JPH052142B2 - - Google Patents

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 on the film in the region other than the region corresponding to the recess. 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 having many irregularities that require high surface precision, such as an exposure mask for producing a DFB laser.

[Example of applicable products]

As shown in FIG. 3, the DFB laser has a structure in which a diffraction grating 8 is formed on a semiconductor chip 7, and an active layer 9 and an electrode 10 are formed above it.
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, if a diffraction grating is simply formed, the phase relationship in the diffraction grating will shift, resulting in the inconvenience that two longitudinal modes of the DFB laser will occur. 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 manufacturing a diffraction grating having such a phase difference, the applicant of the present invention previously proposed a method for manufacturing a diffraction grating having a phase difference.
As No. 57455 (see Special Publication No. 3-22602),
We proposed an exposure method as shown in Figure 5. In FIG. 5, A is a sectional view showing the basic configuration, and B is an enlarged view of the main parts thereof. 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.

2 on the surface of this medium 4 through the mask 3.
Two light beams 5 and 6 are emitted. At that time, luminous fluxes 5 and 6
is incident at an angle of 2θ, and the two light beams interfere 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. 5B, 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 t1 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 and 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. That is, in order to be able to manufacture a large number of DFB lasers at the same time, a large number of stepped portions 11 are formed on the mask 3 at the same pitch as the laser dimension l. two luminous fluxes 5,
When irradiating 6, the optical path lengths on both sides are different with each step 11 as a border, and the light beams 5 and 6 are different.
By tilting the incident direction of the beam by an angle φ with respect to the normal line V and irradiating the beam asymmetrically, a diffraction grating whose phase is shifted with respect to 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 step 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 have a luminous flux 5,
6 to form interference fringes, high surface accuracy is required. 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 beams 5 and 6 are irradiated, diffuse reflection and scattering occur, making it impossible to obtain the desired interference fringes. Further, 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 1 is placed in the position where the recess 2 is to be formed.
4 is 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, in the lift-off method, the thickness of the film 15 is
It is effective when the thickness is about 0.2 μm, but when the thickness is 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. As a result, cracks 16 occur in the stepped portion 11 between the upper removed portion of the mask 14 and the portion remaining as the convex portion 1, and a uniform finish cannot be obtained.

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 accuracy.

[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 is the completed state of the uneven surface, 17
18 is a substrate, 18 is a film laminated thereon, 1 is a convex portion, and 2 is a concave portion. When forming an uneven surface,
First, as in step A, a first mask 19 is formed in the area that is 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 area other than the second mask 22 is etched to the front of the first mask 19, and then the first mask 19 and the second mask 22 are removed, as shown in step E. An uneven surface is formed.

[Effect]

A first mask 19 is placed in advance at the position where the recess 2 is to be formed.
is formed, then the film 18 is formed, and the film 18 is
Since the second mask is provided in the area where the convex part 1 is to be formed above the second mask and etching is performed from above, the film 18 under the second mask remains without being etched at all and becomes the convex part 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 and 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. Second
The drawings are cross-sectional views showing an embodiment of the unevenness forming method according to the present invention in the order of steps, and explanation will be given with reference to these drawings.

(a) A striped Al vapor deposited film 19 with a thickness of 700 Å is applied to a parallel quartz plate 17 with a thickness of 1 mm, both sides of which have been optically polished, using photoresist lift-off. This stripe is 300μm wide and 300μm apart.
The period is 600μm.

(b) Sputter a SiO ₂ film 18 on top of it to a thickness of 2.14 μm.
m layers. This may be done by a technique such as vapor deposition.

(c) Next, by applying photoresist on it and exposing it to light 20 from the back side,
A so-called self-align method is used to form a photoresist pattern 21 by leaving only the area above the Al film 19 with photoresist.

(d) An Al vapor deposited film of 1200 Å is deposited on this, and by lift-off using the previously formed photoresist pattern 21, the second Al film 22 is left only in the area where the first Al film 19 is not present.

(e) Reactive ion etching “RIE” (O ₂ 5%
Using CF ₄ ), the portion of the SiO ₂ film where the second layer Al film 22 is not present is etched to the surface of the first layer Al film 19 . At this time, the Al films 22 and 19 serve as masks, and the SiO ₂ film 18 and quartz substrate 17 below them are not etched.

(f) Finally, by chemical etching, the Al film 19,
22 is removed.

Both the concave portions 2 and the convex portions 1 produced in this way are protected by the Al films 19 and 20 during etching, so that after the chemical etching of the Al films 19 and 20, an optical surface with high surface precision is formed. becomes.

The quartz mask manufactured using this method was
By using it as the transparent mask 3 shown in the figure, the desired diffraction grating 8 is formed without causing diffuse reflection or scattering of light. Furthermore, since the etching is performed until it reaches the lower Al film 19, the stepped portion 11 also becomes steep.

In the embodiment, a self-alignment method is used to form the resist pattern 21 for producing the second mask 22.
It goes without saying that it can also be produced by other methods.

As an example, a case has been described in which an uneven surface is formed on an exposure mask for manufacturing a DFB laser, but it goes without saying that the present invention can also be applied to cases where an uneven surface is formed for other purposes. 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 after etching, the first mask and the second mask are provided.
Since the mask is removed, the bottom surface of the recess 2 and the protrusion 1 become highly accurate planes that are protected by the mask during etching.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view explaining the basic principle of the uneven surface forming method according to the present invention, FIG. 2 is a cross-sectional view showing an embodiment of the uneven surface forming method, FIG. 3 is a cross-sectional view of a DFB laser, and FIG. 4 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, and FIG. FIG. 7 is a diagram showing 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 portion, 2 is a concave portion, 8 is a diffraction grating, 17 is a substrate, 18 is a film, 19 is a first mask, and 22 is a second mask.

Claims (1)

[Claims] 1. A method for forming an uneven surface consisting of convex portions 1 and concave portions 2 on a substrate 17, the method comprising: forming a first mask 19 on a region of the substrate 17 corresponding to the concave portions 2; , the entire upper area has a film 1
8 is formed, 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 the film 18 in the region other than the second mask 22 is covered with the first mask. A method for forming an uneven surface, characterized in that the first mask 19 and the second mask 22 are removed after etching up to just before the mask 19. 2 The substrate 17 and the film 18 are made of a transparent material, and when a resist pattern for forming the second mask 22 is prepared, the substrate 17 is exposed to light from the back side through the first mask 19. 2. A method for forming an uneven surface according to claim 1, characterized in that a method is used for forming an uneven surface. 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 _SiO2 . 4. The method of etching the film 18 is ion beam etching in CF ₄ +O ₂ , and the first and second mask materials 19 and 22 are aluminum. Method for forming an uneven surface.