JPH05234983A - Manufacture of porous silicon - Google Patents

Abstract

PURPOSE:To provide a method for manufacturing a porous silicon which can form a microcoregion on a silicon substrate for marking it porous under high controllability. CONSTITUTION:Fine pores are formed in a desired microregion by moving an anode of a silicon substrate 3 made of crystalline silicon and a cathode of a platinum probe 2 of a conductive probe having a radius of curvature of its end of 0.1mum or less close to a surface of the silicon and electrolytically decomposing it in solution containing 5-48wt.% of hydrofluoric acid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing porous silicon, and more particularly to a method for producing a microscopic region on a silicon substrate with good controllability.

[0002]

2. Description of the Related Art Porous silicon exhibits photoluminescence or electroluminescence in a visible light region, which is impossible with single crystal silicon, and is therefore attracting attention as a light emitting element or an optical IC element. Conventionally, this porous silicon has been produced by electrolyzing in a hydrofluoric acid using a single crystal silicon substrate as an anode to form innumerable micropores having a size of about several to several tens nm. (Applied Physics, Vol. 57, No. 11, pp. 1710-1720, 1988) In addition, by coating a non-porous area with an acid-resistant wax or a silicon nitride thin film, a specific area within the surface of a silicon substrate can be obtained. Is being made porous.

[0003]

When a place to be made porous on the surface of a silicon substrate is specified by coating a place which is not made to be porous with an acid-resistant wax or the like, the position is accurately defined. It is difficult to limit the area. Further, after the silicon nitride thin film is formed on the silicon substrate, the silicon nitride thin film is processed by a photolithography process and used as an etching resist, whereby porous silicon is formed at a specific place on the silicon substrate on which an IC or the like is formed. However, there are issues such as the process becoming complicated.

Further, the conventional manufacturing method has a problem that it is difficult to control the characteristics of the porous silicon because the shape and number of the micropores cannot be controlled with high precision.

An object of the present invention is to provide a method for producing porous silicon having fine pores with excellent controllability.

[0006]

[Means for Solving the Problems] By using crystalline silicon as an anode and a conductive probe having a sharp tip as a cathode to approach the silicon surface, and electrolyzing in a solution containing hydrofluoric acid, A fine hole is formed in a desired fine area. Alternatively, crystalline silicon is used as an anode, and a conductive probe with a sharp tip is used as a cathode, and a voltage is applied while maintaining the distance between the silicon surface and the probe at about 1 nm in a solution containing hydrofluoric acid. Then, the electrolysis is started by the tunnel current.

[0007]

In the above manufacturing method, since the tip of the probe that serves as the cathode is sharp and the distance between the cathode and the silicon substrate surface is small, it is possible to concentrate the electric field only on a minute area of the silicon substrate surface. Only a minute area can be made porous without an etching resist. When the cathode-silicon substrate surface distance is set to about 1 nm and a voltage of several V or less is applied to generate a tunnel current, the magnitude of the tunnel current largely depends on the cathode-silicon substrate surface distance. It is possible to concentrate the current only in the extremely small area, and it is possible to make only the extremely small area porous.

[0008]

EXAMPLE 1 FIG. 1 shows an apparatus for producing porous silicon used in this example. At the center of the Teflon container 1, a platinum probe 2 serving as a cathode and a P-type silicon substrate 3 serving as an anode were arranged in a state of being electrically connected via a DC constant current power source 4 and an ammeter 5. 4 as electrolyte 6
A 1: 1 solution of 5% hydrofluoric acid and ethyl alcohol was used. The platinum probe 2 attached to the mechanical position adjusting device 12 is processed by electrolytic polishing so that the radius of curvature of the tip becomes 100 nm or less, and the side surface is covered with the acid-resistant insulating resin 6 as shown in FIG. .. The tip of the platinum probe 2 and Si
The distance from the substrate 3 was adjusted to 10 μm using the mechanical position adjusting device 12 while observing the microscope. In this state, a platinum constant current source 4 is used as a cathode and a DC constant current power source 4 is used to apply a current of 0.2 μA for 5 minutes to obtain a diameter of approximately
It was possible to form porous silicon having a thickness of 40 μm in a region of 0 μm.

When using an N type silicon substrate, 5
It was possible to make it porous by applying a current while irradiating the light of a tungsten lamp of 00 W from a distance of about 15 cm. Platinum was used as the cathode, but TiC, Si
Any material that was not attacked by hydrofluoric acid, such as C or semiconductor diamond, could be used. Although a 1: 1 solution of 45% hydrofluoric acid and ethyl alcohol was used as the electrolytic solution, porous silicon could be produced with good reproducibility if the hydrogen fluoride concentration was 5% or more. If it is 5% or less, it takes a long time to prepare, and there is a problem that the boundary between the porous region and the non-porous region is not clear. It is desirable that the radius of curvature of the tip of the probe is smaller than the distance between the probe and the silicon surface, and if it is larger than the distance between the probe and the silicon surface, the controllability of the region to be porous becomes poor. When the distance between the tip of the probe 2 and the Si substrate 3 is larger than 100 μm, there is a problem that the boundary between the porous region and the non-porous region is not clear.

