JP3179745B2 - Pattern making method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pattern forming method for forming an etching mask layer for forming a ridge-structured light control element having a projection on a substrate by digging a part of the thickness of the substrate. About.

[0002]

2. Description of the Related Art A part of a substrate is etched to form a ridge pattern, and a Mach-Zehnder-type Ti (titanium) heat diffusion LiN which enables wideband light modulation using the ridge pattern.
As a bO ₃ (lithium niobate) optical modulator, FIG.
(A) and a rate-matched optical modulator shown in FIG. 3 (b) (K. Noguchi, et al., “A Broadband Ti: LiNbO ₃ o
ptical modulator with a ridge structure, ”IEEE Jou
rnal of Lightwave Technology, Vol.LT-13, pp. 1164-11
68, 1995). FIG. 3A is a plan view, and FIG.
FIG. 3 is a sectional view taken along line AA of FIG. In the above conventional example, a Mach-Zehnder-type Ti heat diffusion optical waveguide 2 is formed on a z-axis cut LiNbO ₃ substrate 1 having an electro-optic effect by Ti heat diffusion. This is because a buffer layer 3 made of SiO ₂ is formed on a LiNbO ₃ substrate 1 (omitted in FIG. 3A), and a CPW electrode serving as a center conductor (center electrode) is formed on the buffer layer 3. 4, and a coplanar waveguide (CPW) type traveling wave electrode composed of a CPW electrode 5 which is an earth conductor (earth electrode). Reference numeral 6 denotes a terminating resistor connected between the CPW electrodes 4 and 5, and reference numeral 7 denotes a modulation microwave connected to the CPW electrodes 4 and 5 and supplies a microwave signal for modulation to the CPW electrodes 4 and 5. This is a wave signal feed line (feeding coaxial line). Further, the substrate portion of the region where the microwave electric field intensity is strong near the center conductor constituting the CPW electrode 4 and the ground conductor of the CPW electrode 5 is shown in FIG.
As shown in FIG. 1, a ridge (projection) structure is formed by digging by etching or the like. That is, the substrate portion in the region where the microwave electric field strength is strong is formed in a protruding shape by digging by etching or the like. Thus, the LiNbO having the protruding ridge portion 8 formed thereon is formed.
₍₃₎ On the surface of the substrate 1, a buffer layer 3 is provided. On this occasion,
Two Ti thermal diffusion optical waveguides 2 on the protruding ridge portion 8
One is disposed directly below the CPW electrode 4 as the center conductor with the buffer layer 3 interposed therebetween, and the other optical waveguide 2 is disposed directly below the CPW electrode 5 as the ground conductor. Ti thermal diffusion LiNbO shown in FIGS. 3 (a) and 3 (b)
₃ In the optical modulator, to some extent increase the thickness of the CPW electrodes 4 and 5, while reducing the value of the effective microwave refractive index n _m, characteristic impedance Z decreases concomitantly at that time
Is increased by making the digging depth of the ridge structure as deep as 3 μm to 4 μm, thereby achieving impedance matching with an external circuit. In particular, since the ridge structure is employed, the effective refractive index n _{m of the} microwave is also reduced. Therefore, the thickness of the CPW electrodes 4 and 5 required to realize perfect velocity matching between the microwave and light is reduced. However, it may be thinner than a case without dug-out. Therefore, a decrease in the characteristic impedance Z caused by increasing the thickness of the CPW electrodes 4 and 5 as the traveling wave electrodes can be suppressed to a small value, and the CPW electrodes 4 and 5 as the traveling wave electrodes can be suppressed.
And 5 can be easily manufactured, and further, an advantage such as an increase in microwave propagation loss can be suppressed. Ti thermal diffusion LiNbO shown in FIGS. 3 (a) and 3 (b)
_{The three-} light modulator is manufactured by a process shown in FIGS. 4A to 4F as an example. FIG. 4 shows a process of fabricating a conventional optical waveguide having a ridge structure by a cross-sectional state of a substrate. FIG. 4 (a) shows that LiNbO ₃ substrate 1 has
This shows a state in which the Ti thermal diffusion optical waveguide 2 is formed. to this,
A Ti film 9 having a thickness of about 1 μm is formed on the entire surface [FIG.
(B)] A resist pattern 10 having a groove formed in the dug portion is formed on the Ti film 9 by a normal photo process [FIG. 4 (c)]. Thereafter, the resist pattern 10 as a mask, the Ti film 9 on the LiNbO ₃ substrate 1, CF ₄
Etching by a plasma etching method using gas plasma 12 or the like and dissolving the photoresist,
A Ti pattern 11 having the same shape as the resist pattern is obtained (FIG. 4D). Using the Ti pattern 11 as a mask, the LiNbO ₃ substrate 1 is etched by an ion beam etching method using an argon and fluorine-based ion beam 13 (FIG. 4E), and the Ti film 9 is dissolved with hydrofluoric acid or the like. As a result, an optical waveguide having a ridge structure having a protruding ridge portion 8 having a height of several μm as shown in FIG.

