Patent Application
20220077231
The present invention relates to the field of semiconductor technology and, in particular, to a structure and method for integrating a crystal resonator with a control circuit.
A crystal resonator is a device operating on the basis of inverse piezoelectricity of a piezoelectric crystal. As key components of crystal oscillators and filters, crystal resonators have been widely used to create high-frequency electrical signals for performing precise timing, frequency referencing, filtering and other frequency control functions that are necessary for measurement and signal processing systems.
The continuous development of semiconductor technology and increasing popularity of integrated circuits has brought about a trend toward miniaturization of various semiconductor components. However, existing crystal resonators are not only hard to be integrated with other semiconductor components and bulky themselves.
For example, common existing crystal resonators include surface-mount ones, in which a base is bonded with a metal solder (or an adhesive) to a cover to form a hermetic chamber in which a piezoelectric vibrator is housed. In addition, electrodes for the piezoelectric vibrator are electrically connected to an associated circuit via solder pads or wires. Further shrinkage of such crystal resonators is difficult, and their electrical connection to the associated integrated circuit by soldering or gluing additionally hinders the crystal resonators' miniaturization.
It is an objective of the present invention to provide a method for integrating a crystal resonator with a control circuit, which overcomes the above described problems with conventional crystal resonators, i.e., a bulky size and difficult integration.
According to the present invention, the above objective is attained by a method for integrating a crystal resonator with a control circuit, including:
providing a device wafer having the control circuit formed therein;
forming, in the device wafer, a lower cavity with an opening at a back side of the device wafer;
forming a piezoelectric vibrator including a top electrode, a piezoelectric crystal and a bottom electrode on the back side of the device wafer in alignment with the lower cavity and forming a first connecting structure electrically connecting the top and bottom electrodes of the piezoelectric vibrator to the control circuit;
forming a cap layer over the back side of the device wafer, which hoods the piezoelectric vibrator and delimits an upper cavity of the crystal resonator together with the piezoelectric vibrator and the device wafer; and
bonding a semiconductor die to a front side of the device wafer and forming a second connecting structure electrically connecting the semiconductor die to the control circuit.
It is another objective of the present invention to provide a structure for integrating a crystal resonator with a control circuit, including:
a device wafer in which the control circuit and a lower cavity are formed, the lower cavity having an opening at a back side of the device wafer;
a piezoelectric vibrator including a bottom electrode, a piezoelectric crystal and a top electrode, the piezoelectric vibrator formed on the back side of the device wafer in alignment with the lower cavity;
a first connecting structure formed on the device wafer, the first connecting structure electrically connecting the top and bottom electrodes of the piezoelectric vibrator to the control circuit;
a cap layer formed on the back side of the device wafer, the cap layer hooding the piezoelectric vibrator, the cap layer delimiting an upper cavity together with the piezoelectric vibrator and the device wafer;
a semiconductor die bonded to a front side of the device wafer; and
a second connecting structure electrically connecting the semiconductor die to the control circuit.
In the proposed method, planar fabrication processes are utilized to form the lower cavity in the device wafer containing the control circuit and expose the lower cavity at the back side of the device wafer. As a result, the piezoelectric vibrator is allowed to be formed on the same back side, achieving integration of the control circuit and the crystal resonator on the same device wafer. Moreover, the semiconductor die can be bonded to the same device wafer on the side of the device wafer opposing the piezoelectric vibrator. This can additionally increase a degree of integration of the crystal resonator and enhance its performance by allowing on-chip modulation of its parameters (e.g., for correcting raw deviations such as temperature and frequency drifts).
Therefore, compared with traditional crystal resonators (e.g., surface-mount ones), in addition to being able to integrate with other semiconductor components with a higher degree of integration, the proposed crystal resonator fabricated using the proposed method is more compact, miniaturized in size, less costly and less power-consuming.
In these figures,
100—device wafer; AA—device area; 100U—front side; 100D—back side; 100A—substrate wafer; 100B—dielectric layer; 101—base layer; 102—buried oxide layer; 103—top silicon layer; 110—control circuit; 111—first circuit; 111a—first interconnect; 111b—third interconnect; 112—second circuit; 112a—second interconnect; 112b—fourth interconnect; 120—lower cavity; 211—first connecting wire; 212—second connecting wire; 221—first conductive plug; 222—second conductive plug; 300—planarized layer; 400—support wafer; 500—piezoelectric vibrator; 510—bottom electrode; 520—piezoelectric crystal; 530—top electrode; 600—plastic encapsulation layer; 610—third conductive plug; 700—upper cavity; 710—sacrificial layer; 720—cap layer; 720a—opening; 730—closure plug; 810—plastic encapsulation layer; 820—cap substrate; 900—semiconductor die; 910—first contact pad; 920—second contact pad.
