JP2002323775A - Pattern forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide form resist patterns finer than optical resolution dimensions by using the resist material thus far and exposure means relating to a pattern forming method. SOLUTION: Two layered resist layers consisting of a lower resist layer 2 which is relatively higher in an etching rate with respect to a developer and an upper resist layer 3 which is relatively smaller in an etching rate are exposed to form the resist patterns 1 of an undercut shape and thereafter the resist patterns 1 are subjected to slimming of their widths.

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 example, a track of a giant magnetoresistive film (GMR film) used for a reproducing head (read head) of a magnetic recording device such as a hard disk drive (HDD). The present invention relates to a resist pattern structure for forming a width finer than an optical resolution dimension and a pattern forming method characterized by a method of forming a resist pattern.

[0002]

2. Description of the Related Art Conventionally, as a demand for higher density and higher speed of a hard disk device or the like as an external storage device of a computer has increased, a magnetic sensor for sensing a magnetic field itself has become mainstream as a reproducing magnetic head. Conventionally, as such a magnetic sensor, a sensor utilizing the magnetoresistance (MR) effect has been employed, but now a sensor utilizing the giant magnetoresistance (GMR) effect has been employed.

The reproducing principle of the MR head or GMR head is based on a phenomenon that when a constant sense current is passed from a lead electrode, the electric resistance of a magnetic thin film constituting a magnetoresistive element changes due to a magnetic field from a recording medium. To use.

[0004] With the recent increase in the recording density of hard disk drives, the recording area of one bit has been reduced, and the generated magnetic field has become smaller. The recording density of currently available hard disk drives is 10 Gbit.
/ In ² (≒ 1.55 Gbit / cm ² ), but the increase in recording density is increasing at twice the annual rate. Therefore, it is necessary to cope with a smaller magnetic field range and to be able to sense a small change in the external magnetic field.

As described above, as a magnetic sensor utilizing the giant magnetoresistance effect, a magnetic sensor using a spin valve element is widely used at present. The sensor will be described with reference to FIG. FIG. 7A is a schematic cross-sectional view of a conventional reproducing magnetic sensor, and FIG.
It is a schematic enlarged view in the circle shown by the broken line in FIG. 7 (a).

Referring to FIGS. 7 (a) and 7 (b), NiF is first placed on an Al ₂ O ₃ —TiC substrate 41 serving as a base of a slider via an underlayer 42 such as an Al ₂ O ₃ film.
e-alloy and other lower magnetic shield layer 43 and Al ₂ O
A lower read gap layer 44 such as ₃ is provided, and a spin valve film 45 is deposited on the lower read gap layer 44. Incidentally, the spin valve film 45 in this case is, for example,
A NiFe free layer 47 provided via a Ta underlayer 46,
It comprises a CoFe free layer 48, a Cu intermediate layer 49, a CoFe pinned layer 50, and a PdPtMn antiferromagnetic layer 51, on which a Ta cap layer 52 is provided.

Next, after a resist is applied by a usual two-layer resist process, a resist pattern (not shown) having a predetermined shape is formed by exposure and development, and ion milling is performed using the resist pattern as a mask. Thereby, the spin valve film is patterned to a predetermined width as shown in the figure. In this two-layer resist process, the upper layer is formed of a photoresist having photosensitivity, and the lower layer uses a resist layer having a higher etching rate with respect to the developing solution in order to form an undercut portion. And
Photosensitivity is not required for the lower resist layer.

Next, CoCr is applied to both ends of the spin valve film.
After depositing a hard magnetic film of Pt or the like by a sputtering method, unnecessary portions of the hard magnetic film are removed by a lift-off method of removing a resist pattern used for patterning the spin valve film.
To form

Then, a pair of lead electrodes 54 is formed by depositing a conductive film made of Cr / Au or the like, and then again.
Ni through an upper read gap layer 55 such as Al ₂ O ₃
By providing the upper magnetic shield layer 56 made of an Fe alloy or the like, the basic configuration of the reproducing magnetic sensor using the spin valve element is completed.

In such a spin valve giant magnetoresistive element, the magnetization direction is the PdPtMn antiferromagnetic layer 51.
And a CoFe free layer 4 whose magnetization direction freely rotates according to an external magnetic field.
8 and the angle between the magnetization direction of the NiFe-free Cu 47 and the magnetization direction, the scattering depending on the spin of the conduction electrons changes, and the electric resistance changes. Therefore, the change in the electric resistance is measured by applying a constant sense current to the voltage. By detecting the change as a value, the state of the external magnetic field, that is, the signal magnetic field from the magnetic recording medium is obtained.

