DE2425328B2 - Process for the production of an opto-electronic directional line - Google Patents

Description

The invention relates to a method for producing an optoelectronic directional line according to the Preamble of claim 1.

Such a method is known from DE-OS 15 14 830, for example

From the magazine »Electronic Design« 20 (June 8th, 1972) 12, pages 26-30, it is known to work on the surface of Semiconductor substrates manufacture optical waveguides, for example by applying epitaxial layers or areas of the substrate have been changed by an ion (proton) implantation. the end This reference also discloses an arrangement in which the end of one is deposited on a substrate Waveguide at a distance a laser diode also applied to the surface of the substrate is opposite, so that the light emitted by the laser diode in the distant opposite Can penetrate the end of the light guide. It can be assumed that at the other end of the Light guide can face a photodiode in the same way as the laser diode to the first End of the light guide faces. In the known arrangement, the waveguide has the same thickness like the p- and η-areas of the laser diode together.

It can be seen that such an arrangement is relatively difficult to manufacture because it is selective Requires treatment of different areas of land. The distances and in particular the Precise parallelism between the opposing surfaces of the diodes and waveguides must be adhered to so that an effective light transmission takes place. Because the different treatment of the various surface sections is usually done with the use of masks it is necessary to align several masks to be applied one after the other very precisely. Here in Given the extremely small dimensions such components have, one for mass production is very great significant difficulty because the alignment of the masks must be done with extremely high accuracy.

The invention is based on the object of specifying a method for producing an optoelectronic directional line in which the difficulties arising from the need for precise alignment of masks are avoided, so that the production of such optoelectronic directional lines in large numbers is significantly simplified.
This object is achieved according to the invention by the

ίο method of claim solved.

When using the method according to the invention, a certain area becomes an extended one pn-junction destroyed by proton bombardment, to thereby separate components in the form a radiation source and a radiation detector. The destroyed area forms at the same time a »waveguide coupling area that inevitably both to the radiation source delimited by the proton implantation and to the as well delimited radiation detector adjoins It therefore takes place when using the invention Method a self-alignment of the waveguide coupling area on the radiation source and radiation detector instead, which makes it unnecessary, very tight tolerances in the arrangement of the waveguide coupling region to observe the position of the radiation source and radiation detector. Actually be yes all three areas, namely radiation source, waveguide coupling area and radiation detector Defined by proton bombardment in a single operation. In addition, the optoelectronic directional line according to the invention only requires two implantation process steps, so that a very simple production of such directional lines is also possible in this respect Therefore, the invention makes it possible to produce such optoelectronic directional lines on a large scale to produce with high yield and low cost.

A particular advantage of the method according to the invention is that the delimitation of the Areas to be irradiated can be done not only through the use of masks, but that the Implantation of ions and protons also by means of computer-controlled, sharply focused ion and Proton beams can take place, which further simplifies mass production significantly. About that In addition, controlled beams can be used to achieve better resolution and better edge definition of the implanted areas than using a mask technique.

The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing described and explained. It shows

F i g. 1 Cross-sections through the manufacture of a three-pole optoelectronic directional line resulting intermediates to illustrate the individual steps of the invention Procedure and

bo F i g. 2 cross-sections similar to FIG. 1 for illustration the process steps in the production of a four-pole optoelectronic directional line.

For the production of the optoelectronic directional line shown in FIG. 1 is shown by a

it substrate 51 made of gallium arsenide with a thickness of 250 to 400 μηι assumed that has a specific resistance of about 0.01 ohm · cm. This Substrate 51 is then placed in an oxidation furnace,

in which a SiOi layer 52 with a thickness of about 0.15 to 0.20 µm. The process used for this is a low temperature glass deposition process, with the silane and oxygen reacted in an oxidation furnace at about 380 ° C to generate hydrogen and silicon dioxide according to the following reaction equation:

+ O ₂

380 ° C
warmth

+ SiO ₂ + 2H ₂ .

