IE852643L

IE852643L - Forming negative patterns in photoresist layer

Info

Publication number: IE852643L
Application number: IE852643A
Authority: IE
Original assignee: Ucb Electronics S A
Priority date: 1984-10-26
Filing date: 1985-10-25
Publication date: 1986-04-26
Also published as: JPH0456979B2; IE56708B1; JPH0220869A; ATE48708T1; SU1498400A3; DE3574788D1; JPH065385B2; KR940004423B1; IL76702A; GB8427149D0; CA1275846C; KR860003674A; MY100941A; JPS61107346A; EP0184567A1; IL76702A0; EP0184567B1

Abstract

1. Process for the formation of negative patterns in a photoresist layer, characterised in that it comprises the following steps : (a) coating of a substrate with a layer of photosensitive resin comprising a polymer having functional groups capable of reacting with a silicon compound, said polymer being mixed or bound by a chemical bound to a diazoquinone, said layer having the property of enabling a silicon compound to diffuse selectively into its irradiated portions when it has been exposed to a visible or ultraviolet radiation in said portions ; (b) exposure of the layer of photosensitive resin to ultraviolet or visible light through a mask to expose only selected portions of the layer ; (c) treatment of the layer of photosensitive resin with a silicon compound, so that this compound is selectively absorbed into the irradiated portions of the layer and reacts with the said functional groups of the photosensitive resin in said irradiated portions, said silicon compound being a silylating agent ; and (d) dry development by plasma etching of the thus treated layer of photosensitive resin to remove selectively the non-irradiated portions thereof in order to obtain the desired negative pattern.

Description

6 7 0 8 The present invention relates to a new microlithographic process.

More particularly, it relates to a process of forming a negative pattern in a photoresist layer which enables the production at industrial scale, with high yield, of very large scale integrated microcircuits (VLSI), the linewidth 5 of which can go down to the submicrometer level. The invention also relates to the use of this new process in the manufacture of integrated semiconductor circuits.

The continuing trend towards miniaturization in the field of integrated semi-conductor circuits gives rise to the need to accomodate more active-10 circuits per unit area on the surface of a semiconductor crystal.

As an illustration of this, reference is made to the commercial development of metal oxide semiconductor (MOS) random access memory (RAM) devices from 1 Kbyte in 1975, via 16 Kbyte in 1977 and 64 Kbyte in 1979 to 256 Kbyte in 1982. It is expected that this trend will continue over the next 15 two decades. As a result, the minimum feature size of semiconductor devices is expected to continue to decrease from 8 micrometers for 1 Kbyte MOS RAM devices, over 2 micrometers for 256 Kbyte MOS RAM devices in 1982 to below 1 micrometer before the end of the 1980's.

Microcircuit fabrication requires the selective diffusion of controlled, 20 small quantities of impurities into specific regions of the semiconductor surface to produce the desired electrical characteristics of the circuit, such as transistor/e?ements,rof which a large scale integrated circuit contains several tens of thousands of individual units that are interconnected in complex ways by conductors, such as aluminium or highly doped polycrystalline 25 silicon.

The technique used in the commercial production of integrated circuits to obtain specific patterns is called photolithography or microlithography. The optionally oxidized silicon substrate (wafer), is coated with a photosensitive layer (also called photoresist) and exposed through a mask to ultraviolet light. 30 The chemical and physical properties of the irradiated regions are different from the non-irradiated regions and create the possibility, in a development step, of removing the exposed (in a positive resist) or unexposed part (in a negative resist).

Development processes are mainly based on solubility differences and are carried out by a wet technique. After removal of part of the resist layer, the uncovered substrate surface can be treated (etched, doped, oxidized, nitride treated, plated, etc.).

This photolithography process is repeated (Co more thaa 10 times) before the tree-dimensional circuit geometries necessary for a completed metal oxide semiconductor (MOS) or bipolar device are achieved. The struccure of an integrated circuit is complex, both in the topography of its surface and in its internal composition. Each element of this device has an intricate three 10 dimensional structure that must be reproduced exactly in every circuit. The structure is made up of many layers, each of uhich is a detailed pattern. Some of the layers lie vithin the silicon wafer and others are stacked on the top. The process is described in detail in the book of L.F. THOMPSON, C.G. WILSON and M.J. BOWDEN "Introduction to Microlithography", American Chemical Society 15 Symposium Series 219, Amer.Chem.Soc., Washington D.C., 1983.

As a result of the increasing density of very large scale integrated circuits, the minimum feature size of semiconductor devices decreases and the production processes become more difficult. Achieving a high resolution with good linevidth control on substrates with surface topography is a serious 20 problem. As a result of optical reflections and variations of resist thickness over high steps, linewidth control becomes very difficult and relatively thick resist layers are necessary. Since, for these snail features, lateral dimensions shrink more rapidly than vertical dimensions, higher height-to-width aspect ratios of resist images are required. In addition> dry etch techniques require 25 relative thick and stable resist patterns. However, thick resist layers limit resolution and give depth of focus problems for projection printing. Furthermore, swelling of negative resists in organic solvent developers also makes them unsuitable for high resolution microlithography and restricts the choice to the positive-acting diazoquinone resists. However, even these high contrast and 30 high resolution resists become insufficient when linewidths decrease to the micrometer and submicrometer regime.

Several approaches to obtain higher resolution and better linewidth control have been scudied during the past feu years. New exposure techniques are being investigated, such as electron beaia writings X-ray and deep UV 35 exposure. Electron beam lithography requires very costly equipment,, suffers from low throughput and is unable to produce high aspect ratios as a result of backscattering of electrons, i.e. the so-called proximity effect. X-ray exposure has very high resolution capabilities but equipment and resist materials are still in the developmental stage. The manufacturing of X-ray 5 masks is also a difficult operation. The use of deep UV light decreases diffraction effects, but resolution is still limited by swelling of the negative resists and positive deep UV resists with sufficient sensitivity are not yet available.

In order to eliminate the adverse effects of solvents during wet 10 developing, plasma development of photoresists has been considered (cf. J.N. SMITH, H.G. HUGHES, J.V. KELLER, H.R. GOODNER and T.E. WOOD, in Semiconductor International,^, (1979,n° 10, December) ,p.41-47). The dry development of resists is an important step towards achieving a totally dry microfabrication process, offering better process control, reproducibility 15 and cleanliness. In addition, dry development solves problems such as resolution loss by swelling (particularly in the case of negative resists) and handling of large amounts of inorganic or organic solvents. It also has a much better adaptability to automatic line fabrication processes. However, most dry development resist systems have a low contrast and undergo a serious reduction 20 of resist thickness during development.

