Method for manufacturing an optoelectronic element, and optoelectronic element

Abstract

The invention relates to a method (10) for manufacturing an optoelectronic element (1), the optoelectronic element (1) comprising a semiconductor material having an active region located in the immediate vicinity of a surface of the semiconductor material, the method (10) comprising the following steps: deposition (12) of an electrical insulating layer (4) onto the semiconductor material using a first mask (14) placed on the active region, such that the electrical insulating layer (4) has a recess (5) at the level of the active region; deposition (16) of a metallic layer (18), called the injection layer, onto the assembly obtained in the preceding step, such that the metallic injection layer (18) forms an electrode (7) on the surface of the semiconductor material at the level of the active region. The invention also relates to an optoelectronic element (1) obtained by the manufacturing method (10). Figure for abbreviation: [Fig. 2]

Description

Title of the invention: Method for manufacturing an optoelectronic element, and optoelectronic element technical field

[0001] The present invention relates to a method for manufacturing an optoelectronic element. The optoelectronic element comprises a semiconductor material including an active region located in the immediate vicinity of a surface of the semiconductor material. The invention also relates to an optoelectronic element obtained by the manufacturing method.

[0002] The field of the invention is, without limitation, that of microelectronics. State of the art

[0003] Optoelectronic components are components that form an interface between electrical and optical components. They are generally, but not exclusively, microelectronic components based on semiconductors.

[0004] Optoelectronic components can be divided into emitters and detectors. Emitters are semiconductor components that convert electrical charges into photons, such as lasers and light-emitting diodes. Detectors are components that convert photons into electrical charges, such as photodiodes or solar cells.

[0005] An example of an emitter is a Tamm mode light source. It consists of a Bragg mirror (alternating quarter-wave layers of materials with different refractive indices), containing emitters in its upper layers, for example, quantum dots or quantum wells. A metallic pellet is deposited directly on the upper layer of the Bragg mirror. The pellet allows the formation and lateral confinement of an optical mode, called a Tamm mode. An example of such a source is described in FR 2965665. The optical mode is generated directly at the interface between the Bragg mirror and the metallic pellet. The quality and thickness of the upper layers of the Bragg mirror are therefore essential.

[0006] Generally, such optoelectronic components are manufactured using processes that combine epitaxial, lithographic, and etching steps. When the etching is not sufficiently selective, it can attack and damage the layers adjacent to the etched layers. Exposure to etching can therefore be problematic for layers or structures supporting interactions on micrometer dimensions. In particular, optical modes generated in such regions can be degraded. This applies in particular to Tamm mode light sources, but is also valid for other semiconductor components where the surface, and especially surface quality, plays a predominant role. Description of the invention

[0007] The invention aims to resolve the drawbacks of the prior art described.

[0008] In particular, one object of the invention is to propose a method for manufacturing an optoelectronic element which, during its implementation, protects a sensitive active semiconductor region so that it is not subjected to any physical or chemical deterioration.

[0009] Another object of the present invention is to propose a method for manufacturing an optoelectronic element that allows for the production of a wide variety of such elements that can be implemented in various applications.

[0010] At least one of these objectives is achieved with a method for manufacturing an optoelectronic element, the optoelectronic element comprising a semiconductor material including an active region located in the immediate vicinity of a surface of the semiconductor material, the method comprising the following steps: - deposition of a layer of electrical insulation on the semiconductor material using a first mask placed on the active region, so that the layer of electrical insulation has a recess at the level of the active region; - deposition of a metallic injection layer on the assembly obtained in the previous step, so that the metallic injection layer forms an electrode on the surface of the semiconductor material at the level of the active region.

[0011] In this document, the term "active region" refers to a region of the component in which a conversion of electrical energy into light energy, or vice versa, takes place. This is, for example, the location of an optical mode in which emission occurs in response to an electric field applied to the component.

