CN112415647A

CN112415647A - Semiconductor etalon device and method of manufacturing the same

Info

Publication number: CN112415647A
Application number: CN202010831216.8A
Authority: CN
Inventors: 常宇骅; 董博维; 李正国
Original assignee: National University of Singapore
Current assignee: National University of Singapore
Priority date: 2019-08-21
Filing date: 2020-08-18
Publication date: 2021-02-26

Abstract

A semiconductor etalon device comprising a photodetector disposed on or within a wafer; a first reflector; and a second reflector parallel to and spaced from the first reflector; the first and second reflectors each comprise a photonic crystal and are arranged relative to and spaced from the wafer and in at least partial overlapping relationship with the light-sensing portion of the photodetector.

Description

Semiconductor etalon device and method of manufacturing the same

Technical Field

The present invention relates to a semiconductor etalon device, and a method of manufacturing a semiconductor etalon device. The invention also relates to a device for a semiconductor etalon comprising a photosensor, an imaging device and a spectrometer.

Background

A fabry-perot interferometer is a tunable bandpass filter. Mems enable the mass production of miniaturized (e.g. several square millimeters) fabry-perot interferometers at a low unit cost.

The micro electro mechanical system-Fabry-Perot interferometer is a key component in a non-diffusion infrared system, a micro spectrometer and a hyperspectral imager. For example, gas phase transmission infrared spectroscopy techniques using MEMS-Fabry-Perot interferometers can be applied to the detection and analysis of hydrocarbons, carbon dioxide, and more complex organic compounds. The application fields of the MEMS-Fabry-Perot interferometer also include medical treatment, agriculture, automobile, natural gas safety and indoor air quality detection.

A mems-fabry-perot interferometer comprises two movable mirrors separated by an adjustable air gap. Opto-electronic micro-electro-mechanical systems devices typically employ thin films of aluminum or other metals to enhance reflectivity. The metal mirrors have high/broadband reflectivity and are compatible with most standard mems processes. Also, due to its limited thickness (typically less than 100nm), metal mirrors do not generate too high mechanical stress. But on the other hand, metal mirrors can only operate in reflective mode due to the large ohmic losses, which increases the complexity of the system integration.

Distributed bragg mirrors may be substituted for the metal mirrors. The distributed bragg mirror is composed of several alternating dielectric layers with high and low refractive indices, each layer being one quarter of the target wavelength thick. The distributed bragg reflector utilizes a lossless dielectric material to achieve a wide frequency band, high reflectivity, and high transmissivity. Distributed bragg mirrors are the main solution to realize fabry-perot interferometers. However, conventional fabry-perot interferometer surface micromachining processes involve repeated deposition of distributed bragg mirror layers. The stress created by such repeated deposition presents a significant challenge. Furthermore, it is difficult to prepare air gaps by depositing thick sacrificial layers.

It is an object of the present invention to solve the above problems, or to provide a useful alternative.

Disclosure of Invention

The present invention provides a semiconductor etalon device, comprising:

a photodetector disposed on or within the wafer;

a first reflector; and

a second reflector parallel to and spaced from the first reflector;

the first reflector and the second reflector each comprise a photonic crystal, are arranged relative to and spaced from the wafer, and are in at least partial overlapping relationship with the light-sensing portion of the photodetector.

Some embodiments include a support structure for supporting the first reflector and the second reflector, the support structure having an aperture through which a light-sensing portion of the photodetector is exposed.

The support structure may be a stepped structure comprising a first step supporting the first reflector and a second step supporting the second reflector.

In certain embodiments, the light-sensing portion of the photodetector comprises one or more layers of black phosphor. In other embodiments, other semiconductor materials may also be used in the photodetector, such as graphene, other 2D semiconductor materials, or III-V semiconductor materials.

The photonic crystal may have a silicon film with a plurality of holes formed therein.

Some embodiments include an electrostatic actuator for adjusting the spacing between the first reflector and the second reflector.

The present invention also provides a method of manufacturing a semiconductor etalon device comprising:

fabricating a photodetector on or within a wafer; and

first and second reflectors are prepared in parallel spaced arrangement with respect to the wafer, wherein the first and second reflectors each have a photonic crystal, the first and second reflectors being positioned opposite the photodetector, spaced from the photodetector, and in at least partially overlapping relation with the light-sensing portion of the photodetector.

