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  • H01L24/26—Layer connectors, e.g. plate connectors, solder or adhesive layers; Manufacturing methods related thereto
  • H01L24/31—Structure, shape, material or disposition of the layer connectors after the connecting process
  • H01L24/33—Structure, shape, material or disposition of the layer connectors after the connecting process of a plurality of layer connectors
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  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
  • H01L21/48—Manufacture or treatment of parts, e.g. containers, prior to assembly of the devices, using processes not provided for in a single one of the subgroups H01L21/06 - H01L21/326
  • H01L21/4814—Conductive parts
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  • H01L23/00—Details of semiconductor or other solid state devices
  • H01L23/48—Arrangements for conducting electric current to or from the solid state body in operation, e.g. leads, terminal arrangements ; Selection of materials therefor
  • H01L23/488—Arrangements for conducting electric current to or from the solid state body in operation, e.g. leads, terminal arrangements ; Selection of materials therefor consisting of soldered or bonded constructions
  • H01L23/492—Bases or plates or solder therefor
  • H01L23/4922—Bases or plates or solder therefor having a heterogeneous or anisotropic structure
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  • H01L24/83—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a layer connector
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  • H01L2224/83—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a layer connector
  • H01L2224/8319—Arrangement of the layer connectors prior to mounting
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  • H01L2224/83—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a layer connector
  • H01L2224/838—Bonding techniques
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  • H01L2924/01029—Copper [Cu]
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  • H01L2924/10—Details of semiconductor or other solid state devices to be connected
  • H01L2924/11—Device type
  • H01L2924/12—Passive devices, e.g. 2 terminal devices
  • H01L2924/1204—Optical Diode
  • H01L2924/12042—LASER

Definitions

• This invention relates to methods for diffusion bonding surfaces together and, more particularly, to a method for thermo-compres sion diffusion bonding a structured copper strain buffer directly to one or each of the two major oppos ed surfaces of a substrateles s s emiconductor devic e wafer .
• a structured copper strain buffer comprises a bundle of substantially parallel, closely packed strands of copper of substantially equal length, one common end thereof being thermo-compression diffusion bonded to a metallic sheet.
• One type of prior high power s emiconductor device includes a metallic support plate or substrate, typically compris ed of tungsten or molybdenum, attached to one of the oppos ed surfac es of a s emiconductor devic e wafer to provide the inher ently fragile wafer with structural integrity.
• a metallic support plate or substrate typically compris ed of tungsten or molybdenum
• heat sinks have been attached via structur ed copper strain buffers to one or both sides of the wafer support plate structures .
• the pres ent invention is directed to increasing the conduction of heat away from a semiconductor devic e wafer having respective structured copper strain buffers diffusion bonded to one or each of the two major surfaces thereof.
• the support plate attached to the s emiconductor device wafer as needed in many conventional semiconductor device structures is not required and respective structured copper strain buffers are thermo-compression diffusion bonded "directly" to one or each of the two major surfaces of the wafer.
• a improved press for diffusion bonding metal surfaces of an ass embly together includes first and second metallic plate means, each having a predetermined thermal coefficient of expansion.
• the second plate means are oriented parallel to the first plate means and spaced apart therefrom so as to allow acceptance of the as sembly between the first and second plate means .
• a metallic support connects the first plate means to the second plate means .
• the support is selected to exhibit thermal expansion smaller than the total thermal expansion in thickness of the first and s econd plate means when the press is heated to an elevated temperature.
• the first and second metallic plate means each include first and second raised portions extending therefrom, respectively, and facing each other .
• Each rais ed portion includes a flat surface having an identical geometric pattern, respectively, the patterns being in axial and rotational alignment with each other such that equal and opposite pres sures are extended on the to-be-bonded metallic surfaces of the assembly situated between the first and second rais ed portions thereby squeezing the metallic surfaces together at high pressure when the press is heated to an elevated temperature.
• a method for thermo-compres sion diffusion bonding a structured copper strain buffer to a substrateles s s emiconductor device wafer having two major oppos ed surfaces is provided.
• a substrateless semiconductor device wafer is defined to be one which has no support plate attached thereto. Each of the major oppos ed surfaces is smoothed.
• the strain buffer to be bonded to the wafer includes a bundle of substantially parallel, close-packed strands of copper of substantially equal length.
