WO1997031279A1

WO1997031279A1 - Method of producing a master structure

Info

Publication number: WO1997031279A1
Application number: PCT/DE1996/002273
Authority: WO
Inventors: Roland Mueller-Fiedler; Dietmar Hahn; Franz LÄRMER; Klaus-Michael Mayer; Hans Kragl; Hergo-Heinrich Wehmann
Original assignee: Robert Bosch Gmbh
Priority date: 1996-02-22
Filing date: 1996-11-27
Publication date: 1997-08-28
Also published as: DE19606537A1

Abstract

The invention concerns a method of producing a master structure for a polymer substrate, the semiconductor substrate being coated with a masking layer in which there is a recess below which a waveguide channel is to be produced. The masking layer has a further recess in which an adjusting channel is to be produced. The further recess is masked and the waveguide channel is produced by etching. The recess is masked and the adjusting channel is produced.

Description

Process for producing a master structure

State of the art

The invention relates to a method for producing a master structure for a polymer substrate according to the preamble of the main claim.

German patent application P 42 12 208.2 describes a method for producing optical polymer components with integrated fiber-chip coupling using impression technology. A master structure is produced on a silicon substrate, then a negative mold is galvanically molded from this master structure and the resulting negative mold is used for the production of daughter structures identical to the master structure in the injection molding or injection molding process with polymer plastics. Both the master structure and the optical polymer component to be produced have an optical waveguide trench. In addition, an adjustment groove for glass fibers with a V-shaped cross section is provided both in the master structure and in the optical polymer component to be produced. The V-groove will be there made by anisotropic etching. In the known method, different mask exposures are required for the adjustment groove and for the optical waveguide trench. Since the lateral adjustment between the optical waveguide trench and the adjustment groove is particularly important, the

To keep coupling losses between the glass fiber to be inserted into the alignment groove and a waveguide lying in the optical waveguide trench as low as possible, it is desirable to maintain the lateral positioning accuracy between the optical waveguide trench and the alignment groove as high as possible.

Advantages of the invention

In contrast, the method according to the invention has the advantage that the adjustment groove and the waveguide groove are defined by a common masking layer. This improves the lateral positioning accuracy between a glass fiber to be inserted and a waveguide to be arranged in the waveguide groove.

Advantageous further developments and improvements of the method specified in the main claim are possible through the measures listed in the subclaims.

The step-wise etching through of an auxiliary layer, by first producing depressions and then openings, advantageously serves to keep the number of masking steps as low as possible while maintaining the accuracy of the masking layer and at the same time to maintain selectivity in the etching.

If a separating layer is arranged under the auxiliary layer, this also serves the purpose of maintaining the selectivity and thus the accuracy of the arrangement during the etching. The separating layer can advantageously be etched with a liquid or with a plasma etching process and the auxiliary layer with a dry etching process. There is also an advantage if the mask applied later, be it a protective mask or a mask, has a greater layer thickness than the separating layer, since this reduces the risk that this layer is thinned during an etching process in such a way that structural defects can occur. Placing an additional layer under the

Masking layer, as well as arranging a cover layer under the protective mask, in turn advantageously serve to maintain the selectivity and thus the accuracy of the method according to the invention.

The arrangement of an intermediate layer between the semiconductor substrate and the masking layer advantageously serves to increase the security during the etching by increasing the thickness of the protective material. In addition, by appropriate selection of materials for the

Intermediate layer the undesirable effect of the undercut can be reduced.

The precision of the resulting master structure is increased and thus improved if one for the intermediate layer

Material is selected against which the semiconductor substrate can be selectively etched and which can be selectively etched against the masking layer, since this can ensure that only the desired area is attacked during the etching process.

Reactive ion etching is particularly suitable for producing the waveguide groove, since this etching process does not have the effect of redisposition. It also has the advantage that by utilizing the natural effect of the orientation, doping and / or composition-dependent self-delay of the etching process, a very precise adjustment groove can be produced by producing the adjustment groove by anisotropic etching.

The straightening of the end face of the adjustment groove by sawing or steep wall high-rate etching advantageously serves to make the front-side coupling point between a glass fiber to be inserted and a waveguide located in the waveguide groove particularly high quality.

Smoothing the walls of the waveguide groove by oxidizing and etching reduces the attenuation in the case of a waveguide to be arranged in this waveguide groove.

The use of the method of electrochemical, photo-induced etching represents a very simple and inexpensive method for etching. In addition, this method is suitable for producing waveguide grooves with a variable depth profile.

The selection of an opaque material for the cover mask and the masking layer proves to be advantageous, since as a result these two masks can simultaneously serve as etch-resistant material and as an optical mask for photo-induced, electrochemical etching.

The production of a waveguide groove with a variable depth profile turns out to be advantageous, since such a waveguide groove for optical switches with low radiation losses, the production of taper transitions between waveguides and optical components or Fibers and a harmonious adaptation of the

Waveguide cross section is important for specific application. A further advantage is given by the fact that, in order to achieve a variable etching depth, a laser beam over the area to be etched at variable speed,

Intensity or length of stay is moved, since it is a particularly easy to carry out process.

