Patent ID: 12257610

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over a second feature in the description that follows can include embodiments in which the first and second features are formed in direct contact, and can also include embodiments in which additional features are disposed between the first and second features, such that the first and second features are not in direct contact. In addition, the present disclosure can repeat reference numerals and/or letters in the various examples. This repetition does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein can likewise be interpreted accordingly.

The term “nominal” as used herein refers to a desired, or target, value of a characteristic or parameter for a component or a process operation, set during the design phase of a product or a process, together with a range of values above and/or below the desired value. The range of values can be due to slight variations in manufacturing processes or tolerances.

The term “horizontal,” as used herein, means normally parallel to a level ground.

The term “vertical,” as used herein, means nominally perpendicular to a level ground.

In some embodiments, the terms “about” and “substantially” can indicate a value of a given quantity that varies within 5% of the value (e.g., ±1%, ±2%, ±3%, ±4%, ±5% of the value).

Wafer cleaning is a process to remove contamination introduced during the semiconductor fabrication process. The contamination can include organics (e.g., organic byproducts), metallics (traces of metals), and native oxides. The wafer cleaning process includes dry cleaning methods, wet cleaning methods, or a combination thereof. Further, the wafer cleaning process can be performed in wet tools, which can handle either batches of wafers (e.g., in a bath) or a single wafer at a time (e.g., “single-wafer” tools).

For example, in a single-wafer tool, the wafer enters a cleaning module and is positioned on a wafer stage. The wafer is then subjected to a wafer cleaning process via one or more nozzles positioned above the wafer's surface. The one or more nozzles can flow chemicals (e.g., a chemical solution, deionized water, etc.) under pressure on the wafer's surface to remove contamination. After the wafer cleaning process, the wafer can be dried (e.g., via spinning) and released from the wet cleaning tool.

This disclosure is directed to an apparatus and a method for wafer cleaning that uses a cleaning brush to clean a back surface (e.g., backside) of the wafer. With a cleaning fluid, the brush cleans the back surface of the wafer with a scrubbing motion and ultrasonic vibration. Such apparatus and method improves the removal of the defects from the wafer.

FIG.1is a diagram of an exemplary wafer cleaning apparatus100, in accordance with some embodiments. Wafer cleaning apparatus100can include a wafer holder120, a cleaning nozzle130, and a cleaning brush150. In some embodiments, wafer cleaning apparatus100can include an enclosure105configured to enclose wafer holder120, cleaning nozzle130, and cleaning brush150. In some embodiments, the z-direction inFIG.1can be along a gravitational direction of an environment where wafer cleaning apparatus100is located.

In some embodiments, enclosure105can form an inner space (or a chamber) of wafer cleaning apparatus100in which the wafer cleaning is performed. In some embodiments, enclosure105can include vertical walls (e.g., along the z-axis), a ceiling (e.g., along the x-axis and y-axis), and a floor (e.g., along the x-axis and y-axis and below the ceiling). In some embodiments, one or more openings106can be made in one or more of the vertical walls, ceiling, and floor to install units for gas exchange, e.g., sucking air or expelling exhaust. A noncombustible material can be used to form enclosure105to avoid flammability. The noncombustible material can include, but is not limited to, ethylene chlorotrifluoroethylene (ECTFE), polyvinylidene fluoride (PVDF), perfluoroalkoxy alkane (PFA), or a combination thereof.

Wafer cleaning apparatus100can include wafer holder120configured to hold (or secure) a wafer110inside enclosure105. In some embodiments, wafer holder120can further include a heating plate (not shown inFIG.1) configured to heat wafer110during the wafer cleaning process to enhance the cleaning efficiency. Wafer holder120can also include multiple support pins122and multiple clamp pins124to hold wafer110and prevent wafer110from sliding during the wafer cleaning process. In some embodiments, wafer holder120can include a six-pin design with three additional support pins (e.g., clamp pins, not shown inFIG.1) to reduce wafer slide during wafer cleaning. In some embodiments, an inner flow system (not shown inFIG.1) can be operatively coupled to wafer holder120and configured to introduce gas flow to wafer110during the wafer cleaning process to facilitate the removal of cleaning fluids. Wafer holder120can be further attached to a spin base125. In some embodiments, wafer holder120can spin wafer110via spin base125, which spins wafer110at different speeds during the wafer cleaning process. In some embodiments, wafer holder120can be configured to hold (or secure) the wafer horizontally (e.g., along the x-y plane) or vertically (e.g., along the x-z plane) during the wafer cleaning process.

