For the purposes of illustrating the various aspects of the invention, there are shown in the drawings forms that are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
With reference to the drawings, wherein like numerals indicate like elements, there is shown in
The bonding apparatus 10 includes the following components: a lift and press mechanism 100, an open and close mechanism 200, a spacer mechanism 300, an upper bonding plate mechanism 400, and a lower bonding plate mechanism 500. These main components are coupled to one another and the combination is supported by a base plate 12 and support frame 14. A control unit (not shown), which may include one or more closed control loops, is operable to control the various elements of the bonding apparatus 10 (e.g., by way of a computer program) as will be discussed in more detail below.
Although the operation of the bonding apparatus 10 and certain specific bonding processes will be described in more detail later in this document, a brief introduction of such operation will now be presented. In
In this example, it is assumed that the silicon donor wafer contacts the upper bonding plate mechanism 400, while the glass substrate contacts the lower bonding plate mechanism 500 during the bonding process. For example, the glass substrate may be set down on the lower bonding plate mechanism 500 and the silicon donor wafer may be set atop the glass substrate so that it will be in a position to contact the upper bonding plate mechanism 400 (when the apparatus 10 is closed). (It is understood, however that this orientation may be reversed without departing from the scope of various embodiments of the invention.) In alternative embodiments, the silicon donor wafer may be coupled to the upper bonding plate mechanism 400, for example by clips, chuck mechanisms, vacuum, etc. when the upper bonding plate mechanism 400 is in the open position.
In general, the upper bonding plate mechanism 400 is operable to provide at least one of controlled heating, voltage, and cooling to the silicon donor wafer, while the lower bonding plate mechanism 500 is operable to provide at least one of controlled heating, voltage, and cooling to the glass substrate. The lift and press mechanism 100 is operatively coupled to the upper and lower bonding plate mechanisms 400, 500 and is operable to urge the first and second bonding plate mechanisms 400, 500 toward one another to achieve controlled pressure of the silicon donor wafer against the glass substrate along respective surfaces (i.e., an interface) thereof. The control unit is operable to produce control signals to the upper and lower bonding plate mechanisms 400, 500 and the lift and press mechanism 100 to provide heating, voltage, and pressure profiles sufficient to achieve anodic bonding between the silicon donor wafer and the glass substrate. The control unit is also operable to produce control signals to the upper and/or the lower bonding plate mechanisms 400, 500 to actively cool same and facilitate separation of the exfoliation layer from the silicon donor wafer after bonding.
As shown in
As shown in
A more detailed discussion of the respective elements of the bonding apparatus 10 will now be described.
With further reference to
The lift and press mechanism 100 includes a base 102, a first actuator 104, a second actuator 106, and a lower mount 108. The base 102 includes an upper surface 110 and a lower surface 112. The first actuator 104 may be coupled to the lower surface 112 of the base 102, while the second actuator 106 may be coupled to the upper surface 110 of the base 102. The lower mount 108 is coupled to the second actuator 106 such that the second actuator 106 is interposed between the base 102 and the lower mount 108.
The base 102 is slideable with respect to a plurality of guide posts 114, 116, 118. (Although three guide posts are shown, a lesser or greater number of guide posts may be employed.) By way of example, the base 102 may include respective guide bushings 120, 122, 124 (where bushing 124 is not visible), whereby the respective guide posts 114, 116, 118 are coaxially disposed within the respective guide bushings 120, 122, 124 such that the guide posts 114, 116, 118 may slide longitudinally within the guide bushings 120, 122, 124. The respective guide posts 114, 116, 118 may be anchored to the base plate 12 of the bonding apparatus 10 by way of fasteners 130.
In accordance with one or more embodiments, actuation of the first actuator 104 may achieve the aforementioned pre-loading movement in which the lower bonding plate mechanism 500 moves via the lower mount 108 toward the upper bonding plate mechanism 400 to achieve initial pre-load positioning of the upper and lower bonding plate mechanisms 400, 500 (and thus the glass substrate and the silicon donor wafer). This pre-load movement may be a coarse displacement of the lower bonding plate mechanism 500 toward the upper bonding plate mechanism 400. The first actuator 104 and the second actuator 106 may be mounted in axial alignment with the lower bonding plate mechanism 500 such that the actuation of the first actuator 104 imparts the coarse displacement of both the second actuator 106 and the lower bonding plate mechanism 500.
More particularly, the first actuator 104 may include a shaft 104A that is operable to move the first actuator 104 upward and downward. The shaft 104A may be driven by way of any suitable device, such as an electromechanical solenoid, a hydraulic piston arrangement, etc. Upward and downward movement of the first actuator 104 may cause corresponding movement of the base 102, whereby the planar orientation of the base 102 is maintained by way of the guide posts 114, 116, 118 as they slide within the guide bushings 120, 122, 124. The movement of the base 102 results in corresponding movements of the second actuator 106, the lower mount 108, and the lower bonding plate mechanism 500. The movement of the first actuator 104 by way of the shaft 104A may be mechanically, electrically, and/or hydraulically limited such that the pre-loading movement of the lower bonding plate mechanism 500 is controlled. As shown in
The second actuator 106 of the lift and press mechanism 100 is operable to impart a controllable force (e.g., fine movement as compared with the aforementioned coarse movement) on the lower bonding plate mechanism 500, where the controllable force is substantially perpendicular to the bearing surface (i.e., the surface that contacts the glass substrate) of the lower bonding plate mechanism 500. As the bearing surface of the upper bonding plate mechanism 400 is parallel to the bearing surface of the lower bonding plate mechanism 500, the second actuator 106 of the lift and press mechanism 100 ensures that no (or minimal) lateral forces are applied as between the silicon donor wafer and the glass substrate, which might cause scraping or other impediments to the quality of the anodic bond.
