EP1238423A2 - Methods for separating microcircuit dies from wafers - Google Patents

Methods for separating microcircuit dies from wafers

Info

Publication number
EP1238423A2
EP1238423A2 EP00992379A EP00992379A EP1238423A2 EP 1238423 A2 EP1238423 A2 EP 1238423A2 EP 00992379 A EP00992379 A EP 00992379A EP 00992379 A EP00992379 A EP 00992379A EP 1238423 A2 EP1238423 A2 EP 1238423A2
Authority
EP
European Patent Office
Prior art keywords
wafer
film
dies
protective film
mount
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP00992379A
Other languages
German (de)
French (fr)
Inventor
Maurice Karpman
David Courage
Somdeth Xaysongkham
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Analog Devices Inc
Original Assignee
Analog Devices Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Analog Devices Inc filed Critical Analog Devices Inc
Publication of EP1238423A2 publication Critical patent/EP1238423A2/en
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/544—Marks applied to semiconductor devices or parts, e.g. registration marks, alignment structures, wafer maps
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/683—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping
    • H01L21/6835—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping using temporarily an auxiliary support
    • H01L21/6836—Wafer tapes, e.g. grinding or dicing support tapes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/77—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate
    • H01L21/78—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2221/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof covered by H01L21/00
    • H01L2221/67—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere
    • H01L2221/683—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping
    • H01L2221/68304—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping using temporarily an auxiliary support
    • H01L2221/68327—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping using temporarily an auxiliary support used during dicing or grinding
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2223/00—Details relating to semiconductor or other solid state devices covered by the group H01L23/00
    • H01L2223/544—Marks applied to semiconductor devices or parts
    • H01L2223/5442—Marks applied to semiconductor devices or parts comprising non digital, non alphanumeric information, e.g. symbols
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2223/00—Details relating to semiconductor or other solid state devices covered by the group H01L23/00
    • H01L2223/544—Marks applied to semiconductor devices or parts
    • H01L2223/54453—Marks applied to semiconductor devices or parts for use prior to dicing
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2223/00—Details relating to semiconductor or other solid state devices covered by the group H01L23/00
    • H01L2223/544—Marks applied to semiconductor devices or parts
    • H01L2223/54453—Marks applied to semiconductor devices or parts for use prior to dicing
    • H01L2223/54466—Located in a dummy or reference die
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/0001—Technical content checked by a classifier
    • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/19—Details of hybrid assemblies other than the semiconductor or other solid state devices to be connected
    • H01L2924/1901—Structure
    • H01L2924/1904—Component type
    • H01L2924/19041—Component type being a capacitor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/30—Technical effects
    • H01L2924/301—Electrical effects
    • H01L2924/30105—Capacitance

Definitions

  • This invention relates to processing of semiconductor wafers and, more particularly, to methods for separating microcircuit dies from a wafer containing a plurality of dies.
  • the invention is particularly useful in processing of wafers containing fragile micromechanical devices, but is not limited to such use.
  • FIGS. 1A and I B illustrate an exemplary wafer 10.
  • FIG. 1A is a plan view of a wafer
  • FIG. IB is an enlarged view of section IB in FIG. 1A.
  • Reference numerals 14 denote individual dies
  • reference numerals 12 denote the streets separating the individual dies 14. Streets 12 are areas of the wafer where no componentry has been placed and which define the boundaries of each individual die 14.
  • the integrated circuitry and other componentry appears on only one side, e.g., front side 15, of the wafer.
  • the back side (not shown in FIGS. 1A and IB) has no circuitry or other componentry.
  • the individual dies 14 comprising a wafer are removed from the wafer by sawing through the wafer along all of the streets, thus physically separating the wafer in both axes into the individual dies.
  • U.S. Patent No. 5,345,824, issued September 13, 1994 to Sherman et al. discloses a monolithic accelerometer.
  • U.S. Patent No. 5,326,726, issued July 5, 1994 to Tsang et al. discloses a method for fabricating a monolithic chip containing integrated circuitry and a suspended microstructure.
  • These patents disclose a suspended micro structure for sensing accelerative forces and integrated circuitry for resolving the signal from the sensor into a useful output.
  • the sensor is a variable capacitance capacitor, the capacitance of which changes responsive to acceleration.
  • One node of the capacitor comprises a polysilicon bridge suspended above the substrate on a series of posts.
  • the polysilicon bridge comprises a suspended longitudinal beam having a plurality of fingers extending transversely therefrom. For each beam finger, there is a corresponding stationary finger positioned parallel and in close proximity thereto.
  • the stationary fingers comprise the other node of the capacitor.
  • the bridge and all of the fingers are electrically conductive.
  • the bridge, including the beam fingers, is charged to a different voltage than the stationary fingers.
  • the polysilicon is resilient such that the bridge, comprising the fingers, sways under accelerative force such that the spacing between the beam fingers and the stationary fingers, and thus the capacitance of the sensor, changes.
  • the capacitance signal from the sensor is fed to the resolving circuitry on the same substrate, which creates an output signal indicative of the magnitude of the accelerative force.
  • the integrated circuitry on the chip is coated with passivation to protect it.
  • the microstructure cannot the passivated, since it must be able to move freely.
  • the microstructure is positioned essentially in the center of the microchip. Due to the fact that the microstructure is comprised of extremely small polysilicon elements, and the fact that it is not coated with passivation, the microstructure is extremely fragile. Accordingly, great care must be taken during fabrication, up to and including the final packaging steps, not to damage the microstructure.
  • microstructures would be destroyed.
  • the water jet spray used in the sawing process would destroy the microstructures. If any microstructures survived the water spray during the sawing operation, they would be destroyed during the subsequent spraying and brushing in the cleaning operation. Further, if any microstructures survived those two steps, they would be likely to be destroyed in the pick-and-place station by the vacuum equipped arm which picks up the dies and places them in the grid carrier.
  • the wafer is placed circuit side down on a wafer mount film having holes that correspond to the locations of the microstructures.
  • the wafer is sawn upside down while it is attached to the wafer mount film.
  • the dies are removed from the film one at a time in a process where blunt needles push on the circuit side of the die to lift it from the film, while a vacuum tool pulls on the back side.
  • the individual die is flipped over and is placed, circuit side up, on a second wafer mount film. This process is repeated for each die in the sawn wafer.
  • the disclosed process is generally satisfactory, but has certain disadvantages.
  • the post-saw part of the process req ires a significant amount of custom equipment, and the removal of the dies one at a time from the first wafer mount film can be a lengthy process during which the dies are susceptible to particulate contamination and damage.
  • the dies may be damaged by the blunt needles.
  • a trend in micromechanical devices is toward smaller dies and a larger number of dies on each wafer. As dies become smaller, the margin of error in removing the dies from the first wafer mount film is smaller. Furthermore, more time is required per wafer to transfer the dies one at a time.