The method may include fabricating a support structure for supporting the first mirror and the second mirror, the support structure having an aperture exposing a light sensing portion of the photodetector.

The manufacturing steps of the support structure comprise:

applying a resist over the photodetector; and

the resist is selectively removed in a region covering a light-sensing portion of the photodetector to form a stepped structure including a first-layer step for supporting the first reflector, a second-layer step for supporting the second reflector, and the hole.

In certain embodiments, the first reflector and the second reflector are disposed on the support structure by transfer printing.

The transfer may be achieved by using an elastomeric stamp containing an array of microtip tips.

In certain embodiments, the light-sensing portion of the photodetector comprises one or more layers of black phosphor.

The invention also provides an optical device comprising at least one semiconductor etalon device as disclosed herein.

The optical device may be a photosensor, an imaging device, or a spectrometer.

Drawings

Fig. 1 is a cross-sectional schematic view of a semiconductor etalon device according to an embodiment;

fig. 2(a) to 2(e) illustrate method steps for fabricating a semiconductor etalon device according to an embodiment;

FIG. 3(a) is a scanning electron microscope image of a polydimethylsiloxane decal used in the process of FIGS. 2(a) to 2 (d);

FIG. 3(b) is a 500nm film image captured during transfer of the decal of FIG. 3 (a);

fig. 4(a) is a plan view image of an example of a semiconductor etalon device;

FIG. 4(b) is a photo-current spectrum of the device of FIG. 4 (a);

FIG. 4(c) is an electrostatic actuator design of the device of FIG. 4 (a);

FIG. 4(d) shows simulated transmission spectra of an etalon device in the form of a Fabry-Perot interferometer at different air gaps; and

fig. 5(a) and 5(b) show two examples of etalon devices used in particular applications.

Detailed Description

Embodiments of semiconductor etalon devices are disclosed that are Fabry-Perot interferometers based on tunable photonic crystals of microelectromechanical systems, combined with photodetectors such as black phosphor. Each photonic crystal mirror may be an ultra-thin silicon film with periodic air holes that can have high reflectivity through guided mode resonance.

Embodiments are also related to methods of manufacturing semiconductor etalon devices. In some embodiments, the semiconductor etalon devices may be fabricated by a transfer process. The transfer process can directly transfer the photonic crystal reflecting surface to a target position by using a micro-structure polydimethylsiloxane stamp, so that the photonic crystal reflecting surface is separated from another photonic crystal reflecting surface to manufacture a Fabry-Perot interferometer without depositing a sacrificial layer. The transfer process and the photonic crystal reflector are used together, so that the stress problem occurring when the dielectric layer is repeatedly deposited in the distributed Bragg reflector and the traditional surface micromachining process is solved. The transfer process also makes integration of photodetector materials (e.g., black phosphorus) more flexible and compact.

Embodiments of the present invention provide a photodetector integrated chip-level solution using black phosphorus. Other 2D materials, such as graphene or III-V based materials, may also be used to fabricate etalon devices, since the transfer is done at room temperature, thus allowing heterogeneous integration.

The embodiments of the present invention have the following advantages:

the transfer printing process avoids the problem of stress generated in the surface micromachining process of the traditional micro-electromechanical system, simplifies the manufacturing process and improves the yield.

The photonic crystal reflector adopts an ultrathin silicon film, and high reflectivity is realized. This avoids pressure problems, simplifies the process and improves yield.

Integrated with the black phosphorus detector, providing an integrated, uncooled on-chip mid-infrared photodetector.

Referring now to fig. 1, an embodiment is described wherein a semiconductor etalon device 100 comprises a semiconductor etalon device disposed on a wafer 104 or on a wafer 1The photodetector layer 102 in 04. For example, wafer 104 may contain SiO doped on Si₂。

The photodetector layer 102 includes a passivation layer 103 and a light sensing portion 110, and the light sensing portion 110 is in contact with the electrode 105 for reading out a photocurrent generated by the light sensing portion 110. The passivation layer 103 may be made of Al₂O₃And (4) preparing. The light sensing portion 110 may comprise one or more layers of black phosphor (or other 2D light sensitive material).