The structure shown in FIG. 1b is then treated according to known photolithographic processes, namely by applying a photoresist mask and etching, in such a way that a relatively large-area opening 56 is formed, as shown in FIG. The structures shown in FIG. 1c are irradiated with high-energy positive ions 58 in order to form an implantation region 60. Preferably, positive zinc ions are used which are accelerated in a conventional ion implantation chamber so that they penetrate the exposed upper surface of the structure shown in FIG. 1c under the influence of an accelerating voltage of about 30 kV. The implant dosage has a typical value of 10 ¹⁶ ions / cm ² , whereby a region 60 of the p-type is formed. After a subsequent annealing process, the pn junction reaches a depth of about 1.00 μm.

The last-mentioned annealing process is preferably carried out after the removal of the oxide mask 52 by means of a Hydrofluoric acid solution and the subsequent application of a further oxide layer 62 carried out, with wiedef-dm the low temperature glass deposition process described above can be used. These further oxide layer 62 is shown in FIG. Id shown and again has a typical thickness of about 0.15 to 0.20 μm. The in Fig. The structure shown is annealed at about 900 ° C for about three hours to the above Mentioned depth of the pn transition at the area generated by implanting Zn ions of about 1 μπι to achieve.

After the in Fig. Id structure has been annealed, it is brought into a gold vapor deposition chamber in which a thin gold layer 64 with a thickness of about 1 to 1.5 μm is applied, as FIG. 1e shows. The purpose of this gold layer is to form a proton _{implantation mask which is able to withstand higher particle energies than the SiO 2} mask 52 which was used for the relatively low-energy zinc ions. The gold layer is provided with an opening 66 by applying a photoresist layer (not shown) to the surface of the gold layer 64 and then developing it to form a hardened photoresist mask. This mask has an annular opening through which an ion beam used for processing is directed onto the gold layer in order to remove the exposed gold sections and the oxide sections underneath by sputtering. After the mask with its opening 66 has been produced, protons 68 of high energy are radiated into the area of the structure according to FIG 70 to create. It is an annular area which extends by approximately 2 μm below the previously formed pn junction 73. Typical values for this step are an acceleration voltage of 300 keV and a dosage of 10 ¹⁵ protons / cm ² .

The structure shown in Fig.If is then with a hydrofluoric acid etching solution brought into contact, whereby the silicon oxide layer 62 with the above lying gold layer 64 is removed without attacking the gallium arsenide substrate. After that it will Formation placed in an oxidation furnace, in which again using the low temperature glass deposition process a new silicon oxide layer 76 is applied, as FIG. Ig shows After the oxide layer has reached a thickness of about 0.15 to 0.20 µm, the structure is placed in an annealing furnace brought and heated to 500 to 600 ° C for about an hour. The new oxide layer 76 not only protects the Surface of the structure according to Fig.Ig during the Glß'sens, but is also subsequently used as a permanent passivation oxide mask. on the three-pole monolithic The optoelectronic directional line used in FIG. 1 h is shown

After the annealing, the oxide layer 76 is shown in FIG. 1g using conventional photlithographic techniques Process treated so that the from F i g. 1 h apparent openings are formed. Since all in The metallic contacts shown in FIG. 1h are ohmic contacts, the metal surfaces 78, 80 and 82 in can be generated in a single operation. After applying the metal surfaces, the structure is after Fig. 1h placed in an oven to make metallic contacts 78, 80 and 82 with the gallium arsenide substrate to alloy at a certain temperature, which depends on the type of metallization. In which The present embodiment can be a gold-germanium alloy applied and heated to 45 ° C for about two minutes.

In operation, the pn junction 83 serving as a detector, which has been formed by the zinc implantation according to FIG. The radiation emitted from the pn junction 73 runs radially through the waveguide coupling region 70, which has the properties of a semi-insulator with a specific resistance of about 10 ⁸ ohm · cm, and is with a relatively high coupling efficiency in the region of the in the reverse biased detector junction 83 received. The received radiation generates hole-electron pairs in the vicinity of the pn junction 83, as a result of which a detector output current is generated at the terminals 85 and 87 when these output terminals are connected to an external load, not shown in detail.

It goes without saying that, if necessary, the mutual positions of the radiation sources and detectors described above with a pn junction are interchanged can be so that the detector the central portion of the arrangement and the radiation source Occupies the edge area of the arrangement. It will

eo believed that the optical effectiveness of this proposed alternative arrangement would not be as great is like the optical effectiveness of the arrangements according to FIG. lh. The reason for this is that one peripheral light-emitting pn-junction a substantial part of the radiation generated by the outer Edge of the light source radiated outwards and would thus be lost. However, it is quite possible that facilities, such as a suitable

Reflector near the pn junction of the radiation source, could be provided to avoid such radiation losses to prevent in the alternative arrangement.

