Patent Application
20070166997
The present invention relates generally to the fabrication of semiconductor devices, and more particularly to the fabrication of vertically stacked integrated circuits.
Semiconductor devices are used in a variety of electronic applications, such as computers, cellular phones, personal computing devices, and many other applications. Home, industrial, and automotive devices that in the past comprised only mechanical components now have electronic parts that require semiconductor devices, for example.
Semiconductor devices are manufactured by depositing many different types of material layers over a semiconductor workpiece or wafer, and patterning the various material layers using lithography. The material layers typically comprise thin films of conductive, semiconductive, and insulating materials that are patterned and etched to form integrated circuits (ICs). There may be a plurality of transistors, memory devices, switches, conductive lines, diodes, capacitors, logic circuits, and other electronic components formed on a single die or chip, for example.
After an integrated circuit is manufactured, individual die are singulated from the wafer, and typically, the die is packaged. For many years, the most common way of packaging a die was horizontal placement within individual plastic or ceramic packages. Alternatively, several die may be packaged horizontally in a single package, forming a multi-chip module. Electrical connections are made to terminals or bond pads of the die, e.g., using very small strands of wire, which is routed to pins of the package.
A demand for smaller ICs with higher performance has led to the development of system-on-a-chip devices, where portions of the chip are dedicated to memory and other portions are dedicated to logic or other types of circuitry. However, it can be difficult to manufacture an IC with multiple types of circuitry, due to integration problems of the different circuit fabrication technologies.
One trend in the semiconductor industry is the movement towards three dimensional integrated circuits (3D-ICs), for example, where two or more chips or wafers are stacked and vertically integrated. Parts of a circuit are fabricated on different wafers, and the wafers or die are bonded together with a glue layer such as copper or a polymer based adhesive. Different types of circuits, e.g., memory and logic, as examples, may be manufactured separately and then vertically attached, which may be less expensive and easier to manufacture than combining the two circuit technologies on a single wafer as in system-on-a-chip devices. 3D-ICs are predicted to be used in the future for low power, high speed applications, because the paths of conduction may be shortened by the vertical electrical connections between the circuits, resulting in low power consumption and increased speed.
However, 3D-ICs introduce some design and fabrication challenges. For example, the etch processes required to produce the vertical connections between vertically stacked ICs may be difficult, due to the many different types of material layers and the thickness of the material layers that must be etched.
Thus, improved methods of fabricating 3D-ICs and structures thereof are needed in the art.
These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred embodiments of the present invention, which provide novel methods of connecting two or more ICs together to form 3D-ICs and structures thereof.
In accordance with a preferred embodiment of the present invention, a method of fabricating a semiconductor device includes fabricating a first integrated circuit, fabricating a second integrated circuit, and vertically coupling the second integrated circuit to the first integrated circuit. Fabricating the first integrated circuit includes providing a first workpiece, forming at least one first active area within the first workpiece, and forming at least one deep via within the first workpiece, wherein the at least one deep via provides vertical electrical connection for the first integrated circuit.
The foregoing has outlined rather broadly the features and technical advantages of embodiments of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of embodiments of the invention will be described hereinafter, which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the preferred embodiments and are not necessarily drawn to scale.
The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
An interconnect region comprising conductive lines 110a and conductive vias 111a formed in an insulating material 112a is formed over the workpiece and the active areas 108a. The interconnect region may comprise one or more conductive layers within an insulating material layer, and may comprise a multi-layer interconnect region formed by subtractive etch processes or damascene processes, for example. The interconnect region is labeled 104a to indicate the portion of the integrated circuit 102a that is processed in the back end of line (BEOL), e.g., after the first metallization layer is deposited.
Integrated circuit 102b may comprise similar components and elements as integrated circuit 102a, as indicated by similar element numbers with a “b” suffix. Integrated circuit 102b may comprise a similar circuit or a different type of circuit as the circuit formed on integrated circuit 102a, for example.
