DE10353546B4 - Conductive holding posts in air gap based, optoelectronic devices and manufacturing processes - Google Patents

Abstract

Optoelectronic, vertically oriented component, containing a layer structure (69; 92) with a plurality of optically active layers (10; 53, 56, 57, 58, 59, 62; 83, 87, 89) and at least one gas or liquid filled layer gap (17; 55; 94), wherein the layer structure by means of at least one outer, one Edge region of the layer structure associated edge support (67; 91), characterized in that at least two the layers of the layer structure by a connecting element (14, 15, 16; 68; 90) are firmly connected to each other, wherein the Connecting element is located away from the edge region of the layer structure.

Description

STATE OF TECHNOLOGY

The The present invention relates to opto-electronic devices and Process for their preparation. In particular, it relates vertically oriented components with a layer structure with several, optical effective layers and at least one gas or liquid filled, in particular however, air or vacuum containing layer gap, wherein the Layer structure by means of at least one outer, a respective edge region the layer structure associated edge support is held.

In The last ten years have been vertically oriented, optoelectronic Components opposite to horizontal On a wafer oriented components more and more economical Gained interest. This group includes, for example, the so-called "Vertical Cavity Surface Emitting Lasers ", abbreviated as VCSEL, or "Vertical Cavity Fabry-Pérot Filters ", abbreviated as VCFPF.

The Main advantages of such vertically oriented components over horizontal oriented exist in that vertically oriented components before the packaging on the wafer can already be tested, the is called they do not need to be separated from the wafer to be tested can. This means that the test procedures are much more efficient can be.

One Another advantage is that a more effective coupling to Fiberglass allows which, in a chip housing, containing the vertically oriented optoelectronic components simplified structure is feasible. For optical filters and Lasers face two mirror assemblies separated by the cavity. their Geometry and in particular its length is for the optical properties of great Importance. For vertically oriented optical filters and lasers is the cavity usually very short, therefore, a high, longitudinal mode spacing reached. With VCSEL the active volume is very low, therefore low threshold currents be achieved. The preparation of the mirrors, which are called DBR (Distributed Bragg Reflectors) are, however, still relatively difficult at present, as a very high reflectivity the level of> 99.7 % needed will meet the requirements for commercial use such components are given.

a special branch within the development of the above vertical Oriented components form the technological approach, the layer structure of a DBR mirror through an alternate sequence of material Membrane layers and intermediate air layers (air gaps) to build. In other words, the layer structure of a DBR reflector contains For example, a number n of membrane layers and a number of n-1 intermediate air gaps.

Of the technical structure, functioning in various technical Applications, as well as the main optical properties of vertically oriented, Air-gap based DBR devices are disclosed in "H. Hillmer, J. Daleiden, C. Prott, F. Römer, S. Irmer, V. Rangelov, A. Tarraf, S.

Student, M. Strassner: "Potential For Micromachined Actuation Of Ultra-wide Continuously Tunable Optoelectronic Devices. ", Applied Physics B 75, 3-13 (2002), published on August 08, 2002.

The Use of air gaps as a separation layer between the individual Membrane layers is advantageous because one of these two Layers formed interface (air gap / membrane material) has a very high refractive index jump. This allows the mentioned above high reflectivity of 99.7% of DBRs with only a few periods, e.g. at indium phosphide (InP) / air with 3 membrane layers and 2 intermediate air gaps become.

Of Furthermore, there is a positive side effect: optoelectronic Components, the o.g. Air gap mirror and an air gap cavity (see, e.g. Reference Hillmer et. al.) can, for example, with respect to a important optical property, such as its transmission spectrum, be specifically influenced, for example, if the optically effective Length L the cavity between the two DBR reflectors is increased or decreased. ever after setting the cavity length L is the maximum of the transmitted wavelength range as a sharp peak at different wavelengths. These Tuning may be by means of capacitive (in connection with conductive membranes) or thermal actuation, and appropriate control done.

However, such prior art air gap based devices have the disadvantage of relatively low mechanical stability, although with increasing miniaturization of such devices, the influence of inertial forces on such layers tends to decrease, as the above-mentioned publication shows. Nevertheless, the influence of mechanical stresses in the abovementioned individual membrane layers is nevertheless so great that certain deformations can occur which are difficult to control, in particular in industrial production processes which can cause unwanted changes in the optical and mechanical properties of the components and therefore to a lead to increased reject rate of the components. This relatively great sensitivity to mechanical inaccuracies is due to the extremely high aspect ratio of a DBR layer structure mentioned above, the following values being given as an example:
The diameter of the actual layer structure is about 40 microns, wherein the distance between the individual layers is only a few 100 nanometers, and the thickness of a layer is also only a few 100 nanometers to a few micrometers. Such fine layer spacings have hitherto been difficult to produce, and in particular the mechanical and thus the geometric stability of the layer structure is not yet stable enough.