• One common end of thes e strands is thermo-compression diffusion bonded to a metallic sheet, while the common end of the copper strands opposite the metallic sheet is to be thermo-compression diffusion bonded to the metal-coated major surface of the semiconductor device wafer.
• the uncoated major surface of the semiconductor devic e is positioned in abutment with a flat referenc e surface of a rigid member while the common end of the copper strands opposite the metallic sheet of the strain buffer is positioned in abutment with the metalcoated surface of the s emiconductor device wafer.
• the strain buffer wafer-rigid member as s embly thus formed is surrounded with an inert atmospher e and is squeezed together at high pres sure.
• the assembly is heated at a temperature within the range of 300oC. to 400 oC. while the same is squeezed together. Because the rigid member essentially does not yield under pressure, a thermocompres sion diffusion bond between the structur ed copper strain buffer and the s emiconductor device wafer is produced without wafer fracture.
• a method for thermo-compression diffusion bonding first and second structured copper strain buffers to a substrateless semiconductor device wafer having first and second oppos ed surfac es of unequal lateral extents and a beveled outer edge surface.
• the beveled surface is cleaned to remove contaminants ther efrom and then coated with a pas sivation material.
• the semiconductor devic e wafer with the above-described metallic layers and metallizations dispos ed thereon is s andwiched between the first and s econd structur ed copper strain buffers .
• Each of these strain buffers is of lateral extent equal to or les s or greater than the lateral extent of the respective s emiconductor devic e wafer surfac e in contact therewith such that the beveled edge surfac e either remains uncovered or covered by either of the structured copper strain buffers .
• the strain buffer is positioned so as to overhand the entire outer edge surfac e of the wafer.
• Each structured copper strain buffer is positioned such that the common end of the copper strands opposite the metallic sheet thereof faces the semiconductor device wafer .
• the so-positioned semiconductor device wafer structur e and structur ed copper strain buffers are surrounded by an inert atmosphere.
• a loading force is applied to identical, axially aligned portions of the first and second strain buffers , respectively, to squeeze them together at high pressure and, at the same time, the so-positioned s emiconductor device wafer and structured copper strain buffers are heated at a temperature within the range of 300oC. to 400oC .
• Thermocompres sion diffusion bonds are thus formed between the two major, opposed, metal-coated surfaces of a substrateless , beveled semiconductor device wafer and respective first and second structured copper strain buffers, without wafer fracture.
• first and s econd structured copper strain buffers are thermo-compres sion diffusion bonded to each of the two metallized major surfaces of a semiconductor device wafer.
• the outer edge surface of the semiconductor device wafer is beveled preferably prior to s andwiching the semiconductor device wafer between the first and second structured copper strain buffers.
• the separate metallic layers and metallizations are applied to each of the oppos ed surfaces of the s emiconductor devic e wafer as previously s et forth, but with the metallic layers and metallizations having a lateral extent sufficiently small to avoid overlapping the beveled surface.
• the metallic layer and metallization on the surface of the wafer which is beveled are axially aligned with each other and with the metallic layer and metallization on the opposite surface of the wafer, which likewis e are axially aligned with each other . All metallic layers and metallizations are formed with an equal lateral extent.
• the semiconductor device wafer is then sandwiched between the first and second strain buffers and the s emiconductor devic e wafer and first and second structured copper strain buffers are squeezed together while being heated in an inert atmosphere, as described above.
• the metallic sheet of the first structured copper strain buffer is thereafter cut, preferably with a las er beam to remove the porti on os the first strain buffer not bonded to the semiconductor device wafer.
• the beveled edge surfac e of the wafer is cleaned, typically by sputter etching, and is then pas sivated.
• Thermo-compres sion diffusion bonds are thus formed between the two major oppos ed surfaces of the beveled semiconductor device wafer and respective first and s econd structured copper strain buffers without wafer fracture.
• Figure 1 is a cross-sectional side view of a thermo-compression diffusion bonding press showing materials situated in the press to be bonded together in practicing the invention.
• Figure 2 illustrates the diffusion bonding press of Figure 1 with a layer of compactible material situated between a metallic pressing block and a structured copper strain buffer to avoid the undesirable bonding of the pressing block to the strain buffer in accordance with the invention.
