Though the current invention is also applicable to lithographic processes as used in printing industry, the current invention is mainly concerned with lithography as applied in the production of electronic and electric devices, sensors, and the like. The characteristic length scale, i.e. the design rule of the relevant lithographic pattern is usually in the micron to submicron region. The manufacturing process of these devices is currently almost entirely dominated by methods based on optical or e-beam lithography.
Since the emergence of integrated circuits (ICs) and micromechanical devices, optical lithography has been crucial for the purpose of their mass production: Its convenience, parallel operation and resolution has created a huge market. Fabrication of devices with ever smaller dimensions, necessary to satisfy the demands of storage and computation, becomes increasingly problematic with visible light as processes steadily reach fundamental limits, predominantly set by diffraction. This realization triggered intense research in UV, X-ray, e-beam, and Scanning Probe (SP)
lithography. These methods deliver high resolution with varying success and their economics remain, at best, uncertain. Reasons for these uncertainties include limitations due to wavelength dependent phenomena, the slow writing speeds of e-beam and SP lithographies, and challenges in finding appropriate resists and masks.
A separate and related limitation of current lithographies is the complexity of processes required for modifying or altering a layer at regions defined by the desired lithographic pattern to be written; lithography today relies on bulk transfer of reactive material from the liquid or gas phase, or from a plasma using masks to protect the other regions of the substrate.
An alternative approach to lithography has been published by A. Kumar and G. M. Whitesides in : Appl. Phys. Lett. 1993, 63, 2002-2004. In this process, known as microcontact stamp lithography, stamps are fabricated by casting a replica in poly(dimethylsiloxane) (PDMS) of a master with a negative of the desired pattern. In the one known example of microcontact stamping used for lithography, the PDMS stamp is inked with an alkanethiol, hexadecanethiol, and transferred to gold by transient contact between the stamp and the gold substrate. The thiol covalently binds to the gold in an autophobic reaction: the thiol modifies the wettability of the gold substrate, preventing spread of the bulk liquid phase and thus confining the transferred monolayer to the region of contact between the raised regions of the elastomeric stamp and the substrate. The presence of these thiols allows subsequent lithographic processing of the gold using a cyanide/oxygen etch that selectively removes gold not protected by a monolayer of alkanethiol. Although this system allows reproductions of features in gold down to one micron, its scope remains limited to a special subset of useful materials, i.e. thiols and gold.
In all these lithographic processes, a number of agents are used which pose a considerable potential threat to the environment. Huge efforts are therefore taken to sufficiently protect workers within IC factories and the population living in their surrounding from a possible exposure to these agents. Immense resources are also invested for safely depositing the waste and remains of the IC manufacturing.
The object of the present invention is to avoid limitations in the type of reactions, materials transferred and range of substrates useful in contact based lithography and to demonstrate new strategies of direct processing of substrates without the intervening application of resists.
It is a further object of the inventions to improve the known lithographic processes by providing a method for modifying a surface at precisely determined positions. While being more convenient to apply, the new process should at least have a resolution comparable to state-of-the-art lithography. Another object of the invention is to restrict the amount of agents and material used in the lithographic process, in particular, hazardous waste generated by this process should be minimized.
As mentioned above, lithographic processes are also found in the field of printing. In particular, color printing is found to face similar problems concerning alignment during several separated printing steps as encountered in lithography for semiconductor devices. In four color printing the colors cyan, magenta, yellow and black are applied to four separate printing rollers that transfer the lithographic pattern to the paper in four separate printing steps. The alignment among those four printing steps limits the maximal resolution and quality of color images especially on cheap and low quality paper. Printing can either be done with poor alignment (.about.0.1 mm) and bad image quality on cheap paper or with better alignment (.about.0.01 mm) and better image quality on high quality paper. The rastering dimension has to be adapted to the alignment and consequently is &gt;0.1 mm (&lt;300 dpi) for low quality paper and&gt;0.01 mm (&lt;3000 dpi) for the paper with the highest quality. Photographic reproduction, on the other hand, can be carried out with grain sizes of the order of microns (&lt;0.001 mm). Thus, high quality printing requires expensive equipment able to maintain tolerances of 10 microns over several meters.
It is therefore seen as another object of the invention to improve the conventional color printing procedure, in particular to facilitate the alignment procedure necessary to print several colors.