Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
1999-09-13
2001-08-07
Pham, Long (Department: 2823)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C438S022000, C438S026000, C438S031000
Reexamination Certificate
active
06271049
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for producing an optoelectronic component, having a laser chip as a light emitter and a lens-coupling optical element for the defined projection of the optical beam generated in the laser chip.
Such optoelectronic components are used especially in optical data and communications technology as light emitting components for coupling the laser light generated into a fiber-optic waveguide.
European Patent EP 0 660 467 B1 describes an optoelectronic component that has a silicon substrate, on which the laser chip is mounted. The laser light, emitted by the laser chip parallel to the surface of the silicon substrate, enters a lens-coupling optical element, by which it is deflected 90° and focused. The lens-coupling optical element has a deflection prism, mounted on the substrate, and a laser chip that is present in the beam path behind the deflection prism.
These optoelectronic components are produced by making composite wafers. First, a silicon wafer acting as a common substrate is provided with suitable metal surface structures. After that, spaced-apart, parallel indentations are etched into the silicon wafer. Prism strips of trapezoidal profile are then placed in these indentations and bonded anodically or by soldering techniques. Next, the laser chips are disposed on the silicon wafer at a defined spacing from the prism strips and secured. The separation into separate components (dicing) is done either before or after the mounting of the laser chips, by sawing the silicon wafer apart along parting lines extending transversely to the prism strips. Finally, the laser chips are secured to the individual deflection prisms created by sawing the wafer apart.
This method has the disadvantage that the object distance, that is, the length of the light path between the emitting laser edge and the principal plane of the lens, cannot always be set with the requisite precision. When there is a structurally specified, fixed spacing between the lens and the deflection prism, the object distance is determined by the spacing between the laser chip and the prism strip. It has been demonstrated in practice that this spacing cannot always be preset with the requisite precision using currently available positioning systems. Furthermore, there are production-dictated variations in the focal length of the lenses. To compensate for the unavoidable positional errors of the laser chips, it is therefore necessary, after the positioning step, to individually measure out the spacings between the laser chips and the deflection prisms, as well as the focal lengths of the lenses used, and then to assign the respective laser chip a lens that fits it, in order to attain the desired focusing of the laser beam in a predetermined image plane.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for producing an optoelectronic component, with a laser chip and a lens-coupling optical element that deflects the laser beam, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which makes an economical production of such components possible.
With the foregoing and other objects in view there is provided, in accordance with the invention, a claim
1
.
The object of the invention is attained by a method as defined by claim
1
.
In the method of the invention, first the laser chip is placed in a positionally defined way on the semiconductor wafer. The desired object distance is then set by means of an appropriate adjustment of the lens-coupling optical element. To that end, the laser chip is driven, and the lens-coupling optical element is purposefully displaced on the semiconductor wafer until a predetermined beam condition with regard to the location of the focal plane of the optical image is met.
In this way, the desired focal adjustment of the optoelectronic component can be accomplished without measuring out the spacing between the laser chip and the deflection prism and without measuring out the focal lengths of the lenses to be used. A further substantial advantage of the method of the invention is that prefabricated lens-coupling optical elements can be used.
The predetermined beam condition can for instance be that the laser beam leaving the lens-coupling optical element is collimated, or is focused at an image plane that is located at a predetermined spacing from the surface of the semiconductor wafer.
Once the desired position of the lens-coupling optical element relative to the laser chip has been found, the lens-coupling optical element is secured to the semiconductor wafer, or to a portion of ti. The optoelectronic component is then ready for operation.
Cutting the semiconductor wafer apart into individual pieces (substrates), each with a respective laser chip, can be done chronologically before the adjustment (method steps c through f) of the lens-coupling optical elements. However, it is also possible to perform the aforementioned adjustment steps for each lens-coupling optical element while the composite wafer structure is still entire. In that case, the fully adjusted optoelectronic components are separated at the conclusion of the production method, after the lens-coupling optical elements have been secured to the semiconductor wafer (step f).
One expedient possibility for realizing the method of the invention is that securing the laser chip to the wafer (step b) and securing the lens-coupling optical element to the wafer (step d) are done by soldering, and that in the soldering step for securing the lens-coupling optical element, the heat is supplied locally. The local application of heat can be done for instance by means of a laser beam.
If heat is locally supplied, then preferably before the structures are made, a thermal insulation layer and in particular an SiO
2
layer is applied to the semiconductor wafer and then regionally removed again at least from the positions intended for the laser chips. The thermal insulation layer reduces the conduction of heat from the heated lens-coupling optical element to the laser chip and therefore acts to counter unsoldering thereof. Since there is no thermal insulation layer underneath the laser chip, good thermal coupling of the laser chip to the semiconductor wafer is still assured.
One preferred procedure, when soldering techniques are used for securing the laser chip and the lens-coupling optical element to the be, is that in the soldering step for securing the lens-coupling optical element a solder coating is used that has a lower melting temperature than the solder coating used to secure the laser chip. This provision, too, is a precaution the laser chip from coming unsoldered during the later soldering of the lens-coupling optical element.
Other especially preferred provisions according to the invention pertain to the production of the lens-coupling optical element used.
In a first, preferred production variant, lenses disposed in rows are embodied on one face of a lens carrier substrate, and the rows are spaced apart by a predetermined row spacing. Independently thereof, parallel-extending grooves are made, disposed at the same row spacing, in a deflection prism substrate, and one longitudinal side face of the grooves is mirror-coated, at least over part of its surface. After that, the lens carrier substrate and the deflection prism substrate are joined together positionally correctly by their faces remote from the lenses and oriented toward the grooves, and the composite structure comprising the lens submount substrate and the deflection prism substrate that has thus been formed is cut apart jointly into the individual lens-coupling optical elements.
The lens-coupling optical elements can also be produced from a single substrate, acting as both a lens submount and a deflection prism submount. In that case, lenses disposed in rows side by side are embodied on a first face of the substrate, and parallel-extending grooves are made on a second face opposite the first face. T
Auracher Franz
Gramann Wolfgang
Greenberg Laurence A.
Lerner Herbert L.
Pham Long
Siemens Aktiengesellschaft
Stemer Werner H.
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