Wafer cleaning apparatus100can include a cleaning nozzle130configured to supply a flow of (or dispense) a cleaning fluid145onto a front surface of wafer110. As used herein, the front surface of wafer110refers to a major surface on which semiconductor device(s) can be formed. When wafer110is held onto wafer holder120, the front surface faces towards the ceiling (e.g., in the y-direction) of enclosure105. Cleaning nozzle130can be configured to supply a flow of (or dispense) cleaning fluid145onto the front surface of wafer110at a preset amount onto the front surface of wafer110. In some embodiments, cleaning nozzle130can be a pressure nozzle configured to rinse the wafer. Cleaning nozzle130can be attached to a nozzle arm135, which can pivot around a spindle140during the wafer cleaning process. In some embodiments, wafer cleaning apparatus100can be equipped with more than one cleaning nozzle130depending on the design of wafer cleaning apparatus100. In some embodiments, the distance between cleaning nozzle130and wafer110can be adjusted or remain fixed for the duration of the wafer cleaning process. In some embodiments, the orientation of cleaning nozzle130with respect to the front surface of wafer110(e.g., the angle between cleaning nozzle130with respect to the front surface of wafer110) can also be adjusted or remain fixed, according to some embodiments. Cleaning nozzle130can be connected, via one or more chemical switch boxes (not shown inFIG.1), to external tanks (not shown inFIG.1) with chemicals. The chemical switch boxes can be chemical distribution systems, where valves and chemical distribution lines are housed and chemical solutions are pre-mixed prior to delivery to cleaning nozzle130. In some embodiments, cleaning nozzle130may or may not pivot around spindle140while cleaning fluid145is supplied (or dispensed) on wafer110. At the same time, wafer110may or may not be rotated while cleaning fluid145is supplied (or dispensed) on wafer110.

In some embodiments, a portion of an outer surface of cleaning nozzle130can be covered with a conductive layer134to reduce the risk of static electric charge that can occur at cleaning nozzle130during the wafer cleaning process. In some embodiments, cleaning nozzle130can be made of polychlorotrifluoroethylene (PCTFE) and/or polytetrafluoroethylen (PTFE), which have static electricity values (e.g., −4.58 kV for PCTFE) that can increase the risk of static electric charge during the operation of cleaning nozzle130. By coating a portion of the outer surface of cleaning nozzle130with conductive layer134, such as a conductive material with static electricity higher than about −4 kV (e.g., higher than about −4 kV, about −3.5 kV, about −3 kV, about −2.5 kV, about −2 kV, about −1.5 kV, or about −1 kV), the risk of static electric charge can be reduced. In some embodiments, conductive layer134can include carbon nanotubes with a carbon doping of about between 0.025 weight (wt) % and about 0.1 wt % (e.g., between 0.025 wt % and 0.1 wt %, between 0.03 wt % and 0.09 wt %, between 0.04 wt % and 0.08 wt %, or between 0.05 wt % and 0.07 wt %). In some embodiments, an additional grounding unit (not shown inFIG.1), such as a grounding plate or a conductive wire connecting to an external ground level, can be coupled to cleaning nozzle130to further reduce the risk of static electric charge. In some embodiments, cleaning nozzle130can further include an ionizer (not shown inFIG.1) configured to supply corona discharges to cleaning nozzle130to reduce the static electric charge. Corona discharges can be electrical discharges generated by an ionization of a fluid, such as air, surrounding a conductor (e.g., conductive layer134coated on the outer surface of cleaning nozzle130) that is electrically charged.

Cleaning fluid145can include, but is not limited to, hydrofluoric acid, hydrochloric acid, sulfuric acid, hydrogen peroxide, ammonium hydroxide, acetone, methanol, isopropyl alcohol, deionized water (DI water), or a combination thereof. In some embodiments, cleaning fluid145can be a solution including, but is not limited to, a hydrochloric acid/hydrogen peroxide/DI water (HPM) solution, a sulfuric acid/hydrogen peroxide/DI water (SPM) solution, a hydrochloric acid/ozone/DI water (HOM) solution, a sulfuric acid/ozone/DI water (SOM) solution, an ammonium hydroxide/ozone/DI water (AOM) solution, a hydrofluoric acid/DI water (DHF) solution, an ozone solution (ozone diluted in DI water), or a combination thereof. One or more cleaning fluids can be supplied on the wafer successively and independently from one another at different stages of the wafer cleaning process. For example, an exemplary wafer cleaning process can include a DHF operation and an HPM operation with another cleaning operation in between. Depending on the specific cleaning fluid(s) used for wafer cleaning, the heating plate of wafer holder120can heat wafer110to a suitable temperature. For example, for isopropyl alcohol, wafer110can be heated to from about 190° C. to about 195° C. for about 30 seconds to boil the isopropyl alcohol. In some embodiments, the heating plate of wafer holder120can heat wafer110to from about 75° C. to about 85° C. for about 10 minutes to boil the ammonium hydroxide/hydrogen peroxide/DI water (e.g., SC1 clean). In some embodiments, the heating plate of wafer holder120can heat wafer110to from about 75° C. to about 85° C. for about 10 minutes to boil the hydrochloric acid/hydrogen peroxide/DI water (e.g., SC2 clean).

