Bulk acoustic wave resonator and fabrication method thereof
A fabrication method of a bulk acoustic wave (BAW) resonator includes: sequentially forming a buffer layer, a piezoelectric layer, and a first electrode on a temporary substrate; forming a first dielectric layer on the piezoelectric layer and covering the first electrode; forming a trench in the first dielectric layer; forming a second dielectric layer on the first dielectric layer and in the trench; forming a third dielectric layer on the second dielectric layer and filling in the trench; forming a bonding layer on the third dielectric layer; bonding a resonator substrate to the third dielectric layer via the bonding layer; removing the temporary substrate and the buffer layer to expose a surface layer of the piezoelectric layer; removing the surface layer of the piezoelectric layer; forming a second electrode on the piezoelectric layer; and removing a portion of the first dielectric layer surrounded by the trench to form a cavity.
1. A fabrication method of a bulk acoustic wave (BAW) resonator, comprising:
obtaining a temporary substrate;
forming a buffer layer on the temporary substrate;
forming a piezoelectric layer on the buffer layer;
forming a first electrode on the piezoelectric layer;
forming a first dielectric layer on the piezoelectric layer and covering the first electrode;
forming a trench in the first dielectric layer, the trench surrounding a sacrificial portion of the first dielectric layer;
forming a second dielectric layer on the first dielectric layer and in the trench in the first dielectric layer;
forming a third dielectric layer on the second dielectric layer, the third dielectric layer filling in the trench in the first dielectric layer;
forming a bonding layer on the third dielectric layer;
bonding a resonator substrate to the third dielectric layer via the bonding layer;
removing the temporary substrate and the buffer layer to expose a surface layer of the piezoelectric layer;
removing the surface layer of the piezoelectric layer to obtain a thinned piezoelectric layer;
forming a second electrode on the thinned piezoelectric layer; and
removing the sacrificial portion of the first dielectric layer surrounded by the trench to form a cavity.
2. The fabrication method of claim 1 , wherein the temporary substrate is formed of silicon.
3. The fabrication method of claim 1 , wherein
the forming the buffer layer on the temporary substrate comprises:
depositing an AlN layer on the temporary substrate; and
depositing a GaN layer on the AlN layer, the AlN layer and the GaN layer together constituting the buffer layer, and
the forming the piezoelectric layer on the buffer layer comprises:
depositing an AlN layer or a ScAlN layer on the GaN layer, the AlN layer or the ScAlN layer constituting the piezoelectric layer.
4. The fabrication method of claim 1 , wherein
the forming the buffer layer on the temporary substrate comprises:
forming a silicon oxide layer on the temporary substrate, the silicon oxide layer constituting the buffer layer,
the forming the piezoelectric layer on the buffer layer comprises:
depositing a first AlN layer on the silicon oxide layer;
depositing a second AlN layer or a ScAlN layer on the first AlN layer, the first AlN layer and the second AlN layer or the ScAlN layer together constituting the piezoelectric layer, and
the removing the surface layer of the piezoelectric layer comprises:
removing the first AlN layer.
5. The fabrication method of claim 1 , wherein
the forming the buffer layer on the temporary substrate comprises:
depositing a first AlN layer on the temporary substrate, the first AlN layer constituting the buffer layer, and
the forming the piezoelectric layer on the buffer layer comprises:
depositing a second AlN layer or a ScAlN layer on the first AlN layer, the second AlN layer or the ScAlN layer together constituting the piezoelectric layer.
6. The fabrication method of claim 1 , wherein
the forming the buffer layer on the temporary substrate comprises:
depositing a silicon oxide layer on the temporary substrate, the silicon oxide layer constituting the buffer layer, and
the forming the piezoelectric layer on the buffer layer comprises:
depositing an AlN layer on the silicon oxide layer, the AlN layer constituting the piezoelectric layer.
7. The fabrication method of claim 1 , wherein the forming the buffer layer on the temporary substrate and the forming the piezoelectric layer on the buffer layer comprise:
depositing an AlN layer on the temporary substrate, a lower portion of the AlN layer contacting the temporary substrate constituting the buffer layer, and an upper portion of the AlN layer constituting the piezoelectric layer.
8. The fabrication method of claim 1 , wherein the first dielectric layer is formed of silicon oxide.
9. The fabrication method of claim 8 , wherein the second dielectric layer is formed on the exposed portion of the piezoelectric layer and the exposed portion of the first electrode, and on side surfaces of the trench in the first dielectric layer.
10. The fabrication method of claim 1 , wherein the trench in the first dielectric layer exposes a portion of the piezoelectric layer and a portion of the first electrode.
11. The fabrication method of claim 1 , wherein the second dielectric layer is formed of polysilicon, amorphous silicon, silicon nitride, aluminum nitride, gallium nitride, tantalum nitride, or a stacked combination of two or more of those materials.
12. The fabrication method of claim 1 , wherein the third dielectric layer is formed of silicon oxide, silicon nitride, aluminum nitride, or a stacked combination of two or more of those materials.
13. The fabrication method of claim 1 , wherein
the bonding the resonator substrate to the third dielectric layer comprises:
sputtering, in a vacuum environment, a sputtering target to deposit the bonding layer on the third dielectric layer; and
bonding, in the vacuum environment, the resonator substrate to the third dielectric layer via the bonding layer.
14. The fabrication method of claim 13 , wherein the resonator substrate is used as the sputtering target.
15. The fabrication method of claim 1 , wherein the bonding layer is formed of silicon, and has a thickness ranging from 3 nm to 50 nm.
16. The fabrication method of claim 1 , wherein the resonator substrate is formed of silicon.
17. The fabrication method of claim 1 , wherein the resonator substrate comprises:
a surface layer facing the bonding layer and formed of silicon; and
a body formed of silicon oxide, sapphire (Al 2 O 3 ), gallium nitride, silicon carbide, aluminum nitride, silicon nitride, or a stacked combination of two or more of those materials.
18. The fabrication method of claim 1 , further comprising:
forming one or more release holes in the piezoelectric layer, the one or more release holes exposing the sacrificial portion of the first dielectric layer surrounded by the trench,
wherein the sacrificial portion of the first dielectric layer surrounded by the trench is removed via the one or more release holes.
19. The fabrication method of claim 1 , further comprising:
forming a contact hole in the piezoelectric layer, the contact hole exposing a portion of the first electrode; and
forming a pad metal layer in the contact hole, the pad metal layer electrically connecting the first electrode.