The core idea of the present invention is to provide a structure and method for integrating a crystal resonator with a control circuit, in which planar fabrication processes are utilized to integrate a piezoelectric vibrator on a device wafer where the control circuit is formed. This, on the one hand, results in a size reduction of the crystal resonator and, on the other hand, allows integration of the crystal resonator with other semiconductor components with an increased degree of integration.
Specific embodiments of the proposed structure and method will be described below in greater detail with reference to the accompanying drawings. Features and advantages of the invention will be more apparent from the following description. Note that the accompanying drawings are provided in a very simplified form not necessarily drawn to exact scale and for the only purpose of helping to explain the disclosed embodiments in a more convenient and clearer way.
In step S100, with reference to
In this embodiment, the device wafer 100 has a front side 100U and a back side 100D opposite to the front side, and at least some interconnects in the control circuit 110 extend to the front side 100U of the device wafer, and the extension is exposed at the front side 100U of the device wafer 100. This allows the control circuit 110 to be electrically connected to the subsequently formed piezoelectric vibrator so as to be able to apply an electrical signal thereto.
A plurality of crystal resonators may be formed on the same device wafer 100. Accordingly, there may be a plurality of device areas AA defined on the device wafer 100, and each crystal resonator may be formed in a respective one of the device areas AA.
The control circuit 110 may include a first circuit 111 and a second circuit 112, the first circuit 111 and the second circuit 112 may be electrically connected to a top electrode and a bottom electrode of the subsequently formed piezoelectric vibrator, respectively.
With continued reference to
Similarly, the second circuit 112 may include a second transistor, a second interconnect 112a and a fourth interconnect 112b. The second transistor may be buried in the device wafer 100, and the second and fourth interconnects 112a, 112b may be both connected to the second transistor and extend to the front side 100U of the device wafer 100. For example, the second interconnect 112a may be connected to a drain of the second transistor, and the fourth interconnect 112b to a source thereof.
In this embodiment, the device wafer 100 includes a substrate wafer 100A and a dielectric layer 100B on the substrate wafer 100A. The front side 100U may be provided by a surface of the dielectric layer 100B facing away from the substrate wafer 100A. Additionally, the first and second transistors may be both formed on the substrate wafer 100A and covered by the dielectric layer 100B. The third, first, second and fourth interconnects 111b, 111a, 112a, 112b may be all formed within the dielectric layer 100B and extend to the surface of the dielectric layer 100B facing away from the substrate wafer.
The substrate wafer 100A may be either a silicon wafer or a silicon-on-insulator (SOI) wafer. In this embodiment, the substrate wafer 100A is a SOI wafer including a base layer 101, a buried oxide layer 102 and a top silicon layer 103, which are sequentially stacked in this order in the direction from the back side 100D to the front side 100U.
It is to be noted that, in this embodiment, the interconnects in the control circuit 110 extend to the front side 100U of the device wafer, while the piezoelectric vibrator is to be subsequently formed on the back side 100D of the device wafer. Accordingly, a first connecting structure may be subsequently formed to lead connection ports of the control circuit 110 for electrically connecting the piezoelectric vibrator from the front to back side of the device wafer and brought into electrical connection with the subsequently formed piezoelectric vibrator there.
Specifically, the first connecting structure may include a first connection and a second connection, the first connection is configured for electrically connecting the first interconnect 111a to the bottom electrode of the subsequently formed piezoelectric vibrator and the second connection is configured for electrically connecting the second interconnect 112a to the top electrode of the subsequently formed piezoelectric vibrator.
In addition, the first connection may include a first conductive plug 221 configured for electrical connection at its opposing ends respectively to the first interconnect 111a and the subsequently formed bottom electrode. That is, the first conductive plug 221 may serve to lead a connecting port of the first interconnect 111a in the control circuit from a front side of the control circuit to a back side thereof so as to enable electrical connection of the bottom electrode subsequently formed on the back side of the device wafer to the control circuit from the back side of the control circuit.
Optionally, in this embodiment, the first connection may further include a first connecting wire 211 formed, for example, on the front side of the device wafer. The first connecting wire 211 may connect one end of the first conductive plug 221 to the first interconnect, and the other end of the first conductive plug 221 may be electrically connected to the bottom electrode.
In alternative embodiments, the first connecting wire in the first connection may be formed on the back side of the device wafer. In this case, the first connecting wire may connect one end of the first conductive plug 221 to the bottom electrode, and the other end of the first conductive plug 221 may be electrically connected to the first interconnect in the control circuit.
