CN202543375U - Photo-assisted porous silicon electrochemical etching tank - Google Patents

Abstract

The utility model provides a light-assisted porous silicon electrochemical corrosion tank, comprising: a tank body; a fixing frame located in the tank body for fixing silicon chips to be etched; an electrode located in the tank body, and the electrodes include a cathode electrode and an anode electrode, the cathode electrode and the anode electrode are respectively located on both sides of the fixing frame; and an optical auxiliary structure located in the tank, the optical auxiliary structure is located between the fixing frame and the cathode electrode, To provide light to the silicon wafer to be etched, the light source of the light auxiliary structure is sealed in transparent polycarbonate PC plastic, and has a grid structure to facilitate the flow of etching liquid. When carrying out the double-slot electrochemical etching process, through the photo-assisted structure located in the tank and between the cathode electrode and a silicon wafer to be etched, the silicon wafer to be etched is irradiated at close range and directly, so that the silicon wafer to be etched is effectively etched. A certain concentration of holes is formed in the sheet, thereby ensuring the quality and efficiency of the double-slot electrochemical corrosion process.

Description

Photo-assisted Porous Silicon Electrochemical Etching Cell

technical field

The utility model relates to the technical field of microelectronic mechanical equipment, in particular to a light-assisted porous silicon electrochemical corrosion tank.

Background technique

With the continuous development of micro-electro-mechanical systems (MEMS), porous silicon materials show a very broad application prospect in MEMS because of their good mechanical and thermal properties. First of all, the film layer based on porous silicon material can be prepared very thick, which can replace SiO2 and other materials in MEMS as a sacrificial layer, so that the microstructure can be quickly released without double-sided lithography when the microstructure is processed by bulk micromachining technology, and at the same time The problem that the distance between the structural layer and the substrate is too small can be well solved in the surface micromechanical technology; secondly, because porous silicon has a thermal conductivity far lower than that of the silicon matrix (can be as low as 1W/mK), it can be used in microthermal The use of porous silicon as the thermal insulation layer in the sensitive sensing system can obtain rapid temperature change response and low heat loss, and at the same time avoid the problem of easy adhesion due to the small thickness of the sacrificial layer used in the traditional micro-thermal sensing system. Disadvantages, greatly improving the stability and reliability of the system; third, using the characteristics of positional migration of silicon atoms under the high-temperature process conditions of porous silicon, the pressure chamber of a novel MEMS pressure sensor can be made; fourth, porous silicon technology and standards IC silicon technology compatible. It is precisely because of the above-mentioned structural characteristics and various special properties, coupled with its technical advantages, that porous silicon and its technology have been widely valued and studied.

At present, the most widely used electrochemical etching process for the preparation of porous silicon is mainly divided into single-slot and double-slot electrochemical etching processes. Among them, the single-slot electrochemical etching process is mainly applied to the metal layer on the back of the silicon wafer to be etched, using the metal on the back of the silicon wafer to be etched as the electrode anode, and electrochemically etching the front side of the silicon wafer to be etched. The double-slot electrochemical etching process is used for the etching of porous silicon without a metal layer on the back of the silicon wafer to be etched.

Please refer to FIG. 1 , which is a schematic structural diagram of an existing porous silicon electrochemical etching tank. As shown in Figure 1, the porous silicon electrochemical etching tank comprises: a tank body 104; a fixing frame positioned in the tank body 104, the fixing bracket includes a first fixing bracket 107 and a second fixing bracket positioned below the first fixing bracket Two fixing frame 106; The electrode that is positioned at described tank body 104, described electrode comprises cathode electrode 101 and anode electrode 102, and described cathode electrode 101 and anode electrode 102 are respectively positioned at described fixing frame both sides, and described cathode electrode 101 And the anode electrode 102 is made of metal platinum.

