CN104465328A - Controlled method for removing residual photoresist from graphene-metal contact regions - Google Patents

Abstract

The invention discloses a method for removing residual optical photoresist in a graphene-metal contact area in a controllable manner, which comprises the following steps: assembling an organic layer on the surface of the graphene, and depositing an inorganic layer as a double-layer protection layer of the graphene; spin-coating a layer of photoresist on the double-layer protective layer of the graphene, and carrying out exposure, inversion, flood exposure and development on the photoresist to form a pattern required by the preparation of the metal electrode; by the use of O₂And removing the residual photoresist on the surface of the inorganic layer by using the plasma, corroding the inorganic layer of the graphene-metal contact area by using a wet method, and controllably removing the organic film of the graphene-metal contact area by using an organic corrosive liquid to ensure that no residual photoresist exists on the surface of the graphene-metal contact area. The method solves the problem that the photoresist is easy to remain on the surface of the graphene, the graphene cannot be damaged, the doping degree of the graphene is reduced, and the constructed graphene field effect transistor can keep the high carrier mobility and the device performance of the graphene material.

Description

Controlled method for removing residual photoresist from graphene-metal contact regions

technical field

The invention belongs to the technical field of graphene field-effect transistor manufacture, and in particular relates to a method for controllably removing residual optical photoresist in a graphene-metal contact area.

Background technique

As integrated circuit technology enters the nanometer scale, key technologies are approaching the physical limit dominated by quantum effects, and the difficulty and cost of the process are increasing sharply. The sustainable development of integrated circuits is facing unprecedented challenges. High speed and low power consumption are key technical bottlenecks in the development of integrated circuits, and both are related to carrier mobility. Finding materials with higher mobility to replace the existing silicon channel has become a very urgent task to further extend Moore's Law. High-mobility carbon materials represented by graphene have attracted widespread attention and have broad application prospects in the new generation of high-performance microelectronics and circuits. They are considered to be the materials with the most potential to further extend Moore's Law. The US Defense Advanced Research Projects Agency (DARPA) formulated the CERA (Carbon Electronics for RFApplications) program in 2008, integrating a number of well-known research institutions to conduct research on graphene microelectronic devices, and to develop ultra-high-speed, low-power graphene field effect transistor.

The contact between metal and graphene is an important factor restricting the development of graphene field effect transistors. When metal and graphene are in contact, additional contact resistance is generated at the contact interface. Then, when a voltage is applied to the source/drain of the graphene field effect transistor, the source-drain voltage drops due to the voltage division effect of the contact resistance, which reduces the current driving capability of the device and reduces the transconductance of the device. And due to the contact between metal and graphene, the doping of graphene is formed at the contact interface. When the doping type of metal to graphene is different from the doping type of gate voltage to graphene, there will be a gap between the channel region and the contact A p-n junction is generated at the interface, resulting in different contact resistances between the n-type conduction and p-type conduction regions, thereby destroying the unique bipolar conduction characteristics of graphene transistors. The contact resistance between graphene and metal is not only limited by the type of metal, but also closely related to the state of graphene at the contact interface. In the preparation process of graphene field effect transistors, in order to define graphics, it is inevitable to use photoresist on the surface of graphene. After exposure and development, a large amount of photoresist remains on the surface of graphene, which hinders the contact between metal and graphene. The introduction of additional potential barriers at the contact interface leads to a great reduction in the electrical properties of graphene, which is one of the bottlenecks that limit its further application development. How to reduce the photoresist residue on the surface of graphene, reduce the contact resistance of the graphene-metal region, and reduce the influence of photoresist on the field effect performance of graphene, especially optical photoresist, so as to replace the expensive electron beam photoresist Engraving, to achieve the purpose of reducing process costs, is a work of practical significance. Therefore, a controllable method for removing the residual optical photoresist in the graphene-metal contact area is particularly important.

Contents of the invention

(1) Technical problems to be solved

In view of this, the main purpose of the present invention is to provide a method for controllably removing the residual photoresist in the graphene-metal contact area.

