JPH02253263A - Liftoff processing resist and pattern forming method using the same - Google Patents

Abstract

PURPOSE:To provide a resist to be processed by a liftoff process capable of freely selecting an upper layer to lower layer width ratio and enlarging an allowance of exposure conditions and forming a stable overhang structure by controlling sensitivities of the lower layer, a middle layer, and the upper layer to low, middle, and high levels, respectively, with respect to a developing solvent. CONSTITUTION:The overhang structure 5 can be sufficiently formed with high reproducibility between the upper layer 4 and the middle layer 3 by controlling the sensitivity ratio to about 2:1, but it is necessary to lower the sensitivity of the lower layer resist 2 to <=1/3 those of the layers 4 and 3 in order to form a mushroom-shaped pattern. As the lower layer resist, a positive electron beam resist, causing partial cross-linking reaction due to baking after coating, and lowering in solubility, such as a copolymer of methacrylic acid and methacrylate monomer can be used, and as the resist for the layers 3, 4, a positive type resist, such as polymethacrylate or polyisopropenyl-ketone, can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to lithography techniques for providing semiconductor devices, and more particularly to an improved method for forming gate electrodes of field-effect transistors (FETs). It is.

[Conventional technology]

Conventionally, by using a narrow gate electrode, the FE
Efforts have been made to improve the high frequency characteristics of T. However, it has been found that when the gate width is 0.5 μm or less, the electrical resistance of the gate electrode increases, which deteriorates the high frequency characteristics.

In order to fabricate ultrafine gate electrodes with low resistance, attempts are being made to form electrodes with a mushroom-shaped cross section, narrow at the bottom and wide at the top, by lift-off. Up until now, the mushroom-shaped microscopic lower part was first formed,
Further, an electrode lamination method in which an upper low-resistance portion is again formed on top of this, a method in which two or more types of resist are laminated and exposed to electron beams,
A method has been proposed in which a single layer of resist is irradiated with two types of focused ion beams (F I B) having different penetration distances. However, the method of laminating electrodes has the disadvantage that the process is extremely complicated. In addition, the method using FIB requires a special exposure device, the overlapping method is complicated, and there are problems such as a small margin for controlling the amounts of the two types of ion beams.

On the other hand, the method of laminating two types of electron beam resists can use ordinary electron beam exposure equipment, is easy to overlay, has high precision, and requires only one step of electron beam exposure, development, and lift-off.
By repeating this process twice, there is an advantage that a gate having a mushroom-shaped cross section J[2] can be formed. This process diagram is shown in FIG. In the figure, numeral 1 is a GaAs substrate, 2 is a φ-mac (35
00 people) 3 (PMMΔ (Mw=90000゜3
1008) 4 is 0EBR (3800 people) 6 is Ti (
300 people) 7 means 8u (2000 people).

In this case, the lower resist has lower sensitivity than the upper resist, and a high-dose electron beam is applied to the part corresponding to the bottom of the mushroom shape, and a low-dose electron beam is irradiated to the part corresponding to the wide upper part of the mushroom shape. By doing this (1-1), it is possible to form a punched pattern with a wider width in the upper resist than in the lower resist in one development process (1-2) By depositing metal on this pattern (1-3) A mushroom-shaped gate is formed by lifting off the IJ (1-4).

[Problem to be solved by the invention]

However, in this process, when two layers of normal positive electron beam resist are laminated, if the same type of resist material is used, mixing with the lower layer resist tends to occur when applying the upper layer resist, making it difficult to form a good resist pattern. There is a difficult problem. In particular, in order to facilitate lift-off, it is necessary to form an overhang structure (1-6) in the resist for upper part 1, but when two layers of the same type of resist are laminated,
There is a problem in that the margin of exposure conditions for forming an overhang structure in the upper resist layer is narrow. In addition, if the sensitivity difference between both resists is not sufficient, it will not be possible to provide a large difference in the width of the bottom and top electrodes, which will cause the problem of high resistance even if the gate is shaped like a wedge when forming an extremely fine gate of 0.2 μm or less. there were. To avoid this, when two types of positive resists with significantly different sensitivities are stacked, they usually use different developers, which not only complicates the development process, but also
``There was a problem that a slight mixed layer formed at the interface during resist lamination was difficult to dissolve in either developer, and development did not proceed uniformly.