When using the porous silicon electrochemical etching tank to etch the silicon wafer to be etched to form porous silicon, inject the etching solution 105 into the corresponding tank body 104, place the silicon wafer 103 to be etched in the tank body 104, specifically, by The first fixing frame 107 and the second fixing frame 106 are fixed. At this time, the tank body 104 is divided into two "half tanks" by the silicon wafer 103 to be etched, which are respectively a guide groove 109 and an etching groove 108. The other parts are insulated from each other, and the two "half tanks" are double tanks in the double tank electrochemical corrosion process. After the voltage is applied to the electrodes, due to the effect of the electric field, the current flows from the guide groove 109 to the etching groove 108 through the silicon wafer 103 to be etched, and the holes in the silicon wafer 103 to be etched will flow to the silicon wafer 103 to be etched near the cathode electrode 101 On the other side, the silicon wafer 103 to be etched is electrochemically corroded; on the other side, there is no reaction, and finally porous silicon can be formed.

The principle of the double-slot electrochemical etching process is that the double-slot electrochemical etching porous silicon technology is to use the silicon wafer to be etched as an anode, and under the action of an external electric field, the current flows from the electrochemical guide slot to the silicon wafer to be etched. In the etching tank, the holes in the silicon wafer to be etched will flow to the surface of the silicon wafer to be etched near the cathode electrode, so that the silicon wafer to be etched on this surface is electrochemically corroded, and the silicon wafer to be etched as the anode and the silicon wafer in the etching solution Anions (OH- and F-) undergo an electrochemical reaction under the action of holes (positive charges) in the silicon wafer to be etched to form silicon dioxide, which is then reacted by the etching solution. When the reaction conditions are controlled, the When the reaction process reaches a non-equilibrium state, pores will be formed on the surface of the silicon wafer to be etched, and finally porous silicon will be formed.

However, there are several problems in realizing the double-slot electrochemical etching process by the porous silicon electrochemical etching tank:

First of all, the hole concentration in the silicon wafer to be etched is crucial to the rate of the double-slot electrochemical etching process. However, it is difficult to control the hole concentration in the silicon wafer to be etched in the existing process, resulting in double-slot electrochemical corrosion. The quality and efficiency of the process cannot be guaranteed;

Secondly, during the corrosion process, the electrodes made of metal platinum are easily corroded, resulting in heavy metal contamination on the silicon wafer to be etched, which is not conducive to compatibility with conventional integrated circuit semiconductor processes, and affects the silicon wafer after porous silicon corrosion. Subsequent processing on a semiconductor production line.

Utility model content

The purpose of the utility model is to provide a light-assisted porous silicon electrochemical etching tank to solve the problem that the hole concentration in the silicon wafer to be etched is difficult to control in the prior art double-tank electrochemical etching process, thus causing double-tank electrochemical corrosion. The quality and efficiency of the corrosion process cannot be guaranteed.

In order to solve the above technical problems, the utility model provides a light-assisted porous silicon electrochemical etching tank, comprising:

Tank body;

A fixture for fixing silicon wafers to be etched located in the tank;

An electrode located in the tank body, the electrode includes a cathode electrode and an anode electrode, and the cathode electrode and the anode electrode are respectively located on both sides of the fixing frame;

It also includes: a light auxiliary structure located in the tank, the light auxiliary structure is located between the fixing frame and the cathode electrode, and is used to provide light to the silicon wafer to be etched.

Optionally, in the photo-assisted porous silicon electrochemical corrosion cell, the electrodes are graphite electrodes.

Optionally, in the light-assisted electrochemical etching cell for porous silicon, the silicon wafer to be etched is fixed on the fixed frame, and the etching solution does not leak from the front and back sides of the silicon wafer to be etched.

Optionally, in the light-assisted electrochemical etching cell of porous silicon, the silicon wafer to be etched separates the cell body into a guiding groove and an etching groove.

Optionally, in the light-assisted porous silicon electrochemical corrosion cell, the light-assisted structure includes: a light source and transparent polycarbonate PC plastic, and the light source is sealed in the transparent polycarbonate PC plastic.

Optionally, in the light-assisted electrochemical etching cell for porous silicon, the transparent polycarbonate PC plastic has a grid structure, so that the corrosion solution flows from one side of the transparent polycarbonate PC plastic to the other side.

Optionally, in the light-assisted electrochemical etching cell of porous silicon, the transparent polycarbonate PC plastic is a cell grid structure composed of a plurality of concentric rings.

Optionally, in the light-assisted porous silicon electrochemical corrosion cell, the transparent polycarbonate PC plastic is a vertical comb-shaped groove grid structure.