The second actuator 106 may be a bellows actuator that is operable to move the lower mount 108 upward and downward in response to changing the internal fluid pressure (e.g., liquid or gas pressure) of the bellows. The second actuator 106 may be independently controlled (with respect to the first actuator 104) in order to achieve the aforementioned pressure loading movement in which the glass substrate is pressed against the silicon donor wafer. Careful control of the second actuator 106 by way of the control unit (e.g., control of the pressure within the bellows) may be employed to establish the proper pressure (psi) as between the glass substrate and the silicon donor wafer for anodic bonding. Further, employing a bellows in second actuator 106 permits the lower mount 108, the lower bonding plate mechanism 500, and the glass substrate to float or self-align with respect to the upper bonding plate mechanism 400 (and the silicon donor wafer).
The lift and press mechanism 100 may also include a plurality of mounting elements, such as upwardly directed posts 140 that are coupled to the lower mount 108. The mounting elements 140 are operable to engage and retain the spacer mechanism 300 as will be discussed in more detail later in this description.
As best seen in
An embodiment of the open and close mechanism 200 will now be discussed with further reference to
As to the dual motion opening profile, the lift assembly 202, the actuator assembly 204, the tilt assembly 206, and the mount plate 208 cooperate to achieve two basic movements: (i) a vertical movement of the mount plate 208 with respect to the base plate 12; and (ii) a tilt movement to permit the mount plate 208 to rotate upward with respect to the base plate 12. Noting that the upper bonding plate mechanism 400 is operable to couple to the mount plate 208, the rotation of the mount plate 208 permits access (as discussed above) for inserting the silicon donor wafer and the glass substrate into the bonding apparatus 10 between the upper and lower bonding plate mechanisms 400, 500. The vertical movement of the mount plate 208 (and the upper bonding plate mechanism 400) permits an initial separation motion as between the upper and lower bonding plate mechanisms 400, 500 that is substantially purely vertical. This permits separation without sideways scraping that might otherwise damage the SOG structure. These features will be discussed in more detail below.
The lift assembly 202 includes a base 210, a guide shaft 212, and a guide bushing 214. The base 210 is operable to connect directly or indirectly to the base plate 12 and to provide a rigid reference from which the lift and tilt motions may be launched. The guide shaft 212 is operatively coupled to the base 210 and extends vertically toward the tilt assembly 206 and the mount plate 208. The guide bushing 214 is operable to slidingly engage the guide shaft 212. As will be discussed in more detail below, the sliding movement of the guide bushing 214 with respect to the guide shaft 212 causes the vertical movement and the rotational movement of the mount plate 208. The guide bushing 214 includes a fastening plate 216 that is operable to permit a mechanical linkage to the actuator assembly 204.
The actuator assembly 204 is operable to provide vertical force to the fastening plate 216 of the guide bushing 214, such that controlled sliding of the guide bushing 214 is achieved, again to obtain the lift and tilt motions of the mount plate 208. In one embodiment, the actuator assembly 204 may include a jack 230, such as a Duff-Norton jack, a shaft 232 linked to the jack 230, and a coupling element 234 connected to the fastening plate 216 of the guide bushing 214. In one or more embodiments, the Duff-Norton jack 230 is operable such that application of a rotational force on a shaft 236 causes a vertical movement of the shaft 232 and a resultant vertical movement of the guide bushing 214. The actuation of the jack 230 may be controlled via the control unit, such as by employing an electrical motor to turn the shaft 236.
The mount plate 208 may include a first end 240 that is operable to engage the upper bonding plate mechanism 400, and a second end 242 that is operatively coupled to the tilt assembly 206. In this embodiment, the tilt assembly 206 includes a hinge plate 250 that couples the mount plate 208 to the lift assembly 202 (which will be discussed in more detail below). The tilt assembly 206 also includes first and second stop arms 252, 254 and a pivoting linkage 258 of the hinge plate 250 to the mount plate 208. The stop arms 252, 254 are coupled to the base plate 12 at first ends thereof, and are coupled to the mount plate 208 at second ends thereof. The stop arms 252, 254 may be rotationally coupled to the base plate 12 at the first ends such that vertical movement thereof (with respect to the base plate 12) is prevented but pivotable movement of the second ends about the first ends is permitted. Each of the stop arms 252, 254 include a slot 256 that is operable to receive a corresponding roller or post 244 extending laterally from the second end 242 of the mount plate 208.
The mount plate 208 is operatively coupled to the hinge plate 250 by way of the pivoting linkage 258. More particularly, the hinge plate 250 includes a block 260 that extends at least partially into an aperture 245 of the mount plate 208. The pivoting linkage 258 permits the mount plate 208 to swivel or pivot about the pivoting linkage 258. The aperture 245 may be sized and shaped such that the block 260 may swivel within the aperture 245 without interference.
In response to actuation of the jack 230 (for example, via applying a rotational force to the shaft 236), the shaft 232 may raise/lower the guide bushing 214. In the orientation shown, the guide bushing 214 raises in response to the aforementioned actuation, thereby imparting vertical movement (upward) to the hinge plate 250. In response, the hinge plate 250 applies a vertical force to the mount plate 208 by way of the block 260 and pivoting linkage 258. Notably, the mount plate 208 moves by way of the block 260 in a manner such that the bearing planes of the upper and lower bonding plate mechanisms 400, 500 remain substantially parallel throughout substantially all of a limited travel of the upper bonding plate mechanism 400 during the lift motion.