The same advantage of simplifying the manufacturing process is achieved by using an optical one

Intensity filter with a transparency distribution equivalent to the depth profile.

The arrangement of strip-shaped electrodes above or below the caustic area and their actuation with different electrical currents represents a simple and very variable method of producing a changing depth profile.

drawing

Embodiments of the invention are shown in the drawing and explained in more detail in the following description.

Show it:

FIG. 1 shows a semiconductor substrate with a masking layer,

2 shows a semiconductor substrate with masking layer and

3, a semiconductor substrate with a masking layer,

Mask and waveguide,

4 shows a semiconductor substrate with a masking layer and

Waveguide groove,

FIG. 5 shows a semiconductor substrate with a masking layer and protective mask, FIG. 6 shows a semiconductor substrate with a masking layer,

Protective mask and adjustment grooves,

7 shows a semiconductor substrate with a waveguide groove and

Justieruten, Figure 8 is a semiconductor substrate with intermediate layer and

Masking layer,

FIG. 9 shows a semiconductor substrate with an intermediate layer and structured masking layer,

FIG. 10 shows a semiconductor substrate with an intermediate layer, masking layer and protective mask,

FIG. 11 shows a semiconductor substrate with structured

Intermediate layer, structured masking layer and

Protective mask,

FIG. 12 shows a semiconductor substrate with a structured intermediate layer and a structured masking layer,

FIG. 13 shows a semiconductor substrate with structured

Intermediate layer, structured masking layer and

Adjustment grooves,

FIG. 14 a semiconductor substrate with an intermediate layer, masking layer and cover mask,

FIG. 15 shows a semiconductor substrate with structured

Intermediate layer, masking layer and mask,

FIG. 16 shows a semiconductor substrate with alignment grooves,

17, a semiconductor substrate and a form stamp,

FIG. 18 a stamp and a polymer substrate,

Figure 19 shows a polymer substrate, a lid and

Optical fibers,

FIG. 20 shows a semiconductor substrate with a separating layer and auxiliary layer,

Figure 21 is a cut side view and a

Top view of a semiconductor substrate with auxiliary layer,

Separation layer and masking layer, FIG. 22 shows a cut side view and a top view of a semiconductor substrate with auxiliary layer and depressions in the auxiliary layer,

23 shows a cut side view and a top view of a semiconductor substrate with an auxiliary layer and a cover mask,

FIG. 24 shows a cut-away side view and a top view of a semiconductor substrate with an auxiliary layer and a cover mask and a breakthrough in the auxiliary view,

25 shows a cut-away side view and a top view of a semiconductor substrate with an opening in the separating layer, FIG. 26 shows a cut-away side view and a top view of a semiconductor substrate with an opening in the separating layer and with a waveguide groove, FIG Semiconductor substrate with waveguide groove, in which the mask has been removed, FIG. 28 shows a cut-away side view and one

Top view of a semiconductor substrate with a thermally grown oxide as a protective mask, FIG. 29 shows a cut-away side view and a top view of a semiconductor substrate with a thermally grown oxide as a protective mask and an opening in an auxiliary layer,

FIG. 30 shows a cut-away side view and a top view of a semiconductor substrate with thermally grown oxide as a protective mask and an opening in a separating layer,

FIG. 31 shows a cut-away side view and a top view of a semiconductor substrate with thermally grown oxide as a protective mask and an alignment groove, Figure 32 is a cut side view and a

Top view of a semiconductor substrate with waveguide groove and alignment groove,

FIG. 33 shows a cut side view of a semiconductor substrate with a masking layer,

Figure 34 is a cut side view and a

Top view of a semiconductor substrate with additional layer and structured masking layer,

Figure 35 is a cut side view and a plan view of a semiconductor substrate with structured

Masking layer and structured additional layer,

Figure 36 is a cut side view and a

Top view of a semiconductor substrate with masking layer,

Additional layer and mask, Figure 37 is a cut side view of a

Semiconductor substrate with masking layer, additional layer and

Waveguide groove,

Figure 38 is a cut side view and a

Top view of a semiconductor substrate with additional layer, waveguide groove, in which the mask has been removed,

Figure 39 is a cut side view and a

Top view of a semiconductor substrate with a cover layer,

Figure 40 is a cut side view and a

Top view of a semiconductor substrate with a cover layer and a protective mask,

Figure 41 is a cut side view of a

Semiconductor substrate with a structured cover layer and a protective mask,

FIG. 42 shows a cut side view and a top view of a semiconductor substrate with structured

Top layer, adjustment groove from which the protective mask was removed,

Figure 43 shows a device for photo-induced electrochemical etching. Description of the embodiments

FIGS. 1 to 7 show individual intermediate stages in the process sequence for a first exemplary embodiment for producing a master structure.

1 shows a flat, cuboidal semiconductor substrate 1, on the upper side of which a masking layer 2 is applied. The masking layer 2 has in its center a rectangular, elongated recess 4, which merges into a rectangular recess 3 at the ends thereof. The rectangular cutouts 3 extend to the edge of the masking layer 2.