The purpose of the present invention is to have a high selectivity ratio between the bottom and top widths, a large margin in exposure conditions, a stable overhang structure can be formed, and a simple process that reduces the development speed due to resist mixing. An object of the present invention is to provide a lift-off resist and a lift-off pattern forming method using the same, which can prevent the above.

[Means to solve the problem]

To summarize the present invention, the first aspect of the present invention relates to a resist for lift-off processing, which includes electron beam irradiation,
It is made by laminating three types of resist materials that can form a positive pattern by development, and for the developing solvent used,
It is characterized in that the sensitivities of the lower layer resist, middle layer resist, and upper layer resist are respectively low, high, and intermediate.

The second invention of the present invention relates to a batter forming method, in which the sensitivity of the lower layer resist, middle layer resist, and upper layer resist to the developing solvent used is low, high, and intermediate. A step of laminating three kinds of electron beam positive type materials on a substrate, a step of irradiating this with an electron beam, a step of developing with the developing solvent, and the opening of the exposed part is narrow, wide, and medium from the bottom layer. A step of forming a material made of metal, semiconductor, or dielectric material on the pattern by vapor deposition or sputtering, and a step of lift-off in a solvent that can dissolve the above three types of resist. It is characterized by including each step.

A process diagram showing one embodiment of the present invention is shown in FIG. Reference numerals 1 to 4.6 and 7 in the figure have the same meanings as in FIG. 2, and 5 means an overhang portion.

In the present invention, instead of the conventional two-layer structure, three types of resists are laminated, and the electron beam sensitivity is the lowest for the developing solvent used in the lower layer, the highest in the middle layer, and the upper layer in the middle. It is configured so that In this configuration, the bottom layer corresponds to the bottom of the mushroom shape, and the middle and top layers form the top. Since the middle layer has higher sensitivity than the upper layer, there is an advantage that a stable overhang structure can be formed.

In the present invention, the selection of the three types of resists to be laminated is particularly important. This is to optimize sensitivity and to prevent mixing between layers during coating. In terms of sensitivity,
It is sufficient that there is a difference in sensitivity between the upper layer and the middle layer that allows the overhang structure to be formed with good reproducibility, so it is sufficient that the sensitivity differs by about twice. On the other hand, in order to form a mushroom-shaped pattern, the lower layer resist is several times larger than the upper and middle layers.
The sensitivity must be at least three times lower. Regarding mixing during coating, even if some mixing occurs between the resists when forming an overhang for lift-off between the upper layer and the intermediate layer, it does not have a major effect on the shape.

However, in order to form a mushroom-shaped pattern with good reproducibility between the lower resist and the upper/intermediate layers, and in particular to form the mushroom-shaped bottom pattern corresponding to the gate length with high accuracy, mixing must be minimized as much as possible. There is a need.

The above resist structure consists of two layers: an upper layer and an intermediate layer.
The layers are made of the same kind of polymer materials with different molecular weights, and the molecular weight of the upper layer is higher than that of the intermediate layer so that the solubility of the upper layer is lower than that of the intermediate layer. It is effective to use molecular materials.

In addition, in order to prevent mixing, it is generally effective to use an organic solvent in which the lower layer 1 resist is poorly soluble as a solvent for the intermediate resist. It is effective to use a positive type electron beam resist that has low solubility. As resists that are partially crosslinked by such baking, fluororesists φ-, MAC(
A commercially available resist such as EBR-9 (manufactured by Daikin Industries, Ltd.) (manufactured by Toshi), or a copolymer of methacrylic acid and methacrylic ester-based resin can be used. In addition, as a resist for upper and middle layers, polymethyl methacrylate) (
PMMA) Fluororesist FBM-MO (manufactured by Daisen Industries), Fluororesist FBM-120 (manufactured by Daikin Industries) Positive electron beam resists such as polyisopropenyl ketone can be used4, and instead of changing the molecular weight, The present invention can also be used in resist configurations in which the middle layer has a higher solubility than the upper layer by changing the mixing ratio of the dissolution inhibitor or the dissolution promoter, which are made of the same polymeric material. In addition, when the main components of the upper layer, middle layer, and lower layer are significantly different and the exposure sensitivity is significantly different, there is an advantage that a stable mushroom-shaped structure can be formed because the selection ratio between the widths of the upper and lower portions of the pattern can be increased.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.
The invention is not limited to these examples.

