JPH02137803A - Production of diffraction element - Google Patents

Abstract

PURPOSE:To improve the forward and backward utilization efficiency given by the product of the zero order transmission and first order diffraction efficiency of the diffraction element by incorporating a prescribed ratio of gaseous O2 into an etching gas and executing reactive ion etching in the coated state of a resist film, thereby forming diffraction element pattern grooves. CONSTITUTION:The surface of a transparent substrate 13 is coated with the resist film 14 and this resist film 14 is subjected to exposing and photodeveloping treatments to form the resist film 14 having diffraction element patterns 14a. The reactive ion etching is executed in the coated state of this resist film 14 to form the diffraction element pattern grooves 13a on the transparent substrate 13. The prescribed volume of the gaseous O2 is incorporated into the etching gas to be used. The respective diffraction element patterns 11a, therefore, rise diagonally with the surface of the transparent substrate 13 and constitute the inverted trapezoidal shapes longer in the upper bottom than in the lower bottom. The second and higher order diffractions in the function of the diffraction element 11 are suppressed in this way and the forward and backward utilization efficiency given by the product of the zero order transmission and first order diffraction efficiency is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a diffraction element used in optical pickup for reproducing optically recorded information.

[Conventional technology]

It is very effective to use a diffraction element to make the optical pickup installed in an optical information reproducing device such as a compact disk device small and lightweight, and various proposals regarding this diffraction element have been made in the past.

For example, in the optical information reproducing apparatus shown in FIG. 2, diverging light emitted from a semiconductor laser 1 passes through a diffraction element 2 and is focused onto a recording medium 4 by an imaging lens 3.

The reflected light from the recording medium 4 is guided by the imaging lens 3 to the diffraction element 2, and is diffracted by the diffraction element 2.
The first-order diffracted light is focused on a rectangular photodetector 5. Note that the diffraction element 2 needs to efficiently transmit the laser light irradiated from the semiconductor laser 1, and also efficiently transmits only the first-order diffracted light from the recording medium 4 without outputting higher-order diffracted light as much as possible. (Need to output.

In such an optical information reproducing device, the recording medium 4
Since it is required to condense the light beam into a minute range of about 1 μm in diameter, it is essential to perform so-called focus detection. Therefore, the diffraction element 2 consists of, for example, two equally divided semicircular regions 2a and 2b, while the photodetector 5
is divided into four photodetecting sections 5a to 5d with dividing lines A and B in two directions orthogonal to each other as boundaries.

When the emitted light from the semiconductor laser 1 is accurately focused on the recording medium 4, as shown in FIG. 3(b),
Condensing spora t-6 for diffracted light from region 2a of diffraction element 2
A is formed at one point on the dividing line A between the photodetectors 5a and 5b of the photodetector 5, while a focused spot 6b of the diffracted light from the region 2b of the diffraction element 2 is formed at a point between the photodetectors 5C and 5d. It is formed at one point on the dividing line A. Therefore, the outputs of the photodetectors 5a and 5b are equal, and the outputs of the photodetectors 5c
・The outputs of 5b become equal.

On the other hand, when the recording medium 4 approaches the imaging lens 3, the focal point of the diffracted light from the diffraction element 2 is formed behind the photodetector 5. , area 2a
The focused spot 6a from the area 2b forms a semicircular pattern on the photodetector 5a, while the focused spot 6a from the area 2b
b forms a semicircular pattern on the photodetector 5d.

Furthermore, when the recording medium 4 moves away from the imaging lens 3, the focal point of the diffracted light from the diffraction element 2 will be located in front of the photodetector 5, so as shown in FIG. To,
The focused spot 6a forms a semicircular pattern on the photodetector 5b, and the focused spot 6b forms a semicircular pattern on the photodetector 5c.
Form a semicircular pattern on top.

Therefore, the output signals of the photodetectors 5a to 5d are
-3d, the focus error signal FES is FES=(
Based on this focus error signal FES, the imaging lens 3 is moved along the optical axis by a driving means (not shown) to appropriately focus on the recording medium 4. It looks like this.

The diffraction element 2 that functions as described above has conventionally been manufactured by the following method.

A diffraction element pattern is calculated on an electronic computer, and based on this pattern, an electron beam is scanned using an electron beam lithography method to produce a reticle with a 10 times enlarged pattern. This reticle is optically reduced to 1/1O by a photorepeater to produce a photomask 7 having a predetermined pattern of light-transmitting parts and non-light-transmitting parts, as shown in FIG. 4(a). .

