Generally, LED (Light-Emitting Diode), which are semiconductor light-emitting devices, are manufactured by stacking semiconductor layers of mutually different conductive types on a growth substrate to sandwich an active layer there between and further by forming electrodes on the semiconductor layers of the individual conductive types. Manufactured semiconductor light-emitting devices are subjected to inspections for light emitting performance and the like so that acceptable devices are selected.
As inspections for light emitting performance of semiconductor light-emitting devices in their wafer state, there have conventionally been performed appearance inspection for inspecting the presence of flaws or the like under visible light, and light emitting inspection in which light emitting is executed by providing electric currents between positive and negative pad electrodes with use of a prober. In the light emitting inspection with a prober, since the needle (probe) of the prober needs to be put into contact with the electrodes of individual semiconductor light-emitting devices, there have been involved a quite long time for inspection and a fear of flaws on the semiconductor light-emitting devices due to the contact of the probe. Moreover, with small-sized semiconductor light-emitting devices, because their pad electrodes are also small in size, there has been difficulty in properly contacting of the probe with the devices.
Therefore, as a method of inspection for light emitting performance without providing electric currents through the semiconductor light-emitting devices, there has been proposed a method that the active layer of semiconductor light-emitting devices is excited with light irradiation and photoluminescence light released from the excited active layer is observed.
For example, Japanese Unexamined Patent Application Publication No. 2009-128366 describes a light-emitting device inspection method including the steps of irradiating a semiconductor light-emitting device with ultraviolet light, capturing a light emitting image generated by a photoluminescence effect in the active layer with use of a CCD (Charge Coupled Device) camera and, based on photoluminescence intensity information therefrom, determining quality of the semiconductor light-emitting device.
Referring now to FIG. 2, the method for determining quality of the light-emitting devices by using the photoluminescence intensity released from the active layer is explained. FIG. 2 is an explanatory view for explaining an outline of the light-emitting device inspection method. Also, shown in the field of image of photoluminescence in FIG. 2 are images obtained by capturing an aspect that the active layer of the light-emitting device excited by light irradiation releases photoluminescence.
In the image of photoluminescence of each sample, a black circular region on the right edge side is a non-emitting region where the p-type semiconductor layer and the active layer are eliminated for formation of the n-type electrode so that the region structurally does not emit light.
In the case where the quality of a light-emitting device in semiconductor light-emitting devices is determined based on photoluminescence intensity information as in the inspection method described in Japanese Unexamined Patent Application Publication No. 2009-128366, it is common practice to determine that each semiconductor light-emitting device is determined as acceptable on condition that light released from the semiconductor light-emitting device is equal to or higher than a predetermined intensity.
In the case where the entire surface except the non-emitting region emits light with sufficient intensity as in the case of sample 1, the semiconductor light-emitting device is determined as an acceptable device. In the case where the entire surface emits light with insufficient intensity as in sample 2, the semiconductor light-emitting device is determined as a defective device.
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USPTO Backgrounds