CLOCK DISTRIBUTION NETWORKS AND CONDUCTIVE LINES IN SEMICONDUCTOR INTEGRATED CIRCUITS
A clock distribution network (110) is formed on a semiconductor interposer (320) which is a semiconductor integrated circuit. An input terminal (120) of the clock distribution network is formed on one side of the interposer, and output terminals (130) of the clock distribution network are formed on the opposite side of the interposer. The interposer has a through hole (360), and the clock distribution network includes a conductive feature going through the through hole. The side of the interposer which has the output terminals (130) is bonded to a second integrated circuit (310) containing circuitry clocked by the clock distribution network. The other side of the interposer is bonded to a third integrated circuit or a wiring substrate (330). The interposer contains a ground structure, or ground structures (390, 510), that shield circuitry from the clock distribution network. Conductive lines (150) in an integrated circuit are formed in trenches (610) in a semiconductor substrate.
The present application is a division of U.S. patent application Ser. No. 10/375,218, filed on Feb. 26, 2003, incorporated herein by reference, which is a division of U.S. patent application Ser. No. 10/127,144, filed on Apr. 18, 2002, incorporated herein by reference.
BACKGROUND OF THE INVENTIONThe present invention relates to placement of clock distribution networks and fabrication of conductive lines in semiconductor integrated circuit structures.
Other clock distribution networks are also known. For example, the tree and grid networks can be combined. A circuit block 140 of
A perfect placement of a clock distribution network on a semiconductor die can be difficult due to the presence of other circuitry. A modern integrated circuit may include up to eight metal layers. The clock distribution network uses one of these layers for lines 150. Another metal layer, underlying the lines 150, is used for a ground plane or a ground grid to shield the underlying circuitry from the electromagnetic field generated by high frequency clock signals on lines 150. These two layers are separated by a dielectric. The speed of signal propagation along the clock distribution network is affected by the capacitance between the lines 150 and the ground plane or grid. The capacitance is not uniform across the integrated circuit due to local variations of the dielectric thickness and the capacitive coupling between the lines 150 and other nearby switching lines. As a result, it is difficult to control the impedance of lines 150 and therefore the clock propagation speed.
Further, the ground plane or grid consumes valuable area, increases the cost and complexity of the integrated circuit, and sometimes does not completely eliminate the electromagnetic interference problem because the position of the ground plane or grid can be restricted to allow the same metal layer to be used for other circuit elements.
In
The invention is defined by the appended claims which are incorporated into this section by reference. Some features of the invention are summarized immediately below.
The inventor has observed that in the structure of
In some embodiments of the invention, some or all of the contact pads 323, and at least a contact pad that serves as the input terminal of the clock distribution network, are moved to the bottom of die 320. The bottom contact pads 323 are connected to circuitry at the top of the die by means of conductive features forming large angles (e.g. 90°) with the top and bottom surfaces of die 310. Since large portions of lines 150 extend along the top surface of die 310, the electromagnetic interference and the parasitic capacitance can be reduced.
In some embodiments, contact pads 322 are omitted. The conductive paths to and from die 310 are through die 320. Further reduction of the electromagnetic interference and the parasitic capacitance can be achieved as a result. Also, the structure occupies less area.
The bottom contact pads on die 320 can be bonded to contact pads on another integrated circuit or a wiring substrate. In this case, the die 320 serves as a semiconductor “interposer” positioned between die 310 and other integrated circuits or between die 310 and a wiring substrate.
Die 320 may include ground planes or grids or other grounded lines to shield the circuitry above and below the interposer from the clock distribution network.
In another embodiment, several interposers are provided, with different parts of a clock distribution network on different interposers.
In some embodiments, the clock distribution lines 150 (
Other conductive lines, not belonging to the clock distribution network, can be formed in such trenches.
Other embodiments and variations are described below. The invention is defined by the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The examples in this section are provided for illustration and not to limit the invention. The invention is not limited to particular circuits, materials, processes, process parameters, equipment, or dimensions.
