Method to fill the gap between coupled wafers

A three-dimensional integrated circuit formed by applying a material to fill a gap between coupled wafers and slicing the coupled wafers into dice. A method for filling a gap between coupled wafers. Various embodiments include at least one of spinning a coupled wafer pair, drilling a hole into one of the coupled wafers, and using a vacuum to aid in the dispersion of the material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of three dimensional integrated circuits and more specifically, to a method for forming a coupled wafer pair that prevents edge chipping.

2. Discussion of Related Art

In the manufacture of microelectronic devices, packaging density is becoming increasingly important. Stacking of the dice of a multi-processor microelectronic device is one way to improve the packaging density of a microelectronic device. Stacked microelectronic devices are typically formed by electrically connecting two or more wafers through interconnect layers, and then dicing the stacked wafers into individual stacked devices.

FIGS. 1A–1Dillustrate one method for forming a coupled wafer pair. As shown inFIG. 1A, a first wafer101and a second wafer102are provided. Typically, these wafers are silicon polycrystalline wafers which have a plurality of die that are connected together. Typically, each die is an integrated circuit. Next, as shown inFIG. 1B, an interconnect layer103is formed on the first wafer101and on the second wafer102. The interconnect layer103is typically copper that is formed above a barrier material such as tantalum and a dielectric layer such as silicon dioxide or carbon dioxide. Typically, there are hundreds of copper members in the interconnect layer103.

Next, as shown inFIG. 1C, the first wafer101and its associated interconnect layer103is flipped around and positioned over the second wafer102and its interconnect layer103. Next, inFIG. 1D, a coupled wafer pair100is formed by aligning the interconnect layers103of the first wafer101and the second wafer102and bringing the first wafer101and the second wafer102together. Typically a thermo-compression process is used to couple the first wafer101with the second wafer102.

Typically, as shown inFIG. 1D, thinning107of one of the stacked wafers is performed by use of one or more mechanical and/or chemical processes such as a polishing process for example. These processes may cause mechanical stresses in unsupported portions of the wafer being thinned. As shown in an outer gap106, an area formed by the product of a depth105and a height104is unsupported by the interconnect layer103. Furthermore, a center gap108between individual members of the interconnect layer103may also be unsupported.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Embodiments of the present invention are three dimensional integrated circuit devices having a gap fill and their methods of formation. In the following description numerous specific details have been set forth in order to provide a thorough understanding of the present invention. In other instances, well-known semiconductor fabrication processes and techniques have not been set forth in particular detail in order to avoid unnecessarily obscuring the present invention.

Embodiments of the present invention are a method for applying a material on a coupled wafer pair in order to fill a gap between wafers of the coupled wafer pair. Embodiments of the invention include applying a material through a hole within one of the wafers of the coupled wafer pair and creating a pressure differential to help the material flow between the coupled wafers. Embodiments of the invention include spinning a coupled wafer pair, applying a material on the top of or directly in a gap between the coupled wafer pair, and using a vacuum to create a pressure differential between the coupled wafers. The advantages of the present invention include protecting gaps between a coupled wafer pair from chipping, cracking, corroding, or other damage which may result in the wafer and/or individual stacked devices being unusable.

An example of a method for applying a material on top of a first wafer201of a coupled wafer pair200in accordance with an embodiment of the present invention is illustrated inFIGS. 2A–2B. In one embodiment of the present invention, the coupled wafer pair is formed similarly as described with reference toFIGS. 1A–1D. In one embodiment of the present invention, there are more than two wafers that are coupled together. The coupled wafer pair200is placed over a chuck210having a plurality of vacuum ports211. In one embodiment of the present invention, the vacuum ports211generate a vacuum to secure the coupled wafer pair200to the chuck210.

Next, the chuck210and the coupled wafer pair200are spun around at a first spin speed. In one embodiment of the present invention, the first spin speed is approximately 500–3,000 rotations per minute. In one embodiment of the present invention, the first spin speed is performed at a rate of at least 1000 rpm for approximately 20 seconds if the first wafer201and a second wafer202are 300 mm in diameter.

