WO1988009961A1

WO1988009961A1 - Arrangement for producing a structure by means of photolithography and manufacturing process thereof

Info

Publication number: WO1988009961A1
Application number: PCT/EP1988/000143
Authority: WO
Inventors: Wolfgang Bartsch; Stephani Dietrich
Original assignee: Siemens Aktiengesellschaft
Priority date: 1987-06-10
Filing date: 1988-02-26
Publication date: 1988-12-15
Also published as: EP0367762A1

Abstract

An arrangement comprises a two-layer system with photosensitive paint coats (6, 8) of a specified thickness, which contain a polymer and a photoactive compound serving as an inhibitor in an organic solvant, the adsorption capacity of which is determined by factor A, B and C. According to the invention a lower, thick layer (6) is provided with a lower absorption value and an upper, thin layer (8) with a higher absorption value, having also a different molecular weight. When the adsorption capacity is known, the thicknesses of the two photosensitive paint coatings are matched to a predetermined pure transmission. This photosensitive paint system can be used for making major topographical changes to the surface of a substrate with fine structures.

Description

Arrangement for structuring by means of photolithography and method for its production

The invention relates to an arrangement for structuring by means of photolithography with a two-layer system of photoresist layers, which are each applied in succession with a predetermined thickness. In an organic solvent, these photoresist layers contain a polymer and a photoactive compound serving as an inhibitor, the absorption capacity of which is determined as a function of the exposure energy according to factors. This two-layer system is suitable for manufacturing thin-film magnetic heads and, for example, for vanic processes in microelectronics.

The photoresists belong to the class of positive resists, which are based on diazoquinones or related compounds as inhibitors and novolaks as base polymers. The absorption capacity of these photoresists results - depending on the exposure energy - from the analysis from a factor A for a light-dependent absorption and a factor B for a light-independent absorption as well as a factor C for its optimal sensitivity (Dill in IEEE Transact. on El..Devices Vol. ED-22, No. 7, July 1975, pp. 445-452).

In the known photolithography with commercially available photo lacquers over relatively high steps, the mask on the steps can be under-irradiated during exposure due to diffraction and interference effects. The dimensional accuracy of the desired structure can therefore only be set with a relatively large amount of work. The different lacquer layer thicknesses at the stages result due to the different

MARINE LEAF Pure transmission and thus the layer thickness-dependent development rate in the alkaline medium to a pronounced, so-called "bulk effect" with a strongly varying lacquer profile, which contributes to the reduction in contrast.

At high, highly reflective ^'levels, such as coated with metal levels, the resist profile is additionally affected by langreich- weitige scattering effects, which ren to a weite¬ leads additional reduction in contrast. An additional dye component (dye) has therefore been added to the known systems based on diazoquinone novolak.

With this special lacquer, so-called dye resist, however, only layers up to a few μm thick can be produced and also no high steps can be covered (Bolsen in Microelectronic Engineering 3 (1985), pages 321 to 328).

A two-layer system is also known, in which a photo-resist layer is also provided with an additional CEM layer (contrast enhanced aterial). Mixing of the two layers is prevented by an additional barrier layer. In conjunction with a photoresist layer of, for example, approximately 1 to 2 μm and a CEM layer of, for example, approximately 4000 to 5000 8, an intermediate layer of approximately 850 to 2300 S serving as a barrier layer can be provided, for example. This intermediate layer also prevents the photoresist layer from being attacked by the solvent development with which the CEM layer has to be removed again. With this two-layer system, however, only comparatively small layer thicknesses are possible and it is also not possible to cover high levels (Pavelchek in SPIE, Vol. 538, Optical Microlithographie IV (1985), pages 78 to 85).

As is known, a positive photoresist can be spun on and structured for structuring layers by means of photolithography.

SPARE BLADE finally dried (soft bake) at a relatively low temperature of around 90 to 100 ° C. The photoresist is then exposed with a mask corresponding to the desired structure. The energy supplied with the exposure is adapted to the thickness and the properties of the lacquer layer. For example, an energy of approximately 50 to 150 mJ / cm ^{2 is} supplied for a 1 to 2 μm thick photo lacquer layer. In principle, a different thickness of the lacquer layer at the stages of the material to be structured also requires a corresponding change in the exposure energy supplied. For example, an exposure energy of 500 to 1000 mJ / cm ² would be required for a lacquer layer with a thickness of approximately 16 μm at one step. However, this relatively high radiation energy can lead to under-radiation at thin areas of the lacquer layer. Irradiation increases the solubility of the positive resist in a basic developer. The exposed areas are also attacked or even removed during development. The result is a corresponding reduction in contrast of the manufactured structure. In various technical areas of application, for example in microelectronics and in particular in the production of thin-film magnetic heads, surfaces have to be structured with steps, the height of which can exceed 20 μm, for example.

