JP3140369B2 - Method of forming electrode pattern at deep groove bottom - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming an electrode pattern in a deep groove.

[0002]

2. Description of the Related Art FIG.

Conventionally, on the bottom surface 12 of a groove 11 having a depth of 20 μm or more, a multilayer metal film 1 for an electrode is located at a position substantially equal to or greater than the groove depth from a groove side wall 13.
The method of patterning 4 includes the following forming method.

In FIG. 1A, a groove 11 is formed on a substrate 21 made of silicon or quartz glass by anisotropic etching of silicon or dry etching of quartz glass. A resist 22 is applied to cover the entire groove 11. In (b), the negative or positive resist 22 is patterned by single exposure and development or by repeating exposure and development a plurality of times.
The pattern 23 formed here becomes the pattern of the electrode film. In (c), the electrode metal film 14 is formed using a sputtering device or a vapor deposition device. Here, reverse sputtering is performed before film formation, and at the same time, fine irregularities are formed on the surface of the resist 22 while cleaning the surface of the pattern 23. Further, a film is formed without heating the substrate. In (d), the substrate 21 is impregnated with a stripping solution, and the electrode metal film pattern 15 is patterned by a wet lift-off method. Alternatively, the electrode metal film pattern 15 is patterned by a lift-off method in a dry process by oxygen ashing.

[0005]

The electrode thus patterned on the optical de-hose is recognized as a marker for image processing, and is used for bonding a laser diode or a photodiode as an optical semiconductor element to a desired position. Used. For this reason, the electrode pattern must maintain a shape with the highest possible accuracy.

However, the above-described method has the following disadvantages, and it has been impossible to form a highly accurate electrode pattern.

For example, in the case where the depth of a deep groove formed by anisotropic etching of silicon is 30 μm and a positive resist is used, for example, if the entire groove is covered with a highly viscous positive resist, At the center, the thickness of the resist is about 10 μm, and it is difficult for the ultraviolet rays at the time of exposure to sufficiently reach the lower part of the resist. At a position where the end of the electrode is substantially equal to the side wall of the groove, the thickness of the resist is about 20.
Since the thickness is μm, this portion has a thicker resist film than the central portion, so that ultraviolet rays are harder to reach. In order to form a resist pattern at the bottom of the deep groove including such a portion, a method of forming a pattern by a single exposure and development, a method of forming a pattern by a plurality of exposures and developments, and a method of taking a long exposure time. There are two ways. In the first method, since the exposure time is long, the effect of light diffraction on the side surface of the deep groove appears on the positive resist surface. In addition, when post-baking is performed, the edge of the resist pattern becomes round because of a thick film, and the transfer accuracy of the pattern of the photomask decreases. This phenomenon becomes more conspicuous as the positive resist becomes thicker. If a resist pattern is formed by repeating the next two or three times of exposure and development, alignment of the next same pattern with the previously formed incomplete resist pattern will necessarily cause misalignment, and the effect will ultimately result. Since the shape of the desired resist pattern is changed, the pattern transfer accuracy is reduced. The greater the number of repetitions, the lower the transfer accuracy. As described above, in the portion where the thickness of the positive resist is large,
When the desired photomask pattern is transferred to the resist,
The accuracy of the resist pattern with respect to the photomask was usually poor.

Further, if the film is formed by the above method, a metal film is continuously formed on the resist and a portion where the resist is removed to form a pattern, so that the film is formed. There was also a problem that a residual film of the resist adhered to the edge of the metal film in some places. This causes an error in the position recognition at the time of image processing, and in order to remove the error, a step of further performing oxygen ashing and removing a residual film must be added.

[0009]

In order to solve the above-mentioned problems, an electrode pattern forming method at the bottom of a deep groove according to the present invention comprises a step of roughly patterning a metal film of a sacrificial layer to be finally etched away by a lift-off method. Forming a primary resist pattern on the patterned sacrificial layer; and forming a secondary resist pattern by applying a resist having a lower viscosity than the primary resist to the primary resist pattern portion (opening portion). Removing the patterned sacrificial layer, forming a multilayer electrode film by sputtering, and finally removing the primary and secondary composite resist patterns by lift-off to pattern the multilayer electrode film. The above steps including the step of performing the above steps can be performed sequentially.