The European patent application EP 1 320 157 A2 As a solution to this problem, it is proposed to provide a so-called "support layer" on the side walls of the layer structure, but this measure still provides too little stability, especially in the case of unfavorable aspect ratios.

A further publication such vertically oriented optical components is on July 16, 2003 done online and available in print in Appl. Phys. B 76, 821-832 (2003). In terms of the mechanical stability However, such fine layer structures are trusted exclusively that the mechanical stability the layer structure alone by a sufficiently large miniaturization of the component can take place. But that alone can not be done mechanically produce stable fine layer structure of such components.

Therefore the object of the present invention is to provide an improved Structure of the aforementioned components and a corresponding manufacturing method for the To create components.

ADVANTAGES OF INVENTION

Of the An object with the features of claim 1 solves the first task.

In the dependent claims find advantageous developments and improvements of respective subject of the invention.

According to the main aspect According to the invention, according to the invention, a so-called "connecting element" for the mechanical Joining at least two material membrane layers of the layer structure provided, wherein the connecting element when using only one supporting Edge area away from this, and otherwise, for example, if the layer structure is supported by two edge regions, between these edge regions, preferably as possible close to the optically active area.

With other words and in terms of the topology introduced above become vertical oriented, that is substantially perpendicular to the individual layer planes of the membrane layers extending "holding post" as a connecting element the membrane layers of a DBR reflector or other optoelectronic Created components with a fine layer structure. This results directly the advantage that the entire layer structure or a certain subset of which, depending on which membrane layers are interconnected by a holding post, an increased mechanical stability wins, whereby the above, adverse deformations of the individual layers can be significantly reduced. From application perspective results this has the advantage that the optical properties considerably be improved and the reject rate in a mass production Such components can be significantly reduced.

• 1. zunächst wird eine Struktur aus mehreren Schichten durch Epitaxie oder andere Ablagerungsverfahren hergestellt,
• 2. danach wird durch ein Trockenätzverfahren der laterale Aufbau hergestellt, das heißt ein vertikales Strukturieren der so genannten Mesa wird durchgeführt, und
• 3. künstliche, das heißt nur temporär existierende Schichten des Schichtaufbaus, sogenannte Opferschichten, werden durch ein hoch-selektives nass-chemisches Ätzverfahren entfernt, um die vorgenannten Luftspalte auszubilden. Dabei werden Masken verwendet, die verschiedene Membrangeometrien und mechanische Spannungen anzeigende Strukturen beinhalten, sowie Qualitätssteuerungselemente und Ausrichtungsmarkierungen. Dort ist eine Filterstruktur offenbart, die jeweils im Winkel von 90° an vier Armen aufgehangen ist, die ihrerseits an außen liegenden, quadratischen, abstützenden Rahmenblöcken befestigt sind.

The above publication also discloses a way in which such a layer structure, however, can be produced without the inventive connecting elements. There are three main steps:

• 1. First, a multi-layered structure is prepared by epitaxy or other deposition methods.
• 2. thereafter, the lateral structure is produced by a dry etching process, that is, a vertical structuring of the so-called mesa is performed, and
• 3. artificial, that is only temporarily existing layers of the layer structure, so-called sacrificial layers are removed by a highly selective wet-chemical etching process to form the aforementioned air gaps. Masks are used, which include various membrane geometries and mechanical stress-indicating structures, as well as quality control elements and alignment marks. There, a filter structure is disclosed, which is suspended in each case at an angle of 90 ° to four arms, which in turn are attached to outer, square, supporting frame blocks.

If, for the production of the component according to the invention, this method is to be used as the basis, and the connecting elements according to the invention are to be integrated as a kind of retaining post in the production method, then the connecting elements or at least its outer layer of a material with a high selectivity to a sacrificial layer, which is then etched away as a layer gap in the aforementioned manufacturing process in an etching step.

In Preferably, a connecting element is as close as possible to the optical active region of the layer structure, but without the beam path to disturb it. Depending on the so-called clamping length, which is defined lying between the abovementioned edge supports, can also have more than one connecting element per connecting line between two edge supports be used. This results in the use of four edge supports and a circular one Filter construction, for example, the use of four retaining posts, essentially and preferably with the same radial distance are provided from the center of the filter assembly.

In Preferably, all membrane layers of the layer structure connected together by a connecting element. This allows all membrane layers be mechanically stabilized.

