Electric heating – Metal heating – By arc
Reexamination Certificate
1999-02-23
2001-04-10
Ryan, Patrick (Department: 1725)
Electric heating
Metal heating
By arc
C219S121600, C219S121650, C219S121660, C219S121680, C219S121690
Reexamination Certificate
active
06215099
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to laser surface treatments, particularly to method and apparatus for the generation of laser beams, which permit high throughout and damage-free UV laser removal of foreign materials, as photoresists, particles and the like, from the surfaces of substrates, such as, e.g., semiconductor wafers in various production stages, and to surface treatments wherein said laser beams are generated by the aforesaid method and apparatus.
BACKGROUND OF THE INVENTION
In the manufacturing of various products, it is necessary to apply a layer of protective material on a surface, which must be removed after a specified manufacturing step has been concluded. An example of such a process is the so-called “masking”, where a pattern is created on a surface using a layer of protective material illuminated through a mask, and the surface is then treated with a developer which removes material from the unmasked portions of the surface, therefore leaving a predetermined pattern. The surface is then treated by ion implantation or by etching agents, which introduce the imprinted species into the unmasked portions of the surface, or remove material from unmasked portions. Once these processes are completed, the role of the protecting mask ends and it must be removed. The process is conventional and well known in the art, and is described, e.g., in U.S. Pat. No. 5,114,834.
Two main photoresist stripping methods exist in the modern VLSI/ULSI (Very/Ultra Large Scale Integration) circuits industry:
1) Wet stripping, which uses acids or organic solvents;
2) Dry stripping, which uses plasma, O
3
, O
3
/N
2
O or UV/O
3
-based stripping.
Both methods are problematic and far from being complete, especially when taking into consideration the future miniaturization in the VLSI/ULSI industry. The current technology is capable of dealing with devices having feature sizes of about 0.5 m, but before the end of the century, the expectation is that the workable size of the devices is to be reduced to 0.25 m. The anticipated size change requires considerable changes in the manufacturing technology, particularly in the stripping stage. The prior art photoresist stripping techniques described above will be unsuitable for future devices, as will be explained hereinafter.
Utilizing only the wet stripping method is not a perfect solution, as it cannot completely strip photoresist after tough processes that change the chemical and physical properties of the photoresist in such a way that makes its removal very difficult. Such processes include, e.g., High Dose Implantation (HDI), reactive Ion Etching (RIE), deep UV curing and high temperatures post-bake. After HDI or RIE, the side walls of the implanted patterns or of the etched walls are the most difficult to remove.
In addition, the wet method has some other problems: the strength of the stripping solution changes with time, the accumulated contamination in the solution can be a source of particles which adversely affect the performance of the wafer, the corrosive and toxic content of stripping chemicals imposes high handling and disposal costs, and liquid phase surface tension and mass transport tend to make photoresist removal uneven and difficult.
The dry method also suffers from some major drawbacks, especially from metallic and particulate contamination, damage due to plasma-charges, currents, electric fields and plasma-induced UV radiation, as well as temperature-induced damage, and, especially, incomplete removal. During various fabrication stages, as discussed above, the photoresist suffers from chemical and physical changes which harden it, and this makes the stripping processes of the prior art extremely difficult to carry out. Usually, a plurality of sequential steps, involving wet and dry processes, are needed to completely remove the photoresist.
The art has addressed this problem in many ways, and commercial photoresist dry removal apparatus is available, which uses different technologies. For instance, UV ashers are sold, e.g. by Hitachi, Japan (UA-3150A), dry chemical ashers are also available, e.g., by Fusion Semiconductor Systems, U.S.A., which utilize nitrous oxide and ozone to remove the photoresist by chemical ashing, microwave plasma ashing is also effected, e.g., as in the UNA-200 Asher (ULVAC Japan Ltd.). Also, plasma photoresist removal is employed and is commercially available, e.g., as in the Aspen apparatus (Mattson Technology, U.S.A.), and in the AURA 200 (GASONICS IPC, U.S.A.).
More recently, photoresist removal has been achieved by ablation, using laser UV radiation, in an oxidizing environment, as described in U.S. Pat. No. 5,114,834. The ablation process is caused by strong absorption of the laser pulse energy by the photoresist. The process is a localized ejection of the photoresist layer to the ambient gas, associated with a blast wave due to chemical bonds breaking in the photoresist and instant heating. The partly gasified and partly fragmented photoresist is blown upwards away from the surface, and instantly heats the ambient gas. Fast combustion flash of the ablation products occurs, after each laser pulse, due to the photochemical reaction of the UV laser radiation and the process gases, which may also be due to the blast wave. The main essence of the process is laser ablation with combustion flash of the ablated photoresist, which occurs in a reactive gas flowing through an irradiation zone. The combination of laser radiation and fast combustion provides instantaneous lowering of the ablation threshold of hard parts of the photoresist (side walls). The combusted ablation products are then removed by vacuum suction, or by gas sweeping, leaving a completely clean surface.
While U.S. Pat. No. 5,114,834 provides an important novel process, it still does not provide a high throughput, which is industrially convenient, viz. an industrially acceptable number of wafers that can be stripped during a given time. The laser stripping throughput is determined by the stripping rate or by the number of laser pulses needed for providing complete stripping of a unit area of the photoresist per unit of time.
While reference will be made throughout this specification to the ablation of photoresist from semiconductor wafers, this will be done for the sake of simplicity, and because it represents a well known and widely approached problem. It should be understood, however, that the invention described hereinafter is by no means limited to the stripping of photoresist from wafers, but it applies,
mutatis mutandis
, to many other applications, such as stripping and cleaning of photoresist from Flat Panel Displays (FPD) or removal of residues from different objects, such as lenses, semiconductor wafers, or photo-masks.
The aforementioned U.S. Pat. No. 5,114,834 defines the process window of laser stripping, and indicates that there are certain energy fluence levels of the laser pulse which may damage the wafer being treated. So far, however, the art has failed to provide a method which conveniently permits to utilize the energy of an excimer laser in a way that allows to increase the fluence damage threshold defined in U.S. Pat. No. 5,114,834, without incurring the risk of damaging the surface of the object being treated. The types of damage due to laser energy include thermal damages, such as ripples due in particular to difference in expansion coefficients, e.g., SiO
2
/Si (implanted) and TiN/Al interfaces and related to the fatigue phenomena, aluminum or silicon melting, as well as radiation (ionization) damages, e.g., slight color changes due to small changes in the crystalline structure at SiO
2
/Si interface (implanted).
WO 97/17164 (PCT/IL/00139), the entire content of which is incorporated herein by reference, discloses a method of damage-free laser surface treatment by extending a laser pulse in time and supplying the same pulse energy to a treated surface during a longer period of time. The pulse extension is carried out by optical means, viz. by means of a Passive Optical Pulse Extender, hereina
Baker & Botts L.L.P.
Elve M. Alexandra
Oramir Semiconductor Equipment Ltd.
Ryan Patrick
LandOfFree
Multi-Laser Combustion surface treatment does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multi-Laser Combustion surface treatment, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multi-Laser Combustion surface treatment will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2553482