Similarly, the second connection may include a second conductive plug 222 configured for electrical connection at its opposing ends respectively to the second interconnect 112a and the subsequently formed top electrode. That is, the second conductive plug 222 may serve to lead a connecting port of the second interconnect 112a in the control circuit from the front to back side of the control circuit so as to enable electrical connection of the top electrode subsequently formed on the back side of the device wafer to the control circuit from the back side of the control circuit.
Additionally, in this embodiment, the second connection may further include a second connecting wire 212 formed, for example, on the front side of the device wafer. The second connecting wire 212 may connect one end of the second conductive plug 222 to the second interconnect, and the other end of the second conductive plug 222 may be electrically connected to the top electrode.
In alternative embodiments, the second connecting wire in the second connection may be formed on the back side of the device wafer. In this case, the second connecting wire may connect one end of the second conductive plug 222 to the top electrode, and the other end of the second conductive plug 222 may be electrically connected to the second interconnect in the control circuit.
The first conductive plug 221 in the first connection and the second conductive plug 222 in the second connection may be formed in a single process step. The first connecting wire 211 in the first connection and the second connecting wire 212 in the second connection may also be formed in a single process step.
Specifically, in this embodiment, the formation of the first connection that includes the first conductive plug 221 and the first connecting wire 211 on the front side of the device wafer and of the second connection that includes the second conductive plug 222 and the second connecting wire 212 on the front side of the device wafer may include the steps as follows:
Step 1: Etch the device wafer 100 from the front side 100U of the device wafer 100 so that a first connecting hole and a second connecting hole are formed, as shown in
Step 2: Fill a conductive material in the first and second connecting holes, thereby resulting in the formation of the first and second conductive plugs 221, 222, as also shown in
In this way, both the first and second conductive plugs 221, 222 are located at the bottom closer to the back side 100D of the device wafer than the control circuit. As a result, the first and second conductive plugs 221, 222 both extend from the front side of the control circuit 110 to the back side of the control circuit 110 and are able to be connected to the first and second circuits 111, 112, respectively.
Specifically, the first and second transistors 111T, 112T may be both formed within the top silicon layer 103 above the buried oxide layer 102, while the first and second conductive plugs 221, 222 may each penetrate sequentially through the dielectric layer 100B and the top silicon layer 103 and terminate at the buried oxide layer 102. Thus, it may be considered that the buried oxide layer 102 can serve as an etch stop layer for the etching process for forming the first and second connecting holes. In this way, high etching accuracy can be achieved for the etching process.
In a subsequent process, the device wafer may be thinned from the back side so that the first and second conductive plugs 221, 222 are exposed from the processed back side and brought into electrical connection with the top and bottom electrodes of the piezoelectric vibrator on the back side.
Step 3: Form the first connecting wire 211 and the second connecting wire 212 on the front side of the device wafer 100, the first connecting wire 211 connects the first conductive plug 221 to the first interconnect 111a and the second connecting wire 212 connects the second conductive plug 222 to the second interconnect 112a, as also shown in
In embodiments with the first connecting wire in the first connection and the second connecting wire in the second connection being both formed on the back side of the device wafer, the formation of the first connection that includes the first conductive plug and the first connecting wire and of the second connection that includes the second conductive plug and the second connecting wire may include, for example:
first, forming a first connecting hole and a second connecting hole by etching the device wafer from the front side thereof;
then forming the first conductive plug that is electrically connected to the first interconnect and the second conductive plug that is electrically connected to the second interconnect by filling a conductive material into the first and second connecting holes;
subsequently, thinning the device wafer from the back side thereof so that the first and second conductive plugs are exposed; and
forming, on the back side of the device wafer, the first connecting wire that is connected to the first conductive plug at one end and configured for electrical connection with the bottom electrode at the other end and the second connecting wire that is connected to the second conductive plug at one end and configured for electrical connection with the top electrode at the other end.
It is to be noted that although the first and second conductive plugs 221, 222 have been described above as being formed from the front side of the device wafer 100 prior to the formation of the first and second connecting wires 211, 212, the first and second conductive plugs 221, 222 may be alternatively formed from the back side of the device wafer subsequent to the thinning of the device wafer, as will be described in greater detail below.
Subsequently, the semiconductor die will be bonded to the front side of the device wafer 100, and the piezoelectric vibrator will be formed on the back side of the device wafer 100. The bonding of the semiconductor die to the front side of the device wafer 100 may precede the formation of the piezoelectric vibrator on the back side of the device wafer 100. Alternatively, the formation of the piezoelectric vibrator on the back side of the device wafer 100 may precede the bonding of the semiconductor die to the front side of the device wafer 100.
This embodiment is further described below in the context with the formation of the piezoelectric vibrator on the back side of the device wafer 100 preceding the bonding of the semiconductor die to the front side of the device wafer 100.
Optionally, prior to the formation of the piezoelectric vibrator, the method may further include bonding a support wafer to the front side of the device wafer 100.
