Patent Application
20210057238
Embodiments of the present disclosure generally relate to substrate processing equipment.
Warped substrates prevent the substrates from being chucked fully on a process station pedestal. Such warpage leads to a delay in or ceasing of the substrate processing. For example, a substrate may comprise multiple dies on an interposer and encapsulated with an epoxy mold compound or a substrate may comprise multiple exposed dies. These substrates may bow and warp after thermal processes due to inhomogeneous heating and cooling, causing non-uniform expansion/contraction rates in current process equipment.
Conventional thermal processes utilize directional heat transfer that results in anisotropic expansion and contraction rates. When operated near the thermoplastic regime, non-uniform cooling and, subsequently, contraction rates give rise to a warped substrate. Such warp and bow effects are frequently observed and imply that the substrate is being processed close to the thermoplastic regime of the substrate, giving rise to substrate warpage beyond acceptable levels. Being able to reduce warpage found in substrates would allow otherwise unusable substrates to be used, dramatically increasing production yields. However, physical contact to reduce warpage of substrates having exposed dies damage the exposed dies.
Accordingly, the inventors have provided improved methods and apparatus for reducing warpage found in substrates.
Embodiments of methods and apparatus for reducing warpage of a substrate are provided herein. In some embodiments, a method for reducing warpage of a substrate includes heating the substrate with an epoxy layer to at least a glass transition temperature of the epoxy layer while allowing the substrate to expand; subsequently constraining the substrate with a clamping force exerted towards the substrate from a top direction by applying a high pressure gas to the substrate and from a bottom direction by applying a vacuum pressure to the substrate; and rapidly cooling the substrate while the substrate is constrained.
In some embodiments, a non-transitory, computer readable medium having instructions stored thereon that, when executed, cause a method of reducing warpage of a substrate to be performed, the method including heating the substrate with an epoxy layer to at least a glass transition temperature of the epoxy layer while allowing the substrate to expand; maintaining the at least the glass transition temperature of the substrate until the substrate is constrained; constraining the substrate from a top direction by applying a high pressure gas to the substrate and a bottom direction by applying a vacuum pressure to the substrate via one or more vacuum channels; and rapidly cooling the substrate using a first liquid convection heat sink positioned above the substrate and a second liquid convection heat sink positioned below the substrate.
In some embodiments, an apparatus for reducing warpage of a substrate with an epoxy layer includes a first station comprising a transferable pedestal that holds the substrate, and a heated gas supply disposed opposite the substrate to provide a heated gas to a surface of the substrate, wherein the first station is configured to heat the substrate to at least a glass transition temperature of the epoxy layer; a second station comprising a first cooling module having a substrate support that includes a substrate support surface, a vacuum chuck operatively coupled to the substrate support surface, and cooling channels disposed beneath the substrate support surface, and a second cooling module disposed opposite the first cooling module and having a gas supply and cooling channels, wherein the second station is sealable and pressurizable to create an enclosed volume having the substrate support surface disposed between the first cooling module and the second cooling module and to provide gas from the gas supply at a high pressure to the enclosed volume; and wherein the first station and the second station are configured to transfer the substrate between the first station and the second station with the transferable pedestal while maintaining the at least the glass transition temperature of the substrate.
Other and further embodiments of the present disclosure are described below.
Embodiments of the present disclosure, briefly summarized above and discussed in greater detail below, can be understood by reference to the illustrative embodiments of the disclosure depicted in the appended drawings. However, the appended drawings illustrate only typical embodiments of the disclosure and are therefore not to be considered limiting of scope, for the disclosure may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale and may be simplified for clarity. Elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.
Embodiments of methods and apparatus for reducing warpage of a substrate are provided herein. The methods and apparatus reduce warpage of substrates to allow subsequent semiconductor processing. When a substrate has warpage greater than 2 mm, the substrate is generally deemed unusable. Even backgrinding processes require less than 2 mm in warpage in order to be utilized. In semiconductor back end of the line (BEOL) packaging, 2.5D is a methodology for including multiple dies inside the same package. The 2.5D approach is used for applications where performance and low power are critical. In a 2.5D wafer, communication between chips is established using either a silicon or organic interposer, typically a chip or layer with through-silicon vias (TSV) for communication. 2.5D architectures have been paired with stacked memory modules, such as High-Bandwidth Memory (HBM), to further improve performance. High warpage of 2.5D wafers is a pressing industrial problem as the warpage prevents the 2.5D wafers from flowing on to downstream processes. Wafer handling challenges and reduction in yield are the most common detrimental effects of high 2.5D wafer warpage. The methods and apparatus of the present principles may be applied to advantageously correct warpage of a 2.5D wafer which is fully encapsulated with epoxy mold compound, which has exposed dies, or to correct warpage of any multilayer substrates. The methods and apparatus reduce warpage using only two thermal treatments, saving time and possible damage to delicate circuits, especially those sensitive to thermal budgets and smaller structures that are more easily damaged by thermal changes.