Wafer cleaning apparatus100can include a cleaning brush150configured to clean a back surface (e.g., backside) of wafer110. The back surface (e.g., backside) of wafer110refers to a surface opposite to the front surface of wafer110—e.g., a surface opposite to a major surface of wafer110on which semiconductor device(s) are formed. In some embodiments, cleaning brush150can include a plurality of bristles151configured to scrub wafer110; a brush body152configured to carry (or secure) the plurality of bristles151; a plurality of spray outlets153configured to supply (or dispense) a cleaning fluid onto the back surface of wafer110; and an ultrasonic emitter155configured to ultrasonically vibrate cleaning brush150. In some embodiments, cleaning brush150can also include a pressure sensor157configured to detect the pressure applied to cleaning brush150against wafer110, and a location sensor159configured to track a location of cleaning brush150against wafer110. In some embodiments, wafer cleaning apparatus100can further include a motion mechanism (e.g., not shown inFIG.1) to control a translational or rotational movement of brush150. In some embodiments, the motion mechanism can be configured to press brush150to provide the pressure against wafer110. In some embodiments, the motion mechanism can include a robotic arm (not shown inFIG.1) or a motion stage (not shown inFIG.1).

In some embodiments, plurality of bristles151can be arranged in a plurality of bristle clusters (e.g., 9 clusters as shown inFIG.1). The number of bristle clusters can be any number larger than or equal to 1. For example, the number of bristle clusters can be between about 2 and about 30. In some embodiments, the number of bristle clusters can range from about 1 to about 30, according to some embodiments of the present disclosure. In some embodiments, each bristle cluster can include multiple bristles151having the same length, diameter, hardness, and/or material. In some embodiments, each bristle cluster can include multiple bristles151with different lengths to scrub an uneven or warped regions (not shown inFIG.1) of wafer110. For example, each bristle cluster can include a first group of bristles1511(shown inFIG.2) and a second group of bristles1512(shown inFIG.2), where a length of the bristles in first group of bristles1511can be longer than that of second group of bristles1512. Such bristle cluster with various length of bristles151can conformally contact an uneven or warped surface of wafer110, thus enhancing a cleaning efficiency of brush150. In some embodiments, each bristle cluster can include first group of bristles1511and second group of bristles1512, where each bristle1511can be interleaved with each bristle1512. In some embodiments, each bristle cluster can include first group of bristles1511and second group of bristles1512, where bristles1511can surround bristles1512. Based on the disclosure herein, other lengths and placements of bristles151(e.g.,1511and1512) on brush body152are within the scope and spirit of this disclosure. In some embodiments, each bristle151can have a diameter between about 0.08 mm and about 1 mm. In some embodiments, each bristle151can have a length between about 5 mm and about 8 mm. In some embodiments, the material of plurality of bristles151can include, but is not limited to, polyethylene terephthalate (PET), polypropylene (PP), polyvinyl chloride (PVC), polyamide (PA), or a combination thereof. In some embodiments, each bristle cluster can include multiple bristles151with different length, diameter, hardness, and/or material.

In some embodiments, brush body152can have a drum or a disk shape. Brush body152can be coupled to a rotating shaft, which applies a rotational force from a rotation unit to brush body152. The rotation unit can include a motor, with one or more drive pulleys and a belt for applying the rotational force of the motor to the rotation shaft. Materials for brush body152can be wear-resistant materials, including, but is not limited to, polyoxymethylene (POM), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET or PETE), polystyrene (Styrofoam), polytetrafluoroethylene (Teflon), polyvinylidine chloride (Saran), or a combination thereof. Brush body152can have a diameter between about 20 mm and about 40 mm (e.g., about 30 mm). In some embodiments, plurality of bristles151can be embedded to a depth of about 1 mm to about 3 mm (e.g., about 2 mm) into brush body152.

