JPH033285A - Manufacturing method of semiconductor device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] A method for forming a diffraction grating, particularly in the production of semiconductor lasers used in optical communications, in which a diffraction grating is formed in a resonator to select wavelengths in order to achieve single wavelength oscillation. Regarding the manufacturing method of a mask for forming a diffraction grating on a semi-insulating compound substrate, in order to form a semiconductor laser with high performance, when forming the diffraction grating, a photomask on which the diffraction grating is formed is irradiated with laser light. The interference pattern between the transmitted light and the first-order transmitted diffraction light is used, and the surface in contact with the resist on the substrate on which the diffraction grating is to be formed is a flat, smooth surface that does not damage the resist surface. A diffraction grating pattern made of a layer with a refractive index n2 and a layer with a refractive index n1 in which the diffraction grating pattern is embedded and flattened are provided on a substrate with a refractive index n1. Using a photomask, the flattened surface of the photomask is brought into contact with the photoresist on the semiconductor substrate, and then laser light is irradiated to create an interference pattern between the transmitted light and the first-order transmitted diffraction light. A method for manufacturing a semiconductor device characterized by including a step of transferring onto a photoresist, and a mask pattern formed on a substrate with a refractive index of n1 by a layer with a refractive index of n2 and corresponding to a region in which a phase shift is to be performed. Then, using a photomask provided with a layer with a refractive index n1 that embeds and flattens the mask pattern, and after bringing the flattened surface of the photomask into contact with the photoresist on the semiconductor substrate, two A semiconductor device comprising the step of irradiating with laser beams and transferring an interference pattern caused by the two laser beams and an interference pattern whose phase is shifted by a mask pattern of the photomask onto the photoresist. Contains and constitutes a manufacturing method.

[Industrial application field]

The present invention relates to a method for forming a diffraction grating, particularly in the production of semiconductor lasers used in optical communications, in which a semiconductor laser is provided with wavelength selectivity by forming a diffraction grating within a resonator in order to achieve single wavelength oscillation. The present invention relates to a method of manufacturing a mask for forming a diffraction grating on a semi-insulating compound substrate.

[Conventional technology]

Figure 5 shows DFB (distributed feedback type)
ionFeedback) This is a schematic diagram showing the structure of a laser. In the figure, 51 is a semi-insulating compound substrate n-1n.
P substrate, 52 is InGaAsP waveguide layer, 53 is InG
aAsP active layer, 54 p-1nGaAsP buffer layer, 55 p-1nP layer, 56 n-1nPJi, 57
is a p-1nP layer, 58 is an aAsP cap layer on In, 5
9 is a SiO2 film, 60 is a Cr/^U electrode, and 61 is a zinc diffusion region.

In this DFB laser, the above-mentioned crystals are sequentially grown on the n-1nP substrate 51, but it is necessary to form a diffraction grating on the 1-1nP substrate (hereinafter simply referred to as the substrate) 51. As shown in FIG. 6(a), a photoresist 62 (hereinafter simply referred to as resist) is applied onto a substrate 51, and a He-Cd laser 63 is applied so that an interference pattern 64 is transferred onto the resist 62. Using the diffraction grating pattern 65 shown in FIGS. 6(C) as a mask, the substrate 51 is etched (transferred) to form the diffraction grating 5 as shown in FIG. 6(C).
1a. The present invention relates to a method for forming a mask used to form a diffraction grating on a substrate.

Conventionally, there are three methods for recording the above-mentioned diffraction grating pattern on photoresist: (1) three-beam interference exposure method, (2) electron beam (EB) direct writing method, and (3) transmitted light-diffracted light self-interference method. method is known.

Referring to FIG. 7(a), the three-beam interference exposure method uses, for example, a He-Cd laser beam 6 to transfer an interference pattern (interference fringe) 64 onto a resist 62 coated on a substrate 51.
This is a method of irradiating 3. To do this, as shown in FIG. 6(b), an interference pattern 64 is created using the laser beam emitted from the laser 66 using a half mirror 67 and mirrors 68a and 68b.

Referring to FIG. 8, the EB direct writing method is a method of directly writing a diffraction grating on a resist 62 coated on a substrate 51 using an electron beam 71.