The semiconductor substrate 1 here consists of a

Compound semiconductors (III - V), e.g. Gallium arsenite. For the masking layer 2, a material is to be selected which allows selective etching of the semiconductor substrate 1 with respect to the masking layer 2. For example, gold is suitable as the material for the masking layer 2. The structuring of the masking layer 2 on the semiconductor substrate 1 takes place, for example, in a photolithography process after the entire surface of the top of the semiconductor substrate 1 has been coated. Of course, the etching in the masking layer 2 is also selective with respect to the semiconductor substrate 1.

The arrangement shown in FIG. 2 differs from the arrangement in FIG. 1 by a cover mask 5. The cover mask 5 consists of two rectangular, strip-shaped sections which cover part of the masking layer 2 and the rectangular cutouts 3. The entire surface of the semiconductor substrate 1 is therefore covered with the exception of the elongated recess 4 either by the masking layer 2 or by the cover mask 5. The mask 5, like the masking layer 2, must consist of a material that is etch-resistant for the subsequent etching process of the semiconductor substrate 1 and at the same time selectively etchable with respect to the semiconductor substrate 1. In addition, the mask 5 should be selectively etchable with respect to the masking layer 2. A photoresist can preferably be used for the mask 5. The mask 5 is applied, for example, by means of a full-surface coating and a subsequent photolithography process.

The arrangement from FIG. 2 is subjected to an etching process in which a waveguide groove 6 is formed below the elongate recess 4 in the semiconductor substrate 1. An electrochemical, photo-induced etching can preferably be used for this etching method, as will be described in connection with FIG. 43. In this example, the resulting waveguide groove 6 has a cuboidal contour. In a later one

Method step, the waveguide groove 6 is filled with a polymer adhesive, whereby a waveguide is formed there. The result of this etching process is shown in FIG. 3.

The arrangement shown in FIG. 4 results from the arrangement from FIG. 3 in that the cover mask 5 is removed again from the surface of the semiconductor substrate 1 or the masking layer 2. Accordingly, the semiconductor substrate 1 with the waveguide groove 6 and the masking layer 2 embedded therein remains.

The mask 5 is preferably removed by means of a solvent which only attacks the mask 5. As a further method step, a rectangular protective mask 7 is applied to the arrangement from FIG. 4, which is shown in FIG. 5. The protective mask 7 covers part of the masking layer 2 and the waveguide groove 6. The surface of the semiconductor substrate 1 is now covered with the exception of the rectangular cutouts 3 by the masking layer 2 or the protective mask 7.

The protective mask 7 must consist of a material that is etch-resistant for the subsequent etching process of the semiconductor substrate 1 and must be selectively etchable with respect to the semiconductor substrate 1. The same material can preferably be selected for the protective mask 7 as for the cover mask 5. The protective mask 7 is applied, for example, by means of a full-surface coating and a subsequent photolithography process.

In the following etching process, alignment grooves 8 are formed in the semiconductor substrate 1, which have a V-shaped cross section. They are exactly where the rectangular ones used to be

Cutouts 3 were. This arrangement is shown in Figure 6.

The etching process used for this purpose can preferably be an anisotropic etching process in which the

There is a natural etching stop in the crystal direction of the semiconductor substrate 1, since the etching process slows down automatically when the intersection of the crystal planes is reached. The adjustment grooves 8 are used in the polymer substrate to be created later for the adjustment of ends to be inserted into the adjustment grooves 8 of optical fibers, which are fixed with their outer contour in the adjustment groove 8. The adjustment grooves 8 are aligned with the longitudinal axis of the waveguide groove 6, so that the light guided in the first optical fiber lies through the light in the waveguide groove 6 coming waveguide gets into the further optical fiber. The end face of the adjusting groove 8 on the waveguide side likewise has an inclination here, which is approximately disadvantageous for the coupling between the optical fiber and the waveguide that will be desired later. To remove this oblique face will be explained in more detail in a subsequent paragraph.

The last method step is to remove the protective mask 7 and the masking layer 2 from the surface of the semiconductor substrate 1. FIG. 7 shows what the semiconductor substrate 1 remaining after this method step looks like. It now extends the two inverted roof ridge-shaped elongated adjustment grooves 8, which are located on two sides on the surface of the

Semiconductor substrate 1 face. The adjustment grooves 8 are connected to the waveguide groove 6 along their aligned ridge lines. The semiconductor substrate 1 structured in this way represents the master structure 21. The waveguide groove 6 and the adjustment grooves 8 were defined together in a common exposure process, namely during the structuring of the masking layer 2, as a result of which a very high accuracy of the positions of the grooves 6, 8 relative to one another was achieved . The two process steps of etching the adjustment grooves 8 and

Etching of the waveguide groove 8 are also interchangeable in their order.

FIGS. 8 to 16 show individual intermediate stages of the process sequence for a further exemplary embodiment. For simplification, the numbering from FIGS. 1 to 7 has been retained.

