JPH0145611B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to pattern forming materials for semiconductor devices such as ICs and LSIs, that is, resists, and is applied to negatives when forming patterns using high energy beams such as electron beams, X-rays, and ion beams as exposure energy beams. The present invention relates to a mold resist material and a pattern forming method using the same.

For negative electron beam and X-ray resists, glycidyl methacrylate (PGMA) and glycidyl methacrylate-ethyl acrylate copolymer [P
(GMA-EA)], etc. Also, positive types include polymethyl methacrylate (PMMA), copolymers of PMMA and other acrylic monomers, poly(butene-1
-sulfone) (pBs), etc. have been proposed. However, Si, SiO ₂ , PolySi,
As microfabrication technology for semiconductor substrates and wiring materials such as Al has been put into practical use, it has been reported that with conventional resists, the resist runs out before the substrate or wiring material is completely etched, or the pattern edges become hollow. There's a problem.

The present invention was made in view of the above-mentioned problems.
Improving the resist's resistance to dry etching is achieved by incorporating chemically stable aromatic rings into the resist molecule. In the present invention, the novolac type phenolic resin made by the condensation reaction of phenols and formaldehyde is CF ₄ .C ₃ F ₈ ,
Fluorine-based etching gas such as _CCl4 ,
It was selected as a resist base material because it has extremely high resistance to plasma using chlorine-based etching gases such as BCl ₃ and PCl ₃ , and by optimizing its molecular weight and dispersion degree and adding an appropriate amount of bisazide compound, it has excellent dry resistance. To provide a pattern forming method using a negative resist for ionizing radiation that has high etching properties, has practical sensitivity during electron beam exposure or ion beam exposure, and has high resolution (2 μm line/space resolution). It is something.

Novolac type phenolic resin represented by the following general formula (1) (R: H or a _C1 to _C5 alkyl group, or a phenyl group, provided that the weight average molecular weight (Mw) is 2×
10 ⁴ or more, and the ratio to the number average molecular weight (Mn) and the degree of dispersion (Mw/Mn) are 3 or less), 4,4'-diazidochalcone, 2,6-bis(4'-azidobenzal) Cyclohexanone, 2,6-bis(4'-azidostyryl)acetone, azidostyryl, azidoazomethine, 4,4'-diazidostilbene-2,
forming on a substrate a resist layer made of a pattern forming material to which a bisazide compound selected from 2'-disulfonic acid anilide is added in an amount of 3 to 7% by weight based on the novolak type phenolic resin; and ionizing the resist layer. This is achieved by a pattern forming method that includes the steps of exposing the resist to a pattern with radiation, crosslinking the resist in the exposed areas, and developing the resist layer with a developer made of an organic solvent. The substrate can be dry etched to form a pattern.

The present invention will be explained in detail below.

(1) Novolac type phenolic resin Conventional novolac resin has an average molecular weight of 500.
It is about ~3000. The electron beam sensitivity is on the order of 10 ^-4 to 10 ^-3 coulombs/cm ² (accelerating voltage of electron beam 10 to 30 kV). The minimum practical sensitivity during electron beam exposure is 1×10 ⁻⁵ coulombs/cm ² under the same conditions. In view of this, novolak resin made by the conventional method cannot be used as a resist. The sensitivity of an electron beam resist increases as its molecular weight increases. Therefore, it is necessary to make novolak resins with high molecular weights. Conventionally, a method has been used to polymerize novolac by adding formaldehyde to novolac prepared by a conventional method and condensing it under heating.
However, although polymerization is possible with this method, the fractional degree becomes significantly large and the resolution of the resist deteriorates. A major feature of the present invention is that by fractionating and refining the novolak produced as described above, a product with a higher average molecular weight and a smaller degree of dispersion (3 or less) is produced and used.

The molecular weight of novolac must be w=2×10 ⁴ or more. In other words, when a bisazide compound is added to a novolac resin with w=2×10 ⁴ to sensitize it, the sensitivity becomes the practical sensitivity (1×10 ⁻⁵ coulomb/cm ² Vac
= 10kV). Dispersion degree (w/n)
is 3 or less, preferably 2 or less in order to create a 2 μm line/space pattern with a resist film thickness of 1 μm, and a dispersion of 3 or more will not resolve.

(2) Bisazide compounds Bisazide compounds soluble in solvents that are compatible with novolak resin include 4,4'-diazide chalcone, 2,6-bis(4'-azidobenzal)cyclohexanone, and 2,6-bis(4'). -azidostyryl) acetone, azidostyryl, azidoazomethine, 4,4'-diazidostilbene-2,2'-disulfonic acid anilide, and the like.