[0003]

In the conventional method of manufacturing an optical waveguide having a ridge structure, a Ti thin film formed by a vapor deposition method is used as an etching mask. The Ti thin film has features such as high adhesion to various substrates, a low sputtering rate against argon ions, and relatively easy patterning by plasma etching using a fluorine-based gas. However, when the Ti thin film is patterned to a thickness of about 1 μm, irregularities at the edges of the Ti pattern become large. As a result, when the substrate is etched using the Ti pattern as an etching mask, irregularities (bumps) are transferred to the side walls of the ridge portion, and in the above-described example of the light control circuit, there is a problem that the propagation loss of the optical waveguide increases. The present inventors have conducted intensive studies in order to solve the above problems, and found that the unevenness of the edge of the Ti pattern is caused by the formation of Ti microcrystals in the thin film during the formation of the Ti thin film. Was found. The state is shown in FIGS.
It is shown in (c). 5 (a) and 5 (b) show a BB cross section of FIG. 5 (c) which is a plan view. Ti thin film
Generally, when a film is formed at a relatively low substrate temperature of about room temperature to about 200 ° C., an amorphous Ti film 9 is formed.
Microcrystalline region 1 with nuclei formed on the NbO ₃ substrate 1
4 are formed. When the Ti film 9 including the microcrystalline region 14 is patterned by etching using the photoresist pattern 10, the microcrystalline region 14 formed in the thin film has a higher etching rate than the Ti film 9 in the amorphous region. As a result, FIG. 5B and FIG.
(C) As shown in FIG.
A notch 15 of the pattern is formed. This microcrystalline region 1
No. 4 shows that crystals grow rapidly due to migration during the formation of the Ti film based on the initially formed crystal nuclei.
As the Ti film 9 is made thicker, the microcrystalline region 14 becomes larger,
And the number increases. As shown in the above example, when the Ti film 9 having a thickness of about 1 μm is formed, the microcrystalline region 14 reaches about several μm. Therefore, there is a problem in that the side etch of the Ti pattern becomes large, the unevenness of the ridge side wall becomes large, and the propagation loss of the optical waveguide increases.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art, suppress a side etch of a mask layer, realize a smooth ridge side wall, and produce an optical waveguide with low propagation loss. An object of the present invention is to provide a method for forming a pattern for forming an etching mask layer.