FIG. 8 shows a semiconductor substrate 1 which has the semiconductor substrate 1 over its entire surface covering masking layer 2. An intermediate layer 11 is additionally arranged between the masking layer 2 and the semiconductor substrate 1.

In this case, the semiconductor substrate 1 is not a compound semiconductor (III-V) but an elemental semiconductor (IV). The intermediate layer 11 preferably consists of a compound semiconductor. The arrangement of the intermediate layer 11 makes it possible to selectivity between the masking layer 2 and the

Intermediate layer 11 as well as selectivity between the intermediate layer 11 and the semiconductor substrate 1. This occurs primarily with pure IV semiconductors. For example, phosphoric acid and hydrochloric acid are used for the etching of the intermediate layer 11, if this consists of indium phosphide (InP), while heated potassium hydroxide (KoH), which is suitable for the anisotropic etching of the alignment grooves 8 in the semiconductor substrate 1, if this consists of silicon, can be used Masking Layer 2 would attack from gold. III / V semiconductors can also be etched as a material layer as an intermediate layer 11 on a III / V semiconductor substrate 1. The masking layer 2 in turn serves only as an etching mask for structuring the intermediate layer 11, which performs the function of the masking layer 2 in the process described for producing the master structure on a compound semiconductor. The extent of undercuts therefore remains extremely low, so that the precision of the process is high.

This arrangement is structured, for example by means of a photolithographic process, in such a way that the same recesses 3, 4 are created in the masking layer 2, as already shown in FIG. Such structuring can also be carried out using a lift-off technique or another suitable method. The resulting arrangement is shown in FIG. 9. The masking layer 2 can be selectively etched with respect to the intermediate layer 11.

The elongated recess 4 in the masking layer 2 is in turn covered with a protective mask 7 using e.g. of a photolithography process. Selectivity with respect to the masking layer 2 and the intermediate layer 11 is also required here. Figure 10 shows the resulting arrangement, the entire top of the intermediate layer 11 with the exception of the rectangular recess 3 of the

Masking layer 2 or the protective mask 7 is covered.

Figure 11 shows the arrangement after the completion of the next process step. For this purpose, an etching process was used in which an etching solution was used which only attacks the material of the intermediate layer 11. In this way, further rectangular cutouts 9 also arise in the intermediate layer 11, directly below the rectangular cutouts 3.

After this step, the protective mask 7 is removed again, as shown in FIG. There remains the semiconductor substrate 1 with the intermediate layer 11, the further rectangular recesses 9 present therein and with the masking layer 2 with the rectangular recesses 3 present therein. A further anisotropic etching process now follows, in which an etching solution through the rectangular recesses 3, 9 acts on the surface of the semiconductor substrate 1. This creates adjustment grooves 8, as shown in Figure 13. Here too, the adjustment grooves 8 in turn have the oblique end faces on their side adjacent to the elongated recess 4.

In the subsequent process step, the rectangular cutouts 3, 9 and the adjustment grooves 8 are made with a Mask 5 covered so that only the elongated recess 4 is exposed from the top of the intermediate layer 11. This is shown in FIG. 14.

In the now following etching process, the intermediate layer 11 is structured in such a way that first a recess in the elongated recess 4 is produced through the intermediate layer 11 and then, by etching, a waveguide groove 6 through the elongated recess 4 in the masking layer and in the

Intermediate layer 11 is produced. After this process step there is an arrangement as shown in FIG. 15.

The mask 5, the masking layer 2 and the intermediate layer 11 are then removed. The structure of the semiconductor substrate 1 then corresponds to the arrangement shown in FIG. Here, too, the order of manufacture of the waveguide groove 6 and the adjustment groove 8 can be interchanged.

Since the anisotropic etching of the adjustment grooves 8 also produced an oblique end face of the adjustment grooves 8, it is now advantageous to make a saw cut 10 on the end face of at least one adjustment groove 8, so that a completely vertical end face of the adjustment groove 8 is created. This arrangement is shown in FIG. 16.

When using a III-V semiconductor substrate 1, this saw cut can be omitted, since with a suitable choice of the etching solution (for example H ₃ PO ₄ : HCL) for InP substrate, the inverted roof-ridge-shaped adjustment grooves 8 have almost vertical end faces. FIG. 17 shows how the semiconductor substrate 1 with the waveguide groove 6 and the alignment grooves 8 functions as a master structure 21. For this purpose, an impression is made of the semiconductor substrate 1, for example by applying a material to it by galvanic means. After the removal of the semiconductor substrate 1, a form stamp 20 has been created which has ridge-shaped elevations 28 corresponding to the adjustment grooves 8 and an elongated elevation 26 corresponding to the waveguide groove 6 therebetween.

A metal is particularly well suited as material for this form stamp 20. Nickel in particular is ideally suited for such a form stamp 20.

FIG. 18 shows how the form stamp 20

Daughter structures 30, which are similar to the master structure 21, are molded by the die 20. For this purpose, a casting process (e.g. injection molding, embossing process) takes place, in which a plastic, preferably a polymer plastic, is poured onto the die 20 and removed again after curing. The daughter structure 30 is then the polymer substrate 30 to be produced.

