A method includes receiving a wafer stack having at least two wafers bonded together. At least one blade is inserted between a first wafer of the at least two wafers and a second wafer of the at least two wafers. The blade has a channel configured to inject air or fluid. The first wafer is debonded from the second wafer using the at least one blade. In another embodiment, a detacher having a convex bottom surface is attached to the wafer stack. The first wafer is debonded from the second wafer using the detacher.

BACKGROUND

In the manufacturing of integrated circuits, wafers are used for forming integrated circuits. In some applications, wafers are bonded together to form a wafer stack. During inspection of the bonded wafers, the bonding may be found defective and the wafers may need to be debonded from each other. If the bonding of the wafer stack is successful, some remaining processes may be performed on the wafers to complete the manufacturing process.

However, some wafer stacks are difficult to separate by using conventional mechanical or chemical methods. Also, the wafers are sometimes relatively thin to endure the force applied in such debonding processes. Such wafers may suffer breakage during debonding processes. Accordingly, methods of debonding wafers are desired to prevent wafer breakage.

DETAILED DESCRIPTION

In some fabrication processes, wafers are bonded together to form a wafer stack. During the inspection of the bonded wafers, the bonding may be found defective and the wafers may need to be debonded from each other. However, some wafer stacks are difficult to separate by using conventional mechanical or chemical methods. Also, the wafers are sometimes relatively thin to endure the force applied in such debonding processes. Such wafers may suffer breakage during debonding processes. Debonding schemes to separate wafers that help to reduce wafer damage during a debonding process are disclosed herein.

FIG. 1Ais a top view of a debonding scheme of a wafer stack according to some embodiments.FIG. 1Bis a perspective diagram of the debonding scheme inFIG. 1Aaccording to some embodiments. In the description below, both figures are referred to for reference.

InFIG. 1A, a top view of a wafer stack (101inFIG. 1B) including a top wafer102and a bottom wafer (106inFIG. 1B) is shown, as more clearly illustrated inFIG. 1B. The top and bottom wafers102and106comprise silicon, silicon dioxide, aluminum oxide, sapphire, germanium, gallium arsenide (GaAs), an alloy of silicon and germanium, indium phosphide (InP), silicon on insulator (SOI), or any other suitable material in some embodiments. The wafers102and106may also be made of or include some other suitable elementary semiconductor, such as diamond or germanium; a suitable compound semiconductor, such as silicon carbide, indium arsenide; or a suitable alloy semiconductor, such as silicon germanium carbide, gallium arsenic phosphide, or gallium indium phosphide. Alternatively, the wafers102and106may include a non-semiconductor material such as a glass wafer for thin-film-transistor liquid crystal display (TFT-LCD) devices, or fused quartz or calcium fluoride for a photomask (mask).

In some embodiments, the wafer102and/or106include one or more material layers (e.g., insulating, conductive, semi-conductive, etc.) formed thereon. The wafer102and/or106may include various doped regions, dielectric features, and multilevel interconnects. The wafer102and/or106may further include additional features or layers with various devices and functional features. Active and passive devices, such as transistors, capacitors, resistors, and the like, may be formed on the wafer102and/or106. In some embodiments, the wafer102and/or106includes various doped features for various microelectronic components, such as a complementary metal-oxide-semiconductor field-effect transistor (CMOSFET), an imaging sensor, and a memory cell. As used herein, the term “wafer” includes the various layers, regions, and features described herein.

The top wafer102and the bottom wafer106are bonded together. In some applications, a fusion bonding is used, which is also referred to as direct bonding. A direct bonding is a wafer bonding process without any additional intermediate layers, such as adhesives. The bonding process is based on chemical bonds between two surfaces of wafers, e.g., Si—Si, oxide-oxide, etc. Some requirements may be specified for the wafer surface, such as sufficiently clean, flat, and smooth conditions. Otherwise unbonded areas (also called voids, i.e. interface bubbles) can occur.