  • a method for separating microcircuit dies from a wafer.
  • the wafer comprises a plurality of dies, each containing componentry on a circuit side thereof and streets separating the dies from each other.
  • the method comprises the steps of fixing the circuit side of the wafer to a first wafer mount film, detaching the dies from the other dies on the wafer, typically by sawing the wafer along the streets, with the circuit side of the wafer fixed to the first wafer mount film, thereby forming a divided wafer, fixing a second wafer mount film to the back side of the divided wafer, and removing the first wafer mount film from the divided wafer, so that the dies remain fixed to the second wafer mount film with their circuit sides exposed.
  • the second wafer mount film preferably has greater adhesion to the divided wafer than the first wafer mount film when the first wafer mount film is removed from the divided wafer, so that the first wafer mount film is removed from the divided wafer without removing the second wafer mount film from the divided wafer.
  • the first wafer mount film comprises a protective film having holes aligned with the fragile components on the dies and a cover film that covers the holes.
  • the step of fixing the circuit side of the wafer to the first wafer mount film may comprise fixing the circuit side of the wafer to one side of the protective film with the holes in alignment with the fragile component of each of the dies, and fixing the cover film to the other side of the protective film.
  • the protective film may comprise an ultraviolet-curable film. The ultraviolet-curable film is irradiated with ultraviolet radiation after detaching the dies so as to reduce the adhesion of the protective film to the divided wafer.
  • a method for separating microcircuit dies from a wafer.
  • the wafer comprises a plurality of dies, each containing componentry on a circuit side thereof and streets separating the dies from each other.
  • the method comprises the steps of forming clearance holes in a protective film, each of the clearance holes having a size corresponding to a fragile component on the microcircuit dies, fixing the circuit side of the wafer to one side of the protective film and adhering a cover film to the other side of the protective film.
  • the dies are detached from the other dies on the wafer, typically by sawing the wafer along the streets.
  • a second wafer mount film is then fixed to the back side of the divided wafer, and the protective film and the cover film are removed from the circuit side of the divided wafer, so that the dies remain fixed to the second wafer mount film with their circuit sides exposed.
  • the protective film may comprise an ultraviolet-curable film.
  • a release tape may be affixed to the ultraviolet-curable film prior to the step of forming clearance holes in the protective film. The release tape is removed from the ultraviolet- curable film after the step of forming clearance holes. The release tape reduces the risk of the protective film adhering to the punching tool.
  • FIG. 1 A is a plan view of the front or circuit side of an exemplary wafer comprising a plurality of dies
  • FIG. IB is a plan view of section IB of the wafer shown in FIG. 1 A;
  • FIG. 2 is a plan view of a film frame bearing a protective film after it has been processed through a hole punching station;
  • FIG. 3 is a plan view of the film frame assembly of FIG. 2 having a wafer mounted thereto with the circuit side facing the protective film;
  • FIG. 4 is a partial cross-sectional view of a wafer having a first wafer mount film fixed to the circuit side thereof;
  • FIG. 5 is a partial cross-sectional view of the wafer shown in FIG. 4 after sawing;
  • FIG. 6 is a partial cross-sectional view of the sawn wafer of FIG. 5 having a second wafer mount film fixed to the back side thereof;
  • FIG. 7 is a partial cross-sectional view of the sawn wafer of FIG. 6 with the first wafer mount film removed and the circuit side of the dies facing upwardly;
  • FIG. 8 is a partial cross-sectional view of the first wafer mount film, illustrating an example of the hole punching process.
  • FIG. 9 is a flow diagram of a method for separating microcircuit dies from wafers in accordance with an embodiment of the invention.
  • FIG. 2 shows an example of a film frame 16 for use in the process of the present invention.
  • the film frame 16 is a thin frame constructed, for example, of a metal or plastic and defining a generally circular opening having a perimeter 20.
  • a protective film 26 is mounted to the frame.
  • the protective film 26 is coated with an adhesive on one side which causes the film 26 to adhere to the surface 24 of film frame 16 and to a wafer.
  • the protective film 26 and the film frame 16 constitute a film frame assembly.
  • the film frame assembly is placed on a pallet in a hole punch station.
  • the punching station comprises a punch assembly for punching holes 28 in protective film 26.
  • the punching station is programmed to punch holes 28 in the film in a programmable predetermined pattern corresponding to the relative positions of the fragile components, typically microstructures, on the wafer.
  • the punch is selected to punch holes of a size slightly larger than the microstructures.
  • Alignment holes 30a define a first line in a first direction, while alignment holes 30b define a second line in a second direction which is typically orthogonal to the first direction.
  • Alignment holes 30a and 30b are precision placed relative to holes 28 so that the positions of the lines defined by them relative to the positions of the streets of the wafer when the wafer is adhered to the film are precisely known. It is not necessary that the holes 30a and 30b be on the same line as any given street of the wafer. It is only necessary that the positions of the lines defined by holes 30a and 30b are known relative to the positions of the streets on the wafer.
  • a wafer 32 is then fixed to one side of protective film 26, as shown in FIG. 3.
  • the wafer is placed on a vacuum chuck in a precision aligning and mounting station with the circuit side facing up.
  • the circuit side, or front side, of the wafer 32 is the side where all components, including monolithic integrated circuitry, microstructures and any other components, are fabricated. No components are fabricated on the back side of the wafer.
  • a pair of cameras positioned above the chuck obtains images of different areas of the wafer. The images are transferred to a pair of video screens or are shown split screen on a single monitor. An operator observes the video images and aligns the wafer in a desired position.
  • the film frame assembly is then inserted in a slot above the chuck such that the protective film 26 is facing the circuit side of the wafer.
  • the cameras obtain images of the holes in the film.
  • the operator observes the new images of the holes and aligns them in proper orientation with respect to the wafer.
  • the alignment station is computer controlled and includes pattern recognition software, such that alignment of the holes in the film frame with the wafer is performed automatically.
  • the chuck containing the wafer is brought into contact with the protective film 26 such that the film and the wafer adhere to each other.
  • the film frame assembl is then returned to the film carrier station, and a cover film 42 (FIG. 4) is adhered to the protective film 26.
  • the cover film 42 has no holes and therefore seals one end of each of the holes 28, 30a and 30b in the protective film 26.
  • the cover film 42 can be adhered to the protective film 26 before the wafer is mounted to the film frame assembly, if the cover film 42 is sufficiently light-transmissive to permit alignment of the wafer to the protective film 26.
  • the protective film 26 and the cover film 42 together constitute a first wafer mount film 44.
  • FIG. 3 illustrates the film frame assembly after the wafer 32 has been adhered to the protective film 26 with its back side 33 facing away from the protective film 26. Holes 28 are underneath the wafer and cannot be seen, and holes 30a and 30b are exposed beyond the perimeter of the wafer.