In some embodiments, cleaning brush150can include a plurality of spray outlets153configured to supply a cleaning fluid onto wafer110(e.g., the back surface or backside of wafer110) during the wafer cleaning process. Plurality of spray outlets153can be embedded in brush body152. The number of spray outlets153can be in the range from about 1 to about 30. In some embodiments, a portion of an outer surface of spray outlets153can be covered with a conductive layer154to reduce the risk of static electric charge. In some embodiments, materials for spray outlets153can include polychlorotrifluoroethylene (PCTFE) and/or polytetrafluoroethylen (PTFE), which have static electricity values (e.g., −4.58 kV for PCTFE) that can increase the risk of static electric charge during the operation of spray outlets153. By coating a portion of the outer surface of spray outlets153with conductive layer154, such as a conductive material with static electricity higher than about −4 kV (e.g., higher than −4 kV, −3.5 kV, −3 kV, −2.5 kV, −2 kV, −1.5 kV, or −1 kV), the risk of static electric charge can be reduced. In some embodiments, conductive layer154can be carbon nanotubes with a carbon doping between about 0.025 weight (wt) % and about 0.1 wt % (e.g., between 0.025 wt % and 0.1 wt %, between 0.03 wt % and 0.09 wt %, between 0.04 wt % and 0.08 wt %, or between 0.05 wt % and 0.07 wt %). In some embodiments, an additional grounding unit (not shown inFIG.1) can be coupled to spray outlets153to further reduce the risk of static electric charge. The cleaning fluid supplied by spray outlets153can include, but not limited to, hydrofluoric acid, hydrochloric acid, sulfuric acid, hydrogen peroxide, ammonium hydroxide, acetone, methanol, isopropyl alcohol, deionized water (DI water), or a combination thereof. In some embodiments, the cleaning fluid can be a solution including, but not limited to, a hydrochloric acid/hydrogen peroxide/DI water (HPM) solution, a sulfuric acid/hydrogen peroxide/DI water (SPM) solution, a hydrochloric acid/ozone/DI water (HOM) solution, a sulfuric acid/ozone/DI water (SOM) solution, an ammonium hydroxide/ozone/DI water (AOM) solution, a hydrofluoric acid/DI water (DHF) solution, an ozone solution (ozone diluted in DI water), or a combination thereof. In some embodiments, the cleaning fluid supplied by plurality of spray outlets153can be the same as cleaning fluid145supplied by cleaning nozzle130. The cleaning fluid supplied by plurality of spray outlets153can be different than cleaning fluid145supplied by cleaning nozzle130. The choice of cleaning fluids can be determined by contaminants on the surface of wafer110. By way of example and not limitation, the HPM mixture is an acidic solution capable of removing metals from the surface of the wafer. More specifically, the HPM can be a solution with high oxidation potential (e.g., higher than about 1.3 V) and low pH (e.g., below about 7). Consequently, metal contaminants on the surface of the wafer can be ionized and dissolved in the HPM solution during the wafer cleaning process. Prior to the wafer cleaning process, one or more wafers can be randomly selected to be screened for contaminants and particles to assess the efficiency of the wafer cleaning process. The contaminants can be (i) any unwanted particles, organics, metallics, or native oxides on the wafer's surface that remaining after the wafer cleaning process, (ii) chemical traces from the wet cleaning solutions used during the wet cleaning and drying processing (e.g., water spots, acids, derivatives of ammonia, etc.), or (iii) a combination thereof.

In some embodiments, cleaning brush150can further include an ultrasonic emitter155configured to provide ultrasonic vibration. Ultrasonic emitter155can provide ultrasonic energy propagating into plurality of brush bristles151and the cleaning solution, by transducer crystals, during the wafer cleaning process. The transducer crystals can be energized by a suitable power supply and oscillate at an ultrasonic frequency in the range between about 28 kHz and about 600 kHz. The ultrasonic vibration can remove particles down to at least 0.3 micrometer in diameter, including organic and inorganic impurities, from the surface (e.g., the back surface or backside) of wafer110. The transducer crystals can be piezoelectric crystals (e.g., lead zirconate titanate crystals or cobalt barium crystals). By way of example and not limitation, ultrasonic emitter155can be placed under and in contact with brush body152. In some embodiments, ultrasonic emitter155can be placed under brush body152, pressure sensor157, and/or location sensor159.