The procedural steps of the direct bonding process of wafers may include wafer surface preprocessing, pre-bonding at room temperature, and annealing at elevated temperatures. Direct bonding as a wafer bonding technique is able to process many materials, and silicon and oxide are often used materials. For example, applications for silicon direct bonding include manufacturing of Silicon on insulator (SOI) wafers, sensors, micro-electromechanical system (MEMS), and actuators, etc.

Another wafer bonding process is anodic bonding. Anodic bonding is commonly used to seal glass to thin pieces of silicon in integrated circuit fabrication. This bonding technique is also known as field assisted bonding or electrostatic sealing, and is mostly used for connecting silicon/glass and metal/glass through electric fields. The requirements for anodic bonding may include clean and even wafer surfaces and atomic contact between the bonding wafers through a sufficiently powerful electrostatic field. In some applications, the coefficients of thermal expansion (CTE) of the bonded wafers are similar. In some applications, other materials are used for anodic bonding with silicon, i.e., low-temperature cofired ceramics (LTCC). Exemplary applications for anodic bonding include manufacturing of micro-electromechanical system (MEMS), micro-Total Analysis Systems (μTAS), microfluidic devices, and miniaturized biological reactors, etc.

Yet another wafer bonding process is eutectic bonding. Eutectic bonding is a wafer bonding technique with an intermediate metal layer that can produce a eutectic system. For example, eutectic bonding is used in solder ball bonding. Those eutectic metals are alloys that transform directly from solid to liquid state, or vice versa from liquid to solid state, at a specific composition and temperature without passing a two-phase equilibrium, i.e. liquid and solid state. The fact that the eutectic temperature can be lower than the melting temperature of the two or more pure elements can be important in eutectic bonding.

Eutectic alloys are deposited by sputtering, dual source evaporation, or electroplating. It also can be formed by diffusion reactions of pure materials and subsequently melting of the eutectic composition. The eutectic bonding can be conducted at relatively low processing temperatures, and provides low resultant stress induced in final assembly, high bonding strength, large fabrication yield and a good reliability. Those attributes are dependent on the coefficient of thermal expansion (CTE) between the wafers. Exemplary applications for eutectic bonding include manufacturing of pressure sensors or fluidics, micro-electromechanical system (MEMS), etc.

Four blades104are shown inFIGS. 1A and 1B, while performing a debonding operation of being inserted between the top wafer102and the bottom wafer106. The blades104have a width W ranging from 1 mm to 5 mm, e.g., 2 mm, in some embodiments. The blades104have a horizontal tip angle105in the range of about 10°-about 15° in some embodiments.

In some embodiments, the wafers102and106may have beveled edges at some locations or all around the circumferences of the wafers102and106. The blades104can be inserted in areas between the top wafer102and the bottom wafer106, and the areas may have beveled edges to help the insertion as shown inFIG. 1E. The insertion point can be precisely controlled with a resolution R down to about 50 nm to about 150 nm, e.g., using a motor and/or an optical instrument, in some embodiments.

The blades104can be driven (moved) toward the center of the wafer stack101, and are controlled by a control circuit107in some embodiments. (The control circuit107is not shown in other figures for simplicity.) The blades104are fixed on any suitable fixtures that can be moved towards the center of the wafer stack101in some embodiments. Such fixtures are connected with motors (not shown) that can move the fixtures and the blades104in some embodiments. The force from the insertion point can be detected for a feedback by the impedance current of the motors connected to the fixtures in some embodiments.

The four blades104are arranged at four locations around the circumference of the wafer stack101. In some embodiments, the four locations are separated from each other by an equal distance. The four locations are arranged at 90 degrees apart around the center of the wafer stack102in some examples. Even though four blades104are shown inFIGS. 1A and 1B, any number of blades can be used, such as one, two, three, or more as shown inFIGS. 2C-2E. The blades104are described in more detail with respect toFIGS. 1C and 1Din some embodiments.