Another approach to obtain high resolution and high aspect ratio consists in the use of the multi-layer resist systems. In these processes, excellent step coverage and dry etch resistance of a thick planarizing bottom layer are combined with the high resolution of a thin top imaging layer. Both layers can 25 be optimized for their specific requirements. After exposure and development of the thin top resist, the patterns obtained are transferred almost vertically into the thick underlying layer either by deep UV exposure and development or by oxygen-reactive ion etching. For the latter method, a third intemediate layer is sandwiched between the imaging and the planarizing layer. Usually, a 30 thin layer of plasma-deposited or spin-on silicon oxide is applied on top of the planarizing layer. The exposed and developed patterns in the top resist layer are first transferred into the intermediate (silicon oxide) layer by etching techniques. After romoval of the resist, the thin oxide patterns act as a very effective mask for oxygen-reactive ion etching of the thick bottom 35 layer, resulting in profiles with almost vertical sideualls. Aluminium or silicon nitride have also been used as intermediate layer.

With these techniques, high resolution and high aspect ratios can be realized on substrates with surface topography (cf. J.M. MORAN and D. MAYDAN in the Bell System Technical Journal, 58, (19 79. n°5,May-June, p.1027-1036).

However, the multi-layer resist systems have also several serious draw backs. Thus, formation of interfacial layers occurs when one polymer material is spun on another. Hard bake steps may somewhat reduce this phenomenon but even then additions! treatments are required to remove these layers before pattern transfer. However, baking may induce film stress. Spun-on silicon oxide 10 films are very susceptible to cracking when the baking temperature is too high. On the other hand, a sufficiently high baking temperature is required to avoid interfacial mixing between the oxide and the imaging layer.

Another problem is the optical interference effects. Even with a highly absorptive bottom layer, reflections can occur at the interfaces, resulting in 15 standing waves. A post-exposure bake of the imaging layer can reduce this effect but only at the expense of a contrast loss.

Finally, the thin top resist layers which ere used in multi-layer systems to produce better images make the system more susceptible to pinhole problems. Multi-layer resist systems are discussed in depth by B.J. LIN in the above-20 mentioned book "Introduction to Microlithography", p.287-350.

Another major disadvantage of multi-layer systems is process complexity. Several layers have to be applied and baked and each of them has to be exposed, developed and/or etched. Therefore, efforts have recently been made to simplify these multi-layer systems, without losing their advantages. One 25 example is the two-layer reactive ion etching (RIE) process in which the top imaging layer is a resist containing both organic and inorganic components (for example, poly(dimethyl siloxane) and poly(vinyl-methyl siloxane) (cf.

M. HATZAKIS eit al., in Proceedings of the International Conference on Microlitho-graphy, 1981, p.386-396), copolymers of chloromethylstyrene and trimethylsilyl-30 styrene (cf. M. SUZUKI « al., in J.Electrochem.Soc.130,(1983),P■1962-1964) and copolymers of vinyltrimethylsilane and sulfur dioxide (U.S.Patent Specification No. 4,357,369). The thin top resist layer is exposed and developed, followed by etching of the thick bottom layer by oxygen RIE. During this process, the inorganic components in the resist form refractive oitides 35 which act aa an in situ-formed etch mask. In this way, the top imaging layer -• 5 - and Che intermediate silicon oxide layer of Che three-layer resist system are combined into one organo-metallic resist layer. Processing of these systems is easier than the three-layer resists but is still more complex than single layer resist systems. They have also only been developed so far for 5 electron beam and deep UV exposure and still require wet development in organic solvents. Another example of a simplified multi-layer system consists in the use of a contrast enhancement layer. In this process, a thin photo- * bleachable layer is coated over a standard positive photoresist. During exposure, the dye in the coating bleaches, forming a new mask in intimate 10 contact with the resist surface- After exposure, the layer is removed in a l solvent system and the resist is further processed by standard techniques.

Although this method improves contrast and adds little to the process complexity, it does not overcome the standing waves problem and linewidth variations over steps, In addition, extended exposure times are required.

The ideal would obviously be to have at its disposal a single layer resist system affording the same technical advantages as multi-layer resist systems, but which does not have their drawbacks. In this way, the formation of interfacial layers, optical interference effects and film stress problems would disappear and process complexity would be drastically reduced.

However, the difficulty is to find a single layer resist system, which can be dry developed and which is characterized at the same time by high resolution, high aspect ratios and excellent linewidth control on substrates with surface topography, in order to obtain high quality resist patterns which enable the production with a good reproductibility of very large scale semiconductor 25 circuits.

That is the reason why various attempts have been made in order to improve the single layer resist systems. As an example, in Japanese patent application n" 23937/82, a process is described in which a positive photoresist, coated on a substrate, is exposed to an atmosphere containing an 30 organic silicon compound, more particularly hexantethyIdisilazane. After exposure to ultraviolet light, the photoresist is developed in a conventional manner by dissolving the exposed areas with an alkaline liquid developer. The treatment with the hexamethyldisilazane vapors has as effect to reduce the developing rate of the photoresist in the alkaline developing solution, thus permitting the formation of a resist pattern having a higher contrast (more vertical edges).

It must be emphasized that, apart from the treatment with the hexamethyldisi lazane vapor, this process does not differ in any tray from the conventional 5 photolithographic process. The image formation is still based on solubility differences produced by the creation of carboxylic groups in the photoresist under the effect of the ultraviolet light and developmant is exclusively carried out by wet development in an alkaline developer. Even if the contrast » is enhanced by this process, the we 11 known drawbacks of wet development are 10 not suppressed. The light exposure has to be effected in depth in the resist i layer, with the consequence that effects such as reflections and standing waves cannot be suppressed. This can give rise to linewidth variations (especially on a reflective topography).

D. FOLLET al. ("Polarity reversal of PKMA by treatment with chlorosila-15 nes" - The Electrochemical Society Extended Abstracts,82-2 (1982, October 17-21), p.321-322) describe a process in uhich a poly(methyl methacrylate) resin (hereafter called PMMA) is electron beam irradiated, then sequentially treated with dichlorodimethyIsilane and water vapor, to form polysiloxanes, and finally, developed in an oxygen plasma. According to these authors, there would be 20 selective diffusion of the dichlorodimethylsilane in the irradiated and partially degraded areas of the resist, followed by polymerization of the chlorosilane upon exposure to the water vapor. They find a polarity reversal of the resist from positive into negative: the irradiated and treated areas of the PMMA. offer indeed a higher resistance to the oxygen plasma. A pattern is 25 obtained consisting of 2 lines and h jm spaces and abrupt edge profiles.