On the other hand, as shown in FIG. 3(b), a glass substrate 8 serving as a diffraction element is prepared, and the surface of the glass substrate 8 is cleaned using detergent, water, or an organic solvent.

Next, as shown in the same figure (C), the above-mentioned glass substrate 8
A resist film 9 is coated on the surface using a spin coater.

Then, as shown in FIG. 4(d), the photomask 7 is brought into close contact with the resist film 9 and exposed to ultraviolet rays, thereby forming a latent image of the diffraction element pattern of the photomask 7 on the resist film 9. form.

Next, as shown in FIG. 4(e), the resist film 9 is developed to form diffraction element pattern holes 9a in the resist film 9.

Thereafter, as shown in FIG. 3(f), while the resist film 9 is covered with the diffraction element pattern holes 9a, reactive ion etching is performed in an etching gas such as CF, CHF3, etc. A diffraction element pattern groove 8a is formed directly on the glass substrate 8.

Then, as shown in FIG. 3(g), the resist film 9 that is no longer needed after the reactive ion etching is removed by incineration using a solvent such as acetone or O□ gas. As a result, a diffraction element 10 having diffraction element pattern grooves 10a is obtained.

[Problem to be solved by the invention]

However, according to the above conventional method, in the glue active ion etching, the resist film 9 is eroded only from above by the etching gas, and the resist film 9 is
The six widths C' of the diffraction element pattern maintain the original width C, so that the six grooves 10a (8a) are perpendicular to the surface of the glass substrate 8, and the diffraction element 1
The cross-sectional shape of the grooves 10a at 0 is rectangular. When the cross-sectional shape of the grooves 10a is rectangular, in the function as a diffraction element, higher-order diffracted light of the second order or higher increases, and the product of the zero-order transmittance and the first-order diffraction efficiency in the diffraction element 10 This has the disadvantage that the round-trip utilization efficiency provided is low.

[Means to solve the problem]

In order to solve the above-mentioned problems, a method for manufacturing a diffraction element according to the present invention covers a transparent substrate with a resist film, and subjects the resist film to light exposure and development to form a resist film having a diffraction element pattern. In a method for manufacturing a diffraction element by performing reactive ion etching while covered with this resist film to form a diffraction element pattern groove on the transparent substrate, the reactive ion etching is used for this purpose. The etching gas is characterized in that the etching gas is mixed with a predetermined amount of Ot gas.

(Function) According to the above configuration, in active ion etching, the resist film is eroded not only from above but also from the sides by the etching gas containing a predetermined amount of O2 gas. 6 width gradually becomes narrower than the initial width.As a result, each of the above-mentioned diffraction element pattern grooves rises obliquely to the surface of the transparent substrate, and the shape of the groove is such that the upper base is smaller than the lower base in its cross-sectional shape. It has a long inverted trapezoidal shape.If the groove has such an inverted trapezoidal shape, in its function as a diffraction element, 2
Higher-order diffraction higher than the next order is suppressed, and the round-trip utilization efficiency given by the product of the 0th-order transmittance and the 1st-order diffraction efficiency in the diffraction element is improved.

〔Example〕

The τ embodiment of the present invention will be described below based on FIG.

In the method for manufacturing a diffraction element according to the present invention, FIG.
), the diffraction element 1 manufactured by this method
1 has an inverted trapezoidal diffraction element pattern groove 11a, in which the upper base is longer than the lower base in its cross-sectional shape.

To manufacture such a diffraction element 11, for example, as in the past, a diffraction element pattern is calculated on an electronic computer, and based on this pattern, an electron beam is scanned using an electron beam writing method to create a reticle with a 10 times enlarged pattern. Create. Using this reticle, the photorepeater optically reduces the size to 1/10, and as shown in FIG. 2b... A photomask 12 having a diffraction element pattern is manufactured.

On the other hand, as shown in FIG. 2(b), a glass substrate 13 is prepared as a transparent substrate serving as a diffraction element, and this glass substrate 13 is
Clean the surface using detergent, water, or an organic solvent.

Next, as shown in the same figure (C), the above-mentioned glass substrate 1
A resist film 14 is coated on the surface of 3 using a spin coater.