The wafer stack101is mounted on a bottom stage108as shown inFIG. 1Bin some embodiments. The bottom stage108is a vacuum stage providing vacuum suction on the bottom surface of the bottom wafer106to help stabilize and hold the bottom wafer106of the wafer stack101during the debonding process in some embodiments. There is a vacuum module120connected to the bottom stage108in some embodiments. The bottom stage108has a heating element116to help the debonding process in some embodiments. For example, if the wafer stack101is bonded using eutectic bonding, the temperature of the heating element116could be over 300° C.

A top stage110shown in dotted line inFIGS. 1A and 1Bis used to hold the top wafer102in some embodiments. The top stage110is a vacuum stage providing vacuum suction on the top surface of the top wafer102to help stabilize and hold the top wafer102of the wafer stack101during the debonding process in some embodiments. The top stage110and the bottom stage108can be moved upward and downward respectively during a debonding process to help the separation of the top wafer102and the bottom wafer106in some embodiments. For example, a motor118connected to the bottom stage108can be used to move the bottom stage108. A similar arrangement for movement can be made for the top stage110.

The top stage110and the bottom stage108have a diameter (or surface length) ranging from 310 mm to 350 mm in some embodiments to hold or cover various wafer sizes. The top stage110and the bottom stage108can be made of SiN, stainless steel, aluminum, any combination thereof, or any other suitable material. The vacuum suction force of the top stage110and the bottom stage108may range from −800 mbar to −1600 mbar in some embodiments. In other embodiments, the size, material, and vacuum pressure range of the top stage110and the bottom stage108can be different.

FIG. 1Cis a cross section of the blade104used in the debonding scheme of wafer stack inFIG. 1Aaccording to some embodiments. The blade104has a channel112that can be used to inject or send out air/liquid to help the debonding process. The blade104has a height H1ranging from 0.1 mm to 2 cm, a length L1ranging from 1 mm to 5 cm, a channel112diameter D1ranging from 0.01 mm to 1 mm, and a tip length E ranging from 0 mm to 0.5 mm in some embodiments. The tip length E provides space for air/liquid flow. The blade104has a vertical tip angle113in the range of 1°-3° in some embodiments. In one example, the blade104has the height H1of 0.5 mm, the length L1of 10 mm, the channel112diameter D1of 0.1 mm, and a tip length E of 0.3 mm.

In order not to damage the wafers102and106, the blade104is made of Teflon, glass, ceramic, any combination thereof, or any other suitable material. If the blade104is too hard, the wafers102and106may be damaged. If the blade104is too soft, the blade104may have difficulty when inserting between the wafers102and106. In some embodiments, the blades104have a hardness range from 60 to 70 in durometer type A. The blade104can inject or send out air/liquid flow114to assist the debonding process in some embodiments. For example, the air/liquid flow114rate can be up to 1 c.c. per minute or more in some embodiments. The liquid sent out by the blade104can be deionized (DI) water in some embodiments. The temperature of air or liquid can be at a room temperature. In some embodiments, the temperature of air or liquid is about 22° C.-23° C.

FIG. 1Dis another cross section of the blade104used in the debonding scheme of wafer stack inFIG. 1Aaccording to some embodiments. The blade104inFIG. 1Dhas symmetric angled slopes on both upward and downward directions with respect to the horizontal line (dotted line). The blade104has a vertical tip angle113in the range of 1°-3° in some embodiments. The dimensions and material of the blade104inFIG. 1D, including the channel112, are similar to the blade104inFIG. 1C. The air/liquid flow114that can be sent through the channel112is also similar as described above with respect toFIG. 1C.

FIG. 1Fis a plot of air/liquid flow rate vs. time from the blade inFIGS. 1C and 1Daccording to some embodiments. As shown, the air/liquid flow rate can be constant112, increased124, or decreased126over time in some embodiments. The air/liquid flow rate can change depending on various applications.

FIG. 2Ais another top view of the debonding scheme inFIG. 1Aat a later stage according to some embodiments.FIG. 2Bis a perspective diagram of the debonding scheme inFIG. 2Aaccording to some embodiments. InFIG. 2A, the blades104are driven (moved) toward the center of the wafer stack101. In some embodiments, the blades104are moved toward the center of the wafer stack101about 3 mm to about 5 mm. As the blades104are driven toward the center of the wafer stack101, air or liquid is sent through the channel112of the blades104at an area between the top wafer102and the bottom wafer106to help the separation of the top wafer102and the bottom wafer106.