In some embodiments, cleaning brush150can further include a pressure sensor159configured to detect and monitor the pressure applied to cleaning brush150against wafer110. Pressure sensor159can communicate a pressure reading to a control unit (not shown inFIG.1) that controls the pressure applied to cleaning brush150against wafer110by controlling the movement of cleaning brush150. For example, if the measured pressure is too large and raises concerns of wafer damage, pressure sensor159can send a request signal to the control unit to move cleaning brush150away from wafer110, thus applying less pressure to cleaning brush150against wafer110during the wafer cleaning process. The request signal can be transmitted by a wired communication means or a wireless communication means (e.g., a radio frequency (RF) transmitter, or a Bluetooth (BT) transmitter. Pressure sensor159can include, but is not limited to, a piezoresistive pressure sensor, an electromagnetic pressure sensor, a capacitive pressure sensor, a piezoelectric pressure sensor, and an optical pressure sensor. In some embodiments, a pressure applied to cleaning brush150against wafer110can be between about 0.001 and about 0.05 kg/cm2during the wafer cleaning process to maintain cleaning efficiency without damaging the surface of wafer110. In some embodiments, in response to the pressure being below 0.001 kg/cm2, pressure sensor159can be configured to send a request signal to increase a cleaning time or increase the pressure applied by cleaning brush150against wafer110. In some embodiments, in response to the pressure being above 0.05 kg/cm2, pressure sensor159can be configured to send a request signal to reduce the pressure applied by cleaning brush150against wafer110.

In some embodiments, cleaning brush150can further include a location sensor159configured to track the location of cleaning brush150on wafer110. Location sensor159can transmit real-time location of cleaning brush150on wafer110to a control unit (not shown inFIG.1) to ensure that cleaning brush150covers the entire surface of wafer110. In some embodiments, real-time location of cleaning brush150can be transmitted by a wired communication means or a wireless communication means (e.g., a radio frequency (RF) transmitter, or a Bluetooth (BT) transmitter).

In some embodiments, wafer cleaning apparatus100can further include one or more sensors (not shown inFIG.1) configured to detect one or more attributes associated with wafer110, for example, in real time. In some embodiments, the sensor can be an infrared (IR) sensor or any other suitable sensor that can detect temperature of wafer110(e.g., in real time). In some embodiments, the sensor can be a camera or any other suitable sensor that can generate images in various wavelength ranges at the front surface and/or back surface of wafer110, for example, in real time. The outputs of the sensors can be manually observed and analyzed by an operator and/or automatically received by an analyzing system for processing (e.g., to identify abnormal conditions). The number of sensors used for (e.g., real-time) monitoring of wafer cleaning condition is not limited. In some embodiments, a single sensor can be applied to monitor a single attribute or multiple attributes associated with wafer110. In some embodiments, additional sensor(s) can be used to monitor attributes associated with other units in wafer cleaning apparatus100, such as but not limited to, oxygen concentration in enclosure105, humidity in enclosure105, and a level of contamination in enclosure105to ensure safety and/or manufacturing quality.

In some embodiments, wafer cleaning apparatus100can further include an exhaust unit108configured to expel a vapor generated from the cleaning fluid inside enclosure105. Exhaust unit108can be installed through one or more openings106at the ceiling, one of the vertical walls, or the floor of enclosure105. In some embodiments, exhaust unit108can include a duct located on the vertical walls of enclosure105to form a passageway for the cleaning fluid vapor to exit enclosure105of wafer cleaning apparatus100. The duct can be coated with adsorption materials, such as activated carbon, for adsorbing the cleaning fluid vapor passing through duct. In some embodiments, exhaust unit108can include a rinse nozzle configured to generate a mist and to rinse the cleaning fluid vapor passing through duct with mist. A vapor concentration can be reduced by mist from the rinse nozzle. In some embodiments, the mist can be formed by the rinse nozzle by mixing a fluid and an inert gas, in which the mixture can have a greater vapor adsorbing ability than a liquid rinse alone.

FIG.2is a diagram of an exemplary cleaning brush150and an image sensor204configured to monitor cleaning brush150, in accordance with some embodiments. The discussion of elements with the same annotations inFIGS.1and2applies to each other unless otherwise mentioned. Each bristle151can be coated with a coating layer151Cconfigured to indicate wear of each bristle151. In some embodiments, coating layer151Ccan be a color changing wear indicator. The color changing wear indicator can be characterized in that as the period of use of cleaning brush150progresses, the color of the wear indicator changes so that, when a predetermined color of the wear indicator is reached (e.g., the color red), this indicates that the recommended period of use for cleaning brush150has been reached. At this point, plurality of bristles151or cleaning brush150can be replaced. In some embodiments, the materials of plurality of bristles151can include, but is not limited to, polyethylene terephthalate (PET), polypropylene (PP), polyvinyl chloride (PVC), polyamide (PA), or a combination thereof. In some embodiments, the materials for coating layer151Ccan include, but is not limited to, poly (methyl methacrylate) (PMMA), or acrylonitrile butadiene styrene (ABS). Coating layer151Ccan have a different color (e.g., white) than the color of bristle151(e.g., red). Coating layer151Ccan have a lower wear resistance than that of bristle151. After a period of use for cleaning brush150, coating layer151Ccan be partially worn out showing a change of color. The color of bristle151can change from one color (e.g., the color white showing a completely covered coating layer151C1) to another color (e.g., the color red showing a partially worn out coating layer151C2). In some embodiments, image sensor204can be attached inside enclosure105and oriented toward cleaning brush150to monitor usage of plurality of bristles151by monitoring the color change.

