1. Field of the Invention
The present invention relates to a method for producing and forming semiconductor light emitting diodes (LEDs), as well as to the production of light emitting display devices formed by the light emitting diodes. In particular, the present invention relates to a method of forming densely packed matrices of semiconductor LEDs which may be individually controlled.
2. Description of Related Art
In the field of display devices and displays in general, conventional cathode radiation tubes are being increasingly replaced, in many areas of application, by flat displays such as liquid crystal displays (LCDs). The use of LCDs include a number of known disadvantages, including poor luminosity, directional dependence for visual impression, and slow response speed. Even though these problems are not unsolvable, they can for the most part only be coped with by the use of considerable energy. This is partly based on the fact that the emitted light displayed by the device in the direction of the observer is produced subtractively, i.e. by filtering of externally irradiated light, wherein an active medium, normally a liquid crystal, performs the function of a controllable light filter. An additional source of the present problems stems from the characteristics of the active mediums predominant use of liquid crystals.
As a result of the aforementioned difficulties, there have been considerations of display devices wherein light production processes take place additively, i.e. by independent light emitting elements such as light emitting diodes. The light emitting diodes are normally arranged in a matrix, such as with the cells of a LCD display. In addition it is required that such LEDs be controllable. Such display devices were limited in the past to either display devices of medium informational content such as digital displays, or alphanumerical displays with a low number of pixels in the matrix. But large area display devices with high informational content have proven to be difficult in the past because of their complexity and high loss capacity. As a result, large area displays have not emerged from the experimental stage. Large scale production of large numbers of microscopically small and individually controlled semiconductor light emitting diodes in a tight matrix, i.e. with a very high density, have also not been particularly successful nor satisfactory.
A method for the production and formation of LED semiconductor chips is to known from German reference DE 196 32 626, wherein a semiconductor layering sequence is applied, with an active zone, on a substrate, by metal organic gas phase epitaxy (MOVPE). The layering sequence is equipped with at least one mesa ditch, formed by dry cauterization and having a depth which is sufficient such that the active zone of the layering sequence can be separated. Thereafter, the combination of substrate and layering sequence is sectioned in such a way that at least one semiconductor body, or if desired a number of semiconductor bodies, are individually created with at least one mesa flank. However, the reference does not discuss how a majority of semiconductor bodies can be put under individual control nor further. processed after the separation process.
Japanese reference JP 06350136 A sets out a method wherein an integral semiconductor body, having: a layering sequence; an active zone; and contacting metallizations; is installed on an adhesive area. Thereafter, individual LED chips are produced by etching, such that individual LED chips are arranged on an adhesive area and can be further processed and respectively contacted. But the use of an adhesive area is relatively elaborate, because initially a secure adhesion had to be ensured, and later on in the manufacturing process a chemical process has to employed for the chips removal from the adhesive area.
German reference DE 40 16 698 A1 describes a support carrier using suction for the transfer of pieces, whereby the pieces are detachable from the suction carrier and are specifically positioned and otherwise precisely oriented. The suction carrier provided with Individually controllable chambers for which the pieces to be transferred are assigned. The production and application of LED cells is also described.
European reference 0 683 527 A1 describes a method for producing a light emitting diode arrangement having a high density, wherein on the semiconductor substrate following a first electrical contacting layer of a highly doped semiconductor material, an active layering sequence and a second electrical contacting layer are applied. By etching steps of various depth in columns or lines, electrically insulated LEDs are produced in columns or lines, which are arranged in a matrix shape and can be controlled individually and electrically. But with this method the LEDs themselves are not individually produced.
It is therefore an object of the present invention, to provide a method for production and formation of small semiconductor light emitting diodes. It Is a further object of the present Invention, to produce a display device on the basis of this method, the display device having a high pixel density and comprising semiconductor light emission diodes. In addition, it is an object of the invention to produce the semiconductor LEDs in a tight matrix wherein each LED may be individually controlled. Furthermore, it is an object of the invention that the masks be of sufficient integrity so as to accommodate appropriate etching so as to satisfy tight requirements of a dense matrix. It is another object of the invention to provide a method which can be implemented so as to enable mass production at reasonable engineering effort and expense and with maximally replicable component characteristics. It is still further an object of the invention to enable the production and individual formation of microscopic semiconductor light emitting diodes and subsequently their separate association, via micromechanical tooling, with electrical contacting for use in an additive display device.
The present invention comprises a method for the production and formation of semiconductor light emitting diodes comprising the steps of: producing a semiconductor light emitting device having at least one pn-junction and at least one metallization layer; applying an etching mask having a first mask arrangement on one side of the semiconductor device, said arrangement defining covered and open areas of the semiconductor device; applying a supporting layer on the other side of the semiconductor device; vertically etching the semiconductor material within said open areas from said one side to said carrier; removing said etching mask thereby exposing remaining portions of said semiconductor light emitting device not previously covered by said mask, said remaining portions comprising light emitting diodes; engaging said light emitting diodes with an accommodating device, said device comprising slots arranged to individually receive each of said light emitting diodes; and removing said carrier.
The invention is explained in greater detail below and by reference to exemplary embodiments shown in the drawings.