This process has nevertheless several important drawbacks. Electron beam exposure, even if it allows a high resolution, requires a very expensive equipment, and the irradiation times per silicon wafer are too long. Because of these limitations, up to the present electron beam lithography is only 30 used for direct writing of patterns for devices intended for research. Moreover, PKMA is a material which offers a very weak resistance to dry etching operations because it degrades very rapidly in the plasmas used to this end (5 times faster than the aromatic polymers). Finally, owing to the fact that dichlorodimethyl- 7 - 3ilane is not immediately fixed in the irradiated areas of the PMMA layer (since water vapor is necessary for the conversion in polysiloxanes), it is conceivable that this compound can easily go out again from the layer by diffusion. This will necessarily have a detrimental effect on the reproductibi-5 lity of the characteristics of the obtained patterns, since the concentration of the dichlorodimethylsilane in the layer will be a function of the time which elapses between the treatment with this compound and the treatment with the water vapor.

T.M. WOLF et al., in J.Electrochem.Soc.131,(1984,n"7),p.1664-1670. 10 propose still another process intended to improve the single layer resist systems. The photoresists used by these authors are negative photoresists conventionally used in photolithography. They consist of a partially cyclized polyisoprene containing a bis-azide as photosensitizer (commercial WAYCOAT tC-43 and SELECTILUX N-60). The proposed process comprises the steps of 15 ultraviolet irradiation or electron beam exposure, treatment with a volatile inorganic halide, followed by development by oxygen-reactive ion etching. In the described experiments, these authors use silicon tetrachloride (SiCl^), tin tetrachloride (SnCl^) and dichlorodimethylsilane ((CH^^SiClj) as volatile inorganic halides, since these compounds are able to react with the secondary 20 amines created during the photolysis of the resist. They hoped indeed that this reaction could be used to incorporate the inorganic halides selectively into the exposed areas of the resist, thus allowing the formation by oxidation of a thick inorganic oxide protecting layer in said exposed areas during the following development step by oxygen-reactive ion etching. Only the unexposed 25 areas of the photoresist would thus be removed selectively by oxygen-reactive ion etching.

Nevertheless, they find that the inorganic compounds are sorbed quickly, not only in the exposed areas, but also in the unexposed areas of the resist.

Moreover, they note that, contrary to all expectations, by oxygen-30 reactive ion etching, the unexposed areas of the photoresist are protected by an oxide layer and etched at a significantly lower rate than the exposed areas, whereas these latter are selectively removed during the dry etching development step. In other words, the photoresist behaves as a positive tone resist. The authors explain this phenomenon by the fact that, in the 35 unexposed areas, complexes between the inorganic halide and the azide group of the photosensitizer are also formed, while in the exposed areas, the anticipated reaction with the photolysis products of the resist takes place. Moreover, in the unexposed areas, the formed complexes are readily hydrolyzed by the water vapor present in the ambient atmosphere and converted to refractory inorganic oxides, thus forming an in situ protective masking layer, whereas the reaction products formed in the exposed areas are more slowly hydrolyzed and therefore readily removed as volatile compounds during oxygen-reactive ion etching.

Nevertheless, this process still has important drawbacks.

First, according to the statements made by the authors themselves, this process is satisfactory only provided very strict light exposure times and at the same time very strict treatment times with the inorganic halide are observed. Indeed, in order to obtain a satisfactory result, it is necessary that the exposure of the photoresist to light takes place during 16 seconds and that the treatment with the inorganic halide takes place during 7 seconds. Shorter or longer exposure and/or treatment times give unsatisfactory results. Thus, for example, after a treatment i-rich the inorganic halide for 10 seconds, it is no longer possible to develop the resist by etching, regardless of exposure time. In other words, the operating conditions are very critical, which can only be detrimental to the reproductibility of the resulcs.

Secondly, even in the optimal conditions cited hereinbefore, only 70S of the initial thickness of the photoresist remains after development by dry etching.

Thirdly, as shown in figure 11 of page 1669 of the publication, there remains after development, an important residue in the uncovered/,' "wttlh res idue is very difficult to remove (this fact shows at the same time that the selectivity of the process is insufficient).

To conclude, it can be seen that till now, a microlithographic process has not yet been developed in which a single layer resist system is used which is entirely satisfactory.

It is for these reasons that we have carried out research work to develop a single layer microlithographic process, which would be free from the drawbacks of the hitherto knotm processes, particularly of those described in Japanese patent application n° 23937/32 and in the above mentioned publications of D. FOLLET et^ al., and of T.M. WOLF et al.

This object is fully achieved by the process described hereinafter, which has all the advantages and the simplicity of single layer microlitho- graphy, which allows the use of dry etching techniques, which can be used on standard projection printing equipment and wafer stepper equipment, and /et gives equal or better subiaicrometer resolution than the above-mentioned multi-layer processes.

Thus the present invention provides a process for the foraation of negative patterns in a photresist layer,, comprising the following steps: (a) coating of a substrate with a layer of photosensitive resin comprising a polymer having functional groups capable of reacting with a silicon compound, said polymer being mixed or bound by a chemical bbund to a diazoquinone, said layer having a property of enabling a silicon compound to diffuse selectively into its irradiated portions when it has been exposed to a visible or ultraviolet radiation in said portions; (b) exposure of the layer of photosensitive resin to ultraviolet or visible light throuah a mask to exoose only selected portions of the layer; (c) treatment of the layer of photosensitive resin with a silicon compound, so that this compound is selectively absorbed into the irradiated portions of the layer and reacts with the said functional groups of the photosensitive resin in said irradiated portions,, said silicon compound being a silylating agent; and (d) dry development by plasma etching of the thus treated layer of the thus 20 treated layer of photosensitive resin to remove selectively the non-irradiated portions thereof in order to obtain the desired negative pattern.

According to a preferred embodiment of the present invention, the substrate is a silicon wafer, the photosensitive resin used comprises a phenolic polymer and the photosensitive compound which is mixed or bound to it is a diazoquinone, whereas the silicon compound is an easily vaporizable silylating agent.

According to a particularly preferred embodiment of the present invention, the phenolic polymer is chemically bound to the diazoquinone.

On the other hand, according to the present invention, the treatment with the silicon compound is preferably carried out after exposure of the photo-30 sensitive resin layer to ultraviolet or visible light. However, chose skilled in the art will understand chat, for the purpose of simplicity and readiness of execution, it is possible to carry out the treatment with the silicon compound already during the exposure of Che photosensitive resin layer to light. In other words, it is possible to conduct steps (b) and (c) of the w process simultaneously.

According to a particularly preferred embodiment, the silicon compound is volatilized and brought into contact in vapor form with the photosensitive resin layer- According to a particularly advantageous embodiment of the invention, dry 5 development is carried out by oxygen-reactive ion or oxygen plasma etching.