Such a spin valve magnetoresistive sensor responds to the demand for further miniaturization by shortening the exposure wavelength, increasing the NA of the lens, and improving the resist characteristics. For example, in a two-layer resist process, an ArF excimer laser or the like is used.
Exposure light in the ultraviolet region of a shorter wavelength such as 2 nm is used.

[0012]

However, in such a method of miniaturizing a resist pattern, development of a short wavelength exposure light source after ArF excimer laser light and development of a resist suitable for a short wavelength are increasing in difficulty. The miniaturization as before has not progressed.

Accordingly, an object of the present invention is to form a resist pattern finer than the optical resolution dimension using the conventional resist material and exposure means.

[0014]

FIG. 1 is an explanatory view of the principle configuration of the present invention. Referring to FIG. 1, means for solving the problems in the present invention will be described. In the drawing, reference numeral 6 denotes a base layer of Al ₂ O ₃ or the like. 1A to 1C, in order to achieve the above object, the present invention provides a method for forming a pattern, comprising: forming a lower resist layer 2 having an etching rate relatively higher than a developing solution; The resist pattern 1 is formed by exposing a two-layer resist layer composed of a small upper resist layer 3 to form an undercut resist pattern 1 and then slimming the width of the resist pattern 1.

Alternatively, after exposing a two-layer resist layer composed of a lower resist layer 2 having a relatively low etching rate to a developing solution and an upper resist layer 3 having a relatively high etching rate, the resist pattern 1 is developed by exposure. After forming the resist pattern 1, when performing the slimming of the width of the resist pattern 1, a relatively large amount of the lower resist layer 2 may be removed to form the undercut resist pattern 1.

Alternatively, after forming the undercut single-layer resist pattern 1, the width of the resist pattern 1 may be slimmed while maintaining the undercut shape.

As described above, by slimming the width of the resist pattern 1 after patterning the resist pattern 1, the width of the resist pattern 1 can be made larger than the optical resolution dimension without using a special resist or exposure method. It is possible to make the film 5 to be processed finer than the optical resolution dimension by ion milling using Ar ions 8 or the like, whereby a fine etching pattern 9 can be obtained.

When the resist layer is a two-layer resist layer, it is preferable to use either a phenolic resin resist or a Si-containing resist as the upper resist layer 3 and to use an organic polymer as the lower resist layer 2.

Particularly, as a combination of the upper resist layer 3 and the lower resist layer 2, when the upper resist layer 3 is a phenol resin resist such as a novolak resist, the lower resist layer 2 is formed of PMGI ( Either a polyimide resin such as LOL-1000) or a polyimide resin containing an antireflection type dye such as ARC is desirable, and the undercut portion 4 can be formed in the developing step.

The upper resist layer 3 is made of oxygen plasma 7
In the case of a Si-containing resist having a high resistance to odor, the lower resist layer 2 is preferably made of an anti-reflection type dye-containing polyimide resin having a high resistance to a developing solution such as BARC and a low resistance to oxygen plasma 7, for example, BARC. , The undercut portion 4 can be formed.

As the slimming step, it is preferable to use any one of an oxygen-based plasma treatment, an ozone treatment using ultraviolet irradiation, and an ozone treatment using ozone water. When ultraviolet irradiation is performed, it is preferable to use ultraviolet light having a shorter wavelength, such as ArF excimer laser light having a wavelength of 172 nm.

The above-described pattern forming method is used as a lift-off pattern when patterning a magnetoresistive film such as a spin valve film and when forming a magnetic domain control film (hard bias film). Can be manufactured.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A manufacturing process of a reproducing magnetic sensor according to a first embodiment of the present invention will be described with reference to FIGS. Referring to FIG. 2A, first, as in the conventional case, Al ₂ O serving as a base of the slider is used.
_A lower magnetic shield layer made of a NiFe alloy on a _3- TiC substrate via an Al ₂ O ₃ film (both not shown)
Is provided, a lower read gap layer 11 made of an Al ₂ O ₃ film is provided, and then a spin valve film 12 is formed on the lower read gap layer 11 by a sputtering method.