[0005]

Means for Solving the Problems In order to achieve the object of the present invention, the present invention is configured as described in the claims. That is, the present invention provides a pattern manufacturing method for forming a projection-shaped ridge pattern on a substrate by etching a part of the surface of the substrate as described in claim 1, wherein an etching mask layer is formed on the substrate. Is formed on the thin film layer made of a metal material, and the thin film layer made of the above metal material is repeatedly laminated one or more times on the thin film layer made of the metal material via an intermediate thin film layer made of an oxide material. And a step of forming an etching mask layer having a set pattern by etching the laminated thin film layer using a resist pattern. According to a second aspect of the present invention, there is provided a pattern manufacturing method according to the first aspect, wherein an optical waveguide is formed on a ridge pattern on a substrate. According to a third aspect of the present invention, in the first or second aspect, the step of forming the etching mask layer is a pattern forming method performed by a single etching process. In addition, the present invention provides, as described in claim 4, claims 1 to 3
In any one of the above, the substrate is lithium niobate,
The thin film layer made of silicon or gallium arsenide and made of a metal material is made of at least one selected from titanium, tantalum and nickel, and the thin film layer made of an oxide material is made of silicon oxide (such as SiO ₂ ). This is a method for producing a pattern comprising at least one selected from aluminum oxide (such as Al ₂ O ₃ ) and titanium oxide (such as TiO ₂ ).