One prior art method of forming a 3D-IC 100 is to invert one integrated circuit 102a and bond the top surface of integrated circuit 102a to the top surface of integrated circuit 102b, as shown in
If an adhesive 114 or oxide-to-oxide bond is used to bond together the ICs 102a and 102b, then a vertical connection between the ICs 102a and 102b is required to be made, by forming deep vias within the IC 102a. To form the deep vias, the top surface, e.g., the workpiece 101a of the top integrated circuit 102a, is thinned, as shown in
To form the deep vias 118, a hard mask (not shown) is typically deposited over the thinned workpiece 101a, and a layer of photoresist is deposited over the hard mask and patterned with the desired pattern for the deep vias 118. The layer of photoresist is then used as a mask to pattern the hard mask. The hard mask is then used to pattern the various material layers 101a, 108a, 112a, 111a, and 110a of the top integrated circuit 102a, the bond region 114, and material layers (e.g., insulating material 112b) of the bottom integrated circuit 102b, forming trenches for the deep vias. An insulating liner is formed within the trenches (not shown in
A problem with the prior art method of forming the deep vias 118 shown is that there are several material layers 101a, 108a, 112a, 111a, 110a, 114, and 112b that must be etched, causing the etch process to be lengthy, time-consuming, and costly. The etch process is also difficult to control. Because many different types of materials must be etched, the etch chemistries may need to be changed several times, e.g., about 10 to 15 or more times, because different etch chemistries are required to etch different material types.
Furthermore, the insulating liner on the sidewalls of the trenches for the deep vias 118 cannot be formed using a high temperature thermal nitridation process or by thermal oxidation, because the interconnect regions of the two ICs 102a and 102b include metals (e.g., conductive lines 110a, 110b, and vias 111a and 11lb); thus, the temperature that the 3D-IC 100 may be exposed to is limited to about 400 degrees C. or less. A thermal nitridation process to form a layer of SixNy or a thermal oxidation process to form a liner of SiO2 may require temperatures of about 700 degrees C. or more, for example. Thus, physical vapor deposition (PVD) or Plasma Enhanced Chemical Vapor Deposition (PE CVD) must be used to form the insulating liner, which results in the formation of an insulating liner having poor step coverage, poor quality, and poor bonding with the workpiece 102a.
If metal-to-metal bonds are used to connect the two integrated circuits 102a and 102b, deep vias are required to be made in the workpiece 101a of the top IC 102a, to make electrical contact to the active areas 108a or to the conductive lines 110a and vias 111a. While fewer material layers must be etched in this case to form the deep vias, high temperature processes may still not be used to form the insulating liner of the deep vias because of the presence of the metallization layers of the interconnect regions of the two ICs 102a and 102b, as described above.
Another method used to vertically integrate integrated circuits 102a and 102b is to bond two ICs 102a and 102b “front-to-back,” e.g., wherein a bottom surface of one IC 102a is bonded to a top surface of another IC 102b (not shown in the drawings). In this method, the integrated circuit (e.g., such as IC 102a in
Furthermore, in some prior art 3D-ICs, an additional signal distribution layer may be needed to make the required electrical connections, not shown in the drawings. The signal distribution layer comprises an additional interconnect layer that is used to make the vertical connections between the two ICs.
Thus, what are needed in the art are improved methods of fabricating 3D-ICs and providing electrical connection between vertically stacked ICs.
Embodiments of the present invention provide technical advantages by forming deep vias for providing electrical connection for vertically stacked integrated circuits early in the manufacturing process, before the integrated circuits are vertically attached to other integrated circuits. Thus, fewer material layers are required to be etched during the formation of the deep vias, which provides several advantages, to be described further herein. Furthermore, the deep vias are formed before any metals are deposited (e.g., before the BEOL), so that high temperature processes may be used to form an insulating liner on sidewalls of the trenches of the deep vias.