Referring to FIG. 9, the transmitted light-diffraction light self-interference method uses a mask 41 with a surface carved with a diffraction grating, and Fle-
Cd laser light 63 is irradiated onto this mask, and transmitted light 42 and first-order transmitted diffraction light 43 are created by the diffraction grating on the surface of the mask, thereby obtaining an interference pattern 64.

[Problem to be solved by the invention]

The three-beam interference exposure method (1) is the most commonly used method, but it has the problem that adjustment of the optical system shown in FIG. 7(b) is difficult and time-consuming.

The purpose is to provide a method for forming.

The EB direct writing method (2) takes time to write, the EB generator is expensive, and is not suitable for production, so it is hardly put to practical use.

The transmitted light-diffracted light self-coherence (3) is caused by the fact that the surface of the mask 41 in which the diffraction grating shown in FIG. The surface of the resist 62 may be scratched due to the unevenness of the diffraction grating. Furthermore, since it is not possible to apply an anti-reflection (AR) coating to the surface of fine irregularities, there is a problem that the influence of reflected light from the side of the substrate 51 cannot be eliminated.

Therefore, in the present invention, when forming a diffraction grating, a photomask on which a diffraction grating is formed is irradiated with a laser beam, and an interference pattern between the transmitted light and the first-order transmitted diffraction light is used. [Means for Solving the Problem] The above problem is to provide a mask with a flat surface that is in contact with the resist on the substrate and which does not damage the resist surface. A photomask provided with a diffraction grating pattern made of layers and a layer with a refractive index n1 that embeds and flattens the diffraction grating pattern is used, and the flattened surface of the photomask is exposed to a photoresist on a semiconductor substrate. A method for manufacturing a semiconductor device, comprising the step of contacting a resist with a laser beam, and transferring an interference pattern between the transmitted light and the first-order transmitted diffraction light to the photoresist, and a refractive index. A photomask comprising, on a substrate with a refractive index n1, a mask pattern formed of a layer with a refractive index n2 and formed corresponding to a region in which a phase shift is to be performed, and a layer with a refractive index nl that embeds and flattens the mask pattern. is used to bring the flattened surface of the photomask into contact with the photoresist on the semiconductor substrate, and then irradiates with two laser beams to form an interference pattern by the two laser beams and the photomask. The present invention is solved by a method for manufacturing a semiconductor device, which includes a step of transferring an interference pattern whose phase is shifted by a mask pattern to the photoresist.

[Effect]

In the first embodiment of the present invention, a phase diffraction grating is formed by embedding a substance with a refractive index of n2 on a quartz substrate with a refractive index of n1 to obtain a smooth surface. Since the mask surface on the side in contact with the resist is made smooth, the resist on the substrate surface is not damaged, and the adhesion between the resist on the substrate and the mask is also improved.

Further, in the second embodiment of the present invention, the mask used to form the diffraction grating with a partially shifted phase on the substrate has a flat surface that is in contact with the resist on the substrate on which the diffraction grating is to be formed, and , Ti0z is embedded between SiO□ of the mask substrate and 5iOtO deposited on the mask substrate, interference fringes with partially shifted phases can be obtained.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to illustrated embodiments.

A first embodiment of the invention is shown in FIG.

First, as shown in FIG.
A resist diffraction grating pattern 12 with a thickness of, for example, 0.2 to 0.25 μm is formed on a quartz substrate 11 with a refractive index n1 to make a
Formed at a pitch of

Next, as shown in FIG. 3B, a material having a refractive index of n2, such as titanium dioxide ↑tO!, is applied to the entire surface of the quartz substrate 11. (
refractive index 2-2.5) to a thickness of 1000 nm.

Next, the TiOz film 13 on the resist surface is removed by a known lift-off method, and the TiOz film 13 between the resists 12 is removed.
□Leave the film 13 ((C) in the same figure).

Next, as shown in the same figure (d), 5tOz1 was applied to the entire surface.
Deposit 4 to a thickness of 1-. Subsequently, as shown in FIG. 5(e), a non-reflective film (^R coat) 15 is formed on the surface of the quartz substrate 11 and the surface of 5i (h), and the photomask 10 is coated.
make.

By the above method, a transmitted light-diffracted light self-interference type mask with a smooth surface and AR coats formed on both sides can be obtained.

By the way, unifying the longitudinal mode of a semiconductor laser is an extremely important issue in preventing waveform distortion due to wavelength dispersion in optical communication, reducing noise, and optical application measurement. However, a semiconductor laser having a Fabry-Perot resonator does not have sufficient longitudinal mode selectivity, making it difficult to maintain mode stability.

