IE56708B1

IE56708B1 - A process of forming a negative pattern in a photoresist layer

Info

Publication number: IE56708B1
Application number: IE2643/85A
Authority: IE
Original assignee: Ucb Electronics S A
Priority date: 1984-10-26
Filing date: 1985-10-25
Publication date: 1991-11-06
Also published as: EP0184567A1; JPS61107346A; JPH065385B2; EP0184567B1; ATE48708T1; JPH0456979B2; IL76702A0; IE852643L; GB8427149D0; KR860003674A; IL76702A; KR940004423B1; SU1498400A3; DE3574788D1; JPH0220869A; MY100941A; CA1275846C

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

The present invention relates to a new microlίthographic 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 I inewidth 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 active10 circuits per unit area on the surface of a semiconductor crystal.

As an illustration of this, reference is made to che 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 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, small quantities of impurities into specific regions of the semiconductor surface to produce the desired electrical characteristics of the circuit, such as transistor/eiemencVof 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 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.

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 che 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 (to more than 10 times) before the tree-dimensional circuit geometries necessary for a completed metal oxide semiconductor (MOS) or bipolar device are achieved. The structure 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 dimensional structure that must be reproduced exactly in every circuit. The 4 structure is made up of many layers, each of which is a detailed pattern. Some of the layers lie within the silicon wafer and others are stacked on the top.

The process is described in detail in the book of L.F. THOMPSONB C.G. WILSON and M.J- BOWDEN '*Introduction to Microlithography, American Chemical Society Symposium Series 219, Ame r. 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 1 inewidth control on substrates with surface topography is a serious problem. As a result of optical reflections and variations of resist thickness over high steps, Iinewidth control becomes very difficult and relatively thick resist layers are necessary. Since, for these small 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 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 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 studied during the past few years. New exposure techniques Λ are being investigated, such aa electron beam writing. X-ray and deep UV exposure. Electron beam lithography requires very costly equipment, suffers - 3 from low throughput and Is unable to produce high aspect ratios as a result of backseattering 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 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 developing, plasma development of photoresists has been considered (cf.

J.N. SMITH, H-G. HUGHES, J.V, KELLER, W.R. GOODNER and T.E. WOOD, in Semiconductor International,^,(1979,n°10, December),p.41-47L Tbe dry development of resists is an important step towards achieving a totally dry microfabrication process, offering better process control, reproducibility 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 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 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 intermediate layer is sandwiched between the imaging and the planarizing layer. Usually, a 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 removal of the resist, the thin oxide patterns act as a very effective mask for oxygen-reactive ion etching of the chick bottom layer, resulting in profiles with almost vertical sidewalls. Aluminium or - 6 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,(1979,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 additional treatments are required to remove these layers before pattern transfer. However, baking may induce film stress. Spun-on silicon oxide 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 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 are 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 above20 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 example is the two-layer reactive ion etching (RIB) 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 et al., in Proceedings of the International Conference on Microlitho graphy, 1981, p.386-396), copolymers of chloromethylstyrene and trimethylsilyl30 styrene (cf. M. SUZUKI et al., in J.Electrochem.Soc.00,(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 oxides which act as an in situ-formed etch mask. In this way, the top imaging layer - 5 and the 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 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 photobLeachable layer is coated over a standard positive photoresist. During exposure, the dye in the coating bleaches, forming a new mask in intimate contact with the resist surface. After exposure, the layer is removed in a i solvent system and the resist is further processed by standard techniques.