An upper portion 220 of the workpiece 201 is shown in the figures. The workpiece 201 may comprise a thickness of about 600 μm, yet only the upper 25 μm is shown in the drawings, for example.
Active areas 222/224 are formed proximate the top surface of the workpiece 201, as shown. For example, transistors 224 may be formed proximate the workpiece 201 top surface, e.g., by implanting dopant regions within the top surface of the workpiece 201, and forming gate dielectrics, gates, and sidewall spacers over the doped regions. The transistors 224 may be separated by isolation regions 222 formed in the top surface of the workpiece 201 between adjacent transistors 224, also shown. The isolation regions 222 may comprise a depth within the top surface of the workpiece 201 of about 2,000 Angstroms or less, for example, although alternatively, the isolation regions 222 may comprise a depth of greater than 2,000 Angstroms.
The transistors 224 may comprise p channel field effect transistors (PFETs) and n channel field effect transistors (NFETs) arranged in complementary configurations, e.g., to form complementary metal oxide semiconductor (CMOS) devices, for example. The transistors 224 may also comprise bipolar transistors or other thin film transistors, or combinations thereof with CMOS devices, as examples. An insulating material 226 comprising silicon dioxide or other dielectric material may be deposited over the active areas 222/224, as shown. The active areas 222/224 are preferably formed using FEOL processes (e.g., region 206 is formed in a FEOL), for example. The active areas 222/224 may comprise transistors, as shown, and alternatively may comprise memory devices, switches, diodes, capacitors, logic circuits, other electronic components, or combinations thereof with transistors (not shown), formed within and above the workpiece 201, as examples.
After the FEOL process is completed for the integrated circuit 202, next, deep vias for vertical integration of a 3D-IC device are formed in the top portion 220 of the workpiece 201, as shown in
The hard mask 236 preferably also includes a second layer 232 disposed over the first layer 230, as shown. The second layer 232 may comprise an oxide, a doped oxide, or other masking materials such as boron-doped silicon glass (BSG), as examples. The hard mask 236 may comprise a thickness of about 1 μm, although alternatively, the hard mask 236 may comprise other dimensions. The hard mask 236 may alternatively comprise a single type of material, a single layer, or three or more material layers, as examples.
A layer of photoresist 234 is deposited over the hard mask 236. The layer of photoresist 234 is patterned using lithography (e.g., by exposing portions the layer of photoresist 234 using a lithography mask, and developing the layer of photoresist 234) with the desired shape of the deep vias, as shown in
The layer of photoresist 234 is then used to pattern the hard mask 236. For example, the layer of photoresist 234 is used as a mask while exposed portions of the hard mask 236 are removed, as shown in
The hard mask 236 and optionally also the photoresist 234 is then used as a mask to pattern trenches for deep vias in the insulating layer 226, active areas 222/224, and in a top portion 220 of the workpiece 201, as shown in
A portion of the hard mask 236 may be consumed during the etch process used to form the trenches for the deep vias, e.g., the thickness of the second layer 232 of the hard mask 236 may be reduced after the etch process 238. At least a portion of the hard mask 236 may be removed. For example, the second layer 232 of the hard mask 236 may be removed, e.g., using a dry or wet etch process, or a chemical-mechanical polish (CMP) process adapted to stop on the first layer 230 that functions as an etch stop layer for the removal of the second layer 232, as examples. The first layer 230 may be left remaining in the structure, or alternatively, the first layer 230 may also be removed.
Next, a liner 240 is formed within the trenches for the deep vias, and the trenches for the deep vias are filled with a conductive material 242, as shown in
The liner 240 may also optionally include one or more barrier layers, a seed layer, or both, formed over the insulating material, for example. The liner 240 may comprise a thickness of about 500 Angstroms or less, for example. The liner 240 may comprise SiO2, SixNy, SiON, other nitride materials, Ta, TaN, TiN, Cu, Ru, combinations thereof, or multiple layers thereof, as examples, although other materials may also be used.
