CN103112818B - Method of manufacturing metal electrodes on single micro-nano line by utilizing scanning electron microscope - Google Patents

Abstract

The invention discloses a method for making a metal electrode on a single micro-nano wire by using a scanning electron microscope, which belongs to the field of design and manufacture of micro-nano devices. The present invention only utilizes a simple scanning electron microscope and a coating instrument to fabricate metal electrodes at both ends of a single micro-nano wire. The electrodes cover the micro-nano wires and form a stable electrode contact with the micro-nano wires, which ensures the stability of the signal during the measurement of electrical properties. There are many choices of metals as electrodes, which provides technical support for designing and constructing various forms of micro-nano devices. The production process does not use expensive equipment such as FIB, which achieves the effect of producing the same electrode, saves costs, and is simple and easy. <b/>

Description

A method of fabricating metal electrodes on a single micro-nano wire using a scanning electron microscope

technical field

The invention relates to a method for making a metal electrode on a single micro-nano wire by using a scanning electron microscope, and belongs to the field of design and manufacture of micro-nano devices.

Background technique

Achieving good contact between a single micro-nano wire and a metal electrode has always been a bottleneck key scientific and technical issue in the study of the electrical properties of a single micro-nano wire and the construction of micro-nano devices using a single micro-nano wire. A single micro-nano wire is the basic functional unit in a micro-nano-electromechanical system. Good surface-interface contact between materials and electrodes is the basis for giving full play to the optoelectronic performance of a single micro-nano wire, and is the prerequisite for designing new micro-nano devices. Taking nano-ZnO as an example, the current solution to the contact between a single ZnO micro-nano wire and a metal electrode can be roughly divided into the following four ways.

First, randomly sprinkle ZnO micro-nano wires on the pre-made metal micro-electrodes, and rely on the van der Waals adsorption force between the ZnO micro-nano wires and the electrodes to achieve electrode contact. In 2002, "Nanowire ultraviolet photodetectors and optical switches" (Nanowire ultraviolet photodetectors and optical switches) on "Advanced Materials", vol.14, 158-160 reported the use of metal Au electrodes sprinkled on The contact of ZnO nanowires with Au electrodes, and the UV response performance of single ZnO nanowires were measured. Also on Au electrodes, in 2006, "Nano Letters", vol.6, 263-266, "ZnO nanobelt/nanowire Schottky diodes constructed by electrophoresis between Au electrodes" (ZnO nanobelt/nanowire Schottky diodes Formed by Dielectrophoresis Alignment across Au Electrodes) article reported the use of electrophoresis to make a single ZnO nanobelt/nanowire at both ends to form Schottky contacts with the prepared Au electrodes to form a diode.

Second, the electron beam lithography system (EBL) was used to fabricate metal electrodes at both ends of a single ZnO nanowire. In 2007, "Effect of surface states on electron transport in individual ZnO nanowires" (Effect of surface states on electron transport in individual ZnO nanowires) on "Physics Letters A", vol. 367, 207-210 reported Metal electrodes were fabricated on single ZnO nanowires by EBL, and the effects of surface states on the electrical transport properties of single ZnO nanowires were studied.

Third, metal electrodes were deposited on single ZnO micro-nanowires using focused ion beam equipment (FIB). In 2006, "Nano Letters", vol.6, 1719-1722, "Broadband ZnO single-nanowire light-emitting diode" (Broadband ZnO single-nanowire light-emitting diode) reported on a single ZnO nanowire FIB is used to deposit Ti/Au electrodes, and a single ZnO nanowire and P-type silicon form a pn junction light-emitting diode.

Fourth, the nano-manipulated metal probe is used to form an electrode contact with a single ZnO micro-nano wire. In 2010, "Electrical breakdown of ZnO nanowires in metal-semiconductor-metal structure" (Electrical breakdown of ZnO nanowires in metal-semiconductor-metal structure) on "Applied Physics Letters", vol.96, 253112, used nano The metal W probe was manipulated to contact the two ends of ZnO nanowires to form a loop, and the phenomenon and mechanism of electrical damage of ZnO nanowires were studied.

In the first approach, although a single micro-nano wire can form contact with a metal electrode, the contact is easily loosened due to the fact that the van der Waals adsorption force is very small. The electron beam exposure system used in the second approach needs to be equipped with an electron beam control system on the basis of an ordinary scanning electron microscope. The third way requires the use of expensive FIB equipment, and it will cost a lot if a large number of experiments are required, and many laboratories do not have such conditions. In the fourth approach, the contact point between the nano-manipulation probe and a single micro-nano wire is not fixed, and it is easy to slide, which will affect the accurate measurement of electrical properties.

