Field of Invention
The present invention relates to bonding a wafer including a semiconductor structure to a substrate, then processing the wafer into multiple light emitting devices.
Description of Related Art
Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts are formed on the n- and p-type regions.
With the development of efficient LEDs that emit blue or ultraviolet light, it has become feasible to produce LEDs that generate white light through phosphor conversion of a portion of the primary light emitted by the LED. The phosphor converts a portion of the primary light to secondary light at longer wavelengths. The unconverted primary light may combine with the secondary light to produce white light.
FIG. 13 illustrates a method 100 of forming a phosphor-converted light emitting device, described in more detail in U.S. Pat. No. 7,553,683. First, a sheet of the wavelength converting material is produced (step 102). The sheet of wavelength converting material may be produced using, e.g., a phosphor or other similar luminescent material, that is dispersed in an inorganic material, such as glass. A well homogenized mixture of phosphor and powdered glass is heated in a crucible. After the glass mixture melts, the melt is homogenized in the furnace, then poured onto a plate and permitted to harden in a flat sheet. Once the sheet of wavelength converting material is hardened, the sheet is separated into a number of individual elements (step 104). The individual wavelength converting elements are sized to be mounted over an LED die. A semiconductor light emitting device die is then provided (step 106). The LED die may be a mounted die, e.g., that is mounted in a reflector cup or a submount. Alternatively, the LED die may be unmounted. A wavelength converting element is then bonded to the LED die (step 108).