Optionally, in the light-assisted porous silicon electrochemical etching cell, the transparent polycarbonate PC plastic has a horizontal comb-shaped groove grid structure.

Optionally, in the light-assisted porous silicon electrochemical etching cell, the light source includes an LED lamp.

In the light-assisted porous silicon electrochemical etching tank provided by the utility model, when the double-slot electrochemical etching process is carried out, through the light-assisted structure located in the tank body and between the electrode and a silicon chip to be etched, close, Directly irradiating the silicon wafer to be etched, thereby effectively forming a certain concentration of holes in the silicon wafer to be etched, thereby ensuring the quality and efficiency of the double-slot electrochemical etching process.

Further, in the light-assisted porous silicon electrochemical corrosion tank provided by the utility model, the electrode providing the external electric field is a graphite electrode, and the chemical properties of the graphite are stable, avoiding the use of metal platinum as an electrode, which is easy to have on the silicon wafer to be corroded. The risk of heavy metal contamination is conducive to compatibility with semiconductor processes.

Description of drawings

Fig. 1 is the structural representation of existing porous silicon electrochemical etching tank;

Fig. 2 is the structural representation of the light-assisted porous silicon electrochemical etching tank of the utility model embodiment;

Fig. 3 is one of the structural schematic diagrams of the optical auxiliary structure of the embodiment of the present invention;

Fig. 4 is the second structural schematic diagram of the optical auxiliary structure of the embodiment of the present invention;

Fig. 5 is the third structural schematic diagram of the optical auxiliary structure of the embodiment of the present invention;

Fig. 6 is one of the structural schematic diagrams of the electrode of the embodiment of the present invention;

Fig. 7 is the second structural diagram of the electrode of the embodiment of the utility model.

Detailed ways

The light-assisted porous silicon electrochemical etching tank proposed by the utility model will be further described in detail below in conjunction with the accompanying drawings and specific examples. According to the following description and claims, the advantages and features of the utility model will be more clear. It should be noted that all the drawings are in very simplified form and use inaccurate scales, which are only used to facilitate and clearly illustrate the purpose of the embodiment of the present utility model.

Please refer to FIG. 2 , which is a schematic structural diagram of a light-assisted electrochemical etching cell for porous silicon according to an embodiment of the present invention. As shown in Figure 2, the photo-assisted porous silicon electrochemical etching tank includes:

tank body 204;

A fixture for fixing the silicon wafer 203 to be etched in the tank body 204;

An electrode located in the tank body 204, the electrode includes a cathode electrode 201 and an anode electrode 202, and the cathode electrode 201 and the anode electrode 202 are respectively located on both sides of the fixing frame; and

A light auxiliary structure 208 located in the tank body 204 , the light auxiliary structure 208 is located between the fixing frame and the cathode electrode 201 to provide light to the silicon wafer 203 to be etched.

Specifically, the fixing frame includes a first fixing frame 207 and a second fixing frame 206 located below the first fixing frame 207, and the silicon wafer 203 to be etched passes through the first fixing frame 207 and the second fixing frame. 206 is fixed, and at this time, the etching solution on the front and back sides of the silicon wafer 203 to be etched will not leak. The silicon wafer 203 to be etched separates the tank body 204 into a guide groove 209 and an etching groove 210, and the fixing frame and the silicon wafer to be etched need to be electrically insulated from each other, that is, the so-called double grooves, so that Double tank electrochemical corrosion process.

Here, the optical auxiliary structure 208 is located between the cathode electrode 201 and the silicon wafer 203 to be etched. That is, the optical auxiliary structure 208 and the cathode electrode 201 are located in the etching groove 210 , and the anode electrode 202 is located in the guiding groove 209 .

When carrying out the double-tank electrochemical corrosion process, turn on the power and inject the corrosion solution 205 into the tank body 204. Preferably, the corrosion solution 205 is hydrofluoric acid solution or hydrofluoric acid plus ethanol solution, and its percentage concentration is 15% to 25%.

Here, through the optical auxiliary structure 208 located in the tank 204 and between the cathode electrode 201 and the silicon wafer 203 to be etched, the silicon wafer 203 to be etched is irradiated at close range and directly, so that the silicon wafer 203 to be etched 203 is effectively treated. A certain concentration of holes is formed in the process, thereby ensuring the quality and efficiency of the double-slot electrochemical corrosion process.

