US20020022362A1 - Buried ground plane for high performance system modules - Google Patents
Buried ground plane for high performance system modules Download PDFInfo
- Publication number
- US20020022362A1 US20020022362A1 US09/199,442 US19944298A US2002022362A1 US 20020022362 A1 US20020022362 A1 US 20020022362A1 US 19944298 A US19944298 A US 19944298A US 2002022362 A1 US2002022362 A1 US 2002022362A1
- Authority
- US
- United States
- Prior art keywords
- substrate
- conductor
- conductive metal
- pores
- system module
- 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.)
- Granted
Links
- 239000000758 substrate Substances 0.000 claims abstract description 155
- 238000000034 method Methods 0.000 claims abstract description 100
- 239000004020 conductor Substances 0.000 claims abstract description 74
- 229910052751 metal Inorganic materials 0.000 claims abstract description 62
- 239000002184 metal Substances 0.000 claims abstract description 62
- 239000011148 porous material Substances 0.000 claims abstract description 44
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 37
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 37
- 239000010703 silicon Substances 0.000 claims abstract description 37
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 claims abstract description 22
- 229910052721 tungsten Inorganic materials 0.000 claims abstract description 22
- 239000010937 tungsten Substances 0.000 claims abstract description 22
- 239000000126 substance Substances 0.000 claims abstract description 15
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims abstract description 14
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 14
- 239000011733 molybdenum Substances 0.000 claims abstract description 14
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims abstract description 13
- 229910052802 copper Inorganic materials 0.000 claims abstract description 13
- 239000010949 copper Substances 0.000 claims abstract description 13
- 238000002048 anodisation reaction Methods 0.000 claims abstract description 9
- 239000010410 layer Substances 0.000 claims description 46
- 238000000151 deposition Methods 0.000 claims description 37
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 32
- 238000009413 insulation Methods 0.000 claims description 24
- 239000003870 refractory metal Substances 0.000 claims description 24
- 229910052581 Si3N4 Inorganic materials 0.000 claims description 18
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 claims description 18
- 238000000137 annealing Methods 0.000 claims description 17
- 229920006254 polymer film Polymers 0.000 claims description 16
- 239000000377 silicon dioxide Substances 0.000 claims description 15
- 239000011241 protective layer Substances 0.000 claims description 14
- 235000012239 silicon dioxide Nutrition 0.000 claims description 12
- 239000004642 Polyimide Substances 0.000 claims description 10
- 229920001721 polyimide Polymers 0.000 claims description 10
- 229910021332 silicide Inorganic materials 0.000 claims description 9
- 238000005229 chemical vapour deposition Methods 0.000 claims description 8
- 239000004065 semiconductor Substances 0.000 claims description 8
- FVBUAEGBCNSCDD-UHFFFAOYSA-N silicide(4-) Chemical compound [Si-4] FVBUAEGBCNSCDD-UHFFFAOYSA-N 0.000 claims description 8
- 238000007517 polishing process Methods 0.000 claims description 6
- 238000007743 anodising Methods 0.000 claims 3
- 238000005137 deposition process Methods 0.000 abstract 1
- 238000012545 processing Methods 0.000 description 10
- 230000008021 deposition Effects 0.000 description 5
- 238000005516 engineering process Methods 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 4
- 150000004767 nitrides Chemical class 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 238000001459 lithography Methods 0.000 description 3
- 238000005498 polishing Methods 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 239000011810 insulating material Substances 0.000 description 2
- 230000010354 integration Effects 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000000059 patterning Methods 0.000 description 2
- 229910052814 silicon oxide Inorganic materials 0.000 description 2
- 206010037660 Pyrexia Diseases 0.000 description 1
- BLRPTPMANUNPDV-UHFFFAOYSA-N Silane Chemical compound [SiH4] BLRPTPMANUNPDV-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 238000007792 addition Methods 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 238000012217 deletion Methods 0.000 description 1
- 230000037430 deletion Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000006870 function Effects 0.000 description 1
- 239000007943 implant Substances 0.000 description 1
- 239000012212 insulator Substances 0.000 description 1
- 238000005468 ion implantation Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910021426 porous silicon Inorganic materials 0.000 description 1
- 238000007639 printing Methods 0.000 description 1
- 229910052594 sapphire Inorganic materials 0.000 description 1
- 239000010980 sapphire Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
- WQJQOUPTWCFRMM-UHFFFAOYSA-N tungsten disilicide Chemical compound [Si]#[W]#[Si] WQJQOUPTWCFRMM-UHFFFAOYSA-N 0.000 description 1
- 229910021342 tungsten silicide Inorganic materials 0.000 description 1
Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L23/00—Details of semiconductor or other solid state devices
- H01L23/58—Structural electrical arrangements for semiconductor devices not otherwise provided for, e.g. in combination with batteries
- H01L23/64—Impedance arrangements
- H01L23/66—High-frequency adaptations
-
- 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
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. 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
- H01L21/4803—Insulating or insulated parts, e.g. mountings, containers, diamond heatsinks
-
- 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
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. 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
- H01L21/4846—Leads on or in insulating or insulated substrates, e.g. metallisation
-
- 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
- H01L2924/30—Technical effects
- H01L2924/301—Electrical effects
- H01L2924/3011—Impedance
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S438/00—Semiconductor device manufacturing: process
- Y10S438/96—Porous semiconductor
Definitions
- the present invention relates generally to semiconductor circuits, and more particularly to substrates having buried ground planes and their method of processing.
- a system module may consist of two chips, i.e., a logic chip and a memory chip, with one stacked on the other in a structure called Chip-on-Chip (COC) using a micro bump bonding (MBB) technology.