(2) Technical solution

In order to achieve the above object, the invention provides a method for controllably removing the residual optical photoresist in the graphene-metal contact region, comprising:

Step 1: Self-assemble an organic layer on the surface of graphene, and then deposit an inorganic layer as a double-layer protective layer of graphene;

Step 2: Spin-coat a layer of photoresist on the double-layer protective layer of graphene, and perform exposure, inversion, flood exposure and development operations on the photoresist to form the pattern required for preparing the metal electrode;

Step 3: Use _O2 plasma to remove the residual photoresist on the surface of the inorganic layer, then use a wet method to etch the inorganic layer in the graphene-metal contact area, and use an organic etching solution to treat the organic film in the graphene-metal contact area Controlled removal is performed to ensure that there is no residual photoresist on the surface of the graphene-metal contact area.

In the above scheme, the double-layer protective layer of graphene described in step 1 includes an organic layer capable of controllable dissolution and an inorganic layer capable of processing residual photoresist on the surface, so as to avoid direct contact between graphene and photoresist, wherein, The inorganic layer protects the graphene sample with residual photoresist treated by _O2 plasma, and the organic layer can controllably dissolve and keep the photolithographic pattern perfectly, so as to controllably remove the photoresist in the graphene field effect transistor process.

In the above scheme, the organic layer described in step 1 is selected from a photoresist whose solubility parameter is quite different from that of the photoresist, can form a dense film on the surface of graphene, and can achieve controllable dissolution by adjusting the dissolution rate. Styrene; the inorganic layer described in step 1 is to select metal nickel which can resist the corrosion of alkaline solution and is easy to dissolve the acid corrosion solution.

In the above solution, the organic layer forms a dense film on the surface of graphene with a film thickness of 5nm-30nm; the inorganic layer is a metal nickel layer with a thickness of 10-30nm deposited by electron beam evaporation or magnetron sputtering technology.

In the above solution, the graphene in step 1 is grown by chemical vapor deposition (CVD), and the graphene is transferred to the target substrate by substrate etching.

In the above scheme, the photoresist described in step 2 is a reverse photoresist, wherein: the reverse photoresist is AZ glue, and the photolithography conditions are: the thickness of the photoresist is 1.2-1.7 μm, and the ultraviolet light intensity is 3 ～6, exposure time 4～7 seconds, reverse 110～120℃, pan exposure 50～70 seconds, developing 40～70 seconds; the reverse photoresist is AZ5214, and the photolithography conditions are: the thickness of the photoresist is 1.4 μm, UV intensity 5, exposure time 5 seconds, inversion 115°C, pan exposure 65 seconds, development 60 seconds.

In the above solution, O ₂ plasma is used in step 3 to remove the residual photoresist on the surface of the inorganic layer. The process conditions are O ₂ flow of 20-60 sccm, power of 30-60 W, and etching time of 1-5 minutes. Preferably, in the process conditions, the O ₂ flow rate is 40 sccm, the power is 20 W, and the etching time is 3 minutes.

In the above scheme, the inorganic layer in the graphene-metal contact area is etched away by wet method as described in step 3, and the etching solution is a weakly acidic mixed solution, which is a diluted solution of phosphoric acid and hydrogen peroxide mixed in proportion. liquid, the corrosion rate is Preferably, the dilution of phosphoric acid and hydrogen peroxide mixed in proportion, the mixing ratio is phosphoric acid: hydrogen peroxide: water = 1: 1: 9, and the corrosion rate is

(3) Beneficial effects

The advantage of the present invention is that the organic thin film is used as the mask layer to avoid direct contact between graphene and photoresist, and at the same time, the organic thin film can be controlled to dissolve, thereby achieving the purpose of controllable removal of residual photoresist in the graphene field effect transistor . Another advantage of the present invention is that it does not cause damage to the graphene, and reduces the doping degree of the graphene, and the constructed graphene field effect transistor can maintain the high carrier mobility and device performance of the graphene material.

Compared with the prior art, the present invention has the following characteristics:

1. The organic thin film used in the present invention is non-toxic, cheap, and has no residual and adsorption effects on the surface of graphene.

2. After controlled dissolution, the surface of graphene can be cleaned at the atomic level, and a large-scale clean surface with no photoresist residue and low contact resistance can be obtained.