Although this method improves contrast and adds Little co 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 thisway, 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 ci rcui ts, 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 organic silicon compound, more particularly hexamethyldisilazane. 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 oust be emphasized that, apart from the treatment with the hexamethyldisilazane vapor, this process does not differ in any way from the conventional 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 well 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 et al. (Polarity reversal of PKMA by treatment with chlorosi La15 nes - The Electrochemical Society Extended Abstracts,82-2 (1982, October 1721), p.321-322) describe a process in which a poly(methyl methacrylate) resin (hereafter called PMMA) is electron beam irradiated, then sequentially treated with dichlorodimethylsilane and water vapor, to form polysiloxanes, and finally, developed in an oxygen plasma. According to these authors, there would be 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 obtained consisting of 2 lines and A ^an 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 used for direct writing of patterns for devices intended for research. Moreover, ΡΗΜΑ 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 silane 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 reproductibility 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,ne7),p.1664-1670, 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 IC43 and SELECTILUX N-60). The proposed process comprises the steps of 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^j^SiCl^) as volatile inorganic halides, since these compounds are able to react with the secondary 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 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 oxygenreactive 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 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 che resist takes place. Moreover, in Che unexposed areas, the formed complexes are readily hydrolyzed 5 by the water vapor present in the ambient atmosphere and converted to refractory inorganic oxides, thus forming an in situ protective masking layer, whereas che reaction products formed in the exposed areas are more slowly hydrolyzed and therefore readily removed as volatile compounds during oxygen*» reactive ion etching. j. Nevertheless, this process still has important drawbacks. 4 10 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. IS Shorter or longer exposure and/or treatment times give unsatisfactory results. Thus, for example, after a treatment with 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 results. 20 Secondly, even in the optimal conditions cited hereinbefore, only 702 of the initial thickness of the photoresist remains after development by dry etching. 25 Thirdly, as shown in figure 11 of page 1669 of the publication, there areas remains after development, an important residue in the uncovered/, wnich residue is very difficult to remove (this fact shows at the same time chat the selectivity of the process is insufficient). 30 * To conclude, it can be seen that till now, a microtithographic 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 che hitherto known processes, particularly of chose described in Japanese patent application n° 23937/92 and in the above mentioned publications of D. FOLLET etal., and of T.M. WOLF et al. 4 35 This object is fully achieved by the process described hereinafter, which has all the advantages and the simplicity of single layer raicrolitho- - 9 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 subraicrometer resolution than the above-mentioned multi-layer processes.

Thus the present invention provides a process for the formation 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 bound to a diazoquinone, said layer having a property of enabling a silicon io 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 treated layer of photosensitive resin to remove selectively the non-irradiated portions thereof in order to obtain the desired negative pattern.

According co a preferred embodiment of che present invention, the substrate is a silicon wafer, the photosensitive resin used comprises a phenolic polymer and che 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, che phenolic polymer is chemically bound to the diazoquinone» On the other hand, according to the present invention, che treatment with the silicon compound is preferably carried out after exposure of the photo30 sensitive resin layer to ultraviolet or visible light. However, chose skilled in the art will understand that, for che purpose of simplicity and readiness of execution, it is possible to carry out the treatment with the silicon compound already during the exposure of the photosensitive resin layer to light. In other words, it is possible to conduct steps (b) and (c) of Che process simultaneously. - 10 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 associated with a di azoquinone9 undergo substantial modifications of their properties under the influence of a visible or uLtraviolet radiation. We 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 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 microlithographic 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 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 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 et al. above described, the silicon compounds do not diffuse in all the regions of the photoresist Layer, but only in the irradiated portions of this layer.

The process of the invention is thus based on selective diffusion of che 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 ll reaction of the silicon compounds in either the exposed or the unexposed regions (the silicon compounds being incorporated in every region of the photoresist).

From the technical point of view, this difference has considerable 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 b single layer processes are definitively suppressed. By dry etching, the nonirradiated portions of the photoresist are completely removed and, in the irradiated portions, a silicon oxide mask is very quickly formed in situ, * which remains and protects very efficiently these portions throughout the etching process. After development, the thickness of the obtained pattern is practically identical to the initial thickness of the photoresist; the residual thickness generally represents more than 95% of the initial thickness of the resin layer coated on the substrate. In the uncovered parts, no residue remains. Moreover, the reproductibility is considerably improved since the light exposure times and the treatment times with 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 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 ligth does not occur, film stress problems do not exist and process complexity is drastically reduced· Even if the process of the invention provides a negative acting resist system, it doe9 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 longer a critical parameter. The completely dry processing of the resist results in improved process control and makes this system particularly suitable for automatic line fabrication processes.