Next, as shown inFIG. 2B, an applicator209applies a material208on top of the coupled wafer200. In one embodiment of the present invention, the material208is applied at the center over the top of the wafer201. In another embodiment of the present invention, the material208is applied anywhere on top of the wafer201. In one embodiment the applicator209is a syringe. In another embodiment of the present invention, the applicator209is a dispenser nozzle. In one embodiment of the present invention, an applicator219, instead of the applicator209, applies the material208on the top edge of the coupled wafer200. In one embodiment of the present invention, the material208covers the bevel of the coupled wafer pair200. In one embodiment of the present invention, the material208covers the edge bead removal region of the coupled wafer pair. In one embodiment of the present invention, the material208covers a depth necessary to prevent the coupled wafer pair200from cracking when it is later grinded. In one embodiment of the present invention, the material208covers a depth necessary to prevent an interconnect layer203from corroding.

In one embodiment of the present invention, a low viscosity polymer is preferred for the material208when a height204between the coupled wafers201and202is less than 1 micron in height. In this instance, a low viscosity polymer is preferred in order to maximize the ability of the material208to fill the outer gap106, formed by the product of the height204and a depth205. In one embodiment of the present invention, the gap between the coupled wafers201and202is at least 250 microns in depth and at most 300 microns in the height204. In one embodiment of the present invention, a high viscosity polymer material is preferred for the material208. A high viscosity polymer is preferred when the height204between the coupled wafers201and202is greater than 5 microns. In this instance, a high viscosity polymer is preferred in order to prevent the material208from spinning away and off of the coupled wafer pair200. In one embodiment of the present invention, when the height204between the coupled wafers201and202is between 1 micron and 5 microns, a low viscosity polymer or a high viscosity polymer can be used.

In one embodiment of the present invention, the high viscosity and low viscosity polymer material is selected from a group consisting of SiLK-J, polyimide, spin-on glass, benzocyclobutene, polynorbornene, and polyarylenes. In one embodiment of the present invention, the material208has a viscosity of less than 1,000 centipoise when the height204is less than 1 micron. In another embodiment when the height204is greater than 5 microns, the material208has a viscosity of greater than 1,000 centipoise. In one embodiment of the present invention, the coupled wafer pair200are coupled wafers that are coupled through the interconnect layer203.

Next, the coupled wafer200is spun at a second spin speed after the applicator209finishes dispensing the material208. In one embodiment of the present invention, this second spin speed is approximately 0–50 rotations per minute. Because the second spin speed is so much less than the first spin speed, the material208is wicked around the edge of the first wafer201as a result of capillary forces. The material208then fills the outer gap106, formed by the product of the depth205and the height204in the coupled wafer pair200. In one embodiment of the present invention, the second spin speed is performed at a deceleration rate of approximately 5,000–10,000 rotations per minute.

In one embodiment of the present invention, the material208is cured (e.g., the material208is cured to harden it after it is applied). For instance, the material208may be cured using a polymerization technique. Alternatively, the material208may be cured using thermal curing or UV curing. In one embodiment of the present invention, curing holds the coupled wafer pair200between 75–150 C for 1 hour in air or nitrogen for epoxy type materials. In another embodiment of the present invention, curing holds the coupled wafer pair200between 200–400 C for 1 hour in nitrogen for spin-on polymer materials. In one embodiment of the present invention, curing is performed by epoxy materials that harden without heat (e.g., cross-linking agent is added to a polymer).

In one embodiment of the present invention, the coupled wafer200is spun at a third spin speed to clear the excessive material208. In one embodiment of the present invention, the third spin speed is the same as the first spin speed. In one embodiment of the present invention, the coupled wafer pair200is ground down to a thickness of approximately 10–50 microns after the material208is applied.

