Patent Application
20100122456
This invention relates generally to integrated circuit manufacturing processes, and more particularly to apparatuses and methods for bonding semiconductor dies onto wafers.
With the evolving of semiconductor technologies, semiconductor dies are becoming increasingly smaller. However, more functions need to be integrated into the semiconductor dies. Accordingly, the semiconductor dies need to have increasingly greater numbers of I/O pads packed into smaller areas, and the density of the I/O pads rises quickly. As a result, the packaging of the semiconductor dies becomes more difficult, which causes the yield to be adversely affected.
Packaging technologies can be divided into two categories. One category is typically referred to as a wafer level package (WLP), wherein dies on a wafer are packaged before they are sawed. The WLP technology has some advantages, such as a greater throughput and a lower cost. Further, less under-fill and/or molding compound are needed. However, the WLP suffers from drawbacks. As aforementioned, the sizes of the dies are becoming increasingly smaller, and the conventional WLP can only be fan-in type packages, in which the I/O pads of each die are limited to a region directly over the surface of the respective die. With the limited areas of the dies, the number of the I/O pads is limited due to the limitation of the pitch of the I/O pads. If the pitch of the pads is to be decreased to incorporate more I/O pads on a die, solder bridges may occur. Additionally, under the fixed-ball-size requirement, solder balls must have a certain size, which in turn limits the number of solder balls that can be packed on the surface of a die.
In the other category of packaging, dies are sawed from wafers before they are packaged onto other wafers, and only “known-good-dies” are packaged. An advantageous feature of this packaging technology is the possibility of forming fan-out chip packages, which means the I/O pads on a die can be redistributed to a greater area than the die, and hence the number of I/O pads packed on the surfaces of the dies can be increased.
The bonding of dies to wafers includes dielectric-to-dielectric bonding (also referred to fusion bonding) and copper-to-copper bonding.
The similar situation may also occur with copper-to-copper bonding. Referring to
Conventionally, the above-discussed problems were solved by performing a post-contact leveling after the top die is bonded onto the bottom wafer. However, this incurs additional process steps and longer process time, and results in the reduction in throughput. Accordingly, what is needed in the art is a bonding system and methods for the bonding with a high throughput.
In accordance with one aspect of the present invention, a method for bonding includes providing a first die and a second die; scanning at least one of the first die and the second die to determine thickness variations of the at least one of the first die and the second die; placing the second die facing the first die with a first surface of the first die facing a second surface of the second die; aligning the first surface and the second surface parallel to each other using the thickness variations; and bonding the second die onto the first die. The step of aligning the first surface and the second surface includes tilting one of the first die and the second die.
In accordance with another aspect of the present invention, a method for bonding dies includes providing a bottom wafer including first dies; providing second dies; scanning the bottom wafer to determine first thickness variations of the first dies; placing the second dies in a die tray; scanning the second dies in the die tray to determine second thickness variations of the second dies; picking up one of the second dies from the die tray; and moving the one of the second dies to over one of the first dies. The method further includes tilting at least one of the bottom wafer and the one of the second dies, so that the first surface of the one of the first dies is parallel to a second surface of the one of the second dies, wherein the first surface faces the second surface. The method further includes, after the first surface and the second surface are parallel to each other, bonding the one of the second dies to the one of the first dies.
In accordance with yet another aspect of the present invention, a method for bonding dies includes providing a first die and a second die; placing the first die on a stage; moving the second die to face the first die; tilting at least one of the first die and the second die to make a first surface of the first die facing and parallel to a second surface of the second die; moving the second die toward the first die while keeping the first surface of the first die parallel to the second surface of the second die; and bonding the second die to the first die.
In accordance with yet another aspect of the present invention, an apparatus for bonding dies includes a scanning system configured to scan thickness variations of a die; a control unit connected to the scanning system, the control unit being configured to collect the thickness variations; a bond head connected to the control unit; and a stage for mounting the die thereon. The control unit is configured to control at least one of the bond head and the stage to tilt.
In accordance with yet another aspect of the present invention, an apparatus for bonding a first die with a second die includes a control unit; a stage for mounting a wafer thereon, wherein the wafer includes the first die; and a bond head configured to pick up the second die. The control unit is connected to and configured to tilt at least one of the bond head and the stage to make a first surface of the first die parallel to a second surface of the second die.
The advantageous features of the present invention include greater throughput and improved reliability in the bonding of dies onto dies or wafers.
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:
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.
A novel integrated aligning and bonding system and the methods for the bonding are provided. Throughout the various views and illustrative embodiments of the present invention, like reference numbers are used to designate like elements.
In
Since the thickness variation data of top die 36 and bottom die 34 are known to control unit 22, control unit 22 may compensate for the thickness variations in top die 36 and bottom die 34. In an embodiment, control unit 22 controls bond head 28 to slightly tilt by a small angle α, so that surface 40 of top die 36 is aligned parallel to surface 42 of bottom die 34. In alternative embodiments, stage 24, instead of bond head 28, is tilted by an angle β equal to angle α. In yet other embodiments, both stage 24 and bond head 28 are tilted to make surfaces 40 and 42 parallel to each other.
Next, bond head 28 is moved down (with surfaces 40 and 42 parallel to each other); so that surfaces 40 of top die 36 touch surface 42 of bottom die 34. It is appreciated that the tilting of stage 24 and/or bond head 28 may be performed any time before top die 36 touches bottom die 34. For example, the tilting of bond head 28 may be performed simultaneously with the downward motion of bond head 28. Due to the alignment action, all sides and corners of surfaces 40 and 42 make contact substantially simultaneously. For the bonding, a force is applied to press top die 36 and bottom die 34 against each other. With the non-uniform topology compensated for, the force applied to all sides and corners of top die 36 is substantially uniform. During the bonding, the temperature of bottom wafer 32 and/or top die 36 may be increased to desirable temperatures. The resulting structure after bonding is shown in
In the above-discussed embodiments, die-to-wafer bonding is discussed. In alternative embodiments, die-to-die bonding may be performed. The bonding process is essentially the same as discussed in the preceding paragraphs, except bottom dies may also be scanned when placed in a corresponding die tray. In yet other embodiments, wafer-to-wafer bonding is performed, in which both the bottom wafer and the top wafer are pre-scanned, and the topology of the bottom and top wafers are used for the alignment purpose.
The embodiments of the present invention have several advantageous features. With the thickness variation compensated for, the cold joint problem is at least reduced, and possibly substantially eliminated. By determining the surface topography of the dies and/or wafers to be bonded, the leveling and bonding may be performed at the same time, and hence there is no need to perform an additional leveling after the bonding process. The throughput is thus improved.
Although the present invention and its 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. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and 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.