Wherein, the principle that the photo-assisted structure 208 can stimulate the hole concentration in the silicon wafer 203 to be etched is that when the semiconductor optical silicon material (that is, the silicon wafer to be etched) is irradiated by light, the electrons on its valence band are excited to the conduction Bands, electron-hole pairs are generated, and then the hole concentration required for the reaction is generated, and the corrosion conditions for forming porous silicon are improved.

Further, the electrode is a graphite electrode. Due to the stable chemical properties of graphite, the use of platinum metal as the electrode is avoided, and the risk of heavy metal contamination on the silicon wafer 203 to be corroded is easy to be compatible with the semiconductor process.

In this embodiment, the distance between the optical auxiliary structure 208 and the fixing frame (that is, the silicon wafer 203 to be etched fixed on the fixing frame) is 20 mm˜200 mm. Within this range of distance, the resulting hole concentration can be effectively controlled, thereby improving the quality and efficiency of forming porous silicon.

Please refer to FIG. 3 , which is one of the structural schematic diagrams of the light auxiliary structure of the embodiment of the present invention. As shown in FIG. 3 , specifically, the light auxiliary structure 208 includes: a light source 401 and a transparent polycarbonate PC plastic 402 , and the light source 401 is sealed in the transparent polycarbonate PC plastic 402 . Here, the transparent polycarbonate PC plastic 402 has a groove grid structure, so that the corrosion solution 205 flows from one side of the transparent polycarbonate PC plastic 402 to the other side. Specifically, the transparent polycarbonate PC plastic 402 includes a plurality of concentric rings, and there is a gap 403 between two adjacent rings. The number of the rings is 3-6, and the gap between two adjacent rings is 5mm-20mm. In this embodiment, the diameter of the outermost ring is 150 mm to 160 mm, and the ring width of each ring is 3 mm to 15 mm.

By arranging the transparent polycarbonate PC plastic 402 as a concentric ring with a gap 403, it can be ensured that the silicon wafer 203 to be etched can be uniformly irradiated, and the etching solution 205 injected into the tank body 204 can be easily flowed, thereby Improves the efficiency of etching to form porous silicon.

In this embodiment, the light source is an LED lamp, and the number of the LED lamps is 18-96. The voltage of the LED lamp is 12V-24V, and the power is 6W-36W. Preferably, the number of the LED lights is 18, 27, 36, 45, 54, 63, 72, 81 or 96. A plurality of LED lights are evenly distributed in each ring, that is, the light source is in the shape of a groove grid, thereby giving uniform irradiation to the silicon wafer 203 to be etched, so that the generated holes are evenly distributed in the silicon wafer 203 to be etched, thereby The etching efficiency of each place of the silicon wafer 203 to be etched is equal, and the quality of the formed porous silicon is improved. Certainly, in other embodiments of the present utility model, the light source may also be a cold cathode lamp, which is not limited in the present application.

In other embodiments of the present utility model, the transparent polycarbonate PC plastic can also be a vertical comb-shaped groove grid structure (as shown in Figure 4), or a horizontal comb-shaped groove grid structure (as shown in Figure 5 ), that is, the corrosive liquid can easily flow from one side of the transparent polycarbonate PC plastic to the other side, which is not limited in the present application.

Please refer to FIG. 6 , which is one of the structural schematic diagrams of the electrodes of the embodiment of the present invention. As shown in Figure 6, the shape of the electrodes (i.e. the cathode electrode 201 and the anode electrode 202) is T-shaped, and the T-shaped electrode includes an upper beam and a lower electric plate connected to the upper beam. Correspondingly, the tank body 204 There is a card slot (not shown in FIG. 2 ) on the side wall, whereby the upper beam is locked in the card slot. Here, the lower electric plate is a square with a side length of 200mm. There are a plurality of through holes 301 on the electrode, especially, the through holes 301 are located on the lower electric plate, the diameter D of the through holes 301 is 2 mm to 4 mm, and the diameter D between two adjacent through holes 301 The distance d is 2 mm to 4 mm. Preferably, the number of the through holes 301 is 200-400, and the plurality of through holes 301 are evenly distributed on the electrodes. Thus, it can not only ensure that the silicon wafer 203 to be etched can receive a uniform electric field, but also make the etching solution 205 injected into the tank body 204 easy to flow, thereby improving the efficiency of forming porous silicon by etching.