[0012] The manufacturing process according to the present invention allows, by the step of depositing a layer of electrical insulation onto the surface of the semiconductor material using a mask, the protection of this surface in the active region. The mask covering the surface in the active region makes it possible to create the cavity in the electrical insulation layer without the need to use an etching technique.

[0013] The manufacturing process thus differs from state-of-the-art processes by the effective protection of the semiconductor surface in the active region. This surface is never subjected to any etching. The quality of the surface as well as the The top layer of the semiconductor is therefore not altered by the manufacturing process. This is particularly important when the top layer is made of a brittle material, such as gallium arsenide (GaAs).

[0014] The recess in the electrical insulating layer naturally creates an injection electrode during the deposition of the metallic injection layer, without the need for further technological steps. The electrical insulator surrounding the injection electrode prevents any electrical contact with the semiconductor outside the recess, thus ensuring that the carriers are injected only into the recessed area.

[0015] The injection electrode formed on the semiconducting surface of the active region, i.e. in the recess of the electrical insulating layer, is also referred to as a "paddle" in this document.

[0016] The term “optoelectronic element” refers to any optoelectronic component that can be implemented in an optoelectronic device or system, such as optical sensors, or that can operate independently, such as laser diodes.

[0017] The manufacturing process according to the invention may also include one or more steps enabling the electrical contact of the optoelectronic element, in order to be able to power it electrically when it is implemented.

[0018] According to one embodiment, the process according to the invention may include, prior to the deposition of the injection metallic layer, the creation of a contact electrode on the electrical insulating layer using a second mask, the second mask having a recess offset laterally with respect to the active region for the location of the contact electrode.

[0019] The contact electrode thus created allows easy contact, for example to carry out an electrical injection via the injection electrode.

[0020] An element thus provided with a contact electrode can be easily integrated into an integrated circuit for example.

[0021] Several such optoelectronic elements can thus be made and integrated on the same semiconductor wafer.

[0022] Alternatively, according to one embodiment, the method according to the invention may further comprise, after the deposition of the injection metal layer, the creation of a contact electrode on the metal layer using a second photosensitive mask, the mask having a recess offset laterally with respect to the active region for the location of the contact electrode.

[0023] It is indeed possible to reverse the order of the steps of deposition of the injection metallic layer and of the creation of the contact electrode.

[0024] The order of these steps is chosen in particular according to the choice of metals and their ability to adhere to each other.

[0025] Preferably, the metallic injection layer, and therefore the pellet, is made of silver. The contact electrode is preferably made of gold.

[0026] Silver and gold have very high conductivity, making it possible to minimize losses.

[0027] Of course, other metals can be used for the injection layer and the contact electrode, for example platinum or aluminum. The metals used and their configurations are chosen in particular according to the desired emission (or detection) wavelength.

[0028] According to one embodiment, the creation of the contact electrode may include the following steps: - application of a photosensitive resin onto the assembly obtained in the previous step, lithography and engraving of the resin to obtain the second mask; - directional deposition of a metallic layer, known as the contact layer, onto the second mask; and - lift-off of the second mask,

[0029] the part of the metallic layer, called the contact layer, remaining after the lift-off forming the contact electrode.

[0030] Thanks to the presence of the second mask, the contact electrode is created close to the active region while protecting the latter's semiconductor surface. Indeed, the semiconductor surface of the active region is not subjected to etching for the creation of the contact electrode.

[0031] Advantageously, the method according to the invention may further include the lateral delimitation of the metallic injection layer so that it essentially covers the locations of the active region and the contact electrode, by means of a third mask essentially covering the locations of the active region and the contact electrode.

[0032] This lateral delimitation of the injected metal layer allows the injected metal layer to be spatially restricted in order to form a metal pad extending over the active region and the contact electrode. This metal pad thus defines the extent of the optoelectronic element, for example on a semiconductor wafer comprising several of these optoelectronic elements.

