JP5442648B2 - Infrared sensor - Google Patents

Description

  The present invention relates to an electromagnetic induction type infrared sensor.

  Conventionally, various types of infrared sensors have been put to practical use, but each has the following disadvantages. For example, a device using a thermoelectromotive force effect such as a thermopile has a low response speed. Those using the pyroelectric effect, such as ceramics, have a slow response speed, are insensitive when the intensity of infrared rays is constant, and are easily affected by mechanical vibration. A device using a photoconductive effect such as a bolometer has a large change in output characteristics over time, and a power source for operation must be provided. A device using a quantum tunnel effect such as a photodiode is relatively expensive and has a narrow wavelength band where sensitivity can be obtained, and the long wavelength type requires temperature adjustment by cooling.

  In recent years, in view of the above-described problems, as shown in Patent Document 1, a detection element formed on a semiconductor substrate is directly connected to an antenna having an electromagnetic wave receiving antenna and a silicon / metal interface having a small area. An antenna-coupled electric field detection type photodetecting element having a high-frequency Schottky barrier diode for detection has been proposed.

JP-A-9-162424

However, in the photodetecting element of Patent Document 1, since the Schottky barrier diode for detection is based on a silicon / metal interface having a small area, it cannot be said that the operation speed in the infrared region is high, and particularly the wavelength is several tens of μm or less. It is difficult to obtain sufficient sensitivity in this band. Therefore, the light detection element of Patent Document 1 has a very small detection output, and there is a problem that the infrared rays that can actually be detected are limited to infrared rays having a high energy density such as a CO ₂ laser as disclosed in Patent Document 1. .

  Furthermore, the manufacturing of the photodetecting element of Patent Document 1 requires a semiconductor formation process, which includes an expensive semiconductor. Also in manufacturing, complexity due to processing such as ion doping and contamination are problems. In addition, since the photodetecting element of Patent Document 1 uses a Schottky barrier diode, a bias voltage is required, and the structure and manufacturing are further complicated when a bias circuit is combined in a chip. In addition, the need for a bias load leads to noise, which reduces measurement accuracy.

  The present invention has been made in view of the above background art, and an object thereof is to provide an infrared sensor capable of detecting electromagnetic waves in the infrared region with high sensitivity.

The present invention comprises a pair of antenna patterns formed on a semiconductor substrate with a length corresponding to the wavelength of infrared light, which is an electromagnetic wave to be detected, and a lower metal layer, an insulating layer, and an upper metal layer. is provided between the antenna patterns, and a MIM diode for rectifying the detected electromagnetic wave by the antenna pattern, the MIM diode, the third layer is provided by laminating a thickness direction, said lower metal layer and the In the infrared sensor, an upper metal layer is connected to each of opposite ends of the pair of antenna patterns. The lower metal layer and the upper metal layer of the MIM diode are composed of pairs such as Al-Al, Al-Pt, Al-Ti, Al-Ni, and Ni-Pt, and have a diode characteristic that conducts at a certain voltage or higher. The current-voltage curve of the diode has non-linearity. The semiconductor substrate has a semiconductor layer, and an upper oxide film layer and a lower oxide film layer are formed on a front surface and a back surface of the semiconductor substrate, and the reflection of incident infrared rays is prevented from being reflected on the surface of the upper oxide film layer. Coating is applied, and a mirror coating layer for reflecting infrared rays that have passed through the semiconductor substrate is provided on the outer surface of the lower oxide film layer.

  In particular, the lower metal layer of the MIM diode may be Al formed continuously with the antenna pattern, and the insulating layer may be formed by oxidizing the surface of the lower metal layer.

  Further, the antenna pattern and the MIM diode are covered with a condensing lens provided on the semiconductor substrate. The condensing lens is made of an optical resin, and is integrally provided on the semiconductor substrate so as to cover the antenna pattern.

  In addition, a lead line extending in the vicinity of the MIM diode from an end portion of the antenna pattern connected to the MIM diode is led out to the back surface of the semiconductor substrate through a via provided in the semiconductor substrate.

  The infrared sensor of the present invention rectifies the infrared detected by the antenna pattern with an MIM diode having an insulating layer sandwiched between the same or different metal layers. Therefore, the response speed is faster than that of a Schottky barrier diode, etc. Good sensitivity can be obtained even in a wavelength band of several tens of μm or less. Further, if the shape of the antenna pattern is adjusted, the detectable wavelength can be easily changed according to the wavelength of the infrared ray to be measured.