The semiconductor etalon device 100 further comprises a first reflector 106 and a second reflector 108. The second reflector 108 is positioned parallel to the first reflector 106 and spaced apart from the first reflector 106. The first reflector 106 and the second reflector 108 each comprise a photonic crystal composed of a silicon film with a plurality of holes formed therein. The first and

second reflectors

106, 108 are positioned opposite the photodetectors, spaced from the photodetectors 102, and aligned with and spaced from the light-sensing portion 110 of the photodetectors 102 in at least partially overlapping relation with respect to the wafer 104 in the example shown in FIG. 1, the light-sensing portion 110 is aligned with respect to the

photonic crystal reflectors

106, 108 such that the photonic crystal aperture 120 entirely overlies the light-sensing portion 110.

The semiconductor etalon device 100 further comprises a support structure 112 arranged relative to the wafer 104. For example, the support structure may be disposed directly or on the passivation layer 103 of the photodetector layer 102. The support structure 112 supports the

photonic crystal reflectors

106, 108 on the support structure 112 in spaced relation to each other and also in spaced relation to the light sensing portion 110. The support structure also has an aperture through which the light-sensing portion 110 can be exposed to a light source such that light is reflected or transmitted by the

photonic crystal reflectors

106, 108 to the light-sensing portion 110, wherein the light-sensing portion 110 generates a photocurrent that can be read out through the electrode 105.

In the example of fig. 1, the support structure 112 is a stepped structure comprising a first pair of laterally spaced steps 132 and a second pair of laterally spaced steps 134. The upper surface of the step 132 is used to support the first reflector 106. The upper surface of the step 134 is used to support the second reflector 108. The second pair of laterally spaced steps 134 is positioned higher than the first pair of laterally spaced steps 132. The lateral spacing between the second pair of steps 134 is greater than the lateral spacing between the first pair of steps 132. Since the first and second

photonic crystal reflectors

106, 108 can be easily placed in series on the upper surface of the space between

stages

132, 134, this will facilitate the fabrication of the device 100 by transfer printing, for reasons detailed below.

Fig. 2(a) -2(e) illustrate an overall process flow of a method embodiment of fabricating a semiconductor etalon device 100. In one example, the components of the semiconductor etalon device 100 may be fabricated separately. 2(a) -2(e) each bear like reference numerals from FIG. 1 to correspondingly label like components.

Fig. 2(a) illustrates a method of manufacturing the photodetector 102. The first step in fabricating the photodetector 102 is to form one or more layers of black phosphorus or another 2D photosensitive material on or within the wafer 104. In one embodiment, the thickness of one black phosphor layer may be 40 nm. In some instances, the black phosphorus is mechanically stripped from the bulk material.

The second step in fabricating the photodetector 102 is to generate an electrode pattern for the electrode 105. For example, the electrodes are placed on the wafer 104 or inside the wafer 104. In one embodiment, the electrodes 105 are positioned such that the one or more layers of light sensing portions 110 extend between the electrodes 105.

The third step in forming the photodetector 102 is to deposit a passivation layer 103 by atomic layer deposition. For example, a passivation layer 103 is disposed on one or more layers 110. In one embodiment, Al₂O₃The thickness of the passivation layer 103 is 20 nm.

Fig. 2(b) depicts a method of manufacturing the support structure 112. Referring to fig. 2(a), the first step in fabricating the support structure 112 is to apply a resist 202 on the photodetector 102. The second step is to selectively remove the resistor 202 in the area of the light-sensing portion 110 overlying the photodetector 102 to form a stepped structure. In one example, the support structure 112 may be made by using photoresist PermiNEX 2005. In some embodiments, the support structure 112 may be applied to the photodetector 102 after the step structure is formed.