At 102, the substrate 212 or the substrate 250 is heated to a temperature that is at least a glass transition temperature of the epoxy material used in the epoxy mold encapsulation layer 204 while allowing the substrate 212 or the substrate 250 to freely expand. The epoxy material may vary and, subsequently, the glass transition temperature will also vary. In addition, some epoxy materials utilize fillers in the epoxy material which also may influence heating to the glass transition temperature. In some embodiments, the glass transition temperature of the epoxy material may be from approximately 100 degrees Celsius to approximately 200 degrees Celsius. In some embodiments, the glass transition temperature of the epoxy material may be from approximately 140 degrees Celsius to approximately 180 degrees Celsius.
At 104, the substrate 212, 250 is maintained at the at least glass transition temperature until the substrate 212, 250 is constrained. In some embodiments, the temperature of the substrate 212, 250 is maintained to at least the glass transition temperature of the epoxy material during transfer of the substrate 212, 250 from a heating station to a cooling station. In some embodiments, the temperature may be maintained by using a transferable pedestal (described in detail below) with conduction heating for transferring the substrate 212, 250 between heating and cooling stations. In some embodiments, the temperature may also be maintained by using heated gas dispersed around the substrate (described in detail below) while the substrate is being positioned within a cooling station and until the substrate has clamping forces applied to the substrate.
At 106, the substrate 212, 250 is constrained with a clamping force that is exerted towards the substrate 212, 250 from a top direction by applying high pressure gas and from a bottom direction by applying a vacuum pressure. In some embodiments, the high clamping force may be from approximately 5000N (newtons) to approximately 10,000N (newtons). In some embodiments the high clamping force may be approximately 5000N (newtons). At 108, the substrate 212, 250 is rapidly cooled to lock in the constrained shape of the substrate 212, 250. In some embodiments, at least one liquid convection heat sink may be utilized to rapidly quench cool the substrate 212, 250 while the substrate 212, 250 is constrained to retain the epoxy's elongated and low stress state. The rapid quench cool may occur at a rate of approximately 1300 W/m2°C to a rate of approximately 3100 W/m2°C.
The constraining of the substrate 212, 250, the application of the vacuum pressure and the high pressure gas to the substrate 212, 250, and the rapid cooling of the substrate 212, 250 are accomplished approximately concurrently. In some embodiments, the concurrent constraining of the substrate 212, 250, cooling of the substrate 212, 250, and applying the vacuum pressure and high pressure gas to the substrate 212, 250 occurs for approximately 120 seconds to approximately 600 seconds.
Embodiments in accordance with the present principles may be implemented in hardware, firmware, software, or any combination thereof. Embodiments may also be implemented as instructions stored using one or more computer readable media, which may be read and executed by one or more processors. A computer readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing platform or a “virtual machine” running on one or more computing platforms). For example, a computer readable medium may include any suitable form of volatile or non-volatile memory. In some embodiments, the computer readable media may include a non-transitory computer readable medium.
