JPS6086543A - Formation of micropattern - Google Patents

Abstract

PURPOSE:To enable formation of a micropattern of a superconductive device through a lift-off method using a pattern by forming a photoresist film having phenolic OH groups high in UV absorption in only one time on a substrate, and developing it in only one time to form a pattern. CONSTITUTION:An SiO film is vapor-deposited on a silicon wafer substrate 21 in vacuum, and after deposition of an aluminum plate on this film, a photoresist film 25 having phenolic OH groups, such as p-hydroxystyrene. The film 25 contains a equimolar condensate of 3-(azidostyryl)-5,5'-dimethyl-2-cyclohexen-1-one or the like aromatic azido compd. having an aldehyde group, and isophorone. The desired parts of this film 25 are exposed to UV light of 300-450nm wavelengths to render the exposed parts hardly soluble, and the unexposed parts are eluted with an alkaline soln. to form a pattern having an inverted trapezoid section. A superconductive thin film 24 is vapor-deposited by using this pattern as mask, and the remaining film 25 and the film 24 overlying thereon are removed by the lift-off method. As a result, a micropattern film 24 can be obtained with high- precision size.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method of forming a fine pattern, and more particularly, to a method of forming a fine pattern with high precision using a lift-off method, which is much easier than conventional methods.

[Background of the invention]

Elements formed by the lift-off method include superconducting devices, GaAs F h T% S t L F3
I. There are electrodes and wiring patterns of magnetic bubble memory.

For example, switching elements using superconducting devices have two orders of magnitude better switching time and power consumption than 81 semiconductor elements, and are expected to be used as high-speed logic and memory elements.

The pattern of this superconducting device is formed by lift-off. The formation conditions for this process are at a temperature of 70C or lower to prevent deterioration of the characteristics of the superconducting device.

Furthermore, as a lift-off mask for patterning a superconducting device, a two-layer resist stencil mask, an At stencil mask, a chlorobenzene immersion resist stencil mask, etc. have been conventionally used.

FIGS. 1(a) to (e) show an example of a lift-off process using a K double-layer resist stencil mask.

First, as shown in FIG. 1(a), Ml and a second photoresist having different solubility in a developer are placed on the surface of a substrate 11 on which a desired pattern is to be formed.
ft: Formed in a laminated manner. 70r.

After pre-baking for 30 minutes, apply the second layer through a photomask.
The second photoresist film 13 is selectively exposed to light, and a desired portion of the second photoresist film 13 is removed as shown in FIG. 1(b). Since the developer used at this time does not dissolve the first photoresist film, only desired portions of the second photoresist film are selectively removed. Next, the exposed portion of the first photoresist Jlif12 is removed using a developer capable of developing only the first photoresist. At this time, over-development is performed to cause side etching, and the first
As shown in Figure (C), an eave is formed using a second photoresist film 13.

Next, the material on which the pattern is to be formed, for example, the superconducting film 1
4 is deposited on the entire surface by a vacuum deposition method or the like.

However, since the eaves of the second photoresist film 13 are formed, the deposited superconducting film 1 does not reach the back side of the eaves, and as a result, as shown in FIG. 1(d), The deposited superconducting film 14 does not form a continuous film, but is separately deposited on the back plate 11 and the second photoresist film I113. Next, only the second photoresist film 13 and the superconducting film 14 on which the first photoresist film 12 is deposited remain, and a superconducting film pattern is obtained.

The lift-off method has the advantage of being able to form patterns with high precision, but it is not practical because it requires two types of photoresist films to be laminated and crushed, and then developed 't-2 times, as shown in fl+E above. Above all, it is extremely complicated.
A convenient method is strongly required.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and provide a method for forming a fine pattern that has good pattern/consistency and can be formed extremely easily.

Another object of the present invention is to provide a lift-off method that is extremely easy to operate, using only one type of photoresist film and requiring only one development.

[A essential point of the invention]

The structure of the present invention for achieving the above object is to form a photoresist pattern having an inverted trapezoidal cross-sectional shape by irradiating and developing a photoresist film that has extremely high absorption of ultraviolet light (wavelength: 300 to 450 ftm). , which is used to perform lift-off.

The present invention will be explained in detail below.

As described above, the conventional lift-off method consists of two types of photoresists having different solubility in the existing solution, or two layers of At and photoresist. So-called At stencil,
Complicated steps were required, such as using a resist stencil mask using a chlorobenzene dipping method and performing development or dissolution twice. This is to form the eaves so that the metal film to be left and the metal film to be removed can be separated and formed without being continuous. Therefore, as shown in Figure 2,
If it is possible to form a photoresist pattern 25 having an inverted trapezoidal cross-sectional shape where the upper side is larger than the lower side, the metal film 24 will not be continuous but will be formed separately, and the photoresist 1liJ25 will be separated from the metal film 24 above it. By removing the metal film 24 at the same time, the metal film 24 can be left only on the substrate 21, and a fine pattern made of the metal film 24 is formed.