FIGS. 3A and 3Billustrate a method for applying the material208directly in the outer gap106between a coupled wafer pair300, in accordance with an embodiment of the present invention. The coupled wafer300is placed over the chuck210having a plurality of the vacuum ports211. In one embodiment of the present invention, the vacuum ports211generate the vacuum to bring the coupled wafer pair300down to the chuck210.

Next, the chuck210and the coupled wafer pair300are spun around at a first spin speed. In one embodiment of the present invention, the first spin speed is approximately 500–3,000 rotations per minute.

Next, as shown inFIG. 3B, an applicator309applies the material208directly into the outer gap106in the coupled wafer pair300. Applying the material208directly between the outer gap106prevents later cleanup of material on the top of a wafer, as required inFIG. 2. Furthermore, applying the material208directly between the outer gap106minimizes the quantity of the material208that must be used because material is not wasted on the top of a wafer.

In one embodiment of the present invention, the applicator309applies the material208at a 90 degree angle to the coupled wafer pair300. In one embodiment of the present invention, the applicator309applies a material horizontally, directly into the outer gap106between the coupled wafer pair300. In one embodiment of the present invention, the applicator309is brought into the center gap108before applying the material208. In one embodiment of the present invention, the applicator309applies material at an angle less than 90 degrees to the coupled wafer pair300. The coupled wafer pair300is spun on the chuck210while the applicator309applies material directly into the outer gap106. This causes the entire outer gap106to be filled by the material208. In one embodiment of the present invention, the applicator309is a syringe. In another embodiment of the present invention, the applicator309is a dispenser nozzle. In one embodiment of the present invention, the material208is cured after injection and prior to cutting and/or grinding.

In one embodiment of the present invention, a low viscosity polymer material is preferred for the material208. A low viscosity polymer is preferred when the height204between the coupled wafers201and202is less than 1 micron in height. In this instance, a low viscosity polymer is preferred in order to maximize the ability of the material208to fill the outer gap106formed by the product of the height204and the depth205. In another embodiment of the present invention, a high viscosity polymer material is preferred for the material208. A high viscosity polymer is preferred when the height204between the coupled wafers201and202is greater than 5 microns. In this instance, a high viscosity polymer is preferred in order to prevent the material208from spinning away and off of the coupled wafer pair300because of its greater thickness. In one embodiment of the present invention, when the height204between the coupled wafers201and202is between 1 micron and 5 microns, a low viscosity polymer or a high viscosity polymer can be used. Other embodiments of the present invention as shown inFIGS. 3A and 3Bare similar to those described in detail with reference toFIGS. 2A–2B.

FIGS. 4A and 4Billustrate a method for applying the material208through a hole406in a first wafer401of a coupled wafer pair400, in accordance with an embodiment of the present invention. In one embodiment of the present invention, the hole406is created at the center of the first wafer401of the coupled wafer pair400. In one embodiment of the present invention, the hole406is created before the first wafer401is coupled to the second wafer202. In one embodiment of the present invention, the hole406is created using a hollow cord drill bit. For instance, a hollow cord drill bit ranging in size from approximately 1/16 to ¼ inches to make approximately a ¼ to 1/16 inch hole in diameter. In one embodiment of the present invention, the hole406is created using laser pulsing. For instance, the laser pulsing can last 5 to 15 seconds. In one embodiment of the present invention, the hole406is created using an ion beam.

In one embodiment of the present invention, the hole is the size of a dummified region on the coupled wafer pair400. The dummified region does not contain any integrated circuits but only contains blank die. The hole406should preferably be as small as possible, in one embodiment of the present invention, in order to maximize die yield on the coupled wafer pair400. By limiting the hole406to a dummified region on the first wafer401, die yield impact is not impacted significantly. In one embodiment of the present invention, the hole406is approximately 1 millimeter or larger in order to maximize the amount of the material208that passes through the hole406and the coupled wafer pair400. In one embodiment of the present invention, the hole may be created on the first wafer401and on the second wafer202. In one embodiment of the present invention, multiple holes may be created on various locations of the first wafer401. In one embodiment of the present invention, the hole406may be created on the second wafer202.