FIG. 2B is an enlarged view of the circle shown by the broken line in FIG. 2A. In this case, the spin valve film 12 has a thickness of
For example, a Ta underlayer 13 of 5 nm and a thickness of, for example, 2
nm of the NiFe free layer 14 having a thickness of, for example, 2 nm
CoFe free layer 15 having a thickness of, for example, 2.4 nm
Cu intermediate layer 16 having a thickness of, for example, 2 nm
Pinned layer 17 and Pd having a thickness of, for example, 13 nm
The PtMn antiferromagnetic layer 18 and a thickness of, for example, 6n
m of the Ta cap layer 19 is sequentially formed. The composition ratio of the NiFe free layer 14 in this case is, for example, Ni ₈₁ Fe ₁₉ ,
The composition of the free layer 15 and the CoFe pinned layer 17 is, for example, Co ₉₀ Fe ₁₀ , and the composition ratio of the PdPtMn antiferromagnetic layer 18 is, for example, Pd ₃₁ Pt ₁₇ Mn ₅₂ .

Next, referring to FIG. 2C, the thickness of the spin valve film 12 is, for example,
The 0.1 μm PMGI layer 20 and a thickness of, for example,
A 0.5 μm novolak resist layer 21 is applied to form a two-layer resist. In this case, since the PMGI layer 20 serving as the lower resist layer has no photosensitivity,
Not a photoresist.

Next, as shown in FIG. 3 (d), exposure was performed by irradiating ultraviolet rays having a wavelength of 172 nm using an ArF excimer laser, and then 2.38%.
Is developed by using a developing solution composed of aqueous tetramethylammonium hydroxide having a width of, for example, 0.28 μm.
Then, a resist pattern 22 and a PMGI layer pattern 23 are formed. In this case, since the etching rate of the PMGI layer 20 with respect to the developing solution is large, an undercut portion is formed at the interface with the resist pattern 22 as in the related art.

Next, referring to FIG. 3E, using a parallel plate type plasma etching apparatus,
With the O ₂ gas flowing at 8 sccm and a pressure of 200 Torr, the resist pattern 22 and the PMGI layer pattern 23 are slimmed by the oxygen plasma 24 generated by applying a high frequency power of 25 W (/ 176 cm ² ).

[0028]

[Table 1] As shown in Table 1, when slimming is performed for 1 minute under the above conditions, the resist width of 0.278 μm becomes 0.251 μm.
m about 10% slim, 0.217μm for 2 minutes slimming, 0.181 for 3 minutes slimming
μm, and the undercut shape was almost kept.

Referring to FIG. 3F, the width is reduced to, for example, 0.22 μm by slimming.
The spin valve film 12 is etched until the lower read gap layer 11 is exposed by performing ion milling using Ar ions 25 using the resist pattern 22 that has become m as a mask, and a spin valve element pattern 26 having a predetermined width is exposed. To form

Next, referring to FIG. 4G, the resist pattern 22 and the PMGI layer pattern 23 are used as they are as lift-off patterns, and the thickness is reduced to, for example, 80 by a sputtering method.
A CoCrPt film 27 of nm is deposited.

Next, referring to FIG. 4H, the resist pattern 22 and the PMGI layer pattern 23 together with the Co
By removing the CrPt film 27, a hard bias film 28 bonded to both side surfaces of the spin valve element pattern 26 is formed.

Next, as shown in FIG. 4 (i), for example, the thickness is set to 3
After depositing a Cr adhesion layer having a thickness of 30 nm and an Au electrode layer having a thickness of, for example, 30 nm, ion milling is again performed using a new resist pattern as a mask, thereby forming a lead electrode 29 comprising a pair of Cr / Au films. And then N 2 through an upper read gap layer such as Al ₂ O ₃
An upper magnetic shield layer made of an iFe alloy or the like (in each case,
(Not shown) completes the basic configuration of the reproducing magnetic sensor.

In the first embodiment of the present invention, the exposure and
After the resist pattern is formed by development, the slimming process using oxygen plasma is performed, so the width dimension of the resist pattern is reduced to a size exceeding the optical resolution dimension while using the conventional resist material and exposure method. The dimensions of the magnetic sensor for reproduction can be reduced.

In the first embodiment,
Since PMGI is used as the lower resist layer, an undercut portion can be formed in the developing step, and the undercut shape can be almost maintained also in the slimming step, whereby the lift-off can be reliably performed. .