Figure 2(c) depicts a method of making a photonic crystal reflector. Specifically, the photonic crystal reflective layer is fabricated from a silicon-on-insulator 200 and comprises a sacrificial layer 212, a photonic crystal reflective layer 214, a buried oxide layer 216, and a base layer 218. A sacrificial layer 212 and a photonic crystal reflective layer 214 are disposed on the buried oxide layer 216, and the buried oxide layer 216 is disposed on the base layer 218. In one embodiment, the thickness of the sacrificial layer 212 and the device layer 214 is 500nm, and the thickness of the buried oxide layer 216 is 1 μm. After forming the silicon-on-insulator wafer 200, the photonic crystal reflector fabrication process further includes etching away the sacrificial layer 212 and the buried oxide layer 216 using dilute hydrofluoric acid (HF). Thus, only the photonic crystal reflective layer 214 and the base layer 218 remain, and the silicon on insulator wafer 200 becomes the suspended photonic crystal film 220.

Fig. 2(d) depicts a method of applying the first reflector 106 and the second reflector 108 to the support structure 112. Once the photonic crystal reflective layer 214 is prepared according to fig. 2(c), it can be applied to the support structure 112 as either the first reflective layer 106 or the second reflective layer 108. In particular, the two reflective layers may be applied to the support structure 112 by transfer printing. The transfer printing process avoids the stress problem in the surface micromachining process of the traditional micro-electromechanical system, simplifies the manufacturing process and improves the yield. Referring to fig. 2(d), the transfer uses an elastomeric microstructured polymer (polydimethylsiloxane) decal 222. The decal 222 contains an array of microtip tips. Because of its soft nature, polydimethylsiloxane can be used to handle (without damaging) fragile materials. The key to successful transfer is reversible adhesion, which is achieved by the elastomeric surface of the polydimethylsiloxane decal 222 with the array of microtip tips. Due to the complex interaction between the pressure control contact area and the soft adhesive forces inherent in the viscoelastic properties of elastomers, microtip tip designs are able to achieve very high levels of adhesive switching.

Referring to fig. 2(d), the polydimethylsiloxane decal 220 quickly detects the

reflectors

106 and 108 and gently transfers them to the target locations. Specifically, the target locations of the

reflectors

106 and 108 are located on two steps of the support structure 112 on the photodetector 102, respectively.

FIG. 2(e) illustrates a method of making a polydimethylsiloxane decal 222. The first step is to make a mold 224 for the polydimethylsiloxane decal 222. For example, mold 224 is formed of SiO₂Produced on Si wafers (Si crystal orientation)<100>). In one embodiment, SiO₂Is a hard mask with a thickness of 300 nm. The bottom of the silicon wafer is wet etched to form the array of microtips. A layer of SU-8 material 226 is exposed as a frame to define the extruded portion of the polydimethylsiloxane decal 222. In a second step, the polydimethylsiloxane material is cast into a mold 224 at a base to agent ratio of 5 to 1 to form a polydimethylsiloxane print 220. The polydimethylsiloxane material was then removed from the mold 222 after curing for 2 hours at a temperature of 65 degrees.

Embodiments of the present invention are further illustrated by reference to the following non-limiting examples.

FIG. 3(a) shows a scanning electron microscope image of a 400 μm by 400 μm microstructured polydimethylsiloxane decal. The 400 μm by 400 μm microstructured polydimethylsiloxane decal is a specific example of the polydimethylsiloxane decal 222 of FIGS. 2(d) -2 (e). The inclination of the microtip array is greater than the inclination of the photonic crystal. It will be appreciated that the specific range of the inclination of the array of microtips depends on the stiffness of the photonic crystal film to be transferred. In this example, the pitch of the array of microtips is 45 μm and the base width of each microtip is 15 μm.

Fig. 3(b) is a scanning electron microscope image of a Si suspended photonic crystal film retrieved by the polydimethylsiloxane decal of fig. 3 (a). The translucent region 302 is a photonic crystal portion, the black squares 304 are polydimethylsiloxane microtips, and 304 are visible through the holes of the photonic crystal 302.

Fig. 4(a) is an optical image of an exemplary semiconductor etalon device comprising two photonic crystal films as shown in fig. 3 (b). The two photonic crystal silicon films are transferred to the device, which overlies a black phosphorus photodetector.

Fig. 4(b) is a photocurrent diagram of the device of fig. 4 (a). Preliminary test results showed a design peak at 2.98 μm with a full width at half maximum of about 30 nm.