According to a first aspect of the present invention, a thin film layer made of a metal material as an etching mask layer is formed on a substrate, and an oxidized film is formed on the thin film layer made of the metal material. An etching mask having a set pattern by repeatedly laminating a thin film layer made of the above metal material once or a plurality of times via an intermediate thin film layer made of a material material and etching the laminated thin film layer using a resist pattern. For example, a thin film layer made of a metal material (for example, a Ti thin film layer) is formed on a LiNbO ₃ substrate, and then an intermediate thin film made of an oxide material is formed on the LiNbO ₃ substrate. When a layer (for example, a SiO ₂ thin film layer) is formed thinly and the above-mentioned Ti thin film layer is formed thereon, the microcrystals formed in the Ti thin film layer are formed. Growth can be suppressed by the SiO ₂ film, which is the intermediate thin film layer, so that side etching of the Ti pattern can be suppressed. Therefore, the effect of producing an optical waveguide having a ridge structure with smooth side walls and low propagation loss can be produced. is there. Also, as described in claim 2,
For example, since a substrate in which an optical waveguide is provided on a ridge pattern forming portion on a LiNbO ₃ substrate is used, a high-performance optical waveguide having a smooth ridge side wall and a low propagation loss can be manufactured with a high yield above the optical waveguide. effective. Further, as described in claim 3, for example, the etching of the SiO ₂ intermediate thin film layer can be performed simultaneously with the etching of the laminated Ti thin film layer by using CF ₄ gas or the like.
An etching mask layer can be formed by one etching process, and there is an effect that the efficiency of pattern formation can be further improved. Further, as the substrate, silicon or gallium arsenide can be used as the substrate in addition to lithium niobate, and the thin film layer (mask material) made of a metal material is made of titanium in addition to titanium. ,
Tantalum or nickel can be used, and
The intermediate thin film layer made of an oxide material is made of silicon oxide (SiO 2).
_In addition to ₂ ), aluminum oxide (such as Al ₂ O ₃ ) and titanium oxide (such as TiO ₂ ) can be used, so that the use range of the etching mask layer can be further expanded.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 (a)-
(F) is a process drawing showing the procedure for manufacturing the light control element according to the present invention. In the figure, FIG. 1A shows LiNbO ₃
In this example, a Ti thermal diffusion optical waveguide 2 is formed on a substrate 1. A Ti film 9a having a thickness of about 500 nm, a SiO ₂ film 14 having a thickness of about 100 nm, and a Ti film 9b having a thickness of about 500 nm were sequentially formed thereon [FIG.
(B)]. Next, a photoresist pattern 10 having a trench at the dug portion is formed by a normal photo process to form a Ti film 9.
b (FIG. 1C). Then, LiNbO ₃
The SiO ₂ film 16 and the Ti films 9a and 9b on the substrate 1 are
Etching is performed by a plasma etching method using CF ₄ plasma 12 or the like, and the photoresist is dissolved and removed, so that the same Ti pattern as the photoresist pattern 10 is obtained.
Patterns 11a and 11b and SiO ₂ pattern 17
I got This is etched by an ion beam etching method using an argon and fluorine-based ion beam 13 (FIG. 1 (e)), and the Ti patterns 11a, 11b and the SiO ₂ pattern 17 are dissolved with hydrofluoric acid to obtain [ As shown in FIG. 1F, an optical waveguide having a ridge structure having a protruding ridge portion 8 was manufactured. FIG.
(A) to (c) show details of the ridge structure. Note that FIG.
(A), (b) shows the BB cross section of FIG. 2 (c) which is a plan view. In FIGS. 2A to 2C, LiNbO
_{3. On the} substrate 1, a first Ti film 9a, a SiO ₂ film 16, and a second Ti film 9b are formed.
9b, a microcrystalline region 18 is generated. The difference from the conventional procedure is that the growth of microcrystals in the Ti film 9b stops once at the interface of the SiO ₂ film 16 because the SiO ₂ film 16 is sandwiched in the middle. Therefore, the growth of the microcrystalline region 18 can be suppressed, and as shown in FIG. 2C, the chipped portion 19 of the Ti pattern is replaced with the chipped portion of the Ti pattern shown in FIG. 15, it is possible to manufacture an optical waveguide having a ridge structure with a smooth side wall and a low propagation loss.
Here, for example, when the electron beam evaporation method is used, the first T
Immediately after the formation of the i film 9a, the SiO ₂ film 16 and subsequently the second Ti film 9b can be formed in the same apparatus and in the same batch. The etching of the SiO ₂ film 16 can be performed simultaneously with the etching of the Ti films 9a and 9b by using the CF ₄ plasma 12 of CF ₄ (carbon tetrafluoride) gas, and the etching mask layer can be removed. It is possible to carry out simultaneously with hydrofluoric acid. Therefore, in the method for manufacturing a light control element of the present invention, the SiO ₂ film 1
Except for the addition of the forming process of No. 6, there is an advantage that a ridge pattern can be formed with the same apparatus and process as the conventional one. In the above embodiment, the z-axis cut Li
Although the NbO ₃ substrate was used, an x-axis cut LiNbO ₃ substrate may be used, or another substrate such as a Si substrate or a G substrate may be used.
An aAs substrate may be used. As the thin film layer made of a metal material of the etching mask layer, other metal films such as Ta and Ni in which microcrystals are easily generated may be used in addition to Ti. Further, as the intermediate thin film layer made of an oxide material, SiO ₂
Aluminum oxide (Al ₂ O)
₃ ) or a thin film of titanium oxide (TiO ₂ or the like). In the above-described embodiment, an example in which a Ti film with a thickness of about 500 nm is used as the thin film layer made of a metal material of the etching mask layer is described. Can be appropriately set based on the film thickness (for example, 1 μm) of 200 nm.
About 700 nm is preferable. When the film thickness is less than 200 nm, for example, when a mask layer having a thickness of about 1 μm is set, the number of laminations increases, and it takes a long time to form a film.
If the thickness exceeds 700 nm, microcrystalline regions are likely to grow and become large, and the number of microcrystalline regions is increased. Further, as an intermediate thin film layer made of an oxide material, a Si film having a thickness of about 100 nm is used.
Although an example in which an O ₂ film is used has been described, this can also be appropriately set based on the film thickness of the entire etching mask layer.
It is preferably about m to 200 nm. If the film thickness is less than 10 nm, defects are likely to occur in the thin film, so that the effect of suppressing the growth of the microcrystalline region is small. On the other hand, if it exceeds 200 nm, the etching resistance increases and it becomes difficult to perform patterning in one etching process.