- COC Chip-on-Chip
- MBB micro bump bonding
- the multiple chips mounted on the single substrate in a system module typically include different circuits, i.e., some analog circuits and some digital circuits. This requires a low impedance ground in the system module to suppress digital noise that may appear in the analog circuits of these mixed mode circuits.
- Digital noise is the side effect of the switching of the logic circuits.
- High-speed synchronous digital integrated circuits require large switching currents which can induce noise on the power distribution networks and ground busses due to the finite resistance and inductance in these circuits.
- the noise may consist of voltage spikes appearing at the power supply terminals of the chip with the switching activity. Power supply noise can have a significant effect due to simultaneous switching noise in CMOS integrated circuits. These problems are more severe in mixed-mode circuits and require careful design of the power distribution systems.
- a silicon substrate with a low impedance built-in ground plane is necessary for the system modules to suppress noise. It is also desirable for a built-in ground plane to be planar with the surface of the substrate to maintain a flat surface on the substrate upon which various chips, active circuits, and passive components (such as decoupling capacitors and termination resistors) can be subsequently mounted.
- a conventional method for forming buried conductors in a substrate is the use of heavy ion implantation of conducting atoms into the substrate to form the conductor. This approach, however, is not economically viable due to the required high-current, high-energy implanters, and may also cause damage to the overlying substrate.
- Another conventional method for fabricating a multilevel interconnect is to implant silicon into silicon oxide followed by a selective deposition of tungsten to build a multi-layer structure with low electrical resistivity.
- This method is suitable only for fabricating a buried conductor in a silicon oxide, and not in a silicon substrate as is required in a system module.
- the present invention provides a simple and low-cost scheme for producing a buried ground plane in a silicon substrate.
- the desired conductors are patterned by ordinary lithography on the surface of the silicon substrate in a mesh pattern to leave room for other chips and components to be mounted.
- a porous structure is produced only in the patterned conductors by depositing silicon nitride windows on the silicon and subjecting the wafer to a chemical anodization process. After the formation of the pores, the pores are then filled with a conductive metal by the use of a selective deposition technique. The filled pores may be subjected to a high-temperature annealing process to convert the deposited conductive metal to a metal silicide.
- FIG. 1 illustrates a cross-sectional view of a portion of a silicon substrate with buried ground planes
- FIG. 2 illustrates a top view of a portion of the silicon substrate of FIG. 1 with buried ground planes
- FIGS. 3A, 3B and 3 C illustrate a cross-sectional view of the wafer of FIG. 2 during intermediate processes in accordance with the method of the present invention
- FIG. 4 illustrates a cross-sectional view of a processed wafer with buried ground planes according to a first embodiment of the present invention
- FIG. 5 illustrates a cross-sectional view of a processed wafer according to a second embodiment of the present invention
- FIGS. 6A and 6B illustrate in flow chart form the steps for forming a buried ground plane in accordance with a first and second method of the present invention.
- FIG. 7 illustrates in system module in accordance with the present invention.
- FIGS. 1 - 7 The present invention will be described as set forth in the preferred embodiment illustrated in FIGS. 1 - 7 . Other embodiments may be utilized and structural or logical changes may be made without departing from the spirit or scope of the present invention.
- wafer and “substrate” are used interchangeably and are to be understood as including silicon-on-insulator (SOI) or silicon-on-sapphire (SOS) technology, doped and undoped semiconductors, epitaxial layers of silicon supported by a base semiconductor foundation, and other semiconductor structures.
- SOI silicon-on-insulator
- SOS silicon-on-sapphire
- FIG. 1 A cross-sectional diagram of a portion of a wafer 10 having buried ground planes is illustrated generally in FIG. 1.
- the term buried as used herein refers both to covered conductors, i.e., under the surface and concealed from view, and to conductors that are formed in the substrate whose top surface is planar with the surface of the substrate.
- Wafer 10 consists of a first level top conductor 12 and a first level bottom conductor 14 .
- a silicon interposer 16 is provided between the conductors 12 , 14 .
- Via holes 20 , 22 are provided through the wafer 10 to provide for interconnection between the top and bottom surfaces of wafer 10 .
- a layer 26 of insulating material such as silicon dioxide (SiO 2 ) may be provided between top conductor 12 and silicon interposer 16 .
- a layer of insulating material 28 such as silicon dioxide (SiO 2 ) may be provided between bottom conductor 14 and silicon interposer 16 .
- Buried ground planes 30 are provided within the silicon interposer 16 . The buried ground planes 30 provide a low-impedance ground connection suitable for suppressing noise produced by digital circuits that may be mounted on silicon interposer 16 .
- FIG. 2 illustrates a top view of a portion of the silicon substrate 10 of FIG. 1 across the line a-a′. Space 52 is left between conductors 30 for mounting or integrating chips and/or components. Ground planes 30 may be formed in a mesh pattern to allow for areas such as space 52 .
- the processes for forming buried ground plane conductors in a silicon substrate in accordance with the present invention is as follows.
- the pattern for the desired conductors, such as conductors 30 of FIG. 2 is printed on the surface of silicon substrate 16 by conventional lithography or any other method for printing a pattern on the surface of substrate 16 as is known in the art.
- Space 52 may be left between conductors 30 for other chips and components to be mounted.
- a protective layer 72 such as for example silicon nitride, is deposited to form windows on the surface of the silicon substrate 16 in which only the printed pattern areas for conductors 30 are left exposed.
- FIG. 3A illustrates a cross-sectional diagram of silicon substrate 16 along line b-b′ in FIG. 2 after the deposition of the silicon nitride windows. The deposition of a layer 72 of silicon nitride covers the surface of substrate 16 , except for the areas where the pattern for conductors 30 has been printed. The preferable thickness for the layer 72 of silicon nitride is approximately 100 nm.