Fig. 4(c) shows the electrostatic actuator 401 of the device of fig. 4 (a). This type of actuator may also be used with the device 100 of fig. 1. The electrostatic actuator is used to adjust the spacing between the first reflector 106 and the second reflector 108. The electrostatic actuator of fig. 4(c) may pull the upper membrane (e.g., 108) downward, thereby changing the air gap between the two membranes (e.g., 106, 108). In this example, the electrostatic actuator is V-shaped 402 and is used to move the central photonic crystal portion on the top film 108.

Fig. 4(d) shows simulated transmission spectra of etalon devices in the form of fabry-perot interferometers at different air gaps. It can be seen that the resonance peak shifts to shorter wavelengths as the air gap decreases. The quality factor is optimized at 2.7 μm, where the reflectivity of the silicon photonic crystal is highest. The entire working spectral range is 2.55 μm to 3.5. mu.m.

Standard device embodiments according to the present invention may find wide application, such as miniaturized non-dispersive infrared systems for gas sensing, micro-spectrometers, photo-sensors and hyperspectral imagers.

Fig. 5 shows an example of an etalon device used in a gas sensor 501 for gas detection. The 501 gas sensor uses a micro-electromechanical system tunable fabry-perot interferometer for detection and analysis of hydrocarbons, carbon dioxide and more complex organic compounds. The gas sensor 501 comprises a light source 502, a gas cell 503 containing the gas to be analyzed, an infrared transparent aperture 504, and an etalon device consisting of photodetector 102,

reflectors

106 and 108. It is noted that some applications may require integration with a particular type of light source. For example, an infrared radiation source may be integrated as light source 502 into a non-dispersive infrared system. The light sources 502 may be arranged in different ways. In the layout example shown in fig. 5(a), the gas sensor 501 is linearly integrated. Specifically, the light source 502 is arranged such that light emitted by the light source 502 is transmitted directly to the light-sensing portion of the photodetector 102. In this example 503 is a centimeter-length gas cell that can act as a low detection-limit light path. In another example of the layout shown in fig. 5(b), the light source 502 is disposed so that light reflected from the mirror 505 can reach the light-sensing portion of the photodetector 102. This arrangement utilizes a mirror 505 to reflect the light path to reduce the volume of the gas cell 503, but the light path can remain the same.

In some embodiments, the etalon device can be operated without a MEMS actuator to adjust the gap between the reflective plates. For example, an etalon device according to some embodiments may operate as a static filter in a gas sensing system to select a particular wavelength that matches an absorption peak of a target gas. For example, an etalon device may be configured as a static filter with a selected wavelength of 4.26 μm for use with CO₂And (6) detecting.

Claims

1. A semiconductor etalon device comprising:

a photodetector disposed on or within the wafer;

a first reflector; and

a second reflector parallel to and spaced from the first reflector;

2. A semiconductor etalon device according to claim 1 comprising a support structure for supporting the first reflective surface and the second reflective surface, the support structure having an aperture through which a light sensing portion of said photodetector is exposed.

3. A semiconductor standard plate device according to claim 2, wherein the support structure is a stepped structure comprising a first step supporting the first reflector and a second step supporting the second reflector.

4. A semiconductor reticle device according to claim 1, wherein the light-sensitive portion of said photodetector comprises one or more layers of black phosphor.

5. A semiconductor etalon device according to claim 1 wherein the photonic crystal is a silicon film having a plurality of holes formed therein.

6. A method of fabricating a semiconductor etalon device comprising:

fabricating a photodetector on or within a wafer; and

7. A method according to claim 6, comprising fabricating a support structure for supporting said first reflector and said second reflector, said support structure having an aperture for exposing a light sensing portion of said photodetector.

8. A method according to claim 7, the step of manufacturing the support structure comprising:

applying a resist over the photodetector; and

9. A method according to claim 7 or claim 8, wherein the first and second reflectors are arranged on the support structure by transfer printing.

10. An optical device comprising at least one semiconductor etalon apparatus according to any one of claims 1 to 5, said optical device being a photosensor, an imaging device or a spectrometer.