Conventionally, it was not possible to form a photoresist pattern with an inverted trapezoidal cross-sectional shape as described above, so two types of films with different solubility were used to form the eaves.

The present invention is a polymer IC6 having a phenolic hydroxyl group.
By using a photoresist formed by adding various types of aromatic azide compounds as negative mV cysts, it is not necessary to use two types of photoresists, and a photoresist with an inverted trapezoidal cross-sectional shape can be created by simply adding different kinds of aromatic azide compounds. This is to form a pattern (hereinafter referred to as a lift-off mask).

In other words, when UV light is irradiated on a photoresist prepared by adding an aromatic azide compound to a polymeric compound having phenolic hydroxyl groups, such as a polymer or copolymer of hydroxystyrene, a photochemical reaction occurs and the solubility of the irradiated area decreases. The photoresist exhibits characteristics as a negative type resist.

However, since the above-mentioned photoresist absorbs ultraviolet light extremely well, the attenuation of the irradiated light in the thickness direction is extremely large.As a result, only the surface layer is completely insolubilized, and the degree of insolubilization increases as the depth increases. The smaller the size, the greater the solubility.

If development is carried out in this state, the surface layer of the irradiated area will not dissolve because it has been completely insolubilized, but as mentioned above, the solubility gradually increases as it goes to the lower layer, so the development process will be delayed. As the process progresses, the unreacted portion beneath the irradiated area is gradually removed, as shown in Figure 2.
A lift-off mask 25 having an inverted trapezoidal cross-sectional shape is formed. The cross-sectional shape of the photoresist, that is, the length of the lower side of the photoresist mask, is controlled by the development process.
It can be any desired value. If the concentration of the developer is increased, the etch of the lower layer will increase and the length of the bottom side will become smaller.If the concentration of the developer is kept constant, the longer the development time, the longer the development time will be.
The length of the lower side becomes shorter.

The photoresist used in the present invention contains phenolic hydroxyl groups, has extremely high absorption of ultraviolet light with a wavelength of 400 to 450 nm, and can be easily developed with an alkaline aqueous developer to form a sharp fine pattern. It is necessary to satisfy the following two conditions.

As a photoresist that satisfies these conditions, a polymer having a phenolic hydroxyl group is used as a photosensitive composition, an aromatic azide compound having an aldehyde group, an azide compound which is an equimolar condensate with inophorone, and an alkali-soluble azide compound. It is characterized by containing a polymer compound. The amount of the azide compound, which is a condensate, is preferably 10 to 30% by weight based on the polymer compound component. As the aromatic azide compound forming the condensate, azidobenzaldehyde and azidobenzaldehyde are used.

The condensates obtained as these compounds include 3-(
4'-acidostyryl)-5,5-dimethyl-2-cyclohexen-1-one and 3-(4-p-azidophenyl-1,3-butadienyl)-5,5-cinnamethyl-2
-Contains at least one condensate from the group consisting of cyclohexen-1-one. The polymer component preferably has a phenolic hydroxyl group, such as a hydroxystyrene polymer or copolymer.

As the developer, for example, a sodium silicate aqueous solution,
Tetramethylammonium hydroxide, trisodium phosphate aqueous solution, sodium hydroxide aqueous solution, etc. are used.

It goes without saying that the temperature and development time of these developers vary significantly depending on many factors such as the type of developer used, the type and film thickness of the photoresist, but The time is about 10 to 600 seconds, and the concentration is about 0.1 to 10% by weight.

The film thickness of the photoresist varies depending on the type of photoresist used and the purpose, but it is selected in the range of about 0.5 to 3 μm for #1.

The amount of exposure to these photoresists is appropriately selected depending on the type of photoresist and the cross-sectional shape of the photoresist to be formed. Generally, the exposure amount is about 5 to 100
The exposure time was selected from the range of mJ/cIn2.
~60 seconds.

Examples will be described in detail below.

[Embodiments of the invention]

Example: Polymer component p-hydroxysterene homopolymer, (Maruzen M manufactured by Maruzen Oil Co., Ltd.) resin 20g and 3-(4-p-7)'phenyl-1,3-butadienyl)-5,5-dumeru A photoresist solution was prepared by dissolving 4 g of 2-cyclohexen-1-one and 80 g of t-cyclohexanone and 1 c.

Si was deposited on a silicon wafer substrate by vacuum evaporation.

