Semiconductor device manufacturing: process – Chemical etching – Combined with coating step
Reexamination Certificate
1999-02-16
2001-01-23
Kunemund, Robert (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Combined with coating step
C438S700000, C438S734000, C438S737000
Reexamination Certificate
active
06177352
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for producing at least one semiconductor body. The semiconductor body is formed of a layer sequence with at least one active zone that is applied to a semiconductor wafer by metal organic vapor phase epitaxy, and in which the layer sequence is provided with at least one mesa trench. It relates in particular to a method for producing light emitting diode (LED) chips with a mesa structure by metal organic vapor phase epitaxy (MOVPE).
A method for producing MOVPE LED chips is known for instance from U.S. Pat. No. 5,233,204. In it, by metal organic vapor phase epitaxy (MOVPE), a heterostructure including an n-conductive first InGaAlP boundary layer, an n-conductive active InGaAlP layer, and a p-conductive second InGaAlP boundary layer are deposited on a GaAs semiconductor wafer. A window layer of AlGaAs, GaAsP or GaP is applied by epitaxy to the second InGaAlP boundary layer. Next, an underside contact metallizing is applied to the underside of the semiconductor wafer, and a plurality of top contact metallizings are applied to the top side of the window layer. The semiconductor wafer is subsequently divided up into individual LED chips by sawing or diamond-wheel dicing.
In the LED chips, the window layer serves first to attain a lateral current propagation as much as possible over the entire cross section of the p-n junction, and second to increase the surface area of the LED chips that is available for light output. The ratio between the area of the semiconductor body covered by the top contact to the free surface area of the semiconductor body is increased. However, a large proportion of the radiation generated in the active zone is still lost by the total reflection at the surface of the LED chip.
Furthermore, when the semiconductor wafer is sawed or diced, destruction to the side faces of the epitaxial layers occurs, which among other things causes faster aging (degradation in the brightness of the LED over time) of the LED chips.
From Published, Non-Prosecuted German Patent Application DE 43 05 296 A1, corresponding to U.S. Pat. No. 5,429,954, a method for producing an LED is known in which mesa trenches are formed by wet-chemical etching in a layer sequence applied epitaxially to a substrate body, in order to improve the radiation power.
Such a wet-chemical etching process, however, in LED chips made by MOVPE, leads to selective etching of the MOVPE layer sequence. This creates so-called “mushroom” structures, which in semiconductor chips are provided with plastic sheathing because of mechanical stress, again causing faster aging (degradation in the electrical properties over time).
In U.S. Pat. No. 5,309,001, an MOVPE LED chip with a mesa structure is described that is made by wet-chemical etching or by reactive ion beam etching. The external quantum efficiency of such diodes, however, is still very low.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for producing semiconductor bodies with an MOVPE layer sequence that overcomes the above-mentioned disadvantages of the prior art methods of this general type, which exhibit reducing aging and with which MOVPE LED chips can be produced with improved output of the radiation, generated in the active layer, from the semiconductor body.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for producing at least one semiconductor body, which includes: providing a semiconductor wafer; applying a layer sequence with at least one active zone to the semiconductor wafer by a metal organic vapor phase epitaxy; and dry etching at least one mesa trench in the layer sequence, and varying etching parameters during the dry etching such that with an increasing etching depth a ratio of a vertical etching rate to a horizontal etching rate is increased for creating at least one semiconductor body with at least one side face curved in a concave fashion.
According to the invention, it is provided that on the semiconductor wafer, by a metal organic vapor phase epitaxy (MOVPE), a layer sequence with at least one active zone is applied. The active zone is formed, into a light emitting diode (LED) or photo diode chip, for instance, in such a way that it transmits light when it is acted upon by an electric current and/or that it generates an electric voltage if it receives light. The layer sequence is provided with at least one mesa trench by dry etching, and during the dry etching the etching parameters are varied in such a way that with increasing etching depth the ratio of the vertical etching rate to the horizontal etching rate is increased. In this manner, the semiconductor body with the at least one side face is curved in a concave fashion as viewed from outside the semiconductor body.
During the dry etching, to increase the ratio of the vertical etching rate to the horizontal etching rate, the concentration of the various gases in an etching gas mixture is preferably varied.
For etching the mesa trench in the semiconductor body, which is formed substantially from GaAs, GaP or GaN or at least one alloy of these materials with Al and/or In, an etching gas mixture is preferably used that has at least chlorine and silicon tetrachloride or at least chlorine and boron trichloride; and that the chlorine concentration in the etching gas mixture is varied during the etching. In comparison with conventional etching gas mixtures, which contain only a single one of the gases in the group including silicon tetrachloride, boron trichloride and chlorine, a markedly increased etching rate is attained by adding chlorine and at least one of the components in the group including silicon tetrachloride and boron trichloride. By varying the chlorine concentration in the etching gas mixture, an in-situ variation of the etching rate and thus the establishment of arbitrary etching angles are possible. If the chlorine concentration in the etching gas mixture is reduced with increasing etching depth in according to the invention, the result is a mesa trench with a concavely curved inner surface.
The mesa trench is preferably etched into the MOVPE layer sequence such that the active zone is severed. After that, the composite is divided up into individual semiconductor bodies, each with at least one mesa edge.
In the dry etching, no selective etching of the MOVPE layer sequence takes place. Hence no “mushroom” structures, which would cause increased mechanical stress and consequently faster aging of the semiconductor body, are created. Furthermore, in a semiconductor body produced by the method of the invention, the side faces of the active zone, such as a light-emitting and/or light-receiving p-n junction, advantageously exhibit markedly less destruction than is the case with semiconductor bodies made by sawing or dicing.
Another advantage of the method of the invention is that in the case of light-emitting semiconductor bodies, because of the curvature of the side faces (mesa curvature) of the semiconductor body, as compared with conventionally made semiconductor bodies with flat side faces, a greater proportion of the light generated in the active zone falls onto the boundary between the semiconductor body and the ambient medium (such as air or plastic) at an angle that is less than the limit angle of the total reflection. Less light is therefore reflected back into the semiconductor body, and the optical efficiency is increased.
It is also especially advantageous that by the method of the invention, the mesa etching creates regions of the active zone that are already separated from one another, and which are joined to one another mechanically by the semiconductor wafer that has not been etched all the way through. It is thus possible to measure the function of active zones, separate from one another, in the wafer composite, and only after that to divide up the semiconductor wafer finally into separate semiconductor bodies, for instance by means of sawing.
Thus by way of example and advantageo
Nirschl Ernst
Schönfeld Olaf
Greenberg Laurence A.
Kunemund Robert
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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