• Figure 3 is a cross- sectional view of a beveled semiconductor device with structured copper strain buffers having a lateral extent greater than the lateral extent of the wafer thermo-compression diffusion bonded to each of the opposed surfaces of the wafer.
• Figure 4 illustrates laser cutting of a portion of a structured copper strain buffer in preparation for passivating the semiconductor device wafer diffusion bonded thereto.
• Figure 5 is a top view of the bonded semiconductor device waferstrain buffer structure shown in Figure 4 after removal of the portions of the strain buffer cut away by the laser.
• Figure 6 is a cross-sectional side view of the wafer- strain buffer structure shown in Figure 5, after passivation.
• Figure 7 is a cross-sectional view of a beveled semiconductor device wafer with structured copper strain buffers having a lateral extent greater than the lateral extent of the wafer thermo-compression diffusion bonded to each of the metal-coated, opposed surfaces of the wafer.
• Figure 8 is a cross-sectional side view of an improved thermocompression diffusion bonding press showing materials to be bonded together situated therein.
• FIG 9 is a cross-sectional side view of the thermo-compressi diffusion bonding press of Figure 8 showing materials of alternative configuration situated therein to be bonded together.
• Figure 1 shows a diffusion bonding press 10 which may be used in thermo-compression diffusion bonding a structured copper strain buffer 12 directly to a substrateless semiconductor device wafer 16.
• Press 10 is comprised of an upper metallic plate 22 oriented parallel to a lower metallic plate 24 with a space provided therebetween.
• a metallic pressing block 26 is positioned at the center of the side of upper plate 22 facing lower plate 24.
• Metallic bolts 28 and 30 pass through respective holes in upper plate 22 and lower plate 24 and are threaded into lower plate 24 to connect the two plates together as illustrated in Figure 1.
• Metallic bolts 28 and 30 are comprised of a steel other than stainless steel, while upper plate 22, lower plate 24 and metallic pressing block 26 are comprised of stainless steel.
• Metallic pressing block 26 may alternatively be comprised of Dural, an aluminum alloy, or other metals having a coefficient of thermal expansion greater than that of steel.
• a disk of rigid material 20 having a flat reference surface 20a is situated within press 10 on lower plate 24.
• Member 20 is comprised of a rigid material such as quartz, for example, which will withstand high pressures of 20, 000 through 50, 000 psi without measurably yielding.
• Each of the opposed major surfaces of semiconductor device wafer 16 is smoothened to removed surface damage therefrom. Such surface damage would otherwise cause nonuniform distribution of pressures within wafer 16 and, thus, wafer breakage when the wafer is subjected to the high pressure employed in the thermo-compression diffusion bonding process of the invention.
• This step of smoothing may be accomplished, for example, by polishing or etching each of the opposed major surfaces.
• first metallic layer 21 comprised of one of such metals as titanium , chromium and nickel, coated ther eon.
• a s econd metallic layer 23 compris ed of one of such metals as copper, silver and gold is applied over the metallic layer 21.
• Metallic layers 21 and 23 may be applied to wafer 16 by sputtering or evaporation, for example. Structures to be diffusion bonded together are situated upon surface 20a of member 20. Specifically, wafer 16 is situated on surfac e 20a with the uncoated surface of wafer 16 positioned facing surface 20
• Structured copper strain buffer 12 is positioned in abutment with the exposed surface of metallic layer 23 on wafer 16.
• Strain buffer 12 comprises a bundle of substantially parallel, close-packed strands of copper 40 of substantially equal length, one common end thereof being thermo-compression diffusion bonded into a metallic sheet 14, typically compris ed of copper .
• the remaining common end of strands 40 is situated in abutment with metallic layer 23 on wafer 16.
• a conventional press (not shown) is us ed to squeeze upper plate 22 and lower plate 24 together and while such pressure is applied to thes e plates, bolts 28 and 30 are tightened.
• thermo-compres sion diffusion bond between structured copper strain buffer 12 and semiconductor device wafer 16 is actually formed when press 10 containing rigid member 20, semiconductor device wafer 16 with metallic layers 21 and 23 disposed thereon and structured copper strain buffer 12, positioned as described above and as shown in Figure 1, are placed in an inert atmosphere and heated at a temperature within the range of 300oC. to 400oC , typically 325 oC , for approximately 15 minutes to 5 hours .