The vertical force applied to the mount plate 208 by way of the hinge plate 250 causes the rollers or pins 244 of the mount plate 208 to move upward within the respective slots 256 of the respective stop arms 252, 254. The mount plate 208 will, therefore, rise vertically away from the base plate 12 while maintaining a substantially parallel relationship thereto. The vertical upward movement (or lift), while maintaining a substantially parallel orientation with respect to the base plate 12, will continue for limited travel, i.e., until the rollers or pins 244 of the mount plate 208 engage an upper limit within the slots 256. When the rollers or pins 244 reach this limit, a continued upward force on the mount plate 208 by the block 260 causes the first end 240 of the mount plate 208 to tilt upward in response to a rotational movement about the pivoting linkage 258. (Slight pivoting movement of the stop arms 252, 254 about the first ends thereof is permitted to account for lateral movement of the mount plate 208 in response to pivoting about the pivoting linkage 258.) The degree to which the mount plate 208 tilts may be adjusted by way of stops 257 located at the ends of the respective stop arms 252, 254. By way of example, the stops 257 may include threaded rods and nuts, where the threaded rods may be turned into and out of the associated slot 256 by varying amounts. This adjustment in the usable lengths of the slots 256 permit a change in the permissible travel of the rollers or pins 244 and in the degree to which the mount plate 208 tilts.
A reversal of the actuator assembly 204 results in the mount plate 208 tilting downward to its substantially parallel orientation with the base plate 12, followed by a vertical movement downward where the mount plate 208 maintains a substantially parallel relationship with the base plate 12. The parallel orientation of the mount plate 208 may be adjusted by way of one or more stops 259 of the hinge plate 250. For example, the stops 259 may include threaded bolts that may be threaded into and out of the hinge plate 250 to provide an adjustable resting position for the mount plate 208.
The first end 240 of the mount plate 208 also preferably includes a plurality of locks 246 that are operable to engage and couple to upper ends 114A, 116A, 118A of the guide posts 114, 116, 118 of the lift and press mechanism 100 (see
The first end 240 of the mount plate 208 also includes a plurality of apertures through which various wires, cables, and conduits may pass as will be discussed in more detail hereinbelow.
Reference is now made to
The primary components of the upper bonding plate mechanism 400 include a base 402, an insulator 404, a back plate 406, a heater disk 408, and a thermal spreader 410. The primary functions of the upper bonding plate mechanism 400 include heating the silicon donor wafer, providing pressure to the silicon donor wafer, providing a voltage potential to the silicon donor wafer, and cooling the silicon donor wafer.
The heating function originates at the heater disk 408 and is operable to provide temperatures lower or greater than about 600° C., and may approach or exceed temperatures of 1,000° C. This embodiment of the upper bonding plate mechanism 400 is also operable to provide the heat uniformly to within ±0.5% of the controlled set-point across substantially the entire silicon donor wafer.
The pressure imparted to the silicon donor wafer by the upper bonding plate mechanism 400 is substantially uniformly distributed over the wafer by way of the thermal spreader 410, which provides a counter-force to the upward pressure by the glass substrate (imparted by the lower bonding plate mechanism 500). This results in a pressure profile at the interface of the silicon donor wafer and the glass substrate suitable for anodic bonding. By controlling the upward pressure imparted by the lower bonding plate mechanism 500 (e.g., under the control of the control unit) the pressure profile may include at least a peak pressure of between about 1 pound per square inch (psi) to 100 psi. Lower pressures of between about 10 to 50 psi (for example, about 20 psi) are believed advantageous as they are less likely to crack the silicon donor wafer or the glass substrate.
As discussed above, the silicon donor wafer and the glass substrate are subject to a differential voltage potential of about 1750 volts DC, which is imposed by the respective upper and lower bonding plate mechanisms 400, 500. It is noted that this voltage potential may be achieved by: (i) applying a voltage potential to one of the silicon donor wafer and the glass substrate (while grounding the other); or by (ii) applying respective voltage potentials to both the silicon donor wafer and the glass substrate (such as a positive voltage potential to the silicon donor wafer and a negative voltage potential to the glass substrate). Thus, the ability of the upper bonding plate mechanisms 400 to impart a voltage potential (other than ground) to the silicon donor wafer is an optional feature. If a bonding voltage potential (other than ground) is applied to the silicon donor wafer by the upper bonding plate mechanism 400, such may be distributed by the thermal spreader 410 substantially uniformly over the entire surface of the wafer.
While the present invention is not limited by any theory of operation, it is noted that there may be a general relationship between bonding voltage, temperature, time, and material properties. For example, as the bonding voltage decreases, the temperature, time and/or amount of conductivity ions (e.g., of the glass substrate) may be increased to at least tend toward the same bonding result. The relationship also holds when the temperature, time and/or amount of conductivity ions are the independent variable. The bonding voltage potential between the silicon donor wafer and the glass substrate may be in the range of about 100 volts DC (or lower) to about 2000 volts DC (or greater) and may be measured using peak, average, RMS, or other measurement conventions. For certain type of glass substrates a bonding voltage in the range of about 1000 volts DC to about 2000 volts DC is suitable.
If active cooling of the silicon donor wafer is desired, such may be achieved utilizing controlled fluid flow through the upper bonding plate mechanism 400. These and other features of the upper bonding plate mechanism 400 will be discussed in more detail below.