[0008]

According to the method for producing a pattern of the present invention,
As described in the above, a thin film layer made of a metal material which is an etching mask layer is formed on the substrate, and the metal material is formed on the thin film layer made of the metal material via an intermediate thin film layer made of an oxide material. Or a plurality of thin film layers are repeatedly laminated, and the laminated thin film layer is etched using a resist pattern to form an etching mask layer having a set pattern. For example, LiNbO ₍₃ ) After forming a thin film layer made of a metal material (for example, a Ti thin film layer) on a substrate, an intermediate thin film layer made of an oxide material (for example, a SiO ₂ thin film layer) is formed thin on the thin film layer. When the above-mentioned Ti thin film layer is formed thereon again, the growth of microcrystals in this Ti thin film layer is caused by SiO ₂ which is the above-mentioned intermediate thin film layer.
Since it can be suppressed by the film, side etching of the Ti pattern can be suppressed, and there is an effect that an optical waveguide having a smooth ridge structure and low propagation loss can be manufactured. Further, since a substrate having an optical waveguide formed on a ridge pattern portion on a LiNbO ₃ substrate is used, for example, a high-performance optical waveguide having a smooth ridge side wall and low propagation loss is provided on the upper portion thereof. It can be manufactured with good yield. Further, as described in claim 3, for example, the etching of the SiO ₂ intermediate thin film layer is also performed by the stacked Ti ₂ layer.
Since the etching can be performed using CF ₄ gas or the like at the same time as the etching of the thin film layer, the formation of the etching mask layer is simplified, and the efficiency of pattern formation is improved. Claim 4
As described in above, silicon or gallium arsenide can be used as a substrate in addition to lithium niobate, and tantalum or nickel is used as a mask material (a thin film layer made of a metal material) in addition to titanium. Further, in addition to silicon oxide (such as SiO ₂ ), aluminum oxide (such as Al ₂ O ₃ ) or titanium oxide (such as TiO ₂ ) as an intermediate thin film layer (an intermediate layer made of an oxide material).
₂ ) can be used, so that the usable range of the etching mask layer can be further expanded.

[Brief description of the drawings]

FIG. 1 is a process chart showing a method for manufacturing a light control element having a ridge structure exemplified in the embodiment of the present invention.

FIG. 2 is a diagram showing details of a ridge structure exemplified in the embodiment of the present invention.

FIG. 3 is a schematic diagram showing a configuration of a conventional light control element having a ridge structure.

FIG. 4 is a process chart showing a method for manufacturing a conventional light control element having a ridge structure.

FIG. 5 is a diagram showing details of a conventional ridge structure.

[Explanation of symbols]

1 ... LiNbO ₃ substrate 2 ... Ti thermal diffusion optical waveguide 3 ... buffer layer 4 ... CPW electrode 5 ... CPW electrode 6 ... terminating resistor 7 ... feed line 8 ... ridge 9 ... Ti film 9a ... Ti film 9b ... Ti film 10 ... the photoresist pattern 11 ... Ti pattern 11a ... Ti pattern 11b ... Ti pattern 12 ... CF ₄ plasma 13 ... argon and fluorinated ion beam 14 ... chipped portion 16 ... SiO ₂ film of the microcrystalline regions 15 ... Ti pattern 17 ... SiO ₂ pattern 18: microcrystalline region 19: chipped portion of Ti pattern 20: etched portion

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 6/12-6/14 G02F 1/00-1/125 G02F 1/29-7/00

Claims (4)

(57) [Claims] 1. A method for forming a ridge pattern having a protruding shape on a substrate by etching a part of the surface of the substrate, comprising forming a thin film layer made of a metal material as an etching mask layer on the substrate. Forming a thin film layer of the metal material once or a plurality of times on the thin film layer of the metal material via an intermediate thin film layer of an oxide material; and A method for producing a pattern, comprising a step of forming an etching mask layer having a set pattern by etching using a resist pattern. 2. The method according to claim 1, wherein an optical waveguide is formed on a ridge pattern on the substrate. 3. The pattern manufacturing method according to claim 1, wherein the step of forming the etching mask layer is performed by a single etching process. 4. The thin film layer according to claim 1, wherein the substrate is made of lithium niobate, silicon or gallium arsenide, and the thin film layer made of a metal material is
The thin film layer made of an oxide material is made of at least one selected from titanium, tantalum, and nickel, and is made of at least one selected from silicon oxide, aluminum oxide, and titanium oxide. Pattern making method.