[0033] According to one embodiment, the lateral delimitation of the injected metallic layer may include the following steps: - application of a photosensitive resin onto the assembly obtained in the previous step, lithography and engraving of the resin to obtain the third mask; - chemical attack on the parts of the injected metallic layer not covered by the third mask; and - lift-off of the third mask.

[0034] Advantageously, the electrical insulating layer can be deposited by directional deposition.

[0035] Directional deposition is an anisotropic deposition of material that allows, in particular, for the material to be deposited only on surfaces directly exposed to the beam of the material to be deposited. Surfaces not directly exposed will not be covered by the deposited material. This subsequently allows for differentiated operations to be performed on the surfaces covered by the deposited material and those not covered, such as etching or lift-off.

[0036] According to one embodiment, the semiconductor material may comprise a stack of semiconductor layers comprising, along a direction Z perpendicular to the surface of the semiconductor material, an alternation of layers with high and low refractive index to form an interference mirror.

[0037] Interference mirrors of this type can be implemented in different types of optoelectronic elements and devices.

[0038] For example, a Tamm mode light source includes an interference mirror whose stacking is perfectly periodic (called a Bragg mirror in this case).

[0039] The stacking layers are, for example, made of gallium arsenide (GaAs) and gallium arsenide-aluminum arsenide alloy (GaAlAs). These materials are suitable for the emission and / or detection of electromagnetic radiation in the infrared wavelengths.

[0040] Of course, other combinations of materials can be used for the stacking layers. For example, the combination of gallium nitride (GaN) with different porosities can be used for emission in the visible / near ultraviolet, the combination of silicon (Si) / silicon dioxide (silica, SiO2) in the visible / infrared, or the combination of aluminium nitride (AlN) / aluminium-gallium nitride (AlGaN) in the ultraviolet.

[0041] According to one embodiment, the active region may include at least one light emitter or detector.

[0042] According to examples, at least one light emitter or detector may include a quantum well or a quantum dot.

[0043] At least one light emitter or detector is located near the surface of the semiconductor material.

[0044] For example, for the fabrication of a Tamm mode light source, quantum wells or dots as light emitters are provided in the upper layers of the stack.

[0045] According to another aspect of the same invention, an optoelectronic element is provided, obtained by the manufacturing process according to the invention. Description of the figures and methods of realization

[0046] Other advantages and features will become apparent from the detailed description of non-limiting examples and the accompanying drawings in which: - [Fig.1] [Fig.1] is a schematic representation of a non-limiting example of an embodiment of a manufacturing process according to the invention; - [Fig.2] [Fig.2] is a schematic representation of an example of a realization non-limiting list of steps in the manufacturing process according to the invention; - [Fig. 3] [Fig. 3] is a schematic representation of an example of optoelectronic component that can be obtained by the manufacturing process according to the invention; - [Fig. 4] [Fig. 4] shows a top view of an optoelectronic element obtained by steps in the manufacturing process according to an embodiment of the invention; and - [Fig. 5] [Fig. 5] shows a top view of optoelectronic elements obtained by other steps of the manufacturing process according to an embodiment of the invention.

[0047] It is understood that the embodiments described below are in no way exhaustive. In particular, all the variants and embodiments described may be combined with each other provided there are no technical obstacles to such combination.

[0048] In the figures, elements common to several figures may retain the same reference.

[0049] Figures 1 and 2 are schematic representations of non-limiting embodiments of a manufacturing process according to the present invention.

[0050] The method according to the invention will be described by taking as an example a Tamm mode light source. Such a source is illustrated in [Fig. 3]. This Tamm mode source is an example of an embodiment of an optoelectronic element obtained by the manufacturing method according to the invention.