Contents of the invention

In order to solve the above problems, the purpose of the present invention is to provide a method that can ensure the stability of the signal during the electrical property measurement process, and achieve the effect of making the same electrode without using expensive equipment such as FIB, saving costs, and is simple and easy. A method for fabricating metal electrodes on a single micro-nano wire using a scanning electron microscope.

The technical solution of the present invention is a method for making a metal electrode on a single micro-nano wire by using a scanning electron microscope, which specifically includes the following steps:

a. Spin-coat polymethyl methacrylate PMMA electron beam etching glue on the insulating silicon wafer substrate, and bake the solid film;

b. Electron beam etching: place the insulating silicon wafer after the above steps in the scanning electron microscope, adjust the magnification of the electron microscope, so that the electron beam irradiates a small part of PMMA, and the irradiation area is equal to the representative area of the electron microscope display screen;

c. Development and fixation: Use developer and fixer to wash away PMMA degraded by electron beam irradiation;

d. DC sputtering: put the insulating silicon wafer treated in step c into a DC sputtering apparatus, and perform DC sputtering of metal to form a metal film with a thickness of 100nm;

e. Strip off excess glue: Soak the insulating silicon wafers treated in step d in acetone, ethanol, and isopropanol for 60 seconds respectively, remove and clean the unexposed PMMA, and finally place them on the insulating silicon wafer substrate Get the mark that the material is sputtered metal;

f. Disperse the micro-nano wires in the isopropanol solution and drop them on the insulating silicon substrate after step e. In the scanning electron microscope, read and record the absolute position of the metal mark, and record Calculate the relative coordinate position (X1, Y1) and (X2, Y2) of the metal mark at the prefabricated metal electrode on the absolute position of the prefabricated metal electrode on the micro-nano wire;

g. Repeat step a for the insulating silicon wafer after step f is processed;

h. Place the insulating silicon wafer processed in step g in the scanning electron microscope, focus on the metal mark in the scanning electron microscope, and record the absolute position of the metal mark at this time, according to the relative position of the metal mark at the pre-made metal electrode Position, calculate the absolute position of the pre-made metal electrode at this time, and use the electron microscope sample stage to move the absolute position of the pre-made metal electrode to directly below the electron beam;

i. Repeat the four steps of step b electron beam etching, c development and fixing, d DC sputtering and e peeling off the remaining glue, and finally obtain the required metal electrode covered on the one-dimensional micro-nano wire.

Further, the percentage concentration of methyl methacrylate in the step a is 0.01; spin coating for 30 seconds at a speed of 4000 rpm, and then bake in an oven at 160° C. for two hours to solidify the film.

Further, in the step b, in the scanning electron microscope, adjust the accelerating voltage to 20kV to focus the electron beam on the surface of the insulating silicon wafer and adjust to a suitable magnification. In this experiment, adjust the magnification to 10000 times to make the electron beam radiate When a small part of PMMA is irradiated, the irradiated area is equivalent to the representative area of the electron microscope display screen, and the irradiated time is 120 seconds.

Further, in the step c, the developing solution is formulated with a ratio of 1:3 using methyl isobutyl ketone MIBK and isopropyl alcohol IPA; the fixing solution is isopropyl alcohol IPA, and the developing time is 75 seconds, and the fixing time is 20 seconds.

Further, the micro-nano wire is ZnO, TiO ₂ or carbon nanotube; the DC sputtered metal can form a Schottky contact with the micro-nano wire or a metal that can form an ohmic contact with the micro-nano wire.

The method for making metal electrodes on a single micro-nano wire using a scanning electron microscope provided by the present invention can realize the fixation of a single micro-nano wire on a substrate, and can provide a good and stable electrode for characterizing the electrical properties of a single micro-nano wire Contact can make micro-nano devices.

Compared with the prior art, the present invention has the following advantages and outstanding effects: the electrode is covered on the micro-nano wire, and can form a stable electrode contact with the micro-nano wire, which ensures the stability of the signal during the electrical property measurement process. There are many options for the metal of the electrode. Taking ZnO as an example, it can be metals such as Pt and Au that can form Schottky contacts with ZnO micro-nano wires, or metals that can form ohmic contacts with ZnO micro-nano wires. Ag, Ta, etc. provide technical support for the design and construction of various forms of micro-nano devices. The process of making the electrode only uses the most common scanning electron microscope and the coating instrument matched with the scanning electron microscope. Without using expensive equipment such as FIB, the effect of making the same electrode is achieved, which saves costs and is simple and easy. OK.

Description of drawings

Figure 1 (a) is a scanning electron microscope (SEM) image of metal markers, and (b) is a schematic diagram of the method of using metal markers to locate electrodes.

Figure 2 (a)-(d) is a schematic diagram of the process flow.

Figure 3 is a SEM image of a single micro-nano wire and the fabricated metal electrodes at both ends.