In some embodiments, the flow rate of air/liquid can be changed with the progress of the separation as shown inFIG. 1F. In some embodiments, the air/liquid flow114can have a flow rate up to 1 c.c. per minute or more. In some embodiments, the blade104can inject or send out deionized (DI) water through the channel112. The temperature of the air or liquid can be at a room temperature. In some embodiments, the temperature of air or liquid is about 22° C.-23° C.

As the top wafer102and the bottom wafer106are separated, the bottom stage108is moved downward to help the separation in some embodiments. Also, the top stage110is moved upward to help the separation in some embodiments. The bottom stage108may be moved downward simultaneously as the blades104are inserted to separate the wafers102and106in some embodiments. The vacuum suction of the top stage110and the bottom stage108may range from −800 mbar to −1600 mbar in some embodiments. In other embodiments, vacuum pressure range of the top stage110and the bottom stage108can be different.

The blade104provides a separation force between wafers102and106during insertion and while moving toward the center of the wafer stack101. The air/liquid flow114from the channel112assists the separation in some embodiments. The air/liquid flow114helps to separate the bonded interface of the top wafer102and the bottom wafer106with less damage. The method using the blade104that has the channel112capable of injecting air/liquid to assist the debonding process reduces damages to wafers, thus helps to make the bonding-debonding process to be a re-workable process.

FIGS. 2C-2Eare top views of the debonding scheme according to some other embodiments. InFIG. 2C, one blade104is shown and the blade104is inserted between wafers102and106from one location. InFIG. 2D, two blades104are shown and the blades104are inserted between wafers102and106from two locations, e.g., 180 degrees apart. InFIG. 2E, three blades104are shown and the blades104are inserted between wafers102and106from three locations, e.g., 120 degrees apart. Any other number of blades104is possible in some embodiments.

FIG. 3is a flow diagram illustrating the method of the debonding scheme of the wafer stack inFIGS. 1A-1B, and 2A-2Eaccording to some embodiments. At operation302, a wafer stack101having at least two wafers bonded together (such as102and106) is received. The wafer stack101is mounted and fixed on the bottom stage108. The wafer stack101is also held and fixed under the top stage110by vacuum suction in some embodiments.

At operation304, at least one blade104is inserted between a first wafer (e.g., the top wafer102) and a second wafer (e.g., the bottom wafer106). An inserting force is applied to the blade104to provide debonding energy ranging from 0.3 J/m2-50 J/m2at the bonded interface in some embodiments. The debonding process is assisted by an air/liquid flow114from the channel112of the blade104.

At operation306, the first wafer102is separated from the second wafer106using the at least one blade104. The blade104is moved toward the center of the wafer stack101for the separation of the first wafer102and the second wafer106. The bottom stage108holding the bottom wafer106by vacuum suction is moved downwards to help the separation in some embodiments. The top stage110holding the top wafer102by vacuum suction is moved upwards to help the separation in some embodiments. The debonding process is assisted by an air/liquid flow114from the channel112of the blade104.

For moving the top stage110and/or the bottom stage108, a servo motor driving a ball screw can provide a linear downward movement to the top stage110and/or the bottom stage108in some embodiments. Some servo motor provides debonding energy ranging from 0.3 J/m2-50 J/m2in some embodiments. The downward movement can be applied continuously to complete the debonding process in some embodiments. The impedance of the servo motor can be measured to calculate the debonding force to help debonding mechanism analysis in some embodiments. The whole debonding process is performed in a vacuum chamber with a pressure ranging from about 0.01 mbar to about 955 mbar ambient in order to avoid particle issue and also avoid the force concentration from deformation of bonded wafers102and106at the starting point of the debonding process in some embodiments. Otherwise, the force concentration may damage the wafers102and106in some cases.