• press 10 is heated in this manner, upper plate 22, lower plate 24, and metallic pressing block 26 expand to a greater total extent than do metallic bolts 28 and 30.
• thermocompres sion diffusion bonding is actually formed between the commond end of copper strands 40 opposite metallic sheet 14 and metallic layer 23 on wafer 16.
• thermo-compression diffusion bonding s emiconductor device wafer 16 is subjected to high pressure, specifically, 20, 000 psi to 50, 000 psi. If this force is not purely compressive, that is , if s emiconductor devic e wafer 16 is subjected to bowing or tensile forc es, wafer 16 will likely fracture, resulting in a damaged s emiconductor device. It is thus extremely important that uniform high pres sure be applied over the entire wafer 16.
• the surfaces of the members to be bonded together must be flat and par allel to each other and to the oppos ed, facing surfaces of lower plate 24 and metallic pres sing block 26.
• situating rigid member 20 on lower plate 24 provides an ess entially non-yielding, flat reference surface for s emiconductor device wafer 16 placed thereon.
• Employing rigid member 20 in this manner as sures that semiconductor device wafer 16 is subj ected to substantially pure compres sive forces during thermo-compres sion diffusion bonding, with negligible tensile forc es being exerted on the wafer, enabling the diffusion bond to be achieved without fracture of the substrateless wafer .
• the resulting bonded semiconductor device wafer- strain buffer-heat sink assembly includes no substrate or support plate. Heat is conducted more efficiently away from the wafer to the heat sink than if the ass embly were to include such substrate.
• Figure 2 is identical to Figure 1 with like numerals signifying like components , except forthe plac ement of a layer of nonreactive compactible material 32 between pressing block 26 and strain buffer 12.
• layer 32 is so positioned prior to application of the loading force discus sed in the method s et forth above.
• Such layer of compactible material tends to compress under application of the loading force, filling in any irregularities in the facing surface of metallic sheet 14 and resulting in a more uniform distribution of the loading force on strain buffer 12
• the thermo-compression diffusion bond between strain buffer 12 and wafer 16 is thus made substantially void free.
• Layer 32 additionally prevents strain buffer 12 from undesirably adhering to metallic pressing block 26 during thermo-compres sion diffusion bonding.
• Layer 32 may be compris ed of glas s wood, or Glas s Fiber Filter paper available from Fisher Scientific Company, Clifton, New Jersey, or other similarly compactible materials .
• Figure 3 shows a diffusion bonding press 10 suitable for thermo- compression diffusion bonding a first structured copper strain buffer 12 and a second structur ed copper strain buffer 74, respectively, to the oppos ed major surfaces 16a and 16b of substrateless semiconductor device wafer 16.
• the outer edge surface 16c of s emiconductor device wafer 16 is preferably beveled, as shown in Figure 3, although the invention encompasses wafers both with and without a beveled outer edge surface.
• thermo-compression diffusion bonds between strain buffers 12 and 74 and wafer 16 surfaces 16a and 16b ar e smoothened to remove surfac e damage therefrom. Such surface damage would otherwise cause nonuniform distribution of pres sures within wafer 16 and thus wafer breakage when wafer 16 is subjected to the high pressures employed in the thermo-compression diffusion bonding process of the invention.
• This step of smoothing may be accomplished, for example, by polishing or etching surfac es 16a and 16b.
• Metallic layers 31 and 37 are applied to wafer surfaces 16a and 16b, respectively.
• Each of metallic layers 31 and 37 is comprised of one of such metals as titanium, chromium and nickel.
• Metallizations 34 and 36 are respectively applied over metallic layers 31 and 37.
• Each of metallizations 34 and 36 are respectively comprised of one of such metals as copper, gold and silver .
• Thes e metallic layers and metallizations may be applied to wafer 16 by sputtering or evaporation, for example.
• Structured copper strain buffer 12 is compris ed of a bundle of substantially parallel, closely packed strands of copper 40 of substantially equal length with one common end thereof thermocompression diffusion bonded to a metallic sheet 42, typically comprised of copper.
• the opposite common end of copper strands 40 is positioned in abutment with metallization 34.
• Structured copper strain buffer 14 is es s entially identical to structured copper strain buffer 12 and is comprised of copper strands 50 and metallic sheet 52.
• the common end of copper strands 50 opposite metallic sheet 52 is positioned in abutment with metallization 36.