According to one further, particularly advantageous aspect of the present invention contains a connecting element a contiguous, metallized area, the at least two layers of the layer structure connects to each other. As a result, the interconnected layers can be targeted electrically contact, and / or a targeted heat dissipation or heat distribution is possible in the membrane layers surrounded by air, so that during operation resulting heat targeted to a heat sink can be derived. It is essentially irrelevant whether the retaining post is made entirely of a conductive material or only for Part of it is as long as the conductive connection between the preselected Layers is made.

If the device provided according to the invention now two opposite layer structures with the above mentioned, intermediate cavity has the basic structure of an optical filter, as he often for technical Purpose is used.

According to one Another preferred aspect of the present invention is in a Arrangement as described above, at least one connecting element provided, the cavity-facing end portion with a predetermined length protruding into the cavity, in other words, a "knob" is formed, crossing the boundary between cavity and first Membrane layer is raised. Such knobs can also be present on several connecting elements be. This solves an otherwise existing problem namely in an actuation of two membranes, as mentioned above, for example, by electrostatic forces of attraction between the membranes can be prevented from a certain too large selected Aktuationsspannung the attraction between the membranes becomes too big and the component is destroyed. At this voltage, the so-called "pull in" voltage, the membranes occur according to technology from the prior art, ie without the inventively provided Nubs in contact and stick firmly together. The component will be so without the pimples after passing the "pull destroyed in "tension.

The Effect of the nubs is thus that automatically a spacer to maintain a minimum distance for each layer package is formed. This minimum distance then corresponds to the knob height or for example, the double knob height when the end portions two nubs are exactly opposite stand, and then touch. In any case, a contact of the in itself movable membranes at a "tuning" prevented.

If as gas filling for the Layer interspaces Air is taken, then results in a simple manufacturing process for the Component as it is during Of the manufacturing process itself not in a special way compared to the Environment must be sealed.

Of others can the materials of DBR reflectors also low conductivity for example, if they are essentially made of silicon nitride or silicon dioxide. Due to the lack of conductivity the membranes no electrostatic actuation is possible here. According to the present Invention can however conductive Connecting elements are used, with separated by the air gap, opposite Connecting elements or opposite, existing metal layers an electrostatic actuation of membranes or to allow whole membrane packages.

Especially for electric pumped laser is a high current density in the active optical layers important. If furthermore advantageously the connecting elements according to the invention (holding posts) consist of a conductive core material that is in a non-conductive Shell suitable Thickness is, so can targeted by this type of arrangement only certain layers contacted become. This makes it possible Charge carrier in inject an optically active zone and control the current flow in the active Zone laterally limited by electrical interaction (current confinement).

Of others can the connecting elements for heat conduction or heat distribution to other layers or heat sinks be used. Especially with active optical components is often a lot of heat generated, their exhaustion but especially in air gap-based membrane arrangements otherwise According to the prior art, a large Problem presents.

Of Further can the connecting elements be provided with a contact on the you specifically a tension during of the laser operation can create. Thus, the polarization of the Light can be influenced. This is u.a. a modulation of the light possible.

DRAWINGS

embodiments The invention is illustrated in the drawings and in the following Description closer explained.

It demonstrate:

1 the production of a layer structure according to the invention, as mentioned above, with reference to four (ad) or five (ac, e, f) production stages in order to illustrate the basic structure and the essential method steps in its production;

2 schematically the structure of an electrically pumped, air gap-based VCSEL, which is mechanically actuated as a preferred embodiment of the present invention in a plan view;

3 a sectional view along a line III-III of the arrangement, as shown in 2 shown in plan view;

4 a further preferred embodiment of an air gap-based, opto-electronic filter device with mechanical Aktuierbarkeit as a plan view;

5 The cross section of the filter component in 4 along a line VV;

DESCRIPTION THE EMBODIMENTS

In the same reference numerals designate the same or functionally identical Components.

In reference to 1 In the following, the production of a layer structure according to the invention, as it can be used for optoelectronic components as described above, is described in more detail.

In a first step, see 1A a plane-parallel layer structure is produced (epitaxy), whereby the following materials are selected:
For shift 10 : Indium phosphide (InP), for the layers 11 . 12 Gallium indium arsenide (GaInAs). These materials are deposited by MOCVD (metal organic chemical vapor deposition). In this case, GaInAs is needed as a sacrificial layer, which is selectively etched away in a later process step and then by a gas or a liquid 17 is replaced.

After deposition, vertical cavities are formed in a second process section 13 generated, for example by means of a photoresist mask by a dry chemical etching.