FIGS. 4A-4Dare side views of intermediate stages of another debonding scheme of the wafer stack according to some embodiments. For the debonding process, a wafer stack101having at least two wafers bonded together is received. The bonded wafer stack101is mounted and fixed on a bottom stage401. A detacher400is used to debond the wafer stack101including a top wafer102and a bottom wafer106as described below.

InFIG. 4A, the wafer stack101is mounted on a bottom stage401. The bottom stage401is a vacuum stage providing vacuum suction (with the vacuum module410) on the bottom surface of the bottom wafer106to help stabilize and hold the bottom wafer106of the wafer stack101during the debonding process in some embodiments.

The bottom stage401has a diameter (or a surface length) ranging from 310 mm to 350 mm in some embodiments to handle various wafer sizes. The bottom stage401may be made of SiN, stainless steel, aluminum, any combination thereof, or any other suitable material. The vacuum suction of the bottom stage401may range from about −800 mbar to about −1600 mbar in some embodiments. In other embodiments, the size, material, and vacuum pressure range of the bottom stage401can be different.

The detacher400has a body402and a rotation axis404. The body has a convex bottom surface403. For example, the convex bottom surface403can be a roller shape surface. The body402has a bottom diameter or length L2ranging from about 250 mm to about 450 mm, and a height H2ranging from about 100 mm to about 300 mm in some embodiments. The length L2can be smaller or larger than the diameter of the wafer stack101. In one example, the body402has a bottom diameter or length of about 350 mm and a height of about 175 mm. The body402is made of aluminum, stainless steel, or any other suitable material. In some embodiments, the convex bottom surface403has a roller shape and can be rotated in a roller like motion.

A rotation axis404is connected to the body402. The rotation axis404is configured to rotate the convex bottom surface403. In some embodiments, the rotation axis404rotates the body402at a speed ranging from about 0.1 degree/sec to about 0.2 degree/sec. The rotation axis404has a diameter ranging from 10 mm to 50 mm in some embodiments. The rotation axis404is made of aluminum, stainless steel, or any other suitable material. The rotation axis404has a diameter of about 25 mm in one example.FIG. 4Eis a top view of the detacher inFIGS. 4A-4Daccording to some embodiments. The body402with the length L2and the rotation axis404are shown.

An attachment element406is configured to attach the convex bottom surface403of the body402to a top surface of a wafer stack101. The attachment element406is a vacuum suction module in some embodiments. In other embodiments, the attachment element406can be a glue layer. The glue layer has a strength range greater than 30 MPa in some embodiments. The glue layer as the attachment element406has a thickness up to 3 mm or more in some embodiments. The glue layer is made of a tape layer, UV-curable adhesive layer, acrylic resin, or any other suitable material. In some embodiments, the glue layer may have a cure temperature less than 100° C. If the glue layer has a cure temperature higher than 100° C., the bonding interface strength becomes higher relatively quickly, which can make the debonding process more difficult.

A contact angle405between the top surface of the wafer stack101and the convex bottom surface403(or the attachment element406) is in the range of 1°-10° in some embodiments. The smaller the contact angle405is, the more gradual debonding force can be obtained, which helps to separate the wafers102and106gently. On the other hand, the greater the contact angle405is, the higher debonding speed can be obtained. Thus, balancing the gradual debonding force to not cause damage on the wafers and the debonding speed can be considered to find the optimal contact angle405range.

An air gun408is used to blow air at an area between the top wafer102and the bottom wafer106of the wafer stack101to assist the debonding process in some embodiments. The air gun408does not contact the wafers102and106, and it can be any kind of air flow equipment used in a clean room environment. The air gun408is made of metal or plastic in some embodiments. The temperature of air from the air gun408is about 22° C.-23° C. in some embodiments.

InFIG. 4A, the detacher400makes contact with the top surface of the wafer stack101and downward force is applied to help attach the detacher400to the top wafer102of the wafer stack101. The air gun408can be used to blow air between the top wafer102and the bottom wafer106of the wafer stack101in some embodiments. The contact area between the attachment element406and the top wafer102of the wafer stack101is increased as the detacher400is rotated. The rotation axis404is used to rotate the detacher400and positioned to be parallel to the top surface of the wafer stack101. In some embodiments, the rotation axis404rotates the body402of the detacher400at a speed ranging from about 0.1 degree/sec to about 0.2 degree/sec.