Each step will be briefly described below.

It is easy to use an organic material such as a polyimide resin for the sacrificial layer to be finally removed by etching. However, since a deep groove portion having a depth of 20 μm or more exists on the wafer, when an organic material is applied so as to cover the deep groove portion, the film thickness becomes thicker near the groove side wall. Will differ depending on the position of. Therefore, when the sacrifice layer is patterned, the sacrifice layer becomes uneven in thickness depending on the position of the deep groove bottom, and a sacrifice layer pattern having unevenness is formed on the bottom of the deep groove.
Further, in the application by the spin coating method, a uniform and arbitrary film thickness cannot be obtained irrespective of a patterning place.
In order to solve this problem, a metal film is used for the sacrifice layer, and the sacrifice layer metal film is patterned by 10 μm or more on one side from a desired electrode pattern shape by the conventional lift-off method. At this time, the sacrificial layer is finally removed by etching, so that even if the patterning accuracy is low to some extent or the resist film remains, it does not affect the finally obtained electrode pattern.

Since a metal film is used for the sacrificial layer, when the underlying layer is a highly reflective film and the resist is susceptible to halation, a positive resist for a highly reflective substrate is used for the resist, or the sacrificial layer metal film is used. Is formed by sputtering, and an inorganic antireflection film having a thickness of 50 nm or less made of silicon or the like is further formed by sputtering.

The primary resist pattern is applied so as to cover all the deep grooves including the sacrificial layer pattern with a positive resist, and is repeatedly exposed and developed a plurality of times to form a pattern.
It is formed by providing an opening so as to cover the groove side wall. At this time, the sacrificial layer metal film previously formed in the primary resist pattern portion is exposed. At that time,
It is preferable that the primary resist is subjected to a heat resistance improving curing treatment.

After forming the primary resist pattern, a secondary resist pattern is formed by applying a positive resist of the same type as the primary resist having a lower viscosity than the primary resist or for a highly reflective substrate on the substrate, It is formed by exposure and development.
At this time, spin coating is applied so as to be less susceptible to light diffraction and to be equal to or less than the thickness of the primary resist, thereby improving pattern transfer accuracy. Here, the shape of the secondary resist pattern becomes the shape of the electrode pattern. It is preferable that the secondary resist pattern is also subjected to the same heat-resistance improving curing treatment as the primary resist pattern.

Next, the metal film of the sacrificial layer is removed by wet etching. After the metal film is removed by etching, the substrate is put into a sputtering apparatus and subjected to reverse sputtering with argon ions to clean the surface of the open substrate so that the shapes of the first and second composite resist patterns do not collapse. Thereafter, a multilayer metal film for an electrode is formed in a desired thickness. Finally, lift-off is performed by a wet lift-off method of a stripping solution or the like or a dry lift-off method by oxygen plasma ashing or the like to form a desired electrode pattern.

As described above, when the electrode pattern is formed at a position substantially equal to or greater than the depth of the groove from the side wall of the groove at the bottom of the deep groove having a depth of 20 μm or more, the viscous Low secondary resist is applied to be less than the thickness of the primary resist,
Since the desired electrode pattern is transferred to the secondary resist, the pattern can be transferred with higher precision than the pattern is transferred to the primary resist even at the bottom of the deep groove having a high step.

Since a metal film formed by sputtering is used for the sacrifice layer, the thickness of the metal film is the same at any portion in the bottom of the deep groove when forming the electrode pattern at the above position. The height of the eaves of the composite resist obtained when removed by etching does not vary greatly. Furthermore, when the multilayer metal film for an electrode is formed by sputtering, the wraparound of metal atoms is the same in any part, so that the final electrode pattern can be formed with high precision and can be controlled.