In this embodiment, before the support wafer is bonded and after the first and second connecting wires 211, 212 have been formed, the method may further include forming a planarized layer 300 on the front side 100U of the device wafer 100, which provides the device wafer 100 with a flatter bonding surface.
Specifically, referring to
In this embodiment, the planarized layer 300 may be formed using a polishing process. In this case, for example, the first and second connecting wires 211, 212 may serve as a polish stop such that the top surface of the formed planarized layer 300 is flush with those of the first and second connecting wires 211, 212, and all these surfaces may make up a bonding surface for the device wafer 100.
In step S200, with reference to
In this embodiment, the lower cavity 120 may be formed, for example, using a method including steps S210 and S220 below.
In step S210, with reference to
Specifically, the lower cavity 120 extends deep into the device wafer 100 from the front side 100U and may have a bottom that is closer to the back side 100D of the device wafer 100 than the bottom of the control circuit 110.
In this embodiment, the lower cavity 120 may be formed subsequent to the formation of the planarized layer 300 by sequentially etching through the planarized layer 300 and the device wafer 100. Specifically, an etching process for forming the lower cavity 120 may proceed sequentially through the planarized layer 300, the dielectric layer 100B and the top silicon layer 103 and stop at the buried oxide layer 102.
Thus, in this embodiment, the buried oxide layer 102 may serve as an etch stop layer for both the etching process for forming the first and second connecting holes for the first and second conductive plugs 221, 222 and the etching process for forming the lower cavity 120. As a result, bottoms of the resulting first and second conductive plugs 221, 222 are at the same or similar level as that of the lower cavity 120. As such, it can be ensured that the first conductive plug 221, the second conductive plug 222 and the lower cavity 120 can be all exposed when the device wafer is subsequently thinned from the back side 100D of the device wafer 100.
It is to be noted that the relative positions of the lower cavity 120 and the first and second circuits shown in the figures are merely for illustration, and in practice, the arrangement of the first and second circuits may depend on the actual circuit layout requirements, without limiting the present invention.
In step S220, with reference to
In this embodiment, the lower cavity 120 is bottomed at the buried oxide layer 102. Therefore, as a result of the thinning of the device wafer, the base layer 101 and the buried oxide layer 102 are sequentially stripped away, and the top silicon layer 103 and the lower cavity 120 are both exposed. The exposed lower cavity 120 provides a space in which the subsequently formed piezoelectric vibrator can vibrate. Moreover, the first and second conductive plugs 221, 222 are also exposed as a result of thinning the device wafer. The exposure of the first and second conductive plugs 221, 222 makes it possible to electrically connect them to the subsequently formed piezoelectric vibrator.
Optionally, with reference to
It is to be noted that, in this embodiment, the lower cavity 120 is formed by etching the device wafer 100 from the front side and thinning the device wafer 100 from the back side so that the opening of the lower cavity 120 is exposed at the back side of the device wafer 100.
However, referring to
With particular reference to
At first, the device wafer is thinned from the back side. In case of the substrate wafer being a SOI wafer, this may involve sequential removal of the base layer and the buried oxide layer of the substrate wafer. Of course, the thinning of the substrate wafer may alternatively involve partial removal of the base layer, complete removal of the base layer and hence exposure of the buried oxide layer, or the like.
Next, the device wafer is etched from the back side so that the lower cavity is formed. It is to be noted that the lower cavity resulting from the etching of the device wafer may have a depth as practically required, and the present invention is not limited to any particular depth of the lower cavity. For example, after the device wafer is thinned and the top silicon layer 103 is exposed, the top silicon layer 103 may be etched to form the lower cavity therein. Alternatively, the etching process may proceed through the top silicon layer 103 and further into the dielectric layer 100B, so that the resulting lower cavity 120 extends from the top silicon layer 103 down into the dielectric layer 100B.
As discussed above, in other embodiments, the thinning of the device wafer may be followed by forming the first conductive plug 221 of the first connection and the second conductive plug 222 of the first connection from the back side of the device wafer 100.
Specifically, a method for forming the first and second connecting wires on the front side of the device wafer 100, forming the first and second conductive plugs 221, 222 from the back side of the device wafer 100, connecting the first conductive plug 221 to the first connecting wire 211 and connecting the second conductive plug 222 to the second connecting wire 212 may include the steps below.
At first, prior to the bonding of the support wafer 400, the first and second connecting wires 211, 212 are formed on the front side of the device wafer 100, the first connecting wire 211 is electrically connected to the first interconnect and the second connecting wire 212 is electrically connected to the second interconnect.
Next, after the device wafer 100 is thinned, it is etched from the back side to form therein first and second connecting holes, both of which extend through the device wafer 100 so that the first and second connecting wires 211, 212 are exposed respectively in the holes.