  In addition, this infrared sensor has a simple structure in which an antenna pattern and MIM diodes composed of two metal layers and an insulating layer are stacked in a vertical direction on a semiconductor substrate, so that it is easy to manufacture and does not cost. It is also suitable for nano-order precision processing using EBL.

It is a top view which shows one Embodiment of the infrared sensor of this invention. It is the front view (a) which shows the infrared sensor of this embodiment, and is an enlarged view of a MIM diode part.

  Hereinafter, an infrared sensor according to an embodiment of the present invention will be described with reference to FIGS. The infrared sensor 10 of this embodiment detects infrared rays having a wavelength of several tens of μm or less. The infrared sensor 10 includes a semiconductor substrate 12 made of Si or the like serving as a base, and first and second antenna patterns 14 and 16 that are antenna patterns formed on the semiconductor substrate 12 to detect infrared rays. Further, a metal-insulator-metal diode (hereinafter referred to as MIM diode) 18 that rectifies the output of the electromagnetic waves detected by the first and second antenna patterns 14 and 16, and the first and second antenna patterns 14 and 16 as a whole. And a lens 20 provided so as to cover the lens.

  The semiconductor substrate 12 has a semiconductor layer 22 made of, for example, P-type silicon having a thickness of about 600 μm, and an upper oxide film layer 24 and a lower oxide film, which are silicon oxide layers having a thickness of about 1.5 μm, on the front and back surfaces thereof. Layer 26 is formed. Furthermore, an antireflection coating (not shown) is applied to the surface of the upper oxide film layer 24 in order to prevent incident infrared rays from being reflected. Further, a thin mirror coating layer 28 for reflecting infrared rays that have passed through the semiconductor substrate 12 is provided on the surface of the lower oxide film layer 26 so that the intensity of infrared rays received by the first and second antenna patterns 14 and 16 is reduced. ramp up.

  The first and second antenna patterns 14 and 16 are formed on the surface of the semiconductor substrate 12 and are linearly symmetrically arranged to form a so-called dipole antenna. The lengths of the first and second antenna patterns 14 and 16 are adjusted based on the material of the semiconductor substrate 12 and the wavelength of infrared light to be measured. When the upper oxide film layer 24 uses the semiconductor substrate 12 made of silicon oxide and detects infrared rays in the vicinity of the wavelength λ = 10 μm, for example, the total length of the first and second antenna patterns 14 and 16 is about λ / 2. The first and second antenna patterns 14 and 16 are set to about 3 to 5 μm and the width is set to several tens of nm. In particular, when the semiconductor substrate 12 is silicon, the antenna length is preferably set to 3 μm.

  The MIM diode 18 has a structure in which a lower metal layer 30, an insulating layer 32, and an upper metal layer 34 are stacked in the thickness direction. The lower metal layer 30 is formed on the upper surface of the first joint portion 36 that is the output end portion of the first antenna pattern 14, and the upper metal layer 34 is the second joint portion 38 that is the output end portion of the second antenna pattern 14. It is surface-bonded to the back side.

  The lower metal layer 30 and the upper metal layer 34 are formed of a predetermined material in order to obtain nonlinear current-voltage characteristics having diode characteristics. Examples of the pair of the lower metal layer 30 and the upper metal layer 34 include a pair of Al—Al, Al—Pt, Al—Ti, Al—Ni, and Ni—Pt. As a result, the rectification operation can be performed in a no-load state where the MIM diode 18 has no current bias. Further, an external bias circuit and a power source can be omitted, and an effect of reducing noise generation from the MIM diode 18 can be obtained.

  When the two metal layers 30 and 34 separated by the insulating layer 32 are made of the same material, the diode characteristics show symmetry, and the resistance rapidly decreases at a positive or negative constant voltage or more and becomes conductive. Also, when made of different metal materials, the diode characteristics are asymmetrical, and in the Al—Pt, Al—Ti, and Al—Ni pairs, Al is the lower metal layer 30 and the surface of the lower metal layer 30 is oxidized. Thus, the insulating layer 32 is formed. In the case of the Ni—Pt pair, Ni is used as the lower metal layer 30, and the surface is oxidized to form the insulating layer 32. In these cases, the diode characteristics are asymmetrical, and the resistance rapidly decreases and becomes conductive at a positive or negative constant voltage or higher. Further, by configuring Al as the lower metal layer 30, there is an advantage that an oxide film that is the intermediate insulating layer 32 can be easily formed.

  The first antenna pattern 14, the first joint 36, and the lower metal layer 30 are made of the same metal, and the second antenna pattern 16, the second joint 38, and the upper metal layer 34 are also made of the same metal. Is formed. Therefore, the lower metal layer 30 may be shared by the first joint portion 36, and the upper metal layer 34 may also be shared by the second joint portion 38.