Circuit 310 includes a semiconductor substrate 340. Active areas 340A may have been formed in substrate 340 for transistors, resistors, capacitors, interconnect lines, or other circuit elements. Interposer 320 includes a semiconductor substrate 350. Conductive lines 150 have been formed from one or more metal layers deposited over substrate 350 and insulated from the substrate by insulating layers. An insulating layer may include one or more dielectric layers, a stack of dielectric and semiconductor layers, and other insulating structures, known or to be invented. Alternatively, lines 150 can be formed from diffused (doped) areas of substrate 350, or a combination of metal layers and diffused areas, or from other conductive materials, using any suitable techniques, known or to be invented. Some techniques for forming the lines 150 are described below with respect to
Circuit 310 is bonded to interposer 320 in a flip chip manner, with the active areas 340A at the bottom of substrate 340. Contact pads 374 on the bottom of circuit 310 are bonded to contact pads on the top of circuit 320. Some of contact pads 374 are inputs of circuit blocks 140 (
Contact pads 323 are bonded to pads 388 on wiring substrate 330.
The bonding of circuit 310 to interposer 320 can be accomplished with solder, thermocompression, conductive or anisotropic adhesive, or any other technique, known or to be invented. The same techniques, or other techniques, can be used to bond the contact pads 323 to pads 388.
Active areas 340A may be positioned at the top of circuit 310. Circuit 310 may include contact pads both at the top and at the bottom, with through holes going through substrate 340 to provide suitable interconnections. Other integrated circuits (not shown), including other interposers, can be bonded to contact pads on top of circuit 310. See the aforementioned U.S. Pat. No. 6,322,903. These other integrated circuits may contain parts of clock distribution networks. The integrated circuits may be bonded to each other in any configurations, not necessarily in a stack one above the other. For example, multiple circuits 310 can be bonded side by side to the top surface of interposer 320. Multiple interposers may be present, and they may contain different parts of clock distribution networks, or different clock distribution networks.
In some embodiments, structure 390 is held at a constant non-ground voltage.
Due to the presence of shielding structure 390, it is less important to have a ground plane in circuit 310. The number of metal layers in circuit 310 can therefore be reduced. The incremental cost of each additional metal layer increases with the total number of metal layers in an integrated circuit, so moving a ground plane from circuit 310 to circuit 320 may reduce the total manufacturing cost.
As shown in
Placing the ground structure 390 on the interposer rather than on circuit 310 reduces the capacitive coupling between the ground structure and circuit elements of circuit 310 because the ground structure becomes father from the circuit elements of circuit 310. The capacitive coupling and electromagnetic interference between the ground structure and the conductive features in holes 360 is small because the ground structure and the conductive features in holes 360 are at an angle (near 90°) to each other.
If a ground structure is provided in circuit 310, the capacitive coupling and the electromagnetic interference between this ground structure and the conductive features in holes 360 are reduced for the same reason.
In some embodiments, at least some contact pads 380 are positioned above the respective holes 360 and are connected to respective contact pads 323 without use of horizontal conductive lines. A contact pad 380 can however be laterally spaced from the respective hole 360, and connected to the respective contact pad 323 by a combination of a conductive feature in the hole 360 and horizontal lines.
Substrate 350 is grounded, or held at some other constant voltage, to shield the clock distribution networks from the circuitry in wiring substrate 330 and vice versa. Of course, the active areas 350A do not have to be grounded, but the grounded portion of substrate 350 extends laterally throughout the substrate in some embodiments.
Interposer 320 may contain only a part of a clock distribution network. For example, interposer 320 may contain only a sub-tree 110S (
In
In some embodiments, interposer 320 contains only the clock distribution network or networks, so its fabrication is relatively inexpensive. In other embodiments, interposer 320 also contains decoupling capacitors, diodes, resistors, transistors, and other elements. In some embodiments, the fabrication yield of the entire structure is increased because the fabrication of the clock distribution network does not have to be integrated with the fabrication of circuit 310 except at the packaging stage.