Since the eaves of the composite resist using the primary resist and the secondary resist are formed using the sacrificial layer made of the metal film, an eave of an arbitrary shape can be formed, and the metal film for the electrode is formed on the resist and on the pattern. Thus, the film can be discontinuously formed. Therefore, the residual film of the resist does not adhere to the edge of the metal film. In addition, since the resist pattern has an eaves shape and has a step, the stripping solution easily permeates into the resist, or the resist is easily ashed by oxygen ashing, so that lift-off can be reliably performed. Further, since the primary resist covers the step portion of the deep groove, the multilayer metal film for an electrode does not adhere to an unexpected place.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a sectional view of a deep groove portion in each step of the present invention. Here, the shape of the opening of the deep groove is rectangular, the opening diameter is 1870 × 900 μm, and the depth is 30 μm. Ti with a minimum pattern width of 90 μm: 150 nm at a distance of 50 μm to 360 μm from the groove side wall
/ Pt: 300 nm / Au: 300 nm in case of patterning a metal film for a three-layer electrode. (A), the substrate 2
1 is a novolak positive resist (OFPR800-800c)
p: manufactured by Tokyo Ohka Kogyo Co., Ltd.) at 500 rpm for 5 seconds and 2000 rpm
Apply by spin coating for 40 seconds, 50
Pre-baking for 1 minute, and then irradiating with a 15.5 mW / cm ² ultraviolet ray for 30 seconds through a photomask in which a pattern larger by 10 μm on one side than the desired electrode pattern width is applied, and then tetramethylammonium hydroxide. After developing with a 38 w% aqueous solution (NMD-3 2.38%: manufactured by Tokyo Ohka Kogyo Co., Ltd.) for 60 seconds, rinsing with pure water for 60 seconds, further exposing the same position for the same time, and repeating development and rinsing for the same time, resist After forming the pattern, post-baking is performed at 120 ° C. for 80 minutes to obtain a sacrificial layer patterning resist 31. Here, the material of the substrate 21 is silicon alone, glass alone, or a film formed of glass on silicon. (B)
Then, the substrate 21 is put into a planar magnetron type sputtering apparatus, and the degree of vacuum is adjusted to 3.0 × 10 to ³ Pa or less. Then, argon gas is introduced into the chamber to adjust the pressure to 0.65 Pa.
After reverse sputtering (etching) the substrate 21 with argon ions at an RF voltage of 200 W for 10 minutes, A
1 shows that the sacrificial layer 32 was formed by sputtering 0.8 μm. In (c), the substrate 21 was ultrasonically cleaned twice with acetone for 10 minutes, and then dipped in a 90 ° C. positive photoresist stripping solution (stripping solution-104: manufactured by Tokyo Ohka Kogyo Co., Ltd.) for 20 minutes. This shows that the sacrifice layer 32 is obtained by washing with running pure water for 10 minutes or more and spin-drying. In (d), the substrate 21 is baked at 200 ° C. for 30 minutes using a hot air circulating drier, and then subjected to HMDS treatment on the substrate 21 including the sacrificial layer 32.
A second resist is applied by spin coating at 2000 rpm for 40 seconds, and prebaked at 80 ° C. for 50 minutes to obtain a primary resist 33 having a film thickness of about 10 μm at the center of the deep groove. In (e), the applied primary resist 33 is irradiated with an ultraviolet ray of 15.5 mW / cm ² for 30 seconds through a photomask, developed with an NMD-3 developer for 60 seconds, and rinsed with pure water for 60 seconds. Further, these operations are repeated once, and post-baking is performed at 120 ° C. for 80 minutes to obtain a first resist pattern 34. Here, the relationship between the opening of the primary resist pattern and the pattern width of the sacrificial layer metal film is located in a region satisfying AB ≧ 30 μm and BC ≧ 10 μm, and a photomask pattern is designed so as to satisfy this specification. I have. (F), on the substrate 21 on which the primary resist pattern 34 is formed, a novolak-based positive photoresist (OFPR800-100) having a viscosity of less than 800 cp.
cp: Tokyo Ohka Kogyo Co., Ltd.) at 500 rpm for 5 seconds and 2000 rpm
This shows that a second resist 35 having a film thickness of about 4 μm was obtained by applying by spin coating for 18 seconds and then pre-baking at 80 ° C. for 50 minutes. (G), after irradiating with a 15.5 mW / cm ² ultraviolet ray through a photomask for 15 seconds, developing with an NMD-3 developer for 60 seconds, rinsing with pure water for 60 seconds, and repeating the same operation at 120 ° C. At 50
A second resist pattern 36 is obtained by performing post-baking for 60 minutes or baking at 60 ° C. while irradiating ultraviolet rays in a vacuum. (H), the sacrificial layer 32 is removed by etching with an etchant for Al in which 75% of phosphoric acid, 15% of glacial acetic acid, 5% of nitric acid and 5% of water are mixed, washed with running pure water, and then spin-dried. The eaves of a positive resist having a composite structure in which the secondary resist 33 and the secondary resist 35 are combined are shown. In (i), the substrate 21 is put into the sputtering apparatus described above, and the pressure is reduced to 3.0 × 10 to ³ Pa or less. Then, an argon gas is introduced into the chamber, and the pressure is reduced to 0.65 Pa. Then, an RF voltage of 200 is applied to the substrate 21 with argon gas so that the shape of the eaves does not collapse.
After reverse sputtering (etching) with W for 1 minute, the metal film for electrode 37 (Ti: 150 nm, P
(t: 300 nm, Au: 300 nm) are shown in this order. The thickness of the three-layer electrode film is 0.75 μm. In (j), the substrate 21 was subjected to ultrasonic cleaning twice with acetone for 15 minutes, and then added to a negative and positive photoresist stripping solution (stripping solution -502A: Tokyo Ohka Kogyo Co., Ltd.) at 100 ° C. for 20 minutes. After dipping for 1 minute, dip with strip rinse-4 (manufactured by Tokyo Ohka Kogyo Co., Ltd.), soak in isopropyl alcohol and methyl alcohol, and add 10
This shows that the desired metal film for electrode 38 has been patterned on the bottom of the groove of the substrate 21 by washing with running water for minutes.

