Patent Application
20220143657
The present invention relates generally to the field of cleaning devices, and more specifically to ultraviolet (UVO) cleaning devices.
The UVO method is employed to clean certain specimens, including semiconductor wafers. The UVO method is a photo-sensitized oxidation process in which the contaminant molecules of photoresists, resins, human skin oils, cleaning solvent residues, silicone oils, and flux are excited and/or dissociated by the absorption of short-wavelength UV radiation. Atomic oxygen is simultaneously generated when molecular oxygen is dissociated by 184.9 nm and ozone by 253.7 nm UV. Most hydrocarbons and ozone absorb the 253.7 nm UV radiation. The products of this excitation of contaminant molecules react with atomic oxygen to form simpler, volatile molecules which desorb from the surface. Therefore, when both UV wavelengths are present, the UVO process continuously generates atomic oxygen and ozone is continually formed and destroyed.
Properly placing pre-cleaned samples within five millimeters of an ozone producing UV source, such as a low-pressure mercury vapor UV Grid lamp, enables near atomically clean surfaces in less than one minute. The process does not damage sensitive device structures on semiconductor wafer surfaces such as MOS gate oxide.
Previously available UVO cleaners have one or more high-intensity low pressure mercury vapor UV Grid lamps for optimum generation of atomic oxygen and short-wave UV radiation for effective cleaning. To maximize the cleaning rate, parts to be cleaned are placed on an adjustable tray. Prior units have been equipped with inlet ports for oxygen or other gas media, and an exhaust port for hookup to an exhaust system. Such devices have employed a single chamber wherein all cleaning functions required are performed with the sample located at a single position in the device.
Issues with these prior devices are speed of cleaning. While the most advanced UVO cleaners currently available require less than one minute to clean a properly pre-cleaned sample, applications such as the removal of photoresist may require significantly longer cleaning times. Including the time to load, process, and unload, a savings of seconds can be highly beneficial. Faster processing is highly advantageous in this field. Prior devices vary in processing times and construction, with some UVO cleaning devices being self-contained and others comprising a series of stations applying the necessary steps described.
Self-contained devices performing UVO cleaning are limited due to typical mechanical concerns, primarily heat. While bigger and more powerful components could be used, when such components are installed, the heat generated can adversely affect other components, cleaning can be slowed, or the process may even harm the sample in extreme cases. The challenge is therefore to obtain improved performance while both guarding against problems with the device and keeping the device self-contained and relatively small in size.
It would therefore be desirable to offer a UVO processing device that improves on the processing time of a given sample. Such a device would be preferably self contained and relatively efficient as compared with prior designs.
Thus according to a first embodiment, there is provided an apparatus for cleaning a sample comprising an ultraviolet grid lamp having a forward side, the ultraviolet grid lamp configured to direct ultraviolet light energy from its forward side toward the sample, a quartz plate positioned between the forward side of the ultraviolet grid lamp and the sample, and a nitrogen circulating arrangement configured to circulate nitrogen along the ultraviolet grid lamp.
According to another embodiment, there is provided an apparatus for cleaning a sample comprising an ultraviolet grid lamp having a forward side, the ultraviolet grid lamp configured to direct ultraviolet light energy from its forward side toward the sample, a quartz plate positioned between the forward side of the ultraviolet grid lamp and the sample, and a fan arrangement configured to cool the ultraviolet grid lamp by receiving and passing nitrogen in a path proximate the ultraviolet grid lamp.
According to a further embodiment, there is provided an apparatus for cleaning a specimen comprising an ultraviolet grid lamp having a forward side, the ultraviolet grid lamp configured to direct ultraviolet light energy from its forward side toward the specimen, a quartz plate positioned between the forward side of the ultraviolet grid lamp and the specimen, and a nitrogen circulating arrangement configured to circulate nitrogen along the ultraviolet grid lamp.
These and other advantages of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
For a more complete understanding of the present disclosure, reference is now made to the following figures, wherein like reference numbers refer to similar items throughout the figures:
The following description and the drawings illustrate specific embodiments sufficiently to enable those skilled in the art to practice the system and method described. Other embodiments may incorporate structural, logical, process and other changes. Examples merely typify possible variations. Individual elements and functions are generally optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in, or substituted for, those of others.