The invention further comprises the use of the new microlithographic process in the manufacture of integrated semiconductor circuits.

The process according to the invention is based on the surprising discovery that positive acting photosensitive resins, comprising a polymer i 10 associated with a diazoquinone, undergo substantial modifications of their properties under the influence of a visible or ultraviolet radiation. He have found indeed that the exposure to the radiation modifies to a considerable extent the permeability properties of these resins, and we have taken advantage of this particularity in order to 15 better differentiate the irradiated portions from the non-irradiated portions of a layer of these resins coated on a substrate, and in consequence, to develop an improved single layer microlitivographic process. To this end, according to the invention, the irradiated photosensitive resin layer is subjected to a treatment with a silicon compound, in order to allow, thanks iO to the particularity just mentioned hereinbefore, this compound to penetrate selectively in the irradiated portions of the layer, preferably in the top part thereof, and consequently fix selectively in these irradiated portions by reaction with the functional groups of the photosensitive resin.

Experience has shown that the silicon compounds actually diffuse 25 selectively in the irradiated portions of the layer, whereas such a diffusion does practically not occur in the non-irradiated portions, or only to a minor extent.

Thus, unlike the process of T.M. WOLF e£ al. above described, the silicon compounds do noc diffuse in all the regions of the photoresist layer, but only 30 in the irradiated portions of this layer.

The process of the invention is thus based on selective diffusion of the silicon compounds in the irradiated portions of the photoresist, unlike the process of the state of the art, which is exclusively based on a selective reaction of the silicon compounds in either the exposed or the unexposed regions (the silicon compounds being incorporated in every region of the photoresi st).

From the technical point of view, this difference has considerable 5 repercussions on the results because, in the process according to the invention, after development by dry plasma etching, superior quality patterns are obtained. Moreover, the above-mentioned disadvantages of the known single layer processes are definitively suppressed. By dry etching, the non-irradiated portions of the photoresist are completely removed and, in the 10 irradiated portions, a silicon oxide mask is very quickly formed j_n situ, which remains and protects very efficiently these portions throughout the etching process. After development, the thickness of the obtained pactern is practically identical to the initial thickness of the photoresist; the residual thickness generally represents more than 95% of the initial thickness 15 of the resin layer coated on the substrate. In the uncovered parts, no residue remains. Moreover, the reproducibility is considerably improved since the light exposure times and the treatment times uith the silicon compound do practically not have any effect on the results (contrary to the process of T.M. WOLF et^ al. above described).

Thus, the present invention provides a single layer resist system which can be dry developed and which has all the advantages of the multi-layer resists: planarization, high resolution, high aspect ratios with excellent retention of the initial thickness of the photosensitive resin layer coated on the substrate, good linewidth control over the steps, good reproductibility 25 of the pattern characteristics and suppression of the interference with light reflected at substrate topography. In addition, the described system has several advantages over the multi-layer resist systems. Formation of interfacial layers does not occur, interference with reflected listth does not occur, film stress problems do not exist and process complexity is drastically 30 reduced.

Even if the process of the invention provides a negative acting resist system, it does not need wet development, which definitively suppresses the problems of resolution losses caused by the swelling in development solvents. Moreover, since no solvents are used in the development step, adhesion is no 35 longer a critical parameter. The completely dry processing of che resist results in improved process control and makes this system particularly suitable for automatic line fabrication processes.

The invention will not; be further described uith reference to the accompanying drawing wherein like reference numerals refer to same parts 5 throughout the several views, wherein the layers are greacly exaggerated.

Figure 1 is a partial cross-section of a silicon wafer coated with a photosensitive resin layer before the exposure step.

Figure 2 is a partial cross-section of a silicon wafer coated with a photosensitive resin layer during its exposure to light through a mask.

Figure 3 is a partial cross-section of a silicon wafer coated with a photosensitive resin layer after the treatment with the silicon compound.

Figure 4 is a partial cross-section of a negative pattern obtained after development by oxygen-reactive ion or oxygen plasma etching.

A wide range of oolymers can be used in order to prepare the IS photosensitive resin used in the process according to the invention. However, preferably a phenolic polymer is used, which is selected from: - the condensation products of a phenol, a naphthol or a derivative thereof ring-substituted by an alkyl or aryl radical or a halogen atom, with an aliphatic or aromatic aldehyde, which can be substituted by a halogen atom, - the poly(vinylphenols), the phenolic group of which can be substituted by an alkyl or aryl radical or a halogen atom, - the copolymers of a vinylphenol uith an ethylenically unsaturated compound, and - mixtures of the aforesaid polymers between them or with other aromatic 25 polymers, such as polystyrene or p-(N-vinylcarbazole).

As illustrative but not limitative examples of phenolic polymers, there may be mentioned: phenol-novolacs, cresol-novolacs, condensation products of formaldehyde with alkylphenols (p-tert-butylphenol; p-n-propylphenol; p-ethylphenol; octylphenol and the like), condensation products of benzaldehyde 30 with cresols or naphthols (e.g. l-naphthol), poly(p-vinylphenols), copolymers of p-vinylphenols with p-chlorostyrene, and the like.

The photoactive compound mixed or bound to the polymer is < a diazoquinone such as those used in traditional positive pboto- - 13 resists (see British Patent Specification No. 711,626). As non-limitative examples of these diazoquinones, there may be mentioned: 5-diazo-5,6-dihydro-6-oxo-l-naphthalenesulfonic acid, 6-diazo-5,6-dihydro-5-oito-l-naphthalene-sulfonic acid, 3-diazo-3,4-dihydro-4-oxo-l-naphthalenesulfonic acid, 4-5 diazo-3,4-dihydro-3-oxo-l-naphthalenesulfonic acid, 3-dijzo-J,4-diliyuro- 4-oxo-l-benzenesulfonic acid, the corresponding carboxylic acids, derivatives thereof and mixtures of at least two of the aforesaid compounds.

As an example of a derivative of the aforesaid acids, the condensation t product of 3 moles of 6-diazo-5,6-dihydro-5-oxo-l-naphthalenesulfonyl chloride 10 with 1 mole of 2,3,4-trihydroxybenzophenone may be mentioned. i The photoactive compounds such as diazoquinones can easily be chemically bound to the aforesaid polymers by conventional synthetic processes (see U.S.Patent Specification No. 3,046,119); a typical well-known reaction is the reaction of the derivacives of these photoactive compounds carrying a sulfonyl IS chloride substituent (or carbonyl chloride) with the hydroxyl groups of the phenolic polymers, with formation of sulfonates (or carboxylates).