The invention will now be further described with reference to the accompanying drawing wherein like reference numerals refer to same parts throughout the several views, wherein the layers are greatly 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 polymers can be used in order to prepare the 15 photosensitive resin used in the process according to the inventiono 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 with an ethylenically unsaturated compound, and - mixtures of the aforesaid polymers between them or with other aromatic polymers, such as polystyrene or p-(N-vinylcarbdzole).

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; pethylphenol; octylphenol and the like), condensation products of benzaldehyde with cresols or naphthols (e.g. 1-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 a diazoquinone such as those used in traditional positive pboto13 resists (see British Patent Specification No. 711,626). As non-limitative examples of these diazoquinones, there may be mentioned: 5-diazo-5»6-dihydro6-oxo-l-naphthalenesulfonic acid, 6-diazo-5,6-dihydro-5-oxo-l-naphthalenesulfonic acid, 3-diazo-3,4-dihydro-4-oxo-l-naphthalenesulfonic acid, 4diazo-3,4-dihydro-3-oxo-l-naphthalenesulfonic acid, 3-dijzo-3,4-dihyuro4-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 *. product of 3 moles of 6-diazo-5,6-dihydro-5-oxo-l-naphthalenesulfonyl chloride with 1 mole of 2,3,4-trihydroxybenzophenone may be mentioned. κ 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 ls the reaction of the derivatives of these photoactive compounds carrying a sulfonyl chloride substituent (or carbonyl chloride) with the hydroxyl groups of the phenolic polymers, with formation of sulfonates (or carboxylates).

As shown in Figure I, in Che 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 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.

When che photosensitive resin is coated on the substrate from a dilute solution in a solvent» the solvent may be selected from a wide range of products, depending on solubility parameters, evaporation rate at processing temperatures and desired rheological characteristics. Examples of solvents which can be used include ketones, esters such as acetates, propionates, and the Like, ethers, ether esters, polyethers, 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 resin layer. - 14 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 practice, temperatures of about 50° to about 15O*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 che 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 thickness of the photosensitive resin layer (1) is generally between I and 2,5 jm.

As is shown in Figure 2, the substrate (2) coated with the photosensitive resin layer (I) is then exposed to visible or ultraviolet radiation (3) through a photoimaging mask (4). The wavelenght of the applied radiation can vary within a range of from about 100 to 600 nm, preferably of from about 350 to 450 nm. Under the effect of visible 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 permeabiLity properties of che 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 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 in the following step of the process. - 15 Light absorbance of the photosensitive resin layer can possibly be increased by adding specific dyes, as described by M.M. O'TOOLE, E.D. LIU and M.3. 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 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 similar agents can also be added to the photosensitive resin· As already explained above, the treatment of Che 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 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-liraitative examples of useful silicon compounds, the following silylating agents can be mentioned: tetrachlorosilane and alkyl- and arylhalosilanes (e.g. trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, trimethylbromosilane, trimethyliodosilane, tr ipheny Ichlorosilane), disi lazanes (e.g. hexamethyldisilazane, heptamethyldisilazane, hexaphenyldisilazane and l,3-bis(chloromethyl)-*-l,l,5,3-tetramethyldisi.lazane), N-trimethylsilylimidazole, N-trimethylsilylacetamide, N-trimethylsilyldimethylamine, N-trimethyIsilyldiethylamine, hexamethylsilanediarnine, N,0bis(triethylsilyl)acetimide, Ν,Ν1-bis(trimethylsilyl)urea, Ν,Ν'-dipheny1-N(trimethylsilyl)urea and mixtures of at least two of these compounds.