The bisazide compound is added as an electron-sensitive (X-ray) crosslinking agent to the fractionated novolac shown in item (1),
Improve sensitivity.

The amount added is 3 to 7wt% based on the novolak resin, and if it is less than 3wt%, the sensitizing effect will be small and if it is more than 7wt%, no sensitization will occur even if the amount added is increased (it will become saturated).
Furthermore, the density with the substrate is reduced.

Example 1 Raw material novolak resin (Meiwa Kasei #100) 80g
was dissolved in 500 g of methyl ethyl ketone (MEK), and then transferred to No. 2 separating funnel. 420 ml of cyclohexane was poured into this as a precipitant, and the mixture was allowed to stand for a day and night to precipitate high molecular weight novolak (first step).
After the precipitate was drained out using a conventional method, 40 ml of cyclohexane was added and left to stand for one day to form a precipitate (second division). This second
The precipitate from each division was collected and used as a sample. Yield 9.5g
It was hot. The first fraction cannot be used because it contains a gel fraction and extremely high molecular weight molecules.

Molecular weight and molecular weight distribution were determined by liquid chromatography (du Pont 830 Shimadzu HSG 30+60 column)
Measured at Tetrahydrofuran was used as the solvent and mobile phase, the sample volume was 500 μl, the sample concentration was 0.5%,
Measurement was carried out at a column pressure of 35 Kg/cm ² and a measurement temperature of 30°C. The weight average molecular weight (w) and number average molecular weight (n) were calculated by the line segment method based on a standard polystyrene calibration curve.

FIG. 1 shows the molecular weight distribution of the raw materials and the novolak resin produced by the above method. The raw material novolak resin is n=2.0×10 ³ , w=3.0×10 ⁴ , w/n
= 15.0, the produced novolak resin is n = 3.3×
10 ⁴ , w=5.0×10 ⁴ w/n=1.5.

This prepared novolak was made into a 16.7wt% cyclohexanone solution and further added to the novolak resin.
After adding and dissolving 4wt% 4,4'-diazide chalcone, the sample was coated on a silicon wafer to a film thickness of 1.4 to 1.6 μm and prebaked at 60°C for 10 minutes. was irradiated with an electron beam. For development, use a mixture of n-butyl acetate/monochlorobenzene = 1/5 as the developer at a solution temperature of 23 to 25°C.
This was done by immersing it in water for 80 to 100 seconds and then rinsing it in a 1/6 mixture of n-butyl acetate/monochlorobenzene for 30 seconds. FIG. 2 shows the sensitivity curves of the raw novolac resin, the fractionated novolac resin, and the novolac resin containing 4% by weight of 4,4'-diazide chalcone. Comparing the sensitivity at Dg ^0.5 (the amount of electron beam exposure at a normalized residual film thickness of 0.5), fractionated novolak is about 25 times more sensitive than the raw material, and diazide chalcone-added novolak resin is about 125 times more sensitive. In addition, the sensitivity of the novolak type resin containing diazide chalcone is
At Dg ^0.5 , it is 1.6×10 ^-6 coulombs/cm ² and has practical sensitivity in electron beam exposure.

The sensitivity of diazide chalcone improves up to an addition amount of 4 wt%, but it tends to become saturated when the amount is more than 4 wt%. Furthermore, if the amount added is more than 7 wt%, the adhesion may deteriorate and the pattern may peel off.

Regarding the resolution, when a line and space pattern was drawn by vector scanning with an electron beam with a 1/e of 0.2 μm, it was found that a 1 μml/S pattern (initial resist film thickness 1.4 μm) could be resolved.

Example 2 The same procedure as in Example 1 was carried out except that 5 wt % of 2,6-bis(4'-azidobenthal)cyclohexanone was used instead of 4,4'-diazidochalcone.
The electron beam sensitivity of this resist is 2×10 ^-6 coulombs/
cm ² (Dg ^0.5 ). In addition, the resolution is 1μml/S
It was hot.

Example 3 The same procedure as in Example 1 was carried out except that 5 wt % of 2,6-bis(4'-azidostyryl)acetone was used instead of the additive 4,4'-diazidochalcone. The electron beam sensitivity is 2.5×10 ^-6 coulombs/cm ² (Dg ^0.5 ),
Resolves 1μml/S.

