JP2012039016A - Manufacturing method of porous silicon optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming micropores with high controllability in a porous silicon layer formed by an anode oxidation method that can increase the luminous efficiency and narrow the band of the emission wavelength.SOLUTION: A manufacturing method of a semiconductor optical element including a single-crystal silicon substrate 101, a porous silicon layer 102 embedded in its surface and used as a light emission layer or a light reception layer, a transparent electrode 103 connected to the porous silicon layer, and an ohmic electrode 104 provided for a rear surface of the single-crystal silicon substrate comprises performing anode oxidation on the surface of the single-crystal silicon substrate while applying ultrasonic vibration, so that the porous silicon layer serving as the light emission layer or the light reception layer is formed.

Description

  The present invention relates to a method for manufacturing a porous silicon optical device, and more particularly to a method for manufacturing a porous silicon optical device using a porous silicon layer formed by an anodic oxidation method as a light emitting layer or a light receiving layer.

  When the silicon single crystal is miniaturized to the Bohr radius, the energy increases due to the uncertainty principle, and the electrons or holes of the miniaturized silicon crystal are delocalized by wave number selection relaxation, Recombination is possible by direct transition. This is known as a quantum size effect, and is known as a phenomenon in which silicon, which is an indirect transition semiconductor, directly transitions and emits visible light.

  Specifically, a technology for forming a light-receiving element or a light-emitting element by forming porous silicon having, for example, micropores with a diameter of 2 to 50 nm on the surface of a silicon single crystal substrate by an anodic oxidation method is disclosed in Japanese Patent It is disclosed in Document 1.

  FIG. 6 shows a schematic diagram of this type of porous silicon optical device. The porous silicon optical element shown in FIG. 6 is formed on the porous silicon layer 102 after forming a porous silicon layer 102 having micropores by anodizing a part of the surface of the single crystal silicon substrate 101. A transparent electrode 103 that transmits light emitted from the porous silicon layer 102 is formed, and an ohmic electrode 104 is formed on the back surface of the single crystal silicon substrate 101. The surface of the single crystal silicon substrate 101 is covered with an insulating film 105 made of a silicon oxide film or a silicon nitride film for insulation from the transparent electrode 103.

  The porous silicon layer 102 for forming the light emitting layer or the light receiving layer easily forms micropores when formed by an anodic oxidation method in which the surface of the single crystal silicon substrate 101 is electrochemically etched in a hydrofluoric acid aqueous solution. be able to.

  FIG. 7 shows an explanatory diagram of a conventional anodic oxidation method for forming a porous silicon layer. After the ohmic electrode 104 is formed on the back surface of the single crystal silicon substrate 101 and covered with the hydrofluoric acid resin 13 so that a part of the surface of the single crystal silicon substrate 101 in the region where the porous silicon layer is to be formed is exposed. Then, the hydrofluoric acid aqueous solution 14 is put into the hydrofluoric acid resistant container 15. The hydrofluoric acid aqueous solution 14 is a mixed aqueous solution in which an appropriate amount of hydrofluoric acid and ethyl alcohol are mixed. Then, the anode of the constant current source 16 is connected to the ohmic electrode 104, and the cathode is connected to the platinum negative electrode 17 serving as a counter electrode. A voltmeter 18 and an ammeter 19 are also connected to monitor anodizing conditions.

  When a current is supplied from the constant current source 16 under a predetermined condition in such a state, the porous silicon layer 102 can be formed.

Japanese Patent No. 3306077

  In general, it is known that the emission wavelength and emission energy of silicon microcrystals increase in inverse proportion to the square of the crystal diameter. That is, as the crystal grain size becomes uniform and small, uniform and highly efficient light emission can be obtained. Therefore, when the porous silicon layer formed by the anodic oxidation method is used as the light emitting layer or the light receiving layer, it is necessary to control the micropores formed by the anodic oxidation method at the nanometer level. However, in the conventionally proposed anodic oxidation method, the micropores can be controlled at the nanometer level only by optimizing various conditions such as the concentration of the hydrofluoric acid solution, the applied current density, and the anodic oxidation time. As a result, the grain size of the silicon microcrystal becomes non-uniform, and it is difficult to obtain a desired emission wavelength and emission intensity, and there is a limit in achieving practical use.

  The present invention solves the above-mentioned problems and forms a porous silicon layer capable of narrowing the luminous efficiency and emission wavelength, so that when the porous silicon layer is formed by an anodic oxidation method, it is fine with good controllability. An object is to provide a method of forming a hole.