The present design is a relatively small, self contained design similar in size to previous UVO cleaning devices that provides improved cleaning capability. The present device includes a unique cooling system, wherein a nitrogen atmosphere is employed to achieve a beneficial result, and a quartz plate that provides beneficial heating qualities. The present design may include a heated tray in one embodiment that speeds processing. The result is a device that provides cleaning in less time than previously achievable.
The UV Grid lamp 204 is a high intensity UV lamp with densely packed, small diameter tubing. Bends are formed to enable a very tight tube radius and a minimal gap between tubes. Relatively small electrodes can provide the most consistent high UV output. One example of a UV Grid lamp that may be employed in such a design is shown in
In one embodiment, the UV Grid lamp 204 is powered by a ballast usable in larger lamps. Use of this larger ballast provides a relatively high electrical output as compared with standard power supplies, further increasing UV intensity. As compared with previous lamps in similar devices, the current lamp intensity is greater, and in one embodiment approximately 2.5 times greater per given area.
The higher power applied to the UV Grid lamp 204 causes the lamp to generate significantly more heat than previous designs. The higher temperatures adversely affect lamp performance, thus reducing UV emissions. Heat also leads to increasing lamp pressure and voltage that the power supply eventually cannot support, resulting in shutdown of UV Grid lamp 204. To keep the lamp temperature within an acceptable operating range, the system employs a unique cooling system that recirculates air along the lamp body using cooling fans and ductwork.
Recirculating the air around the lamp body increases the likelihood of unwanted particles inside the cleaning chamber. Keeping out dust and foreign particles is critical to the process, particularly in semiconductor cleaning applications. To prevent moving particles from coming contact with the substrate, the process chamber of the present design comprises two chambers, an upper lamp chamber and a lower process (cleaning) chamber. Dividing these two chambers is quartz plate 203 with O-ring seals (not shown) on both sides secured with a stainless-steel flange or frame (also not shown)). Quartz plate 203 in one embodiment includes synthetic quartz material that facilitates high transmission of shortwave UV radiation.
The cooling system in this embodiment includes a hot/cold plate 213 that employs the Peltier effect. The Peltier effect calls for application of voltage to two electrodes connected to semiconductor or similar material. The result is the transfer of heat from one medium or material to another. Development of condensation can negatively affect many types of heat exchangers. In addition to moisture, a high concentration of ozone generated by the UV Grid lamp 204 can lead to corrosion and premature failure of electrical components such as the cooling fans, electrical wires and lamp terminals. In the present design, the upper (lamp) chamber is filled with nitrogen, reducing ozone generation inside the lamp chamber. The result is a decreased moisture content in the cooling media. Decreased moisture content reduces corrosion in electronic and electrical components. In some instances, the UV Grid lamp and/or the substrate may be preheated using the using hot/cold plate 213.
The system pressurizes the lower chamber 501 during the cleaning process, wherein the cleaning process employs air, oxygen, and/or ozone, or a combination thereof. Force acting upon the quartz window limits the maximum pressure available from such pressurization. A thicker quartz plate 203 provides lower UV transmission. The system operates such that the pressure in both upper (lamp) chamber and lower (cleaning) chamber can be increased in one while simultaneously decreasing pressure in the other to minimize the pressure differential between chambers. Sensors are provided, shown as sensors 510 and 511 in
One possible cleaning distance between the substrate or sample and UV Grid lamp 204 is nonzero, in one embodiment less than ¼ inch. In one embodiment, quartz plate 203 below the UV Grid lamp 204 is ⅛ inch thick with a sealing flange around quartz plate 203 about ⅜ inch thick, but other dimensions may be provided depending on various factors. An operator may load the sample or substrate onto substrate tray 202 for the cleaning process. The substrate tray 202 may be loaded manually or automatically into drawer 201. The system may include, for example, an air cylinder 208 that closes the drawer, but other devices may be employed such as linear motion slide. In one embodiment the drawer has an O-ring providing an airtight seal against the exterior housing 214. The substrate or sample is positioned below the UV Grid lamp 204. However, the distance between the substrate and UV Grid lamp 204 may be too large to perform a rapid and effective cleaning of the substrate because the O-ring seals around the underside of the quartz plate occupy the space needed to load the substrate tray 202 at an acceptable distance from the UV Grid lamp 204 to provide effective and efficient cleaning.