In some embodiments, the first station 404 may include a heat sensor assembly 416 that includes at least one heat sensor 418 that is configured to read 420 a bottom surface of the substrate 402. In some embodiments, the at least one heat sensor 418 may be an infrared heat sensor and the like. The at least one heat sensor 418 may be in communication with the system controller 408 to provide feedback on the heating of the substrate 402. The substrate 402 is supported by a transferable pedestal 422. In some embodiments, the transferable pedestal 422 includes a heater 424 bonded to a lower surface of the transferable pedestal 422. In some embodiments, the heater 424 is a conduction heater. The transferable pedestal 422 may be in communication with the system controller 408 to determine a position or status or the like of the transferable pedestal 422. Similarly, the heater 424 may be in communication with the system controller 408 so that the heater 424 can be configured to maintain at least a glass transition temperature of an epoxy material in the substrate 402. In some embodiments, the transferable pedestal 422 may have slots or holes through the transferable pedestal 422 to allow the at least one heat sensor 418 to directly read the bottom surface of the substrate 402 and/or to allow the transferable pedestal 422 to place the substrate 402 on lift pins 426 in the second station 406 (see
The first station 404 may also have a gas distribution assembly 428 above the transferable pedestal 422. The gas distribution assembly 428 provides heated gas 430 to heat the substrate 402 to at least the glass transition temperature of the epoxy material in the substrate 402. The heated gas may be heated by at least one infrared lamp 432 in the gas distribution assembly 428. In some embodiments, the gas distribution assembly 428 provides a gas at a temperature of approximately 200 degrees Celsius to approximately 300 degrees Celsius. In some embodiments, the gas distribution assembly 428 provides a gas at a temperature of approximately 240 degrees Celsius. In some embodiments, the gas distribution assembly 428 provides a gas at a pressure of approximately 1 bar to approximately 2.5 bar. In some embodiments, the gas distribution assembly 428 provides a gas at a pressure of approximately 1 bar to approximately 2 bar. In some embodiments, the gas may be nitrogen, nitrogen/air, and/or other inert gases. The gas distribution assembly 428 (including the at least one infrared lamp) may be in communication with the system controller 408 to configure the first station 404 to heat the substrate 402 to the at least the glass transition temperature of the epoxy material in the substrate 402. The first station 404 heats the substrate 402 to the at least the glass transition temperature of the epoxy material using the heater 424 of the transferable pedestal 422 and the gas distribution assembly 428. When the substrate 402 reaches at least the glass transition temperature of the epoxy material, the heater 424 of the transferable pedestal maintains the at least the glass transition temperature of the epoxy material as the transferable pedestal 422 moves with the substrate 402 into the second station 406 as indicated by the arrow 434.
The second station 406 includes a first cooling module 436, a second cooling module 438 disposed opposite the first cooling module 436, and a gas distribution assembly 440. At least one of the first cooling module 436 an the second cooling module 438 are moveable between a transfer position, where the first cooling module 436 is spaced from the second cooling module 438, and a process position, where the first cooling module 436 interfaces with the second cooling module 438 to define an enclosed volume therebetween (e.g., enclosed volume 610 of
In some embodiments, the first cooling module 436 may be affixed to an actuator 444 that is configured to move the first cooling module 436 in an upward and downward direction 446. In some embodiments, the second cooling module 438 may be held in a fixed position while the first cooling module 436 is moved upward by the actuator 444 when the substrate 402 is on the first cooling module 436 to define the enclosed volume therebetween. In some embodiments, the second cooling module 438 may be movable while the first cooling module 436 may remain in a fixed position to define the enclosed volume therebetween. In some embodiments, the first cooling module 436 may move upward and the second cooling module 438 may move downward to define the enclosed volume therebetween.
The first cooling module 436 includes a substrate support 425 having a substrate support surface 448. In some embodiments, the second cooling module 438 may also include a lift pin assembly 494 with a plurality of lift pins 426 that are configured to raise and lower 454 the substrate 402 on and off of the substrate support surface 448. In such embodiments, the substrate support 425 includes openings to allow the plurality of lift pins 426 to pass through the substrate support 425. In some embodiments, a vacuum chuck is operatively coupled to the substrate support surface 448. The vacuum chuck includes vacuum channels 490 fluidly coupled to a pump 450. In some embodiments, the vacuum channels 490 extend from a single inlet on a bottom surface of the substrate support 425 to a plurality of outlets 496 on the substrate support surface 448. In some embodiments, the vacuum channels 490 include a vertical portion and a horizontal portion that extends radially outward from the vertical portion.
The second cooling module 438 includes a body 462 and sidewalls 452 extending from the body 462 towards the first cooling module 436. In some embodiments, the body 462 includes a gas channel 472 extending through the body 462 to provide a gas supply to a processing region 480 disposed between the sidewalls 452 and the body 462. The gas channel 472 is fluidly coupled to a gas source 474 to supply a high pressure gas to the substrate 402 via the processing region 480. A valve 478 may be disposed between the gas source 474 and the gas channel 472 to control at least one of a flow rate and a pressure of the gas supplied to the processing region 480. In some embodiments, the valve 478 is a gate valve, or the like.
