Fishing – trapping – and vermin destroying
Patent
1989-04-06
1994-03-29
Hearn, Brian E.
Fishing, trapping, and vermin destroying
437225, 156643, H01L 2100, H01L 2102, H01L 21465, B44C 122
Patent
active
052984664
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of plasma processing, more particularly to the dry processing of polymers and other materials and the dry development of photoresist for use, e.g. in the microelectronics industry.
Many different plasma systems are known: reactive ion etching; high pressure plasma etching; magnetron ion etching; microwave etching; and electron-cyclotron resonance.
The patterning of substrates necessarily involves selective etching of some material. This is typically done using a masking layer (such as photoresist) which has been previously patterned (e.g. using conventional photolithography and wet development) and which will be used to mask the substrate during the subsequent etch. Also, as more and more polymers are used in manufacturing, the need for fast and clean processing of those materials becomes important. In many cases, and this is specially true in the microelectronics industry, the dimensional control becomes more and more stringent due to the decreasing minimum linewidths. Also, the defect densities need to be reduced to increase the yield of the processes. To achieve this, it is often decided to replace the wet chemical processing steps by dry processes. In general, the etching of a material by use of plasma is carried out in a specially configured chamber at reduced pressure An etchant gas (or gaseous liquid) is introduced in the reaction vessel. The gas as such is mostly not reactive and will have no effect on the substrate to be etched. To make the gas reactive, it is ionized by powering electrodes located in the reaction vessel. The ionization is often done using microwaves (GHz) or radio-frequencies (RF)(MHz).
From U.S. Pat. No. 4,253,907 it is known to use etching at audio-frequencies; this known etching method is not practical because a power density of lower than 0.01 Watt/cm.sup.3 is used.
The present invention has for its object to provide a method for dry processing or etching, that is fast and shows a high degree of anisotropy; an apparatus designed for this method can be kept simple.
Therefor the present invention provides a method for dry processing or etching a substrate, in which: the substrate is brought into a processing area; a vacuum is applied over the processing area; a audio frequency signal is applied at electrodes of the processing area, such as to create a plasma at the processing area, having a power density substantially above 0.01 Watt/cm.sup.3.
Further an apparatus for carrying out this method comprises a self-DC-bias on the electrode.
The matching network of the power system of the apparatus according to the prevent invention is designed such as to obtain a self-DC-bias on the cathode. The matching unit together with the plasma, will provide an equivalent load which matches the generators output impedance, resulting in an optimal power transfer to the plasma. The self-DC-bias will sustain the plasma at those low frequencies so that a stable working regime can be obtained. In a specific embodiment, the volume power densities can be much higher (typically ranging from 0.03 to 1 Watt/cm.sup.3), resulting in a highly ionized plasma. The combination of the audio-frequencies and the self-DC-bias of the plasma results in a high density plasma, well suited for advanced processes of different types of materials such as polymers, oxides, nitrides, polycrystalline materials, etc. Indeed, as the ions can follow the audio frequency alternating electrical field (with radio-frequency plasmas (13.56 MHz), the ions cannot follow the alternating field due to their low mobility), they will be forced to strike the substrate perpendicularly, having an energy which is approximately proportional to the DC-self-bias (if no collisions occur in the dark sheath). This means that the ions will also have a sputtering effect, enhancing the anisotropy by promoting the directional sputter assisted etch component. In a practical system, the DC-self-bias voltages range from several volts to several hundreds of volts while the ionization--being defined as the number of ionized
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Cobrain N.V.
Everhart B.
Hearn Brian E.
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