KR20100009822A - The method to fabricate the porous silicon arrays having various fabrication conditions on a single substrate - Google Patents

Abstract

PURPOSE: A method for producing porous silicon array is provided to reduce material consumption and apply to a sensor and drug delivery system. CONSTITUTION: A method for producing porous silicon array comprising two or more components of same or different preparation condition comprises: a step of forming porous silicon layer through anodized oxidation; a step of removing porous silicon layer from a substrate through electrolytic polishing, NaOH solution etching or combination of electrolytic polishing and NaOH solution etching; and a step of obtaining porous silicon layer on recycled substrate again through anodized oxidation.

Description

The method to fabricate the porous silicon arrays having various fabrication conditions on a single substrate}

Porous silicon is fabricated by electrochemically anodizing a single crystal silicon substrate in HF solution. The fabricated porous silicon has a myriad of pores with nanometer size, and the thickness and density of the layer depend on the fabrication conditions such as current density flowed during anodization, HF solution concentration, anodic oxidation time, and type of single crystal silicon substrate. Depends on [1].

Porous silicon exhibits strong luminescence due to excitation light with energy of ultraviolet light [2]. This finding has led to active research for the development of silicon-based optoelectronic devices. In addition, since it has a very large specific surface area capable of reacting with the test substance, application researches on sensor materials [3] and drug carriers [4] for detecting gas and biomaterials are being conducted.

In order to perform these studies, the production of numerous porous silicon under different conditions is required, and each performance evaluation is required. However, since the porous silicon fabrication apparatus that has been used up to now structurally locks a single crystal silicon substrate in HF solution and anodizes it, there is a problem in that it is necessary to fabricate each on a different substrate when samples having various fabrication conditions are required. In order to solve this problem, it is necessary to invent a technique for constructing a porous silicon array having various fabrication conditions on a single silicon substrate. Applying this technique has many advantages such as securing structural simplicity, consistency of performance, mass production, and realization in practical device development.

Anodizing apparatuses conventionally used for fabricating porous silicon can be classified into three types in terms of method and structure.

First is the lateral anodization cell [1,5]. The device inserts a silicon substrate and a platinum electrode, a counter electrode, perpendicular to the surface of the HF solution, and then flows a current between them to produce a porous silicon layer through anodization. The device is relatively simple in structure and can naturally escape hydrogen bubbles from the anodic oxidation process to form a homogeneous porous silicon layer.

Second is the single tank cell [1,6]. The device inserts a silicon substrate and a platinum wire in parallel to the water surface of the HF solution, and then flows a current between them to produce porous silicon. This device is most commonly used. Since the hydrogen bubbles generated during the anodic oxidation process are hidden by the platinum electrode and cannot escape naturally, a part of the porous silicon layer is not uniformly formed.

Third is the double tank cell [1,7]. The device is centered on a silicon substrate, and the front and back sides of the substrate are filled with HF solution, and then a platinum electrode is installed therein. Therefore, like the two anodic oxidation devices described above, the front side of the substrate is not contacted by HF solution and the back side is contacted by HF solution. Therefore, the homogeneity of the porous silicon layer is very high. However, there is a drawback that is technically very difficult to manufacture the device.

The common feature of the anodic oxidation apparatus is that the silicon substrate is anodized after being submerged in HF solution. Therefore, in order to make porous silicon having different manufacturing conditions, each has to be manufactured on different substrates. Therefore, fabrication of porous silicon arrays with various fabrication conditions on a single substrate is not possible.

In order to solve this problem, the present invention uses a process for preparing porous silicon while inserting or removing a silicon substrate in a vertical direction with respect to the water surface of the HF solution, and using a substrate recycling technology based on electropolishing and NaOH solution etching. By removing the porous silicon layer, a porous silicon array with various fabrication conditions is fabricated on a single substrate.

The core of substrate recycling technology is electropolishing [8] and NaOH solution etching [9]. When the current density is flowed in HF solution to a very large value, the porous silicon layer is not formed and the silicon substrate is polished. This is called electropolishing, and it is possible to remove the already formed porous silicon layer from the substrate. In NaOH solution etching, when a porous silicon layer is placed in a NaOH solution, the layer is corroded and dissolved. This technique has been used to measure the porosity of the porous silicon layer.