The base 402 of the upper bonding plate mechanism 400 is of substantially cylindrical construction and defines an interior volume for receiving the insulator 404. By way of example, the base 402 may be formed from a machinable glass ceramic (e.g., MACOR), which provides structural integrity as well as high temperature capabilities. Other suitable materials may additionally or alternatively be employed to form the base 402. The insulator 404 is operable to limit or impede heat flow from the heater disk 408 into the base 402 (and other portions of the bonding apparatus 10). By way of example, the insulator 404 may be formed from a ceramic foam insulating material, such as 40% dense fused silica. Other suitable insulating materials may additionally or alternatively be employed. The insulator 404 should provide significant insulating capabilities inasmuch as the heater disk 408 is operable to attain temperatures of 600° C. or more, such as reaching or exceeding 1,000° C. It is noted that insufficient insulation that would permit significant heat flow into the base 402 could have catastrophic consequences in terms of the proper operation of other portions of the bonding apparatus 10. In addition, a relatively high degree of insulation as between the base 402 and the heater disk 408 insures a relatively low thermal inertia of the upper bonding plate mechanism 400, which assists in achieving rapid thermal cycling capabilities.
The back plate 406 is insulated from the base 402 by way of the insulator 404. The back plate 406 is operable to provide at least one cooling channel 420 through which cooling fluid may flow when it is desirable to actively reduce the temperature of the SOG structure, specifically the silicon donor wafer. By way of example, the back plate 406 may be formed from hot pressed boron nitride (HBN) in order to withstand high temperatures and relatively rapid changes in temperature (as is the case when cooling fluid is introduced into the channel 420). Other suitable materials may additionally or alternatively by employed to form the back plate 406. At least one inlet tube 422 is operable to introduce cooling fluid into the channel 420, while at least one outlet tube 424 (not viewable in
Active cooling may be achieved by controlling the temperature and flow rate of the cooling fluid through the channel 420 using the control unit. For example, the cooling profile of the upper bonding plate mechanism 400 may be actively controlled (e.g., by the control unit) to provide at least one of differing rates of cooling and differing levels of cooling (e.g., dwells) to the silicon donor wafer. It is believed that providing differing cooling profiles to the silicon donor wafer and the glass substrate, respectively, facilitates better separation of the exfoliation layer from the silicon donor wafer. Notably, the active cooling feature of the upper bonding plate mechanism 400 is optional as the differential cooling profiles as between the silicon donor wafer and the glass substrate, respectively, may be achieved through active cooling of the glass substrate (and not the silicon donor wafer) via the lower bonding plate mechanism 500 (as will be discussed in more detail below).
A cap ring 426 (see
The heater disk 408 is operable to generate heat in response to electrical excitation (voltage and current), while also providing electrical insulation properties such that the potential applied to the silicon donor wafer is not applied to the back plate 406 or the base 402. Indeed, the relatively high voltage potential applied to the silicon donor wafer should be confined. Thus, the heater disk 408 may be formed from a material that exhibits substantial electrical insulting properties and substantial thermal conductivity. One such suitable material is pyrolytic boron nitride (PBN).
With reference to
The heater disk 408A of
The heating elements 409A and 409B may be formed from pyrolytic graphite (PG), THERMAFOIL, etc. THERMOFOIL material is a thin, flexible material having heating properties, which include an etched foil resistive element laminated between layers of flexible insulation. While THERMOFOIL may exhibit better reliability in a vacuum environment, non-vacuum environments (which may include one or more oxidizing agents, such as air environments) are also contemplated herein. In a non-vacuum atmosphere, the heating elements 409A and 409B may be formed from INCONEL, which includes a family of high strength austenitic nickel-chromium-iron alloys that have good anti-corrosion and heat-resistance properties.
In one or more embodiments, the heater elements 409A and 409B may be vertically offset to assist in thermal edge loss compensation. For example, the heater element 409B in the central zone may be located toward a bottom side of the heater disk 408A, while the heater element 409A in the annular zone may be disposed at or toward the upper side of the heater disk 408A. This reduces the thermal resistance between the heater element 409A at the periphery of the heater disk 408A and the silicon donor wafer as compared with the thermal resistance between the heater element 409B at the center of the heater disk 408A and the silicon donor wafer. The offset feature may be achieved, for example, by interposing a spacer element (not shown), e.g., a sheet of material, between the heater elements 409A, 409B. This may also permit the terminals 411B to exit laterally rather than downward as illustrated in
The heater disk 408B of
Irrespective of the heater element construction, the resistance of the heating element(s) may be on the order of about 10-20 Ohms (e.g., about 15 Ohms). To achieve the aforementioned heating levels of about 600° C. to 1000° C., a voltage of about 220 volts (AC) may be applied across the heating elements, which causes a heat dissipation on the order of about 3250 Watts RMS.
In one or more embodiments, the heater disk 408 exhibits relatively low thermal inertia, due at least in part by the choice of materials and construction. The heater disk may measure about 2 mm thick using the materials and construction details discussed above. The relatively low thickness (as compared with prior art heating elements measuring 1-2 inches thick) contributes to a lower thermal mass and thermal inertia, which assists in achieving rapid thermal cycling capabilities.
The thermal spreader 410 is in thermal communication with the heater disk 408 and is operable to integrate the heating profile presented by the heater disk 408 such that a more uniform presentation of heat is imparted to the silicon donor wafer. The thermal spreader 410 may be both electrically and thermally conductive, as it is in direct contact with the silicon donor wafer and facilitates heating the wafer and applying the aforementioned high voltage thereto.
Among the materials that may be employed to implement the thermal spreader 410, electrically conductive graphite is desirable, such as THERMAFOIL. In a non-vacuum atmosphere (e.g., air), the thermal spreader 410 may be formed from other materials that may exhibit better reliability in oxidizing environments, such as a non-oxidizing electro-thermal conductive element, copper with a non-oxidizing coating (such as electroless nickel, platinum, molybdenum, tantalum, etc.), THERMOFOIL with a non-oxidizing coating (such as electroless nickel, platinum, molybdenum, tantalum, etc.), silicon carbide (which may or may not be coated) KEVLAR with a metal coating (such as electroless nickel, platinum, molybdenum, tantalum, etc.).