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

The treatment uith 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 reacting uith the functional groups of the resin. On the other hand, in the non-irradiated portions, there is practically no diffusion of che 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 (5) 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 che 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 with 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 that 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 linewidch variations over highly reflective steps, such as metal interconnectors, ate 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 Che 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 15O°C, and preferably of from 60 to 14O°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 time can vary between a feu 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 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 Che silicon compound does pratically not diffuse in the non-irradiated portions of the photosensitive resin and that these portions are thus easily removed by the further development by dry etcning by means of oxygen gas plasma or oxygen-reactive ion etching.

In the last step of the process of Che 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 devices used for their execution, are well known by chose skilled in the art and need not be described in detail.

As is shown iri Figure 4, development by dry etching has as consequence that the non-irradiated portions of the photoresist are quickly removed, whereas che irradiated portions ¢5) resist perfectly owing to the in situ formed silicon oxide etch mask.

When the non-irradiated portions are completely removed up to the 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 thantalf a micrometer wide and spaces near half a micrometer wide can be obtained, a perfect retention of the 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 che present invention. In these examples, the values given for the UV exposure energy are measured at a wavelength of 400 nanometers.

Example I.

Silicon wafers with thermal oxide of approximately 120 nanometers thickness are primed with hexamethyldisilazane as adhesion promoter. As photosensitive resin, the partial esterification product of 6-diaxo-5,o-dihydro-5-oxo-L- IS naphthalenesulfonic chloride with the condensation product of p-tert-butylphenol and formaldehyde, is used· This resin is dissolved in a solvent mixture containing 802 by weight of 2-ethoxyetiianol, 102 by weight of xylene and 102 by weight of n-butyl acetate, in order to obtain a 252 by weight solution· This solution is spin-coated on the silicon wafers at a spin speed of 3000 rpm. tn this way, a resin layer of 1.7 thickness is obtained on each wafer.

The thus coated wafers are baked in a convection oven ac 90’C for 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 the 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-diaza-5,6-dihydro-5oxo-l-naphthalenesulfonic chloride with one mole of 2,3,4-trihydroxybenzophenone· This mixture is dissolved in 250 g of a solvent mixture containing 802 by weight of 2-ethoxyethanol, 102 by weight of xylene and 102 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 mJ/cm , then treated with hexamethyldisilazane vapor during 30 minutes at 65°C. After development, negative patterns having a residual thickness of 1.2 ^un are obtained, i.e. 862 of the initial resin layer thickness.

Exanple 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-diaao-5,6"dihydro-5-oxo-*l-naphthalenesulfonic chloride. 25 g of this resin are dissolved in 100 g of 2-ethoxyethyl acetate. The formed resin - 19 layer has a thickness of 1.5 pxa. After prebaking, it is exposed to UV rays through a mask, the exposure energy being 85 mJ/cra2, then treated with hexaroe thyLdisilazane vapor for 10 minutes at 80eC. After development, negative patterns with a residual thickness of 1.4 pm are obtained, i.e. 932 of the initial resin layer thickness.

Example 4.

The procedure of Example I is followed, but the photosensitive resin used is the partial esterification product of 6-diazo-5,6-dihydro-5-oxo-lnaphthalenesulfonic chloride with poly(p-vinyIphenol). 25 g of this resin are dissolved in 100 g of 2-ethoxyethyl acetate. The formed resin layer has a thickness of 1.7 pm. After prebaking, it is exposed to UV rays through a mask, the exposure energy being 85 mJ/cm2, then treated with hexanrathyldisilazane 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 pm., i.e. 972 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 photoresin layer; it proves, moreover, that the silicon compound is able to react with the phenolic polymer.