F i g. 2a shows a gallium arsenide substrate 51 of the η type as the starting material, which is doped with chromium and has a very high specific resistance. This material is specifically used for the manufacture of a quadrupole opto-electric directional line, which will be described below. The specific resistance of 10 ⁷ to 10 ⁸ ohm · cm of the substrate 51 is significantly higher than the specific resistance of 0.01 ohm · cm of the substrate 51 of FIG. 1 described above. Chromium-doped substrates are commercially available from a number of suppliers and are usually manufactured by adding chromium to the melt from which the GaAs single crystals are drawn. The chromium serves to form deep-lying traps in the forbidden band, which trap electrons and thereby increase the specific resistance of the pulled crystal to the order of magnitude of 10 ⁷ to 10 ⁸ ohm cm, which is a concentration of about 10 ⁹ charge carriers / cm ³ is equivalent to

Using conventional lapping and polishing methods, the substrate is lapped and polished to a thickness of 250 to 400 μm. Then a thin (0.15 to 0.2 μm) silicon dioxide layer 52 is applied to the surface of the substrate 51 by the above-mentioned low-temperature glass deposition method, as FIG. 2b shows. The silicon dioxide layer 52 is then masked with a suitable photoresist and then etched, as is customary in photolithography, in order to form a relatively large opening 56 , as shown in FIG. 2c shows this first silicon dioxide layer must be sufficiently thick to be impermeable to a first implantation of high-energy sulfur ions in which a deeper implanted n-region 100 is formed, which is shown in FIG. 2c is indicated. A thickness of the oxide layer of 0.60 μm is sufficient for the mask 52. Typical values for sulfur implantation are an acceleration voltage of around 600 kV and an ion dosage of around 10 ¹⁶ ions / cm ² . The depth of the containing sulfur ions implanted region 100 takes up about 3 to μπι when the assembly is annealed after ion implantation at about 900 ⁰ C. However, this annealing is not carried out immediately, but rather after a subsequent implantation of zinc ions.

The structure shown in FIG. 2c is then etched in hydrofluoric acid in order to remove the mask 52 , after which the glass deposition process is used again in order to apply a further silicon dioxide layer 62 on the surface of the once-implanted arrangement. An annular opening 105 is then made in the silicon dioxide layer 62 using the usual process steps of photoresist masking and etching. The structure obtained in this way is shown in FIG. 2d. The opening 105 determines the width of the area in which an implantation of zinc ions 58 takes place, which are accelerated at about 30 kV and applied in a dose of about 10 ¹⁶ ions / cm ² . This zinc implantation step is identical to the zinc implantation step described above. The annealing for the sulfur and tin implantation takes place after completion of the tin implantation and after cleaning the arrangement shown in FIG. 2d with hydrofluoric acid and subsequent application of a new oxide layer, as FIG. 2e shows. The structure shown in FIG. 2e with the new oxide layer 64 is then placed in an annealing furnace, in which it is ^{annealed for about three hours at about 900 °} C. before a gold layer is applied according to FIG. 2f is prepared.

The structure according to Fig.2f is made by applying a gold layer, creating a mask from photoresist and ion beam micromachining made,

ίο as it has been described above for the structure according to Fig. If. The masking serves to determine the width of the annular opening 66 , which is shown in FIG. 2f. High-energy protons 68 are radiated through this opening 66 , which are also the

is penetrate previously formed pn junctions 101 and 107 to form a high resistivity waveguide coupling region 70 shown in FIG. 2g is shown. The structure according to FIG. 2g has a semi-insulating area 70 which is annealed after the surface of the gallium arsenide substrate has been provided with an oxide layer 76 again. Here, too, the glass deposition process is used to apply the oxide layer 76 to the surface of the gallium arsenide substrate before the areas of the proton implantation are heated ^{to about 500 to 600 ° C. for about one hour.}