Example I A fluororesist φ-MAC resist (manufactured by Daikin Industries, Ltd.) was used as a lower layer resist on a Ga substrate with a film thickness of 0.
35. am coated and incubated at 200°C for 1 hour. A 0.31 μm thick intermediate layer was laminated thereon by spin-coding a chlorobenzene solution of PMMA (manufactured by Aldrich, molecular weight 93.000) as an intermediate layer resist, and baked at 200° C. for 20 minutes. On top of this, 0EBR-1000 (Tokyo Ohkabu PMMA resist, molecular weight approximately 600,000) was spin-coded as an upper layer resist, and the film thickness was 0.3.
A film of 8 μm was formed. FIG. 3 shows the measurement results of the electron beam exposure sensitivity curves of these three resists developed in xylene/ethylcyclohexane (4:1) at 22° C. for 1 minute and rinsed with ethylcyclohexane for 30 seconds. That is, FIG. 3 is a graph showing the relationship between the electron beam irradiation amount (C/c!, horizontal axis) and the resist remaining film rate (%, vertical axis).

The sensitivity ratio of the upper resist layer/intermediate resist layer/lower layer resist is 1:1.4:16:3.

Next, as shown in Figure 4, the lower part of the electrode is
m, 2000 μC/cIll, and the upper part of the electrode was made to have a width of 1.
Exposure was made at 5 μm 1330 μC/cI11. This sample was developed for 3 minutes with a t-sylene developer (xylene:ethylcyclohexane=4:1), and then rinsed with ethylcyclohexane for 30 seconds. The resist pattern obtained at this time is shown in the scanning electron micrograph of FIG. 5-1.

As is clear from the photo, a good overhang structure has been obtained in the upper and middle layers. Furthermore, 30% titanium was added to this sample.
The appearance of the electrode after evaporating 200 nm of gold and 200 nm of gold and lifting off using methyl ethyl ketone is also shown in the scanning electron micrograph of FIG. 5-2.

As is clear from the photograph, a mushroom-shaped electrode with a width of 0.25 μm at the bottom and a width of 1.5 μm at the top is formed.

Example 2 The same three-layer resist as in Example 1 was formed on a Ga substrate. When these three resists were developed in dichlorobenzene/ethylcyclohexane (4:1) at 22°C for 2 minutes, the sensitivity ratio of the upper layer resist/middle layer resist/lower layer resist was 1:1.7:14.3. be.

Next, as shown in FIG. 4, the lower part of the electrode is
μm, 800μC/cn! Then, the width of the upper part of the electrode is 1.5
μm, exposed at 110 μC/cd. When this sample was developed for 3 minutes with a dichlorobenzene developer (dichlorobenzene: ethylcyclohexane = 4:1) and rinsed with ethylcyclohexane for 30 seconds, a good resist pattern similar to Example 1 was obtained. Furthermore, when 30'nm of titanium and 200nm of gold were deposited on this sample and lift-off was performed using methyl ethyl ketone, the width at the bottom became 0.
An electrode having a width of 1.6 μm at the top and a width of 21 μm was formed.

Example 3 PMMΔ(
Manufactured by Aldrich, molecular 1193.000) spin-coded glue 0 lobenzene solution, PM with a film thickness of 0.32 μm
A MΔ film was formed and baked at 200° C. for 20 minutes. On top of this, a methyl isobutyl ketone/isopropyl alcohol (1:1) solution of 70 rolls FBM-120 (manufactured by Daikin Industries, molecular weight approximately 600,000) was spin-coded.
The mixture was incubated at 170° C. for 30 minutes to form a film with a thickness of 0.3 μm. On top of this, Proloresist FBM-120 (manufactured by Daikin Industries, molecular weight approximately 1.5 million) is used as an upper layer resist.
Methyl isobutyl ketone/isopropyl alcohol (
1:l) solution was spin-coded and beta-coated at 170°C for 20 minutes to form a film with a thickness of 0.25 μm. When these three resists were developed in methyl isobutyl ketone/isopropyl alcohol (1:125) at 22°C for 1 minute,
The electron beam sensitivity ratio of upper layer resist/middle layer resist/lower layer resist was 1:1 Jl19.