In one or more embodiments, the thermal spreader 410 also exhibits relatively low thermal inertia, due again at least in part by the choice of materials and construction. The thermal spreader 410 may measure about 0.5-6 mm thick using the materials and construction details discussed above.
The relatively low thicknesses of the heater disk 408 and the thermal spreader 410, coupled with the high insulation properties exhibited by the insulator 404 and other material choices discussed above, contribute to very low thermal mass and thermal inertia of the upper bonding plate mechanism 400. Thus, the upper bonding plate mechanism 400 may heat a material sheet from room temperature to about 1000° C. in about 2 minutes and cool same to room temperature in about 10 minutes or less. This is in comparison to prior art substrate heaters, which may take about one-half hour to one hour to elevate a material sheet from room temperature to only about 600° C., and may take about 20 minutes to cool the material sheet to room temperature.
The control unit is operable to program the upper bonding plate mechanism 400 to follow any desired heat-up or cool down ramp and dwell at any desired processing temperature.
As shown in
In one or more embodiments, the back plate 406 may include a single, contiguous channel 420 or multiple separate channels 420. As illustrated in
Notably, the thermal spreader 410 includes a plurality of fins 436 that extend radially outward from a peripheral edge of the thermal spreader 410. The fins 436 provide a peripheral surface that is utilized to maintain the thermal spreader 410 in position and to provide a connection to a high voltage source. As best seen in
As discussed above, the upper bonding plate mechanism 400 may optionally include the aperture 450, which may be implemented by way of separate apertures 450 of the base 402, the insulator 404, the back plate 406, the heating disk 408, and the thermal spreader 410. The aperture 450 may be centrally located such that access to a central region of the silicon donor wafer (e.g., the center thereof) may be obtained. A use of the access to the silicon donor wafer provided by the aperture 450 will be discussed in more detail below.
Reference is now made to
As best seen in
As best seen in
Although not shown, the upper bonding plate mechanism 400 may also include one or more vacuum conduits that extend to the thermal spreader 410, through the base 402, the insulator 404, the back plate 406, and the heater disk 408. If employed, the vacuum conduits permit the application of a vacuum to the silicon donor wafer when it is placed against the thermal spreader 410 such that the wafer will be coupled to the thermal spreader 410 when the upper bonding plate mechanism 400 is in the upwardly rotated (open) position, as shown in
As discussed above, the upper bonding plate mechanism 400 may optionally include the aperture 450 to permit access to the silicon donor wafer during the bonding process. When the aperture 450 is employed, a preferred use thereof is to permit a preload pressure and/or seed voltage to be applied to the silicon donor wafer prior to application of the bonding voltage. The purpose of the preload pressure and seed voltage is to initiate anodic bonding in a localized area of the interface between the silicon donor wafer and the glass substrate prior to application of the bonding voltage, which facilitates anodic bonding across substantially the entire area of the interface. The seed voltage may be of the same or different magnitude as the bonding voltage, however, a lower or equal voltage is believed to be superior, e.g., about 750-1000 volts DC. The aperture 450 may be centrally located such that the initial anodic bonding occurs at or near a central region of the interface between the silicon donor wafer and the glass substrate.
Reference is now made to
A first compression spring 488 mechanically and electrically couples the electrode 484 and the terminal 478 such that the slideable movement of the plunger 480 does not disturb the electrical connection between the terminal 478 and the electrode 484. The first compression spring 488 also urges or biases the electrode 484 (and the plunger 480) forward such that the stop 482 engages the housing 472. A second compression spring 490 also urges the plunger 480 forward such that the stop 482 engages the housing 472 and biases the plunger 480 and the electrode 484 in an extended orientation. An axially directed force on the electrode 484 and the plunger 480 is absorbed by the respective compression springs 488, 490 such that the tip 486 of the electrode 484 is biased toward and maintains an electrical connection with the silicon donor wafer. The electrode 484 thus delivers the seed voltage to the silicon donor wafer. In one or more embodiments, the electrode 484 may slide within the plunger 480, such that the plunger 480, itself, is also biased toward and applies (alone or in combination with the electrode 484) the preload pressure on the silicon donor wafer.
In a preferred embodiment, the tip 486 of the electrode 484 extends below the thermal spreader 410 of the upper bonding plate mechanism 400 such that it contacts the silicon donor wafer when the lift and press 100 mechanism coarsely displaces the lower bonding plate mechanism 500 toward the upper bonding plate mechanism 400 (i.e., as shown in
Similar to the application of the bonding voltage to the silicon donor wafer and the glass substrate, the seed voltage potential may be achieved by: (i) applying a voltage potential to one of the silicon donor wafer and the glass substrate (while grounding the other); or by (ii) applying respective voltage potentials to both the silicon donor wafer and the glass substrate. Thus, even if initial bonding in a localized area of the interface between the silicon donor wafer and the glass substrate is desired, the ability of the upper bonding plate mechanisms 400 to impart the seed voltage potential to the silicon donor wafer is an optional feature. Indeed, as will be discussed later in this description, the seed voltage potential may be applied to the glass substrate by way of the lower bonding plate mechanism 500 (while grounding the silicon donor wafer).
