JPS6218561A - Formation of rugged surface - Google Patents

Abstract

PURPOSE:To expose a surface which is protected by masks and has high surface accuracy by providing the 1st mask to a region corresponding to recesses on a substrate the providing a film over the entire surface, providing the 2nd mask to the regions except the region corresponding to the recesses on the film, etching the film just before the 1st mask and finally removing the 1st and 2nd masks. CONSTITUTION:After the 1st mask 19 is preliminarily formed to the position where the recesses 2 are to be formed, the film 18 is formed and the 2nd mask is provided to the region on the film 18 where projecting parts 1 are to be formed. Since the film is etched from above said region, the film 18 under the 2nd mask remains without being etched at all and forms the projecting part 1. The region where there is no 2nd mask 22 is etched just before the 1st mask 19 and forms the recesses 2. The 1st mask 19 and the 2nd mask 22 are both removed by etching and therefore, the surface protected by the 1st and 2nd masks 19, 22 is exposed and the surface having the high surface accuracy is obtd.

Description

[Detailed Description of the Invention] [Summary] A first mask is provided in the region corresponding to the recess on the substrate, a film is provided over the entire surface from above, and a first mask is provided in the region other than the region corresponding to the recess on the layer. A second mask is provided, etching is performed up to the front of the first mask, and finally the first and second masks are removed to expose the surface with high surface precision protected by the mask.

[Industrial application field]

The present invention relates to a method for manufacturing a product that has many irregularities that require high surface precision, such as an exposure mask for DFB laser manufacturing.

[Example of common goods]

As shown in Figure 3, the DFB laser consists of a semiconductor chip 7.
A diffraction grating 8 is formed on top, and an active layer 9 and an electrode 1 are formed above it.
It has a structure in which 0 is formed. When electricity is applied between the positive and negative electrodes of this laser, laser oscillation occurs in the diffraction grating 8 and active layer 9, and laser light is emitted.

However, simply forming a diffraction grating causes the phase relationship in the diffraction grating to shift, resulting in the inconvenience that two longitudinal modes of the DFB laser are generated. In order to solve this problem, it is known to shift the pitch of the diffraction grating 8 with the center C of laser oscillation as a boundary, as shown in FIG. 4, thereby shifting the left and right phase relationship in advance.

As a method for producing a diffraction grating with a phase difference like this,
The applicant of the present invention previously proposed an exposure method as shown in FIG. 5 in Japanese Patent Application No. 60-57455.

FIG. 5(A) is a sectional view showing the basic configuration, and FIG. 5(B) is an enlarged view of the main parts. 4 is a medium forming a diffraction grating, and a transparent mask 3 made of glass or the like is placed thereon.

This mask 3 has a step 11 between the convex portion 1 and the concave portion 2 on the oscillation center C, and the optical path lengths on both sides thereof are different. Alternatively, the refractive index may be different on the left and right sides with the oscillation center C as a boundary.

Two light beams 5 and 6 are irradiated onto the surface of the medium 4 through the mask 3. At this time, the light beams 5 and 6 are incident at an angle of 2.theta., and interference between the two light beams occurs on the medium 4. Moreover, the central axis A formed by the two light beams 5 and 6 is inclined by an angle φ with respect to the normal line v, and the light beams are irradiated in an asymmetrical state.

As shown in FIG. 5(B), the thickness of the mask 3 varies across the stepped portion 11, with the thickness t2 on the right side being smaller than the thickness tl on the left side. Therefore, the optical path lengths are different on the left and right sides of the stepped portion 11, and the two light beams 5.6 are irradiated asymmetrically with an angle φ, so that the phase of the interference fringes is shifted with the stepped portion 11 as a boundary. As a result, the phase of the diffraction grating 8, which is formed by exposing the interference fringes of the two light beams, is also shifted across the stepped portion 11.

The mask 3 having this stepped portion 11 is actually manufactured by a method as shown in FIG. i.e. many DFBs at the same time
In order to manufacture a laser, a large number of stepped portions 11 are formed on the mask 3 at the same pitch as the laser dimension β. When two light beams 5.6 are irradiated, the optical path lengths on both sides are different with each stepped portion 11 as a boundary, and the incident direction of the light beams 5.6 is tilted by an angle φ with respect to the normal ■, making it asymmetrical. By irradiating the light beams on the medium 4, a diffraction grating whose phase is shifted with each stepped portion 11 as a boundary is formed on the medium 4.