- the substrate 16 is then subjected to a chemical anodization process, as is well known in the art, to form a porous layer in the areas not covered with the layer 72 of silicon nitirde, i.e., the areas where the pattern for conductors 30 has been printed.
- Porous silicon may be formed by the anodization of silicon in aqueous solutions of hydroflouric acid. Pores are etched into the silicon during the anodization process. The resulting structure is illustrated in FIG. 3B.
- the areas of silicon substrate 16 which have been printed with the pattern for conductors 30 contain a porous layer 74 in substrate 16 created by the anodization process. Those portions of the substrate 16 covered with layer 72 of silicon nitride do not have a porous layer. It is well known that under appropriate anodic conditions, silicon can be converted into a highly porous material.
- the porosity may be controlled in the 30%-85% range, i.e., the pores in the silicon can comprise approximately 30 to 85% of the total volume within the silicon substrate 16 .
- a porosity of 50% indicates a material in which half of its volume is comprised of pores within the material.
- a conductor 30 is formed by filling the pores with a conductive metal 76 . Since the conductors 30 usually must be able to withstand subsequent high temperature processing, it is preferable to use refractory metals to form the conductors, such as tungsten (W) or molybdenum (Mo) or their silicides. Refractory metals are difficult to pattern by chemical mechanical polishing or standard photolithographic techniques since they are chemically inert. As such, it is desirable to have a self-aligned process that does not require any patterning of the metal.
- refractory metals such as tungsten (W) or molybdenum (Mo) or their silicides. Refractory metals are difficult to pattern by chemical mechanical polishing or standard photolithographic techniques since they are chemically inert. As such, it is desirable to have a self-aligned process that does not require any patterning of the metal.
- tungsten used, the chemical vapor deposition (CVD) may be based on tungsten hexaflouride (WF 6 ).
- WF 6 tungsten hexaflouride
- the chemical-vapor-deposited tungsten process using either WF 6 /H 2 or WF 6 /SiH 4 chemistry is well known in the art.
- the tungsten hexaflouride will react with the areas of the exposed substrate 16 , but not with the areas of substrate 16 covered with layer 72 of silicon nitride.
- FIG. 3C illustrates the silicon substrate 16 after the conductive metal 76 , such as tungsten or molybdenum, has been deposited as described above.
- the chemical vapor deposition of the metal fills in the pores in the areas where the conductors 30 have been patterned, but does not react with the layer 72 of silicon nitride.
- copper may be used as the conductive metal for applications which will not require a subsequent high processing temperature.
- the copper may be deposited into the pores of the areas where conductors 30 have been patterned by a chemical vapor deposition technique similar to that as described above with respect to the chemical vapor deposition of tungsten or molybdenum.
- the excess metal and nitride windows may be removed by a chemical mechanical polishing process as is known in the art.
- an insulation layer 80 formed of silicon dioxide (SiO 2 ), or alternatively, a high-temperature polymer film with a low dielectric constant, such as for example polyimide, may be deposited.
- the substrate 16 can be further processed to fabricate the conductors 30 with a refractory metal silicide. This may be preferable for applications in which a very high subsequent processing temperature will be required.
- the substrate 16 may be subjected to a high temperature annealing to convert the metal in the pores to a silicide.
- Preferable parameters for this annealing process for tungsten are a temperature greater than approximately 900° C. for up to 30 minutes. This annealing step may be combined with other processes at a later stage if desired.
- the resulting tungsten silicide has a typical resistivity of 18-20 micro-cm-cm, and can be subjected to subsequent high temperature processing. As illustrated in FIG. 5, the nitride window and excess metal in the channel area may be removed by chemical mechanical polishing to provide a flat and smooth surface for subsequent processing.
- An insulation layer (not shown), formed of silicon dioxide or a hightemperature polymer film such as polyimide, may be deposited over the surface of substrate 16 .
- FIGS. 6A and 6B A first and second method of processing buried ground planes in accordance with the present invention is illustrated in flow chart form in FIGS. 6A and 6B. Like steps are referred to by like numerals in each method.
- the pattern for conductors 30 is printed on the surface of the silicon wafer 16 by conventional lithography or any other method as is known in the art.
- the pattern for conductors 30 may be in a mesh pattern as illustrated in FIG. 2 to allow sufficient space between conductors 30 for other chips and components to be mounted.
- step 620 a layer of silicon nitride, preferably 100 nm thick, is deposited on the surface of the substrate 16 to form silicon nitride windows.
- the layer of silicon nitride does not cover the areas where the pattern for conductors 30 has been printed.
- step 630 the wafer is subjected to a chemical anodization process, as is known in the art, to produce a porous layer in the substrate 16 in the areas where the pattern for conductors 30 has been printed.
- a conductor is formed by depositing a conductive metal into the pores of the porous layer produced in the substrate.
- a conductive metal such as tungsten (W) or molybdenum (Mo) are preferable for applications in which the substrate 16 must be able to withstand subsequent high temperature processing.
- the metal may be deposited using a selective deposition technique as is known in the art.
- copper may be used as the conducting metal.
- the copper may be deposited by a chemical vapor deposition as is known in the art.
- step 650 the excess metal and nitride windows may be removed utilizing a chemical mechanical polishing process as is known in the art or any other method.
- step 660 an insulation layer 80 , formed of silicon dioxide, or alternatively a high-temperature polymer film with a low dielectric constant, such as polyimide, may be deposited on the surface of the substrate 16 .