A total film thickness of 2QQnm was deposited, and on top of this a 5m thick film of A4 was deposited as a coupling material. After this, a photoresist solution was spin-coated to a thickness of 1 μm, and a prebaking process was performed at 70C for 30 minutes. After that, a high-pressure mercury lamp with an output of 300 W was used as a light source, and the wavelength was 436 nm (g-eye).
A desired pattern was exposed for 15 seconds at a light intensity of 7 mW/cm''.The exposed photoresist film was developed for 90 seconds with a 4% aqueous solution of tetramethylammonium hydroxide.As a result, the lengths of the top and bottom sides were However, photoresist patterns with a cross section of approximately 5 μm and 3 μm and an inverted trapezoid were obtained.Using this as a lift-off mask, a 0.3 μm thick superconducting film was deposited by vacuum evaporation.
After being deposited as shown in Figure 2, the lift-off mask was removed together with the superconducting film deposited on it by evaporation in acetone, resulting in a striped superconducting film pattern with a line width of 2 μm. was formed with good accuracy. Also, lift-off could be handled very easily.

Example 2 Using a photoresist with the same composition as in Example 1, the line width was 2.5.
We patterned a superconducting logic device consisting of micrometer control lines.

FIG. 3 shows its cross-sectional view.

The substrate has a diameter of 50 mmφ and a thickness of 350 μm.

A (100) Si substrate 31 was used. Note that a thermal oxide film of 50 Qnm was formed on the Si substrate.

A 300 nm thick Nb film was deposited on this Si substrate 31 by DC high speed sputtering to form a ground plane 32.

Next, NbzOs 33 was formed to a thickness of 150 nm on the surface of the Nb by anodization, and then 55 nm was formed as an interlayer insulating film.
IOA4 was deposited to a thickness of 200 nm, and after one layer, At as a coupling phase was deposited to a thickness of 5 nm. Next, the bottom t
The manufacturing conditions of a lift-on mask for forming a li4M pattern will be described.

A photoresist having the same composition as in Example 1 was applied on the base layer 34 at a thickness of 1 μm.
m thickness, and then heated at 70G and 30cm in air.
A pre-bake process was performed for 1 minute. Next, the wavelength is 436 nm.
(g-1ine), and a desired pattern was exposed for 15 seconds at a light intensity of 7 mW//m2. Development after exposure was carried out for 90 seconds using a 4% aqueous solution of tetramethylammonium hydroxide. The undercut width of the formed resist lift-off mask (the amount of penetration of the pattern on the lower side with respect to the pattern edge on the upper side was 1 μm. Next, the SI substrate 31 on which the lift-off mask was formed was inserted into a vacuum chamber and 5iOs4
v:, Ar to remove moisture and dirt adsorbed on the surface of
I did some spack cleaning.

The conditions at this time are rf output 5W% Ar pressure 3Xi Q-"
porr, sputtering time is 3 minutes. Next, after reducing the degree of vacuum in the vacuum chamber to 5×10 −' TorrK, DAul Pb and In were deposited in this order using a resistance heater. The thickness of each film is 4 nm.

160 nm and 36 nm. After the vapor deposition, in order to form a surface protective film, 02 scum was introduced into the vacuum chamber and the pressure was raised to 1 atmosphere, and then the temperature inside the vacuum chamber was maintained at 60 C and oxidation treatment was performed for 60 minutes. Next, the substrate 31 was taken out of the vacuum chamber and lifted off in acetone. As a result of this treatment, only the lower electrode 35 on which the purulent-retaining film was formed was left, and the lift-off mask and the vapor deposited film deposited thereon were completely removed. Next, a resist mask for the window hole 37 is formed in the same manner as the lower electrode pattern, and Ar sputter cleaning is performed again in the vacuum chamber.
At a thickness of 250 nm/11 times, At was continuously deposited to a thickness of 5 nm. Lift-off was performed in the same manner as for the lower electrode described above to form window holes 37. Next, a lift-off mask for the upper electrode was formed in the same manner as for the lower electrode, and sputter cleaning was performed on the lower t[pole 35 surface with 02 residue in a vacuum chamber. Conditions are the same as for the base electrode. Subsequently, 0 to form a tunnel barrier.
2 gases were introduced, 0□ gas pressure 2X10-2 Torr,
The tunnel barrier layer 36 was formed using an rf output of 5 W and an rf oxidation time of 15 minutes. Next, after reducing the pressure in the vacuum chamber to a degree of vacuum of 5×1 (V7 Torr), Pb-AU-Pbt were simultaneously vapor-deposited using a resistance heater to give film thicknesses of 200 nm and 1Q nm, respectively.

200 nm deposited, followed by continuous SiO on top of the layer.
A film thickness of 1100 r1 was deposited as a protective film.