Then, as shown in FIG. 2D, the photomask 12 is brought into close contact with the resist film 14 and exposed to ultraviolet rays, thereby exposing the resist film 14 to the latent diffraction element pattern of the photomask 12. form an image.

Next, as shown in FIG. 3(e), the resist WA14 is developed to form diffraction element pattern holes 14a in the resist film 14.
・Form.

Thereafter, as shown in FIG. 0 at a volume ratio of 5-10%
Reactive ion etching is performed using a gas containing two gases to form diffraction element pattern grooves 13a directly on the glass substrate 13.

Then, as shown in FIG. 3(g), the resist film 14 that is no longer needed after the reactive ion etching is removed by incineration using a solvent such as acetone or Ot gas. As a result, the diffraction element pattern grooves 11a-...(13a-
) is obtained.

According to the above configuration, in the glue active ion etching in the step of FIG. The 6th line D' in the diffraction element pattern of the resist film 14 becomes somewhat narrower than the original width. That is, the resist film 14 not only decreases in thickness but also gradually becomes narrower in width. As a result, the aforementioned six grooves 11a (13a)
has a shape that stands obliquely with respect to the surface of the glass substrate 13, and the shape of the groove 11a is, as described above, an inverted trapezoidal cross-sectional shape in which the upper base is longer than the lower base. When the grooves 11a have such an inverted trapezoidal shape, higher-order diffraction higher than the second order is suppressed in the function as a diffraction element, and the zero-order transmittance and first-order diffraction efficiency of the diffraction element 11 are improved. It is possible to improve the round-trip utilization efficiency given by the product of

〔Effect of the invention〕

As described above, the method for manufacturing a diffraction element according to the present invention includes coating a resist film on a transparent substrate, exposing and developing the resist film to form a resist film having a diffraction element pattern, In a method of manufacturing a diffraction element by performing reactive ion etching with the film coated to form a diffraction element pattern groove on the transparent substrate, the reactive ion etching is performed in an etching gas used for the process. The configuration is such that the gas is mixed with a predetermined amount of 0□ gas.

As a result, each of the diffraction element pattern grooves rises obliquely with respect to the surface of the transparent substrate, and the groove has an inverted trapezoidal cross-sectional shape in which the upper base is longer than the lower base. When the groove has such an inverted trapezoidal shape, in its function as a diffraction element, higher-order diffraction higher than the second order is suppressed, and the round-trip rate given by the product of the 0th-order transmittance and the 1st-order diffraction efficiency in the diffraction element is suppressed. Utilization efficiency improves. Therefore, the amount of light incident on the photodetector of the optical pickup increases, and it is possible to obtain a carrier wave output with sufficient margin against noise.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the present invention.
(a) is a cross-sectional view of the photomask, (b) is a cross-sectional view of the glass substrate, (C) is a cross-sectional view of the glass substrate coated with a resist film, and (d) is a cross-sectional view of the resist film on the glass substrate. (e) is a cross-sectional view of the developed resist film, (f) is a cross-sectional view of the glass substrate after etching, and (g) is a cross-sectional view of the glass substrate after it has been etched. A cross-sectional view of the diffraction element, FIG. 2 is a schematic diagram of the optical pickup, FIG. An explanatory diagram showing a focused spot on a photodetector in a focused state, (C) is an explanatory diagram showing a focused spot on a photodetector in an unfocused state, and Fig. 4 shows a conventional example. Figures (a) to (g) are cross-sectional views showing each step of the manufacturing process of the diffraction element. 11 is a diffraction element, lla is a diffraction element pattern groove 12 is a photomask, 13 is a glass substrate (transparent substrate), 14 is a resist film, and 14a is a diffraction element pattern hole. Figure (a) Figure (b) Mouth m here]~13 Figure (C) Figure (d) Figure (e) Figure (9) Figure (a) Figure (b) Lolo = =Nii=Hi8 Figure 4 (C) Figure (d) Figure (e) Figure 4 (f) Figure (9)

Claims (1)

[Claims] 1. A resist film is coated on a transparent substrate, and this resist film is exposed and developed to form a resist film having a diffraction element pattern. In the method of manufacturing a diffraction element by etching to form a diffraction element pattern groove on the transparent substrate, the reactive ion etching is performed by mixing a predetermined amount of O_2 gas into the etching gas used for the reactive ion etching. A method for manufacturing a diffraction element, characterized in that the manufacturing method is performed using a gas.