- FIG. 6B A second method for producing a buried ground plane in accordance with the present invention is illustrated in FIG. 6B. Steps 610 , 620 , and 630 are identical to those of FIG. 6A and the description will not be repeated here.
- the conductor is created by depositing a refractory metal into the pores in step 740 using a selective deposition technique as is known in the art.
- the substrate 16 is subjected to a high temperature annealing to convert the metal in the pores to a silicide.
- Preferable parameters for this annealing process for tungsten are a temperature greater than approximately 900° C. for up to 30 minutes.
- step 760 the nitride window and excess metal in the channel area may be removed by chemical mechanical polishing to provide a flat and smooth surface for subsequent processing.
- step 770 an insulation layer, formed of silicon dioxide, or alternatively a high-temperature polymer film with a low dielectric constant, such as polyimide, may be deposited on the surface of the substrate 16 .
- a buried ground plane can be formed in a silicon substrate simply and inexpensively, without damaging the surrounding environment within the substrate.
- FIG. 7 illustrates a portion of a system module having buried ground planes constructed in accordance with the present invention.
- a high performance system module may be provided with a silicon interposer, such as substrate 102 , onto which semiconductor chips or active or passive components can be easily mounted.
- a first chip 104 may be stacked on a second chip 100 using MBB technology as is known in the art to result in a chip-on-chip module.
- the resulting chip-on-chip module structure may be mounted onto substrate 102 along with additional active or passive components.
- Substrate 102 may have a plurality of such chip-on-chip module structures and components mounted on its surface.
- Each of the system modules may consist of at least two chips, some of which may be analog circuits and others digital circuits.
- Substrate 102 in accordance with the present invention, may be provided with buried low impedance ground conductors 106 to suppress digital noise in the analog circuits of the modules.
Abstract
Description
- 1. Field of the Invention
- The present invention relates generally to semiconductor circuits, and more particularly to substrates having buried ground planes and their method of processing.
- 2. Description of the Related Art
- As improved technology is developed, the size of semiconductor components, and correspondingly the size of end-product equipment in which they are used, continues to decrease. This has led to the concept of a “system on a chip.” This concept of a “system on a chip” has been around since the very large scale integration (VLSI) era. As integrated circuit technology enters the ultra large scale integration (ULSI) era, the desire for a “system on a chip” is increasing.
- The concept of a system on a chip refers ideally to a computing system in which all the necessary integrated circuits are fabricated on a single wafer or substrate, as compared with today's method of fabricating many chips of different functions, i.e., logic and memory, and connecting them to assemble a system. There are problems, however, with the implementation of a truly high performance system on a chip because of vastly different fabrication processes and different manufacturing yields for the logic and memory circuits. To overcome some of these problems, a “system module” has been developed. A system module may consist of two chips, i.e., a logic chip and a memory chip, with one stacked on the other in a structure called Chip-on-Chip (COC) using a micro bump bonding (MBB) technology. The resulting dual-chip structure is mounted on a silicon substrate. Additional components and chips may also be mounted on the silicon substrate.
- The multiple chips mounted on the single substrate in a system module typically include different circuits, i.e., some analog circuits and some digital circuits. This requires a low impedance ground in the system module to suppress digital noise that may appear in the analog circuits of these mixed mode circuits. Digital noise is the side effect of the switching of the logic circuits. High-speed synchronous digital integrated circuits require large switching currents which can induce noise on the power distribution networks and ground busses due to the finite resistance and inductance in these circuits. The noise may consist of voltage spikes appearing at the power supply terminals of the chip with the switching activity. Power supply noise can have a significant effect due to simultaneous switching noise in CMOS integrated circuits. These problems are more severe in mixed-mode circuits and require careful design of the power distribution systems.
- Thus, a silicon substrate with a low impedance built-in ground plane is necessary for the system modules to suppress noise. It is also desirable for a built-in ground plane to be planar with the surface of the substrate to maintain a flat surface on the substrate upon which various chips, active circuits, and passive components (such as decoupling capacitors and termination resistors) can be subsequently mounted. A conventional method for forming buried conductors in a substrate is the use of heavy ion implantation of conducting atoms into the substrate to form the conductor. This approach, however, is not economically viable due to the required high-current, high-energy implanters, and may also cause damage to the overlying substrate. Another conventional method for fabricating a multilevel interconnect is to implant silicon into silicon oxide followed by a selective deposition of tungsten to build a multi-layer structure with low electrical resistivity. This method, however, is suitable only for fabricating a buried conductor in a silicon oxide, and not in a silicon substrate as is required in a system module.
- Thus, there exists a need for an apparatus and method for simply and inexpensively fabricating a buried ground plane in a silicon substrate for use in multi-chip system modules.
- The present invention provides a simple and low-cost scheme for producing a buried ground plane in a silicon substrate. In accordance with the present invention, the desired conductors are patterned by ordinary lithography on the surface of the silicon substrate in a mesh pattern to leave room for other chips and components to be mounted. A porous structure is produced only in the patterned conductors by depositing silicon nitride windows on the silicon and subjecting the wafer to a chemical anodization process. After the formation of the pores, the pores are then filled with a conductive metal by the use of a selective deposition technique. The filled pores may be subjected to a high-temperature annealing process to convert the deposited conductive metal to a metal silicide.
- These and other advantages and features of the invention will become apparent from the following detailed description of the invention which is provided in connection with the accompanying drawings.