The invention is based on the object of specifying an arrangement for structuring by photolithography with photoresist which is suitable for high levels with good contrast.

As is well known, the photoresist layer thickness remaining after development depends on the exposure energy. The exposure and the development must therefore be coordinated so that a predetermined layer thickness of the photoresist remains after the development. A photoresist layer with a thickness of, for example, 0.4 μm is completely coated with the development in an alkaline medium after exposure to 100 mJ / cm ² .

REPLACEMENT LEAF solves. This must be taken into account in the exposure through a mask, since under-irradiated areas are also developed further. A change in the distribution of the photoactive compound both within the photoresist layer in accordance with the absorption capacity and in a lateral direction parallel to the mask plane in accordance with the under radiation is thus obtained after exposure through a predetermined mask.

The above-mentioned object is now achieved according to the invention with the characterizing features of claim 1. The lower photoresist layer with low absorption and high molecular weight means that the relatively high level is somewhat planarized without this layer losing photosensitivity, since only relatively low soft beacon Temperatures of preferably 100 to 110 ^* C are required to dry this first layer. The second photoresist layer with high absorption and lower molecular weight is applied in accordance with the layer thickness of this photoresist layer which occurs at the step, the layer thickness to be set of this second photoresist layer being measured for the pure transmission required for development given the absorption capacity of both materials .

The different absorption of the two photoresist layers is obtained from the ratio of the absorption coefficients in the unexposed state. This ratio (A + B) of the upper layer / (A + B) of the lower layer is at least 1.5. In a preferred embodiment it is at least 2, but we do not significantly exceed 3.

The ratio of the molecular weights MW of both photoresist layers MW upper layer / MW. bottom layer is at least 1.2. In a preferred embodiment, it is about 1.8; however, it will not significantly exceed a factor of 3.

REPLACEMENT LEAF A barrier layer between the two photoresist layers is not necessary because of the different molecular weights. This two-layer system does not lose any sensitivity to light; for example, for a composite with a total thickness of 7.5 μm, only a low exposure energy of about 370.mJ / cm ^{2 is} required. It also has the particular advantage that after exposure through a given mask, both layers can be developed in a common development process using a single alkaline medium.

To further explain the invention, reference is made to the drawing, in which FIG. 1 shows a section through part of a two-layer system according to the invention. FIG. 2 shows the absorption of various photoresists as a function of the energy radiation in a diagram.

According to FIG. 1, the surface of a substrate 2 is provided in a predetermined region, which is not limited in the figure, with a surface layer 4, for example a metal layer, to be structured by photolithography, which is applied over a step with a height H of, for example, 20 μm. The surface is covered with a first photoresist layer 6 with low absorption but high molecular weight. The step gives this first photoresist layer 6 a different thickness. For example, the thickness a at the foot of the step may be approximately 16 μm, while the thickness b in the areas above the step and next to the step is approximately 8 μm and the thickness c at the beginning of the waste flank, which is not described in any more detail is about 3 to 4 μm. This achieves a certain planarization of the relatively large level.

This photoresist layer 6 is provided in the same way with a further photoresist layer 8 with high absorption and a lower molecular weight. The thickness of this second photoresist layer

REPLACEMENT LEAF 8 is chosen so that the ratio of the layer thickness of the lower photoresist layer 6 to the layer thickness of the upper photoresist layer 8 - measured in the plane - is preferably between 0.7 and 4. The layer thickness is determined by the height of the step, the layer thickness distribution of the lower layer at points a, b, and c, and by the pure transmission required for development with the greatest possible gain in contrast. The thickness of the second photoresist layer 8 with large absorption is preferably substantially less than the thickness of the first photoresist layer 6 with less absorption is .and vor¬ preferably at most half the thickness of the lower Fotolack¬ layer 6 and may be the entire area at the points a _{2 »} B ₂ and c _{2 are,} for example, approximately 4 μm.

So that they do not mix, the two layers 6 and 8 ^'have different molecular weights. They differ by a factor

K = dn ¹ 1.5

V and preferably at least K> 2, where d is the layer thickness in μm, n is the rotational speed / min during spin coating and V is the solids content of the layer specified by the manufacturer in%.

To produce the two-layer system, the first photoresist layer 6 can preferably be spun on at a speed of about 3000 rpm. Subsequently, the first layer 6 is Fotolack¬ at a temperature of about 70 "C to 180 ^* C., preferably from about 90 ^* C to 120 ^* C, for a period of 60 min to about 2, preferably about 5 min to 15 The second photoresist layer 8 can preferably be applied in the same way and is then also used at a temperature.

REPLACEMENT LEAF temperature of about 70 ° C to 110'C, preferably at a temperature of 90 ^β C to 100'C, for a time of about 2 to 60 min, preferably about 5 to 15 min, dried.

The photoresist layers 6 and 8 can also be applied by spray painting, dip coating or by so-called roller painting.