The structure according to FIG. 2g is then masked using conventional photolithographic processes in order to form the illustrated openings in the silicon dioxide layer 76. A number of ohmic contacts 126, 128, 130 and 132 are then formed, all of which are located on the upper surface of the structure shown in FIG. 2h. The contacts 128, 130 and 132 advantageously have an annular shape. No electrode is required on the back of the substrate for this four-pole optoelectronic directional line. The forward voltage for the light-emitting pn junctions 125 and 127 is applied between the center contact 126 and the inner ring contact 128. The junctions 129 and 131 serving as detectors are reverse-biased by applying a DC voltage between the center ring contact 130 and the outer ring contact 132

The deep, sulfur-implanted area 100 provides the necessary insulation for the four-pole arrangement according to FIG. 2h. The radiation emitted by the pn junctions 125 and 127 is radially through the semi-insulating annular waveguide coupling region 70

so passed and collected in the detector pn junctions 129 and 131. It is noted that the deep implanted with sulfur area 100 both in surface contact with the center electrode 126 and the outer ring electrode 132 is such that all operating voltages to the upper Surface of the optoelectronic directional line can be fed. This property enables the assembly of the arrangement according to FIG. 2h on many types of sockets where rear contacts are not useful.

In the method according to the invention, all suitable p-type ions can be used for p-implantation can be used, such as cadmium, beryllium and magnesium, as well as for n-implantation all suitable ions of the η-type can be used, such as selenium, tellurium, silicon, Sulfur and tin if the right process conditions be respected. All of these potentiating substances are suitable for reducing radiation-emitting ph over-

to create corridors whose radiation is in the wavelength range from 0.900 to 1,000 μm. Furthermore, all suitable layers can be used for the production of insulating layers Low temperature glass deposition processes such as pyrolytic decomposition can be used of tetraethyl orthosilicate.

For certain combinations of metals and dopants required for directional lines according to the invention can be used, the corresponding annealing and alloying steps may require temperatures such that they disturb each other. Therefore, in some cases it may be necessary to do some or all of the again to combine or isolate the required annealing and alloying steps. In the latter case are Changes to the described sequence of procedural steps are unavoidable.

Another possible modification of the method and the device according to the invention makes implantation of η-type ions into p-type substrates.

It is also within the scope of the invention, the illustrated, special annular structure of change optoelectronic directional lines. For example, it can be used for certain applications Directional lines are appropriate, areas arranged in a straight line one behind the other, the radiation source, Detector and waveguide form to use. It is true that the ring shape shown increases the effectiveness the coupling between the radiation source and detector is maximized, which is the case for most applications Directional conduits is desirable, but a monolithic disk may very well be desirable to be divided into the individual components after production, without going around ring-shaped areas have to. For example, it may be desirable to have a special disk between the area of the radiation source and the waveguide coupling area or between the area of the detector and the To cut waveguide coupling area to separate two thirds of the structure of the optoelectronic directional line from the other third. These

ι ο Technology can be very useful if an existing one discrete radiation source or a discrete detector with a partial combination of waveguide and Detector or a partial combination of waveguide and radiation source must be combined.

Another possible geometric design is the use of a single radiation source with a pn junction, which is located in the center of an arrangement with a large number of isolated detectors conditional, which are arranged at a distance from each other surrounding the radiation source. For example detectors can be arranged 90 ° apart in the four squares of an area, which surrounds the radiation source with the pn junction and be isolated from one another there. Any detector could be created by a proton bombardment, isolated from the other optical channel with the be connected to the central radiation source. With such an arrangement, the individual detectors be applied separately from each other to voltage, so that the only one emitted by the radiation source Signal from each detector processed separately according to the specific detector voltages applied will.

For this purpose 2 sheets of drawings

Claims (1)

Claim: Process for the production of an optoelectronic directional line from a radiation source and a radiation detector, both of which are each made up of one of the same surface Semiconductor material existing substrate adjacent planar pn junction are formed, and there is an area of the substrate connecting the radiation source and the radiation detector, and the one waveguide coupling region connecting the radiation source and the radiation detector forms, characterized by that an extended pn junction is produced in the substrate by ion implantation and then activated by annealing, so that part of the pn junction is used as a radiation source and "another part can be used as a radiation detector, and then that between these parts lying area irradiated with protons and thereby in this area to the formation of the Waveguide coupling area, the pn junction is destroyed and the refractive index is increased.