Next, the manufacturing process of the reproducing magnetic sensor according to the second embodiment of the present invention will be described with reference to FIG.
Except for the two-layer resist process, it is completely the same as the above-described first embodiment, so that the description will be simplified. First, as in the first embodiment, an Al ₂ O ₃ —TiC substrate serving as a slider base is placed on an Al ₂ O 3
_After a lower magnetic shield layer made of a NiFe alloy or the like (all not shown) is provided via the _three films, a lower read gap layer 11 of Al ₂ O ₃ or the like is provided, and then a spin valve film is formed by sputtering. 12 is deposited.

Next, a BARC layer 31 having a thickness of, for example, 0.1 μm is formed on the spin valve film.
After applying a 0.5 μm Si-containing resist layer to form a two-layer resist layer, the same exposure and development processing as in the first embodiment is performed. In this case, the BARC layer 31 is hardly etched because the BARC layer 31 has high resistance to a developing solution composed of tetramethylammonium hydroxide water, and only the Si-containing resist is developed, and the width is, for example, 0.28 μm. A Si-containing resist pattern 32 is formed. Note that BARC is an ARC made of a polyimide resin containing an anti-reflection dye that has improved resistance to a developing solution.

Next, by performing a slimming process using the oxygen plasma 24 under the same conditions as in the above-described first embodiment, the width of the Si-containing resist pattern 32 is reduced to, for example,
Slim down to 0.22 μm.

In this case, the Si-containing resist pattern 32
Has a high oxygen plasma resistance, whereas the BARC layer 3
1 has a small oxygen plasma resistance, the exposed portion of the BARC layer 31 is etched while the Si-containing resist pattern 32 is slimmed, and the BA having an undercut shape is formed.
An RC layer pattern 33 is formed.

After that, as in the first embodiment, the spin valve film 12 is exposed by performing ion milling using Ar ions 25 using the Si-containing resist pattern 32 as a mask. The spin valve film pattern 26 is formed by removing the portion.

Hereinafter, although not shown, a hard bias film is formed by using a lift-off method, and then a pair of lead electrodes, an upper read gap layer, and an upper magnetic shield layer are sequentially formed, thereby achieving the present invention. The basic structure of the reproducing magnetic sensor according to the second embodiment is completed.

In the second embodiment as well, the only difference is in the process of forming the undercut portion. As in the first embodiment, the width of the resist pattern can be reduced while using the conventional resist material and exposure method. The dimensions can be fine dimensions beyond the optical resolution dimensions,
The reproduction magnetic sensor can be miniaturized.

Next, with reference to FIG. 6, a description will be given of a manufacturing process of the reproducing magnetic sensor according to the third embodiment of the present invention.
Except for the resist process, it is completely the same as the above-described first embodiment, so that the description will be simplified. Referring to FIG. 6 (a), an Al ₂ O ₃ -TiC substrate serving as a slider base is placed on an Al ₂ O ₃ -TiC substrate just like the first embodiment.
_After a lower magnetic shield layer made of a NiFe alloy or the like (all not shown) is provided via the _three films, a lower read gap layer 11 of Al ₂ O ₃ or the like is provided, and then a spin valve film is formed by sputtering. 12 is deposited.

Next, a resist SIPR9706 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) having a thickness of, for example, 0.5 μm is applied on the spin valve film, and then subjected to the same exposure and development processing as in the first embodiment. Done, the width of the top is, for example,
A resist pattern 35 of 0.28 μm is formed. In this case, the resist SIPR9706 (trade name of Shin-Etsu Chemical Co., Ltd.)
Has a characteristic of being formed into an inversely tapered shape by development, so that an inversely tapered resist pattern 35 is obtained.

Next, as shown in FIG. 6B, a slimming process using oxygen plasma 24 is performed under the same conditions as in the first embodiment, so that the resist pattern 35 is maintained while maintaining the reverse tapered shape.
Is slimmed down to, for example, 0.22 μm.

Referring to FIG. 6C, thereafter, similarly to the first embodiment, the exposed portion of the spin valve film 12 is formed by performing ion milling using the Ar ions 25 with the resist pattern 35 as a mask. This is removed to form a spin valve film pattern 26.

Although not shown in the drawings, a hard bias film is formed by a lift-off method, and a pair of lead electrodes, an upper lead gap layer, and an upper magnetic shield layer are sequentially formed. The basic structure of the reproducing magnetic sensor according to the third embodiment is completed.