In the arrangement shown in FIG. 19, it is shown how an optical component can be produced from such a molded polymer substrate 30 with waveguide grooves 36 and adjustment grooves 38 and a matching cover 31 which also has corresponding adjustment grooves 38. For this purpose, one end of optical fibers 40 is inserted into the V-shaped adjustment grooves 38. For pre-adjustment, the optical fibers 40 are connected to a pre-adjustment device 42. A polymer adhesive 41 is then introduced between the polymer substrate 30 and the cover 31 using an injection mold 43, and the cover 31 is lowered onto the polymer substrate 30 with the optical fibers 40 inserted. The Polymer adhesive 41 fills the waveguide loops 36 and at the same time brings about a firm connection between the polymer substrate 30 and the cover 31. The filled waveguide grooves 38 now form waveguides in continuation to the optical fibers 40. By integrating optical components in the cover 31 or also in the polymer substrate 30, optical signals carried in the optical fibers 40 can be processed.

A third exemplary embodiment is shown in intermediate stages in FIGS. 20 to 32. Again, the numbering from the previous figures has been retained.

FIG. 20 shows the cut side view of a semiconductor substrate 1 which has been coated over its entire surface with a separating layer 15. An auxiliary layer 12 was additionally deposited on the separating layer 15. The separating layer 15 is preferably an oxide layer (SiÜ ₂ ), which preferably has a thickness of 100 nm, and for the auxiliary layer 12, for example, a nitride is selected (Si3N_ι), which preferably has a thickness of 200 nm. Silicon, for example, is used here as the semiconductor. However, other materials can also be used, it being only necessary to note that the auxiliary layer 12 must be selectively etchable with respect to the separating layer 15, just as there must be selectivity between the separating layer 15 and the semiconductor substrate 1.

FIG. 21 shows how the arrangement from FIG. 20 was additionally coated with a masking layer 2. The masking layer 2 has in its center a rectangular, elongated recess 4, at one end of which a rectangular recess 3 is arranged. In particular, a photoresist can be used here as the masking layer 2. A photoresist is structured in a known manner by exposure and development.

In Figure 22 the result is the next one

Process step shown starting from Figure 21. The arrangement from FIG. 21 was subjected to a dry etching process, the masking layer 2 serving as an etching mask. The exposed area of the auxiliary layer 12 is attacked during the dry etching process, the etching process after the etching preferably being stopped by approximately half the layer thickness of the auxiliary layer 12 by checking the etching time, so that in the area of the rectangular recess 3 or the elongated, rectangular recess 4 the auxiliary layer 12 has a smaller layer thickness. In this example, the auxiliary layer 12 was reduced to half its thickness there, so that it is only about 100 nm thick there and about 200 nm at the non-etched points. The masking layer 2 is then removed, which is no longer is required because the recesses 3, 4 have been imaged in depressions 13, 14 in the auxiliary layer 12.

FIG. 23 shows how the arrangement just described was subjected to the next method step, namely the application of a cover mask 5, which covers the surface of the auxiliary layer 12 at least in the area of the rectangular recess 13. The mask for attaching the masking mask 5 structured in this way does not require high adjustment requirements, since it can only cause an inaccuracy in the axial direction of the ridge line of the inverse roof ridge-shaped adjustment groove to be produced. For example, a mask with approximately 50 μm alignment accuracy is sufficient. Another etching process follows, in which the auxiliary layer 12 is reduced in thickness. Due to the difference in thickness of the auxiliary layer 12 between the elongated recess 14 and the portion of the auxiliary layer 12 surrounding this recess 14, this difference in thickness remains even during the etching process, so that when the thicker portion of the auxiliary layer 12 is etched back to a smaller thickness, the elongated recess is converted 14 takes place in an upper elongated opening 17. The auxiliary layer remains in this upper elongated opening 17

12, albeit with reduced thickness. The result of this method step is shown in FIG. 24. The mask 5 served as protection for the auxiliary layer 12 at least in the area of the rectangular recess 13. In addition, this etching does not or only insignificantly attacks the separating layer 15, since this has a selectivity with respect to the auxiliary layer 12.

In the following method step, the result of which is shown in FIG. 25, a further etching process takes place through the upper, elongated opening 17, the material of the separating layer 15 lying under this opening 17 being etched. In this etching process, the auxiliary layer 12 again acts as a mask for the separating layer 15. A lower elongated breakthrough 18 is formed in the separating layer 15 directly below the upper elongated opening 17. Examples of materials for this etching process are aqueous hydrofluoric acid or a selectively etching plasma, e.g. CHF3 / ar in question.

In the next process step, dry etching is carried out, for example by reactive ion etching, a waveguide groove 6 being formed. In this case, the mask 5 protects the auxiliary layer 12 and at the same time the separating layer 15 protects the area of it covered Semiconductor substrate l. This completes the first half of the method by producing the waveguide groove 6. Following this method step, the mask 5 is removed again, which is shown in FIG. 27.