In the picture:

1. Insulating silicon wafer, 2. PMMA methyl methacrylate, 3. Micro-nano wire, 4. Metal electrode, 5. Metal mark.

detailed description

The technical solutions of the present invention will be further described below in conjunction with specific embodiments.

Example 1:

1. Spin-coat polymethyl methacrylate (PMMA) electron beam etching glue and bake the solid film, drop PMMA positron beam etching glue 2 with a percentage concentration of 0.01 on the insulating silicon wafer 1, and use 4000rpm Rotating speed, spin coating for 30s, and then bake in an oven at a temperature of 160°C for two hours to volatilize the solvent in the PMMA, and form a layer of PMMA film 2 on the insulating silicon wafer 1;

2. Electron beam etching. Place the silicon insulating wafer 1 in the scanning electron microscope, adjust the accelerating voltage to 20kV, focus the electron beam on the surface of the insulating silicon wafer, and adjust the magnification of the electron microscope to a suitable multiple, such as in this experiment, adjust the magnification to 10000 times , making the PMMA in the electron beam irradiation electron microscope display screen, the irradiation time is 120 seconds;

3. Developing and fixing. Use methyl isobutyl ketone (MIBK) and isopropanol (IPA) to prepare a developer solution at a ratio of 1:3, use IPA as a fixer solution, and place the insulating silicon wafer in the developer solution at a fixed temperature of 25°C. Soak in the medium for 75 seconds, then put it into the fixer for about 20 seconds, take it out and then blow dry the remaining IPA fixer, and the film on the etched part will be washed away;

4. DC sputtering metal thin film. Put the insulated silicon wafer into a coating apparatus, and DC sputter the required Pt metal film to 100nm;

5. Peel off the remaining film. Soak the insulating silicon wafer in acetone, ethanol, and isopropanol for 60 seconds respectively, remove and clean the unexposed PMMA, and finally obtain a mark 5 made of metal Pt on the insulating silicon wafer substrate. , as shown in Figure 1(a);

6. Disperse the micro-nano wire (3) in isopropanol, and drop it onto the insulating silicon wafer substrate, place the insulating silicon wafer in a scanning electron microscope, read and record the Pt mark 5 Absolute coordinate position, and record the absolute coordinate position of the prefabricated metal electrode 4 on the micro-nano wire 3, calculate the relative coordinate position (X1, Y1) and (X2, Y2), as shown in Figure 1(b);

7. Spin-coat PMMA glue 2 on the insulating silicon wafer 1 and solidify the film, repeat step 1, as shown in Figure 2(a);

8. Focus on the metal Pt mark 5 on the insulating silicon wafer in the scanning electron microscope, and record the absolute coordinate position of the metal Pt mark 5 at this time, according to the relative coordinates of the metal Pt mark 5 at the pre-made metal electrode 4 Position (X1, Y1) and (X2, Y2), calculate the absolute position of the pre-made metal electrode 4 at this time, and use the electron microscope sample stage to move the absolute coordinate position of the pre-made metal electrode 4 to directly below the electron beam;

9. Electron beam etching, repeat step 2;

10. For developing and fixing, repeat step 3, and the final result is shown in Figure 2(b);

11. DC sputtering metal film, repeat step 4, as shown in Figure 2(c);

12. Peel off the remaining adhesive film, repeat step 5, as shown in Figure 2(d), and finally obtain the required metal electrode 4 covering the micro-nano wire 3, and the actual SEM photo is shown in Figure 3.

Example 2

1. Spin-coat polymethyl methacrylate (PMMA) electron beam etching glue and bake the solid film, drop PMMA positron beam etching glue with a concentration of 0.01 on the insulating silicon wafer, at a speed of 4000rpm, Spin coating for 30s, then bake in an oven at 160°C for two hours to volatilize the solvent in PMMA, and form a layer of PMMA film on the insulating silicon wafer;

2. Electron beam etching. Place the insulating silicon wafer in a scanning electron microscope, adjust the accelerating voltage to 20kV, focus the electron beam on the surface of the insulating silicon wafer, adjust the magnification of the electron microscope to a suitable multiple, such as adjusting the magnification to 10000 times in this experiment, Make the PMMA in electron beam irradiation electron microscope display screen, and irradiation time is 120 seconds;

3. Developing and fixing. Use methyl isobutyl ketone (MIBK) and isopropanol (IPA) to prepare a developer solution at a ratio of 1:3, use IPA as a fixer solution, and place the insulating silicon wafer in the developer solution at a fixed temperature of 25°C. Soak in the medium for 75 seconds, then put it into the fixer for about 20 seconds, take it out and then blow dry the remaining IPA fixer, and the film on the etched part will be washed away;

4. DC sputtering metal thin film. Put the insulating silicon wafer into a film coater, and DC sputter the required metal Au film to a thickness of 100nm;

