Light sensor using wafer-level packaging
The present invention provides systems, devices and methods for fabricating miniature low-power light sensors. With the present invention, a light sensitive component, such as a diode, is fabricated on the front side of a silicon wafer. Connectivity from the front side of the wafer to the back side of the wafer is provided by a through silicon via. Solder bumps are then placed on the back side of the wafer to provide coupling to a printed circuit board. The techniques described in the present invention may also be applied to other types of semiconductor devices, such as light-emitting diodes, image sensors, pressure sensors, and flow sensors.
1. An integrated light sensor comprising:
a semiconductor wafer having a first side and an opposing second side;
a light-detecting diode fabricated on the first side of the wafer;
a solder bump positioned on the second side of the wafer for connecting the wafer to a printed circuit board; and
a via between the first side and the second side of the wafer, the via comprising a metal layer that is an unexposed, internal layer within the sensor and that is directly coupled to the light-detecting diode and that conducts electricity between the light-detecting diode and the solder bump.
2. The integrated light sensor of claim 1 wherein the wafer is a silicon wafer and the via is a through-silicon-via.
3. The light sensor as in claim 1 wherein the first side of the silicon wafers is protected by attaching either a protective substrate or by attaching a protective tape to the first side of the silicon wafer.
4. The light sensor as in claim 1 wherein the first side of the silicon wafer has an optical filter layer located above of the diode, the optical layer selectively filters electro-magnetic spectrum.
5. The light sensor as in claim 1 further comprising a plurality of diodes that are integrated on the silicon wafer to form a light sensor.
6. The light sensor as in claim 2 wherein the through-silicon-via is patterned and deep reactive ion etched from the first side to the second side of the silicon wafer.
7. The light sensor as in claim 2 wherein the through-silicon-via is formed by deep reactive ion etch from the second side to the first side of the silicon wafer.
8. The light sensor as in claim 6 wherein the through-silicon-via is formed by wet etching from the second side to the first side of the silicon wafer.
9. The light sensor as in claim 6 wherein the through-silicon-via is a two-step through-silicon-via manufactured by performing the steps comprising of:
forming a first via portion on the first side of the silicon wafer using a first deep reactive ion etch;
forming a second via portion on the second side of the silicon wafer using a second deep reactive ion etch; and
depositing the via metal layer on a first surface of the first via portion and on a second surface of the second via portion, the via metal layer providing an electrical connection between the diode and the solder bump.
10. A method for fabricating an integrated light sensor, the method comprising the steps of:
fabricating a light-detecting diode on a first side of a silicon wafer;
forming a through-silicon-via between the first side and a second side of the wafer;
depositing a via metal layer on a surface of the through-silicon-via, the via metal layer being an unexposed, internal layer within the sensor and being directly coupled to the light-detecting diode and providing electrical connectivity between the diode and the second side of the wafer; and
depositing a solder bump on the second side of the silicon wafer, the solder bump being electrically coupled to the diode through by the via metal layer.
11. A method of fabricating a light sensor as in claim 10 wherein the through-silicon-via is patterned and deep reactive ion etched from the first side to the second side of the silicon wafer.
12. A method of fabricating a light sensor as in claim 10 wherein the through-silicon-via is formed by deep reactive ion etch from the second side to the first side of the silicon wafer.
13. A method of fabricating a light sensor as in claim 10 wherein the through-silicon-via is formed by wet etching from the second side to the first side of the silicon wafer.
14. A method of fabricating a light sensor as in claim 10 wherein the through-silicon-via is a two-step through-silicon-via manufactured by performing the steps comprising of:
forming a first via portion on the first side of the silicon wafer using a first deep reactive ion etch;
forming a second via portion on the second side of the silicon wafer using a second deep reactive ion etch; and
depositing the via metal layer on a first surface of the first via portion and on a second surface of the second via portion, the via metal layer providing an electrical connection between the diode and the solder bump.
15. A method of fabricating a light sensor as in claim 10 further comprising the step of bonding the wafer to either a protective substrate or a protective tape.
16. An integrated semiconductor device comprising:
a wafer having a first side and an opposing second side;
a semiconductor sensing element fabricated on the first side of the wafer;
a solder bump positioned on the second side of the wafer for connecting the wafer to a board; and
a via between the first side and the second side the wafer, the via comprising a metal layer that is an unexposed, internal layer within the sensor and that is directly coupled to a semiconductor sensing element integrated and deposited on a surface of the via and that conducts electricity between the semiconductor sensing element and the solder bump.
17. The integrated semiconductor device of claim 16 , further comprising a pressure sensor.
18. The integrated semiconductor device of claim 16 , further comprising an image sensor.
19. The integrated semiconductor device of claim 16 , further comprising a flow sensor.
20. The integrated semiconductor device of claim 16 , further comprising a light-emitting diode.
21. The integrated semiconductor device of claim 16 , wherein the solder bump has a diameter of 150-350 micrometers.