Next, an adjustment groove 8 is to be produced. For this purpose, the area of the arrangement above the waveguide groove is protected by applying a protective mask 7, in particular in the form of a thermally grown oxide. As shown in FIG. 28, the oxide grown by thermal oxidation preferably has a particularly high thickness, for example 0.5 to 1 μm. The thermal oxidation is particularly easy to carry out if a material has been selected for the auxiliary layer 12 on which thermally no oxide or only a very small oxide can be grown. For example, when nitride is used as the material for the auxiliary layer 12, only such a small oxide layer grows there that it can be removed by briefly rinsing it with an HF solution. This is called local oxidation.

Now the auxiliary layer 12 is again etched, and here too, as in the production of the waveguide groove 6, the difference in thickness in the course of FIG

Auxiliary layer 12 now has the effect that the rectangular recess 13 is imaged in an upper rectangular opening 22. The result of this is again shown in FIG. 29. The subsequent method step, the result of which is shown in FIG. 30, involves etching the

Separating layer 15, a rectangular lower opening 23 being formed in the separating layer 15 below the rectangular upper opening 22. Here too, the etching can be realized by liquid etching or plasma etching. It can happen that the protective mask 7 also approximately is attacked. However, by providing a higher layer thickness for the protective mask 7, for example in the case of thermal oxidation, it can be prevented that the layer thickness of the protective mask 7 is reduced in such a way that a falsified result is obtained in the structuring.

Finally, an anisotropic etching process follows (e.g. with KOH etching), as a result of which an adjustment groove 8 is created below the rectangular upper opening 22 and the rectangular lower opening 23. The protective mask 7 acts as a cover and protection for the semiconductor substrate 1 against the etching process.

As a last method step, the protective mask 7, the auxiliary layer 12 and the separating layer 15 are removed from the surface of the semiconductor substrate 1, so that only the semiconductor substrate 1 with the alignment groove 8 and the waveguide groove 6 remains, as shown in FIG. 32.

So it is clear that this too

Embodiment, the masking layer 2 represents the only structure-determining mask, while all further steps of the method require only rough covers. By using small layer thicknesses for the auxiliary layer 12 and the separating layer 15, the lateral undercut during the etching of the adjustment groove 8 can be kept particularly low, as a result of which the adjustment groove 8 is given a particularly precise structuring. This structuring is relevant with regard to the height adjustment of a fiber to be inserted into the adjustment groove 8, but which has a much smaller effect than a lateral deviation. Since the alignment of the masking layer 2 with the crystal direction of the semiconductor substrate 1 plays a major role with the method described here, the alignment of the masking layer 2 with one is suitable Fiat structure of a semiconductor wafer or on a pre-etched Justiemut, which reveals the exact crystal direction.

A fourth exemplary embodiment of the method according to the invention is shown in FIGS. 33 to 42. The same numbers here again designate the same element as in the previous figures.

The method is based on a semiconductor substrate 1 which is coated on its upper side with an additional layer 24 and over it with a masking layer 2 (cf. FIG. 33). A photoresist is suitable for the masking layer 2 and silicon dioxide (Si0 ₂ ) for the additional layer 24.

A rectangular cutout 3 and an elongated rectangular cutout 4, which touch each other, are produced in the masking layer 2 by exposure and development. The cutouts 3, 4 correspond in shape and position to the cutouts according to FIG. 21. The structure thus created is shown in FIG. 34.

The arrangement described is next subjected to an etching process, further recesses 63, 64 corresponding to these being formed under the recesses 3, 4. Both wet chemical and dry chemical media can be used as the etching medium. The masking layer 2 remains in this process. If this masking layer 2 consists of photoresist, for example, this can be achieved by hard baking (polymerizing).

As shown in FIG. 36, a mask 5 is then brought onto the area of the arrangement where the rectangular recess 3 or the further rectangular 63 are located. The area on the other hand remains free Semiconductor substrate 1, over which the elongated, rectangular recess 4 or the further elongated, rectangular recess 64 lie. A photoresist is again suitable as the material for the mask 5. This is followed by a further etching process in which a waveguide groove is now created below the further elongated, rectangular recess 64. The masking layer 2 protects the additional layer 24, which in turn protects the semiconductor substrate 1. In addition, the mask 5 protects the semiconductor substrate 1 from the etching medium. The arrangement resulting from this method is shown in FIG. 37.

The arrangement shown in FIG. 38 results from the arrangement from FIG. 37, in which the cover mask 5 and the masking layer 2 are removed from the arrangement. This is now possible because the dimensions of the structure-determining recesses 3, 4 from the masking layer 2 are retained on the semiconductor substrate 1 by means of the further recesses 63, 64 in the additional layer 24.