The gas distribution assembly 440 is configured to provide hot gas into the second station 406 to facilitate in maintaining the at least the glass transition temperature of the epoxy material in the substrate 402 until the substrate 402 is constrained by the first cooling module 436 and the second cooling module 438. In some embodiments, the gas distribution assembly 428 provides a gas at a temperature of approximately 200 degrees Celsius to approximately 300 degrees Celsius. In some embodiments, the gas distribution assembly 440 provides a gas at a temperature of approximately 240 degrees Celsius. In some embodiments, the gas distribution assembly 440 provides a gas at a pressure of approximately 1 bar to approximately 2.5 bar. In some embodiments, the gas distribution assembly 440 provides a gas at a pressure of approximately 1 bar to approximately 2 bar. In some embodiments, the gas may be nitrogen, nitrogen/air, and/or other inert gases.
In some embodiments, the gas distribution assembly 440 is an annular gas distribution assembly 702 as illustrated in
In some embodiments, the first cooling module 436 includes cooling channels 492 that are configured to rapidly cool a bottom surface of the substrate 402 via a coolant that flows therethrough. The cooling channels 492 are disposed beneath the substrate support surface 448. In some embodiments, the body is formed of an aluminum material. In some embodiments, the body 462 includes cooling channels 470 that are vacuum brazed. The vacuum brazing allows the cooling channels 470 to be formed without using copper liners, advantageously increasing thermal conductivity.
In some embodiments, the body 462 includes cooling channels 470 that are configured to rapidly cool a top surface of the substrate 402 via a coolant that flows therethrough. In some embodiments, the body is formed of an aluminum material. In some embodiments, the body 462 includes cooling channels 470 that are vacuum brazed. The vacuum brazing allows the cooling channels 470 to be formed without using copper liners, advantageously increasing thermal conductivity. In some embodiments, the coolant that flows through cooling channels 470 and cooling channels 492 is water.
The cooling rates of the first cooling module 436 and the second cooling module 438 may be controlled in unison or independently by the system controller 408. The pressure and flow rate of the high pressure gas supplied to the processing region 480 may be controlled by the system controller 408. The independent control of the cooling rates and/or the pressure and flow rate of the high pressure gas advantageously provides for fine tuning of a warpage control process.
During the warpage control process, the lift pins 426 are in the raised position with hot gas 456 being projected from the gas distribution system 440 as the transferable pedestal 422 places the substrate 402 onto the lift pins 426. The transferable pedestal 422 continues to heat the substrate 402 with the heater 424 as the substrate 402 is moved from the first station 404 to the second station 406. The transferable pedestal 422 places the substrate 402 onto the lift pins 426 and retreats back to the first station 404 as illustrated in view 600A of
The substrate 402 is then raised into position between the first cooling module 436 and the second cooling module 438 by the actuator 444. In a process position, the sidewalls 452 are configured to interface and form a seal with the substrate support 425 such that an enclosed volume 610 is defined between the sidewalls 452, the body 462, and the substrate support 425. As such, the substrate support surface 448 is disposed between the first cooling module 436 and the second cooling module 438. In the process position, the hot gas 456 stops and a cooling process begins as illustrated in view 600C of
The second cooling module 438 is configured to apply a high pressure gas to the substrate 402 during the cooling process. The high pressure gas provided by the second cooling module 438 advantageously provides a downward clamping force towards the substrate 402 without physically contacting the substrate 402. In some embodiments, a pressure of the high pressure gas at the substrate support surface 448 is about 1.5 bar to about 2.6 bar. As discussed above, the first cooling module 436 and the second cooling module 438 are also configured to provide rapid heat transfer from the substrate 402 in order to cool the substrate 402. After the cooling process, the second cooling module 438 is lowered and the lift pins 426 raise the substrate 402 off of the substrate support surface 448 of the substrate support 425 as illustrated in view 600D of
In some embodiments, the transferable pedestal 516 has a projection 514 that interacts with a rod 512 driven by an actuator 510. In some embodiments, the projection 514 may include an insulated portion 538 that prevents the transferable pedestal 516 from heating the rod 512 and actuator 510. The actuator 510 is in communication with the system controller (e.g., 408 of
While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof.
