Three dimensional IC device and alignment methods of IC device substrates

[0001] 1. Field of the Invention

[0002] The invention relates in general to IC device substrates alignment and in particular to semiconductor substrates with alignment structures for three dimensional IC fabrication.

[0003] 2. Brief Discussion of the Related Art

[0004] The conventional process to align an IC device substrate is practiced by forming several alignment patterns on the front side of the substrate. Here, a semiconductor wafer W, as shown in FIG. 1a, is used as an example. The semiconductor wafer W comprises a silicon substrate S on its backside WB. An interconnection structure C is formed on the front side WF of the semiconductor wafer W for defining a plurality of IC features. Several alignment patterns M, such as cross patterns, are generally formed on the front side WF for alignment. In some specific fabrication processes, such as metallization or damascene processes, however, the alignment patterns M may be difficult to detect from the backside WB due to obstruction of opaque metallic material in the interconnection structure C. Additional processes for removing a part of the opaque material can be involved thereby improving visibility of the alignment patterns M, however, fabrication costs may potentially increase.

[0005] To detect and recognize the alignment patterns M from the backside WB when obstructed by opaque material, as shown in FIG. 1a, a traditional IR imaging apparatus D is applied. The IR imaging apparatus D can capture an image of each alignment pattern M from the backside WB for aligning the wafer W during processes, however, the accuracy and resolution are adversely limited due to IR wavelength substantially longer than 0.75 um. A resolution better than 0.1 um is usually required for the modern semiconductor process, such as the 90 nm technology and beyond.

[0006] In three dimensional IC fabrications, such as MEMs and SOI devices, two or more substrates W1 and W2 are bonded and aligned by alignment patterns M as shown in FIG. 1b. The front sides WF1 and WF2 of the substrates W1 and W2 are bonded face to face. Both front sides WF1 and WF2 define a plurality of IC features and comprise alignment patterns M thereon. It may be difficult, however, to detect the alignment patterns M from the backsides WB1 and WB2 of the two substrates W1 and W2 by IR detection during bonding. Hence, conventional wafer alignment is not convenient for three dimensional IC fabrications, and the accuracy can be adversely limited due to IR wavelength when opaque material obstructs the alignment patterns M on the front sides WF1 and WF2 of the substrates W1 and W2.

[0007] Three dimensional IC device and alignment methods of IC device substrates are provided. An exemplary embodiment of a first IC device substrate has a first front side for defining a plurality of first IC features, a first backside opposite the first front side, and a first alignment pattern formed on the first front side or the first backside. A second IC device substrate has a second front side for defining a plurality of second IC features, a second backside opposite the second front side, and a second alignment pattern formed on the second front side or the second backside. A first optical detector and a second optical detector are applied to detect the first and second alignment patterns, so as to align the first and second IC device substrates. Specifically, the first and second alignment patterns face toward the first and second optical detectors in opposite directions. The first and second optical detectors transmit position information of the first and second alignment patterns to a processor. Subsequently, the processor outputting an adjustment signal to control the movement of the IC device substrates, and the first and second IC device substrates are aligned with each other precisely according to the required accuracy.

[0008] An embodiment of a three dimensional IC device comprises a first IC device substrate and a second IC device substrate. The first IC device substrate comprises a first front side defining a plurality of first IC features, a first backside opposite the first front side, and a first alignment pattern formed on the first backside or the first front side. The second IC device substrate comprises a second front side for defining a plurality of second IC features, a second backside opposite the second front side, and a second alignment pattern formed on the second backside or the second front side. The first and second alignment patterns face outward with respect to the three dimensional IC device for alignment.

[0009] further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, arc given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

[0019] An embodiment of a three dimensional IC device with alignment patterns is illustrated in FIG. 2A. The three dimensional IC device T is fabricated by bonding a first IC device substrate W1 with a second IC device substrate W2 face to face, such as bonding two semiconductor wafers with IC device fabricated thereon. The first IC device substrate W1 comprises a first front side WF1 for defining a plurality of IC features and a first backside WB1 opposite to the first front side WF1. Similarly, the second IC device substrate W2 comprises a second front side WF2 for defining a plurality of IC features and a second backside WB2 opposite to the second front side WF2.

[0020] In FIG. 2A, several first alignment patterns M1 are formed on the first backside WB1, and several second alignment patterns M2 are formed on the second backside WB2 for alignment. An optical detector system P is provided for detecting the positions of the first and second alignment patterns M1 and M2. The optical detector system P comprises a processor and optical detectors P1 and P2 to detect the alignment patterns M1 and M2 from the first and second backsides WB1 and WB2, respectively. The optical detectors P1 and P2 transmit position information of alignment patterns M1 and M2 to the processor, and the optical detector system P subsequently outputs an adjustment signal to a moving stage (not shown), thereby appropriately adjusting the positions of the IC device substrates W1 and W2. According to the adjustment signal, the first and second IC device substrates W1 and W2 thus can be precisely aligned with each other during the bonding process.