[0051] This is a semiconductor source 1 comprising a stack 2 of quarter-wave dielectric, or semiconductor, layers with refractive indices ni and n2, with ni > n2, forming an interference mirror, also called a Bragg mirror, when the stack 2 is perfectly periodic. It is also possible to have variations in the thickness of the layers. The layers are stacked along a vertical direction z. The stack 2 includes light emitters 3, for example quantum boxes or wells, located in the upper layers of the stack 2. An electrical insulating layer 4 is deposited on the upper layer of the stack 2, the insulating layer having an opening 5 at which the upper layer is not covered by insulation. A metallic layer 6 is deposited on the insulating layer 4, thus forming a metallic pellet 7 deposited on the upper layer of The stacking configuration consists of two parts. The pellet 7 can be circular, elliptical, or any other shape. The size of the opening 5 in the insulating layer 4, and therefore of the pellet 7, will define the lateral dimension of the Tamm mode. The source also includes a metallic contact 8 to supply power to the metallic pellet 7.

[0052] The stack 2 is placed on a semiconductor substrate S, this substrate S being placed on a metallic layer CO constituting an ohmic contact.

[0053] In such a device, the active region is located immediately below the electrode 7 present in the opening of the insulating layer 4, at the location of the light emitters 3 near the interface formed by the upper layer of the stack and the electrode. It is indeed near this interface that the Tamm mode can be created. By way of example, the Tamm mode extends a few tens of nm in the metal layer 7 and a few hundred nm in the stack, starting from the metal / semiconductor interface.

[0054] The beam M exiting the pad 7 represents the coupling of the Tamm mode with laser waves when the optoelectronic element is implemented as a laser diode.

[0055] Due to the reduced lateral dimensions of the electrode-top layer interface of the stack, the Tamm mode is also confined in the lateral direction, orthogonal to the stacking direction. The metal pellet 7 allows both the confinement and / or manipulation of the Tamm mode and the introduction of carriers to perform the electrical injection (illustrated by the arrows e). The metal pellet 7 can also be called the injection electrode.

[0056] The layers of stack 2 are, for example, made of gallium arsenide (GaAs) and gallium arsenide-aluminum arsenide alloy (GaAlAs), with the top layer being GaAs. Of course, other combinations of materials can be used for the layers to form an interference mirror.

[0057] The metal pellet 7 is preferably made of silver, and the insulating layer of yttrium(III) oxide (Y2O3) or silica (SiO2). The substrate may also be made of GaAs.

[0058] The process 10, shown in [Fig.1], includes a phase 12 of creating an electrical insulating layer 4 with an opening 5 on a Bragg mirror 2, forming part of an optoelectronic element (not shown) as described above.

[0059] The top layer of the Bragg mirror 2 is preferably made of GaAs.

[0060] Phase 12 of creating the electrical insulator includes a step 22 of depositing a Protective layer 13 on the Bragg mirror 2. The protective layer 13 can, in particular, be a photosensitive resin. The resin can be deposited by spin coating.

[0061] Next, during a photolithography step 23, the photosensitive resin is exposed to light irradiation using a mask to define the future location of The metal pellet. The resin 13' outside this location is soluble in a developer. During development, the soluble portion of the resin 13' as well as the top layer 2' are etched. The insoluble portion of the resin, shaped like a stud 14, protects the future location of the metal pellet from the developer.

[0062] As illustrated in [Fig. 1], after development, the resin pad 14, placed on the top layer of etched GaAs, remains. The resin pad 14 has a longitudinal cross-section in the shape of an isosceles trapezoid, with the shorter side facing the Bragg mirror 2. This shape is indeed important for the proper execution of the subsequent steps of the process 10.

[0063] Phase 12 of the insulator creation process then comprises a step 24 of depositing a layer of electrical insulator 4 over the entire etched surface of the top GaAs layer and the resin pad 14. The deposition is carried out by pulsed laser deposition (PLD) at room temperature. The insulator can be, for example, SiO2 or Y2O3. The thickness of the insulator layer can be on the order of 100 nm. Thanks to the inverted isosceles trapezoidal cross-section of the resin pad 14 and a directional deposition of the insulator, the insulator layer does not cover the sides of the pad 14, but only its top surface.