InFIG. 4B, the attachment element406of the detacher400is attached to the top surface of the wafer stack101firmly. As the detacher400is rotated around the rotation axis404, the contact area of the detacher400to the wafer stack101increases, and the debonding force to separate wafers102and106also increases. The rotational motion of the detacher400causes it to apply an upward force on the wafer stack101. In the illustrated embodiment, detacher400rotates in a counter-clockwise direction, which rotates the convex bottom surface403to press against the wafer stack101on the left side of the illustrated embodiment, while pulling away from the wafer stack on the right side of the illustrated embodiment, thus causing the debonding force to separate the wafers. With the rotation of the detacher400, the corner of the top wafer102attached to the detacher400and the bottom wafer106held by the bottom stage401begin to be separated. The air gun408can be used to blow air between the top wafer102and the bottom wafer106to assist breaking the bonding in some embodiments.

InFIG. 4C, as the detacher400is rotated further around the rotation axis404, the break between the top wafer102and the bottom wafer106increases to further separate the wafers102and106. The air volume of the air gun408can be increased to assist breaking the bonding between the top wafer102and the bottom wafer106, thus facilitating the separation of the wafers102and106in some embodiments.

InFIG. 4D, the detacher400is further rotated around the rotation axis404, and completely separate the top wafer102from the bottom wafer106. In some embodiments, the detacher400and the rotation axis404can be lifted upward (indicated by an arrow412) as the top wafer402is separated from the bottom wafer406. In some embodiments, the bottom stage401holding the bottom wafer106can be moved downward during a debonding process to help the separation of the top wafer102from the bottom wafer106. After the separation is complete, the air gun408stops blowing air in some embodiments.

In some embodiments, the air flow from the air gun408is adjusted throughout the debonding process inFIGS. 4A-4D.FIG. 4Fis a plot of air flow rate vs. time from the air gun inFIGS. 4A-4Daccording to some embodiments. For example, the air gun408starts blowing air inFIG. 4Awith an initial flow rate Finit, then increases the air flow as the detacher400rotates inFIGS. 4B and 4Cto assist breaking the bonding between the top wafer102and the bottom wafer106. The air gun408can reach a maximum air flow Fmax as the wafers102and106are separated. After the separation of the top wafer102and the bottom wafer106inFIG. 4D, the air gun408stops the air flow in some embodiments.

In some embodiments, the detacher400is moved up or down to facilitate attaching the detacher400to the wafer stack101and separating the top wafer102and the bottom wafer106. In some embodiments, a servo motor is used to rotate the rotation axis404and the body402of the detacher400. The servo motor can provide the debonding energy ranging from 0.3 J/m2to 50 J/m2in some embodiments. The whole debonding process is performed in a high vacuum chamber with a pressure ranging from about 0.01 mbar to about 955 mbar ambient in order to avoid the force concentration that can damage the wafers102and106in some embodiments.

In some embodiments, a mechanical robot hand (not shown) can be used to separate the detacher400from the top wafer102when a glue layer was used as the attachment element406. The robot hand holds the top wafer102with a pressure ranging from about −200 mbar to about −500 mbar in some embodiments. Any suitable robot hand available in the industry can be used. For example, the robot hand can be made of stainless steel or aluminum. The bottom stage401using vacuum suction can hold the bottom wafer106with an applied pressure ranging from about −800 mbar to about −1600 mbar in some embodiments.

The rotary and rolling movement of the detacher400for debonding the wafer stack101helps to reduce damage to the wafer stack101, due to the gradual contacting trajectory of the bottom surface403to the wafer stack101in some embodiments. Compared to other debonding methods, using the detacher400helps to reuse the debonded wafers from the wafer stack101by reducing the bonded wafer stack101damage during the debonding process, which saves costs. The air flow from the air gun408also helps to create the breaking point of debonding in some embodiments. The method using the detacher400reduces damages to wafers, thus the bonding-debonding process becomes more of a re-workable process.