  In order to achieve the above object, the present invention provides a single crystal silicon substrate, a porous silicon layer embedded on the surface of the single crystal silicon substrate, a transparent electrode provided to connect to the porous silicon layer, A semiconductor light having an ohmic electrode provided on a back surface of the single crystal silicon substrate, and applying the voltage between the transparent electrode and the ohmic electrode to make the porous silicon layer a light emitting layer or a light receiving layer. In the element manufacturing method, when exposing a part of the surface of the single crystal silicon substrate and anodizing it in an aqueous hydrofluoric acid solution, the exposed single crystal silicon substrate surface is anodized while applying ultrasonic vibration. A step of forming the porous silicon layer to be a light emitting layer or a light receiving layer, a step of forming a transparent electrode connected to the surface of the porous silicon layer, Characterized by comprising a step of forming the ohmic electrode on the back surface of the crystalline silicon substrate.

  According to the method for manufacturing a porous silicon optical device of the present invention, by applying ultrasonic vibration to the silicon substrate in the anodizing process, the variation in the microcrystalline particle size of the porous silicon is reduced, and the silicon light It is possible to narrow the band of the light emission efficiency and light emission wavelength of the element.

It is explanatory drawing of the anodic oxidation method of this invention. It is a figure explaining the photo-luminescence spectrum of the porous silicon optical element formed by this invention. It is a figure explaining the ultrasonic oscillation output dependence of the photoluminescence intensity | strength of the porous silicon optical element formed by this invention. It is a figure explaining the ultrasonic oscillation frequency dependence of the photoluminescence intensity | strength of the porous silicon optical element formed by this invention. It is a figure which shows the manufacturing method of the porous silicon optical element of this invention. It is a figure explaining a general porous silicon optical element. It is a figure explaining the conventional anodic oxidation method.

  The method for producing a porous silicon optical device of the present invention is to form uniform micropores by performing anodization while applying ultrasonic vibration, and as a result, porous silicon having a small variation in silicon crystallite grain size. A major feature is the formation of a layer. Examples of the present invention will be described in detail below.

  Hereinafter, the manufacturing method of the porous silicon optical device of the present invention will be described. First, a p-type single crystal silicon substrate 101 having a plane orientation (100) and a specific resistance of 2 to 4 Ωcm is prepared. Next, an ohmic electrode 104 made of aluminum is formed on the back surface of the single crystal silicon substrate 101 by vacuum deposition or the like. The ohmic electrode 104 forms a porous silicon optical element by applying a voltage to a transparent electrode, which will be described later, and is connected to the anode of the power source when anodizing is performed to constitute one electrode To do. Then, the hydrofluoric acid resin 13 is covered so that a part of the surface of the single crystal silicon substrate 101 is exposed so as to open a region where the porous silicon layer is to be formed.

  On the other hand, 50 wt% hydrofluoric acid and ethyl alcohol are mixed at a mixing ratio of 1: 1 to prepare a hydrofluoric acid aqueous solution 15 for anodic oxidation.

  The anode of the constant current source 16 is connected to the ohmic electrode 104, and the cathode is connected to the platinum negative electrode 17 serving as a counter electrode. In addition, a voltmeter 18 and an ammeter 19 are connected to monitor various conditions of anodization. In the present invention, the hydrogen fluoride acid resistant container 15 is immersed in the pure water 12 in which the ultrasonic generator 11 is arranged so that ultrasonic waves can be applied when anodizing. .

Thereafter, anodization is performed while applying ultrasonic waves. As an example, while applying ultrasonic vibration with an oscillation frequency of 45 kHz and an oscillation output of 100 W from the ultrasonic generator 11, a constant current with a current density of 50 mA / cm ² is supplied from the constant current source 16, and anodized for 120 seconds to be porous. A quality silicon layer 102 is formed.

  In the anodic oxidation method, as in the conventional method, by supplying holes from the single crystal silicon substrate 101, the elution reaction of silicon proceeds locally and autonomously only at the tips of the micropores. The micropores preferentially advance in the direction opposite to the electric field applied between the single crystal silicon substrate 101 serving as the anode and the platinum negative electrode 17 serving as the cathode.

  Here, in the present invention, by performing anodic oxidation while applying ultrasonic vibration, the anode and the cathode vibrate regularly, and accordingly, the application direction of the electric field also vibrates. As a result, the advancing direction of the elution reaction, that is, the formation direction of the micropores is regularly changed, so that porous silicon with little particle size variation can be formed. Specifically, the porous silicon layer 102 in which silicon microcrystals having a particle size of several nm are regularly deposited can be formed.

  Next, a method for forming a porous silicon optical element using the polycrystalline silicon layer 12 formed by the above method will be described.