In some embodiments, metal 624 fills the trenches only partially. Metal 624 can be a thin film on the trench surfaces. Also, metal 624 can be replaced with multiple metal layers separated by dielectric. Different metal layers may provide different lines 150 in the same trench. Alternatively, different metal layers may be interconnected to provide a single line 150. Use of multiple metal layers instead of a single layer filling the trench reduces thermomechanical stress. Two of the metal layers in a trench can be used for the opposite phases of a differential clock signal. Alternatively, the opposite phases can be implemented by metal lines formed in adjacent trenches running in parallel.
In one embodiment, substrate 350 is monocrystalline silicon. Trenches 610 have a width W of about 0.1 μm to 10 μm and a depth D of 1 to 20 μm. The length of the trenches is determined by lines 150. Dielectric 620 is silicon dioxide, silicon nitride, or some other dielectric, possible having a low dielectric constant. Dielectric 620 can also contain air gaps. See U.S. Pat. No. 6,265,321 issued Jul. 24, 2001, entitled “AIR BRIDGE PROCESS FOR FORMING AIR GAPS”, incorporated herein by reference. An exemplary thickness of dielectric 620 is 0.1-5 μm. Dielectric 620 can be formed by thermal oxidation, chemical vapor deposition (CVD), or other techniques, known or to be invented. Dimensions other than those mentioned above are also possible. The width W and the other dimensions may vary from one line 150 to another in the same interposer.
Forming the lines 150 in the trenches can make the RC value of lines 150 more controllable. Consider the example of
In addition, the RC value can be reduced by increasing the trench depth D without increasing the lateral area occupied by the clock distribution network. When D is increased by some factor K, the resistance R of lines 150 is reduced by the same factor K. The capacitance component associated with the sidewalls of lines 150 increases by the same factor K, but the capacitance associated with the top and bottom surfaces of lines 150 does not change. Therefore, the total capacitance increase does not offset the reduced resistance.
In many integrated circuits fabricated with conventional techniques, clock distribution lines 150 cannot be formed in trenches in a semiconductor substrate because large portions of the substrate are taken by active areas. Moving the clock distribution networks, or parts of the clock distribution networks, to the interposer facilitates fabrication of lines 150 in the trenches.
In some embodiments, interposer 320 is absent. A part or all of clock distribution lines 150 is formed in trenches in substrate 340.
In
Other conductive lines, not necessarily parts of clock distribution networks, can be formed in trenches in the substrate. In
As shown in
Additional integrated circuits (e.g. memory, logic, RF circuits) or passive components (e.g. decoupling capacitors, filters) can be bonded to the bottom of interposer 320 between the interposer and the wiring substrate.
In
Some or all of the clock distribution circuitry may be located in circuit 920.
The areas between the adjacent circuits 310, and the areas between the circuits 310 and the interposer wafer 320W, are filled with a flowable material 1520 (
Interposer wafer 320W is thinned on the bottom to expose the contacts 323 (
Wafer 320W is diced into individual interposers 320 (
Each interposer 320 may have the same lateral dimensions as the corresponding circuit 310.
In
The process of
The invention is not limited to the particular processes, dimensions, or materials described above. Metal can be replaced with other conductive materials. Contact pads 323 can be connected to other circuitry with discrete wires. Other embodiments and variations are within the scope of the invention, as defined by the appended claims.
Claims
1. A method for operating an integrated circuit, the integrated circuit comprising:
- a trench in a semiconductor substrate;
- a conductive line in the trench to interconnect two laterally spaced nodes of circuitry;
- a first conductive layer located between the conductive line and surfaces of the trench;
- a first dielectric insulating the first conductive layer from the conductive line; and
- a second dielectric between the first conductive layer and surfaces of the trench;
- the method comprising holding the first conductive layer at a constant voltage while providing an alternating voltage on the conductive line when the integrated circuit is operated.