As one method for solving such problems, a DFB laser in which a diffraction grating is built into a resonator has been developed.

However, conventional DFB lasers with a similar structure as a whole have 2
There was a problem that two longitudinal modes could oscillate. Methods for suppressing bimodal oscillation of FB lasers include using a diffraction grating that has a phase shift equivalent to the wavelength in the vicinity of the center of the diffraction grating, and giving asymmetrical reflection to the laser end face. is considered. Among these methods, it has been theoretically derived that the method using a phase-shifted diffraction grating allows oscillation at the Bragg wavelength in a resonator formed by the diffraction grating. The operation of the phase shift laser DFB laser was first confirmed by fabricating a second-order diffraction grating using an electron beam. Therefore, there has been a desire for a method that is based on exposure using laser light interference and that adds a phase shift to this exposure, which can stably produce fine diffraction gratings.

One currently known method is called the positive/negative method, which uses two types of resist, positive and negative, and inverts the phase of each of these areas to create a phase shift equivalent to four wavelengths. This is how it is done. This positive/negative method will be explained with reference to a schematic diagram of FIG.
A positive resist 62a and a negative resist 62b are used together on the substrate 1, and He--Cd laser light is irradiated thereon. In these resists, the uneven pattern is reversed during development, and a λ/4 shift is realized.

However, with the positive/negative method, there is a problem that a diffraction grating with a completely uniform shape and depth cannot be created because the sensitivities of each resist are not the same and the transfer must be performed by etching separately. .

On the other hand, as a means to obtain an effect equivalent to a phase shift, there is also a method of effectively producing a phase shift by changing the optical distance near the center without changing the spatial phase of the diffraction grating. be.

The present applicant has developed a simple method for directly exposing and forming a phase shift diffraction grating using laser light interference.

To this end, we newly introduced the concept of a contact mask to add a phase shift during exposure. That is, using a contact mask for generating a phase difference, which adds a predetermined phase shift that varies relatively depending on the region on the substrate forming the diffraction grating so that the exposure laser beam reaches the substrate; We investigated whether this method could produce a phase-shifted diffraction grating with the same resolution as a regular uniform diffraction grating. First, we developed a technology to form a deep pattern, which is essential for manufacturing this mask. Next, we created a mask using this technology, and then used this mask to create a phase-shift grating pattern on an InP substrate. exposed.

The basic principle and function of the mask developed by the applicant will be explained. The principle of shifting the phase of a diffraction grating in interference exposure method is as follows.

Since the amplitudes of the two laser beams for interference are equal (G), a periodic interference pattern as shown in Figure 11 is created in the space where the two beams exist, and the part with strong electric field strength is the angle between the two beams. Proceed in the direction of the bisector.

On the other hand, when these two light rays are incident on a transparent material, they are each refracted at the surface according to Snell's law. At that time, as shown in FIG. 12, when these light rays are asymmetrically incident on the transparent material and the angle of incidence is different, the light rays undergo different refraction. Therefore, the peak of light intensity traveling in the direction of the bisector of the angle formed by these two rays is
The direction of movement changes on the surface of the material. Moreover, since the electric field of S-polarized light is continuous at the boundary between air and glass, the region where the electric field is concentrated passes continuously through the boundary between air and glass, and appears to follow the solid line in Figure 11, like refraction. I will move on. Therefore, when these two light beams are transmitted asymmetrically through a parallel flat plate made of a transparent material, the interference pattern shifts laterally in proportion to the thickness of the flat plate. Therefore, as shown in FIG. 12, if a transparent material with different thicknesses depending on the region is used as a contact mask,
The interference pattern formed on the substrate undergoes a relative phase shift at locations where the mask thickness differs.

Next, in order to quantitatively define this shift amount, the following parameters were used. Let the incident angles of the left and right rays on the mask surface be θL and θ1, and the refraction angles be θ and ′ as shown in Figure 13.
, θ7, incident angle of light intensity peak.

The angle of refraction is θ. , θ. '. At this time, θ. −(θ, −
θl)/2 θ. '-(θ,'-θm')/2, and Snell's law holds between θ, θ,', θ1 and θ,'. After substituting the following parameters and designing the mask, synthetic quartz, which transmits ultraviolet light with a wavelength of 3,250 nm, was used as the material for the mask.