The procedure of ExampLe 1 is followed, but a non-photosensitive resin is used consisting solely of poiy(p-vinylphenol) i.e. without photoactive compound. 25 g of this resin are dissolved in 100 g of 2-ethoxyethyI acetate, and this solution is spin-coated on silicon wafers so as to obtain a resin Layer of 1.7 um thickness. After prebaking, this layer is exposed to UV rays ’ 4 2 through a mask, the exposure energy being 130 mJ/cm . The samples are then treated in two different ways with hexamethyldisilazane vapor: a) at 13O*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 L55*C 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 - 20 <* is prepared by partial esterification of the condensation product of p-npropylphenol and formaldehyde, with 6-diazo-5,6-dihydro-5-oxo-L-naphthalenesulfonic chloride. 30 g of this resin are dissolved in 100 g of 4-methyl-2pentanone. The formed resin layer has a thickness of 2.3 yjm. After prebaking, it is exposed to UV rays through a mask, the exposure energy being 85 mJ/cm , then treated for 8 minutes at L15°C with hexamethyLdisiLazane vapor.

Development affords negative patterns with high resolution (lines ot 0.45 pa wide and spaces 0.85 pn wide), with vertical side-walls; they have a residual thickness of 2.15 pa, i.e. about 942 of the initial resin layer thickness.

Example 7.

The procedure of Example I is followed, but che photosensitive resin used consists of a mixture of 10 g of polystyrene and 20 g of the partial esterification product of 6-diazo-5,6-dihydro-5-oxo-l-naphthalenesulfonic chloride with the condensation product of p-ethylphenol and formaldehyde. This mixture is dissolved in 100 g of cyclohexanone. A layer of 1.8 pa thickness is formed, which after prebakLng, is exposed to UV rays through a mask, the exposure 2 energy being 110 mJ/cm . This Layer is then treated with trinethylchlorosilane vapor for 10 minutes at 100°C. After development, high resolution negative patterns with vertical side-walls and a residual thickness of 1.5 ^un are obtained, i.e. about 852 of the initial resin Layer thickness.

Example 8.

The procedure of Example I is followed, but the photosensitive resin consists of the partial esterification product of 6-diazo-5,6-dihydro~5-oxo-lnaphthalenesulfonic chloride with the condensation product of cresols and 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 pa. After prebaking, it is exposed to UV rays through a mask, the exposure energy being 90 mJ/cm^· then treated for 8 minutes at L25°C with hexamethy Idisi lazane vapor. After development, high resolution negative patterns with vertical side-walls and a residual thickness of 1.6 pa are obtained, i.e. 94a of the initial resin layer thickness.

Example 9.

The procedure of Example I ia followed, but the photosensitive resin consists of a mixture of 3 g of poly(N-vinylcarbazole) and 20 g of the partial esterification product of 6-diazo-5,6-dihydro-5-oxo-l-naphthalenesulfonic chloride with the condensation product of 1-naphtol and benzaldehyde. This mixture is dissolved in 100 g of bis (2-me thoxye thy pettier. The formed resin layer has a thickness of 1.8 ^im. After prebaking on a hot plate at 95*C for 45 seconds, it is exposed to UV rays through a mask, che exposure energy being 115 nU/cm , then treated for 10 minutes at l20eC with he Maine thy Idisilazane vapor. After development, high resolution negative patterns with vertical side-walls and a residual thickness of 1.65 jut are obtained, i.e. 922 of the initial resin layer thickness.

Exanple 10.

The procedure of Example I is followed, but the photosensitive resin is prepared by partial esterification of a copolymer of p-vinylphenol and pchlorostyrene, with 6-diazo-5,6-dihydro-5-oxo-l-naphthalenesulfonic chloride. g of this resin are dissolved in 100 g of 5-methyl-2-hexanone. The formed resin layer has a thickness of 1.7 ^un. After prebaking, it is exposed to UV rays through a mask, the exposure energy being 85 mJ/cm^, then treated for LO minutes at 125’C with hexanethyldisilazane vapor. After development, high resolution negative patterns with vertical side-walls and a residual thickness of 1.6 ^ua are-obtained,- i.e.- 942 of the initial resin layer thickness. Example 11.