In the following process step, see 1C , the sacrificial layers are etched wet-chemically. Then the cavities are filled with a material 14 , in this case filled with a material of relatively high thermal conductivity and good electrical conductivity, in whole or in part, see 1D according to left or right picture. In another section of the method, with reference to 1E the sacrificial layers 11 . 12 etched wet-chemically, and by gas or liquids 17 replaced. In the simplest case, this is air. The vertically drawn structures 14 . 15 , and 16 serve as holding posts in the context of the present invention.

Contacting individual layers is also possible. This is after the already means 1A to 1C first described method steps, a non-conductive material 15 in the cavity 13 filled. Subsequently, for example, by a dry chemical etching with a photoresist mask in the middle of a new isolated cavity created ( 1F ), then with a conductive material 16 is replenished ( 1G ). Subsequently, the sacrificial layers are again removed wet-chemically and by gas or liquids ( 17 ) replaced.

In reference to 2 and 3 In the following, further explanations are given of an embodiment of the present invention, which represents an electrically pumped, air gap-based VCSEL with mechanical actuability.

In a first manufacturing step, the individual, in 3 epitaxially produced, superimposed layers:
On a substrate 62 For example, from p-doped InP is an alternating layer sequence of p-doped GaInAs 54 and InP 53 , consisting of a total of six layers, applied. Subsequently, an intrinsic GaInAs layer 61 defining the later length of the cavity, an n-doped InP layer 58 , an n-doped GaInAs layer 60 , a highly doped n ⁺ InP layer 59 , InP embedded quantum well (QW) layers 57 of gallium indium arsenide phosphide (GaInAsP) and a highly doped p ⁺ InP layer 56 deposited. Finally, a layer sequence consisting of a total of 8 layers of p-doped GaInAs 54 and InP 53 , applied.

When Next Process section becomes a first lithography for electric conductive Connecting elements for the individual sub-layers carried out in the form of retaining posts.

These are cavities in another dry chemical process section 50 etched vertically downwards, which later absorbed the metallizations 52 to serve for metallized hollow post as a connecting element according to the embodiment.

Then, in another process section, the lithography for the metallization of the hollow posts is performed, and in a subsequent metallization step, a metal layer 52 , which is also used in the following for further etching as a mask, on the inner walls of the above-mentioned cavities 50 applied to the outside of the retaining posts according to the invention 68 to build.

After the central optical area 51 was protected by means of an additional mask, for example made of silicon nitride, the corresponding mesen etches and contacts 63 respectively. 64 be applied. Finally, all GaInAs sacrificial layers are controlled with the exception of the inner regions of the area-wide edge supports 67 etched away wet-chemically and replaced by gas or liquid.

The GaInAsP QW layers 57 are etched much slower.

The membrane structure is after undercutting by edge supports 67 because they were not completely undercut due to their size. Through the between p ⁺ layer and hollow post 68 formed contacts 65 , which due to the metallized hollow posts very close to the optically active region 66 and the laterally etched QW layers, there is a current flow confinement of the current in the region 66 instead, which is very advantageous for laser operation of the VCSEL. Furthermore, the heat generated in this area over the metal layer 52 der Haltepfosten be derived.

Another preferred embodiment will be described below with reference to 4 and 5 describing an air gap-based filter with mechanical actuability:
On an InP substrate 89 are alternately, a total of six, doped GaInAs, see reference numerals 88 , and InP layers 87 deposited. Subsequently, an intrinsic layer GaInAs 85 , which defines the later length of the cavity, and again a layer stack of 7 alternating dielectric layers of silicon nitride 83 and silicon 84 applied. Subsequently, by means of lithography and subsequent dry chemical, anisotropic etching cavities 80 generated in the upper layer package, which are as close as possible to the later used optical beam path, but this does not affect. In the next step, the cavities are partially or completely filled with conductive material 82 filled, causing retaining posts 90 be formed.

After the mesa etching and structuring of the contacts 86 and 93 , the controlled undercutting, a selective etching of all GaInAs layers as well as a selective etching of the silicon layers with the exception of the area-wide edge regions takes place 91 , The remaining, free-standing silicon nitride membranes are now supported in addition to the edge region by the holding posts in the vicinity of the optically active region. One at the contacts 93 and 86 applied stress then causes attractive forces between the layer 87 and the conductive support post 90 , whereby a mechanical actuation is possible.

The present invention may be used for many different purposes and in various embodiments, subject to certain adjustments known to one of ordinary skill in the art, other than the above embodiment:
For example, for electrically pumped (actuatable), micromechanically tunable VCSEL, for filters to build detectors, multiplexers, demultiplexers, modulators, switches or amplifiers, the advantages mentioned above come to advantage.