Next, the lower part of the electrode was made with a width of 0.2 μm and a width of 600 μc/cnf.
Then, the upper part of the electrode was exposed to light with a width of 3.0 μm and 8 μC/αnr. After developing this sample in methyl isobutyl ketone/isopropyl alcohol (1:125) at 22°C for 1 minute,
Rinse with isopropyl alcohol for 30 seconds. Further, 30 nm of titanium and 200 nm of gold were deposited on this sample.
When lifted off using methyl ethyl ketone, an electrode with a width of 0.22 μm at the bottom and a width of 3.3 μm at the top was formed.

〔Effect of the invention〕

As explained above, three types of resist materials capable of forming a positive pattern by electron beam irradiation and development are used, depending on the developing solvent used: lower layer resist, intermediate layer resist,
In resists stacked so that the sensitivity of the upper layer resist is low, high, and in between, the lower resist has a narrow opening, and the upper and middle resists have wide openings, and there is no overlap. Because a pattern with a hang structure is obtained, lift-off processing
This method has the advantage that a well-shaped mushroom-shaped pattern can be formed with good reproducibility.

In particular, the middle layer resist and the upper layer resist are mainly composed of polymers obtained by polymerizing the same type of monomer, and by making the upper layer resist have a higher molecular weight than the middle layer resist, the sensitivity of the upper layer resist is slightly higher than that of the middle layer resist. The main components of the lower resist are different from these,
By using a material with significantly low sensitivity to electron beams, the width of the upper and lower portions corresponding to the mushroom shape can be controlled within a very wide range, so there is the advantage that a mushroom-shaped pattern of any shape can be obtained.

[Brief explanation of drawings]

Fig. 1 is a process diagram showing an embodiment of the present invention, Fig. 2 is a process diagram of a conventional mushroom-shaped pattern forming method using a two-layer resist method using electron beam exposure and lift-off processing, and Fig. 3 is a process diagram of the EBi of various resists. FIG. 4 is a graph showing the photosensitivity, FIG. 4 is a graph showing the EBN light amount, FIG. 5-1 is a resist pattern (after development) formed in an embodiment of the present invention, and FIG. 5-2 is a graph showing a mushroom-shaped electrode pattern ( These are scanning electron micrographs after lift-off. 1. Ga substrate, 2. . . φ-mac
(3500A), 3. ・PMMA (Mw=90
000, 3100 people) 4・・0EBR(3800
person) 5...°・overhang part, 6...Ti(
300 people) 7・＾u (2000 people) Resistance High R car (%) Figure 5-7 Figure 5-2

Claims (1)

[Claims] 1. Three types of resist materials capable of forming a positive pattern by electron beam irradiation and development are laminated, and a lower layer resist, an intermediate layer resist, and an upper layer resist are used for the developing solvent used. A resist for lift-off processing characterized by having low sensitivity, high sensitivity, and intermediate sensitivity. 2. The resist for lift-off processing according to claim 1, wherein the intermediate layer resist and the upper layer resist mainly contain a polymer obtained by polymerizing monomers of the same type, and the upper layer resist has a higher molecular weight than the intermediate layer resist. . 3. A step of laminating three types of electron beam positive resist materials on the substrate, in which the sensitivity of the lower layer resist, intermediate layer resist, and upper layer resist is low, high, and intermediate, respectively, with respect to the developing solvent used; A process of irradiating electron beam, developing with the developing solvent, and the opening of the exposed part becomes narrower, wider, or narrower from the bottom layer.
A step of obtaining an inner cross-sectional shape, a step of forming a material made of metal, a semiconductor, or a dielectric material on the pattern by vapor deposition or sputtering, and a step of lift-off in a solvent that can dissolve the above three types of resist. A pattern forming method comprising the steps of: