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Method of cleaning a probeRelated Patent Categories: Abrading, Abrading Process, Roll, Roller, Shaft, Ball, Or Piston AbradingMethod of cleaning a probe description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070178814, Method of cleaning a probe. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This is a divisional of application Ser. No. 11/218,932 filed Sep. 2, 2005, now pending, which is a continuation-in-part of application Ser. No. 10/298,310 filed Nov. 14, 2002, which is a continuation of International Application No. PCT/JP02/03335 filed Apr. 3, 2002, which claims priority on Japanese Patent Application 2001-135090 filed May 2, 2001. BACKGROUND OF THE INVENTION [0002] This invention relates to a method of removing foreign substances attached to the tip and side surfaces of a probe used for inspecting a planar target object such as a semiconductor device having integrated circuits installed thereon. [0003] Chips are produced by installing semiconductor elements and integrated circuits on a semiconductor wafer through various wafer-producing processes. The chips thus produced on a semiconductor wafer are cut off from the wafer after a current-passing test and are packaged. Tests with a current are carried out also before and after the packaging to separate faulty products stringently from qualified products. [0004] Such current-passing tests are carried out by means of a test apparatus of a known kind such as a wafer prober. A position-matching process of moving a prober needle ("probe") serving as an electrode of a tester and the electrodes on the chip (pads or lead lines) and a contacting process between the probe and the chip electrodes are repeated for carrying out electrical measurements of different kinds. [0005] While such position-matching and contacting processes are repeated by moving the probe and the electrodes on the chips, the tip of the probe slides over the electrodes on the chips, scraping off portions of the electrodes. Such portions of the electrodes that have been scraped off become attached to the tip and the side surfaces of the probe as foreign substances. [0006] The foreign substances, that thus become attached to the probe, are metals such as aluminum. If such a metal is oxidized, the electrical contact resistance between the probe and the electrodes on the chip becomes larger, making it impossible to carry out accurate electrical measurements. Thus, it is necessary to clean the tip portion of the probe regularly after each time a specified number of contact processes have been carried out in order to remove such foreign substances from the probe. [0007] Removal of such foreign substances from the tip portion of a probe is carried out by using the same apparatus used for the current-passing tests such as the aforementioned wafer prober, except the target object to be tested such as a semiconductor wafer attached to the apparatus is replaced with a cleaning device having a similar shape. Examples of a prior art cleaning device of this kind include hard polishing plates of a grinding stone, glass and a ceramic material (as disclosed, for example, in Japanese Patent Publications Tokkai 7-199141, 5-209896, 5-166893, 4-96342 and 3-105940) and sheets with a polishing layer formed on an uneven surface of an elastic member having protrusions and indentations (as disclosed, for example, in Japanese Patent Publication Tokkai 2000-332069). The probe is pressed against the surface of such a cleaning device, as done in the aforementioned current-passing test. [0008] If a polishing plate of a hard material is used as the cleaning device and the probe is pressed too hard against it, its tip portion will become deformed and hence it is necessary to reduce the pressure with which the probe can be pressed against the cleaning device. As a result, only the portions very close to the tip can be cleaned. If a cleaning device of the type with a polishing layer formed on an elastic member is used, on the other hand, the tip of the probe penetrates the polishing layer and cannot be cleaned sufficiently. Thus, the common practice has been to provide separately a device for cleaning the tip and another device for cleaning the side surfaces, attaching them to a current-passing test apparatus consecutively one at a time. It was therefore both cumbersome and time-consuming to clean a probe. SUMMARY OF THE INVENTION [0009] It is therefore an object of this invention in view of the above to provide an improved method of cleaning a probe. [0010] A cleaning sheet which may be used according to this invention (hereinafter also referred to as a cleaning sheet of this invention or a cleaning sheet embodying this invention) may be characterized as comprising a base sheet, a foamed layer of a porous material which is formed on the base sheet and includes non-fibrous abrading particles and air bubbles, and a polishing layer formed on the foamed layer. [0011] Such a cleaning sheet may be produced by preparing a paint having air bubbles dispersed therein by mechanically foaming a foaming material comprising a foaming resin material and abrading particles, forming on a base sheet a foamed layer having abrading particles dispersed inside by coating a surface of the base sheet with this paint and drying it, and forming a polishing layer on a surface of the foamed layer. [0012] Such paint may be produced by sending air into the foaming material while stirring the foaming material and thereby dispersing the air bubbles and the abrading particles inside the paint. Because it is by a mechanical means that the foaming material is caused to be foamed, the abrading particles and the air bubbles can be dispersed uniformed throughout the interior of the foamed layer without strictly maintaining the conditions for the foaming reaction such as the reaction time and temperature. [0013] A probe having a tip may be cleaned with a cleaning sheet embodying this invention, structured and produced as described above, by causing a surface of its polishing layer to be pressed against the tip of the probe and thereby causing the tip of the probe to penetrate the polishing layer and further to be inserted into the foamed layer having abrading particles dispersed inside. As the tip penetrates the polishing layer and becomes inserted into the foamed layer having abrading particles dispersed inside, both the tip and the side surfaces of the probe become cleaned not only by the abrading particles inside the polishing layer but also those in the foamed layer. [0014] In summary, with a cleaning sheet thus structured and/or produced, the tip and the side surfaces of a probe can be effectively and simultaneously cleaned. BRIEF DESCRIPTION OF THE DRAWINGS [0015] FIG. 1 is a sectional view of a cleaning sheet embodying this invention when a tip portion of a probe is being cleaned therewith. [0016] FIG. 2 is a schematic side view of a wafer prober. DETAILED DESCRIPTION OF THE INVENTION [0017] FIG. 2 shows a wafer prober 20 of a known kind. When a cleaning process according to this invention is effected, a cleaning sheet 10 embodying this invention to be described below and shown in FIG. 1 is attached to such a wafer prober 20 instead of a target object to be inspected such as a semiconductor wafer which is normally attached thereto. As shown in FIG. 1, the cleaning sheet 10 is comprised of a base sheet 11, a foamed layer 12 formed on a surface of the base sheet 11 and a polishing layer 13 formed on the surface of the foamed layer 12. The foamed layer 12 is a layer of a porous foamed material containing non-fibrous abrading particles 14 and many air bubbles inside. Such a cleaning sheet may be produced by first preparing a paint material by mechanically foaming a material including a foaming resin and abrading particle. A surface of the base sheet 11 is then coated with this paint material and it is dried so as to form the foamed layer 12 with the abrading particles dispersed therein. The polishing layer 13 is thereafter formed on the surface of this foamed layer 12. [0018] The foaming material to be used in the production method described above may be obtained by mixing a foaming agent such as a salt of fatty acid, an acrylic thickener, a fluorine or silicon type stabilizer, and also powder of aluminum hydroxide with average diameter of 0.01-70 .mu.m for improving the stabilization effect, and further by mixing in an epoxy cross linking agent. As the abrading particles 14, particles of aluminum oxide, silicon carbide, chromium oxide, iron oxide, diamond, boron carbide, cerium oxide or silicon oxide with average diameter of 0.01-70 .mu.m are also mixed into the foaming material in an amount of 5-80 weight %. Throughout herein, the expression "particles" is intended to be interpreted in a narrow sense of the word, excluding any small objects that may be referred to as being fibrous or a fiber particle. [0019] The mechanical foaming of the foaming material thus prepared is effected with stirring while sending in air at a specified rate into the foaming material containing the abrading particles 14. As a result of this process, the abrading particles 14 and the air bubbles 15 become uniformly dispersed inside the foaming material and a paint with a high degree of viscosity containing air bubbles is obtained. The foaming multiplicity of the paint is in the range of 2-5 times. Such a mechanical foaming process may be carried out by using a continuous high-pressure foaming apparatus (such as TW-70 produced by Aikosha Seisakusho of Japan) used for the continuous mixing process of raw cream. [0020] The paint material with air bubbles may be applied on a surface of the base sheet 11 by a known method and with a known means such as the knife coater method and the so-called direct coating method. A sheet with a flat surface of a plastic material such as polyester and polyethylene terephthalate (PET) may be used as the base sheet 11. The drying process for the paint applied on the base sheet 11 may be effected in an environment with temperature in the range of 90.degree. C.-160.degree. C. In order to completely solidify the paint, a far infrared ray may be applied additionally. For forming a stable foamed layer 12 with abrading particles dispersed on the surface of the base sheet 11, furthermore, a ventilating means such as a fan may be used to cool it after the foaming paint coated on the surface of the base sheet 11 is completely dried. After such a drying process, a foamed layer 12 with air bubbles 15 and abrading particles 14 uniformly dispersed throughout is formed on the surface of the base sheet 11. The thickness of the foamed layer 12 thus produced is within the range of 50 .mu.m-200 .mu.m. Continue reading about Method of cleaning a probe... 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