photoresist
After bets formed a resist pattern appearing alternately, O
_2. Irradiating only the radical component of the plasma removes unnecessary portions of the photoresist. For this reason,
The resist pattern approaches the original correct shape and
It becomes possible to etch the grating pattern .

[Brief description of drawings]

FIG. 1 is a sectional view of a plasma etching apparatus for irradiating a substrate with only radical components of O ₂ plasma.

FIG. 2 is an explanatory view of a process of an embodiment of the present invention for manufacturing a blazed diffraction grating.

FIG. 3 is an explanatory view of a process of an embodiment of the present invention for manufacturing a laminar diffraction grating.

FIG. 4 is a plan view (a), a cross-sectional view (b), and a cross-sectional view (c) after the unnecessary portion is removed, showing the generation of unnecessary portions of the resist pattern.

[Explanation of symbols]

10 ... Barrel type plasma etching apparatus 12 ... Etching tunnel 13 ... Resist pattern substrate 20, 30 ... Quartz substrate 21, 31 ... Photoresist 22, 32 ... Laser light plane wave 23, 33 ... Resist pattern 24, 34 ... Ion beam 25 ... Grating 35 ... Laminar groove 26, 36 ... Reflective film 40 ... Substrate 43 ... Photoresist 44, 45 ... Unnecessary photoresist

Claims (1)

[Claims] 1. A a) The photoresist is applied to a substrate, b) by performing a holographic exposure and development, appear alternately and covered linear portion with a linear portion and a photoresist substrate is exposed the resist pattern is formed, c) above in the resist pattern method of making a grating by etching the substrate according to the shape of, d) before performing the etching after forming a resist pattern, a radical component of the O ₂ plasma substrate A method for producing a grating, which comprises removing unnecessary portions of the photoresist by irradiating only the photoresist.