2. The method of claim 1 wherein the two nodes are located at two different ends of the conductive line.
3. The method of claim 1 wherein the trench is part of a trench network having conductive lines formed therein.
4. The method of claim 1 wherein the integrated circuit further comprises dielectric insulating the conductive line from the substrate.
5. The method of claim 1 wherein the first conductive layer is formed before the conductive line.
6. The method of claim 1 wherein the first conductive layer is present below a top surface of the conductive line.
7. The method of claim 1 wherein the first conductive layer is present below the conductive line above the trench's bottom surface.
8. The method of claim 1 wherein the conductive line is part of a clock distribution network.
9. The method of claim 1 wherein the integrated circuit further comprises a third dielectric overlying the conductive line, and a second conductive layer overlying the conductive line and insulated from the conductive line by the third dielectric, with at least a portion of the second conductive layer lying directly above at least a portion of the conductive line, wherein the second conductive layer physically contacts the first conductive layer so as to be at the same voltage as the first conductive layer.
10. The method of claim 9 wherein the second conductive layer crosses over the trench over the conductive line.
11. A manufacturing method comprising:
- forming a trench in a semiconductor substrate; and
- forming a conductive line in the trench to interconnect two laterally spaced nodes of circuitry;
- forming a first conductive layer located between the conductive line and surfaces of the trench;
- forming a first dielectric insulating the first conductive layer from the conductive line; and
- before forming the first conductive layer, forming a second dielectric between the first conductive layer and surfaces of the trench;
- wherein the trench is part of a tree network of trenches, and the conductive line is part of a tree network of conductive lines.
12. The method of claim 11 wherein the first conductive layer is formed before the conductive line.
13. The method of claim 11 wherein the first conductive layer is present below a top surface of the conductive line.
14. The method of claim 11 wherein the first conductive layer is present below the conductive line above the trench's bottom surface.
15. A manufacturing method comprising:
- forming a trench in a semiconductor substrate; and
- forming a conductive line in the trench to interconnect two laterally spaced nodes of circuitry;
- forming a first conductive layer located between the conductive line and surfaces of the trench;
- forming a first dielectric insulating the first conductive layer from the conductive line; and
- before forming the first conductive layer, forming a second dielectric between the first conductive layer and surfaces of the trench;
- wherein the trench is part of a trench network comprising a grid of trenches, and the conductive line is part of a grid network of conductive lines.
16. The method of claim 15 wherein the first conductive layer is formed before the conductive line.
17. The method of claim 15 wherein the first conductive layer is present below a top surface of the conductive line.
18. The method of claim 15 wherein the first conductive layer is present below the conductive line above the trench's bottom surface.
19. A method for operating an integrated circuit, the integrated circuit comprising:
- a trench in a semiconductor substrate;
- a conductive line in the trench;
- a first conductive layer located between the conductive line and surfaces of the trench;
- a first dielectric insulating the first conductive layer from the conductive line; and
- a second dielectric between the first conductive layer and surfaces of the trench;
- the method comprising holding the first conductive layer at a constant voltage while providing a clock signal on the conductive line when the integrated circuit is operated.
20. The method of claim 19 wherein the trench is part of a trench network having conductive lines formed therein which comprise said conductive line on which the clock signal is provided.
21. The method of claim 19 wherein the integrated circuit further comprises dielectric insulating the conductive line from the substrate.
22. The method of claim 19 wherein the first conductive layer is present below a top surface of the conductive line.
23. The method of claim 19 wherein the first conductive layer is present below the conductive line above the trench's bottom surface.
24. The method of claim 19 wherein the integrated circuit further comprises a third dielectric overlying the conductive line, and a second conductive layer overlying the conductive line and insulated from the conductive line by the third dielectric, wherein the second conductive layer crosses over the trench over the conductive line, wherein the second conductive layer physically contacts the first conductive layer so as to be at the same voltage as the first conductive layer.
Type: Application
Filed: Nov 14, 2006
Publication Date: Mar 29, 2007
Inventor: Oleg Siniaguine (San Carlos, CA)
Application Number: 11/559,805
International Classification: H01L 23/48 (20060101);