[0021] Since the alignment patterns M1 and M2 are formed on the outside of the three dimensional IC device T, facing outward toward the optical detectors P1 and P2 in opposite directions, the optical detectors P1 and P2 can directly detect the alignment patterns M1 and M2 for precise alignment without obstruction, as shown in FIG. 2A. In some embodiments, a three dimensional IC device can also be constructed by bonding more than two semiconductor wafers or thin semiconductor substrates, as shown in FIG. 2B, wherein a dummy silicon substrate W3 is inserted between the IC device substrates W1 and W2.

[0022] Auxiliary alignment structures can be applied to the first and second IC device substrates W1 and W2 thereby facilitating precise alignment. As shown in FIG. 3, several notches N1 and N2 are correspondingly formed at the periphery of the first and second IC device substrates W1 and W2. The optical detector system P can output an adjustment signal by detecting not only the alignment patterns M1 and M2, but also the notches N1 and N2 from the first and second backsides WB1 and WB2 of the first and second IC device substrates W1 and W2, respectively. According to the adjustment signal, the positions of the first and second IC device substrates W1 and W2 can be appropriately aligned by aligning the alignment patterns M1, M2 and the notches N1 and N2.

[0023] In some embodiments, as shown in FIG. 4, the second IC device substrate W2 comprises several alignment patterns M2 on the second backsides WB2 and an inner alignment pattern M2′ on the second front side WF2 facing the first IC device substrate W1. To detect the inner alignment patterns M2′, a through hole H1, such as a laser drilled hole, is correspondingly disposed on the first IC device substrate W1. Hence, the optical detector P1 can directly detect the inner alignment patterns M2′ through the hole H1 without obstruction. In FIG. 4, the notches N1, the alignment patterns M1 on the first backside WB1 and the inner alignment pattern M2′ on the second front side WF2 are detected by the first detector P1, and the notches N2 and the alignment patterns M2 on the second backside WB2 are detected by the second detector P2, respectively. The optical detector system P can output an adjustment signal by detecting not only the alignment patterns M1, M2 and M2′ but also the notches N1 and N2. According to the adjustment signal, the positions of the first and second IC device substrates W1 and W2 can be appropriately aligned.

[0024] In some embodiments of three dimensional IC device fabrications, the first and second IC device substrates W1 and W2 are bonded back to back as shown in FIG. 5. To facilitate precise alignment, the alignment patterns M1 are formed on the first front side WF1 of the first IC device substrates W1, and correspondingly, the alignment patterns M2 are formed on the second front side WF2 of the second IC device substrates W2 for alignment. Since the alignment patterns M1 and M2 are formed on the outside of the three dimensional IC device T, facing outward toward the optical detectors P1 and P2 respectively, the optical detectors P1 and P2 can directly detect the alignment patterns M1 and M2 from the first front side WF1 and the second front side WF2 without obstruction.

[0025] In some embodiments, as shown in FIG. 6, the first front side WF1 of the first IC device substrate W1 is bonded to the second backside WB2 of the second IC device substrate W2 for three dimensional IC device fabrications. Specifically, the first alignment patterns M1 are formed on the first backside WB1 of the first IC device substrate W1, and correspondingly, the second alignment patterns M2 are formed on the second front side WF2 of the second IC device substrate W2. Since the alignment patterns M1 and M2 are disposed on the outside of the three dimensional IC device T, facing outward toward the optical detectors P1 and P2 respectively, the optical detectors P1 and P2 can directly detect the alignment patterns M1 and M2 without obstruction.

[0026] Since the alignment patterns are formed on the backsides of the IC device substrates, available areas for IC features on the front sides increase. Moreover, as the alignment patterns M1 and M2 are formed on the outside of the three dimensional IC device T, facing outward toward the optical detectors P1 and P2 respectively, the optical detectors P1 and P2 can directly detect the alignment patterns M1 and M2 for precise alignment without obstruction.

[0027] Instead of utilizing a conventional IR apparatus, visible light can be employed by the optical detector system P to directly detect the alignment patterns, thereby increasing the alignment accuracy and simplifying the bonding process. In some embodiments, the IC device substrates such as semiconductor wafers, may comprise alignment patterns on both the front side and the backside for precise alignment during the bonding process. In some embodiments, detection of alignment patterns, notches or laser drilled holes can be widely applied in two or more wafers bonding processes for three dimensional IC fabrication.

[0028] While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited therto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.