FIG. 39 shows how a cover layer 25 is applied over the entire surface of the surface of the semiconductor substrate 1 with the additional layer 24 as the next method step. Subsequently, a protective mask 7 is applied to the cover layer 25, the protective mask 7 covering the area above the waveguide groove 6, but leaving the area above the further rectangular recess 63 free. The adjustment accuracy of the protective mask 7 is again not particularly demanding. Here too, the accuracy concerns only an axial component, which does not play a very important role in the coupling of a glass fiber and a waveguide. In a subsequent process step, the part of the cover layer 25 that is not covered by the protective mask 7 is passed through Wet or plasma etching (eg CHF ₃ ) removed again. The arrangement is now at a stage which is shown in FIG. 41. Finally, here too, an anisotropic etching process follows, in which an adjustment groove 8 is produced below the further rectangular recess 63.

In this etching process, for example in aqueous KOH, EPD, TMAHW or another anisotropic etching medium with high selectivity compared to the additional layer 24, the protective mask 7 can also be dissolved in the etching medium, but the cover layer 25 remains as protection for the

Semiconductor substrate 1. This is followed by removal of the additional layer 24 and the cover layer 25, which is no longer shown in the figure, whereupon the semiconductor substrate 1 with the alignment groove 8 and the waveguide groove 6 remains, as shown in FIG. 31.

After etching the adjustment groove 8 and the waveguide groove 6, the transition between the two structures must be straightened for direct contact of an optical fiber to be inserted with a waveguide that is still to be formed. A cut with a wafer saw along the end of the adjustment groove 8 on the waveguide groove side is suitable for this in a manner known per se, it being advantageous if the cut is a depth of the fiber radius (for example 62.5 μm for standard glass fiber) plus half the depth of the waveguide having. For easy demoldability, the cut should also have particularly smooth walls without undercuts. In addition, this mechanical post-processing can be accomplished with diamond milling tools, by laser ablation or also by reactive laser cutting. Furthermore, high-rate etching of vertical shafts is provided, for example for silicon as the semiconductor substrate 1 in connection with a resist mask. The width of the transition area to be removed is usually approximately 100 to 200 μm. Therefore, the individual face masks that come with the structure for mutual coverage for the Justiemut 8 and the waveguide groove 6 are used, can only be adjusted with this accuracy, which is a relatively coarse accuracy.

Roughness of the waveguide smaller than approx. 100 nm is required for optical optical waveguide components. In order to remove any existing wall roughness from the dry etching processes, semiconductor polishing etching is possible, as is thermal oxidation and subsequent selective etching of the silicon oxide. Oxidation and etching can be repeated several times, which increases the smoothing effect. Another possibility is etching in Nf3 plasma or isotropic, pure fluorine etching.

Furthermore, it is provided that some of the etching processes, in particular the etching process for producing the waveguide groove 6, are carried out by electrochemically photo-induced etching. This etching method can also be used to produce a waveguide groove 6 which has a variable depth profile.

FIG. 43 shows an arrangement for electrochemically photo-induced etching. The

Semiconductor substrate 1 is in this case connected to a trough 51 via a sealing ring 56, so that the semiconductor substrate forms the bottom of trough 51. The semiconductor substrate 1 has a plurality of electrodes 50 on the underside. A plurality of wire electrodes 55 are arranged inside the tub 51. The wire electrodes 55 are covered within the tub 51 by a liquid electrolyte 57. There is a lens 52 above this arrangement and a light source 54 above the lens 52 A light filter 54 and the lens 52, a filter disc 53 is arranged.

With this arrangement, an electrical voltage is applied between the electrodes 50 and the wire of the electrodes 55. In addition, light from the light source 54 passes through the filter disk 53 and the lens 52 onto the surface of the electrolyte 57. The light passes through the transparent electrolyte 57 onto the surface of the semiconductor substrate 1, where photo-induced electrochemical etching takes place due to the incidence of light. Due to different darkening within the filter disk 53, the surface of the semiconductor substance 1 is irradiated with different light intensities. For this reason, the etching process takes place with different local intensities. The masking layer 2 located on the semiconductor substrate 1 and the cover mask 5 or the protective mask 7 are preferably opaque. Then they perform two functions at once: on the one hand they serve as an optical mask for suppressing photo-induced electrochemical etching and on the other hand they serve as an etching resist in this or other etching processes during the process.

Instead of the individual lens 54, an optical system consisting of several components can also be used. As a further method for controlling the local etching intensity, the electrodes 50 or wire electrodes 55 can be controlled with different currents.

It is further proceeded to use a strongly bundled light source, such as a laser, for example, instead of the light source 54, the light beam of which is moved over the surface of the semiconductor substrate 1. By varying the intensity or the speed of movement of the A variable etching intensity distribution can also be generated on the light beam on the semiconductor substrate surface.

One area of application for the method described is optical switching matrices with optical switches with small radii of curvature of the waveguides contained. The arrangement of a taper transition produced with the method to achieve a small waveguide cross section serves to reduce the

Loss of curvature. Other applications are coupling points between waveguides and Bragg gratings as well as laser diodes or to fibers.

Instead of the saw cut 10, it is also provided to create a trench with vertical walls by the photo-induced electrochemical etching.