Next, the coupled wafer pair400is placed on the chuck210. The coupled wafer pair400is held on the chuck210through the vacuum211that is applied on the coupled wafer pair400to hold the coupled wafer pair400in place. UnlikeFIG. 2BandFIG. 3B, the coupled wafer pair400and the chuck210are not spun in one embodiment of the present invention, as illustrated inFIG. 4B.

Next, the material208is applied by an applicator409through the hole406in the first wafer401. In one embodiment of the present invention, the applicator409is the same applicator as the applicator209described with reference toFIG. 2B. By applying the material208directly into the center of the coupled wafer pair400through the hole406, the center gap108between members of the interconnect layer203are supported. In addition, by applying the material208directly into the center of the coupled wafer pair400, the interconnect layer203does not corrode and individual devices that are cut from the coupled wafer pair400are better supported. In one embodiment of the present invention, the material208may also flow to the outer gap106in addition to the center gap108of the coupled wafer pair400. In one embodiment of the present invention, the applicator409is a syringe. In another embodiment of the present invention, the applicator409is a dispenser nozzle. In one embodiment of the present invention, the material208is cured after injection and prior to cutting and/or grinding.

In one embodiment of the present invention, when the height204between the coupled wafers401and202is between 1 micron and 5 microns, a low viscosity polymer or a high viscosity polymer can be used. In one embodiment of the present invention, the high viscosity and low viscosity polymer material is selected from a group consisting of SiLK-J, polyimide, spin-on glass, benzocyclobutene, polynorbornene, and polyarylenes. In one embodiment of the present invention, the material208has a viscosity of less than 1,000 centipoise when the height204is less than 1 micron. In another embodiment when the height204is greater than 5 microns, the material208has a viscosity of greater than 1,000 centipoise. In one embodiment of the present invention, the gap between the coupled wafers401and202is at least 250 microns in depth and at most 300 microns in the height204. In one embodiment of the present invention, the coupled wafer pair400is ground down to a thickness of approximately 10–50 microns after the material208is applied. Other embodiments of the present invention as shown inFIGS. 4A and 4Bare similar to those described with reference toFIGS. 2A and 2B.

FIGS. 5A and 5Billustrate a method of applying the material208through the hole406in the first wafer401of a coupled wafer pair500and spinning the coupled wafer pair500, in accordance with an embodiment of the present invention.FIGS. 5A and 5Bshow the coupled wafer pair500that is similar to the coupled wafer pair inFIGS. 4A and 4B, except that the coupled wafer pair500is spun on the chuck210. Spinning the coupled wafer pair500on the chuck210assists the material208to flow to the edge of the first wafer401in addition to passing through the hole406into the center gap108of the coupled wafer pair500. As a result, a larger portion of the outer gap106is filled by the material208. In one embodiment of the invention, the outer gap106is an area formed by the product of the height204and the depth205. In one embodiment of the invention, the material208is a low viscosity polymer or a high viscosity polymer depending on the height204as described with reference toFIGS. 2A–2B. In one embodiment of the present invention, the material208is cured after injection and prior to cutting and/or grinding. Other embodiments of the present invention as shown inFIGS. 5A and 5Bare similar to those described with reference toFIGS. 4A and 4B.

FIG. 6illustrates a process flow for creating a pressure differential to assist a material in filling a gap between a coupled wafer pair having at least one hole. In601, the hole406is created at the center of the first wafer401, as described with reference toFIGS. 4A–4B. In one embodiment of the present invention, the hole406can be anywhere on top of the first wafer401. In one embodiment of the present invention, the hole406can be on the second wafer202. In one embodiment of the present invention, the hole406can be anywhere on the first wafer401and/or the second wafer202. In one embodiment of the present invention, the hole406is created at the center of the first wafer401of coupled wafer pair. In one embodiment of the present invention, the hole406is created before the first wafer401is coupled to the second wafer202. In one embodiment of the present invention, the hole406is created using a hollow cord drill bit. For instance, a hollow cord drill bit ranging in size from approximately 1/16 to ¼ inches to make approximately a ¼ to 1/16 inch hole in diameter. In one embodiment of the invention, embodiments of the hole406are the same as that described with reference toFIGS. 4A–4B.