Advantageously, because metallization layers have not been deposited yet, a relatively high temperature, e.g., greater than about 400 degrees C., may be used to form at least a portion of the liner 240. More preferably, an insulating portion of the liner 240 is formed at a temperature of about 700 degrees C. or greater, in accordance with an embodiment of the present invention. Thus, the formation of the novel deep vias is not restricted to temperature limits for BEOL processes, advantageously. Furthermore, the liner 240 may be left remaining on the bottom surface of the trenches, e.g., the insulating portion of the liner 240 is not required to be removed from the bottom surface of the trenches for the deep vias.
If the conductive material 242 comprises copper, the liner 240 preferably comprises a material suitable to provide a barrier for diffusion of the copper into adjacent material such as the workpiece 201 and the active areas 222/224, for example. In this embodiment, the liner 240 preferably comprises a diffusion barrier layer of Ta, TaN, or both, e.g., a bilayer of Ta/TaN. Furthermore, the liner 240 may include a seed layer comprising Cu or Ru, for example, for the formation of the copper conductive material 242, if a plating process is used to fill the trenches, for example. The liner 240 may comprise a thin layer of SiO2, SixNy, or other insulating material formed within the trenches before the seed layer and/or diffusion barrier layer is formed, for example.
The conductive material 242 and liner 240 may be formed by: first; forming the liner 240 over the top surface of the first layer 230 of the hard mask and over the sidewalls and bottom surface of the trenches, using chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), or other deposition techniques, and second; depositing or plating the conductive material 242 over the liner 240, filling the trenches and covering the liner 240 on the top surface of the first layer 230 (or insulating material 226 if the first layer 230 of the hard mask 236 has been removed). The conductive material 242 may comprise Cu, W, Ru, TiN, combinations thereof, other metals, combinations of two or more metals, or a semiconductive material such as silicon, doped silicon, or polysilicon, as examples. A CMP process may then be used to remove excess conductive material 242 and the liner 240 from over the top surface of the first layer 230 of the hard mask 236, leaving the structure shown in
A BEOL process is then used to form an interconnect region 210/211/212 over the workpiece 201, e.g., over the first layer 230 of the hard mask, if left remaining in the structure, as shown in
Note that if the filling of the deep via trenches comprises filling the trenches with a metal, then the BEOL process effectively begins with the filling of the deep via trenches, in this embodiment, because a first metal layer is deposited with the filling of the deep via trenches. The distinction of a BEOL process from a FEOL process may be important in some applications. FEOL processes include high temperature processes such as anneal processes that cannot be performed after some metals are deposited, for example. The maximum temperature of a BEOL process may be about 400 degrees C., whereas temperatures may reach about 1,050 degrees C. in some FEOL processes, for example.
Thus, a novel IC 250 is formed having deep vias 240/242 formed in a top portion 220 of the workpiece 201, as shown in
Face-to-face vertical attachment of the novel IC 250 to another IC in accordance with an embodiment of the present invention is illustrated in
The bonding of the first interconnect region 210a/211a/212a to the second interconnection region 210b/21lb/212b preferably comprises a metal-to-metal bond that provides electrical connection between portions of the first interconnect region 210a/211a/212a to the second interconnection region 210b/21lb/212b. The metal-to-metal bonds may be formed by activating the surfaces of the conductive lines 210a and 210b, positioning the ICs 250a and 250b so that some of the conductive lines 210a and 210b align, and applying temperature and/or pressure to the ICs 250a and 250b to bond the conductive lines 210a and 210b together, for example. For such a direct bonding the mating surfaces (e.g., the surfaces of the conductive lines 210a and 210b, and also the insulating materials 212a and 212b) are preferably extremely clean, smooth, (e.g., preferably having a surface roughness of less than about 10 Å root mean square (RMS)) and globally coplanar. Preferably, for example, an adhesive is not used for the face-to-face bonding, so that electrical connection of the conductive lines 210a and 210b of the first interconnect region 210a/211a/212a and the second interconnection region 210b/21lb/212b, respectively, is achieved.