As shown in-Figure 1, in the first step of the process of the invention, a thick photosensitive resin layer (1) is coated on a silicon wafer or substrate (2). This coating is generally effected by spin-coating from a 20 dilute solution of the photosensitive resin in a suitable solvent. The thickness of the photosensitive resin layer may vary depending upon the topography of the substrate. The presence of the polymer in the photosensitive resin facilitates formation of smooth, even-levelled surfaces on the substrate. 23 When the photosensitive resin is coated on the substrate from a dilute solution in a solvent, Che solvent may be selecced from a wide range of products, depending on solubility parameters, evaporation rate at processing temperatures and desired Theological characteriscics. Examples of solvencs which can be used include ketones, esters such as acetates, propionates, and 30 the like, ethers, echer escers, polyechers, alcohols, aliphatic and aromatic hydrocarbons, tetrahydrofuran, dimethylformamide, pyrolidones, and the like.

The nature of the solvent is irrelevant to the subject of the present invention as long as a solution is obtained with film-forming properties. The concentra- • tion of the solution depends upon the required thickness of the photosensitive 35 resin layer.

After having been coated on the substrate, the photosensitive resin layer (1) is generally dried by baking to remove the solvent.

The conditions used during this baking step are not critical, as long as solvent is efficiently removed and a tack-free surface is obtained. In 5 practice, temperatures of about 50° to about 150*C, and preferably of about 80 to 120°C are used. The baking time can be shortened when the baking temperature is increased. This time will also depend upon the ease of evaporation of the solvent, or of the solvent mixture used. Baking time used in practice varies between a few seconds and 1 hour. After baking, the 10 thickness of the photosensitive resin layer (l> is generally between 1 and 2,5 yuan.

As is shown in Figure 2, the subscrate (2) coated with the photosensitive resin layer (I) is then exposed to visible or ultraviolet radiation (3) through a photoimaging mask (4). The vavelenght of the applied radiation can 15 vary within a range of from about 100 to 600 nm, preferably of from about 350 to 450 nm. Under the effect of vimible or ultraviolet radiation, the chemical and physical properties of the irradiated portions (5) of the photosensitive resin layer undergo considerable modifications as compared with the non-irradiated portions.

Though mechanisms of the reaction and/or decomposition caused by the exposure to visible or ultraviolet light have not been fully elucidated yet, it is well known that, when the photoactive compound is a diazoquinone, nitrogen is evolved and an indenecarboxylic acid is formed, in the presence of water. However, as already explained above, a very substantial modification of the 25 permeability properties of the photosensitive resin layer occurs simultaneously.

The visible or ultraviolet exposure energy can be adjusted so as to induce this modification of the permeability in the photosensitive resin layer at the desired depth. According to a preferred embodiment of the process of the invention, this modification is only induced in the top part, near the 30 surface of the layer.

Typically, but not in a limitative manner, the applied exposure energy may vary from 10 to 130 millijoules per square centimeter, measured at a wavelenght of 400 nm; the quantity of energy to be applied depends obviously on the nature of the photosensitive resin and of the silicon compound used 35 in the following step of the process.

Light absorbance of the photosensitive resin layer can possibly be increased by adding specific dyes, as described by M.M. 0'TOOLE, E.D. LIU and M.S. CHANG in Proc. SPIE Int.Soc.Opt.Eng.,275,(1981) (Semicond.Microlithogr. VI),p.128-135 and by M. CHEN et al., in U.S. Patent Specification 5 No. 4,362,809. These dyes should absorb significantly at the wavelenghts used to expose the photosensitive resin (100 to 600 nm, preferably 350-450 , but they have to be transparent in a part of the visible region to make alignment possible during printing. A proper concentration of such a dye will restrict exposure to a thin upper layer in the photoresist. Photosensitizers or other 10 similar agents can also be added to the photosensitive resin.

As already explained above, the treatment of the photosensitive resin layer uith the silicon compound can be effected during the exposure to light, but preferably after this exposure, for simple reasons of ease of handling.

Furthermore, this treatment can be carried out in the liquid or in the 15 vapor phase. According to a preferred embodiment of the invention, this treatment is carried out in the vapor phase. This latter process is preferred since it enables the use of silicon compounds and more particularly of silylating agents easily vaporizable at appropriate temperatures and pressures.

As non-limitative examples of useful silicon compounds, the following 20 silylating agents can be mentioned: tetrachlorosilane and alkyl- and aryl-halosilanes (e.g. trimethylchlorosilane, dimethyldichlorosilane, methy1-trichlorosilane, trimethylbromosilane, trimethyliodosilane, triphenylchloro-silane), disilazanes (e.g. hexamethyldisilazane, heptamethyldisilazane. hexaphenyldisilazane and 1,3-bis(chloromethy1)-1,1,3,3-tetraraethyldisilazane), 25 N-trimethylsilylimidazole, N-trimethylsilylacetamide, N-trimethylsily1- dimethylamine, N-trimethylsilyldiethylamine, hexamethylsilanediamine, N,0-bis(triethylsilyl)acetimide, N,N'-bia(trimethyIsilyl)urea, N,N'-diphenyl-N-(trimethylsilyl)urea and mixtures of at least tuo of these compounds.

The treatment of the photosensitive resin layer with the silicon compound 30 can be carried out in a separate reaction chamber or in a wafer stepper equipment.

The treatment with the silicon compound produces, as already explained above, the selective diffusion of the silicon compound in the irradiated portions (5) of the layer; this compound is then fixed in these portions by 35 reacting with the functional groups of the resin. On the other hand, in the non-irradiated portions, there is practically no diffusion of the silicon compound or only to a minor extent at the surface. Thus, the incorporation of the silicon compound occurs only in the irradiated portions of the layer, and not in the non-irradiated portions thereof. This fact has been ascertained by analysis with AUGER electron spectroscopy (see example 12).

As is shown in Figure 3, the silicon compound can advantageously be built into the top part (6) of the irradiated portions (S) of the photosensitive resin layer. The thickness of the silicon-containing layer is governed by the laws of diffusion and will vary with the nature of the silicon compound and its concentration and the composition of the photosensitive resin. For a given system, it will depend upon the exposure dose, the time, the temperature and the pressure of the treatment, and, therefore, can be directed by readily controllable parameters.

Since imaging can occur in a very thin planar layer at the top part of the photoresist, high quality images can be obtained by standard projection printing vith sharply focussed light. It will indeed be sufficient to limit light exposure to a thin layer at the top part of the photosensitive resin, in such a way chat light is sufficiently extinguished by absorption in che remaining part of the layer, before interference of reflected light can occur. As a result, problems such as standing waves and linewidth variations over highly reflective steps, such as metal interconnectors, are eliminated.

