Apparatus and methods for development of resist patterns

Details Apparatus and methods for development of resist patterns Apparatus and methods for development of resist patterns

2000-05-17

2003-04-22

Mathews, Alan A. (Department: 2851)

Photography

Fluid-treating apparatus

Heating, cooling, or temperature detecting

C396S571000, C396S612000, C118S641000

Reexamination Certificate

active

06550989

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a novel apparatus for the development of resist patterns on substrates, for example lithographic printing plates, and to methods of using such novel apparatus. The invention is of particular, but not exclusive, interest in relation to the development of lithographic printing plates, especially thermal lithographic printing plates.
2. Background Information
The objects to be developed using the apparatus of this invention are commonly printing plates, but this is not a necessity. They could comprise any substrate which requires the development of a resist pattern in order to produce a required pattern in a coating on the substrate surface. The resists could be used in the manufacture of electronic parts, for example printed circuit boards. A desired wiring pattern may be imaged in the resist coating on, for example, a copper board. The board is then processed in a developer to remove either imaged or non-imaged portions of the resist coating, and an acid etch then removes only the portions of the copper board no longer bearing the coating.
Thermal lithographic plates are plates which are imaged by infra-red radiation and/or heat. With certain thermal plates, the infra-red radiation may initiate a photochemical reaction in, for example, an onium compound, present in a coating on the plates. In such embodiments an infra-red dye, also present in the coating, acts as a photosensitizer, absorbing the infra-red radiation and sensitizing the decomposition of the onium compound.
So-called CTP (“Computer-To-Plate”) technology has in part been responsible for the further development of thermal lithographic plates. The required pattern in the coating on the lithographic plate may be “written” by an infra-red laser, under digital control.
An exemplary class of thermal plates works as follows:
Plates are exposed to imaging infra-red radiation as described for the first class of plates above. They are then subjected to an overall heating step, after imaging but before development. This is typically referenced as a “preheat step.” This heating step is believed to selectively crosslink those regions of the coating which were selectively imaged, and render them preferentially less soluble in a developer. Thus, on development of such a plate, the regions which were not imaged are selectively developed away. These are negative working thermal plates, and are exemplified by the THERMAL PRINTING PLATE/830 manufactured by Kodak Polychrome Graphics. Such technology is described in U.S. Pat. Nos. 5,340,699, 5,372,907 and 5,491,046. The contents of these patents are incorporated herein by reference.
The most common way of preparing such a thermal plate for a negative working process (so requiring preheating) is to place the plates in very large ovens, which are a separate apparatus from the plate setter and from the processor, thus requiring a large floor space and also high power consumption. Large ovens were desirable in the prior art, inter alia, to passively ensure even heat distribution throughout the plate, by providing a large central region having uniform temperature and ensuring a long dwell time for the plate in the central region. If this does not occur, substantial temperature differences from one part of the plate to another will cause different degrees of crosslinking which can manifest itself as different dot sizes along the plate; but in such printing plates even a lesser temperature difference can be very detrimental. The printing plate may look the same in terms of size of dot after development, but may give poor run length on printing.
Processors are known in which there is an integral preheat section upstream of the chemical development section, but these have been designed for use with conventional negative working plates. “Conventional negative working plates” refers herein to negative working plates imaged by ultra-violet or visible radiation. With such plates the photo-sensitive coating on the plate is given a top coat of an oxygen migration barrier material, for example polyvinyl alcohol. This must be removed after the preheat and before development, thus the processor must have a wash section between the preheat oven and the chemical development section. The use of a preheat oven upstream of a development section in a single processor is much more straightforward to accomplish with conventional negative working plates than with thermal plates. This is because conventional negative working plates are very “robust” in terms of the amount of heat which can be delivered to them before development, and yet are even quality. In other words, there is a very wide operating window in terms of heat input and there is less difficulty in terms of process control, in employing a very simple preheat oven. Despite their robustness, the processing of and the resulting image on such plates can be improved by controlled preheat and baking. With thermal plates the situation is different; as described herein it has been found that the operating window is narrower (in terms of heat input), such that the use of a small footprint preheat oven integrated with a development processor of a type employed to previously in an apparatus intended for development of conventional negative working plates may not be suitable for thermal plates.
Most prior processors do not employ any preheat oven. However products which are believed to employ a preheat oven for conventional plate processing are the PHW 32 processor sold by Technigraph of Thetford, UK and the INTERPLATER 85 HD/135 HD Polymer processor available from Glunz & Jensen.
A particular problem with attempts to develop thermal lithographic plates in processors such as those mentioned above is that the trailing edge of the plate, as the plate proceeds through the processor, becomes relatively hotter than the other portions of the plate and the front edge of the plate may be heated less than the other portions of the plate. This is believed to be because, when using a constant temperature preheat oven heat conduction from heated regions of the plate to regions yet to be heated, which thus enter the preheat oven at a raised temperature, causes a temperature gradient within the plate. In the middle of the plate this does not appear to be as significant a problem because an equilibrium temperature may be reached as heat is conducted toward trailing regions which can act as a heat sink. However at the trailing edge of the plate the heat thus conducted to it can be conducted no further back, and the trailing edge of the plate may become so hot that “fogging” occurs; in effect, the trailing edge of the plate has been exposed to excessive heat causing the coating to crosslink in unexposed areas reducing the differentiation between imaged and non-imaged areas. Furthermore, problems can arise with variations in properties across the plate, due to temperature differences in the transverse direction.
Thus, in using such an integrated preheat/processor apparatus designed for conventionally imaged negative working lithographic plates in attempts to develop thermal at plates, there is a temperature gradient rising, for example from the front to the rear of the plates in the preheat oven and, it is believed, rising exponentially in the rearwards direction. Evidently the conventionally imaged negative working lithographic plates are sufficiently “robust” that they can be used in such a preheat oven, but thermal plates are not; the “fogging” at the trailing edge region and lower temperature at the leading edge is often unacceptable.
With many lithographic plates or other resists it may be desirable to provide heating after development, simply to strengthen the residual coating and extend the lifespan of the product—in the case of a printing plate, resistance to aggressive press chemicals, and also the run length. It is the industry norm to employ, for this purpose, post-development ovens which are separate from the processor. These ovens are typically very large and expensive pieces of equipme

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