Next, the workpiece of the top IC 250a is thinned using a thinning process 254, as shown in
Advantageously, at least the insulating portion of the liner 240 is removed from the ends of the deep vias 240a/242a during the thinning process 254 so that the exposed ends of the deep vias 240a/242a are conductive and may be connected to other circuitry, e.g., to an external connection of the 3D-IC 260 (not shown), or vertically to another IC 250, for example (also not shown). Bond pads (not shown) may be formed over the ends of the deep vias 240a/242a, and a passivation layer (not shown) may be deposited between the bond pads. The bond pads may be positioned adjacent the ends of the deep vias 240a/242a, providing an electrical connection. The workpiece 201b of the bottom IC 250b may be thinned by attaching the top of the 3D-IC to a carrier wafer or workpiece and thinning the workpiece 201b, wherein after the thinning process, the bottom workpiece 201b comprises a thickness of about 300 μm, for example.
The 3D-IC 260 may be placed in a package or circuit board, e.g., by attaching the bottom surface of the workpiece 201b to the package or circuit board. Wires may then be bonded to the bond pads, and the other end of the wires may be attached to pins of the package or other ICs attached to the circuit board. The lower workpiece 201b may be grounded or coupled to a return voltage, for example. The deep vias 240a/242a provide electrical connection to the conductive portion 224a of the active areas 222a/224a of the top IC 250a through the workpiece 201a. The deep vias 240a/242a also provide electrical connection to the conductive portion 224b of the active areas 222b/224b of the bottom IC 250b, e.g., through the conductive lines and vias 210a, 211a, 210b, and 21lb.
Thus, a 3D-IC 260 is formed, wherein two ICs 250a and 250b are bonded together at their interconnect regions 210a/211a/212a and 210b/211b/212b, and wherein at least one of the ICs 250a comprise deep vias 240a/242a formed in the workpiece 201a to provide electrical connection to the active areas 222a/224a. In the drawings shown in
Back-to-face vertical attachment of the novel IC 250 to another IC in accordance with an embodiment of the present invention is illustrated in
Note that the thinning processes 254 and 264 described herein may include an end point detection means, e.g., so that the process may be stopped when the deep via 240/242 material is reached, or stopped after a predetermined time after the deep vias 240/242 material is reached. Alternatively, the thinning processes 254 and 264 may comprise a timed thinning process, for example. The insulating portion of the deep vias 240/242, e.g., at least a portion of the liner 240 is preferably removed during the thinning process 264.
Referring next to
The deep vias 240a/242a preferably make electrical connection to a portion of the interconnect region 210b/211b/212b, e.g., to a top portion of conductive lines 210b, as shown. The conductive lines 210b may be bonded to the exposed ends of the deep vias 240a/242a by metal-to-metal bonds, for example. Thus, a 3D-IC 270 is formed wherein the deep vias 240a/242a provide vertical electrical connection between conductive portions 224a of the active areas 222a/224a and conductive portions 224b of the active areas 222b/224b of the two ICs 250a and 250b, respectively, e.g., through conductive lines 210b and vias 211b. As described with reference to the 3D-IC 260 shown in
Like numerals are used for the various elements that were described in
Referring to
An etch process 338 is used to form trenches in the workpiece 301, as shown in
The trenches of patterns 382 and 384 may then be filled with a liner 340 and a conductive material 342, as shown in
The material 342 used to fill the wider deep via shown on the left side of
In one embodiment, the deep via on the left side of the figure may be protected during transistor processing, e.g., during the lithography process, etch, fill, and planarization processing steps, as shown in
In some embodiments, the deep via trenches on the left side may be filled with a different material than the shallower trenches on the right side of the drawing, not shown in the drawings. For example, the deep via trenches (e.g., pattern 382 in
After the trenches are formed and filled, and after active areas are formed in a FEOL process, interconnect regions are formed (not shown in
In some embodiments, shown in
In the embodiments shown in