While the preload pressure and seed voltage may be applied as discussed above, it is desirable to limit the contact area of the silicon donor wafer and the glass substrate while the preload pressure and seed voltage are applied in order to limit the area over which pre-bonding is permitted. In this regard, the spacer mechanism 300 may be used in combination with the aforementioned preload plunger 470. In general, the spacer mechanism 300 is coupled to the lower bonding plate mechanism 500 (see
Reference is now made to
The spacer mechanism 300 is of substantially annular construction and includes a mount ring 302, a swivel ring 304, and a plurality of shim assemblies 306. The mount ring 302 is of substantially annular construction including a central aperture 308 and a peripheral edge 310. A plurality of mounting elements (such as apertures) 312 are disposed about the peripheral edge 310 and are of complementary construction as the mounting elements 140, which may be upwardly directed posts 140 (see
The swivel ring 304 is also of substantially annular construction and further defines the central aperture 308. The swivel ring 304 is rotationally coupled to the mount ring 302 and, therefore, may rotate with respect to the mount ring 302 and the lower mount 108 of the lift and press mechanism 100. The swivel ring 304 includes a plurality of cams 320 (e.g., cam slots) disposed at a peripheral edge thereof, which may include one such cam 320 for each of the shim assemblies 306. One of the cams 320A is a geared cam, including a plurality of teeth that are of a pitch that corresponds with a gear 142 of a stepper motor 144 of the lift and press mechanism 100 (see
Each shim assembly 306 may include a shim 330 coupled to a slide block 332. The shim 330 is sized and shaped to fit between, and separate, the silicon donor wafer and the glass substrate. The shim is operable to achieve radial inward and outward movement with respect to a center area of the spacer mechanism 300 (and thus a central area of the interface between the silicon donor wafer and the glass substrate). This radial movement is achieved by way of slideable engagement between the slide block 332 and the mount ring 302. For example, each shim assembly may include one or more guide bushings 334 that slidingly engage a corresponding one or more pins 336. The pins 336 may extend radially away from the peripheral edge 310 of the mount ring 302 such that sliding movement of the guide bushings 334 along the pins 336 results in the aforementioned radial movement of the slide block 332 and the shim 330.
Each slide block 332 also includes a cam guide (not visible), such as a roller or post, that engages the respective cam slot 320. Rotation of the swivel ring 304 (via actuation of the stepper motor 144) applies radial forces to the respective slide blocks 332 such that they slide in a controlled fashion along the posts 336 (via the guide bushings 334). Thus, all the shims 330 move in symmetric motion, which prevents any uneven frictional loads as between the silicon donor wafer and the glass substrate. It is noted that the rotation of the swivel ring 304 may be achieved using other actuation means, such as a pneumatic cylinder, linear motor, solenoid arrangement, etc. The shims 330 are preferably electrically insulated such that the voltage potential(s) of the SOG are not permitted to couple to the mount ring 302 and other portions of the bonding apparatus 10. For example, the slide blocks 332 may be formed with ceramic material. The mount ring 302 and swivel ring 304 may be positioned below the high heat zone of the lower bonding plate mechanism 500, which protects them from excessive heat input.
As best seen in
The structural details of one or more embodiments of the lower bonding plate mechanism 500 will now be described. The primary functions of the lower bonding plate mechanism 500 are complimentary to those of the upper bonding plate mechanism 400, namely, heating the glass substrate, providing pressure to the glass substrate, providing a voltage potential to the glass substrate, and cooling the glass substrate.
In accordance with one or more embodiments, the lower bonding plate mechanism 500 may include any number of the features of the embodiments of the upper bonding plate mechanism 400 described above. For example, in the embodiment illustrated in
The heating function of the lower bonding plate mechanism 500 is operable to provide temperatures lower or greater than about 600° C., which may approach or exceed temperatures of 1,000° C. The lower bonding plate mechanism 500 may be operable to provide heat uniformly to within ±0.5% of the controlled set-point across substantially the entire glass substrate. The voltage potential (about 1,750 volts DC) may optionally be applied to the glass substrate by the lower bonding plate mechanism 500, and may be distributed substantially uniformly over the entire surface of the substrate. Alternative embodiments of the lower bonding plate mechanism 500 may provide for active cooling of the glass substrate utilizing controlled fluid flow.
While the embodiment of the lower bonding plate mechanism 500 illustrated in
The base 502 is coupled to a lower portion of the housing 506, thereby forming a substantially cylindrical structure defining an interior volume for receiving the insulator 504. By way of example, but not limitation, the base 502 may be formed from a machinable ceramic material (e.g., Cotronics 902 machinable alumina silicate), which provides structural integrity as well as high temperature capabilities. The insulator 504 is operable to limit heat flow from the heater disk 508 into the base 502, housing 506 and other portions of the bonding apparatus 10. By way of example, but not limitation, the insulator 504 may be formed from a ceramic foam insulating material, such as 40% dense fused silica. The temperature insulating properties of the insulator 504 should prevent heat flow from the heater disk 508 into the base 502 (and other components) and provide a relatively low thermal inertia of the lower bonding plate mechanism 500 (for rapid thermal cycling capabilities).
The heater disk 508 and the insulator 504 may be bonded together using a ceramic adhesive, such as Cotronics RESBOND 905.
The heater disk 508 is operable to generate heat in response to electrical excitation (voltage and current), while also providing electrical insulation properties such that any voltage potential directly or indirectly applied to the glass substrate is not applied to the base 502 or housing. Thus, the heater disk 508 may be formed from a material that exhibits substantial electrical insulting properties and substantial thermal conductivity.