The treatment of the photosensitive resin layer with the silicon compound is carried out at a suitable temperature, which depends of the nature of the resin and of the silicon compound used; this temperature is selected in such a manner that a selective diffusion of the silicon compound occurs in the irradiated portions of the resin; it can be selected between the volatilization temperature of the silicon compound (which depends itself of the pressure prevailing in the system, which may vary from a relative vacuum to several bars) and the thermal decomposition temperature of the components of the photosensitive resin. Practically, the temperature of this treatment can vary within a range of from about -20 to 150°C, and preferably of from 60 to 140°C.

The time of the treatment with the silicon compound is not critical; it depends essentially on the temperature used, and accessorily on the nature of the photosensitive resin and of the silicon compound. Practically, this tine can vary between a few seconds and one hour and preferably between 1 and 45 minutes.

After treatment of the photosensitive resin with the silicon compound, excess thereof may be removed for reasons of further ease of handling; this removal, is preferably carried out by vacuum evaporation. Nevertheless, it is 5 not compulsory to remove excess silicon compound, since the qualities of the patterns obtained by the process of the invention are as quite as good without the removal of excess silicon compound as with this removal; this can be explained by the fact that the silicon compound does pratically not diffuse in the non-irradiated portions of Che photosensitive resin and that these 10 portions are thus easily removed by the further development by dry etcning by means of oxygen gas plasma or oxygen-reactive ion etching.

In Che last step of the process of the invention, the photosensitive resin layer treated as described above, is dry developed using preferably an oxygen plasma or oxygen-reactive ion etching technique. These techniques, as well as 15 devices used for their execution, are well known by those skilled in the art and need not be described in decail.

As is shown in Figure 4, development by dry eCching has as consequence that the non-irradiated portions of the photoresist are quickly removed, whereas che irradiaced porCions (5) resisC perfeccly owing Co the iii situ 20 formed silicon oxide etch mask.

Uhen the non-irradiated portions are completely removed up to che surface of the substrate (2), excellent quality negative patterns are obtained. Indeed, as is further shown in the examples, these patterns have vertical side-walls, high resolution, whereby lines of less than laIf a micrometer wide and spaces 25 near half a micrometer wide can be obtained, a perfecC recencion of Che initiaL resist layer thickness, no measurable variation in linewidth over steps and high aspect ratios, with heights over 2 micrometers. Furthermore, the uncovered regions contain no residue.

The following examples are given only for the purpose of illustrating 30 the present invention. In these examples, the values given for the UV exposure energy are measured at a wavelength of 400 nanometers.

Example 1.

Silicon wafers wich thermal oxide of approximately 120 nanometers thickness are primed with hexamethyldisilazane as adhesion promoter. As photosensitive 35 resin, the partial escerification product of 6-diaro-5,o-dihydro-5-oxo-l- naphthalenesulfonic chloride uith the condensation product of p-tert-buty l-pheool and formaldehyde, is used. This resin is dissolved in a solvent mixture containing 80* by weight of 2-ethoxyetiianol, IOZ by weight of xylene and 102 by weight of n-butyl acetate, in order to obtain a 25% by weight 5 solution.

This solution is spin-coated on the silicon wafers at a spin speed of 3000 rpm. In this way, a resin layer of 1.7 yim thickness is obtained on each wafer.

The thus coated wafers are baked in a convection oven at 90°C for 30 minutes. Then they are exposed through a pattern mask to UV rays, in a conventional equipment producing UV light, the wavelength of which lies 2 between 350 and 440 nanometers; the exposure energy is 60 mj/cm .

The exposed wafers are then treated with hexamethyldisilazane vapor at 91°C for 4 minutes.

After development by oxygen-reactive ion etching, negative patterns with vertical side-walls are obtained in the exposed parts. Furthermore, the thickness of the patterns is practically identical to the initial thickness of the resin layer coated on each wafer.

Example 2.

The procedure of Example 1 is followed, but che photosensitive resin used consists of a mixture of 100 g of a commercial cresol-formaldehyde novolac and 25 g of the condensation product of three moles of 6-diazo-5,6-dihydro-5-oxo-l-naphthalenesulfonic chloride with one mole of 2,3,4-trihydroxybenzo-phenone. This mixture is dissolved in 250 g of a solvent mixture containing 25 80S by weight of 2-ethoxyethanol. 10% by weight of xylene and 10% by weight of n-butyl acetate. The formed resin layer has a thickness of 1.4 ^im. After prebaking, it is exposed to UV rays through a mask, the exposure energy being 2 70 mJ/cm , then treated with hexamethyldisilazane vapor during 30 minutes at 65°C. After development, negative patterns having a residual thickness of 30 1.2 yim are obtained, i.e. 86a of the initial resin layer thickness.

Example 3.

The procedure of Example I is followed, but the photosensitive resin used is prepared by partial esterification of a commercial cresol-formaldehyde novolac with 6-diazo-5,6-dihydro-5-oso-l-naphthalenesulfonic chloride. 25 g of 35 this resin are dissolved in 100 g of 2-ethoicyethyl acetate. The formed resin layer has a thickness of 1.5 yim. After prebaking, it is exposed to UV rays through a uwistc, the exposure energy being 85 mJ/cra2, then treated with hexamethyldisilazane vapor for 10 minutes at 80°C. Afti-r development, negative patterns with a residual thickness of 1.4 yim are obtained, i.e. 93% of the 5 initial resin layer thickness.

Example 4.

The procedure of Example 1 is followed, but the photosensitive resin used is the partial esterification product of 6-diazo-5,6-dihydro-5-oxo-l-naphthalenesulfonic chloride with poly(p-vinyIphenol). 25 g of this resin are 10 dissolved in 100 g of 2-ethoxyethyl acetate. The formed resin layer has a thickness of 1.7 ^im. After prebaking, it is exposed to UV rays through a mask, the exposure energy being 85 mJ/cm2, then treated with hexamethyldisilazane vapor for 3 minutes at 125°C. The negative patterns obtained after development have vertical side-walls;they have a residual thickness of 1.65 ^im, i.e. 97% 15 of the initial resin layer thickness.

Example 5.

This Example shows that the presence of the photoactive compound is essential to obtain a selective reaction in the exposed areas of the photo-resin layer; it proves, moreover, that the silicon compound is able to react 20 with the phenolic polymer.