[0064] In step 25, the resin pad 14 covered with insulation is removed by a lift-off technique, using a solvent such as acetone. Since the sides of the resin pad 14 are not covered by the insulation, the pad 14 is soluble in the solvent.

[0065] At the end of phase 12 of deposition of the electrical insulating layer 4, the Bragg mirror 2 is covered with the electrical insulating layer 4 except for the future location of the metal pellet where the insulating layer has an opening 5.

[0066] The process 10, as represented in the embodiment of [Fig.1], continues with a phase 14 of creating a contact electrode 8.

[0067] The phase 14 of deposition of the contact electrode 8, as shown in [Fig. 1], includes a step 31 of deposition of a resin mask 9, by photolithography, on the electrical insulating layer 4 and its opening 5. The resin mask 9 has a recess near the opening 5 of the insulating layer 5, but covers the opening 5 well. The GaAs layer in the opening 5 is thus well protected by the resin mask 9 for the next step.

[0068] In a step 32, a first metallic layer 15, called the contact layer, is deposited onto the resin mask 9 by evaporation. The first metallic layer 15 is preferably made of gold. It may be supplemented by an intermediate layer 19, between the contact metallic layer 15 and the mask 9, serving as an adhesion layer, as illustrated in the embodiment of [Fig. 1]. The adhesion layer 19 may be, for example, made of chromium or titanium. The first metallic layer 15 is not in contact with the upper layer of the Bragg mirror 2 present in the aperture 5 of layer 4.

[0069] Next, in step 33, the resin mask 9 is removed by a lift-off technique, using a solvent such as acetone. This results in a contact electrode 8 placed on the insulating layer 4, near the opening 5, the future location of the metal pellet.

[0070] An image (obtained by bright-field optical microscopy) showing a top view of the optoelectronic element obtained at this stage is shown in [Fig. 4]. The top of the contact electrode 8 is visible.

[0071] The method 10 according to the invention further comprises a phase 16 of creating an injection electrode 7.

[0072] The phase 16 of deposition of the injection electrode 7, as shown in [Fig. 1], comprises a step 41 of deposition of a second metallic layer 18, called the injection layer, over essentially the entire surface of the optoelectronic element obtained during the previous phases of the process. The injection layer 18 is preferably made of silver.

[0073] During a step 42 of the process 10, a resin mask 17, produced by photolithography, is deposited on the second metal layer 18. The mask 17 covers the second metal layer 18 at the opening 5 in the insulating layer 4 as well as the contact electrode 8.

[0074] Phase 16 of the process then comprises a step 43 of lateral delimitation, or structuring, of the metal injection layer 18, during which the lateral extent of the second metal layer 18 is defined. This step can be carried out, for example, by etching the layer 18 with a solution of potassium iodide (Kl) and diiodine (I2) in water. The etched areas 6' then become non-conductive. When the injection layer 18 is silver, the exposed areas are then transformed into silver iodide (Agi).

[0075] The resin mask 17 is then removed by a lift-off technique, using a solvent such as acetone.

[0076] The final step 43 defines a metallic pad 6, for example made of silver, which covers the contact electrode 8 as well as the aperture 5. The portion of the pad 6 covering the upper layer of the Bragg mirror constitutes the previously mentioned metallic pellet 7, functioning as an injection electrode. A Tamm mode can be generated and confined to the interface between the pellet 7 and the upper layer of the Bragg mirror.

[0077] A top view image (obtained by bright-field optical microscopy) of four optoelectronic elements 1 obtained after step 16 of the process is shown in [Fig. 5]. The metal pads 6 and the pellets 7 are clearly visible, the metal pads 6 covering the contact electrodes, respectively. The pellets 7 in the [Fig.5] have different diameters, allowing for emitting regions of variable size.

[0078] According to another embodiment of the method according to the invention, the phases of creating a contact electrode 8 and creating an injection electrode 7 can be reversed. Indeed, it is possible to first create the injection electrode 7 and the metal pad 6 and then place the contact electrode 8 on the metal pad 6.