(Embodiment 2) FIG. 3 shows an apparatus for producing porous silicon used in this embodiment. At the center of the Teflon container 1, a platinum probe 2 serving as a cathode and a P-type silicon substrate 3 serving as an anode were arranged in a state of being electrically connected via a DC power supply 7 and an ammeter 8. The platinum probe 2 was processed by electrolytic polishing so that the radius of curvature of the tip was 50 nm or less, and the side surface was covered with the acid-resistant insulating resin 6 as shown in FIG. The output signal from the ammeter 8 is transmitted to the three-dimensional fine movement device 9 through the feedback control circuit 10, and the distance between the platinum probe 2 and the silicon substrate 3 can be controlled so that the current becomes constant. The three-dimensional fine movement device 9 is a combination of piezoelectric bodies in three orthogonal directions, and by using this, the platinum probe 2 can be moved to an arbitrary position on the surface of the silicon substrate according to an instruction from the computer 11. As the electrolytic solution 6, a 1: 1 solution of 20% hydrofluoric acid and ethyl alcohol was used.

The method for producing porous silicon using this apparatus will be described below. First, the position of the probe 2 was adjusted using the mechanical position adjusting device 12 while observing the microscope so that the distance between the tip of the platinum probe 2 and the Si substrate 3 was about 10 μm. A DC power supply 7 applied a voltage of 1 V so that the platinum probe 2 became the cathode and the silicon substrate 3 became the anode. The current value at this time was about 50 pA. The probe 2 was gradually made to approach the silicon substrate 3 while monitoring the current value using the three-dimensional fine movement device 9 and the mechanical position adjusting device 12, and the approach was stopped when the current value became 1 nA. At this time, the current rapidly increases exponentially as the distance decreases, so most of the current is a tunnel current, and it is considered that the distance between the probe 2 and the silicon substrate 3 is about 1 nm.
By fixing the probe 2 in this state and holding the voltage for 5 minutes, a region having a diameter of 50 nm and a depth of 5 μm could be made porous just below the probe 2.

When performing electrolysis using a tunnel current, the radius of curvature of the tip of the probe is preferably 0.1 μm or less, and when it is larger, the tunnel current becomes unstable or the porous region becomes large. In some cases, it was not possible to produce porous silicon with good controllability. Moreover, after the probe 2 is separated from the silicon substrate 3 by using the three-dimensional fine movement device 9, the probe 2 is moved to another place and the same operation is repeated to form porous silicon at an arbitrary place in the surface of the silicon substrate. I was able to do it. Further, after the distance between the probe 2 and the silicon substrate 3 is approached to about 1 nm, electrolysis is performed while moving the probe 2 in the in-plane direction of the substrate to form a porous silicon pattern on the silicon substrate 3. I was able to create it.

[0013]

According to the present invention, any place on a silicon substrate can be made porous into any shape without forming an etching resist pattern on the silicon substrate by a photolithography process or the like. It becomes possible to easily manufacture a device in which an IC formed on a silicon substrate and porous silicon are combined.

Further, it is possible to form porous silicon with extremely good controllability in an extremely small area which could not be formed by the conventional manufacturing method, and to control the optical and electrical characteristics of the porous silicon with high precision. it can.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an electrolyzer used in a porous silicon manufacturing process in an example of the present invention.

FIG. 2 is a cross-sectional view showing a platinum probe used in a manufacturing process of porous silicon according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view showing an electrolyzer used in a porous silicon manufacturing process in another example of the present invention.

[Explanation of symbols]

 1 Teflon container 2 Platinum probe 3 Silicon substrate 4, 7 DC power supply 5, 8 Ammeter 6 Insulating resin 9 Three-dimensional fine movement device 10 Feedback control circuit 11 Computer 12 Mechanical position adjustment device

Claims (8)

[Claims] 1. A method of using a crystalline silicon as an anode and a conductive probe having a sharp tip as a cathode to approach the surface of the silicon and electrolyzing in a solution containing hydrofluoric acid to obtain desired fine particles. A method for producing porous silicon, which comprises forming pores in a region. 2. The distance between the conductive probe and the silicon surface is 10
The method for producing porous silicon according to claim 1, wherein the thickness is 0 μm or less. 3. The method for producing porous silicon according to claim 1, wherein the radius of curvature of the tip of the conductive probe is smaller than the distance between the conductive probe and the silicon surface. 4. A state in which crystalline silicon is used as an anode, a conductive probe having a sharp tip is used as a cathode, and the distance between the silicon surface and the probe is kept at about 1 nm in a solution containing hydrofluoric acid. A method for producing porous silicon, characterized in that a voltage is applied at a temperature to start electrolysis by a tunnel current. 5. The method for producing porous silicon according to claim 4, wherein the radius of curvature of the tip of the conductive probe is 0.1 μm or less. 6. The method for producing porous silicon according to claim 1, wherein a side surface of the conductive probe is covered with an insulating material. 7. The method for producing porous silicon according to claim 1, wherein the surface of the silicon is electrolyzed by irradiating the surface of the silicon with visible light or ultraviolet light. 8. The method for producing porous silicon according to claim 1, wherein the conductive probe is made of a metal containing platinum as a main component.