• a layer 54 of nonreactive compactible material is situated in abutment with metallic sheet 42 of structured copper strain buffer 12.
• Layer 54 may be comprised of glas s wood or Glas s Fiber Filter paper available from Fisher Scientific Company, Clifton, New Jersey, or other similarly compactible material.
• a layer of compactible material 56 preferably comprised of the same material as layer 54 is positioned in abutment with metallic sheet 52 of structured copper strain buffer 14.
• the combined structure formed by s emiconductor device wafer 16, structured copper strain buffers 12 and 74, and metallic layers 31 and 37 and metallizations 34 and 36 dispos ed therebetween and compactible layers 54 and 56 is positioned in pres s 10 between pr essing block 26 and lower plate 24.
• a conventional press (not shown) is us ed to squeeze upper plate 22 and lower plate 24 together and while such pressure is applied to thes e plates, bolts 28 and 30 are tightened.
• the thermo-compression diffusion bonds between structured copper strain buffer 12 and wafer 16, and between structured copper strain buffer 74 and wafer 16 are actually formed when pres s 10 containing the above-described combined structure, illustrated in Figure 1, is surrounded by an inert atmosphere and heated at a temperature within the range of 300oC. to 400oC , typically 325o C , for approximately 15 minutes to 5 hours .
• press 10 is heated in this manner, upper plate 22, lower plate 24 and metallic pressing blo ck 36 expand to a greater total extent than do metallic bolts 28 and 30.
• a forc e is exerted between pr essing block 26 and lower plate 24, resulting in the squeezing of structured copper strain buffers 12 and 14 and semiconductor devic e wafer 16 together and the thermocompression diffusion bonding of buffers 12 and 14 to wafer 16.
• the now-formed strain buffer- wafer ass embly 60 is removed from pres s 10 by loos ening bolts 28 and 30.
• thermo-compres sion diffusion bonding of strain buffer 12 to wafer 16 and strain buffer 74 to wafer 16 for simplicity of description, thos e skilled in the art will appreciate that the actual thermo-compression diffusion bonds are formed at the interface between the common end of copper strands 40 and metallization 34, and at the interface between the common end of copper strands 50 and metallization 36.
• thermo-compression diffusion bonding substrateles s semiconductor device wafer 16 is subjected to high pressures, specifically, 20, 000 psi to 50, 000 psi. If this force is not purely compressive, that is, if semiconductor device wafer 16 is subj ected to bowing or tensile forces, wafer 16 will likely fracture, resulting in a damaged s emiconductor device. It is thus extremely important that uniform high pres sur e be applied over the entir e wafer 16 .
• thermo-compression diffusion bonding Prior methods of thermo-compression diffusion bonding us ed a support plate attached to the s emiconductor device wafer to enable the wafer to withstand some degr ee of bowing forces and nonuniform pressure without fracture.
• a support plate attached to the s emiconductor device wafer to enable the wafer to withstand some degr ee of bowing forces and nonuniform pressure without fracture.
• the lateral extent of structured copper strain buffers 12 and 74 is made greater than the lateral extent of wafer 16 such that buffers 12 and 74 overhang wafer 16 around the entirety of its edge surface.
• Layers of compactible material 54 and 56 are positioned as described above to assure that during thermo-compression diffusion bonding, structured copper strain buffer 12 does not adhere undesirably to pressing block 26 and to as sure that structured copper strain buffer 74 similarly does not bond to lower plate 24.
• Use of such layers of compactible material helps as sure the creation of uniform, substantially void-free diffusion bonds . Voids in diffusion bonds may result when a thermo-compres sion diffusion bond between a compliant metallic member (such as a structured copper strain buffer) and another member having some degree of surface irregularity is attempted.
• the layers of compactible material fill in the irregularities in the surfac e of the respective structured copper strain buffers allowing the diffusion bonding press 10 to apply a more evenly distributed pr essure to the members which are to be bonded together.
• Use of layers of compactible material 54 and 56 is preferable but not es sential to practice of the method of the invention.
• wafer 16 is of the nonbeveled variety, no further processing in accordance with the invention is required. However, if wafer 16 includes a beveled outer edge surfac e 16c, as illustrated, it is desirable that surface 16c be cleaned and pas sivated to protect it from external contamination. As shown in Figure 4, beveled edge surface 16c lies rec es s ed under structur ed copper strain buffer 12 and is thus inaccessible for cleaning and pas sivation purpos es .