FIGS.3A and3Bare diagrams of an exemplary wafer cleaning apparatuses300and350under different operation modes: a horizontal wafer orientation (FIG.3A) and a vertical wafer orientation (FIG.3B), in accordance with some embodiments. Each of apparatus300and350can be an embodiment of apparatus100. The discussion of apparatus100can be applied to apparatuses300and350unless mentioned otherwise. Further, the discussion of elements with the same annotations inFIGS.1,3A, and3Bapplies to each other unless otherwise mentioned. In the horizontal wafer orientation mode, wafer110's surface normal can be along the z-direction (e.g., along the gradational direction), as shown inFIG.3A. Therefore, in the horizontal wafer orientation mode, wafer holder120(shown inFIG.1, not shown inFIGS.3A and3B) can be configured to hold or secure wafer110horizontally (e.g., wafer110's surface can be along the x-y plane shown inFIG.3A). In some embodiments, in the horizontal wafer orientation mode, brush150can be configured to vibrate along direction305(e.g., in the z-direction) using ultrasonic emitter155(not shown inFIG.3A) and displace along direction303(e.g., along the x-y plane) to scrub and clean wafer110. On the other hand, in the vertical wafer orientation mode, wafer110's surface normal can be perpendicular to the z-direction (e.g., perpendicular to the gravitational direction). As a result, wafer holder120can be configured to hold or secure wafer110vertically (e.g., wafer110's surface can be along the x-z plane shown inFIG.3B) Further, as shown inFIG.3B, wafer cleaning apparatus100can further include a connecting nozzle arm137configured to rotate cleaning nozzle130(e.g., rotating about the y-axis) to spray cleaning fluid145horizontally (e.g., in the y-direction) towards vertically (e.g., in the z-direction) oriented wafer110. In some embodiments, connecting nozzle arm137can be configured to be rotational (e.g., about the y-axis) and translational (e.g., along the x-z plane;FIG.3B) and spray cleaning fluid145via cleaning nozzle130towards vertically oriented wafer110. In some embodiments, in the vertical wafer orientation mode, brush150can be configured to vibrate along direction353(e.g., in the y-direction) using ultrasonic emitter155(not shown inFIG.3B) and displace along direction355(e.g., along the x-z plane) to scrub and clean wafer110.

FIG.4is a flow chart of an exemplary wafer cleaning method400, in accordance with some embodiments. Operations shown in method400are not exhaustive; other operations can be performed as well before, after, or between any of the illustrated operations. In some embodiments, operations of method400can be performed in a different order. Variations of method400are within the scope of the present disclosure.

In operation401, a wafer (e.g., wafer110) is loaded onto a wafer holder (e.g., wafer holder120). For example, as shown inFIG.1, the loading of the wafer can include placing the wafer on wafer holder120. In some embodiments, the loading of the wafer can include heating the wafer by a heating plate of the wafer holder before or during a wafer cleaning process (e.g., operations402-404can be embodiments of the wafer cleaning process) to enhance a cleaning efficiency. In some embodiments, the loading of the wafer can include holding or securing the wafer on wafer holder120via multiple support pins (e.g., support pins122) and multiple clamp pins (e.g., clamp pins124) that can prevent the wafer from sliding during a wafer cleaning process (e.g., operations402-404). The wafer holder can be configured to hold (or secure) the wafer horizontally (e.g., the wafer surface's normal can be along a gravitational direction, shown inFIG.1) or vertically (e.g., the wafer surface's normal can be parallel to a gravitational direction, shown inFIG.3B) during the wafer cleaning process. For example, the loading of the wafer can include horizontally (e.g., along the x-y plane ofFIG.1) placing the wafer on the wafer holder, securing the wafer on the wafer holder using one or more support pins and/or clamp pins, and rotating the wafer about 90 degrees to hold the wafer vertically (e.g., along the x-z plane ofFIG.1andFIG.3B).