After exposing to light to form a diffraction grating, the medium 4 is separated at the positions indicated by chain lines 12 . . . so that the stepped portion 11 is centered.

[Conventional technology and its problems]

By the way, both the surface of the convex portion 1 and the surface of the concave portion 2 are required to have excellent surface precision because interference fringes are formed by irradiating the light beam 5.6.

To form an uneven surface, as shown in FIG. 7, chemical etching or dry etching is performed with a mask 13 placed over the positions where the protrusions 1 are to be formed, thereby forming the recesses 2, and then removing the mask 13. It is possible to remove . However, with this method, although the surface of the convex portion 1 can be formed with high precision,
Since the etched surface remains on the bottom surface of the recess 2, the surface becomes rough, and when the light beam 5.6 is irradiated, diffuse reflection and scattering occur, making it impossible to obtain the desired interference fringes.

Furthermore, the step portion 11 is not a steep step, but a gentle slope.

If the lift-off method is used as shown in FIG. 8, the surface accuracy of the recess 2 will be improved. In this figure, first, as shown in (A), a mask 14 is formed in advance at the position where the recess 2 is to be formed, and a film 15 made of the same material as the mask 3 is formed thereon by a method such as vapor deposition. Thereafter, when the mask 14 is removed with a solvent, the film 15 above it is also removed, resulting in the state shown in (b). The bottom surface of the recess 2 after removing the mask 14 becomes a surface with high surface accuracy. However, the lift-off method is effective when the thickness of the film 15 is about 0.2 μm, but when the thickness becomes about 2 to 3 μm, such as the product targeted by the present invention, even if the mask 14 is removed, It is difficult to remove the film 15 thereon. Therefore, cracks 16 may occur in the stepped portion 11 between the upper removed portion of the mask 14 and the portion remaining as the convex portion 1, making it impossible to obtain a uniform finish.

A technical object of the present invention is to solve such problems in the conventional unevenness forming method and to realize a method that can form convex portions, concave portions, and stepped portions with high precision.

[Means for solving problems]

FIG. 1 is a diagram showing the basic principle of the method for forming an uneven surface according to the present invention in the order of steps, and the processes are performed in the order of A, B, . . . .

E shows the finished state of the uneven surface, 17 is the substrate, 18 is a film laminated thereon, 1 is a convex portion, and 2 is a concave portion. In forming the uneven surface, first, as in step A, a first mask 19 is formed in the region to become the recess 2, and then, as in step B, a film 18 is formed over the entire upper region. Next, as in step C, a second mask 22 is formed in a region other than the region to become the recess 2, and then, as in step D, the film 18 in the region other than the second mask 22 is formed with a first mask. By etching to the front of the mask 19 and then removing the first mask 19 and the second mask 22, an uneven surface is formed as shown in step E.

[Effect]

A first mask 19 is formed in advance at the position where the concave portion 2 is to be formed, and then the film 18 is formed, and a second mask is provided on the layer 18 in the region where the convex portion 1 is to be formed. Since etching is performed from above, the film 18 on the lower side of the second mask is not etched at all and remains, forming the convex portion 1. Further, the area without the second mask 22 is etched to the front side of the first mask 19, and becomes the recess 2. Since both the first mask 19 and the second mask 22 are removed by etching, the surfaces protected by the first and second masks 19, 22 are exposed, resulting in surfaces with high surface precision.

〔Example〕

Next, how the method for forming an uneven surface according to the present invention is actually implemented will be explained using examples. FIG. 2 is a cross-sectional view showing an embodiment of the unevenness forming method according to the present invention in the order of steps;
This will be explained according to this figure.

(a) A striped Al vapor deposition film 19 is applied by 700 people using photoresist lift-off to a parallel quartz plate 17 with a thickness of 1 mm, both sides of which have been optically polished. This stripe is 600 μm wide with a width of 300 μm and an interval of 300 μm.
Period.

(b) A Sing film 18 is deposited on it by sputtering.
．． Laminated to a thickness of 14 μm. This may be done by a technique such as vapor deposition.