  • the film frame assembly, including the wafer 32, is now placed on a pallet at a sawing station.
  • the pallet may be a vacuum chuck in which a vacuum is applied to force the wafer onto a support surface.
  • the sawing station includes a camera which obtains an image of the film frame assembly and determines the positions of holes 30a or 30b.
  • the sawing station is programmed with a map of the wafer, indicating the relative position of each street relative to the lines defined by holes 30a and 30b.
  • the pallet and film frame assembly are then advanced through the saw and are shifted laterally to the saw blade cutting direction as many times as necessary to saw each street in the first direction.
  • the pallet is then rotated 90°, realigned and to the second set of alignment holes, and the pallet and film frame assembly are advanced into the saw and laterally shifted again a number of times necessary to saw through all of the streets in the second direction. If the sawing station tolerances are small enough with respect to the 90° rotation and linear distance, it may not be necessary to realign the wafer with respect to the second set of alignment holes.
  • the height of the saw blade is selected to cut completely through the wafer and to score the first wafer mount film 44 without cutting completely through it.
  • the wafer 32 As is common in the sawing of wafers, jets of deionized water are sprayed on the wafer 32 for cooling during the sawing process, and another jet of water is sprayed on the saw blade in order to keep it cool. Because the wafer is adhered to first wafer mount film 44 with its circuit side facing down, the microstructures on the wafer are sealed between the wafer 32 and the film such that water cannot penetrate into the circuit side of the wafer to damage the microstructures. After the sawing process, the film frame assembly, including the wafer 32, goes through a normal cleaning process, which includes additional spraying with deionized water and brushing to remove any silicon slurry. The microstructures and all other circuitry remain sealed from the water and are not affected.
  • Wafer 32 may include microstructures 40 and integrated circuitry (not shown) at locations corresponding to each of the microcircuit dies.
  • each microstructure 40 is the fragile component of the microcircuit die.
  • First wafer mount film 44 includes protective film 26, having holes 28 aligned with microstructures 40, and cover film 42, which covers holes 28.
  • Protective film 26 is adhered to the front side, or circuit side, 50 of wafer 32, and cover film 42 is adhered to protective film 26.
  • microstructures 40 are sealed from the external environment by first wafer mount film 44 and are prevented by holes 28 from contacting first wafer mount film 44.
  • streets 60 define microcircuit dies 62.
  • FIG. 5 shows wafer 32 after sawing along streets 60 as described above.
  • the sawn, or divided, wafer comprises separated microcircuit dies 62.
  • the first wafer mount film 44 remains adhered to the circuit side 50 of the sawn wafer and thus is adhered to the circuit sides of microcircuit dies 62.
  • first wafer mount film 44 is on top (but still adhered to the circuit sides of microcircuit dies 62).
  • a second wafer mount film 70 is adhered to the back side of the sawn wafer and, in particular, is adhered to the back sides of microcircuit dies 62.
  • second film 70 has less adhesion to the sawn wafer than first wafer mount film 44. This requirement is discussed in more detail below.
  • microcircuit dies 62 are sandwiched between first wafer mount film 44 and second film 70.
  • the second film 70 is preferably mounted to a film frame similar to the film frame 16 shown in FIG. 2.
  • the film frame assembly including film frame 16, first wafer mount film 44 and the sawn wafer, may be positioned such that the sawn wafer contacts second film 70 on its own film frame.
  • the sawn wafer and the first wafer mount film 44 may be cut from film frame 16 by cutting around the perimeter of the sawn wafer. The back side of the sawn wafer, with first wafer mount film 44 adhered to its circuit side, is then brought into contact with second film 70 on its own film frame.
  • first wafer mount film 44 is then removed from the sawn wafer, leaving microcircuit dies 62 with their back sides adhered to second film 70 and their circuit sides 50 facing upwardly.
  • the microcircuit dies 62 are now properly positioned for being accessed by a pick-and-place station which mounts the microcircuit dies in packages.
  • the microcircuit dies 62 have been positioned on second film 70 for further processing without requiring them to be removed one at a time from the first wafer mount film 44 and without the potential risk of damage to the componentry by the blunt needles used in prior art processes to remove the microcircuit dies from the first wafer mount film.
  • first wafer mount film 44 and in particular the adhesion of protective film 26, to the circuit side 50 of the sawn wafer should be less than the adhesion of second film 70 to the back side of the sawn wafer to insure that first wafer mount film 44 can be removed from the sawn wafer, while second film 70 remains adhered to the back side of the sawn wafer.
  • This requirement can be achieved by utilizing a second film 70 having inherently greater adhesion than protective film 26.
  • Some adhesive films have adhesions that are variable in response to environmental factors, such as heating or radiation. For example, ultraviolet-curable films may exhibit reduced adhesion after exposure to ultraviolet radiation.
  • the above requirement on relative adhesions may be refined by stating that the first wafer mount film should have lower adhesion than the second film at the time when the first wafer mount film is removed from the sawn wafer. Additionally, with reference to FIG. 6, it may be observed that protective film 26 does not contact the sawn wafer in the areas of holes 28, thereby reducing the total adhesion between protective film 26 and the sawn wafer. Thus, the adhesion requirement may be defined more precisely by stating that the effective adhesion of the first wafer mount film 44 to the sawn wafer should be less than the effective adhesion of the second film 70 to the sawn wafer at the time when the first wafer mount film 44 is removed from the sawn wafer.
  • protective film 26 of first wafer mount film 44 is an ultraviolet-curable film.
  • the high initial adhesion of the ultraviolet-curable film is advantageous during the sawing process in preventing leakage of water into microstructures 40.
  • a conventional low adhesion film was utilized for protective film 26, some leakage was observed, thereby damaging microcircuit 40.
  • the high adhesion ultraviolet-curable film may adhere to the tool used to punch holes 28 in protective film 26. A process for overcoming this difficulty is described with reference to FIG. 8, which shows a partial cross-sectional view of a configuration utilized for punching holes 28 in protective film 26.
  • release layer 80 Prior to punching holes 28, a release layer 80 is adhered to the adhesive surface of protective film 26.
  • Release layer 80 is not required to have an adhesive surface and may be a silicone coated polyester, for example Adwill SP PET 3811(S) sold by Lintec, having a thickness of 35 micrometers. Holes 28 are punched through release layer 80 and protective film 26 in a direction indicated by arrows 82, thus avoiding adherence of protective film 26 to the punching tool.
  • the release layer 80 is then removed from protective film 26.
  • wafer 32 is adhered to one side of protective film 26 with microstructures 40 aligned with holes 28, as shown in FIG. 4, and cover film 42 is adhered to the other side of protective film 26.
  • first wafer mount film 44 is irradiated with ultraviolet radiation, as indicated by arrows 90 in FIG. 6, to reduce the adhesion of protective film 26 to the circuit side 50 of the microcircuit dies 62.