With reference to
As substantially uniform heating is desired, the heater disk 508 may include thermal edge loss compensation. In this embodiment, the heater disk 508 may include two heating zones, one substantially centrally located and the other in the form of an annular ring around the central zone. The heating zones may be implemented within the resistive heater layer 508A. For example, the respective heating zones may be formed by varying respective widths of resistive material as the material spirals outward from a center of the layer 508A. This results in a varying resistance (and thus the heating characteristics) of the material depending on the radial distance of same from the center of the layer 508A. This permits use of a single voltage and current excitation to achieve the thermal edge loss compensation because the heater element will respond (heat) differently to the excitation voltage and current due to the differences in the resistance as a function of radial position.
The voltage and current excitation to the resistive heater layer 508A is provided by a power source (not shown) and controlled by the control unit to achieve temperature regulation (which may employ feedback control as discussed below). The control unit may be operable to program the lower bonding plate mechanism 500 to follow any desired heat-up or cool down ramp and dwell at any desired processing temperature. Terminals 552 (
The thermal spreader 510 is in thermal communication with the heater disk 508 and is operable to integrate the heating profile presented by the heater disk 508 such that a more uniform presentation of heat is imparted to the glass substrate. The thermal spreader 510 may be both electrically and thermally conductive, as it is in direct contact with the glass substrate and facilitates heating the substrate and optionally applying a bonding voltage thereto. Again, the bonding voltage applied to the silicon donor wafer and the glass substrate may be achieved by: (i) applying a voltage potential to one of the silicon donor wafer and the glass substrate (while grounding the other); or by (ii) applying respective voltage potentials to both the silicon donor wafer and the glass substrate. Thus, the ability of the lower bonding plate mechanism 500 to impart a voltage potential (other than ground) to the glass substrate is an optional feature. If a bonding voltage potential (other than ground) is applied to the glass substrate by the lower bonding plate mechanism 500, such may be distributed substantially uniformly over the entire surface of the substrate, and may be in the range of about 1,750 volts DC.
Among the materials that may be employed to implement the thermal spreader 510, electrically conductive graphite is desirable, such as THERMAFOIL. Terminal 553 permits electrical connection from the high voltage power source (not shown) to the thermal spreader 510. The control unit may be operable to program the voltage level from the high voltage power source to attain the desired voltage (such as 1750 volts DC).
Reference is now also made to
By way of example, a preload plunger 570 may be employed to achieve the aforementioned pre-charge functionality. The preload plunger 570 may be of substantially the same construction as the preload plunger 470 discussed above with respect to
The lower bonding plate mechanism 500 may include one or more further apertures to permit the insertion of a thermocouple through the assembly such that it may thermally engage the heater disk 508 and provide a temperature feedback signal to the control unit (which permits tight temperature regulation of the heater disk 508 and the glass substrate). The structure and location of the aperture(s) for the thermocouples (and the thermocouple itself) may be substantially the same as those discussed above with respect to the upper bonding plate mechanism 400.
Reference is now made to
With reference to
Further details regarding the operation of the bonding apparatus 10 will now be described with reference to
An exfoliation layer 622 is created by subjecting the implantation surface 621 to an ion implantation process to create a weakened region below the implantation surface 621 of the donor semiconductor wafer 620, which defines the exfoliation layer 622. By way of example, the implantation surface 621 may be subject to hydrogen ion implantation, or other rare earth ions, such as boron, helium, etc. The donor semiconductor wafer 620 may be treated to reduce, for example, the hydrogen ion concentration on the implantation surface 621. For example, the donor semiconductor wafer 620 may be washed and cleaned and the implantation donor surface 621 of the exfoliation layer 622 may be subject to mild oxidation. The mild oxidation treatments may include treatment in oxygen plasma, ozone treatments, treatment with hydrogen peroxide, hydrogen peroxide and ammonia, hydrogen peroxide and an acid or a combination of these processes. It is expected that during these treatments hydrogen terminated surface groups oxidize to hydroxyl groups, which in turn also makes the surface of the silicon wafer hydrophilic. The treatment may be carried out at room temperature for the oxygen plasma and at temperature between 25-150° C. for the ammonia or acid treatments. Appropriate surface cleaning of the glass substrate 602 (and the exfoliation layer 622) may be carried out.
Assuming that the bonding apparatus 10 is in an initial orientation whereby the upper bonding plate mechanism 400 is rotated upward (as in
Next, the upper bonding plate mechanism 400 is operable to rotate downward (via the open and close mechanism 200) such that the upper and lower bonding plate mechanisms 400, 500 are spaced apart in parallel orientation. More particularly, as discussed above with respect to
The lift and press mechanism 100 may then impart coarse displacement of the lower bonding plate mechanism 500 (and the glass substrate 602 and donor semiconductor wafer 620) toward the upper bonding plate mechanism 400. As the electrode 484 of the preload plunger 470 extends below the thermal spreader 410 of the upper bonding plate mechanism 400, it contacts the donor semiconductor wafer 620 when the lift and press 100 mechanism coarsely displaces the lower bonding plate mechanism 500 toward the upper bonding plate mechanism 400. As the shims 330 of the spacer mechanism 300 prevent the peripheral edges of the donor semiconductor wafer 620 and the glass substrate 602 from touching one another, the preload plunger 470 will tend to bow the donor semiconductor wafer 620 such that the central portion thereof touches the glass substrate 602. Thus, application of the preload pressure and seed voltage may initiate the anodic bonding of the donor semiconductor wafer 620 and the glass substrate 602 before full pressure, temperature, and voltage is applied.