  The thickness of the insulating layer 32 is set to 0.5 nm to 5 nm, preferably 1 nm to 2 nm in consideration of increasing nonlinearity of current-voltage characteristics. The size of the insulating layer 32 is set in consideration of the high speed response of the MIM diode 18 and the detection wavelength. The operation of the MIM diode 18 uses the quantum tunnel effect as in the photodiode, and the response speed depends on the insulation resistance and junction capacitance of the insulating layer 32. Here, in order to be able to detect infrared rays having a frequency of several THz or more (wavelength is several tens of μm or less), the thickness of the insulating layer 32 is 1 nm to 2 nm and the dielectric constant inherent to the insulating layer 32 is taken into consideration. In order to keep the junction capacitance below a certain level, the size of the insulating layer 32 is set to about 100 nm × 100 nm or less, more preferably 50 nm × 50 nm to 20 × 20 nm.

  First and second output lead lines 40 and 42 for taking out the rectified output of the MIM diode 18 are extended in the vicinity of the first and second joint portions 36 and 38 of the first and second antenna patterns 14 and 16. ing. A pair of vias 44 and 46 are formed in the central portion of the semiconductor substrate 12 so as to connect to the first and second output lead lines 40 and 42 and penetrate the semiconductor substrate 12. The pair of vias 44 and 46 penetrates the semiconductor substrate 12 through an insulating layer, and is connected to an unillustrated back surface lead line on the back surface side so as to be connectable to an external circuit.

  When the integrated circuit for signal processing and the infrared sensor unit are formed integrally with the semiconductor substrate 12, the pair of vias 44 and 46 penetrating the semiconductor substrate 12 through the insulating layer are formed in the substrate. Provided to connect to an integrated circuit.

  The lens 20 collects infrared rays to be measured on the first and second antenna patterns 14 and 16 to increase sensitivity. Here, the first and second antenna patterns 14 and 16 are made of resin for optical lenses. The first and second antenna patterns 14 and 16 and the MIM diode 18 are covered so as to be integrally formed on the upper surface of the semiconductor substrate 12.

  The infrared sensor 10 described above can be manufactured, for example, by the following method. First, the upper and lower oxide film layers 24 and 26 are formed by thermally oxidizing the semiconductor layer 22 which is a P-type silicon substrate in a high temperature environment. Further, an antireflection coating is applied to the upper oxide film layer 24, and the lower oxide film 26 is formed. Is covered with the mirror coating layer 28, and the semiconductor substrate 12 is produced.

  Next, a back surface lead line (not shown) is formed on the surface of the mirror coating layer 28 of the semiconductor substrate 12 via an insulating layer. For example, a conductor such as Au is vapor-deposited on the surface of the insulating layer of the mirror coating layer 28, a resist layer is formed, exposure is performed using a mask inner, patterning is performed, development is performed by immersion in a developing solution, and etching. Finally, an unnecessary resist layer is removed and formed. As another process, a lift-off process in which a pattern is directly formed by vapor-depositing a conductor from above the mask may be used. Further, before or after this, a pair of vias 44 and 46 connected to the back surface lead line are formed in the semiconductor substrate 12.

  Next, the first and second antenna patterns 14 and 16, the first and second output lead lines 40 and 42, and the MIM diode 18 are formed on the surface of the upper oxide film layer 24 of the semiconductor substrate 12. Since the shape of this part has a great influence on the performance of the infrared sensor 10, a processing technique with extremely high accuracy is required. For the processing, for example, electron beam lithography (hereinafter referred to as EBL) that realizes nano-order processing accuracy is used.

  When forming the pattern, first, a resist layer for EBL is formed on the surface of the upper oxide film layer 24, and the first and second antenna patterns 14, 16 and the first and second output lead lines 40, 42 are drawn by EBL. The first and second output lead lines 40 and 42 are connected to a pair of vias 44 and 46. Next, the lower metal layer 30 is deposited on the first joint portion 36 of the first antenna pattern 14 using EBL, and the upper layer portion is oxidized in an oxygen atmosphere to form the insulating layer 32, and the upper surface thereof is formed. A top metal layer 34 is deposited using EBL. And the 2nd junction part 38 which connects the upper metal layer 34 and the 2nd antenna pattern 16 is formed, and an unnecessary resist layer is finally removed. When the lower metal layer 30 is also used as the first joint portion 36, the step of depositing the lower metal layer 30 is omitted, and when the upper metal layer 34 is also used as the second joint portion 38, the upper metal layer 34 is deposited. The step of making is omitted.