Thus the system employs vertical positioning. The system vertically positions the substrate using lifting pedestal 206 rising from beneath the substrate tray 202. Lifting pedestal 206 is driven by an air cylinder 207, but alternative devices such as a linear motion slide could be employed. The lifting mechanism raises the substrate tray and substrate or sample while gas is being provided to the system, such as the aforementioned air, oxygen, and/or ozone, or any combination thereof, in one embodiment prior to ignition of the UV Grid lamp 204.
In some situations, the system may heat the substrate tray 202 and subsequently the substrate. This may be beneficial for some cleaning methods such as the stripping of photo resist.
The cleaning process time can be varied and the exhaust process can also be adjusted. Ozone is drawn through a catalyst material and destroyed.
Of particular interest in the present design is the use of a nitrogen atmosphere and the path of nitrogen through the system, the ability to balance pressures, and the use of the quartz plate. The higher intensity lamp is also noteworthy, as it puts out more UV energy than previously employed, and requires the advanced cooling system disclosed herein.
As noted, the sample or substrate is placed on substrate tray 202 and loaded via drawer 201, which then transitions to lifting pedestal 206 and is raised by pedestal cylinder 207. Both the substrate tray 202 and substrate may be heated. The sample is located a nonzero distance from UV Grid lamp 204 by upward motion of pedestal cylinder 207 and lifting pedestal 206. Once in position, the sample or substrate is in position with quartz plate 203 positioned between the sample and UV Grid lamp 204. UV Grid lamp 204 may be turned on, generating a significant amount of heat. Nitrogen may be provided to the system and nitrogen may be pumped in and out of the system or may be provided in the system and circulated, and periodically changed as necessary. Nitrogen may pass through heat sink 212, along ductwork 209, and in one embodiment, along reflector 205, then upward when striking the wall adjacent the UV Grid lamp 204. Nitrogen is then drawn by cooling fan 211 and returns to heat sink 212. Hot/cold plate 213 and the associated fan assist in the cooling process. Once the cleaning process has progressed for a period of time, the UV Grid lamp 204 may be switched off and the sample lowered, nitrogen flow may be turned off, and the sample may be retrieved from the device. Typical processing time can depend on the amount of cleaning necessary, but in many cases, a 40 percent decrease or more in processing time may be achieved.
Thus the present design includes an apparatus for cleaning a sample comprising an ultraviolet grid lamp having a forward side, the ultraviolet grid lamp configured to direct ultraviolet light energy from its forward side toward the sample, a quartz plate positioned between the forward side of the ultraviolet grid lamp and the sample, and a nitrogen circulating arrangement configured to circulate nitrogen along the ultraviolet grid lamp.
According to another embodiment, there is provided an apparatus for cleaning a sample comprising an ultraviolet grid lamp having a forward side, the ultraviolet grid lamp configured to direct ultraviolet light energy from its forward side toward the sample, a quartz plate positioned between the forward side of the ultraviolet grid lamp and the sample, and a fan arrangement configured to cool the ultraviolet grid lamp by receiving and passing nitrogen in a path proximate the ultraviolet grid lamp.
According to a further embodiment, there is provided an apparatus for cleaning a specimen comprising an ultraviolet grid lamp having a forward side, the ultraviolet grid lamp configured to direct ultraviolet light energy from its forward side toward the specimen, a quartz plate positioned between the forward side of the ultraviolet grid lamp and the specimen, and a nitrogen circulating arrangement configured to circulate nitrogen along the ultraviolet grid lamp.
The foregoing description of specific embodiments reveals the general nature of the disclosure sufficiently that others can, by applying current knowledge, readily modify and/or adapt the system and method for various applications without departing from the general concept. Therefore, such adaptations and modifications are within the meaning and range of equivalents of the disclosed embodiments. The phraseology or terminology employed herein is for the purpose of description and not of limitation.