The shape of the mask is as shown in FIG. 12, but when actually manufacturing the mask, both sides of the step must be optical surfaces with high planar accuracy, and the step must be made steeply. However, it is difficult to create a thick step that satisfies these conditions using conventional methods such as lift-off and etching. Therefore, we developed a method as shown in Figure 14, which is based on laminating a quartz film on a quartz plate to a thickness of 2.14 m in area selective manner.Next, we will explain the procedure according to the diagram. .

(1) First, a parallel flat plate 31 of quartz whose both sides are optically polished.
Then, a striped first layer Al film 32 is applied using photoresist lift-off. This stripe is 3 wide
00n and a period of 600n with an interval of 300n (FIG. 14(a)).

(2) Sputter a 5iO1 film 33 on top of the 2.1
Stack 4 meters (Fig. 1(b)).

(3) Next, a photoresist 34 is applied on top of the photoresist 34, and when it is exposed to light from the back side, the self-alignment will cause the photoresist 34 to appear.
The photoresist 34 remains only in the area where the film is present (Fig.
)).

(4) A second layer of Al film 35 is attached on top of this, and lift-off is performed using the previously formed photoresist pattern, so that only the area where the first layer A1 film 32 is not formed is covered with the second layer Aff.
The i-film 35 is left (FIG. 4(d)).

(5) Use reactive ion etching (CF4+0□) to create the second layer of AII! Etch 5 ift of the portion without i to the surface of the first layer Al film. At this time, the Sing and quartz substrate in the lower part are protected by the He2 film,
It is not etched ((e) in the same figure).

(6) Remove the Al film by chemical etching.

A quartz mask 36 was produced according to the above process.

As a result of examining the level difference of this mask by stylus measurement, it was found to be 2.15-
This was in very good agreement with the design value of 2.14 m ((f) in the same figure).

When the step difference of the mask manufactured according to the above process was investigated by stylus measurement, it was 2.15 μm, which was in close agreement with the design value. A spatial position shift is obtained as shown by Φ. FIG. 4 shows an example of the use of the quartz mask 36 shown in FIG. 14. The illustrated interference pattern is transferred to the resist 62 on the substrate 51. However, when aligning the substrate 51 and the quartz mask 36, the resist 62 and the surface of the quartz mask 36 on which the step is formed are brought into close contact, and at this time, the resist may be scratched by the corner of the step of the quartz mask. The second embodiment of the present invention relates to a method of forming a phase shift mask that solves this problem, and is intended to prevent the mask from having a step.

As a means to solve this problem, the refractive index n
A material having a refractive index of n2 is embedded in a quartz substrate of No. 1 to obtain a phase shift of a diffraction grating pattern with a smooth surface. According to this method, the plane of the mask on the side in contact with the substrate is formed to be smooth, so that not only the resist on the surface of the substrate is not damaged, but also the adhesion between the substrate and the mask is improved.

FIG. 2 shows a cross-sectional view of the main parts of a phase shift mask according to a second embodiment of the present invention.

First, as shown in the same figure (a), the refractive index of the quartz (Sing) substrate 21 C51O with a refractive index n1 is 1.47.
5) Prepare. In a later step, an ^i film 22 is formed in a region 21a of the substrate 21 in which a material having a refractive index n2, for example, titanium dioxide (TiOz, a refractive index 2 to 2.5) is not embedded. The region 21b of the substrate 21 filled with TiO□ is the region 21a.
It's between. To obtain such a structure, A is applied to the entire surface of the quartz substrate.
4 is deposited to a thickness of 1000 nm, and the film is patterned so as to leave Af in the region 21a where Ti01 is not buried.

Next, as similarly shown in (b), when the Tie film 23 is deposited to a thickness of 3 pta over the entire surface, the Aj2 film 23 is deposited not only on the region 21b where TiO2 is buried, but also on the region 21a where TiO2 is not buried. A TiO□ film 23 is formed on the film 2.

Next, as shown in FIG. 2(C), an All film type 4 is formed by vapor deposition to a thickness of 2000 mm so as to be opposite to the pattern shown in FIG. 2(a).

Next, using the A2 film 24 as a mask, the Ti01 film 23 is etched by dry etching to form a step as shown in FIG. 4(d). In this step, r is applied only on the region 22b.
A structure in which the IoT film 23a remains is obtained.