In operation402, a flow of a cleaning fluid (e.g., cleaning fluid145) is supplied (or dispensed) onto the wafer (e.g., a wafer's front surface where semiconductor devices are formed) through a cleaning nozzle (e.g., cleaning nozzle130). The cleaning fluid can include, but is not limited to, hydrofluoric acid, hydrochloric acid, sulfuric acid, hydrogen peroxide, ammonium hydroxide, acetone, methanol, isopropyl alcohol, deionized water (DI water), or a combination thereof. In some embodiments, a portion of an outer surface of the cleaning nozzle can be covered with a conductive layer (e.g., conductive layer134), such as carbon nanotubes to reduce the static electric charge formed at the cleaning nozzle during operation. In some embodiments, the supply of the flow of the cleaning fluid can include attaching the cleaning nozzle to a nozzle arm (e.g., nozzle arm135), and pivoting the nozzle arm around a spindle (e.g., spindle140). In some embodiments, the supply of the flow of the cleaning fluid can include rinsing the front surface of the wafer with the cleaning fluid. In some embodiments, the rinsing the front surface of the wafer can be concurrently performed by pivoting the nozzle arm around the spindle. In some embodiments, the supply of the flow of the cleaning fluid can include forming a stream of the cleaning fluid via a pressure nozzle and injecting the stream of the cleaning fluid towards the front surface of the wafer (e.g., the cleaning nozzle can be a pressure nozzle to rinse of the wafer). Further, operation420can also include spinning the wafer on the wafer holder via a spin base (e.g., spin base125) at different speeds and/or heating the wafer using the wafer holder. In some embodiments, the spinning and/or the heating of the wafer can be conducted concurrently with the supply of the cleaning fluid.

In operation403, a cleaning fluid is dispensed (or sprayed) onto a back surface (e.g., backside) of the wafer through plurality of spray outlets (e.g., plurality of spray outlets153) located on the cleaning brush (e.g., cleaning brush150). The cleaning fluid for cleaning the back surface (e.g., backside) of the wafer in operation403can be made of the same or different chemicals as that for cleaning the front surface of the wafer (e.g., the cleaning fluid described in operation402). In some embodiments, dispensing the cleaning fluid on the backside of the wafer can include rinsing the back surface of the wafer. In some embodiments, dispensing the cleaning fluid can include forming a stream of the cleaning fluid and directing the cleaning fluid through the spray outlets and towards the back surface of the wafer. In some embodiments, dispensing the cleaning fluid on the back side of the wafer can include heating the wafer using the wafer holder. In some embodiments, one or more operations described in402and403can be performed concurrently. In some embodiments, a portion of an outer surface of the spray outlets can be covered with a conductive layer (e.g., conductive layer154) to reduce the risk of static electric charge.

In operation404, the back surface (e.g., backside) of the wafer is brushed via the cleaning brush. For example, the back surface of the wafer can be brushed via cleaning brush150, while the wafer can be placed or secured on wafer holder120. In some embodiments, brushing the back side of the wafer via the cleaning brush can include applying a pressure to the cleaning brush against the back surface of the wafer, spinning the wafer, and rotating/displacing the cleaning brush (referred herein as “scrubbing mode”) using a motion mechanism (e.g., a robotic arm or a motion stage) to scrub the wafer. In the scrubbing mode, the cleaning brush can be rotated at a rotational speed less than a threshold (e.g., about 2500 rpm) to ensure a stability control of the cleaning brush (e.g., the cleaning brush's motion stability). In some embodiments, in the scrubbing mode, the wafer can be stationary while the cleaning brush is rotating/displacing to scrub the wafer's back surface. In some embodiments, in the scrubbing mode, rotating the cleaning brush can include spinning the cleaning brush counterclockwise or clockwise. In some embodiments, in the scrubbing mode, rotating the cleaning brush can include interleaving a counterclockwise rotation of the cleaning brush with a clockwise rotation of the cleaning brush. Namely, rotating the cleaning brush can include alternatively rotating the cleaning brush counterclockwise and clockwise.

In some embodiments, brushing the back side of the wafer can include contacting the back surface of the wafer with the cleaning brush, spinning the wafer, and vibrating the cleaning brush by, for example, an ultrasonic vibration device (referred herein as “vibration mode”). In the vibration mode, the ultrasonic vibration of the cleaning brush can be performed at a frequency between about 28 kHz and about 600 kHz. Vibrating the cleaning brush can include swinging the cleaning brush along the wafer's back surface's normal (e.g., vibrate the cleaning brush along in z-direction inFIG.3A, or along the y-direction inFIG.3B). In some embodiments, brushing the back side of the wafer via the cleaning brush can include performing both the scrubbing mode and the vibration mode on the wafer's back surface. In some embodiments, brushing the back side of the wafer can include concurrently performing one or more operations (e.g., applying the pressure or rotating the cleaning brush) previously described in the scrubbing mode and one or more operations (e.g., vibrating the cleaning brush) previously described in the vibration mode. In some embodiments, brushing the back surface of the wafer can include sequentially alternating between scrubbing mode and vibration mode.