5. Peel off the remaining film. Soak the insulating silicon wafer in acetone, ethanol, and isopropanol for 60 seconds respectively, remove and clean the unexposed PMMA, and finally obtain a mark made of Au on the insulating silicon wafer substrate;

6. Disperse the _TiO2 micro-nanowires in isopropanol and drop them onto the silicon-insulator substrate, place the silicon-insulator wafer in a scanning electron microscope, read and record the absolute coordinates of the Au mark position, and record the absolute coordinate position of the pre-made metal electrode on a single TiO ₂ micro-nano line, and calculate the relative coordinate position (X1, Y1) and (X2, Y2) of the Au mark at the pre-made metal electrode;

7. Spin-coat PMMA glue on the insulating silicon wafer and solidify the film, repeat step 1;

8. Focus on the Au mark on the insulating silicon wafer in the scanning electron microscope, and record the absolute coordinate position of the Au mark at this time, according to the relative coordinate position (X1, Y1) of the Au mark at the pre-made metal electrode and (X2, Y2), calculate the absolute position of the prefabricated metal electrode at this time, and use the electron microscope sample stage to move the absolute coordinate position of the prefabricated metal electrode to directly below the electron beam;

9. Electron beam etching, repeat step 2;

10. For developing and fixing, repeat step 3;

11. DC sputtering metal film, repeat step 4;

12. Peel off the remaining adhesive film, repeat step 5, and finally obtain the desired metal electrode covered on the one-dimensional TiO ₂ micro-nano wire.

Claims (5)

1. utilize ESEM in single micro-nano line, make a method for metal electrode, it is characterized in that:

A. at upper spin coating polymetylmethacrylate electron beam lithography glue (2) of silicon-on-insulator substrate (1), and the solid film of baking;

B. electron beam lithography: the silicon-on-insulator after above-mentioned steps process is placed in ESEM, adjustment Electronic Speculum multiplication factor, make electron beam irradiation sub-fraction PMMA, irradiated area is equal to Electronic Speculum display picture and represents area;

C. developing fixing: use developer solution and fixing solution to wash away the PMMA degraded by electron beam irradiation;

D. d.c. sputtering: the silicon-on-insulator after step c process is put into d.c. sputtering instrument, carries out the d.c. sputtering of metal, forming thickness is the metallic film of 100nm;

E. remaining glue is peeled off: to be steeped respectively by the silicon-on-insulator after steps d process in acetone, ethanol, isopropyl alcohol each ultrasonic 60 seconds, still unexposed PMMA is removed and cleaned up, finally on silicon-on-insulator substrate, obtains the mark that material is splash-proofing sputtering metal;

F. micro-nano line is dispersed in aqueous isopropanol, and be added drop-wise on the silicon-on-insulator substrate after step e process, in ESEM, read and record the absolute position of metal marker, and record the absolute position at the upper precompose metal electrode place of micro-nano line (3), calculate precompose metal electrode place to the relative coordinate position (X1, Y1) of metal marker and (X2, Y2);

G. step a process is repeated at the silicon-on-insulator after step f process;

H. the silicon-on-insulator after step g process is placed in ESEM, focus in ESEM and aim at metal marker, and record the absolute position of now metal marker, according to precompose metal electrode place to the relative position of metal marker, calculate the absolute position at now precompose metal electrode place, utilize electron microscopic sample platform to move to immediately below electron beam by the absolute position at precompose metal electrode place;

I. repeat step b electron beam lithography, c developing fixing, d d.c. sputtering and e and peel off remaining glue four steps, finally obtain the required metal electrode covered in one dimension micro-nano line.

2. method according to claim 1, is characterized in that: in described step a, the percentage concentration of methyl methacrylate is 0.01; With the rotating speed of 4000rpm, spin coating 30s, then in an oven 160 DEG C baking two hours with solid film.

3. method according to claim 1, it is characterized in that: described step b is in ESEM, will speed up voltage and be transferred to 20kV, make Electron Beam Focusing to silicon-on-insulator surface, be transferred to suitable multiplication factor, in this experiment, multiplication factor be transferred to 10000 times, make electron beam irradiation sub-fraction PMMA, irradiated area is equal to Electronic Speculum display picture and represents area, and exposure time is 120 seconds.

4. method according to claim 1, is characterized in that: in described step c developer solution be use methylisobutylketone MIBK and isopropyl alcohol IPA with 1: 3 ratio be deployed into; Described fixing solution is isopropyl alcohol IPA, and developing time is 75 seconds, and fixing time is 20 seconds.

5. method according to claim 1, is characterized in that: described micro-nano rice noodles are ZnO, TiO ₂or CNT; The metal of described d.c. sputtering is to form the metal of Schottky contacts with micro-nano line or can form the metal of Ohmic contact with micro-nano line.