This invention relates to the manufacture of semiconductor devices and, in particular, to the manufacture of light emitting and light sensitive semiconductor devices including segments of optical fiber.
As used herein, "optical fiber" refers to one or more strands, e.g. 2 mm (0.2 inch) or less in diameter, of light conducting material, e.g. glass or transparent polymers. "Light" is intended to include both the spectrum visible to human beings as well as wavelengths to which semiconductive materials are or can be made sensitive.
In copending application Ser. No. 952,189, filed Oct. 16, 1978, and assigned to the assignee of the present invention, a fiber optic active element interface connector is described in which a ferrule is mounted over a semiconductor device to hold a segment of optical fiber in position over the semiconductor die and to act as a connector to passive portions of an optical communications system. While providing distinctly improved performance over other types of devices in the art, the alignment of the end of the fiber with the light emitting portion of the die requires careful assembly techniques.
The care required in assembly results from two broad, slightly overlapping, considerations; namely the mechanics of manufacturing and using the device and optical performance. The optical fiber must be precisely aligned along three perpendicular axes with the active area of the semiconductor for good optical coupling. However reliability considerations dictate that the fiber must not touch the die. During manufacture and use, the die and package encounter widely varying temperatures and temperature gradients. Since the fiber and plastic package materials have significantly different temperature coefficients of expansion, the fiber must be positioned slightly above the die so that contact is not made even when the die is warm or when a large temperature gradient exists in the package, since this would damage the surface of the die and degrade optical performance. Conversely, too great a distance between the end of the fiber and the die also degrades optical performance.
Prior art techniques in which the fiber touches the die and is withdrawn slightly, with or without an uncured adhesive, may damage the die. Alternatively, positioning the fiber without contact and then applying an adhesive may result in the fiber being moved laterally by the adhesive. Since optical coupling between the die and the fiber is much more sensitive to lateral displacement than to axial displacement of the fiber, the latter method is least desirable.