The procedure of Example 1 is followed, but a non-photosensitive resin is used consisting solely of poly(p-vinyIphenol) i.e. without photoactive compound. 25 g of this resin are dissolved in 100 g of 2-ethoxyethyl acetate, and this solution is spin-coated on silicon wafers so as to obtain a resin 25 layer of 1.7 um thickness. After prebaking, this layer is exposed to UV rays ' t 7 through a mask, the exposure energy being 130 mJ/cm . The samples are then treated in two different ways with hexamethyldisilazane vapor: a) at 130°C during 30 minutes. In this case, development by oxygen-reactive ion etching results in complete removal of the resin layer, without patterns being obtained; b) at 155*0 during 10 minutes. In this case, the resin layer is completely resistant to oxygen-reactive ion etching. No noticeable decrease of its thickness occurs, even after prolonged etching. No patterns are obtained.

Example 6.

The procedure of Example 1 is followed, but the photosensitive resin used is prepared by partial esterification of the condensation product of p-n-p ropy Iphenol and formaldehyde, with 6—diaio-5,6-dihydro-5—oxo-l-naphthalene-sulfonic chloride. 30 g of this resin are dissolved in lOO g of 4-methy1-2-puntanone. The formed resin layer has a thickness of 2.3 yjm. After prebaking, 5 it is exposed to UV rays through a mask, the exposure energy being 85 mJ/cm , then treated for 8 minutes at 11S°C uith hexamethyldisilazane vapor.

Development affords negative patterns uith high resolution (lines oi 0.45 jan wide and spaces 0.85 yimwide), uith vertical side-trails; they have a residual * thickness of 2.15 ym, i.e. about 94Z of the initial resin layer thickness.

LO Example 7.

* The procedure of Example I is followed, but che photosensitive resin used consisb of a mixture of 10 g of polystyrene and 20 g of the partial esterifica-tion product of 6-diazo-5,6-dihydro-5-oxo-l-naphthalenesulfonic chloride uith the condensation product of p-ethylphenol and formaldehyde. This mixture is dissolved in 100 g of cyclohexanone. A layer of 1.8 yim thickness is formed, which after prebaking, is exposed to UV rays through a mask, the exposure 2 energy being 110 nsJ/cm . This layer is then treated with trimsthylchlorosilane vapor for 10 minutes at 100°C. After development, high resolution negative patterns with vertical side-walls and a residual thickness of 1.5 are 20 obtained, i.e. about 85* of the initial resin layer thickness.

Example 8.

The procedure of Example 1 is followed, but the photosensitive resin consists of the partial esterification product of 6-diazo-5,6-dihydro-5-oxo-l-naphthalenesulfonic chloride with the condensation product of cresols and 25 benzaldehyde. 25 g of this resin are dissolved in 100 g of bis(2-methoxyethyl)-ether. The formed resin layer has a thickness of 1.7 jm. After prebaking, it is exposed to UV rays through a mask, the exposure energy being 90 mJ/cm^, then treated for 8 minutes at 125aC with hexamethyldisilazane vapor. After development, high resolution negative patterns with vertical side-walls and a 30 residual thickness of 1.6 are obtained, i.e. 94& of the initial resin layer thickness.

Example 9.

The procedure of Example 1 is followed, but the photosensitive resin * consists of a mixture of 3 g of poly(N-vinylcarbazole) and 20 g of the partial 35 esterification product of 6-diazo-5,6-dihydro-5-oxo-l-naphthalenesulfonic chloride with the condensation product of l-naphtol and benzaldehyde. This mixture is dissolved ia 100 g of bis(2-methoxyethyl)ether. The formed resin layer has a thickness of 1.8 yim. After prebaking on a hot plate at 95°C for 45 seionds, it is exposed to UV rays through a mask, the exposure energy being 115 ml/cm , ihen treated for 10 minutes at 120°C with liexametiiy ldi si lazane 5 vapor. After development, high resolution negative patterns with vertical side-walls and a residual thickness of 1.65 jm are obtained, i.e. 92% of the initial resin layer thickness.

Example 10.

The procedure of Example 1 is followed, but the photosensitive resin is 10 prepared by partial esterification of a copolymer of p-vinyIphenol and p- chlorostyrene, with S-diazo-5,6-dihydro-5-oxo-l-naphthalenesulfonic chloride. 25 g of this resin are dissolved in 1(H) g of S-methyl-2-hexanone. The formed resin layer has a thickness of 1.7 yim. After prebaking, it is exposed to UV rays through a mask, the exposure energy being 85 mJ/cm^, then treated 15 for 10 minutes at 125°C with hexamethyldisilazane vapor. After development, high resolution negative patterns with vertical side-walls and a residual thickness of 1.6 ^in are-obtained; i.e.- 94% of the initial resin layer thickness.

Example 11.

The procedure of Example 1 is followed, but the photosensitive resin is 20 prepared by partial esterification of 6-diazo-5,6-dihydro-5-oxo-l-naphchalene- sulfonic chloride with the condensation product of octylphenol and formaldehyde. 30 g of this resin are dissolved in 100 g of cyclohexanone- The formed resia layer has a thickness of 1.9 jm~ After prebaking at 95°C for 45 seconds on a hot place, it is exposed to UV rays through a mask, the exposure energy being 2 50 mJ/cm , then treated for 10 minutes at 125°C with hexamethyldisilazane vapor. Afcer development, high resolution negative patterns with vertical side-walls and a residual thickness of 1.7 yim are obtained, i.e. about 90% of the initial resin layer thickness.

Example 12.

This Example shows that the differentiation which occurs between the irradiated portions and the non-irradiated portions of the photosensitive resin, during its exposure to light, is essentially caused by an increase of the diffusion rate of the silicon compound in the irradiated portions of the resin.

This example shows at the sama time that the silicon compound penetrates 35 the more deeply in these irradiated portions the more the applied UV exposure dose is increased.

Silicon wafers uith thermal oxide of approximately 120 nm thickness are primed with hexamethyldisilazane as adhesion promotor. As photosensitive resin, the partial esterification product of 6-diazo-5,6-dihydro-5-oxo-l-naphthalene-sulfonic chloride with the condensation product of p-tert-butylphenol and formaldehyde, is used. 25 g of this resin are dissolved in 100 g cyclohexanone. The thus obtained solution is spin-coated on the silicon wafers so as to obtain a photosensitive resin layer of 1.5 ^im thickness.

The coated wafers are prebaked on a hot plate at 95°C for 45 seconds. They are then exposed to ultraviolet radiation, applying different exposure energies on each sample. Samples are thus obtained, which have received an exposure dose 2 respectively of 0, 13, 25, 38 and 50 mj/cm . The exposed wafers are then treated with hexamethyldisilazane vapor at 125°C for 10 minutes.