For the etching of the waveguide groove 6, a reactive ion etching method is particularly suitable, which brings about a sidewall passivation with the addition of polymer-forming gases during the etching. And thus enables almost vertical or slightly positive etching edges. Other processes for this purpose can use mixtures of CL2 / O2 or HCLO2 or HBR / O ₂ which in themselves are anisotropic etching and which can lead to a positively inclined profile by repositioning some of the etched products on the side walls.

Claims

Expectations

1. A method for producing a master structure for a polymer substrate, which has at least one waveguide groove and at least one adjustment groove for one on its upper side

Optical fiber, the master structure being produced from a semiconductor substrate and also having at least one waveguide groove and the at least one adjustment groove on its upper side, characterized in that the semiconductor substrate (1) is coated with a masking layer (2) which has a recess at least there (4), where at least one waveguide groove (6) is to be created and which also has a further recess (3) where the at least one adjustment groove (8) is to be created and that the further recess (3) is covered with a mask (5 ) is covered and the at least one waveguide groove (6) in the semiconductor substrate (1) is produced by etching, and that the recess (4) is covered with a protective mask (7) and the at least one adjustment groove (8) in the semiconductor substrate (1) Etching is produced.

2. A method for producing a master structure according to claim 1, characterized in that between the, preferably consisting of a photoresist masking layer

(2) and the semiconductor substrate (1) an auxiliary layer (12), preferably made of a nitride, is arranged and that in the auxiliary layer (12) with the aid of the masking layer (2) under the recesses (3, 4) by etching a first and a second recess (13, 14) are produced and that after the application of the cover mask (5) or the protective mask (7) the uncovered recess (13, 14) is expanded by etching to form an upper opening (17, 22).

3. A process for producing a master structure according to claim 2, characterized in that a separating layer (15), preferably made of an oxide, is arranged under the auxiliary layer (12), and that a lower opening (17, 22) is located under the upper opening (17, 22). 23, 18) is produced in the separating layer (15) by etching.

4. Process for producing a master structure according to

Claim 3, characterized in that the separating layer (15) with a liquid etching process, e.g. using hydrofluoric acid or a plasma etching process, e.g. is etched using CHF3.

5. A method for producing a master structure according to one of claims 2 to 4, characterized in that the auxiliary layer (12), with a dry etching process, e.g. is etched using xy.

6. A method for producing a master structure according to one of claims 2 to 5, characterized in that of the protective mask (7) and the mask (5) which is applied later, preferably from a thermal grown oxide existing mask, has a higher layer thickness than the separating layer (15).

7. A method for producing a master structure according to claim 1, characterized in that an additional layer (24), preferably made of an oxide, is arranged between the masking layer (2), preferably consisting of a photoresist, and the semiconductor substrate (1) and in that Additional layer (24) with the aid of the masking layer (2) under the recesses (3, 4) by etching a first and a second recess (63, 64).

8. A method for producing a master structure according to claim 7, characterized in that a cover layer (25), preferably made of an oxide, is arranged under the protective mask (7), which preferably consists of a photoresist, which counteracts the etching process for etching the adjustment groove (8 ) is resistant.

9. A method for producing a master structure according to claim 1, characterized in that an intermediate layer (11) is arranged between the semiconductor substrate (1) and the masking layer (2).

10. Process for producing a master structure according to

Claim 9, characterized in that the intermediate layer (11) is selected from a material against which the semiconductor substrate (1) can be selectively etched and which can be selectively etched with respect to the masking layer (2).

11. A method for producing a master structure according to one of claims 1 to 10, characterized in that the waveguide groove (6) is preferably dry-etched by reactive ion etching.

12. A method for producing a master structure according to one of claims 1 to 11, characterized in that the adjusting groove (8) is produced by anisotropic etching, preferably using KOH.

13. A method for producing a master structure according to claim 12, characterized in that a resulting at the anisotropic etching, waveguide groove side, ε angled end flank of the adjustment groove (8) is preferably straightened by sawing or high-speed etching.

14. A method for producing a master structure according to one of claims 1 to 13, characterized in that the walls of the waveguide groove (6) are smoothed by oxidation and etching.

15. A method for producing a master structure according to one of claims 1 to 14, characterized in that the waveguide groove (6) is photo-induced etched.

16. A method for producing a master structure according to claim 15, characterized in that opaque materials are selected for the cover mask (5) and the masking layer (2).

17. A method for producing a master structure according to claim 15 or 16, characterized in that the Waveguide groove (6) is produced with a variable depth profile.

18. A method for producing a master structure according to claim 17, characterized in that for producing the variable depth profile in photo-induced electrochemical etching, a laser beam is moved over the area to be etched with variable speed, intensity or dwell time.

19. A method for producing a master structure according to claim 17 or 18, characterized in that an optical intensity filter (53) with a transparency distribution equivalent to the depth profile between the area to be etched and a light source (54) is arranged to produce the variable depth profile in photo-induced electrochemical etching becomes.

20. A method for producing a master structure according to one of claims 17 to 19, characterized in that for the production of the variable depth profile in photo-induced electrochemical etching strip-shaped electrodes (50, 55) are attached below and / or above the area to be etched, which have different electrical currents can be controlled.