- FIG. 1 illustrates a cross-sectional view of a portion of a silicon substrate with buried ground planes;
- FIG. 2 illustrates a top view of a portion of the silicon substrate of FIG. 1 with buried ground planes;
- FIGS. 3A, 3B and3C illustrate a cross-sectional view of the wafer of FIG. 2 during intermediate processes in accordance with the method of the present invention;
- FIG. 4 illustrates a cross-sectional view of a processed wafer with buried ground planes according to a first embodiment of the present invention;
- FIG. 5 illustrates a cross-sectional view of a processed wafer according to a second embodiment of the present invention;
- FIGS. 6A and 6B illustrate in flow chart form the steps for forming a buried ground plane in accordance with a first and second method of the present invention; and
- FIG. 7 illustrates in system module in accordance with the present invention.
- The present invention will be described as set forth in the preferred embodiment illustrated in FIGS.1-7. Other embodiments may be utilized and structural or logical changes may be made without departing from the spirit or scope of the present invention.
- The terms “wafer” and “substrate” are used interchangeably and are to be understood as including silicon-on-insulator (SOI) or silicon-on-sapphire (SOS) technology, doped and undoped semiconductors, epitaxial layers of silicon supported by a base semiconductor foundation, and other semiconductor structures.
- Furthermore, when reference is made to a “wafer” or “substrate” in the following description, previous process steps may have been utilized to form regions or junctions in the base semiconductor structure or foundation.
- A cross-sectional diagram of a portion of a
wafer 10 having buried ground planes is illustrated generally in FIG. 1. The term buried as used herein refers both to covered conductors, i.e., under the surface and concealed from view, and to conductors that are formed in the substrate whose top surface is planar with the surface of the substrate. Wafer 10 consists of a first leveltop conductor 12 and a firstlevel bottom conductor 14. Asilicon interposer 16 is provided between theconductors holes wafer 10 to provide for interconnection between the top and bottom surfaces ofwafer 10. Alayer 26 of insulating material, such as silicon dioxide (SiO2), may be provided betweentop conductor 12 andsilicon interposer 16. Similarly, a layer ofinsulating material 28, such as silicon dioxide (SiO2), may be provided betweenbottom conductor 14 andsilicon interposer 16. Buriedground planes 30 are provided within thesilicon interposer 16. The buriedground planes 30 provide a low-impedance ground connection suitable for suppressing noise produced by digital circuits that may be mounted onsilicon interposer 16. - FIG. 2 illustrates a top view of a portion of the
silicon substrate 10 of FIG. 1 across the line a-a′.Space 52 is left betweenconductors 30 for mounting or integrating chips and/or components.Ground planes 30 may be formed in a mesh pattern to allow for areas such asspace 52. - The processes for forming buried ground plane conductors in a silicon substrate in accordance with the present invention is as follows. The pattern for the desired conductors, such as
conductors 30 of FIG. 2, is printed on the surface ofsilicon substrate 16 by conventional lithography or any other method for printing a pattern on the surface ofsubstrate 16 as is known in the art.Space 52 may be left betweenconductors 30 for other chips and components to be mounted. - Once the pattern for
conductors 30 has been printed on the surface ofsubstrate 16, aprotective layer 72, such as for example silicon nitride, is deposited to form windows on the surface of thesilicon substrate 16 in which only the printed pattern areas forconductors 30 are left exposed. FIG. 3A illustrates a cross-sectional diagram ofsilicon substrate 16 along line b-b′ in FIG. 2 after the deposition of the silicon nitride windows. The deposition of alayer 72 of silicon nitride covers the surface ofsubstrate 16, except for the areas where the pattern forconductors 30 has been printed. The preferable thickness for thelayer 72 of silicon nitride is approximately 100 nm. - The
substrate 16 is then subjected to a chemical anodization process, as is well known in the art, to form a porous layer in the areas not covered with thelayer 72 of silicon nitirde, i.e., the areas where the pattern forconductors 30 has been printed. - Porous silicon may be formed by the anodization of silicon in aqueous solutions of hydroflouric acid. Pores are etched into the silicon during the anodization process. The resulting structure is illustrated in FIG. 3B. The areas of
silicon substrate 16 which have been printed with the pattern forconductors 30 contain aporous layer 74 insubstrate 16 created by the anodization process. Those portions of thesubstrate 16 covered withlayer 72 of silicon nitride do not have a porous layer. It is well known that under appropriate anodic conditions, silicon can be converted into a highly porous material. The porosity may be controlled in the 30%-85% range, i.e., the pores in the silicon can comprise approximately 30 to 85% of the total volume within thesilicon substrate 16. Thus, a porosity of 50% indicates a material in which half of its volume is comprised of pores within the material. - After the formation of the pores in the
substrate 16, aconductor 30 is formed by filling the pores with aconductive metal 76. Since theconductors 30 usually must be able to withstand subsequent high temperature processing, it is preferable to use refractory metals to form the conductors, such as tungsten (W) or molybdenum (Mo) or their silicides. Refractory metals are difficult to pattern by chemical mechanical polishing or standard photolithographic techniques since they are chemically inert. As such, it is desirable to have a self-aligned process that does not require any patterning of the metal. The use of a selective deposition technique, as is known in the art, provides a self aligned process that does not require any patterning of the metal. For example, if tungsten is used, the chemical vapor deposition (CVD) may be based on tungsten hexaflouride (WF6). The chemical-vapor-deposited tungsten process using either WF6/H2or WF6/SiH4 chemistry is well known in the art. The tungsten hexaflouride will react with the areas of the exposedsubstrate 16, but not with the areas ofsubstrate 16 covered withlayer 72 of silicon nitride. This will selectively deposit the tungsten in theporous layers 74 insilicon substrate 16 in the areas where the pattern forconductors 30 are printed but not on the areas covered with thesilicon nitride layer 72. Molybdenum can be deposited in a similar fashion as tungsten. The deposition of the conductive metal in the pores creates a low impedance buried conductive plane. - FIG. 3C illustrates the