In the conventional method of fabricating porous silicon, since both the silicon substrate and the platinum electrode are put into an HF solution and then anodized by passing a current, it has to be manufactured on different substrates in order to produce samples having various manufacturing conditions. In order to solve this problem, the present invention forms a porous silicon layer by placing or removing a silicon substrate and a platinum electrode in the vertical direction of the HF solution, and use a substrate recycling technique based on electropolishing and NaOH solution etching on a single substrate. A method of making an array of porous silicon with different fabrication conditions was devised.

In order to fabricate a porous silicon array having various manufacturing conditions on a single substrate, an apparatus as shown in FIG. 1 is required. 1 inserts a silicon substrate 12 and a platinum wire 15 in the HF solution 16 in a vertical direction through a stepping motor 18 connected to a controller 19, and the electrode on the back of the silicon substrate 12 ( 14) and the platinum wire 15 is connected to the power supply 20 to flow an electric current to anodize. At this time, the HF solution 16 is contained in the container 17 made of Teflon, and the silicon substrate is surrounded by the Teflon tape 13 to exclude the anodic oxidation except for the portion where the porous silicon 11 is formed by anodization. .

Therefore, when the silicon substrate 12 is placed in the HF solution 16 at a specific concentration and then a specific anodic oxidation current density is flowed through the power supply 20 for a certain time, the porous silicon layers having the same fabrication conditions are one-dimensionally. Arranged to form an array. However, since the array is made under the same fabrication conditions, it is necessary to apply the substrate recycling technology in the present invention to make an array composed of porous silicon having various fabrication conditions.

Figure 2 shows a process of making a porous silicon array having a variety of manufacturing conditions on a single substrate by applying a substrate recycling technology. FIG. 2 (a) shows an array of three elements 111 of the same porous silicon layer made under certain fabrication conditions after all silicon substrate 12 has been placed in HF solution 16. The fabricated array drives the stepping motor 18 to remove only the first element from the HF solution 16, and then the porous silicon layer is removed from the substrate through electropolishing, which flows a very high current density to the second and third elements. Isolate. In this process, however, part of the porous silicon layer remains without being completely separated from the substrate. Therefore, following the electropolishing process, the silicon substrate is removed from the HF solution, and the second and third array elements are inserted into the NaOH solution except the first element. Through this process, the porous silicon layer can be completely removed from the silicon substrate, and the first porous silicon element 111 and the recyclable substrate surface 21 are left on the silicon substrate as shown in FIG.

FIG. 2 (c) shows that the array element 222 having different fabrication conditions from the first array element 111 is manufactured after only the recycled substrate surface 21 is placed in the HF solution. 2 (d) shows a process of removing the third element except the first element 111 and the second element 222 through electropolishing and NaOH solution etching.

Finally, FIG. 2 (e) shows an element 333 having fabrication conditions different from those of the first element 111 and the second element 222 after only the recycled substrate surface 21 in FIG. ).

Through this series of processes, it is possible to realize the fabrication of porous silicon arrays having various fabrication conditions on a single substrate to be pursued in the present invention.

According to the present invention, porous silicon arrays having various fabrication conditions are implemented on a single substrate, and thus, various types of drugs are filled into a porous array of porous silicon nanostructures having different sizes. It can be actively used for research on drug carriers that can be injected into the human body or through the skin. In addition, it is possible to simplify circuits and structures in terms of device manufacturing, such as practical porous silicon LED (Light Emitting Diode), and to expect operation stability compared to using different substrates. It can also be used to develop thin-film display devices using cold electrons [10] emission characteristics of porous silicon. In addition, further research on this technology can be expected to develop porous silicon ultra-fine array technology.

3 is a scanning electron microscope (JEOL, JSM-6335F) image of the cross-section of each element and the shape of the porous silicon array consisting of the elements having five different fabrication conditions using the substrate recycling process of FIG. It is shown. The fabrication conditions of the elements constituting the array are shown in Table 1, and the concentration of HF solution was 10%. The resistivity of the silicon substrate used was 0.06 to 0.12 Ω · cm and was a p-type (100) single crystal substrate. The size of each element constituting the array was 1 cm x 1 cm. For the electropolishing required for the substrate recycling process, a current density of 100 mA / cm ² was flowed for 10 s and etched using 1 M NaOH solution.