Next, as shown in the same figure (e), A1. The film 22 and the Hel film 24 are peeled off, and the I film 2 is deposited only on the TiO2 film 23.
5 is formed by vapor deposition to a thickness of 1000 mm.

Next, as shown in the interlayer 6(f) of the SiO□ film 26, 3
When deposited to a thickness of n, SiO
A film 26a and an SiO□ film 26b are also formed on the substrate.

Subsequently, a ^2 film 27 is formed to a thickness of 2000 mm by vapor deposition in a pattern opposite to that of the A1 film 25 shown in FIG.

Next, by dry etching, a TiO□ film of 23 film type 3Si
The NG film 26a is x-etched, and the Sing film 26 on the substrate is
b remains ((h) in the same figure). Next, Aj2 membrane 2 membrane top 5! The film 27 is peeled off to form a photomask 20 shown in FIG. 2(i). Comparing this mask 20 with the conventional example shown in FIG. 4, the stepped portion formed in the quartz mask 36 of the conventional example was hollow, but in the second embodiment it is filled with a tie. , there are no steps, and the surface of the mask in contact with the resist is smooth.

In this second embodiment, in which the 300n wide gap in the conventional example shown in FIG. It has been confirmed that there is a shift in
A semiconductor laser with a 0n opening is obtained.

[Effects of the Invention] As described above, the present invention provides a transmitted light-diffraction light self-interference type mask with a smooth surface and a non-reflection film formed on both sides of the mask, and a phase shift type diffraction grating with a smooth surface. Masks are obtained, and these masks are in contact with the photoresist formed on the substrate without any steps, so the surface of the photoresist is not damaged, and these masks are effective in accurately forming a diffraction grating on the substrate.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the first embodiment of the present invention, Fig. 2 is a sectional view of the second embodiment of the invention, Fig. 3 is a diagram showing the use of the second embodiment of the invention, and Fig. 4 is the use of the conventional example. Figure 5 is a diagram showing the structure of a λ/4 shift) DFB laser, Figure 6 is a diagram showing a method of forming a diffraction grating, Figure 7 is a diagram showing a three-beam interference exposure method, and Figure 8 is a diagram showing a method of forming a diffraction grating. Figure 9 is a diagram showing the EB direct writing method, Figure 9 is a diagram showing the transmitted light-diffracted light self-interference method, Figure 10 is a diagram showing the positive/negative method, Figure 11 is a diagram showing the principle of phase shift, and Figure 12 is a diagram showing the principle of phase shift. 13 is a diagram showing the configuration of the phase mask, FIG. 13 is a diagram showing the definition of angles, and FIG. 14 is a sectional view of the mask manufacturing method. In the figure, 10 and 20 are photomasks, 11.21 is a quartz substrate, 12 is a resist grating pattern, 13.23.23a is a TiO2 film, 14.26.26a, 26b, 33 is a Si0g film, and 15 is an AR. Coat, 21a is a region of the substrate where TiO□ is not buried, 21b is a region of the substrate where TiO2 is buried, 22.24.25.27
．． 32.35 is A! 31 is a parallel plate, 34.62 is a resist (photoresist), 36 is a quartz mask, 42 is transmitted light, 43 is first-order transmitted diffraction light, 51 is an n-1nP substrate, and 64 is an interference pattern.

Claims (2)

[Claims] (1) Using a photomask in which a diffraction grating pattern made of a layer with a refractive index n2 and a layer with a refractive index n1 in which the diffraction grating pattern is embedded and flattened are provided on a substrate with a refractive index n1, A step of bringing the flattened surface of the photomask into contact with a photoresist on a semiconductor substrate, and then irradiating the laser beam to transfer an interference pattern between the transmitted light and the first-order transmitted diffraction light onto the photoresist. A method of manufacturing a semiconductor device, comprising: (2) On a substrate with a refractive index n1, a mask pattern formed of a layer with a refractive index n2 corresponding to the region where the phase shift is to be performed, and a layer with a refractive index n1 in which the mask pattern is embedded and flattened. Using the provided photomask, the planarized surface of the photomask is brought into contact with the photoresist on the semiconductor substrate, and then two laser beams are irradiated to form an interference pattern by the two laser beams. and a step of transferring an interference pattern whose phase has been shifted by a mask pattern of the photomask to the photoresist.