In some embodiments, the cleaning fluid (e.g., cleaning fluid145) can be concurrently supplied to the wafer (e.g., the wafer's front surface and/or back surface), while the wafer's back surface is brushed by the cleaning brush (e.g., one or more operations described in operation404can be performed concurrently with one or more operations described in operation402and/or operation403.)

Further, in operation404, brushing the back surface of the wafer via the cleaning brush can include detecting and adjusting a pressure of the cleaning brush against the wafer via a pressure sensor (e.g., pressure sensor159). In some embodiments, the pressure to the cleaning brush against the wafer can be between about 0.001 and about 0.05 kg/cm2to maintain a cleaning efficiency without damaging the surface of the wafer. In some embodiments, if the detected pressure is above 0.05 kg/cm2, the pressure sensor can send a request signal to a control unit to increase a separation between the cleaning brush and the wafer to reduce the pressure. In some embodiments, if the detected pressure is below 0.001 kg/cm2, the pressure sensor can send a request signal to a control unit to decrease a separation between the cleaning brush and the wafer to enhance the pressure.

Further, in operation404, the brushing of the back surface of the wafer can include tracking a location of the cleaning brush via a location sensor (e.g., location sensor159). The location sensor can transmit (e.g., real-time) location of the cleaning brush to a control unit to ensure that the cleaning brush covers the entire back side surface of the wafer during the wafer cleaning process.

Further, in operation404, brushing of the back surface of the wafer via the cleaning brush can include detecting a visual signature of the cleaning brush, comparing the detected visual signature to a baseline signature, and replacing the cleaning brush based on the comparison. In some embodiments, detecting the visual signature of the cleaning brush can include monitoring a color appearance of bristles associated with the cleaning brush using an image sensor (e.g., image sensor204inFIG.2). The detected color appearance (e.g., the color of coating layer151C2of a worn cleaning brush shown inFIG.2) can be compared to a baseline color signature of a qualified cleaning brush (e.g., the color coating layer151ciof a new cleaning brush shown inFIG.2). If the comparison indicates the cleaning brush is worn out, the cleaning brush needs to be replaced. In some embodiments, detecting the visual signature, comparing the visual signature, and replacing the cleaning brush can be performed prior to the scrubbing mode and the vibration mode described previously (e.g., examine and replace the cleaning brush before starting to clean the wafer).

Various embodiments in accordance with the present disclosure provide an apparatus and a method for wafer cleaning in semiconductor device manufacturing. The apparatus can include a wafer holder configured to hold a wafer; a cleaning nozzle configured to dispense a cleaning fluid onto a first surface (e.g., front surface) of the wafer; and a cleaning brush configured to clean a second surface (e.g., back surface) of the wafer. The cleaning brush can clean a back surface of the wafer with scrubbing and ultrasonic vibration and with a cleaning fluid. Such apparatus and method can provide an enhanced and more effective cleaning to remove the defects from the wafer.

In some embodiments, an apparatus for wafer cleaning can include a wafer holder configured to hold a wafer; a cleaning nozzle configured to dispense a cleaning fluid onto a first surface of the wafer; and a cleaning brush configured to clean a second surface, opposite to the first surface, of the wafer. The cleaning brush can include a plurality of bristles and a plurality of spray outlets configured to dispense the cleaning fluid onto the second surface of the wafer. The apparatus can further include an enclosure configured to enclose the wafer holder, the cleaning nozzle and the cleaning brush.

In some embodiments, a method for cleaning a wafer can include loading the wafer onto a wafer holder, dispensing a cleaning fluid onto a surface of the wafer, spinning the wafer, and applying a pressure on the surface of the wafer via a cleaning brush and a motion mechanism.

In some embodiments, a method for cleaning a wafer is disclosed. The method can include loading the wafer onto a wafer holder; rinsing a first surface of the wafer by dispensing a cleaning fluid onto the first surface of the wafer; dispensing, with spray outlets on a cleaning brush, the cleaning fluid onto a second surface, opposite to the first surface, of the wafer; and cleaning, with the cleaning brush, the second surface of the wafer. In some embodiments, cleaning the second surface of the wafer can include applying a pressure to the cleaning brush against the wafer, rotating the cleaning brush and vibrating the cleaning brush.

It is to be appreciated that the Detailed Description section, and not the Abstract of the Disclosure, is intended to be used to interpret the claims. The Abstract of the Disclosure section can set forth one or more but not all exemplary embodiments contemplated and thus, are not intended to be limiting to the subjoined claims.

The foregoing disclosure outlines features of several embodiments so that those skilled in the art can better understand the aspects of the present disclosure. Those skilled in the art will appreciate that they can readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art will also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they can make various changes, substitutions, and alterations herein without departing from the spirit and scope of the subjoined claims.