  First, the porous silicon layer 102 is formed on the surface of the single crystal silicon substrate 101 by the above-described method, and the hydrofluoric acid resistant resin 13 is removed (FIG. 2a).

  An insulating film 105 such as a silicon oxide film or a silicon nitride film is deposited on the entire surface of the single crystal silicon substrate 101 to a thickness of about 3000 nm using a sputtering apparatus for insulation from the transparent electrode 103 (FIG. 2b).

  The insulating film 105 is etched by a normal photolithography method using buffered hydrofluoric acid or a dry etching process to expose the surface of the previously formed porous silicon layer 102 (FIG. 2c).

  A transparent electrode 103 that transmits light emitted from the porous silicon layer 102, such as ITO (indium, tin oxide film), is deposited on the entire surface by a thickness of about 3000 nm, and patterned into a desired shape. A porous silicon optical device is completed (FIG. 2d).

  Next, the characteristics of the porous silicon optical element formed by the above method will be described. FIG. 3 shows a comparison between the photoluminescence spectrum of the silicon optical device of the present invention and the photoluminescence spectrum of a silicon optical device produced by a conventional anodic oxidation method. These photoluminescence spectra were measured at room temperature in the same measurement system using a He—Cd laser having the same intensity and wavelength of 325 nm as excitation light.

  As shown in FIG. 3, the photoluminescence emission was obtained at 680 nm in the silicon optical device of the present invention. Moreover, it was confirmed that the intensity was higher than that of the conventional example and the luminous efficiency was high. Furthermore, the spread of the photoluminescence spectrum compared with the half width is 168 nm in the present invention, whereas it is 200 nm in the conventional example, indicating that the photoluminescence spectrum of the present invention is narrower. Furthermore, as a result of observing the in-plane distribution of the surface of the silicon substrate of the photoluminescence spectrum, it was confirmed that the uniformity of the characteristics of the entire silicon substrate was good.

  FIG. 4 shows the ultrasonic oscillation output dependence of the photoluminescence intensity of the silicon optical device of the present invention. It can be confirmed that the emission intensity increases as the ultrasonic oscillation output increases. Note that when no ultrasonic vibration is applied, the light emission intensity is 0.2. Therefore, it can be seen that when the ultrasonic vibration is applied, the light emission intensity is higher than when the ultrasonic vibration is not applied. In addition, what is necessary is just to set optimal conditions for the ultrasonic oscillation output by other various conditions of anodization.

  FIG. 5 shows the ultrasonic oscillation frequency dependence of the photoluminescence intensity of the silicon optical device of the present invention. It can be confirmed that the emission intensity also depends on the ultrasonic oscillation frequency. The higher the ultrasonic oscillation frequency, the more uniform the crystal grain size of silicon microcrystals, and the grain size can be controlled on the order of several nm. Therefore, it is necessary to appropriately set the ultrasonic vibration oscillation output, the oscillation frequency, and the anodizing conditions so that the silicon crystallites have a desired grain size.

  As described above, it has been confirmed that the optical characteristics of the porous silicon optical element are improved by applying ultrasonic vibration when anodizing. Furthermore, according to the present invention, when a porous silicon layer is formed on a single crystal silicon substrate having a diameter of about 15 nm, it can be confirmed that there is little in-plane variation, and it is also confirmed that a porous silicon optical device can be formed with a high yield. It was.

11: Ultrasonic generator, 12: Pure water, 13: Hydrogen fluoride acid resistant resin, 14: Hydrofluoric acid aqueous solution, 15: Hydrogen fluoride acid resistant container, 16: Constant current power source, 17: Platinum negative electrode, 18: Voltmeter, 19: Ammeter, 101: Single crystal silicon substrate, 102: Porous silicon layer, 103: Transparent electrode, 104: Ohmic electrode, 105: Insulating film

Claims (1)

A single crystal silicon substrate; a porous silicon layer embedded on the surface of the single crystal silicon substrate; a transparent electrode provided to connect to the porous silicon layer; and a back surface of the single crystal silicon substrate. In the method of manufacturing a semiconductor optical device having an ohmic electrode, and applying a voltage between the transparent electrode and the ohmic electrode, the porous silicon layer is a light emitting layer or a light receiving layer.
When a part of the surface of the single crystal silicon substrate is exposed and anodized in an aqueous hydrofluoric acid solution, the exposed single crystal silicon substrate surface is anodized while applying ultrasonic vibration, and a light emitting layer or a light receiving layer is received. Forming the porous silicon layer to be a layer;
Forming a transparent electrode connected to the surface of the porous silicon layer;
Forming the ohmic electrode on the back surface of the single crystal silicon substrate.

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