silicon substrate 16 after theconductive metal 76, such as tungsten or molybdenum, has been deposited as described above. The chemical vapor deposition of the metal fills in the pores in the areas where theconductors 30 have been patterned, but does not react with thelayer 72 of silicon nitride. - As an alternative to the above, copper may be used as the conductive metal for applications which will not require a subsequent high processing temperature. The copper may be deposited into the pores of the areas where
conductors 30 have been patterned by a chemical vapor deposition technique similar to that as described above with respect to the chemical vapor deposition of tungsten or molybdenum. - After the deposition of the conducting
metal 76, the excess metal and nitride windows may be removed by a chemical mechanical polishing process as is known in the art. As illustrated in FIG. 4, aninsulation layer 80, formed of silicon dioxide (SiO2), or alternatively, a high-temperature polymer film with a low dielectric constant, such as for example polyimide, may be deposited. - Alternatively, instead of depositing an insulating
layer 80, thesubstrate 16 can be further processed to fabricate theconductors 30 with a refractory metal silicide. This may be preferable for applications in which a very high subsequent processing temperature will be required. After the pores have been filled with the refractory metal, thesubstrate 16 may be subjected to a high temperature annealing to convert the metal in the pores to a silicide. Preferable parameters for this annealing process for tungsten are a temperature greater than approximately 900° C. for up to 30 minutes. This annealing step may be combined with other processes at a later stage if desired. The resulting tungsten silicide has a typical resistivity of 18-20 micro-cm-cm, and can be subjected to subsequent high temperature processing. As illustrated in FIG. 5, the nitride window and excess metal in the channel area may be removed by chemical mechanical polishing to provide a flat and smooth surface for subsequent processing. An insulation layer (not shown), formed of silicon dioxide or a hightemperature polymer film such as polyimide, may be deposited over the surface ofsubstrate 16. - A first and second method of processing buried ground planes in accordance with the present invention is illustrated in flow chart form in FIGS. 6A and 6B. Like steps are referred to by like numerals in each method.
- In accordance with a first method of the present invention as illustrated in FIG. 6A, in
step 610, the pattern forconductors 30 is printed on the surface of thesilicon wafer 16 by conventional lithography or any other method as is known in the art. The pattern forconductors 30 may be in a mesh pattern as illustrated in FIG. 2 to allow sufficient space betweenconductors 30 for other chips and components to be mounted. - In
step 620, a layer of silicon nitride, preferably 100 nm thick, is deposited on the surface of thesubstrate 16 to form silicon nitride windows. The layer of silicon nitride does not cover the areas where the pattern forconductors 30 has been printed. Instep 630, the wafer is subjected to a chemical anodization process, as is known in the art, to produce a porous layer in thesubstrate 16 in the areas where the pattern forconductors 30 has been printed. - In
step 640, a conductor is formed by depositing a conductive metal into the pores of the porous layer produced in the substrate. As noted previously, refractory metals such as tungsten (W) or molybdenum (Mo) are preferable for applications in which thesubstrate 16 must be able to withstand subsequent high temperature processing. The metal may be deposited using a selective deposition technique as is known in the art. For applications in which thesubstrate 16 will not be subjected to subsequent high processing temperatures, copper may be used as the conducting metal. The copper may be deposited by a chemical vapor deposition as is known in the art. - In
step 650, the excess metal and nitride windows may be removed utilizing a chemical mechanical polishing process as is known in the art or any other method. Instep 660, aninsulation layer 80, formed of silicon dioxide, or alternatively a high-temperature polymer film with a low dielectric constant, such as polyimide, may be deposited on the surface of thesubstrate 16. - A second method for producing a buried ground plane in accordance with the present invention is illustrated in FIG. 6B.
Steps substrate 16 instep 630, the conductor is created by depositing a refractory metal into the pores in step 740 using a selective deposition technique as is known in the art. Instep 750, thesubstrate 16 is subjected to a high temperature annealing to convert the metal in the pores to a silicide. Preferable parameters for this annealing process for tungsten are a temperature greater than approximately 900° C. for up to 30 minutes. This annealing step may be combined with other processes at a later stage if desired. Instep 760, the nitride window and excess metal in the channel area may be removed by chemical mechanical polishing to provide a flat and smooth surface for subsequent processing. Instep 770, an insulation layer, formed of silicon dioxide, or alternatively a high-temperature polymer film with a low dielectric constant, such as polyimide, may be deposited on the surface of thesubstrate 16. - In accordance with the present invention, a buried ground plane can be formed in a silicon substrate simply and inexpensively, without damaging the surrounding environment within the substrate.
- FIG. 7 illustrates a portion of a system module having buried ground planes constructed in accordance with the present invention. A high performance system module may be provided with a silicon interposer, such as
substrate 102, onto which semiconductor chips or active or passive components can be easily mounted. For example, afirst chip 104 may be stacked on asecond chip 100 using MBB technology as is known in the art to result in a chip-on-chip module. The resulting chip-on-chip module structure may be mounted ontosubstrate 102 along with additional active or passive components.Substrate 102 may have a plurality of such chip-on-chip module structures and components mounted on its surface. Each of the system modules may consist of at least two chips, some of which may be analog circuits and others digital circuits.Substrate 102, in accordance with the present invention, may be provided with buried low impedance ground conductors 106 to suppress digital noise in the analog circuits of the modules. - While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, deletions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as limited by the foregoing description but is only limited by the scope of the appended claims.