The samples prepared in this way are subjected to AUGER Electron Spectroscopy. Argon ion sputtering of the resist layer at a rate of 3 nm/minuce enables the depth profile of Che relative silicon concentration in the layer to be obtained. To this end, the intensity of the silicon peak, which is proportional to the concentration of silicon in the resist layer, is monitored as a function of sputter time.

It is found that the silicon concentration reaches a certain value, whatever the applied exposure dose may be. After a certain sputter tine, the intensity of the silicon peak decreases abruptly and the peak finally disappears. This time is clearly a function of the applied UV exposure dose. Thus, at exposure 2 doses of 0, 13, 25, 38 and 50 mj/cm , the silicon peaks disappear respectively after approximately 5, 20, 60, 110 and 160 minutes.

On the other hand, similar samples are prepared, in order to obtain patterns in the layer, subjecting them to the same treatment as described above, but followed by oxygen-reactive ion etching rather than AUGER spectroscopy. It thus appears that an exposure dose in between 13 and 25 mJ/cm^ is sufficient for good pattern formation. Taking into account the sputter rate of 3 nm/minute, it may be concluded that a penetration depth of the silicon compound in the resist Layer of approximately 100 nm slows down the etch rate sufficiently to allow complete clearance of the non-irradiated portions. This correlates well with the residual thicknesses of 90 to 95% obtained according the process of the invention.

The analysis by AUGER electron spectroscopy thus shows that the diffusion of the silicon compound in the resist is negligible, or insignificant, when it is not subjected to UV radiation (radiation energy =» 0). This analysis shows also that when the applied exposure dose increases, the silicon compound 5 penetrates more in depth in the resist layer, whereas the concentration of fixed silicon is independant of the applied exposure dose. This fact is best explained so that the conversion of the resist layer under the effect of the exposure, changes its pentieability and makes it possible for the silicon compound to selectively diffuse in the irradiated portions. 4

Claims

1. Process for the formation of negative patterns in a photoresist layer, comprising the following steps: 5 (a) coating of a substrate with a layer of photosensitive resin comprising a polynsr having functional groups capable of reacting with a silicon compound, said polymer being mined or bound by a chemical bound to a diazoquinone, said layer having the property of enabling a silicon compound to diffuse selectively into its Irradiated portions 10 when it has besn exposed to a visible or ultraviolet radiation in said portions; (b) exposure of the layer of photosensitive resin to ultraviolet or visible light through a mask to expose only selected portions of the layer; 15 (c) treatment of the layer of photosensitive resin with a silicon compound, so that this compound is selectively absorbed into the irradiated portions of the layer and reacts with the said functional groups of the photosensitive resin in said irradiated portions, said silicon compound being a silylating agent ; and 20 (d) dry development by plasma etching of the thus treated layer of photosensitive resin to remove selectively the non-irratiated portions thereof in order to obtain the desired negative pattern.

2. Process according to claim 1, wherein the diazoquinone is 25 selected from the group consisting of 5-diazo-5,6-dihydro-6-oxo-1-naphtha1enesu1fonic acid, 6-diazo-5,S-dihydro-5-oxo-l-naphthalenesu1fonic acid, 3-d i azo-3,4-d ihydro-4-oxo-1-naphthalenssu1fonic acid, 4-diazo-3,4-dihydro-3-oxo-l-naphthalenesulfonic acid, 30 3-diazo-3,4-dihydrO"4-oxo-l-benzenesulfon1c acid, the corresponding carboxylic acids, their derivatives and the mixtures of at least two of the aforesaid compounds.

3. Process according to any of claims 1 and 2, wherein the polymer 35 is a phenolic polymer.

4. Process according to claim 3, wherein the phenolic polynsr is -25- selected from - the condensation products of a phenol or a naphthol, or a derivative thereof ring-substituted by an alkyl or aryl radical or by a halogen atom, with an aliphatic or aromatic aldehyde, which can be substituted 5 by a halogen atom, - the poly(vinylphenols), the phenolic group of which can be substituted by an alkyl or an aryl radical or a halogen atom, - the copolymers of a vinvlphenol with ethylenically unsaturated t compounds, and 10 - the mixtures of the aforesaid polymers between them or with other aromatic polymers.

5. Process according to any of claims 1 to 4, wherein the photosensitive resin further comprises a dye. 15

6. Process according to any of claims 1 to 5, wherein the silicon compound is an easily vaporizable silylating agent.

7. Process according to any of claims 1 to 6, wherein the silicon 20 compound is a silylating agent selected from tetrachlorosilane, trimethylchlorosilane, dimathyldichlorosilane, msthyltrichlorosilane, trimethybromos i1ane, tr imethyliodosi1ane, tri phenylch1orosi1ane, hexamethy1d i s i1azane, heptamethy1di s i1azane, hexapheny1d i s i1azane, 1,3-bis(chloromethyl)-l,1,3,3-tetramethyldisilazane, 25 N-trimethylsilylimidazole, N-trimethylsilylacetamide, N-trimethylsilyldimethylamine, f3-trimethylsilyldiethylamine, hexamethylsilanediamine, H,0-bis(triethylsilyl)acetimide, (J.W'-bis(trimethylsilyl)urea, N,W'-diphenyl-N-(trimethylsily)urea and the mixtures of at least two of these compounds. 30

8. Process according to claim 7, wherein the silylating agent Is hexamethyldislazane.

9. Process according to any of claims 1 to 8, wherein the treament 1 35 of the layer of photsensitive resin with the silicon compound is carried out at a temperature between -20 and 150°C. >

10. Process according to claim 9, wherein the treatment -26- of the layer of photosensitive resin with the silicon compound is carried out at a temperature between 60 and 140°C.

11. Process according to any of claims 1 to 10, wherein the time of 5 the treatment of the layer of photosensitive resin with the silicon compound is between a few seconds and one hour.

12. Process according to claim 11, wherein the time of the treatment of the layer of photosensitive resin with the silicon compound is 10 between 1 and 45 minutes.

13. Process according to any of claims 1 to 12, wherein the dry development is carried out by oxygen reactive ion or oxygen plasma etching. 15

14. Use of the process according to any one of claims 1 to 13 for the manufacture of integrated semiconductor circuits.

15. A process of forming a negative pattern in a photoresist layer 20 substantially as hereinbefore described with reference to the accompanying drawings.

16. A process of forming a negative pattern in a photoresist layer substantially as hereinbefore describe with reference to the examples. 25

17. An intergrated semiconductor circuit made by a process as claimed in any of claims 1 to 13, 15 or 16. Dated this the 25th day of October 1985. 30 BY: TONKINS & CO., 4ppli\:ants' Agents, (Signed) 1^- 5, Dartmouth Road, DUBLIN 6. 35 -27-