The procedure of Example I is followed, but the photosensitive resin is prepared by partial esterification of 6-diazo-5,6-dihydro-5-oxo-l-naphthalenesulfonic chloride with the condensation product of octylphenol and formaldehyde. 30 g of this resin are dissolved in 100 g of cyclohexanone. The formed resin layer has a thickness of 1.9 ^tm. After prebaking at 95’C for 45 seconds on a hot plate, it is exposed to UV rays through a mask, the exposure energy being mJ/cm , then treated for 10 minutes at 125°C with hexamethyldisilazane vapor. After development, high resolution negative patterns with vertical side-walls and a residual thickness of 1.7 ^mt are obtained, i.e. about 902 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 che silicon compound in the irradiated portions of the resin.

This example shows at the same time that the silicon compound penetrates the more deeply in these irradiated portions the more the applied UV exposure - 22 dose is increased.

Silicon wafers with thermal oxide of approximately 120 nm thickness are primed with hexamethyldisilazane as adhesion promoter. As photosensitive resin* the partial esterification product of 6-diazo-5,6-dihydro-5-oxo-l-naphthalenesulfonic 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 thickness.

The coated wafers are prebaked on a hot plate at 95eC 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/minute enables the depth profile of the 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 time* 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 SO 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 chem 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 95X obtained according the process of the invention. - 23 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 co UV radiation (radiation energy 0). This analysis shows also that when the applied exposure dose increases, the silicon compound penetrates more in depth in the resist layer, whereas the concentration of fixed silicon is independent 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 permeability and makes it possible for the silicon i& compound to selectively diffuse in the irradiated portions.

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 polymer 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 been exposed to a visible or ultraviolet radiation in said k > portions; (b) exposure of the layer of photosensitive resin fo ultraviolet or visible light through a mask fo 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-l-naphthalenesulfonic acid, 6- diazo-5,6-dihydro-5-oxo°l-naphthalenesu1fonic acid,

3. -diazo-3, 4. -dihydro°4-oxo-l-naphthalenesulfonic acid, 4*diazo-3,4-dihydro-*3°oxo«l<-naphthalenesulfonic acid, 30 3-diazo->3,4-dihydrO4-oxo-l-bdnzenesulfon1c acid, the corresponding carboxylic acids, their derivatives and the mixtures of at least two of the aforesaid compounds. t 3. Process according to any of claims 1 and 2, wherein the polymer 35 is a phenolic polymer.

4.* 4. Process according to claim 3, wherein the phenolic polymer is -25selected 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 vinylphenol 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.

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, dimethyldichlorosilane, methyltrichlorosilane, trimethybromosilane, trimethyl iodosilane, triphenylchlorosilane, hexamethyldisilazane, heptamethyldisilazane, hexaphenyldisilazane, l,3-bis(chloromethyl)-l,l,3,3-tetramethyldisilazane, 25 N-trimethylsilylimidazole, N-trimethylsilylacetamide, N-trimethylsilyldimethylamine, N-trimethylsilyldiethylamine, hexamethylsilanediamine, h,O-bis(triethylsilyl)acetimide, ^^‘-bisitrimethylsilyljurea, N,N‘-diphenyl-N-(triinethylsily)urea and the mixtures of at least two of these compounds.

8. Process according to claim 7, wherein the silylating agent is hexamethy1dis1azane.

9. Process according to any of claims 1 to 8, wherein the treament j 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 -2615 of the layer of photosensitive resin with the silicon compound is carried out at a temperature between 60 and 140°C.

11. Process according fo any of claims 1 to 10, wherein the time of 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 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.

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

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

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

17. An intergrafed semiconductor circuit made by a process as claimed in any of claims 1 to 13, 15 or 16.