Example 4 80 g of novolac resin (Meiwa Kasei #100), which was the same raw material as in Example 1, was dissolved in 500 g of MEK and then transferred to a 2-separating funnel. 500 ml of cyclohexanone was poured into this, and the mixture was left to stand for a day and night to precipitate the novolac in the first division. After this was drained and removed, 50 ml of cyclohexane was added and left to stand for 1 day to precipitate the second portion. This second divided novolak was collected as a sample. The molecular weight is n=1.2×10 ⁴ w=2.1×10 ⁴ w/n
It was =1.8.

4,4'-Diazidocachalcone was added to this sample in the same manner as in Example 1, and the sensitivity was measured.
It was 10 ^-5 coulombs/cm ² (Dg ^0.5 ).

This corresponds to the lower limit of sensitivity required for electron beam exposure. FIG. 3 shows the relationship between the sensitivity (Dg ^0.5 ) and w of the fractionated novolac resin and the resist obtained by adding 4 wt % of 4,4'-diazide chalcone to the fractionated novolac resin. From this figure, it can be seen that in order to obtain 1×10 ⁻⁵ coulombs/cm ² , w is required to be 2×10 ⁴ or more, and the sensitivity increases as the molecular weight increases. A similar tendency is observed when other bisazide compounds are added, and in order to obtain practical sensitivity, w must be 2.
×10 ⁴ or more is required.

Example 5 Although the second split novolak resin was obtained in the sample preparation of Example 1, samples with different degrees of dispersion were obtained by varying the amount of cyclohexane added.

These are line and
Evaluation was made by drawing a Space pattern with an electron beam and observing the pattern after development. As a result, as with conventional resists, resolution tends to increase as the degree of dispersion decreases;
The 1.5 resolution resolves 1μm line and space.
Also, to resolve 2μm line and space, a dispersion degree of 2 or less is required, and 3μm line and
Space requires a dispersion degree of 3 or less. Therefore, the line width of wiring used in IC, LSI, etc. is 3μm.
The degree of dispersion of the novolac resin must be 3 or less since the diameter is about 1 μm in VLSI.

As is clear from the above explanation, when the weight average molecular weight (w) of the present invention is 2×10 ⁴ or more, the degree of dispersion (
A bisazide compound soluble in a solvent that is compatible with the novolak resin is added in an amount of 3 to 7 wt% to the novolak type phenolic resin whose w/Mn) is 3 or less.
By using the added pattern forming material, it is possible to provide a resist material that has high dry etching properties, has practical sensitivity, and exhibits high resolution.

In this example, an example is given in which an electron beam is used as the energy beam, but the sensitivity of the resist when using each energy beam is somewhat different. For example, between an electron beam and an ion beam, the ion beam is better. is 10 times more sensitive. (When the same energy is given, ion beam exposure causes a larger chemical change in the resist.) In either case, for example, if the sensitivity with an electron beam is used as a standard, it can be expressed by multiplying it by a certain magnification. It can be used as an energy beam.

[Brief explanation of drawings]

Figure 1 shows the molecular weight distribution of the raw material and fractionated novolak resin, Figure 2 shows the raw material novolak resin, the fractionated novolak resin, and 4,4'-diazide chalcone.
Diagram showing the sensitivity curve of 4wt% added novolak resin,
FIG. 3 is a diagram showing the relationship between the electron beam sensitivity and the weight average molecular weight (w) of the fractionated novolac and the novolac containing 4 wt % of 4,4'-diazide chalcone.

Claims (1)

[Claims] 1. Novolac type phenolic resin represented by the following general formula (1) (R: H or a _C1 to _C5 alkyl group, or a phenyl group, provided that the weight average molecular weight (Mw) is 2×
10 ⁴ or more, and the ratio to the number average molecular weight (Mn) and the degree of dispersion (Mw/Mn) are 3 or less), 4,4'-diazidochalcone, 2,6-bis(4'-azidobenzal) Cyclohexanone, 2,6-bis(4'-azidostyryl)acetone, azidostyryl, azidoazomethine, 4,4'-diazidostilbene-2,
A step of forming a resist layer on a substrate made of a pattern forming material in which 3 to 7% by weight of a bisazide compound selected from 2'-disulfonic acid anilide is added to the novolak type phenolic resin, and ionizing the resist layer. A method for forming a pattern, comprising the steps of exposing the resist layer in a pattern to radiation and crosslinking the resist in the exposed areas, and developing the resist layer with a developer made of an organic solvent.