As described above, since the thickness of the secondary resist 36 is smaller than the thickness of the primary resist 33, the pattern transfer accuracy of the photomask is higher than that of direct patterning on the primary resist 33. The pattern accuracy of the film pattern 38 naturally increases. In addition, since the formed resist pattern has a step (eave) having the same height as the thickness of the sacrificial layer 32, the electrode metal film 37 is formed discontinuously even by sputtering in which metal particles are greatly wrapped around. It is possible to prevent the resist from adhering to the end of the film 37. If the thickness of the sacrificial layer 32 is equal to or greater than the thickness of the electrode metal film 37, the electrode metal film 37 can be reliably formed discontinuously.

[0022]

According to the present invention, when patterning a multi-layer electrode film at a position at a distance from a groove side wall at a depth substantially equal to or greater than the groove depth at a deep groove bottom having a depth of 20 μm or more, It is possible to form an electrode pattern with high precision and high adhesion without the remaining film of the resist adhering to the edge of the film.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a conventional process of patterning an electrode film on the bottom of a deep groove.

FIG. 2 is an explanatory view showing an electrode film patterning process at the bottom of a deep groove according to the present invention.

[Explanation of symbols]

21 ... substrate, 31 ... sacrificial layer patterning resist, 3
Reference numeral 2: sacrificial layer, 33: primary resist, 34: primary resist pattern, 35: secondary resist, 36: secondary resist pattern, 37: metal film for electrode, 38: metal film pattern for electrode.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/28-21/288 H01L 21/44-21/445 H01L 29/40-29/43 H01L 29 / 47 H01L 29/872

Claims (1)

(57) [Claims] 1. A method of patterning a metal film for an electrode pattern on a bottom surface of a groove having a depth of 20 μm or more at a position equal to or greater than the depth of the groove from a side wall of the groove, the method comprising: Patterning the metal film by a lift-off method, and forming a primary resist so as to cover the patterned metal film and the groove.
And patterning the primary resist to form the gold
A step of overall Shokumaku to form an opening so as to expose the front
A step of applying a secondary resist again on the region including the opening and patterning the secondary resist so that a part of the metal film is exposed ; and removing the metal film by wet etching. Forming a composite resist pattern;
Forming a metal film for an electrode on the entire surface of the wafer including the resist pattern; and obtaining a desired shape of the metal film for an electrode by a lift-off method. .