Next, in602, a pressure differential is created between the hole406in at least one of the coupled wafers and the center gap108and the outer gap106between the coupled wafer pair. In one embodiment of the present invention, a vacuum creates a pressure differential between the hole406and the outer gap106. In one embodiment of the present invention, a vacuum is applied directly into the hole406and the material208is applied at the gap. In one embodiment of the present invention, a vacuum is applied directly into a gap between the coupled wafer pair400and the material208is applied at the hole406. This embodiment switches the place of the vacuum and the applicator and may provide preferred characteristics for the diffusion of the material208in some embodiments of the present invention. In one embodiment of the present invention, a positive pressure is applied at the outer gap106in addition to an applicator509to increase the diffusion of the material208toward the center gap108of coupled wafer pair.

In603, the material208fills the outer gap106and the center gap108by spreading through the coupled wafers because of the pressure differential. In one embodiment of the present invention, the material208is applied similarly as described with reference toFIGS. 3A–3B. In one embodiment of the present invention, the material208is drawn toward the hole406through the application of a vacuum as described with reference to602. In one embodiment of the present invention, a high viscosity or a low viscosity polymer is used for the material208depending on the height204, as described with reference toFIGS. 3A–3B. In one embodiment of the invention, a pressure differential is created by a vacuum applied at the hole406and a positive pressure applied at the outer gap106. In one embodiment of the present invention, the material208is cured after injection and prior to cutting and/or grinding.

FIGS. 7A and 7Billustrate a method for applying the material208directly in the outer gap106between a coupled wafer pair700and applying a vacuum750through the hole406in a first wafer701of the coupled wafer pair700, in accordance with an embodiment of the present invention. InFIG. 7B, the vacuum750is applied to the hole406of the coupled wafer pair700. This vacuum750creates a pressure differential between the center gap108of the coupled wafer pair700and the edge of the coupled wafer pair where an applicator709is applied. The applicator709applies the material208directly in between a gap of the coupled wafer pair700. The chuck210spins the coupled wafer pair700prior to applying the material208as described with reference toFIGS. 2A–2B.

In addition, various embodiments of the present invention can be used to create the hole406as described with reference toFIGS. 4A–4B. In addition, the vacuum750is applied during the application of the material208. As such, the material208moves from the outer gap106toward the center gap108of the coupled wafer pair700because of the pressure differential created by the vacuum750. In one embodiment of the present invention, the vacuum750is applied directly into a gap between the coupled wafer pair700and the material208is applied at the hole406. This embodiment switches the place of the vacuum750and the applicator709and may provide preferred characteristics for the diffusion of the material208in some embodiments of the present invention. In one embodiment of the present invention, a positive pressure is applied at the outer gap106in addition to the applicator709to increase the diffusion of the material208toward the center gap108of the coupled wafer pair700. In one embodiment of the present invention, the material208is cured after injection and prior to cutting and/or grinding. Other embodiments of the present invention as shown inFIGS. 7A and 7Bare similar to those described with reference toFIGS. 2A–2B,FIGS. 4A–4B, andFIGS. 5A–5B.

FIGS. 8A–8Billustrates a method of applying the material208through the hole406in a first wafer801of a coupled wafer pair800, spinning the coupled wafer pair800and applying a vacuum850directly in the outer gap106between the coupled wafer pair800, in accordance with an embodiment of the present invention.FIG. 8Bincludes the coupled wafer800, which is similar to the coupled wafer700as described with reference to FIGS.7A–7B. However, an applicator809is applied through the hole406on the coupled wafer800, and the vacuum850is applied directly in between the outer gap106of the coupled wafer pair800. As a result, the material208is pulled toward the outer gap106by a pressure differential between the hole406and the outer gap106of the coupled wafer800. In one embodiment of the present invention, the material208is cured after injection and prior to cutting and/or grinding. Other embodiments of the present invention as shown inFIGS. 8A and 8Bare similar to those described with reference toFIGS. 2A–2B,FIGS. 4A–4B,FIGS. 5A–5B, andFIGS. 7A–7B.