• pas sivation of beveled surface 16c is achieved in the following manner.
• metallic layers 31 and 37 Prior to sandwiching wafer 16 between structured copper strain buffers 12 and 74, metallic layers 31 and 37, applied to major surfaces 16a and 16b, respectively, of wafer 16, are formed with a lateral extent sufficiently small so as to avoid overlapping beveled surface 16c . That is , the lateral extent of layers 31 and 37 may be equal to or less than the lateral extent of surface 16a.
• Metallizations 34 and 36 are thereafter applied over metallic layers
• thermo-compres sion diffusion bonding process is carried out upon the metallized wafer structure 16, the common end of copper strands 40 opposite metallic sheet 42 of strain buffer 12 becomes thermo-compression diffusion bonded only to the metallized portions of surface 16a. Similarly, the common end of copper strand 50 opposite metallic sheet 52 of strain buffer 74 diffusion bonds only to metallized portions of surface 16b.
• a laser device 62 such as a puls ed las er, typically having a peak pulsed power of 16 KW although not limited thereto, generates a beam of coherent light which is directed along a selected path on metallic sheet 42 of strain buffer wafer assembly 60, fabricated as previously described, so as to form an incision 64 in sheet 42 and thus allow the removal of most of the portion of strain buffer 12 not bonded to wafer metallization 34.
• the portion of structured copper strain buffer 12 outside incision 64 is removed to form wafer-buffer structure 170 shown in Figure 5.
• the remaining portion of strain buffer 12 is designated strain buffer 12 . Beveled edge surface 16c is thus made accessible for cleaning and pas sivation.
• thermo-compres sion diffusion bonding is preferred because it inherently achieves superior thermal conductivity between the joined metallic members .
• a s emiconductor device wafer 16 includes oppos ed major surfaces 16a and 16b and beveled edge surface 16c .
• First and s econd metallic layers 31 and 37 are coated respectively on surfaces 10a and 10b.
• Metallizations 34 and 36 are coated, r espectively, on metallic layers 31 and 37.
• Structured copper strain buffers 12 and 74 are thermocompres sion diffusion bonded respectively to metallizations 34 and 36.
• Structured copper strain buffer 12 includes a bundle of substantially parallel closely packed strands of copper 40, one common end thereof thermo-compression diffusion bonded into a metallic sheet 42.
• Structur ed copper strain buffer 74 is substantially similar to strain buffer 12 and includes copper strands 50 and metallic sheet 52. As pointed out above, structured copper strain buffers 12 and 74 are formed in such a manner as to have a lateral extent greater than that of silicon wafer 16, so as to prevent the silicon wafer 16 from being subjected to bowing forces which cause wafer fracture.
• thermo-compres sion diffusion bonding structured copper strain buffer s to be a substrateles s semiconductor device wafer.
• One embodiment of the invention desirably allows cleaning of the beveled surface via conventional chemical etching and pas sivation prior to diffusion bonding.
• a press apparatus 10 is provided to bond first and second structured copper strain buffers 55 and 65, respectively, to the opposed major surfaces 70a and 70b of substrateless s emiconductor device wafer 70.
• the outer edge 70c of semiconductor devic e wafer 70 is beveled as shown in Figure 8.
• Bonding pres s 10 includes an upper metallic plate 22 oriented parallel to a lower metallic plate 24 with a space provided therebetween.
• Metallic bolts 28 and 30 pass through respective holes in upper plate 22 and lower plate 24 and are thr eaded into lower plate 24 to connect the two plates together as illustrated in Figur e 8.
• a metallic pressing block (or expansion block) 88 is po sitioned at the center of the lower surface of upper plate 22 and attached thereto .
• a similar metallic pr essing block (or expansion block) 90 is positioned at the center of the upper surfac e of lower plate 24 and attached thereto. Pressing blocks 88 and 90 each include rais ed portions 88a and 90a respectively extending therefrom and facing each other .
• Raised portions 88a has a flat surface of a s elected geometric pattern, circular, square, rectangular or various other polygons , for example, which is axially and rotationally aligned with a like flat surface of identical geometric pattern on rais ed portion 90a.
• the flat surfaces of rais ed portions 88a and 90a are parallel to each other.