  • protective film 26 may be a type Adwill D-554 ultraviolet-curable film manufactured by Lintec and having a thickness of 200 micrometers.
  • Cover film 42 may be a type DT100H adhesive film manufactured by NEPTCO, Inc. and having a thickness of 90 micrometers.
  • cover film 42 is transparent or nearly transparent to the ultraviolet radiation used to cure the adhesive on protective film 26, and the adhesive on cover film 42 is not ultraviolet-curable.
  • Second film 70 may be type Adwill D- 520T adhesive film manufactured by Lintec and having a thickness of 200 micrometers. It will be understood that the above film parameters are given by way of example only and are not limiting as to the scope of the present invention. As noted previously, a general requirement is that the first wafer mount film 44 have lower effective adhesion to the microcircuit dies 62 than the second film 70 at the time when the first wafer mount film 44 is removed from the microcircuit dies.
  • step 100 release layer 80 is adhered to protective film 26, as shown in FIG. 8.
  • step 102 holes 28 are punched through protective film 26 and release layer 80.
  • step 104 the circuit side of wafer 32 is adhered to one side of protective film 26 with microstructures 40 in alignment with holes 28, as shown in FIG. 4.
  • step 108 cover film 42 is adhered to the other side of protective film 26, wherein pro ective film 26 and cover film 42 constitute first wafer mount film 44.
  • step 110 the wafer 35 is sawn along streets 60 to separate microcircuit dies 62, as shown in FIG. 5.
  • step 1 12 second wafer mount film 70 is adhered to the back side of the sawn wafer, as shown in FIG. 6.
  • the protective film 26 is irradiated with ultraviolet radiation through cover film 42, as indicated by arrows 90 in FIG. 6, so as to reduce the adhesion of protective film 26 to the circuit sides of dies 62.
  • First wafer mount film 44 is then removed from the circuit side of the sawn wafer in step 1 16.
  • the microcircuit dies 62 are then available on second film 70 with their circuit sides facing upwardly.
  • the second film 70 having the microcircuit dies 62 adhered thereto may be forwarded to a pick- and-place station for further processing.
  • the first wafer mount film 44 may comprise a single film or more than two films in appropriate applications. Where the components on the microcircuit dies can withstand contact with the first wafer mount film, the holes 28 in protective film 26 may be omitted, thereby eliminating the need for cover film 42. Furthermore, the protective film 26 is not required to be an ultraviolet-curable film. As discussed above, one requirement is that the first wafer mount film 44 be configured to minimize the risk of damage to the circuitry on the microcircuit dies 62 during sawing and subsequent processing.
  • first wafer mount film 44 and second film 70 should be selected such that first wafer mount film 44 may be removed from the circuit sides of microcircuit dies 62, while the second film 70 remains adhered to the back sides of microcircuit dies 62
  • steps 100 and 104 which relate to release layer 80, may be omitted if released layer 80 is not required for punching holes in protective film 26.
  • Step 106 wherein the circuit side of the wafer is adhered to one side of the protective film, and step 108, wherein the cover layer is adhered to the other side of the protective film, may be reversed in order if the wafer can be aligned with the protective film 26 with the cover film 42 in place.
  • Step 114 wherein the protective film 26 is irradiated with ultraviolet radiation, may be omitted when an ultraviolet-curable film is not utilized.
  • the invention is not limited to die separation by sawing. For example, the invention may be utilized with scribe and break die separation techniques.
  • the invention is not limited to forming holes in the protective film by punching.
  • the holes in the protective film may be formed by laser trepanning or ablation While there have been shown and described what are at present considered the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Dicing (AREA)

Abstract

Methods are provided for separating microcircuit dies from a wafer, which includes microcircuit dies containing componentry on a circuit side thereof and streets separating the dies from each other. A first wafer mount film is affixed to the circuit side of the wafer, and the dies are detached along the streets with the circuit side of the wafer fixed to the first wafer mount film, thereby forming a divided wafer. A second wafer mount film is fixed to the back side of the divided wafer, and the first wafer mount film is removed from the divided wafer so that the dies remain fixed to the second wafer mount film with their circuit sides exposed. The second wafer mount film preferably has greater adhesion to the divided wafer than the first wafer mount film when the first wafer mount film is removed from the divided wafer. The first wafer mount film may comprise a protective film having holes aligned with fragile components on the dies and a cover film that covers the holes. The protective film may be an ultraviolet-curable film that exhibits reduced adhesion to the divided wafer after exposure to ultraviolet radiation.

Description

METHODS FOR SEPARATING MICROCIRCUIT DIES FROM WAFERS
Field of the Invention This invention relates to processing of semiconductor wafers and, more particularly, to methods for separating microcircuit dies from a wafer containing a plurality of dies. The invention is particularly useful in processing of wafers containing fragile micromechanical devices, but is not limited to such use.
Background of the Invention
In the fabrication of microchips for use in the electronics and computer industries, a wafer typically comprises a plurality of individual dies, or chips, arranged in a grid pattern. The portions of the wafer between the individual dies are termed "streets." FIGS. 1A and I B illustrate an exemplary wafer 10. FIG. 1A is a plan view of a wafer, and FIG. IB is an enlarged view of section IB in FIG. 1A. Reference numerals 14 denote individual dies, and reference numerals 12 denote the streets separating the individual dies 14. Streets 12 are areas of the wafer where no componentry has been placed and which define the boundaries of each individual die 14. The integrated circuitry and other componentry appears on only one side, e.g., front side 15, of the wafer. The back side (not shown in FIGS. 1A and IB) has no circuitry or other componentry. The individual dies 14 comprising a wafer are removed from the wafer by sawing through the wafer along all of the streets, thus physically separating the wafer in both axes into the individual dies.