In the third embodiment, the undercut portion is formed by a single-layer resist, so that the resist process is simplified and the first process is performed.
As in the first embodiment, the width of the resist pattern can be reduced to a fine dimension exceeding the optical resolution dimension while using the conventional resist material and the exposure method, whereby the reproducing magnetic The sensor can be miniaturized.

The embodiments of the present invention have been described above. However, the present invention is not limited to the configuration described in each embodiment, and various modifications are possible. For example, in the description of each of the above embodiments, the slimming process is performed using oxygen plasma. However, the present invention is not limited to the oxygen plasma process, and may be an ozone process.

For example, the oxygen gas introduced into the reaction chamber is
For example, slimness may be achieved by irradiating ultraviolet rays of 172 nm using Xe excimer light to generate ozone and exposing the resist pattern to the generated ozone.

Alternatively, the generated ozone may be dissolved in ultrapure water to produce ozone water, and the slimness may be reduced by a wet treatment in which a resist pattern is immersed in the ozone water.

In the first embodiment, PMGI is used as the lower resist layer.
The invention is not limited to PMGI, and other organic polymers may be used. For example, an ARC made of a polyimide resin containing an anti-reflection dye may be used.

In the first embodiment, a novolak resist, which is a phenol resin resist, is used as the upper resist layer. However, the present invention is not limited to the novolak resist. In any case, any positive resist having high sensitivity to ultraviolet rays may be used.

In each of the above embodiments, the magnetoresistive element is a single spin valve element having an antiferromagnetic layer on the upper side, but a single spin valve element having an antiferromagnetic layer on the lower side. A valve element or a dual spin valve element may be used.
Ordinary MR elements may be used.

In each of the above embodiments, the lead electrode is a magnetic sensor having an overlay structure in contact with the Ta cap layer. However, following the deposition of the hard magnetic film for the hard bias film, A hard bias film and a lead electrode may be formed in a self-aligned manner by depositing a conductive film of the above method and lift-off.

The materials of the magnetic layer, the antiferromagnetic layer, and the conductive layer described in each of the above embodiments are merely examples, and various known magnetic materials, antiferromagnetic materials, and conductive materials may be used. It goes without saying that a combination of materials may be used.

Further, in the description of each embodiment of the present invention, a single magnetic sensor for a reproducing head is described. However, the present invention is not limited to a single magnetic sensor, but an inductive thin film. It goes without saying that the present invention is also applied as a magnetic sensor for a reproducing head constituting a composite type thin film magnetic head laminated with a magnetic head.

Further, the present invention has been described as a pattern forming method used in a manufacturing process of a reproducing magnetic sensor. However, the present invention is not limited to a manufacturing process of a reproducing magnetic sensor, and a photolithography process using ultraviolet rays. And a lift-off process for forming a fine pattern. The fine pattern can be formed easily and with high throughput by an electron beam exposure method.

Here, referring to FIG. 1 again, the detailed features of the present invention will be described. 1 (a) to 1 (c) (Supplementary Note 1) A two-layer resist layer composed of a lower resist layer 2 having a relatively high etching rate with respect to a developer and an upper resist layer 3 having a relatively low etching rate. A pattern forming method, comprising: performing exposure and development to form a resist pattern 1 having an undercut shape, and then slimming the width of the resist pattern 1 while maintaining the undercut shape. (Supplementary Note 2) The resist pattern 1 is developed by exposing and developing a two-layer resist layer including a lower resist layer 2 having a relatively low etching rate with respect to a developing solution and an upper resist layer 3 having a relatively high etching rate with respect to a developing solution. After forming,
When slimming the width of the resist pattern 1,
A pattern forming method, wherein a relatively large amount of the lower resist layer 2 is removed to form an undercut resist pattern 1. (Supplementary Note 3) The pattern according to Supplementary Note 1 or 2, wherein either the phenolic resin-based resist or the Si-containing resist is used as the upper resist layer 3 and an organic polymer is used as the lower resist layer 2. Forming method. (Supplementary Note 4) The pattern according to Supplementary Note 3, wherein the upper resist layer 3 is made of a phenol resin-based resist, and the lower resist layer 2 is made of any of a polyimide resin or a polyimide resin containing an antireflection type dye. Forming method. (Supplementary Note 5) The pattern according to Supplementary Note 3, wherein the upper resist layer 3 is made of a Si-containing resist, and the lower resist layer 2 is made of an anti-reflection type dye-containing polyimide resin having high resistance to the developer. Forming method. (Supplementary Note 6) A pattern forming method, wherein after forming a single-layer resist pattern 1 having an undercut shape, slimming of the width of the resist pattern 1 is performed while maintaining the undercut shape. (Supplementary Note 7) The slimming step is any one of an oxygen plasma treatment, an ozone treatment using ultraviolet irradiation, and an ozone treatment using ozone water. Pattern formation method. (Supplementary Note 8) The resist pattern 1 according to any one of Supplementary notes 1 to 7, wherein the resist pattern 1 is a pattern for patterning a magnetoresistive film and a lift-off pattern when a magnetic domain control film is formed. Pattern formation method.