Claims (95)
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/199,442 US6432724B1 (en) | 1998-11-25 | 1998-11-25 | Buried ground plane for high performance system modules |
US09/515,083 US6670703B1 (en) | 1998-11-25 | 2000-02-28 | Buried ground plane for high performance system modules |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/199,442 US6432724B1 (en) | 1998-11-25 | 1998-11-25 | Buried ground plane for high performance system modules |
Related Child Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US09/515,083 Division US6670703B1 (en) | 1998-11-25 | 2000-02-28 | Buried ground plane for high performance system modules |
Publications (2)
Publication Number | Publication Date |
---|---|
US20020022362A1 true US20020022362A1 (en) | 2002-02-21 |
US6432724B1 US6432724B1 (en) | 2002-08-13 |
Family
ID=22737520
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US09/199,442 Expired - Fee Related US6432724B1 (en) | 1998-11-25 | 1998-11-25 | Buried ground plane for high performance system modules |
US09/515,083 Expired - Fee Related US6670703B1 (en) | 1998-11-25 | 2000-02-28 | Buried ground plane for high performance system modules |
Family Applications After (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US09/515,083 Expired - Fee Related US6670703B1 (en) | 1998-11-25 | 2000-02-28 | Buried ground plane for high performance system modules |
Country Status (1)
Country | Link |
---|---|
US (2) | US6432724B1 (en) |
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20030148598A1 (en) * | 2001-11-20 | 2003-08-07 | King-Ning Tu | Methods of fabricating highly conductive regions in semiconductor substrates for radio frequency applications |
US20050029555A1 (en) * | 2002-12-23 | 2005-02-10 | Figueroa David Gregory | Silicon building blocks in integrated circuit packaging |
US20070049019A1 (en) * | 2005-09-01 | 2007-03-01 | Wai Chien M | Method of selectively depositing materials on a substrate using a supercritical fluid |
US20090291545A1 (en) * | 2005-07-19 | 2009-11-26 | Micron Technology, Inc. | Process for enhancing solubility and reaction rates in supercritical fluids |
WO2012000015A1 (en) * | 2010-07-02 | 2012-01-05 | Newsouth Innovations Pty Limited | Metal contact scheme for solar cells |
US20140151892A1 (en) * | 2012-11-30 | 2014-06-05 | Nvidia Corporation | Three dimensional through-silicon via construction |
Families Citing this family (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6867491B2 (en) * | 2001-12-19 | 2005-03-15 | Intel Corporation | Metal core integrated circuit package with electrically isolated regions and associated methods |
JP2004071923A (en) * | 2002-08-08 | 2004-03-04 | Fujitsu Ltd | High temperature superconductive device |
US20040075170A1 (en) * | 2002-10-21 | 2004-04-22 | Yinon Degani | High frequency integrated circuits |
US7157791B1 (en) | 2004-06-11 | 2007-01-02 | Bridge Semiconductor Corporation | Semiconductor chip assembly with press-fit ground plane |
US7245023B1 (en) | 2004-06-11 | 2007-07-17 | Bridge Semiconductor Corporation | Semiconductor chip assembly with solder-attached ground plane |
US8021926B2 (en) * | 2009-09-22 | 2011-09-20 | Freescale Semiconductor, Inc. | Methods for forming semiconductor devices with low resistance back-side coupling |
Family Cites Families (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4074342A (en) * | 1974-12-20 | 1978-02-14 | International Business Machines Corporation | Electrical package for lsi devices and assembly process therefor |
KR900008647B1 (en) * | 1986-03-20 | 1990-11-26 | 후지쓰 가부시끼가이샤 | A method for manufacturing three demensional i.c. |
GB9108176D0 (en) * | 1991-04-17 | 1991-06-05 | Secr Defence | Electroluminescent silicon device |
JPH05145094A (en) * | 1991-11-22 | 1993-06-11 | Mitsubishi Electric Corp | Semiconductor device and manufacture thereof |
US5304293A (en) * | 1992-05-11 | 1994-04-19 | Teknekron Sensor Development Corporation | Microsensors for gaseous and vaporous species |
US6017811A (en) * | 1993-09-09 | 2000-01-25 | The United States Of America As Represented By The Secretary Of The Navy | Method of making improved electrical contact to porous silicon |
EP0895293B1 (en) * | 1993-11-02 | 2006-06-14 | Matsushita Electric Industrial Co., Ltd. | Semiconductor device comprising an aggregate of semiconductor micro-needles |
EP0666595B1 (en) * | 1994-02-07 | 1998-08-19 | Siemens Aktiengesellschaft | Method of manufacture of a cubic integrated circuit structure |
US5805425A (en) * | 1996-09-24 | 1998-09-08 | Texas Instruments Incorporated | Microelectronic assemblies including Z-axis conductive films |
US6052286A (en) * | 1997-04-11 | 2000-04-18 | Texas Instruments Incorporated | Restrained center core anisotropically conductive adhesive |
WO1998048456A1 (en) * | 1997-04-24 | 1998-10-29 | Massachusetts Institute Of Technology | Nanowire arrays |
US6268660B1 (en) * | 1999-03-05 | 2001-07-31 | International Business Machines Corporation | Silicon packaging with through wafer interconnects |
-
1998
- 1998-11-25 US US09/199,442 patent/US6432724B1/en not_active Expired - Fee Related
-
2000
- 2000-02-28 US US09/515,083 patent/US6670703B1/en not_active Expired - Fee Related
Cited By (18)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20030148598A1 (en) * | 2001-11-20 | 2003-08-07 | King-Ning Tu | Methods of fabricating highly conductive regions in semiconductor substrates for radio frequency applications |
US7176129B2 (en) * | 2001-11-20 | 2007-02-13 | The Regents Of The University Of California | Methods of fabricating highly conductive regions in semiconductor substrates for radio frequency applications |