Following the initial bonding of the central portions of the donor semiconductor wafer 620 and the glass substrate 602, the spacer mechanism 300 may be commanded to withdraw the shims 330. The control unit may command the stepper motor 144 to rotate the gear 142 such that the swivel ring 304 rotates with respect to the mount ring 302, thereby withdrawing the shims 330 from between the donor semiconductor wafer 620 and the glass substrate 602. The shims 330 move in symmetric motion, which prevents any uneven friction loads as between the donor semiconductor wafer 620 and the glass substrate 602. Advantageously, if the bonding process is taking place in a vacuum, the bonding of the central portions of the donor semiconductor wafer 620 and the glass substrate 602 followed by withdrawal of the shims 330 permits any gasses from between the donor semiconductor wafer 620 and the glass substrate 602 to be evacuated. Thus, the likelihood of gas (e.g., air) impeding a proper bond between the donor semiconductor wafer 620 and the glass substrate 602 may be reduced.
With reference to
The exfoliation layer 622 of the donor semiconductor wafer 620, and the glass substrate 602 are heated under a differential temperature gradient. The glass substrate 602 may be heated to a higher temperature (via the lower bonding plate mechanism 500) than the donor semiconductor wafer 620 and exfoliation layer 622 (via the upper bonding plate mechanism 400). By way of example, the temperature difference between the glass substrate 602 and the donor semiconductor wafer 620 (and the exfoliation layer 622) may be anywhere between about 6° C. to about 200° C. or more. This temperature differential is desirable for a glass having a coefficient of thermal expansion (CTE) matched to that of the donor semiconductor wafer 620 (such as matched to the CTE of silicon) since it facilitates later separation of the exfoliation layer 622 from the semiconductor wafer 620 due to thermal stresses. The glass substrate 602 and the donor semiconductor wafer 620 may be taken to a temperature within about ±650° C. of the strain point of the glass substrate 602.
Mechanical pressure is also applied to the intermediate assembly. The pressure range may be: between about 1 to about 100 pounds per square inch (psi), between about 6 to about 50 psi, or about 20 psi. Although application of higher pressures, e.g., pressures at or above 100 psi are possible, such pressures should be used cautiously as they might cause breakage of the glass substrate 602. As discussed above with respect to
A voltage is also applied across the intermediate assembly, for example with the donor semiconductor wafer 620 at a positive potential and the glass substrate 602 at a lower potential. The application of the voltage potential causes alkali or alkaline earth ions in the glass substrate 602 to move away from the semiconductor/glass interface further into the glass substrate 602. This accomplishes two functions: (i) an alkali or alkaline earth ion free interface is created; and (ii) the glass substrate 602 becomes very reactive and bonds strongly to the exfoliation layer 622 of the donor semiconductor wafer 620 with the application of heat at relatively low temperatures.
The pressure, temperature differential, and voltage differential are applied for a controlled period of time (e.g., approximately 6 hr or less). Thereafter, the high level voltage potential is brought to zero and the donor semiconductor wafer 620 and the glass substrate 602 are permitted to cool to at least initiate the separation of the exfoliation layer 622 from the donor semiconductor wafer 620. The cooling process may involve active cooling, whereby cooling fluid is introduced into one or both of the upper and lower bonding plate mechanisms 400, 500. In one or more embodiment, the active cooling profile may involve cooling the donor semiconductor wafer 620 and the glass substrate 602 at different profiles (e.g., cooling rates, dwells and/or levels) to impact the degree and quality of the exfoliation process.
As illustrated in
Any unwanted or rough semiconductor material may be removed from the surface 623 via thinning and/or polishing techniques, e.g., via CMP or other techniques known in the art to obtain the semiconductor layer 604 on the glass substrate 602 as illustrated in
It is noted that the donor semiconductor wafer 620 may be reused to continue producing other SOG structures 600.
In accordance with one or more further embodiments of the present invention, the bonding apparatus 10 may be employed to emboss micro-structures in a substrate, such as glass, glass ceramic, ceramic, etc. Conventional approaches to producing replicated patterns on substrates such as glass have employed additive processes (e.g. using UV cured polymers), or subtractive processes (e.g. chemical etching, Reactive Ion Etching). These convention approaches are not desirable in every application; indeed, polymer structures are very versatile but may not have the desired material properties, and etching methods can produce fine structures but are often very slow and costly. In accordance with one of more aspects of the present invention, however, patterns are impressed/embossed into a substrate from a master tool through heating. The master tool is constructed from material that is structurally rigid and has a melting point above that of the substrate. The tool and/or substrate are heated to level(s) where the substrate flows into micro-structures of the tool. Thereafter, the components are cooled and separated.
In one or more embodiments, the bonding apparatus 10 may be adapted to rapidly heat the tool and/or substrate (e.g., glass) allowing for high throughput. The aforementioned active cooling features, controlled compression features, vacuum atmosphere, etc. of the bonding apparatus 10 may also increase throughput.
With reference to
The bonding apparatus 10 may then be closed (as discussed above) and the temperature taken above the Tg of the glass substrate 702. The pattern or structure is thus transferred from the tool 700 to the glass substrate 702. The replication process may be conducted under high pressure from the controlled pressure features of the bonding apparatus 10 as described above. Alternatively, gravity and atmospheric pressure may be employed to facilitate the flow of the glass substrate 702 into the micro-structures 710 of the tool 700.
The tool 700 may be constructed of material that will not change structurally at temperatures elevated to, or above the flow temperature of the substrate 702, such as the Tg of a glass substrate. By way of example, fused silica may be employed to implement the tool 700. The micro-structures 701 may be formed in the tool 700 by Reactive Ion Etching (RIE). A surface treatment of the tool 700 and/or substrate 702 may also be employed, such as a diamond coating.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.
Number | Date | Country | |
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60793976 | Apr 2006 | US |