Semiconductor devices incorporating microstructures, also known as micromechanical devices, with moving parts have been disclosed in the prior art. U.S. Patent No. 5,345,824, issued September 13, 1994 to Sherman et al., discloses a monolithic accelerometer. U.S. Patent No. 5,326,726, issued July 5, 1994 to Tsang et al., discloses a method for fabricating a monolithic chip containing integrated circuitry and a suspended microstructure. These patents disclose a suspended micro structure for sensing accelerative forces and integrated circuitry for resolving the signal from the sensor into a useful output. The sensor is a variable capacitance capacitor, the capacitance of which changes responsive to acceleration. One node of the capacitor comprises a polysilicon bridge suspended above the substrate on a series of posts. The polysilicon bridge comprises a suspended longitudinal beam having a plurality of fingers extending transversely therefrom. For each beam finger, there is a corresponding stationary finger positioned parallel and in close proximity thereto. The stationary fingers comprise the other node of the capacitor. The bridge and all of the fingers are electrically conductive. The bridge, including the beam fingers, is charged to a different voltage than the stationary fingers. The polysilicon is resilient such that the bridge, comprising the fingers, sways under accelerative force such that the spacing between the beam fingers and the stationary fingers, and thus the capacitance of the sensor, changes. The capacitance signal from the sensor is fed to the resolving circuitry on the same substrate, which creates an output signal indicative of the magnitude of the accelerative force. When a monolithic accelerometer chip is fabricated, the integrated circuitry on the chip is coated with passivation to protect it. However, the microstructure cannot the passivated, since it must be able to move freely. Typically, the microstructure is positioned essentially in the center of the microchip. Due to the fact that the microstructure is comprised of extremely small polysilicon elements, and the fact that it is not coated with passivation, the microstructure is extremely fragile. Accordingly, great care must be taken during fabrication, up to and including the final packaging steps, not to damage the microstructure. If a wafer including a set of monolithic accelerometer dies was passed through the standard die separation process, the microstructures would be destroyed. The water jet spray used in the sawing process would destroy the microstructures. If any microstructures survived the water spray during the sawing operation, they would be destroyed during the subsequent spraying and brushing in the cleaning operation. Further, if any microstructures survived those two steps, they would be likely to be destroyed in the pick-and-place station by the vacuum equipped arm which picks up the dies and places them in the grid carrier.
A process for separating circuit dies from a wafer, which may include fragile microstructures, is disclosed in U.S. Patent No. 5,362,681, issued November 8, 1994 to
Roberts, Jr. et al. In the disclosed process, the wafer is placed circuit side down on a wafer mount film having holes that correspond to the locations of the microstructures. The wafer is sawn upside down while it is attached to the wafer mount film. After sawing, the dies are removed from the film one at a time in a process where blunt needles push on the circuit side of the die to lift it from the film, while a vacuum tool pulls on the back side. The individual die is flipped over and is placed, circuit side up, on a second wafer mount film. This process is repeated for each die in the sawn wafer. The disclosed process is generally satisfactory, but has certain disadvantages. The post-saw part of the process req ires a significant amount of custom equipment, and the removal of the dies one at a time from the first wafer mount film can be a lengthy process during which the dies are susceptible to particulate contamination and damage. For example, the dies may be damaged by the blunt needles. A trend in micromechanical devices is toward smaller dies and a larger number of dies on each wafer. As dies become smaller, the margin of error in removing the dies from the first wafer mount film is smaller. Furthermore, more time is required per wafer to transfer the dies one at a time.
Accordingly, there is a need for improved methods for separating microcircuit dies from wafers, which have low probability of damaging the dies, which have low risk of contamination of the dies, and which provide high throughput.
Summary of the Invention
According to a first aspect of the invention, a method is provided for separating microcircuit dies from a wafer. The wafer comprises a plurality of dies, each containing componentry on a circuit side thereof and streets separating the dies from each other. The method comprises the steps of fixing the circuit side of the wafer to a first wafer mount film, detaching the dies from the other dies on the wafer, typically by sawing the wafer along the streets, with the circuit side of the wafer fixed to the first wafer mount film, thereby forming a divided wafer, fixing a second wafer mount film to the back side of the divided wafer, and removing the first wafer mount film from the divided wafer, so that the dies remain fixed to the second wafer mount film with their circuit sides exposed.
The second wafer mount film preferably has greater adhesion to the divided wafer than the first wafer mount film when the first wafer mount film is removed from the divided wafer, so that the first wafer mount film is removed from the divided wafer without removing the second wafer mount film from the divided wafer.
In one embodiment, the first wafer mount film comprises a protective film having holes aligned with the fragile components on the dies and a cover film that covers the holes.
The step of fixing the circuit side of the wafer to the first wafer mount film may comprise fixing the circuit side of the wafer to one side of the protective film with the holes in alignment with the fragile component of each of the dies, and fixing the cover film to the other side of the protective film. The protective film may comprise an ultraviolet-curable film. The ultraviolet-curable film is irradiated with ultraviolet radiation after detaching the dies so as to reduce the adhesion of the protective film to the divided wafer.
According to another aspect of the invention, a method is provided for separating microcircuit dies from a wafer. The wafer comprises a plurality of dies, each containing componentry on a circuit side thereof and streets separating the dies from each other. The method comprises the steps of forming clearance holes in a protective film, each of the clearance holes having a size corresponding to a fragile component on the microcircuit dies, fixing the circuit side of the wafer to one side of the protective film and adhering a cover film to the other side of the protective film. The dies are detached from the other dies on the wafer, typically by sawing the wafer along the streets. A second wafer mount film is then fixed to the back side of the divided wafer, and the protective film and the cover film are removed from the circuit side of the divided wafer, so that the dies remain fixed to the second wafer mount film with their circuit sides exposed. As indicated above, the protective film may comprise an ultraviolet-curable film. A release tape may be affixed to the ultraviolet-curable film prior to the step of forming clearance holes in the protective film. The release tape is removed from the ultraviolet- curable film after the step of forming clearance holes. The release tape reduces the risk of the protective film adhering to the punching tool.
Brief Description of the Drawings For a better understanding of the present invention, reference is made to the accompanying drawings, which are incorporated herein by reference and in which:
FIG. 1 A is a plan view of the front or circuit side of an exemplary wafer comprising a plurality of dies;
FIG. IB is a plan view of section IB of the wafer shown in FIG. 1 A; FIG. 2 is a plan view of a film frame bearing a protective film after it has been processed through a hole punching station;
FIG. 3 is a plan view of the film frame assembly of FIG. 2 having a wafer mounted thereto with the circuit side facing the protective film;
FIG. 4 is a partial cross-sectional view of a wafer having a first wafer mount film fixed to the circuit side thereof; FIG. 5 is a partial cross-sectional view of the wafer shown in FIG. 4 after sawing;
FIG. 6 is a partial cross-sectional view of the sawn wafer of FIG. 5 having a second wafer mount film fixed to the back side thereof;
FIG. 7 is a partial cross-sectional view of the sawn wafer of FIG. 6 with the first wafer mount film removed and the circuit side of the dies facing upwardly;
FIG. 8 is a partial cross-sectional view of the first wafer mount film, illustrating an example of the hole punching process; and
FIG. 9 is a flow diagram of a method for separating microcircuit dies from wafers in accordance with an embodiment of the invention.
Detailed Description
The process of the present invention is described with reference to a wafer comprising monolithic accelerometer dies as described above and in the above-identified patents incorporated herein. It will be understood however, that the process described herein can be applied to other microcircuit dies. The process is particularly useful when applied to microcircuit dies having microstructures, or micromechanical devices, but is not limited to such applications.
FIG. 2 shows an example of a film frame 16 for use in the process of the present invention. The film frame 16 is a thin frame constructed, for example, of a metal or plastic and defining a generally circular opening having a perimeter 20. A protective film 26 is mounted to the frame. The protective film 26 is coated with an adhesive on one side which causes the film 26 to adhere to the surface 24 of film frame 16 and to a wafer. The protective film 26 and the film frame 16 constitute a film frame assembly.