[0079] Figure 2 illustrates steps in phase 12 of creating an electrical insulating layer 4 and in phase 16 of creating an injection electrode 7. Phase 12 of creating an insulating layer 4 with its opening 5 is identical to that detailed with reference to Figure 1. During phase 16 of creating the injection electrode, the metallic injection layer 18 is deposited directly onto the insulating layer 4 and its opening, in order to form the injection pellet 7 at the opening 5. The contact electrode can then be deposited onto the injection layer 18.

[0080] The choice of the order in which these steps are carried out depends on the materials used. For example, it is easier to bond silver to gold than vice versa.

[0081] Of course, the invention is not limited to the examples just described and many modifications can be made to these examples without departing from the scope of the invention.

Claims

Demands

1. A method (10) for manufacturing an optoelectronic element (1), the optoelectronic element (1) comprising a semiconductor material (2) having an active region located directly under a surface of the semiconductor material, the method (10) comprising the following steps: - deposition (12) of an electrical insulating layer (4) on the semiconductor material using a first mask (14) placed directly on the active region, such that the electrical insulating layer (4) has a recess (5) at the level of the active region; - deposition (16) of a metallic layer (18), called an injection layer, on the assembly obtained in the previous step, such that the metallic injection layer (18) forms an electrode (7) on the surface of the semiconductor material at the level of the active region.

2. Method (10) according to the preceding claim, characterized in that it further comprises: - prior to the deposition (16) of the injection metal layer (18), creation (14) of a contact electrode (8) on the electrical insulation layer (4) using a second mask (9), the second mask (9) having a recess offset laterally with respect to the active region for the location of the contact electrode (8).

3. Method (10) according to claim 1, characterized in that it further comprises: - after the deposition (16) of the injection metal layer (18), creation of a contact electrode on the metal layer using a second photosensitive mask, the mask having a recess offset laterally with respect to the active region for the location of the contact electrode.

4. Method (10) according to any one of claims 2 to 3, ca- characterized in that the creation (14) of the contact electrode (8) comprises the following steps: - deposition of a photosensitive resin on the assembly obtained in the previous step, lithography and etching of the resin to obtain the second mask (9); - directional deposition (32) of a metallic layer (15), called the contact layer, on the second mask (9); and - lift-off (33) of the second mask (9); the part of the metallic contact layer (15) remaining after the lift-off forming the contact electrode (8).

5. A manufacturing method (10) according to the preceding claim, characterized in that it further comprises: - lateral delimitation (43) of the injection metal layer (18) so that it essentially covers the locations of the active region and the contact electrode (8), by means of a third mask (17) essentially covering the locations of the active region and the contact electrode.

6. Method (10) according to the preceding claim, characterized in that the lateral delimitation (43) of the injection metal layer (18) comprises the following steps: - deposition of a photosensitive resin on the assembly obtained in the preceding step, lithography and etching of the resin to obtain the third mask (17); - chemical attack of the parts of the injection metal layer not covered by the third mask (17); and - lift-off of the third mask (17).

7. Method (10) according to any one of the preceding claims, characterized in that the electrical insulating layer (4) is deposited by directional deposition.

8. A method (10) according to any one of the preceding claims, characterized in that the semiconductor material comprises a stack (2) of semiconductor layers comprising, according to a

9.

10.

11.

12. direction Z perpendicular to the surface of the semiconductor material, an alternation of layers of high and low refractive index to form an interference mirror. Method (10) according to any one of the preceding claims, characterized in that the active region comprises at least one light emitter (3) or detector. Method (10) according to the preceding claim, characterized in that at least one light emitter or detector comprises a quantum well (3) or a quantum dot (3). Method (10) according to claim 9 or 10, characterized in that at least one light emitter (3) or detector is located near the surface of the semiconductor material. Optoelectronic element (1) obtained by the manufacturing process (10) according to any one of the preceding claims.

Images