  Next, the lens 20 is molded into a predetermined shape using an optical resin on the surface of the semiconductor substrate 12, and then the semiconductor substrate 12 is accommodated in a package (not shown), wiring is connected, and packaging is completed. To do.

  The infrared sensor 10 described above detects and rectifies infrared rays, which are electromagnetic waves detected by the first and second antenna patterns 14 and 16, with the MIM diode 18, so that even in the infrared region, particularly in the band where the wavelength is several tens of μm or less. Good sensitivity can be obtained. Further, the generation of noise is small, and it is not necessary to provide an operating power supply outside, and since operation at room temperature is possible, temperature management such as cooling is unnecessary.

  Further, the detectable infrared wavelength (or frequency) can be easily changed by adjusting the length and the like of the first and second antenna patterns 14 and 16. For example, in the case of a temperature adjusting sensor at the bottom of a cooking heater, the pattern length may be adjusted so that infrared rays having a wavelength of about 6 μm to 8 μm can be detected. Similarly, infrared rays having a wavelength of about 2 μm to 4 μm can be detected if the application is a carbon dioxide concentration monitoring sensor for building air conditioning, and infrared rays having a wavelength of about 10 μm is used for a human body detection sensor for facility energy management. What is necessary is just to adjust the length of the 1st and 2nd antenna patterns 14 and 16 so that detection is possible. As described above, an infrared sensor optimal for each application can be manufactured using the same manufacturing equipment or a similar manufacturing process.

  The infrared sensor 10 has a simple structure in which the first and second antenna patterns 14 and 16, the metal layers 30 and 34 of the MIM diode 18, the insulating layer 32, and the like are stacked on the semiconductor substrate 12 in the layer thickness direction. Therefore, it is advantageous in terms of manufacturing cost, and is also suitable for performing nano-order precision processing using EBL or the like. Furthermore, the semiconductor substrate 12 to the lens 20 can be integrally formed, and the compatibility with the semiconductor C-MOS structure is good. In addition to the via structure, a circuit such as an amplifier is integrally formed on the semiconductor substrate 12. It is also possible.

  The present invention is not limited to the above embodiment, and the MIM diode becomes an insulating layer between metal layers in addition to the MOM (Metal-Oxide-Metal) type in which an oxide film on the metal surface is used as an insulating layer. An MBM (Metal-Barrier-Metal) diode with a barrier layer in between may be used, and the insulating layer can be selected as appropriate. Other than that, the antenna pattern can be configured almost two-dimensionally and can be applied to the detection of the infrared frequency band. Also good. Further, the infrared condensing lens may be omitted if necessary, and the form of the wiring and package for outputting the output of the MIM diode to the external output terminal can be appropriately changed.

DESCRIPTION OF SYMBOLS 10 Infrared sensor 12 Semiconductor substrate 14 1st antenna pattern 16 2nd antenna pattern 18 MIM diode 20 Lens 30 Lower metal layer 32 Insulating layer 34 Upper metal layer

Claims (2)

It consists of a pair of antenna patterns formed on a semiconductor substrate with a length corresponding to the wavelength of infrared rays, which are electromagnetic waves to be detected, and a lower metal layer, an insulating layer, and an upper metal layer. And an MIM diode that rectifies the electromagnetic waves detected by the antenna pattern,
The MIM diode, the third layer is provided by laminating a thickness Direction, said lower metal layer and said upper metal layer is connected to the opposite ends of the pair of antenna patterns, under the MIM diode The metal layer and the upper metal layer are made of the same or different metals selected from Al, Pt, Ti, Ni,
The semiconductor substrate has a semiconductor layer, and an upper oxide film layer and a lower oxide film layer are formed on a front surface and a back surface of the semiconductor substrate, and the reflection of incident infrared rays is prevented from being reflected on the surface of the upper oxide film layer. Coating is applied, and on the outer surface of the lower oxide film layer is provided a mirror coating layer that reflects infrared light that has passed through the semiconductor substrate,
The antenna pattern and the MIM diode are covered with a condensing lens made of an optical resin integrally provided on the semiconductor substrate, and from the semiconductor substrate to the condensing lens are integrally formed,
An infrared ray characterized in that a lead line extending in the vicinity of the MIM diode from an end portion of the antenna pattern connected to the MIM diode is led out to the back surface of the semiconductor substrate through a via provided in the semiconductor substrate. Sensor. The infrared sensor according to claim 1, wherein the lower metal layer of the MIM diode is Al formed continuously with the antenna pattern, and the insulating layer is formed by oxidizing the surface of the lower metal layer.

Images