The film frame assembly is placed on a pallet in a hole punch station. The punching station comprises a punch assembly for punching holes 28 in protective film 26. The punching station is programmed to punch holes 28 in the film in a programmable predetermined pattern corresponding to the relative positions of the fragile components, typically microstructures, on the wafer. The punch is selected to punch holes of a size slightly larger than the microstructures. When a wafer is fixed to the film frame assembly, it is crucial to align the wafer with the holes such that the holes are aligned with the microstructures. Additional alignment holes 30a and 30b are punched in the protective film 26 such that they are located beyond the perimeter of the wafer when the wafer is adhered to the film. Alignment holes 30a define a first line in a first direction, while alignment holes 30b define a second line in a second direction which is typically orthogonal to the first direction. Alignment holes 30a and 30b are precision placed relative to holes 28 so that the positions of the lines defined by them relative to the positions of the streets of the wafer when the wafer is adhered to the film are precisely known. It is not necessary that the holes 30a and 30b be on the same line as any given street of the wafer. It is only necessary that the positions of the lines defined by holes 30a and 30b are known relative to the positions of the streets on the wafer. It is known that when a wafer is adhered to the film such that the microstructures match up with holes 28, there is a street parallel to the line defined by holes 30a, but offset a known distance from that line and that all of the streets in the first orthogonal direction are parallel to this street and offset from each other by another known distance. Alternatively, alignment ink dots may be placed on the film instead of alignment holes, as described in the aforementioned Patent No. 5,362,681.
A wafer 32 is then fixed to one side of protective film 26, as shown in FIG. 3. First, the wafer is placed on a vacuum chuck in a precision aligning and mounting station with the circuit side facing up. The circuit side, or front side, of the wafer 32 is the side where all components, including monolithic integrated circuitry, microstructures and any other components, are fabricated. No components are fabricated on the back side of the wafer. A pair of cameras positioned above the chuck obtains images of different areas of the wafer. The images are transferred to a pair of video screens or are shown split screen on a single monitor. An operator observes the video images and aligns the wafer in a desired position. The film frame assembly is then inserted in a slot above the chuck such that the protective film 26 is facing the circuit side of the wafer. When the film frame assembly is inserted into the machine, the cameras obtain images of the holes in the film. The operator then observes the new images of the holes and aligns them in proper orientation with respect to the wafer. In a more preferred embodiment of the invention, the alignment station is computer controlled and includes pattern recognition software, such that alignment of the holes in the film frame with the wafer is performed automatically. Then the chuck containing the wafer is brought into contact with the protective film 26 such that the film and the wafer adhere to each other. The film frame assembl is then returned to the film carrier station, and a cover film 42 (FIG. 4) is adhered to the protective film 26. The cover film 42 has no holes and therefore seals one end of each of the holes 28, 30a and 30b in the protective film 26. Alternatively, the cover film 42 can be adhered to the protective film 26 before the wafer is mounted to the film frame assembly, if the cover film 42 is sufficiently light-transmissive to permit alignment of the wafer to the protective film 26. The protective film 26 and the cover film 42 together constitute a first wafer mount film 44.
FIG. 3 illustrates the film frame assembly after the wafer 32 has been adhered to the protective film 26 with its back side 33 facing away from the protective film 26. Holes 28 are underneath the wafer and cannot be seen, and holes 30a and 30b are exposed beyond the perimeter of the wafer. The film frame assembly, including the wafer 32, is now placed on a pallet at a sawing station. The pallet may be a vacuum chuck in which a vacuum is applied to force the wafer onto a support surface. The sawing station includes a camera which obtains an image of the film frame assembly and determines the positions of holes 30a or 30b. The sawing station is programmed with a map of the wafer, indicating the relative position of each street relative to the lines defined by holes 30a and 30b. The pallet and film frame assembly are then advanced through the saw and are shifted laterally to the saw blade cutting direction as many times as necessary to saw each street in the first direction. The pallet is then rotated 90°, realigned and to the second set of alignment holes, and the pallet and film frame assembly are advanced into the saw and laterally shifted again a number of times necessary to saw through all of the streets in the second direction. If the sawing station tolerances are small enough with respect to the 90° rotation and linear distance, it may not be necessary to realign the wafer with respect to the second set of alignment holes. The height of the saw blade is selected to cut completely through the wafer and to score the first wafer mount film 44 without cutting completely through it.
As is common in the sawing of wafers, jets of deionized water are sprayed on the wafer 32 for cooling during the sawing process, and another jet of water is sprayed on the saw blade in order to keep it cool. Because the wafer is adhered to first wafer mount film 44 with its circuit side facing down, the microstructures on the wafer are sealed between the wafer 32 and the film such that water cannot penetrate into the circuit side of the wafer to damage the microstructures. After the sawing process, the film frame assembly, including the wafer 32, goes through a normal cleaning process, which includes additional spraying with deionized water and brushing to remove any silicon slurry. The microstructures and all other circuitry remain sealed from the water and are not affected.
A partial cross-sectional view of wafer 32 and first wafer mount film 44 is shown in FIG. 4. Wafer 32 may include microstructures 40 and integrated circuitry (not shown) at locations corresponding to each of the microcircuit dies. In this example, it is assumed that each microstructure 40 is the fragile component of the microcircuit die. First wafer mount film 44 includes protective film 26, having holes 28 aligned with microstructures 40, and cover film 42, which covers holes 28. Protective film 26 is adhered to the front side, or circuit side, 50 of wafer 32, and cover film 42 is adhered to protective film 26. Thus, microstructures 40 are sealed from the external environment by first wafer mount film 44 and are prevented by holes 28 from contacting first wafer mount film 44. On wafer 32, streets 60 define microcircuit dies 62.
FIG. 5 shows wafer 32 after sawing along streets 60 as described above. The sawn, or divided, wafer comprises separated microcircuit dies 62. The first wafer mount film 44 remains adhered to the circuit side 50 of the sawn wafer and thus is adhered to the circuit sides of microcircuit dies 62.
Referring now to FIG. 6, the sawn wafer is inverted with respect to FIG. 5, so that first wafer mount film 44 is on top (but still adhered to the circuit sides of microcircuit dies 62). At this point, a second wafer mount film 70 is adhered to the back side of the sawn wafer and, in particular, is adhered to the back sides of microcircuit dies 62. As a general proposition, second film 70 has less adhesion to the sawn wafer than first wafer mount film 44. This requirement is discussed in more detail below. As shown in FIG. 6, microcircuit dies 62 are sandwiched between first wafer mount film 44 and second film 70.