Under certain circumstances, it may be appropriate to saturate this two-layer system with water vapor.

Depending on the total thickness of the layers 6 and 8 v approximately 12 μm, the exposure is carried out with an energy of, for example, approximately 550 mJ / cm ² to 1300 mJ / cm ² in the contact, proximity or projection exposure method. The development in an alkaline medium with a pH of, for example, about 10 to 14 takes place depending on the total layer thickness and exposure over a time of about 60 to 360 s.

In the diagram according to FIG. 2, the absorption per μm layer thickness is plotted as a function of the incident energy E on a rithmic scale for two different photoresists with different layer thicknesses of the lacquers. From the kung curves (bleaching curves) it can be seen that the absorption of the various photoresists in the region of low energy radiation remains approximately the same according to the absorption coefficient A + B, then according to its optical sensitivity according to a sensitivity factor C which decreases in contrast to the known one Sensitivity factor C (na Dill) is influenced by the layer thickness, and then only slightly absorbed at high energy radiation according to the absorption coefficient. The layer thicknesses of the two materials are chosen in accordance with their known absorption capacity, so that those indicated in dash-dot lines in the diagram

REPLACEMENT LEAFS Slopes in area C differ significantly from each other. This ensures that the slope of the action curve of the composite of two photoresists according to the invention is increased in region C in comparison to the slope of the action curve of the lower photoresist layer, which serves as a mask in the subsequent etching process of the surface layer 4. According to the diagram, a contrast-enhanced lacquer profile is thus obtained from the photoresist layers 6 and 8 after the development process of the two-layer system.

REPLACEMENT LEAF

Claims

1. Arrangement for structuring by photolithography with a two-layer system with photoresist layers, which are applied in succession, each with a predetermined thickness, and contain in an organic solvent a polymer and a photoactive compound serving as an inhibitor, the absorption capacity of which Function of exposure energy by a factor A for light-dependent absorption,

B for light-independent absorption and

C is determined for its optimal sensitivity, characterized by the following features: a) the lower photoresist layer (6) has a low absorption b) the upper photoresist layer (8) has a high absorption c) there are photoresist layers (6 , 8) provided with different molecular weights d) the lower photoresist layer (6) can be spin-coated in the plane up to a thickness of at least 3.3 μm at a speed of about 4000 rpm e) the thicknesses of the two photoresists -Layers (6, 8) are tuned to a predetermined clean transmission with known absorption capacity f) the ratio of the layer thicknesses of the lower photoresist layer (6) to the upper photoresist layer (8) is 0.7 to 4.

2. Arrangement according to claim 1, g e k e n n z e i c h n e t by the following features: a) the lower layer (6) with low absorption has one

factor

A from 0.4 to 0.5 / μm,

B from 0.04 to 0.06 / μm and

C from 40 to 60 mJ / cm ²

REPLACEMENT3LATT b) the upper layer (8) with high absorption has one

factor

A from 0.8 to 1.1 / μm

B from 0.09 to 0.14 / µm and C from 40 to 80 mJ / cm ² .

3. Arrangement according to claim 1 with spun-on photoresist layers (6, 8), d a d u r c h g e k e n n e e c h ¬ n e t that the photoresist layers (6, 8) by a

differ, where d is the layer thickness, n is the speed and V is the solids content.

4. Arrangement according to claim 3, d a d u r c h g e k e n n ¬ z e i c h n e t that

K ^ 2 is.

5. A method for producing an arrangement according to one of claims 1 to 4, characterized in that the drying of the lower layer 6 takes place at a temperature between 70 ^* C and 180 ^* C, preferably between 90 ^* C and 120 ^* C. ,

6. A method for producing an arrangement according to one of claims 1 to 4, that the development of the two-layer system takes place in an alkaline medium with a pH between 10 and 14.

7. A method for producing an arrangement according to claim 6, d a d u r ch g e k e n n z e i c h n e t that the Ent-

E SAϊΣBLATT The two-layer system is developed in such a way that the basicity of the development media increases with increasing development time.

8. A method for producing an arrangement according to one of claims 1 to 4, characterized in that the layer thicknesses of the two photoresist layers (6, 8) are matched to one another in such a way that the action curves of these layers in their central region (C) differ by approximately twice the slope (Fig. 2).

in

The arrangement contains a two-layer system with photoresist layers (6, 8) with a predetermined thickness, which contain, in an organic solvent, a polymer and a photoactive compound serving as an inhibitor, the absorption capacity of which is determined by factors A, B and C.

According to the invention, a lower, thick layer (6) with low absorption and an upper, thin layer (8) with high absorption and different molecular weights are provided. The thicknesses of the two photoresist layers are matched to a predetermined pure transmission if the absorption capacity is known.

With this photoresist system, particularly strong topography changes on the surface of a substrate can be covered with fine structures.

FIG. 1