Subsequently, a conductive material is filled in the first and second connecting holes, resulting in the formation of the first and second conductive plugs 221, 222. The first conductive plug 221 is connected at one end to the first connecting wire 211 and configured for electrical connection with the bottom electrode of the piezoelectric vibrator at the other end. The second conductive plug 222 is connected at one end to the second connecting wire 212 configured for electrical connection with the top electrode of the piezoelectric vibrator at the other end.
In an alternative embodiment, a method for forming the first and second connecting wires on the back side of the device wafer 100, forming the first and second conductive plugs 221, 222 from the back side of the device wafer 100, connecting the first conductive plug 221 to the first connecting wire and connecting the second conductive plug 222 to the second connecting wire may include the steps detailed below.
At first, the device wafer 100 is thinned from the back side, followed by etching the device wafer 100 from the back side and thus forming first and second connecting holes therein.
Next, a conductive material is filled in the first and second connecting holes, resulting in the formation of the first and second conductive plugs. The first conductive plug is electrically connected at one end to the first interconnect, and the second conductive plug is electrically connected at one end to the second interconnect.
Subsequently, the first and second connecting wires are formed on the back side of the device wafer 100. One end of the first connecting wire is connected to the other end of the first conductive plug, and the other end of the first connecting wire is configured for electrical connection with the bottom electrode. One end of the second connecting wire is connected to the other end of the second conductive plug, and the other end of the second connecting wire is configured for electrical connection with the top electrode.
In step S300, with reference to
Specifically, the formation of the piezoelectric vibrator 500 may include, for example, the steps as follows:
Step 1: Form the bottom electrode 510 on the back side of the device wafer 100, as shown in
In this embodiment, the bottom electrode 510 surrounds the lower cavity 120 and covers the first conductive plug 221. As a result, the bottom electrode 510 is electrically connected to the first circuit 111 and hence to the first transistor via the first conductive plug 221.
It is to be noted that in embodiments with the first connecting wire in the first connection being formed on the back side of the device wafer, the bottom electrode 510 may be brought into electrical connection with the first connecting wire.
The bottom electrode 510 may be formed of, for example, silver, and the formation of the bottom electrode 510 may involve successive processes of thin-film deposition, photolithography and etching. Alternatively, the bottom electrode 510 may be formed using a vapor deposition process.
Step 2: With continued reference to
Step 3: Form the top electrode 530 on the piezoelectric crystal 520, as shown in
Notably, in this embodiment, the bottom electrode 510, the piezoelectric crystal 520 and the top electrode 530 are successively formed over the device wafer 100 using semiconductor processes. However, in other embodiments, it is also possible to form the top and bottom electrodes on opposing sides of the piezoelectric crystal and then bond the three as a whole onto the device wafer 100.
As noted above, in the resulting piezoelectric vibrator 500, the bottom electrode 510 is electrically connected to the first circuit via the first connection, and the top electrode 530 is electrically connected to the second circuit via the second connection.
Thus, the piezoelectric vibrator 500 is electrically connected to the control circuit 110 from the back side of the control circuit 110, allowing the control circuit 110 to apply an electrical signal to the bottom and top electrodes 510, 530 of the piezoelectric vibrator 500 to form an electric field between the bottom electrode 510 and the top electrode 530, which causes the piezoelectric crystal 520 of the piezoelectric vibrator 500 to change its shape. When the electric field in the piezoelectric vibrator 500 is inverted, the piezoelectric crystal 520 will responsively change its shape in the opposite direction. Therefore, when the control circuit 110 applies an AC signal to the piezoelectric vibrator 500, the piezoelectric crystal 520 will change shape alternately in opposite directions and thus alternately contract and expand due to oscillations of the electric field. As a result, the piezoelectric crystal 520 will vibrate mechanically.
In case of the first connection including the first conductive plug 221 and the first connecting wire 211, the bottom electrode 510 may extend beyond the piezoelectric crystal 520 thereunder over the first conductive plug 221, thus the bottom electrode 510 coming into electrical connection with the control circuit via the first connection.
In this embodiment, in addition to the second conductive plug 222 and the second connecting wire 212, the second connection may further include a third conductive plug 610, which is connected to the second conductive plug 222 at the bottom and to the top electrode 530 at the top while providing the top electrode 530 with support.
Specifically, the formation of the third conductive plug 610 in the second connection and of the top electrode 530 may include the steps below.
First of all, with reference to
Next, with continued reference to
Subsequently, a conductive material is filled in the through hole, resulting in the formation of the third conductive plug 610, which is electrically connected to the second conductive plug 222 at the bottom and exposed from the plastic encapsulation layer 600 at the top.