FIGS. 9A–9Billustrates a method for applying the material208and a positive pressure950through the hole406in a first wafer901of a coupled wafer pair900, spinning the coupled wafer pair900and applying a vacuum960directly in the outer gap106between the coupled wafer pair900, in accordance with an embodiment of the present invention. The coupled wafer900is similar to the coupled wafer800, as described with reference toFIGS. 8A–8B. The only difference between the coupled wafer900and the coupled wafer pair800is that the positive pressure950is applied in addition to the material208through the hole406in the coupled wafer pair900. This positive pressure950is applied in addition to the vacuum960that is applied directly in between the outer gap106of the coupled wafer pair900. By having the positive pressure950in addition to the vacuum960at the edge, a larger pressure differential is created and the material208is better able to reach the outer gap106of the coupled wafer pair900. In one embodiment of the present invention, an applicator909is designed specifically for use with the positive pressure950. In one embodiment of the present invention, the material208is cured after injection and prior to cutting and/or grinding.

FIG. 10illustrates a top view of the coupled wafer pair900having a plurality of dice1001and a gap fill, in accordance with an embodiment of the present invention. In one embodiment of the present invention, top view as shown inFIG. 10is the first wafer901of the coupled wafer pair900. In one embodiment of the present invention, coupled wafer pair contains a plurality of the dice1001having integrated circuits that are sliced and diced from the coupled wafer pair900into single stack chip die.FIG. 10also illustrates the hole406in the coupled wafer pair900that fills the center gap108with the material208. In on embodiment of the invention, the material208also fills the outer gap106between the coupled wafer pair900as shown inFIG. 9B. In one embodiment of the present invention, the material208is applied into a gap between the coupled wafer pair900as described with reference toFIGS. 2A–9B. In one embodiment of the present invention, the material208is cured after injection and prior to cutting and/or grinding.

FIG. 11illustrates a die1001that is cut from the coupled waferpair900having a gap fill, in accordance with an embodiment of the present invention. InFIG. 11, the die1001is one of a plurality of dice as illustrated withFIG. 10. In one embodiment of the present invention, the die1001is a single stack chip die. InFIG. 11, a substrate1101is connected to a substrate1102through in the interconnect layer203. The material208fills the region having gaps in between the substrates1101and1102. In one embodiment of the present invention, a copper vias1103in the substrate1102connect the die1001to a solder bumps1104. In one embodiment of the present invention, the solder bumps1104connect the die1001to a packaging layer of an integrated circuit. In one embodiment of the present invention, the die1001is a three-dimensional integrated circuit device having a first integrated circuit and a second integrated circuit. In one embodiment of the present invention, the die1001is a three-dimensional integrated circuit device having a first integrated circuit and a second integrated circuit that are parts of a single microprocessor. In one embodiment of the present invention, the die1001is a stacked chipset. In one embodiment of the present invention, a material203is polymer foam. In one embodiment of the present invention, the material208is cured after injection and prior to cutting and/or grinding. In one embodiment of the present invention, the material203is similar to the material as described with reference toFIGS. 2A–2B.

It should be noted that the embodiments disclosed herein may be applied to the formation of any stacked microelectronic device. Certain features of the embodiments of the claimed subject matter have been illustrated as described herein, however, may modifications, substitutions, changes and equivalents will be evident to those skilled in the art. Additionally, while several functional blocks and relationships have been described in detail, it is contemplated by those of skill in the art that several of the operations may be performed without the use of the others, or additional functions or relationships between operations may be established and still remain in accordance with the claimed subject matter. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the claimed subject matter.