(C) Next, a photoresist is applied thereon and exposed by irradiating light 20 from the back side, using the so-called self-line method to form a photoresist pattern, leaving the photoresist only in the upper area of the A1 film 19. 21.

(d) Apply 1,200 Aff vapor deposited films on top of this, and perform lift-off using the photoresist pattern 21 that was previously applied to create the first AI! The second layer A1 film 22 is left only in the area where the film 19 is not present.

+e) Reactive ion etching RIE” (0□5%
CF4) is used to etch the 5in2 film in the area where the second layer A2 film 22 is not present to the first layer AAAAl2O surface.At this time, the A6 film 22.19 serves as a mask and the 5in2 film 18 below it is etched. And the quartz substrate 17 is not etched.

(f) Finally, chemical etching is performed to form an Al film 9.
22 is removed.

Both the concave portions 2 and the convex portions 1 produced in this way are protected by the A1 film 19.20 during etching, so after the chemical etching of the Al film 9.20, a high surface precision is obtained. It becomes an optical surface.

By using the quartz mask manufactured by such a method as the transparent mask 3 shown in FIG. 5, the desired diffraction grating 8 can be formed without causing diffuse reflection or scattering of light. Also, the lower A
Since it is etched until it reaches the film 9, the step part 11 is etched.
It is also in a steep state.

In the example, the self-line method is used to form the resist pattern 21 for producing the second mask 22, but it goes without saying that the second mask 22 can be produced by other methods. .

As an example, the case where an uneven surface is formed on an exposure mask for manufacturing a DFB laser has been described, but the present invention
It goes without saying that the present invention can also be applied to forming uneven surfaces for other uses. For example, it is also effective when performing epitaxial growth on the bottom surface of the recess 2 with high precision.

〔Effect of the invention〕

As described above, according to the present invention, the first mask is provided on the bottom surface of the recess 2, and the second mask is provided on the surface of the convex portion 1, and the first and second masks are removed after etching. Therefore, the bottom surface of the concave portion 2 and the convex portion 1 become highly accurate planes that are protected by a mask during etching.

[Brief explanation of drawings]

FIG. 1 is a sectional view explaining the basic principle of the uneven surface forming method according to the present invention, FIG. 2 is a sectional view showing an embodiment of the uneven surface forming method, FIG. 3 is a sectional view of a DFB laser, and FIG. 4 is DF
FIG. 5 is a cross-sectional view showing a method for forming phase difference interference fringes; FIG. 6 is a side view showing a method for simultaneously forming a large number of phase difference diffraction gratings; FIG. The figure shows a typical method for forming recesses, and FIG. 8 is a sectional view showing a method for forming recesses by lift-off of a thick film. In the figure, 1 is a convex part, 2 is a concave part, 8 is a diffraction grating, and 17
18 is a substrate, 19 is a first mask, and 22 is a second mask. Patent applicant: Minoru Aoyagi, agent for Fujitsu Limited, patent attorney: Figure 1: Oil fluid: Figure 2: DFB racer'-ball η゛6d Figure 3: Cross-section showing phase difference metal 6, solid resistance width 1 Figure 4: Method for forming four islands of phase difference chipping Figure 5 Figure 6 Figure 7 Force method for forming recesses by lift-off Figure 8

Claims (4)

[Claims] (1) A method of forming an uneven surface consisting of a convex part (1) and a concave part (2) on a substrate (17), the method comprising: A mask (19) is formed, and a film (19) is formed over the entire area above the mask (19).
8), and then a second mask (22) is formed on the film (18) in a region other than the region corresponding to the recess (2), and then a second mask (22) is formed in the region other than the second mask (22). A method for forming an uneven surface, characterized in that the film (18) is etched up to just before the first mask (19), and then the first mask (19) and the second mask (22) are removed. (2) The substrate (17) and the film (18) are made of transparent materials, and when producing the resist pattern for forming the second mask (22), the first A method for forming an uneven surface according to claim 1, characterized in that a self-alignment method is used in which exposure is performed through a mask (19). (3) The method for forming an uneven surface according to claim (1) or (2), wherein the substrate (17) and the film (18) are made of SiO_2. (4), the etching method of the film (18) is CF_4
The method for forming an uneven surface according to claim 1, wherein the method is ion beam etching in +O_2, and the first and second mask materials (19) and (22) are aluminum.