Thereafter, with continued reference to
Afterward, with reference to
It is to be noted that in embodiments with the second connecting wire in the second connection being formed on the back side of the device wafer, the third conductive plug of the second connection may be brought into electrical connection with the second connecting wire at the top.
Of course, in alternative embodiments, in addition to the second connecting wire 212, the second conductive plug 222 and the third conductive plug, the second connection may further include an interconnecting wire. In such embodiments, the third conductive plug may be connected to the second conductive plug 222 at the bottom and to one end of the interconnecting wire at the top, and the other end of the interconnecting wire may overlap at least part of the top electrode 530, and thus come into electrical connection with the top electrode 530.
Specifically, in these embodiments, the formation of the third conductive plug and the interconnecting wire may include, for example, the steps below.
At first, a plastic encapsulation layer is formed over the back side of the device wafer 100. The plastic encapsulation layer may be formed subsequent to the formation of the top electrode 530 in such a manner that the top electrode 530 is exposed from the plastic encapsulation layer.
Next, a through hole is formed in the plastic encapsulation layer, which extends through the plastic encapsulation layer so that the second conductive plug 222 is exposed in the hole, and a conductive material is filled in the through hole to result in the formation of the third conductive plug that is electrically connected at the bottom to the second conductive plug 222.
Subsequently, the interconnecting wire is formed on the plastic encapsulation layer. The interconnecting wire covers at least part of the top electrode 530 and extends from the top electrode 530 over the third conductive plug. The plastic encapsulation layer is then removed. Thus, the top electrode 530 is electrically connected to the second conductive plug 222 via the interconnecting wire and the third conductive plug.
In step S400, with reference to
Specifically, the formation of the cap layer 420 that delimits the upper cavity 400 may include, for example, the steps below.
In a first step, with reference to
In a second step, with continued reference to
The space occupied by the sacrificial layer 710 corresponds to the internal space of the subsequently formed upper cavity. Therefore, a depth of the resulting upper cavity may be adjusted by changing a height of the sacrificial layer. It will be recognized that the depth of the upper cavity may be determined as practically required, without limiting the present invention in any sense.
In a third step, with reference to
As a result, the piezoelectric vibrator 500 is enclosed in the upper cavity 700 so that it can vibrate in the lower and upper cavities 120, 700.
Optionally, with reference to
With continued reference to
In step S500, with reference to
In this embodiment, the semiconductor die may be bonded to the front side of the device wafer 100 after the support wafer is removed. In the semiconductor die, for example, a drive circuit for providing an electrical signal may be formed. The electrical signal is applied by the control circuit to the piezoelectric vibrator 500 so as to control shape change of the piezoelectric vibrator 500.
Referring to
Step 1: Form contact holes by etching the planarized layer 300. In this embodiment, first and second contact holes in which the third and fourth interconnects 111b, 112b are exposed may be formed.
Step 2: Form contact plugs by filling a conductive material in the contact holes, as shown in
In this way, the semiconductor die 900 can be bonded to the front side of the device wafer, with the third and fourth interconnects being brought into electrical connection with the semiconductor die 900 by the first and second contact plugs 910, 920.
In alternative embodiments, a rewiring layer connecting the control circuit may be formed on the front side of the device wafer, and contact pads for electrically connecting the semiconductor die may be formed on the rewiring layer.
The semiconductor die may be heterogeneous from the device wafer 100. That is, the semiconductor die may include a substrate made of a material different from that of the device wafer 100. For example, in this embodiment, differing from the device wafer 100 that is made of silicon, the substrate of the heterogeneous die may be formed of a Group III-V semiconductor material or a Group II-VI semiconductor material (specific examples include germanium, germanium silicon, gallium arsenide, etc.)
Optionally, with reference to
The cap substrate 820 may be, for example, a silicon substrate. In the cap substrate 800, a depression for receiving the semiconductor die 900 may be formed in advance. Accordingly, the cap substrate 820 may be bonded to the front side of the device wafer so that the opening of the lower cavity exposed at the front side of the device wafer is covered and closed, with the semiconductor die 900 being received in the depression formed in the cap substrate 820.
As noted above, in this embodiment, the formation of the piezoelectric vibrator and cap layer on the back side of the device wafer precedes the bonding of the semiconductor die to the front side of the device wafer. However, in other embodiment, the bonding of the semiconductor die to the front side of the device wafer may precede the formation of the piezoelectric vibrator and cap layer on the back side of the device wafer.