US7772117B2 (en) | 2001-11-20 | 2010-08-10 | The Regents Of The University Of California | Methods of fabricating highly conductive regions in semiconductor substrates for radio frequency applications |
US20070117345A1 (en) * | 2001-11-20 | 2007-05-24 | The Regents Of The University Of California | Methods of fabricating highly conductive regions in semiconductor substrates for radio frequency applications |
US20050029555A1 (en) * | 2002-12-23 | 2005-02-10 | Figueroa David Gregory | Silicon building blocks in integrated circuit packaging |
US7205638B2 (en) * | 2002-12-23 | 2007-04-17 | Intel Corporation | Silicon building blocks in integrated circuit packaging |
US20090291545A1 (en) * | 2005-07-19 | 2009-11-26 | Micron Technology, Inc. | Process for enhancing solubility and reaction rates in supercritical fluids |
US8043944B2 (en) | 2005-07-19 | 2011-10-25 | Micron Technology, Inc. | Process for enhancing solubility and reaction rates in supercritical fluids |
US8329595B2 (en) | 2005-07-19 | 2012-12-11 | Micron Technology, Inc. | Process for enhancing solubility and reaction rates in supercritical fluids |
US8524610B2 (en) | 2005-07-19 | 2013-09-03 | Micron Technology, Inc. | Process for enhancing solubility and reaction rates in supercritical fluids |
US20090291556A1 (en) * | 2005-09-01 | 2009-11-26 | Micron Technology, Inc. | Method of selectively depositing materials on a substrate using a supercritical fluid |
US7582561B2 (en) * | 2005-09-01 | 2009-09-01 | Micron Technology, Inc. | Method of selectively depositing materials on a substrate using a supercritical fluid |
US20070049019A1 (en) * | 2005-09-01 | 2007-03-01 | Wai Chien M | Method of selectively depositing materials on a substrate using a supercritical fluid |
US7897517B2 (en) | 2005-09-01 | 2011-03-01 | Micron Technology, Inc. | Method of selectively depositing materials on a substrate using a supercritical fluid |
WO2012000015A1 (en) * | 2010-07-02 | 2012-01-05 | Newsouth Innovations Pty Limited | Metal contact scheme for solar cells |
US20140020746A1 (en) * | 2010-07-02 | 2014-01-23 | Newsouth Innovations Pty Limited | Metal contact scheme for solar cells |
US20140151892A1 (en) * | 2012-11-30 | 2014-06-05 | Nvidia Corporation | Three dimensional through-silicon via construction |
CN103855135A (en) * | 2012-11-30 | 2014-06-11 | 辉达公司 | Three dimensional through-silicon via construction |
Also Published As
Publication number | Publication date |
---|---|
US6670703B1 (en) | 2003-12-30 |
US6432724B1 (en) | 2002-08-13 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
JP5285829B2 (en) | Interposer and manufacturing method thereof | |
US5424245A (en) | Method of forming vias through two-sided substrate | |
US6962866B2 (en) | System-on-a-chip with multi-layered metallized through-hole interconnection | |
US5583739A (en) | Capacitor fabricated on a substrate containing electronic circuitry | |
JP4776618B2 (en) | Back-end process transmission line structure for semiconductor devices (Method of forming a suspended transmission line structure in back-end process) | |
US6593644B2 (en) | System of a package fabricated on a semiconductor or dielectric wafer with wiring on one face, vias extending through the wafer, and external connections on the opposing face | |
US6355950B1 (en) | Substrate interconnect for power distribution on integrated circuits | |
US6174803B1 (en) | Integrated circuit device interconnection techniques | |
US6057226A (en) | Air gap based low dielectric constant interconnect structure and method of making same | |
WO2004100232A1 (en) | Method for forming the top plate of a mim capacitor with a single mask in a copper dual damascene integration scheme | |
KR20060033866A (en) | Electronic device, assembly and methods of manufacturing an electronic device | |
US6432724B1 (en) | Buried ground plane for high performance system modules | |
US6759746B1 (en) | Die attachment and method | |
US6277765B1 (en) | Low-K Dielectric layer and method of making same | |
US7452804B2 (en) | Single damascene with disposable stencil and method therefore | |
US20230378048A1 (en) | Semiconductor structure and method for manufacturing the same | |
KR20110049893A (en) | A semiconductor device comprising a carbon based material for through hole vias | |
US20240096783A1 (en) | Flexible wiring architecture for multi-die integration | |
US20240071929A1 (en) | Dielectric caps for power and signal line routing | |
CN113035810A (en) | Through silicon via structure, packaging structure and manufacturing method thereof | |
JP2000228445A (en) | Semiconductor device and its manufacture |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: MICRON TECHNOLOGY, INC., IDAHO Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:AHN, KIE Y.;FORBES, LEONARD;REEL/FRAME:009634/0430;SIGNING DATES FROM 19981113 TO 19981116 |
|
FPAY | Fee payment |
Year of fee payment: 4 |
|
FEPP | Fee payment procedure |
Free format text: PAYER NUMBER DE-ASSIGNED (ORIGINAL EVENT CODE: RMPN); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY Free format text: PAYOR NUMBER ASSIGNED (ORIGINAL EVENT CODE: ASPN); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY |
|
FPAY | Fee payment |
Year of fee payment: 8 |
|
REMI | Maintenance fee reminder mailed | ||
LAPS | Lapse for failure to pay maintenance fees | ||
STCH | Information on status: patent discontinuation |
Free format text: PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES UNDER 37 CFR 1.362 |
|
FP | Lapsed due to failure to pay maintenance fee |
Effective date: 20140813 |