JP3132120B2 - Porous silicon and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

This invention relates to porous silicon.
In particular, the present invention relates to a manufacturing method capable of making a minute region on a silicon substrate porous with good controllability.

[0002]

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

[0003]

When the place to be made porous is coated with an acid-resistant wax or the like to specify the place to be made porous in the silicon substrate surface, the position is specified with high precision. Or it is difficult to limit the area. In addition, after a silicon nitride thin film is formed on a silicon substrate, the silicon nitride thin film is processed by a photolithography process and used as an etching resist, thereby forming porous silicon at a specific location on the silicon substrate on which an IC or the like is formed. However, there are problems such as complicated processes.

Further, in the conventional manufacturing method, since the shape and number of the fine holes cannot be controlled with high precision, there is a problem that it is difficult to control the characteristics of the porous silicon.

[0005] An object of the present invention is to provide porous silicon in which fine pores having excellent controllability are formed.

[0006]

Means for Solving the Problems A crystalline silicon is used as an anode, and a sharply pointed conductive probe is used as a cathode to approach the silicon surface and is electrolyzed in a solution containing hydrofluoric acid. A fine hole is formed in a desired minute area. Alternatively, 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, using crystalline silicon as the anode and a sharply pointed conductive probe as the cathode. Then, electrolysis is started by the tunnel current.

[0007]

In the above manufacturing method, since the tip of the probe serving 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 in a minute area on the silicon substrate surface. Only a minute region can be made porous without using an etching resist. When the distance between the cathode and the silicon substrate surface is about 1 nm and a voltage of several volts or less is applied to generate a tunnel current, the magnitude of the tunnel current greatly depends on the distance between the cathode and the silicon substrate surface. 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]

(Embodiment 1) FIG. 1 shows an apparatus for producing porous silicon used in this embodiment. A platinum probe 2 serving as a cathode and a P-type silicon substrate 3 serving as an anode were arranged in the center of the Teflon container 1 while being electrically connected via a DC constant current power supply 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 tip radius of curvature becomes 100 nm or less, and the side surface is coated with the acid-resistant insulating resin 6 as shown in FIG. . The tip of platinum probe 2 and Si
The distance from the substrate 3 was adjusted using the mechanical position adjustment device 12 while viewing the microscope so that the distance was 10 μm. In this state, a current of 0.2 μA is passed for 5 minutes by the DC constant current power supply 4 using the platinum probe 2 as a cathode, and the diameter is about 2 μm.
Porous silicon having a thickness of 40 μm could be formed in a region of 0 μm.

When an N type silicon substrate is used, 5
By applying a current while irradiating the light of a tungsten lamp of 00 W from a distance of about 15 cm, it was possible to make the film porous. Although platinum was used as the cathode, TiC, Si
Any material that was not affected by hydrofluoric acid, such as C and semiconductor diamond, could be used. Although a 1: 1 solution of 45% hydrofluoric acid and ethyl alcohol was used as the electrolyte, porous silicon could be produced with good reproducibility if the hydrogen fluoride concentration was 5% or more. If it is less than 5%, 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 be smaller than the distance between the probe and the silicon surface. If the radius of curvature 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. A platinum probe 2 serving as a cathode and a P-type silicon substrate 3 serving as an anode were arranged at the center of the Teflon container 1 in a state where they were electrically connected via a DC power supply 7 and an ammeter 8. The platinum probe 2 was processed by electrolytic polishing so that the tip radius of curvature became 50 nm or less, and the side surface was covered with an 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 a piezoelectric body in three orthogonal directions. Using this, the platinum probe 2 can be moved to an arbitrary position on the surface of the silicon substrate by an instruction from the computer 11. As the electrolytic solution 6, a 1: 1 solution of 20% hydrofluoric acid and ethyl alcohol was used.

Hereinafter, a method for producing porous silicon using this apparatus will be described. First, the position of the probe 2 was adjusted using the mechanical position adjuster 12 while looking at the microscope so that the distance between the tip of the platinum probe 2 and the Si substrate 3 was about 10 μm. A voltage of 1 V was applied by a DC power supply 7 so that the platinum probe 2 became a cathode and the silicon substrate 3 became an anode. The current value at this time was about 50 pA. Using the three-dimensional fine movement device 9 and the mechanical position adjustment device 12, the probe 2 was gradually approached to the silicon substrate 3 while monitoring the current value, and the approach was stopped when the current value reached 1 nA. At this time, since the current decreases exponentially as the distance decreases, most of the current is a tunnel current, and the distance between the probe 2 and the silicon substrate 3 is considered to be about 1 nm.
In this state, the probe 2 was fixed and the voltage was maintained for 5 minutes, whereby a region having a diameter of 50 nm and a depth of 5 μm could be made porous immediately below the probe 2.

When the electrolysis is carried out by using a tunnel current, the radius of curvature of the tip of the probe is desirably 0.1 μm or less, and when it is larger, the tunnel current becomes unstable or the porous region becomes large. In some cases, porous silicon could not be produced with good controllability. Further, after the probe 2 is separated from the silicon substrate 3 by using the three-dimensional fine movement device 9, it is moved to another place and the same operation is repeated to form porous silicon at an arbitrary place in the silicon substrate surface. I was able to. 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 probe, thereby forming a pattern of porous silicon on the silicon substrate 3. Could be created.

[0013]

According to the present invention, an arbitrary location on a silicon substrate can be made porous in an arbitrary shape without forming an etching resist pattern on the silicon substrate by a photolithography process or the like. It is possible to easily manufacture a device or the like in which an IC formed on a silicon substrate is bonded to porous silicon.

In addition, porous silicon can be produced with good controllability in an extremely small area which cannot be produced by the conventional production method, and the optical and electrical characteristics of the porous silicon can be controlled with high precision. it can.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an electrolyzer used in a process for producing porous silicon according to one embodiment of the present invention.

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

FIG. 3 is a cross-sectional view showing an electrolyzer used in a process for producing porous silicon according to another embodiment of the present invention.

[Explanation of symbols]

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

Continuation of the front page (56) References JP-A-63-310122 (JP, A) JP-A-2-213500 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21 / 3063 C25F 3 / 12,3 / 30

Claims (7)

(57) [Claims] 1. A crystalline silicon as an anode, on the silicon surface a conductive probe tip sharply pointed as a cathode, the
A method for producing porous silicon, wherein pores are formed in a desired minute region by bringing the electrodes close to each other so as to have a distance of 100 μm or less and performing electrolysis in a solution containing hydrofluoric acid. 2. 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. 3. A state in which the distance between the silicon surface and the probe is maintained at about 1 nm in a solution containing hydrofluoric acid using crystalline silicon as an anode and a sharply pointed conductive probe as a cathode. A method for producing porous silicon, characterized in that a voltage is applied in (1) and electrolysis is started by a tunnel current. 4. The method for producing porous silicon according to claim 3 , wherein the radius of curvature of the tip of the conductive probe is 0.1 μm or less. 5. The process for producing a porous silicon according to claim 1 or 3 sides of the conductive probe is characterized in that it is coated with an insulating material. 6. The electrolysis while irradiating visible or ultraviolet light to the silicon surface.
4. The method for producing porous silicon according to item 3 . 7. A method for producing a porous silicon according to claim 1 or 3 conductive probe is characterized in that it consists of metal mainly composed of platinum.