The lift-off process was performed in the same manner as for the lower electrode described above to form the upper electrode 38 and the protective film 5iO39. Next, a lift-off mask for the interlayer insulating film was formed in the same manner as the lower electrode pattern, and after sputter cleaning with Ar again, S10 was deposited to a thickness of 600 nm, and At was continuously deposited to a thickness of 5 nm. It was covered. The lift-off was formed in the same manner as the lower electrode described above, and the glabellar insulating film 40 was formed.

Next, a lift-off mask for the control line was set to a film thickness of 1.5 μmK, and after coating, it was heated at 70C in air.

Prebaking was performed for 30 minutes. Next, the minimum line width is 2.5
A control line pattern consisting of a line conductor with a wavelength of 43 μm is
Light intensity at 5 nm 7 m W/cm” T2
Exposure was performed for 5 seconds. The development process after exposure was carried out for 120 seconds using the same composition as for forming the lift-off mask of the lower electrode. The undercut width of the formed lift-off mask was such that the amount of penetration of the edge on the bottom side was 0.5 μm with respect to the gill/edge on the top side. Insert it into the vacuum chamber again, and after sputter cleaning with Ar, 5 x 10
-'l'orr or less, Pb and ALII In were deposited in this order.

The film thickness is 540J1m% 1 (1111% 25
It is 0 nm. After the deposition, it was taken out from the Makabe tank and lifted off in acetone in the same manner as the lower and upper electrodes described above to form a control line 41. Finally, SiO was deposited as a protective film to a thickness of 1.3 μm and formed by a lift-off method.

〔Effect of the invention〕

As described above in this example, as a result of forming a superconducting logic device by using the photoresist according to the present invention as a lift-off mask, the minimum pattern size was 2.5 μm.
A superconducting electrode pattern with extremely high dimensional accuracy was obtained with good reproducibility, with almost no fine lines observed even on steps in the control line pattern consisting of line bears of m.

Furthermore, if the photoresist pattern of the present invention is used as a mask for lift-off, it becomes possible to fabricate a lie/bare with a minimum pattern size of 1 μm, making it possible to stably form a fine pattern in a low-temperature process. Furthermore, the photoresist of the present invention is not affected by the substrate (pattern configurations with different reflectances), can form fine patterns as described above, and has extremely good adhesion to the substrate even under 70C Gribake treatment. became clear. Furthermore, since soda lime glass can be used for the photomask substrate, the cost of making a mask has been reduced. Furthermore, the process of the present invention can be applied to a 10:1 reduction projection exposure apparatus (a
PA), 5:1 reduction projection exposure apparatus (R,PA),
As a result of applying the method to a 1:1 projection exposure apparatus (PA), it was possible to form a fine pattern with high dimensional accuracy and no narrow holes even on steps, as described above.

[Brief explanation of drawings]

FIGS. 1(a) to (e) are cross-sectional views showing the steps of the conventional lift-off method, FIG. 2 is a cross-sectional view for explaining the present invention in detail, and FIG. 3 is a superconductor in one embodiment of the present invention. A cross-sectional view of the device is shown. 11.21...Substrate, 12,13,25...Photoresist film, 14.24...Superconducting film, 31...Substrate (including Si wafer and thermal oxide film), 32...Nb ground Brane, 33...NbzOs film, 34...
・Interlayer insulating film, 35...lower electrode (A u-P b-
I n ), 36... Tunnel barrier layer, 37 River window hole sio film, 38-... Upper electrode (Pb-AU-P
b), 39...peritoneal membrane (for upper electrode), 4o... interlayer insulating film sio. 41...Control line (Pb-Au-Pb), 4
2-...Protective light 1 Entrance Z Continuation of figure 1 page [Phase] Inventor 1) Minoru Naka Kokubunji City Higashikoigakubo 1 Central Research Institute Uchi-28 Hata Hitachi, Ltd. Naka-chome 28 Hata Hitachi, Ltd. Inside the factory

Claims (1)

[Claims] 111) A step of forming a photoresist film having phenolic hydroxyl groups on the surface of the substrate on which fine heternes are to be formed;
(3) developing the photoresist film to remove the non-irradiated areas to form a photoresist pattern having an inverted trapezoidal cross-sectional shape; , (4) a step of depositing a vapor deposited film of the material on which a fine pattern is to be formed, (57) a step of removing the photoresist pattern along with a film of the material deposited thereon; Method. 2. The photosensitive component of the photoresist is characterized in that it contains an azide compound that is an equimolar condensate of an aromatic azide compound having an aldehyde group and inholon, and an alkali-soluble polymer compound, and the condensate is a 3- (azidostyryl)-5゜5-dimethyl-2-cyclohexeno-1-
at least one condensed 3-one selected from the group consisting of A method for forming a fine pattern, characterized in that the amount of the azide compound, which is a photosensitive component, is 104 with respect to the phenolic hydroxyl group, which is a polymer compound, and the privet is a superconducting thin film at 60 to 80 C in the above step (υ).