The first element of the array (A in Table 1) produced a monolayer by flowing a constant current density of 10 mA / cm ² for 200 s during anodization. The second element (B in Table 1) then flows a current density of 10 mA / cm ² for 200 s, followed by 4 cycles of 50 mA / cm ² and 10 mA / cm ² for 3 s and 90 s, respectively. Flowing through to produce a multilayer structure having a total of nine layers. It is well known that the multilayer structure of porous silicon can be produced by periodically flowing a current density having different values [11]. The third component (C in Table 1) gave four cycles of current densities of 10 mA / cm ² and 50 mA / cm ² for 90 s and 3 s respectively, and the fourth component (D in Table 1) It was manufactured to have a symmetrical structure with each other through anodization conditions in the reverse order to the elements (B of Table 1). Finally, the fifth element (E in Table 1) combined the fabrication conditions of the third and second elements to produce a multilayer structure with a total of 17 layers.

As shown in FIG. 3, it can be seen that an array of five porous silicon elements having different fabrication conditions is made on a single substrate. At this time, the electron microscope image of FIG. 3 was aligned based on the top of the porous silicon layer for comparison, and all were observed at a magnification of 15,000 times. As shown in FIG. 1, the first element A has a single layer, the second element B and the fourth element D have a symmetrical structure, and the third element C has a multilayer structure. . In addition, the fifth element (E), as expected, it can be seen that the third and second elements are made by combining sequentially.

As described above, the porous silicon array composed of elements having different fabrication conditions on a single substrate is impossible by the conventional fabrication technology, but it is clearly understood that the porous silicon array can be fabricated through the substrate recycling process as shown in FIG. Can be.

Element Anodic oxidation current density (mA / cm ² ) Anodization time (s) Periodic repeat count Number of floors (A) 10 200 One One (B) 10 200 One One 50 10 3 90 4 8 (C) 10 50 90 3 4 8 (D) 10 50 90 3 4 8 10 200 One One (E) 10 50 90 3 4 8 10 200 One One 50 10 3 90 4 8

* references *

[1] Leigh Canham, Properties of porous silicon , (INSPEC, 1997).

[2] LT Canham, Appl. Phys. Lett. 57 , 1046 (1990).

[3] M .S. Salem, M. J. Sailor, K. Fukami, T. Sakka, YH Ogata, J. Appl. Phys. 103 , 083516 (2008).

[4] Sharon Kingman, Drug Discovery Today. 6 , 1186, (2001).

[5] SN Sharma, Ratnabali, Ratnabali Banerjee, Debabrata Das, S. Chattopadhyay, AK Barua, Applied Surface Science. 182 , 333 (2001).

[6] Finny P. Mathew, Evangelyn C. Alocilja, Biosensors and Bioelectronics, 20 , 1656 (2005).

[7] A. Ould-Abbas, M. Bouchaour, N.-E. Chabane-Sari, S. Berger, A. Kaminski, A. Fave, J. Therm. Anal. Cal. 76 , 685 (2004).

[8] Markus Rauscher, Herbert Spohn, Phys. Rev. E. 64 , 031604 (2001).

[9] B. Coasne, A. Grosman, C. Ortega, M. Simon, Phys. Rev. Lett. 88 , 256 102 (2002).

[10] Y. Nakajima, A. Kojima, N. Koshida, Appl. Phys. Lett. 81 , 2472 (2002).

[11] G. Vincent, Appl. Phys. Lett. 64 , 2367 (1994).

1 is a cross-sectional view of the anodizing device for realizing the present invention

2 is a schematic diagram of a fabrication process of a porous silicon array using a substrate recycling technique

3 is an embodiment of a porous silicon array manufactured according to the specific contents for the practice of the invention

Explanation of symbols on the main parts of the drawings

11: porous silicon

12: single crystal silicon substrate

13: teflon tape

14: electrode

15: platinum electrode

16: HF solution

17: Teflon container

18: stepping motor

19: controller

20: power supply

21: Recycled substrate side

Claims (4)

In the process of fabricating porous silicon, a single silicon substrate is stepped in or out in the vertical direction of the HF solution to form a porous silicon layer through anodization, and electrolytic polishing or NaOH solution etching, or electropolishing and NaOH solution etching are combined. Method for fabricating a porous silicon array consisting of two or more elements with the same or different fabrication conditions on a single substrate, characterized by the use of substrate-based substrate recycling technology The method of claim 1, wherein the porous silicon layer is removed from the substrate by electrolytic polishing or NaOH solution etching, or a combination of electropolishing and NaOH solution etching, and the porous silicon layer is again fabricated through anodization on the recycled substrate. Substrate Recycling Method The porous silicon array of claim 1, wherein two or more array elements having the same or different fabrication conditions are formed on a single substrate. The method of claim 1, wherein the porous silicon layer is manufactured through anodization while inserting or removing the silicon substrate in a vertical direction based on the water surface of the HF solution.

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