• Rais ed portions 88a and 90a are held in alignment by a guide member 92 positioned in abutment with pres sing blocks 88 and 90.
• Guide member 92 is conveniently of cylindrical shape having an inner diameter sufficiently large to accommodate the maximum lateral extent of pressing blocks 88 and 90 therein.
• Metallic pressing blocks 88 and 90 are compris ed of a metal having a thermal coefficient of expansion greater than that of metallic bolts 28 and 30.
• pres sing blocks 88 and 90 may be compris ed of such metals as stainless steel, Dural and other aluminum alloys .
• Guide member 92 is comprised of a material having a thermal coefficient of expansion equal to or greater than that of pres sing blocks 88 and 90.
• B eveled surface 70c is then cleaned to remove contaminants therefrom.
• a chemical etch may be used to perform this cleaning since at this juncture the structured copper strain buffers are not yet bonded to wafer 70 and thus there is no opportunity for the etch to chemically attack the structured copper strain buffers.
• sputter etching may be used to clean beveled surface 70c.
• beveled surface 70c is coated with a passivation material 102 such as polyimide siloxane, for example. Pas sivation material 102 may partially extend on to maj or surfaces 70a and 70b without causing the undesirable generation of bowing forces in wafer 16 during subsequent thermo-compression diffusion bonding.
• the wafer-metallic-layer-metallization-passivation ass embly thus formed is sandwiched between structured copper strain buffers
• Structured copper strain buff er 55 is comprised of a bundle of substantially parallel, clos ely packed strands of copper 62 of substantially equal length with one common end thereof being thermo-compression diffusion bonded to a metallic sheet 57. The opposite common end of copper strands 62 is positioned in abutment with metallization 98.
• Structured copper strain buffer 65 is es s ential identical to structured copper buffer 55 and is comprised of copper strands 58 and metallic sheet 59. The common end of copper strands 58 opposite metallic sheet 59 is positioned in abutment with metallization 100.
• Strain buffers 55 and 65 each have a laterial extent equal to or les s than the lateral extent of the r espective wafer 70 surface in contact therewith such that beveled surface 70c remains uncovered by either of the strain buffers . Additionally, the lateral extent of strain buffers 55 and 65 is sufficiently small such that buffer s 55 and 65 do not overlap any passivation material 102 which may be pres ent on wafer surfaces 70a and 70b, respectively. If such overlap were to occur, undesirable bowing forces would likely result.
• a layer 104 of nonreactive, compactible material is situated in abutment with metallic sheet 57 of structured copper strain buffer 55.
• Layer 104 may be comprised of glass wool or Glass Fiber Filter paper available from Fisher Scientific Company, Clifton, New Jersey, or other similarly compactible materials .
• a layer of compactible material 106 compris ed of the same material as layer 104 is positioned in abutment with metallic sheet 59 of structured copper strain buffer 65.
• a conventional pres s (not shown) is us ed to squeeze upper plate 22 and lower plate 24 together and while such pressure is applied to thos e plates , bolts 28 and 30 are tightened.
• thermo-compres sion diffusion bonds between structured copper strain buff er 55 and wafer 70, and between structured copper strain buffer 60 and wafer 70 are actually formed when pres s 10 containing the above-described as sembly, shown in Figur e 8, is surrounded by an inert atmospher e and heated at a temperatur e within the range of 300oC. to 400°C. , typically 325°C , for approximately 15 minutes to 5 hours .
• upper plate 22, lower plate 24 and metallic pres sing blocks 88 and 90 expand to a greater total extent than do metallic bolts 84 and 86.
• thermo-compression diffusion bonding of buffers 55 and 65 to wafer 70 The respective thermo-compression diffusion bonds are formed between the portions of wafer 70 and buffers 55 and 65, which experience compres sive stres s .
• Guide members 92 expands with temperature to an equal or greater total extent than do metallic pressing blocks 88 and 90 such that guide 92 does not become thermocompression diffusion bonded thereto.
• thermo-compression diffusion bonding of strain buffers 55 and 65 to wafer 70 Although reference is made herein to the thermo-compression diffusion bonding of strain buffers 55 and 65 to wafer 70 for simplicity of description, those skilled in the art will appreciate that the actual thermo-compression diffusion bonds are formed at the interface between the common end of copper strands 62 and metallization 98, and at the interface between the common end of copper strands 58 and metallization 100.