The second film 70 is preferably mounted to a film frame similar to the film frame 16 shown in FIG. 2. The film frame assembly, including film frame 16, first wafer mount film 44 and the sawn wafer, may be positioned such that the sawn wafer contacts second film 70 on its own film frame. Alternatively, the sawn wafer and the first wafer mount film 44 may be cut from film frame 16 by cutting around the perimeter of the sawn wafer. The back side of the sawn wafer, with first wafer mount film 44 adhered to its circuit side, is then brought into contact with second film 70 on its own film frame.
As shown in FIG. 7, first wafer mount film 44 is then removed from the sawn wafer, leaving microcircuit dies 62 with their back sides adhered to second film 70 and their circuit sides 50 facing upwardly. The microcircuit dies 62 are now properly positioned for being accessed by a pick-and-place station which mounts the microcircuit dies in packages. Thus, the microcircuit dies 62 have been positioned on second film 70 for further processing without requiring them to be removed one at a time from the first wafer mount film 44 and without the potential risk of damage to the componentry by the blunt needles used in prior art processes to remove the microcircuit dies from the first wafer mount film.
As indicated above, the adhesion of first wafer mount film 44, and in particular the adhesion of protective film 26, to the circuit side 50 of the sawn wafer should be less than the adhesion of second film 70 to the back side of the sawn wafer to insure that first wafer mount film 44 can be removed from the sawn wafer, while second film 70 remains adhered to the back side of the sawn wafer. This requirement can be achieved by utilizing a second film 70 having inherently greater adhesion than protective film 26. Some adhesive films have adhesions that are variable in response to environmental factors, such as heating or radiation. For example, ultraviolet-curable films may exhibit reduced adhesion after exposure to ultraviolet radiation. Thus, the above requirement on relative adhesions may be refined by stating that the first wafer mount film should have lower adhesion than the second film at the time when the first wafer mount film is removed from the sawn wafer. Additionally, with reference to FIG. 6, it may be observed that protective film 26 does not contact the sawn wafer in the areas of holes 28, thereby reducing the total adhesion between protective film 26 and the sawn wafer. Thus, the adhesion requirement may be defined more precisely by stating that the effective adhesion of the first wafer mount film 44 to the sawn wafer should be less than the effective adhesion of the second film 70 to the sawn wafer at the time when the first wafer mount film 44 is removed from the sawn wafer.
As indicated above, ultraviolet-curable films, or tapes, have high initial adhesion but exhibit little or no adhesion after exposure to ultraviolet radiation. In a preferred embodiment, protective film 26 of first wafer mount film 44 is an ultraviolet-curable film. The high initial adhesion of the ultraviolet-curable film is advantageous during the sawing process in preventing leakage of water into microstructures 40. When a conventional low adhesion film was utilized for protective film 26, some leakage was observed, thereby damaging microcircuit 40. However, the high adhesion ultraviolet-curable film may adhere to the tool used to punch holes 28 in protective film 26. A process for overcoming this difficulty is described with reference to FIG. 8, which shows a partial cross-sectional view of a configuration utilized for punching holes 28 in protective film 26. Prior to punching holes 28, a release layer 80 is adhered to the adhesive surface of protective film 26. Release layer 80 is not required to have an adhesive surface and may be a silicone coated polyester, for example Adwill SP PET 3811(S) sold by Lintec, having a thickness of 35 micrometers. Holes 28 are punched through release layer 80 and protective film 26 in a direction indicated by arrows 82, thus avoiding adherence of protective film 26 to the punching tool. The release layer 80 is then removed from protective film 26. Then, wafer 32 is adhered to one side of protective film 26 with microstructures 40 aligned with holes 28, as shown in FIG. 4, and cover film 42 is adhered to the other side of protective film 26. After sawing of wafer 32 and before removal of first wafer mount film 44 from the sawn wafer, first wafer mount film 44 is irradiated with ultraviolet radiation, as indicated by arrows 90 in FIG. 6, to reduce the adhesion of protective film 26 to the circuit side 50 of the microcircuit dies 62. In a preferred embodiment, protective film 26 may be a type Adwill D-554 ultraviolet-curable film manufactured by Lintec and having a thickness of 200 micrometers. Cover film 42 may be a type DT100H adhesive film manufactured by NEPTCO, Inc. and having a thickness of 90 micrometers. Preferably, cover film 42 is transparent or nearly transparent to the ultraviolet radiation used to cure the adhesive on protective film 26, and the adhesive on cover film 42 is not ultraviolet-curable. Second film 70 may be type Adwill D- 520T adhesive film manufactured by Lintec and having a thickness of 200 micrometers. It will be understood that the above film parameters are given by way of example only and are not limiting as to the scope of the present invention. As noted previously, a general requirement is that the first wafer mount film 44 have lower effective adhesion to the microcircuit dies 62 than the second film 70 at the time when the first wafer mount film 44 is removed from the microcircuit dies.
The preferred process of the present invention is summarized in the flow chart of FIG. 9. In step 100, release layer 80 is adhered to protective film 26, as shown in FIG. 8. In step 102, holes 28 are punched through protective film 26 and release layer 80. Then, release layer 80 is removed from protective film 26 in step 104. In step 106, the circuit side of wafer 32 is adhered to one side of protective film 26 with microstructures 40 in alignment with holes 28, as shown in FIG. 4. In step 108, cover film 42 is adhered to the other side of protective film 26, wherein pro ective film 26 and cover film 42 constitute first wafer mount film 44. In step 110, the wafer 35 is sawn along streets 60 to separate microcircuit dies 62, as shown in FIG. 5. In step 1 12, second wafer mount film 70 is adhered to the back side of the sawn wafer, as shown in FIG. 6. In step 114, the protective film 26 is irradiated with ultraviolet radiation through cover film 42, as indicated by arrows 90 in FIG. 6, so as to reduce the adhesion of protective film 26 to the circuit sides of dies 62. First wafer mount film 44 is then removed from the circuit side of the sawn wafer in step 1 16. The microcircuit dies 62 are then available on second film 70 with their circuit sides facing upwardly. The second film 70 having the microcircuit dies 62 adhered thereto may be forwarded to a pick- and-place station for further processing.