Specifically, according to another embodiment, the method may include, for example:
forming the lower cavity by etching the device wafer from the front side thereof;
bonding the semiconductor die to the front side of the device wafer so that the semiconductor die is electrically connected to the control circuit via the second connection;
bonding the cap substrate to the front side of the device wafer so that the cap substrate covers the semiconductor die and the opening of the lower cavity exposed at the front side of the device wafer;
thinning the device wafer from the back side thereof until the lower cavity is exposed;
successively formed the piezoelectric vibrator and the cap layer on the back side of the thinned device wafer;
forming the plastic encapsulation layer over the back side of the device wafer; and
optionally removing the support wafer.
A crystal resonator corresponding to the above method according to an embodiment will be described below with reference to
a device wafer 100, the control circuit and a lower cavity are formed in the device wafer 100, the lower cavity having an opening at a back side of the device wafer;
a piezoelectric vibrator 500 including a top electrode 530, a piezoelectric crystal 520 and a bottom electrode 510, the piezoelectric vibrator 500 formed on the back side of the device wafer 100 in alignment with the lower cavity 120;
a first connecting structure formed on the device wafer 100, the first connecting structure electrically connecting both the top and bottom electrodes 530, 510 of the piezoelectric vibrator 500 to the control circuit;
a cap layer 720 formed on the back side of the device wafer 100 so as to hood the piezoelectric vibrator 500, the cap layer 720 delimiting an upper cavity 700 together with the piezoelectric vibrator and the device wafer;
a semiconductor die bonded to the front side of the device wafer 100; and
a second connecting structure electrically connecting the semiconductor die 500 to the control circuit. Thus, the piezoelectric vibrator 500 and the drive circuit can be integrated together by forming the lower cavity 120 in the device wafer 100 and fabricating the cap layer 720 using semiconductor processes, which encloses the piezoelectric vibrator 500 within the upper cavity 700 and thus ensures that the piezoelectric vibrator 500 can oscillate within the upper and lower cavities 700, 120. In addition, the semiconductor die bonded to the device wafer 100 can enhance performance of the crystal resonator by on-chip modulation under the control of the control circuit 110 for correcting raw deviations of the crystal resonator such as temperature and frequency drifts. Therefore, in addition to an enhanced degree of integration, the crystal resonator of the present invention fabricated using semiconductor processes is more compact in size and thus less power-consuming.
Specifically, in the semiconductor die 900, for example, a drive circuit for providing an electrical signal may be formed, which can be transmitted by the control circuit 110 to the piezoelectric vibrator 500. The semiconductor die may be heterogeneous from the device wafer 100. For example, in this embodiment, differing from the device wafer 100 that is made of silicon, the substrate of the heterogeneous die may be formed of a Group III-V semiconductor material or a Group II-VI semiconductor material (specific examples include germanium, germanium silicon, gallium arsenide, etc.)
With continued reference to
Specifically, the first circuit 111 may include a first transistor, a third interconnect 111b and a first interconnect 111a. The first transistor may be buried within the device wafer 100, and the first and third interconnects 111a, 111b may be both electrically connected to the first transistor and extend to the front side of the device wafer 100. The first interconnect 111a may be electrically connected to the bottom electrode 210 and the third interconnect 111b to the semiconductor die.
The second circuit 112 may include a second transistor, a fourth interconnect 112b and a second interconnect 112a. The second transistor may be buried within the device wafer 100, and the second and fourth interconnects 112a, 112b may be both electrically connected to the second transistor and extend to the front side of the device wafer 100. The second interconnect 112a may be electrically connected to the top electrode 230 and the fourth interconnect 112b to the semiconductor die.
The first connecting structure may include a first connection and a second connection. The first connection may be connected to the first interconnect 111a and the bottom electrode 210 of the piezoelectric vibrator. The second connection may be connected to the second interconnect 112a and the top electrode 230 of the piezoelectric vibrator.
The first connection may include a first conductive plug 221, which penetrates through the device wafer 100 so as to extend to the front side of the device wafer 100 into electrical connection with the first interconnect at one end and to extend to the back side of the device wafer 100 into electrical connection with the bottom electrode 510 of the piezoelectric vibrator at the other end.
The first connection may further include a first connecting wire 211. In this embodiment, the first connecting wire 211 is formed on the front side of the device wafer 100 and the first connecting wire 211 connects the first conductive plug 221 to the first interconnect 111a. In alternative embodiments, the first connecting wire 211 may be formed on the back side of the device wafer 100 and connect the first conductive plug to the bottom electrode.
With this arrangement, the first connecting wire 211 and the first conductive plug 221 collaboratively lead a connection port of the first interconnect 111a from the front side of the device wafer 100 to the back side thereof. In this way, the connection port is allowed to be electrically connected to the bottom electrode 510 of the piezoelectric vibrator 500 that is formed on the back side of the device wafer 100.
In this embodiment, the bottom electrode 510 is formed on the back side of the device wafer 100 and has an extension that laterally extends beyond the piezoelectric crystal 520 over the first interconnect 221, thus coming into electrical connection with the bottom electrode 510.