• substrateless semiconductor device wafer 70 is subjected to high pressures, specifically, 20, 000 psi to 50, 000 psi. If this force were not purely compressive, that is , if the s emiconductor device wafer 70 is subject to bowing forces, especially in the region of beveled surface 70c, wafer 70 would likely fracture, resulting in; a damaged, unusable semiconductor device. It is thus extremely important that uniform, high pres sure be applied over wafer 70.
• Prior bonding methods utilized a support plate attached to the semiconductor device wafer to enable the wafer to withstand some degree of bowing forces and nonuniform pressure without fracturing.
• No such support plate structure is necessary in the present invention, however, since essentially equal pressures are applied to essentially identical selected regions of wafer surfaces 70a and 70b, respectively which are precisely aligned both axially and rotationally.
• Such pressures are applied via rais ed portions 88a and 90a through the intermediate layers of compactible material 104 and 106, strain buffers 55 and 65, metallizations 98 and 100, and metallic layers 94 and 96. Because wafer 70 thus experiences purely compressive pressures, it is not subjected to bowing forces and fracturing that may result therefrom.
• Layers of compactible material 104 and 106 are positioned as described above to assure that during thermo-compression diffusion bonding, structured copper strain buffers 55 and 65 do not undesirably diffusion bond to rais ed surfac es 88a and 90a, respectively.
• Use of such layers of compactible material facilitates the creation of uniform, substantially void-fr ee diffusion bonds which can otherwise occur when the bonding together of irregular surfac es is attempted.
• the layers of compactible material fill in the irregularities in the surfaces allowing rais ed surfaces 88a and 90a to apply a more evenly distributed pressur e to strain buffers 50 and 60 and hence to each of the individual members which are to be bonded together .
• Us e of layers of compactible material 104 and 106 is preferable but not ess ential to practice of the invention.
• an "oversized" st ructured copper strain buffer 160 that is, a strain buffer having a lateral extent equal to or greater than the larger major surface of substrateles s wafer 70 having a beveled edge surface 70c , is thermo-compression diffusion bonded to surface 70b of wafer 70, and a structured copper strain buffer 55 having a lateral extent sufficiently small so as to overlap beveled surfac e 70c of wafer 70 is thermo-compres sion diffusion bonded to surface 70a of substrateless wafer 70.
• FIG. 9 shows press 10 with materials situated ther ein for bonding. Pres s 10 of Figure 9 is similar to that of Figure 8, with like numerals indicating like elements .
• the method for creating such thermo-compres sion diffusion bonds between wafer 70 and each of strain buffer 55 and "oversized" strain buffer 160 is identical to that described in conjunction with Figure 8, except for the following differ enc es . "Oversized" strain buffer 160 is employed instead of strain buffer 65 shown in Figure 8.
• beveled surface 70c is cleaned and pas sivated only after the desired thermo-compres sion diffusion bonds have been formed, preventing passivation material intended for beveled surface 70c from coating portions of major surfaces 70a and 70b near beveled surfac e 70c before bonding and thereby creating an irregularity in these major surfac es which might result in generation of some unacceptable bowing force during thermo- compres sion diffusion bonding and consequential wafer fracture.
• beveled surface 70c is cleaned by such techniques as sputter etching, for example, which is preferable to conventional hot chemical etch cleaning because such an etch likely would chemically attack the structured copper strain buffers bonded to semiconductor devic e wafer 70.
• a passivation material 202 such a polyimide siloxane, for example.
• heat sinks are respectively attached to metallic sheets 57 and 59 of strain buffers55 and 65. This is accomplished by thermo-compres sion diffusion bonding during the course of the bonding of strain buffers 55 and 65 to wafer 70, or at a later time as is convenient. Alternatively, heat sink attachment may be accomplished by other suitable means of joining metals together, such as soldering, for example. Thermocompression diffusion bonding, however, is preferred because it inherently results in superior thermal conductivity between the metallic members which it joins together, allowing more efficient removal of heat from the s emiconductor device wafer .

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• 1980
  • 1980-03-05 JP JP55500713A patent/JPS6142430B2/ja not_active Expired
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  • 1980-03-05 DE DE8080900618T patent/DE3070263D1/de not_active Expired
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