TECHNICAL FIELD

The present invention generally relates to vertical cavity surface emitting lasers (VCSELs) and, more particularly to, a flip chip VCSEL which eliminates the need for bond wires and bond pads thereby reducing the footprint of the flip chip VCSEL device and which utilizes planarization of trenches formed between pillars in the VCSEL pillar array for ease of subsequent photolithography and metal related manufacturing processes.

BACKGROUND

Semiconductor lasers are being used in many imaging applications which require high power illumination such as structured light sources for 3D imaging, Laser Detection and Ranging (LADAR), Time of Flight (TOF) 3D imaging, aviation defense, and fusion research, among others. Vertical Cavity Surface Emitting Lasers (VCSELs), are commonly used in many semiconductor laser applications due to the low power applications and high frequency superiority and manufacturing advantages over other type of semiconductor laser devices.

A VCSEL is a semiconductor micro-laser diode that emits light in a generally cylindrical beam. The beam is emitted vertically from the surface of the substrate on which it is fabricated. Because the beams in VCSELs emit vertically from the surface of the substrate, they can be tested on-wafer, before they are separated into individual devices. This reduces the fabrication cost of the devices. It also allows VCSELs to be built not only in one-dimensional, but also in two-dimensional arrays.

VCSELs generally have larger output apertures compared to most edge-emitting lasers. This may allow VCSELs to produce a lower divergence angle of the output beam, and makes possible high coupling efficiency with optical fibers. VCSELs also have high reflectivity mirrors, compared to most edge-emitting lasers, which may reduce the threshold current of VCSELs, resulting in low power consumption. The low threshold current also permits high intrinsic modulation bandwidths in VCSELs. The wavelength of VCSELs may also be tuned, within the gain band of the active region, by adjusting the thickness of the reflector layers.

In a VCSEL package assembly, the VCSEL device is frontside mounted to a substrate of the package by solder or epoxy. Wire bonding may then be used to attach the VCSEL device to external circuitry. The drawback of wire bonding of a front side emitting VCSEL is that wire bonding increases the footprint of the VCSEL package assembly. Also, since the active region (where the heat is being generated) is on the top side of the wafer, the heat source is farther away from the heatsink which is located at the back of the wafer. This will significantly raise the junction temperature of the VCSEL as the heat is not removed quickly from the front side of the wafer.

Therefore, it would be desirable to provide a device and method that overcome the above problems.

SUMMARY

In accordance with one embodiment, a method of forming a flip chip backside Vertical Cavity Surface Emitting Laser (VCSEL) package is disclosed. The method comprises: forming a VCSEL pillar array; applying a dielectric layer to the VCSEL pillar array, the dielectric layer filling trenches in between pillars forming the VCSEL pillar array and covering the pillars; planarizing the VCSEL pillar array to remove the dielectric layer covering the pillars exposing a metal layer on a top surface of the pillars; applying a metal coating on the metal layer on a top surface of the pillars, the metal layer defining a contact pattern of the VCSEL pillar array; and applying solder on the metal coating to flip chip mount the VCSEL pillar array to a substrate package.

In accordance with one embodiment, a method of forming a flip chip backside Vertical Cavity Surface Emitting Laser (VCSEL) package is disclosed. The method comprises: forming a VCSEL pillar array comprising: forming a first mirror device on a substrate; forming an active region on the first mirror device; forming a second mirror device formed on the active region; applying a metal layer on the second mirror device; and forming a plurality of pillars, the pillar exposing a portion of the first mirror device, the active region and the second mirror device; applying a dielectric layer to the VCSEL pillar array, the dielectric layer filling trenches in between pillars forming the VCSEL pillar array and covering the pillars; planarizing the VCSEL pillar array to remove the dielectric layer covering the pillars exposing a metal layer on a top surface of the pillars; applying a metal coating on the metal layer on a top surface of the pillars, the metal layer defining a contact pattern of the VCSEL pillar array, wherein the metal coating may attach a plurality of pillars together; and applying solder on the metal coating to flip chip mount the VCSEL pillar array to a substrate package.

In accordance with one embodiment, a flip chip backside Vertical Cavity Surface Emitting Laser (VCSEL) package is disclosed. The flip chip backside Vertical Cavity Surface Emitting Laser (VCSEL) package has a VCSEL pillar array. A dielectric layer fills trenches in between pillars forming the VCSEL pillar array. The VCSEL pillar array is planarized to expose a metal layer on a top surface of the pillars. A metal coating is applied on the metal layer on the top surface of the pillars. The metal layer defines a contact pattern of the VCSEL pillar array, wherein the metal coating attaches a plurality of pillars together. Solder is applied on the metal coating to flip chip mount the VCSEL pillar array to a substrate package.