The second connection may include a second conductive plug 222, which penetrates through the device wafer 100 so as to extend to the front side of the device wafer 100 into electrical connection with the second interconnect at one end and to extend to the back side of the device wafer 100 into electrical connection with the top electrode 530 of the piezoelectric vibrator at the other end.
The second connection may further include a second connecting wire 212. In this embodiment, the second connecting wire 212 is formed on the front side of the device wafer 100 and connects the second conductive plug 222 to the second interconnect 112a. In alternative embodiments, the second connecting wire 212 may be formed on the back side of the device wafer 100 and connect the second conductive plug to the top electrode.
Likewise, the second connecting wire 212 and second conductive plug 222 collaboratively lead a connection port of the second interconnect 112a from the front to back side of the device wafer 100. Thus, the connection port is allowed to be electrically connected to the top electrode 530 of the piezoelectric vibrator 500 that is formed on the back side of the device wafer 100.
In this embodiment, the second connection may further include a third conductive plug 610, which electrically connects the top electrode 530 to the second conductive plug 222 and hence to the second interconnect in the second circuit 112.
Specifically, the third conductive plug 610 in the second connection may be formed on the back side of the device wafer in such a manner that its one end is electrically connected to the top electrode 530 and the other end is electrically connected to the second conductive plug 222. It can be considered that the top electrode 530 overlaps at least part of the piezoelectric crystal 520 and extends beyond the piezoelectric crystal 520 over the third conductive plug 610, thus bridging the top electrode 530 to the second conductive plug 222.
In alternative embodiments, in addition to the second conductive plug 222, the second connecting wire 212 and the third conductive plug, the second connection may further include an interconnecting wire. In such embodiments, the third conductive plug may be formed on the back side of the device wafer in such a manner that it is electrically connected to the second conductive plug 222 at the bottom. Additionally, the interconnecting wire may cover at least part of the top electrode 530 at one end and overlap the third conductive plug at the other end, thus coming into connection with the third conductive plug. It will be recognized that, in such cases, the third conductive plug also serves to support the interconnecting wire.
The second connecting structure may include contact pads, which are electrically connected to the control circuit at the bottom and to semiconductor die 900 at the top. In this embodiment, the contact pads in the second connecting structure include a first contact pad 910 and a second contact pad 920. The first contact pad 910 is electrically connected to the third interconnect 111b at the bottom and to the semiconductor die 900 at the top. The second contact pad 920 is electrically connected to the fourth interconnect 112b at the bottom and to the semiconductor die 900 at the top.
With continued reference to
With continued reference to
The crystal resonator may further include a plastic encapsulation layer 810 formed on the back side of the device wafer 100, which covers an external surface of the cap layer 720 outside the upper cavity. In other words, the plastic encapsulation layer 810 covers all the structures formed on the back side of the device wafer, thus providing protection to the underlying structures.
In this embodiment, the lower cavity extends through the device wafer. Accordingly, a cap substrate 820 may be bonded to the front side of the device wafer to cover the semiconductor die and close the opening of the lower cavity present at the front side of the device wafer. The cap substrate may be composed of, for example, a silicon wafer. Moreover, in the cap substrate 820, a depression for receiving the semiconductor die 900 may be formed in advance. In this case, the cap substrate 820 may be so bonded to the front side of the device wafer that the opening of the lower cavity exposed at the front side of the device wafer is covered and closed, with the semiconductor die 900 being received in the depression formed in the cap substrate 820.
In summary, in the proposed method, the lower cavity is formed in the device wafer containing the control circuit, and the device wafer is then thinned from the back side to expose the lower cavity, followed by the formation of the piezoelectric vibrator over the back side of the device wafer. The cap layer is then fabricated using planar fabrication processes to enclose the piezoelectric vibrator within the upper cavity, thus resulting in the formation of the crystal resonator. Moreover, the semiconductor die containing, for example, a drive circuit may be bonded to the device wafer. In this way, the semiconductor die, control circuit and crystal resonator are all integrated on the same device wafer. This is favorable to on-chip modulation for correcting raw deviations of the crystal resonator such as temperature and frequency drifts.
Obviously, compared with traditional crystal resonators (e.g., surface-mount ones), the proposed crystal resonator fabricated using planar fabrication processes is more compact in size and hence less power-consuming. Moreover, it is able to integrate with other semiconductor components more easily with a higher degree of integration.
The description presented above is merely that of a few preferred embodiments of the present invention without limiting the scope thereof in any sense. Any and all changes and modifications made by those of ordinary skill in the art based on the above teachings fall within the scope as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201811643072.2 | Dec 2018 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2019/115653 | 11/5/2019 | WO | 00 |