[0059]

According to the present invention, slimming is performed after forming a resist pattern, so that a resist pattern finer than the optical resolution dimension is formed using the conventional resist material and exposure means. This greatly contributes to the spread and cost reduction of high-density HDD devices.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a basic configuration of the present invention.

FIG. 2 is an explanatory diagram of a manufacturing process partway through the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a manufacturing process of the first embodiment of the present invention up to the middle of FIG. 2;

FIG. 4 is an explanatory diagram of a manufacturing process of the first embodiment of the present invention after FIG. 3;

FIG. 5 is an explanatory diagram of a manufacturing process according to a second embodiment of the present invention.

FIG. 6 is an explanatory diagram of a manufacturing process according to a third embodiment of the present invention.

FIG. 7 is a schematic configuration diagram of a conventional reproducing magnetic sensor.

[Explanation of symbols]

Reference Signs List 1 resist pattern 2 lower resist layer 3 upper resist layer 4 undercut portion 5 film to be processed 6 base layer 7 oxygen plasma 8 Ar ion 9 etching pattern 11 lower read gap layer 12 spin valve film 13 Ta base layer 14 NiFe free layer 15 CoFe free layer 16 Cu intermediate layer 17 CoFe pinned layer 18 PdPtMn antiferromagnetic layer 19 Ta cap layer 20 PMGI layer 21 Novolak resist layer 22 Resist pattern 23 PMGI layer pattern 24 Oxygen plasma 25 Ar ion 26 Spin valve element pattern 27 CoCrPt film 28 hard bias film 29 lead electrode 31 BARC layer 32 Si-containing resist pattern 33 BARC layer pattern 35 a resist pattern 41 Al ₂ O ₃ -TiC substrate 42 underlying layer 3 Lower magnetic shield layer 44 Lower read gap layer 45 Spin valve film 46 Ta underlayer 47 NiFe free layer 48 CoFe free layer 49 Cu intermediate layer 50 CoFe pinned layer 51 PdPtMn antiferromagnetic layer 52 Ta cap layer 53 Hard bias film 54 Lead Electrode 55 Upper read gap layer 56 Upper magnetic shield layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H025 AA02 AB17 AC04 AC08 CB28 CB32 DA13 FA17 FA41 2H096 AA27 GA08 HA18 HA23 KA02 5D034 BA03 CA06 DA07 5F046 LA18 NA01 NA15

Claims (5)

[Claims] An exposure is performed on a two-layer resist layer comprising a lower resist layer having a relatively high etching rate with respect to a developing solution and an upper resist layer having a relatively low etching rate, followed by developing to form an undercut shape. After forming a resist pattern, slimming of the width of the resist pattern is performed while maintaining the undercut shape. 2. A resist pattern is formed by exposing and developing a two-layer resist layer including a lower resist layer having a relatively low etching rate with respect to a developing solution and an upper resist layer having a relatively high etching rate with respect to a developing solution. A pattern forming method, characterized in that, when slimming the width of the resist pattern, a relatively large amount of the lower resist layer is removed to form an undercut resist pattern. 3. The pattern according to claim 1, wherein the upper resist layer is made of either a phenolic resin resist or a Si-containing resist, and the lower resist layer is made of an organic polymer. Forming method. 4. A pattern forming method comprising: forming a single-layer resist pattern having an undercut shape; and slimming the width of the resist pattern while maintaining the undercut shape. 5. The slimming process according to claim 1, wherein the slimming process is any one of an oxygen-based plasma process, an ozone process using ultraviolet irradiation, and an ozone process using ozone water. Item 2. The pattern forming method according to Item 1.