Furthermore, the present invention can be modified in many ways to obtain certain technical characteristics. It is understood in particular that the connecting elements according to the invention need not necessarily be produced by the production method, as described above by way of example, since there are a wide variety of production variants in the prior art. Also, the selection of the above materials is not intended to limit the inventive idea, as long as a relatively strong, mechanical connection between inventive connecting element (holding post) and a respective membrane layer made who that can.

Finally, the Features of the dependent claims essentially free with each other and not by the present in the claims Sequence can be combined with each other, provided they are independent of each other are.

Claims (14)

Optoelectronic, vertically oriented component comprising a layer structure ( 69 ; 92 ) with several optically active layers ( 10 ; 53 . 56 . 57 . 58 . 59 . 62 ; 83 . 87 . 89 ) and at least one gas or liquid-filled layer gap ( 17 ; 55 ; 94 ), wherein the layer structure by means of at least one outer, an edge region of the layer structure associated edge support ( 67 ; 91 ), characterized in that at least two of the layers of the layer structure by a connecting element ( 14 . 15 . 16 ; 68 ; 90 ) are firmly connected to each other, wherein the connecting element is located away from the edge region of the layer structure. Optoelectronic component according to claim 1, wherein the connecting element ( 14 . 15 . 16 ; 68 ; 90 ) as close as possible to an optically active region ( 66 ) of the layers is arranged. Optoelectronic component according to claim 1, wherein the connecting element ( 14 . 15 . 16 ; 68 ; 90 ) is oriented substantially perpendicular to a layer plane. Optoelectronic component according to claim 1, wherein all layers of the layer structure ( 69 ; 92 ) with each other by connecting elements ( 14 . 15 . 16 ; 68 ; 90 ) are connected. Optoelectronic component according to claim 1, wherein the material of the connecting element ( 14 . 15 . 16 ; 68 ; 90 ) a high selectivity to a sacrificial layer ( 11 . 12 ; 54 . 60 . 61 ; 84 . 85 . 88 ) in an etching process of the manufacturing process, in which the layer interspaces ( 17 ; 55 ; 94 ) are etched away as sacrificial layers. Optoelectronic component according to claim 1, wherein the connecting element ( 14 . 15 . 16 ; 68 ; 90 ) a conductive, contiguous area ( 52 ; 82 ) containing at least two layers of the layer structure ( 69 ; 92 ) connects to each other. Optoelectronic component according to claim 1, wherein the connecting element ( 14 . 15 . 16 ; 68 ; 90 ) includes a conductive, contiguous core region and a non-conductive shell is provided. Optoelectronic component according to claim 1, wherein the device two opposing layer structures having an intermediate cavity. Optoelectronic component according to the preceding claim, wherein at least one connecting element ( 14 . 15 . 16 ; 68 ; 90 ) in a layer structure ( 69 ; 92 ) is provided, the cavity-facing end portion protrudes with a predetermined length into the cavity. Optoelectronic component according to the preceding Claim, wherein two layer structures with at least one connecting element each other opposite are provided, wherein in vertical deflection of the layer structures the end portions of the opposing ones Touch connecting elements. Optoelectronic component according to one of the preceding Claims, designed as a Bragg mirror device (DBR). Manufacturing method for a vertically oriented, optoelectronic component comprising a layer structure ( 69 ; 92 ) with several optically active layers ( 10 ; 53 . 56 . 57 . 58 . 59 ; 83 . 87 . 89 ) and at least one gas or liquid-filled layer gap ( 17 ; 55 ; 94 ), wherein the layer structure by means of at least one outer, a respective edge region of the layer structure associated edge support ( 67 ; 91 ), comprising the steps of: a) producing the layer structure ( 69 ; 92 ) using suitable sacrificial layer materials for the layer interspaces ( 17 ; 55 ; 94 b) creating a vertical cavity ( 13 ; 50 ; 80 ), which is used to form a connecting element ( 14 . 15 . 16 ; 68 ; 90 ), c) removing the sacrificial layers ( 11 . 12 ; 54 . 60 . 61 ; 84 . 85 . 88 ) d) filling the cavity ( 13 ; 50 ; 80 ) with a material of preselected electrical and thermal conductivity as well as preselected mechanical strength. Manufacturing method according to the preceding claim, wherein the cavity ( 13 ; 50 ; 80 ) is filled with materials of different electrical conductivity or different thermal conductivity in each preselected areas, each specific spatial areas of the cavity are selectively filled with a respective material. Manufacturing method according to the preceding claim, wherein the cavity ( 13 ; 50 ; 80 ) is filled so that a inner core and an outer shell made of different materials.