In other embodiments of the present utility model, the electrode can also be in other shapes, for example: the shape of the electrode is T-shaped, and the T-shaped electrode includes an upper beam and a lower electric plate connected with the upper beam. The electric board is circular/elliptical (as shown in FIG. 7 ), etc., which is not limited in this application.

In this embodiment, the thickness of the electrode is 5mm-10mm, the voltage loaded on the electrode is 20V-100V, and the current loaded on the electrode is a direct current of 1A-5A or a positive and negative pulse current, The peak value of voltage/current is 20~100V/(1~5A) pulse power supply. Among them, the current density of DC power supply is 12-80mA/cm ² , the forward current density of pulse power supply is 2-10mA/cm ³ , the time is 20-100ms, the reverse current density is 0-1mA/cm ³ , the time is 2 ~ 10ms.

Preferably, the distance between the anode electrode 202 and the holder (that is, the silicon wafer 203 to be etched fixed on the holder) is 10 mm to 30 mm; the cathode electrode 201 and the holder ( That is, the distance to the silicon wafer to be etched (203) fixed on the fixing frame is 50 mm to 200 mm.

In this embodiment, the shape of the tank body 204 is cuboid, the length is 20cm-50cm, the width is 20cm-30cm, and the depth is 20cm-40cm, that is, the porous silicon electrochemical corrosion tank is suitable for treating 6-inch silicon wafer. Of course, according to the size of the silicon wafer to be etched, for example, an 8-inch silicon wafer to be etched needs to be processed, the size of the tank body 204 can be changed accordingly.

The above description is only a description of the preferred embodiments of the present utility model, and is not any limitation to the scope of the present utility model. Any changes and modifications made by those of ordinary skill in the field of the utility model according to the above disclosures all belong to the protection scope of the claims .

Claims (10)

1. A light-assisted electrochemical etching cell for porous silicon, comprising: Tank body; A fixture for fixing silicon wafers to be etched located in the tank; An electrode located in the tank body, the electrode includes a cathode electrode and an anode electrode, and the cathode electrode and the anode electrode are respectively located on both sides of the fixing frame; It is characterized in that it also includes: a light auxiliary structure located in the tank, the light auxiliary structure is located between the fixing frame and the cathode electrode, and is used to provide light to the silicon wafer to be etched. 2 . The light-assisted porous silicon electrochemical corrosion cell according to claim 1 , wherein the electrodes are graphite electrodes. 3 . 3 . The light-assisted porous silicon electrochemical etching cell according to claim 1 , wherein the silicon wafer to be etched is fixed on the fixing frame, and the etching solution does not leak from the front and back sides of the silicon wafer to be etched. 4 . 4 . The light-assisted porous silicon electrochemical etching cell according to claim 3 , wherein the silicon wafer to be etched separates the cell body into a guiding groove and an etching groove. 5. The light-assisted porous silicon electrochemical corrosion cell as claimed in claim 3 or 4, wherein the light-assisted structure comprises: a light source and transparent polycarbonate PC plastics, and the light source is sealed on the transparent polycarbonate Ester PC plastic inside. 6. light-assisted porous silicon electrochemical etching cell as claimed in claim 5, is characterized in that, described transparent polycarbonate PC plastics is groove grid structure, makes corrosion solution flow to the other from one side of transparent polycarbonate PC plastics side. 7. The light-assisted porous silicon electrochemical etching cell according to claim 6, characterized in that, the transparent polycarbonate PC plastic is a cell grid structure composed of a plurality of concentric rings. 8 . The light-assisted porous silicon electrochemical etching cell according to claim 6 , wherein the transparent polycarbonate PC plastic is a vertical comb-shaped groove grid structure. 9 . The light-assisted porous silicon electrochemical etching cell according to claim 6 , wherein the transparent polycarbonate PC plastic is a horizontal comb-shaped groove grid structure. 10 . The light-assisted porous silicon electrochemical etching cell according to claim 5 , wherein the light source comprises an LED lamp. 11 .

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