The invention relates to a method of chemically modifying an oxidic substrate surface according to a pattern, in which method the substrate surface is brought into contact with a photosensitive alkoxy silane which comprises a quinone-diazide group, thereby forming a silane layer on the substrate surface, after which the silanated substrate surface is exposed to light in accordance with a pattern, causing the quinone-diazide groups to be convened into carboxylic acid groups in the exposed areas.
The invention also relates to a method of manufacturing a black matrix of metal on a glass face plate of a display device, such as a colour display tube and a liquid crystal display device (LCD).
Chemical surface modification makes it possible to change the properties of surfaces without altering the bulk properties of the substrate and the surface morphology. Said modification is obtained by applying a layer having a thickness of one or a few molecules to the substrate surface. For this purpose, the molecules of the layer comprise two functional groups, i.e. one group which reacts with the substrate surface and one group which determines the new property of the substrate surface. Preferably, the bond between these bifunctional molecules and the substrate is covalent. Organosilanes are often used as the bifunctional molecules. By applying a thin layer of silane (less than 10 nm) the adhesion between the substrate and polymers, such as certain adhesives, lacquers and photoresists, can be improved or corrosion of the substrate surface can be counteracted. Also release problems, which occur for example with moulds, can be controlled with a silane layer. Silane layers are also used to reduce leakage currents in semiconductor devices. Silane layers are further used as orientation layers for liquid crystals in liquid crystal display devices (LCDs).
Often only a part of the substrate surface has to be modified, whether or not in the form of a pattern. For this purpose, the silane layer can be locally removed from the substrate surface, for example, by local irradiation using deep UV light or another type of high-energy radiation, such as electron rays or X-rays or by means of reactive ion etching (RIE). This has the disadvantage that the customary lithographic imaging techniques are not suited for this purpose due to the long wavelength of the light used (in general longer than 300 nm). To overcome this problem, photosensitive silanes have been developed, i.e. silanes which are not only sensitive to electron rays and deep UV light (wavelength shorter than 300 nm), but also to light having wavelengths which are longer than 300 nm, such as light produced by a UV mercury vapour lamp (wavelength 360 nm). These photosensitive silanes are the reaction product of a quinone-diazide compound (also referred to as diazoquinone compound) comprising a reactive group, such as a sulphonyl chloride group (SO.sub.2 Cl) with an organosilane which also comprises a reactive group. The photosensitive silane is applied in the form of a layer to a substrate surface and, subsequently, exposed to patterned radiation with light having a wavelength of, for example, 360 nm. By exposing quinone-diazide groups, they are convened into carboxylic acid groups which exhibit a different reactivity with respect to, for example, solvents.
Such photosensitive silanes are known per se from European Patent Specification EP-B-147127. In accordance with said Patent Specification, for example, 2,1-diazonaphthoquinone-5-sulphonyl chloride is made to react with an organosilane comprising at least one reactive group, thereby forming a photosensitive silane. Said silane is applied to a substrate in a layer thickness ranging between 150 nm and 25 .mu.m. After patterned exposure to UV light having a wavelength in the range between 200 and 450 nm, the exposed silane is removed with an alkaline solvent. The remaining silane pattern is used as an etch mask during plasma etching in an oxygen atmosphere.
It is known that exposure to UV light causes a diazonaphthoquinone group to be converted via a ketene group into an indenecarboxylic acid group under the influence of water. The indenecarboxylic acid group can cede protons and has other properties than the diazonaphthoquinone group in the unexposed areas. For example, it was found that, after wetting with aqueous solutions, both groups exhibited a different wetting behaviour. The wetting behaviour can be established by means of a contact angle measurement. In a contact angle measurement, a drop of a liquid is placed on the substrate surface to be measured and the contact angle .theta.(.degree.) between the substrate surface and the tangent to said liquid drop is determined in a point where the substrate surface, the liquid drop and air have a common boundary line. If water is used as the liquid, then .theta. is a measure for the wettability of the substrate surface with water. If .theta.=0.degree., then the substrate surface is completely wettable and is termed hydrophilic. If .theta.&gt;0.degree., then the substrate surface is less readily wettable and the hydrophobic character of the substrate surface increases. The greater the value of .theta., the greater the water-repelling capacity of the substrate surface. It was found that the above-mentioned exposed areas having indenecarboxylic acid groups can be wetted completely (.theta.=0.degree. C.) with alkaline solutions having a pH&gt;10, while solutions having a pH-value of 4-6 yield a .theta.-value of 40.degree.. The unexposed areas having diazonaphthoquinone groups are hydrophobic, and .theta.=60.degree.-65.degree..
A disadvantage of the known method is that, for certain applications, the difference in water-repelling capacity between exposed and unexposed areas is insufficient. A further disadvantage is that as a result of the use of relatively thick silane layers (150 nm to 25 .mu.m) the known method is relatively unsuitable for providing very fine patterns (lateral resolution&lt;1 .mu.m), because interference and absorption phenomena occur when these relatively thick silane layers are exposed to light.