FIG. 5is a flow diagram illustrating the method of the debonding scheme according to some embodiments.

At operation502, at least two wafers such as102and106are bonded together to form a wafer stack101using any suitable method. For example, fusion bonding, eutectic bonding, anodic bonding described above can be used in some embodiments.

At operation504, a non-destructive inspection method is used to inspect the bonded surface of the wafer stack101. For example, an infrared (IR) or C-mode scanning acoustic microscope (C-SAM) can be used for the inspection of the bonded surface of the wafer stack101. The non-destructive inspection monitors whether the bonding is defective and/or the bonding alignment is correct,

At operation506, whether the bonded surface of the wafer stack101passes or fails the inspection is decided, e.g., based on the bonding quality and/or misalignment. If the wafer stack101passes the inspection, a post bond process can begin at operation508, such as finishing the product. If the wafer stack101fails the inspection, debonding using the disclosed methods herein is performed at operation510. After the debonding process is complete, the wafers102and106are cleaned to remove any impurities or contaminants before re-bonding in some embodiments. Then the wafers102and106go back to operation502for another bonding process and repeat the operations until the bonded wafer stack101passes the inspection. By using the debonding methods disclosed herein, wafer damage during the debonding process is reduced. Thus, more wafers can be reused for rebonding, and the fabrication cost is saved.

For cleaning the wafers102and106before re-bonding, a plasma cleaning process can be used in some embodiments. Plasma cleaning involves the removal of impurities and contaminants from surfaces through the use of an energetic plasma or dielectric barrier discharge (DBD) plasma created from gaseous species. Gases such as argon and oxygen, as well as mixtures such as air and hydrogen/nitrogen are used in some embodiments. The plasma is created by using high frequency voltages ranging from 1 kHz to over 1 MHz to ionize the gas in low pressure (typically around 1/1000 atmospheric pressure) or in atmospheric pressure in some embodiments.

If a fusion bonding is used for bonding the wafer stack101at operation502, the wait time (Q-time) should be maintained to be less than 1 hour between the bonding and debonding stations to help the debonding process in some embodiments. The fusion bonded wafer stack101should not be annealed after being determined as a failure at operation506after the C-SAM or IR inspection at operation504to facilitate the debonding process.

Debonding schemes are disclosed herein. In one method, at least one blade is used to separate a wafer stack having at least two bonded wafers by inserting the blade between the wafers. Air or liquid is injected through the channel of the blade to assist the debonding process in some embodiments. In another method, a detacher having a convex bottom surface is attached to the top surface of the wafer stack and rotated to debond the wafers. An air gun is used to assist the separation of wafers in some embodiments.

According to some embodiments, a wafer stack having at least two wafers bonded together is received. At least one blade is inserted between a first wafer of the at least two wafers and a second wafer of the at least two wafers. The at least one blade has a channel configured to inject air or fluid. The first wafer is separated from the second wafer using the at least one blade.

According to some embodiments, an apparatus includes a bottom stage configured to hold a bottom surface of a wafer stack including at least two wafers. A top stage is configured to hold a top surface of the wafer stack. At least one blade is configured to be inserted between two adjacent wafers of the wafer stack. The at least one blade has a channel configured to inject air or fluid.

According to some embodiments, a method includes receiving a wafer stack having at least two wafers. The at least two wafers includes a first wafer and a second wafer bonded together. A detacher having a convex bottom surface is attached to the wafer stack. The convex bottom surface faces a top surface of the wafer stack. The first wafer is separated from the second wafer using the detacher.

According to some embodiments, an apparatus includes a body having a convex bottom surface. A rotation axis is connected to the body. The rotation axis is configured to rotate the convex bottom surface in a roller type motion. An attachment element is configured to attach the convex bottom surface of the body to a top surface of a wafer stack. The wafer stack includes at least two wafers bonded together.