Numerous changes and variations are included within the scope of the present invention. For example, the first wafer mount film 44 may comprise a single film or more than two films in appropriate applications. Where the components on the microcircuit dies can withstand contact with the first wafer mount film, the holes 28 in protective film 26 may be omitted, thereby eliminating the need for cover film 42. Furthermore, the protective film 26 is not required to be an ultraviolet-curable film. As discussed above, one requirement is that the first wafer mount film 44 be configured to minimize the risk of damage to the circuitry on the microcircuit dies 62 during sawing and subsequent processing. In addition, the relative adhesions of first wafer mount film 44 and second film 70 should be selected such that first wafer mount film 44 may be removed from the circuit sides of microcircuit dies 62, while the second film 70 remains adhered to the back sides of microcircuit dies 62
Referring to FIG. 9, steps 100 and 104, which relate to release layer 80, may be omitted if released layer 80 is not required for punching holes in protective film 26. Step 106, wherein the circuit side of the wafer is adhered to one side of the protective film, and step 108, wherein the cover layer is adhered to the other side of the protective film, may be reversed in order if the wafer can be aligned with the protective film 26 with the cover film 42 in place. Step 114, wherein the protective film 26 is irradiated with ultraviolet radiation, may be omitted when an ultraviolet-curable film is not utilized. The invention is not limited to die separation by sawing. For example, the invention may be utilized with scribe and break die separation techniques. In addition, the invention is not limited to forming holes in the protective film by punching. For example, the holes in the protective film may be formed by laser trepanning or ablation While there have been shown and described what are at present considered the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims

-13-CLAIMS
What is claimed is:
5 1. A method for separating microcircuit dies from a wafer comprising a plurality of dies, each containing componentry on a circuit side thereof, including at least a first component, the wafer comprising streets separating the dies from each other, said method comprising the steps of: fixing the circuit side of the wafer to a first wafer mount film; ] 0 detaching the dies, along said streets, from the other dies on the wafer to form a divided wafer; fixing a second wafer mount film to the back side of the divided wafer; and removing the first wafer mount film from the divided wafer, so that the dies remain fixed to the second wafer mount film with their circuit sides exposed. 15
2. A method as defined in claim 1 wherein the second wafer mount film has greater adhesion to the divided wafer than the first wafer mount film.
3. A method as defined in claim 1 wherein said second wafer mount film has greater 0 adhesion to the divided wafer than the first wafer mount film when the first wafer mount film is removed from the divided wafer.
4. A method as defined in claim 1 wherein said second wafer mount film has greater effective adhesion to the divided wafer than the first wafer mount film when the first wafer 5 mount film is removed from the divided wafer, wherein the first wafer mount film is removed from the divided wafer without removing the second wafer mount film from the divided wafer.
5. A method as defined in claim 1 wherein the first wafer mount film comprises a 0 protective film having holes aligned with the first components of the dies and a cover film, and wherein the step of fixing the circuit side of the wafer to the first wafer mount film comprises fixing the circuit side of the wafer to one side of the protective film with the holes in alignment with the first component of each of the dies and fixing the cover film to the other side of said protective film.
6. A method as defined in claim 5 wherein the protective film and the second wafer mount film have the same nominal adhesion.
7. A method as defined in claim 5 wherein the protective film comprises an ultraviolet- curable film.
8. A method as defined in claim 7 further comprising the step of irradiating the protective film with ultraviolet radiation after the step of detaching the dies, wherein the adhesion of the protective film is reduced.
9. A method as defined in claim 5 further comprising the steps of mounting the protective film to a first wafer mount film frame before the step of fixing the wafer to one side of the protective film and fixing the second wafer mount film to a second film frame before the step of fixing the second wafer mount film to the back side of the divided wafer.
10. A method as defined in claim 1 further comprising the step of removing the dies from the second wafer mount film for further processing.
11. A method as defined in claim 1 wherein the step of detaching the dies comprises sawing the wafer along said streets.
12. A method for separating microcircuit dies from a wafer comprising a plurality of dies each containing componentry on a circuit side thereof, including at least a first component, the wafer comprising streets separating the dies from each other, said method comprising the steps of: forming clearance holes in a protective film, each of said clearance holes having a size corresponding to said first component; fixing the circuit side of the wafer to one side of the protective film; adhering a cover film to ihe other side of the protective film, wherein the protective film and the cover film constitute a first wafer mount film; detaching the dies, along said streets, from the other dies on the wafer to form a divided wafer; fixing a second wafer mount film to the back side of the divided wafer; and removing the first wafer mount film from the divided wafer, so that the dies remain fixed to the second wafer mount film with their circuit sides exposed.
13. A method as defined in claim 12 wherein the second wafer mount film has greater adhesion than the protective film.
14. A method as defined in claim 12 wherein the second wafer mount film has greater adhesion to the divided wafer than the protective film when the protective film is removed from the divided wafer.
15. A method as defined in claim 12 wherein the second wafer mount film has greater effective adhesion to the divided wafer than the protective film when the protective film and the cover film are removed from the divided wafer, wherein the protective film and the cover film are removed from the divided wafer without removing the second wafer mount film from the divided wafer.
16. A method as defined in claim 12 wherein the protective film comprises an ultraviolet- curable film.
17. A method as defined in claim 16 further comprising the step of irradiating the protective film with ultraviolet radiation after the step of detaching the dies, wherein the adhesion of the protective film to the divided wafer is reduced.
18. A method as defined in claim 16 further comprising the step of fixing a release tape to the protective film prior to the step of forming clearance holes in the protective film and removing the release tape from the protective film after the step of forming clearance holes.
19. A method as defined in claim 12 further comprising the step of removing the dies from the second wafer mount film for further processing.
20. A method as defined in claim 12 further comprising the steps of mounting the protective film to a first wafer mount film frame prior to the step of fixing the wafer to one side of the protective film and mounting the second wafer mount film to a second film frame prior to the step of fixing the second wafer mount film to the back side of the sawn wafer.
21. A method as defined in claim 12 wherein the step of detaching the dies comprises sawing the wafer along said streets.
22. A method for separating microcircuit dies from a wafer comprising a plurality of dies, each containing componentry on a circuit side thereof, including at least a microstructure, the wafer comprising streets separating the dies from each other, said method comprising the steps of: mounting a protective film on a first wafer mount film frame; forming clearance holes in the protective film, each of said clearance holes having a size corresponding to said microstructure; fixing the circuit side of the wafer to one side of the protective film; adhering a cover film to the other side of the protective film, wherein the protective film and the cover film constitute a first wafer mount film; sawing the wafer along said streets, wherein the dies are detached from the other dies on the wafer; mounting a second wafer mount film on a second film frame; fixing the second wafer mount film to the back side of the sawn wafer; and removing the protective film and the cover film from the sawn wafer, so that the dies remain fixed to the second wafer mount film with their circuits sides exposed.
23. A method as defined in claim 22 wherein the second wafer mount film has greater effective adhesion to the sawn wafer than the protective film when the protective film and the cover film are removed from the sawn wafer, wherein the protective film and the cover film are removed from the sawn wafer without removing the second wafer mount film from the sa*wn wafer.
24. A method as defined in claim 22 wherein the protective film comprises an ultraviolet- curable film, said method further comprising the step of irradiating the protective film with ultraviolet radiation after the step of sawing the wafer, wherein the adhesion of the protective film to the sawn wafer is reduced.
25. A method as defined in claim 24 further comprising the step of fixing a release tape to the ultraviolet-curable film prior to the step of forming clearance holes in the protective film and removing the release tape from the ultraviolet-curable film after the step of forming clearance holes.
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