Etching a substrate: processes – Gas phase etching of substrate – Application of energy to the gaseous etchant or to the...
Reexamination Certificate
2002-04-16
2004-04-13
Cuneo, Kamand (Department: 2829)
Etching a substrate: processes
Gas phase etching of substrate
Application of energy to the gaseous etchant or to the...
C438S690000, C438S795000
Reexamination Certificate
active
06719916
ABSTRACT:
FIELD OF THE INVENTION
The invention resides in the field of direct laser ablation of material. In particular, it relates to laser patterning of layers in the manufacturing of integrated semiconductor circuits and to such circuits made thereby. In more specific applications, the invention is a technique of patterning a metallic layer on an organic sublayer with minimal ablation or damage due to melt and/or carbonization of the underlying organic sublayer during processing of the metallic layer.
BACKGROUND OF THE INVENTION
Manufacture of integrated circuits involves deposition of a layer or layers on a substrate and etching parts of the layer or layers in desired patterns. Often these steps are repeated to produce a stacked structure. A variety of materials are used as layers and equally a variety of etching techniques are used for production of desired patterns. Cured laser etching or patterning is gaining wide acceptance in the field of IC (integrated circuits) manufacture.
The demand for low-cost and lower power small displays, digital projection and other personalized applications, has created a steady growing interest in organic light emitting materials that can be deposited using relatively inexpensive processes, such as spin-coating. However, organic materials are extremely sensitive to environmental conditions such as oxygen and moisture and to the chemical treatment used in the processing of photosensitive resins. As a result, pattering of organic-based devices cannot be easily realized with conventional methods of micro-fabrication since all-dry etching processing is required.
Shadow-masking is popular for the manufacture of organic light emitting diode (OLED) displays and can be applied to the fabrication of other organic electronics or photonics, but its lateral resolution is limited to ~100 &mgr;m. In addition, the shadow masking method requires sophisticated vacuum-compatible alignment tools. Laser ablation has the potential to attain much higher resolution at significantly lower cost.
In order to manufacture these compact displays, there is a strong demand for the ability to pattern multilayer microstructures with the high vertical resolution with special attention to confining the patterning process within an individual layer. Direct laser etching Is an all-dry etching processing suited for patterning and by using a short wavelength, a laser beam can be made to ablate materials with a high vertical resolution. The standard methods of laser patterning, however have one shortcoming. They fail to meet the requirement of operating below an ablation damage threshold for certain cases, that is to say, the etching process should not damage the underlying layer. The ablation damage threshold of a material is a threshold of a laser fluence above which the laser beam damages the structure of the material. The damages are generally in the form of carbonized organic material which may cause short circuits. In manufacture of certain ICs, the ablation damage threshold for the structure located in an underlying layer is often below that for the top layer. For example a structure consisting of th metallic thin film deposited on top of an organic material presents a typical case where traditional laser patterning does not produce satisfactory results. More specifically, ablation of an organic material with excessive laser energy, in addition to the deterioration of lateral resolution in patterning, can lead to material carbonization. A carbonized layer of organics is responsible for electrical short-cutting between the edges of ablated metallic film.
U.S. Pat. No. 4,490,211 Dec. 25, 1984 Chen et al discloses a laser induced chemical etching of metals with excimer lasers. According to the patent, a metalized substrate is exposed to a selected gas, e.g., a halogen gas, which spontaneously reacts with the metal forming a solid reaction product layer on the metal by a partial consumption of the metal. A pulsed beam of radiation is then applied from an excimer laser to the reaction product in a desired pattern. The laser radation has a wavelength which can be absorbed by the reaction product. Whenever the excimer laser radiation strikes, due to heating caused by absorption of the radation, the thin layer of reaction product is vaporized and driven off exposing a fresh layer of metal. A new layer of reaction product is formed on the freshly exposed metal, as before, by reacting the metal with the gas. This new layer of reaction product, in turn, is removed by irradiating with a pulse of laser radiation. In this manner, the metal is etched with a high resolution. The reaction product of copper chloride and several excimer lasers with different wavelengths are described in the patent. The patent describes this etching technique in connection with manufacturing of ICs using a silicon substrate. There are no organic layers in the structure described in the patent and no consideration is given to ablation damages to any layers. This method also requires a halogen gas atmosphere.
U.S. Pat. No. 5,536,579 Jul. 16, 1996 Davis et al discloses a method of manufacturing a multilayer electronic circuit utilizing two organic layers having varying optical absorbencies to applied laser light, wherein a first organic polymeric dielectric material has a first optical absorbency to an ablating wavelength of laser light, and a second organic polymeric dielectric material has a second optical absorbency to the ablating wavelength of laser light. A first layer of the first or the second organic polymeric materials overlays at least one surface of the at least one electrically conductive plane and a second layer of the other of the first and second organic polymeric materials overlays the first layer. With this multilayer structure, a laser beam only ablates the top layer, thus creating a blind hole without damaging an underlaying layer. The patent, however, describes drilling a blind hole through one of the two organic layers and it does not describe patterning the metal layer. Patterning of metallic layer without damaging the underlying organic layer cannot be achieved using this method.
U.S. Pat. No. 5,514,618 May 7, 1996 Hunter, Jr. et al describes a process for manufacture of flat panel liquid crystal display using direct laser etch. According to the patent, all the patterning of the display is done preferably by deposition followed by direct laser ablation. In the patent, patterned direct laser ablation of metals are described to form different components of the displays. The laser ablation is conducted on a metal layer lying over either another metal layer, polysilicon layer or a glass substrate. The patent mentions no organic layers upon which a metal layer to be ablated is provided.
Patterning of devices that comprise organic materials requires all-dry-etching processes, or sophisticated methods of thin film deposition, such as the separator technique, that would make possible a laterally selective deposition of the anode (cathode) material. Conventional methods of patterning are not suitable for application to organic materials because of technological steps that involve wet processing. In addition, the processing of organic materials with energetic ions in a dry etching chamber results in damage induced to the fragile chemical structure of such materials, which may reduce the fluorescence efficiency, affect electrical conductivity of the layer and lead to a catastrophic failure of a device so manufactured due to short circuit.
It is therefore an object of this invention to provide a method of patterning multilayer microstructures with special attention to confining the patterning process within an individual layer such that patterning of conductive metal electrodes deposited on top of an organic material is possible without significant ablation of the organic material in the underlying layer.
SUMMARY OF THE INVENTION
In one aspect, the invention relates to a method of ablating a layer of a material having an ablation damage threshold by a laser beam. The method includes steps of providing a sour
Dubowski Jan J.
Py Christophe
Tao Ye
Cuneo Kamand
Geyer Scott B.
National Research Council of Canada
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