The capping layer 492 may be deposited using a spin-on process to completely fill the area within the trenches for the deep vias above the conductive material 442, in one embodiment. However, other deposition processes may be used that are conformal and may result in the pinching off of the capping layer 492 at the top of the trenches, as shown in
The voids 494 that may optionally be formed within the capped conductive material 442 do not present a problem and may be left remaining in the structure if properly processed (for example, if the conductive material 442 is covered with the capping layer 492), because the conductive material 442 still provides a path for electrical conduction from one end of each deep via 440/442 to the other end, for example. A capping layer 492 or a capping layer 492 with voids 494 formed therein may be formed in the trenches for the deep vias 240/242 and 340/342 in the embodiments of the present invention shown in
Advantages of embodiments of the invention include providing novel integrated circuit structures and methods of fabrication thereof, wherein deep vias 240/242, 340/342, and 440/442 for vertical connection to other ICs are formed before two ICs are vertically coupled together. Fewer material layers are required to be etched, because the deep vias 240/242, 340/342, and 440/442 are formed earlier in the manufacturing process of the integrated circuit, which results in an improved process window.
When the workpiece 201/301 is thinned, endpoint detection may be used to determine when the end of the deep via 240/242, 340/342, and 440/442 is reached and thus exposed. Signal routing is made more flexible by the use of embodiments of the present invention, and less interconnect “real estate” is used on an integrated circuit.
Because the deep vias 240/242, 340/342, and 440/442 are formed early in the manufacturing process, e.g., before the BEOL, it is not necessary to reserve space in the BEOL circuitry, e.g., in the interconnect region, for the placement of the deep vias 240/242, 340/342, and 440/442. In the prior art, if deep vias will extend through an interconnect region, space must be reserved for the deep vias within the interconnect region pattern, because some metals such as Cu cannot be etched, for example. This is a problem for several reasons: the deep via regions cannot be used for interconnect, and dummy patterns cannot be used in the reserved deep via regions, which are often used in the fabrication process to reduce dishing during CMP processes, which can occur when damascene processes are used to form conductive lines. Because the deep vias of embodiments of the present invention do not extend through the interconnect regions 210a/211a/212a and 210b/211b/212b, a higher interconnect integration density may be achieved, and dummy patterns may be formed (e.g., in the material layers for conductive lines 210a and 210b and vias 211a and 211b within the insulating material layers 212a and 212b) that improve the CMP process and avoid dishing of the conductive features 210a, 210b, 211a, and 211b.
The novel deep vias 240/242, 340/342, and 440/442 formed early in the manufacturing process at the single die level or at the wafer level allow the use of an insulating liner 240, 340, and 440 for the deep vias 240/242, 340/342, and 440/442 that may be formed using a high temperature thermal process, e.g., at temperatures of about 400 degrees or greater, and more preferably at temperatures of about 700 degrees or more, in some embodiments, resulting in the formation of liners 240, 340, and 440 having improved insulating properties and improved step coverage, for example. The interface characteristics of the liners 240, 340, and 440 may comprise a high quality comparable to the interface characteristics of gate oxides of transistors, for example.
Furthermore, the workpiece 201, 301, and 401 may be thinned to a thickness of less than about 100 μm, decreasing the vertical size of the 3D-IC. Alternatively, the workpiece 201, 301, and 401 may be thinned to a thickness of greater than or equal to 100 μm, which may be an advantage in some applications.
Additionally, a dedicated interconnect layer for routing connections between two vertically stacked ICs is not required by embodiments of the present invention. Rather, the deep vias 240/242, 340/342, and 440/442 provide the vertical interconnection for the 3D-ICs 260 and 270.
In the embodiments shown in
Although embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, it will be readily understood by those skilled in the art that many of the features, functions, processes, and materials described herein may be varied while remaining within the scope of the present invention. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