3. The present invention does not cause damage to graphene, and reduces the doping degree of graphene, and the constructed graphene field effect transistor can maintain the high carrier mobility and device performance of graphene materials.

Description of drawings

Fig. 1 is the flow chart of the method for the controllable removal of residual optical photoresist in the graphene-metal contact area provided by the present invention;

Fig. 2 is the process flow diagram of the controllable removal of residual optical photoresist in the graphene-metal contact area provided by the present invention;

Fig. 3 is the optical photo in the removal process in embodiment 1;

Fig. 4 is the atomic force micrograph of the double-layer graphene-metal contact region after etching mask layer among the embodiment 1;

Fig. 5 is the electrical characteristic of the graphene field effect transistor in embodiment 1;

Fig. 6 is the optical photo in the removal process in embodiment 2;

Fig. 7 is the electrical characteristic of graphene field effect transistor in embodiment 3.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

The present invention adopts organic layer to add inorganic layer double-layer mask technology as the protective layer of graphene, avoids graphene and photoresist direct contact, meanwhile, inorganic thin film protection O ₂ plasma (plasma) handles the graphite of residual photoresist Graphene samples, the organic film can be controlled to dissolve and the photolithographic pattern can be perfectly maintained, so as to achieve the purpose of controllable removal of residual photoresist in the graphene-metal contact area. The method does not cause damage to the graphene, and reduces the doping degree of the graphene, and the constructed graphene field effect transistor can maintain the high carrier mobility and device performance of the graphene material.

As shown in Figure 1, Figure 1 is a flow chart of the method for controllably removing the residual optical photoresist in the graphene-metal contact area provided by the present invention, the method may include the following steps:

Step 1: Self-assemble an organic layer on the surface of graphene, and then deposit an inorganic layer as a double-layer protective layer of graphene;

In this step, the double-layer protective layer of graphene includes an organic layer capable of controllable dissolution and an inorganic layer capable of processing residual photoresist on the surface, so as to avoid direct contact between graphene and photoresist, wherein the inorganic layer protects O ₂ Plasma treatment of graphene samples with residual photoresist, the organic layer can be controlled to dissolve and the photolithography pattern can be perfectly maintained, so as to controllably remove the photoresist in the graphene field effect transistor process. The organic layer is an organic polymer whose solubility parameter is quite different from that of the photoresist, can form a dense film on the surface of graphene, the film thickness is 5nm to 30nm, and can achieve controllable dissolution by adjusting the dissolution rate, preferably It is polystyrene. The inorganic layer is a metal that is resistant to alkaline solution corrosion and easy to dissolve acid corrosion solution, preferably metal nickel, and deposited by electron beam evaporation or magnetron sputtering technology with a thickness of 10-30nm. Graphene is grown by chemical vapor deposition (CVD), and the graphene is transferred to the target substrate by substrate etching.

Step 2: Spin-coat a layer of photoresist on the double-layer protective layer of graphene, and perform exposure, inversion, flood exposure and development operations on the photoresist to form the pattern required for preparing the metal electrode;

In this step, the photoresist is a reverse photoresist, wherein: when the reverse photoresist is AZ glue, the photolithography conditions are: the thickness of the photoresist is 1.2-1.7 μm, the ultraviolet light intensity is 3-6, The exposure time is 4-7 seconds, the reversal is 110-120°C, the pan exposure is 50-70 seconds, and the development is 40-70 seconds; when the reversal photoresist is AZ5214, the photolithography conditions are: the thickness of the photoresist is 1.4 μm, UV light intensity 5, exposure time 5 seconds, inversion 115°C, pan exposure 65 seconds, development 60 seconds.

Step 3: Use _O2 plasma to remove the residual photoresist on the surface of the inorganic layer, then use a wet method to etch the inorganic layer in the graphene-metal contact area, and use an organic etching solution to treat the organic film in the graphene-metal contact area Perform controlled removal to ensure that there is no residual photoresist on the surface of the graphene-metal contact area;

In this step, the inorganic layer in the graphene-metal contact area is etched away by a wet method, and the etching solution is a weakly acidic mixed solution, which is a dilution of phosphoric acid and hydrogen peroxide mixed in proportion, and the corrosion rate for Preferably, the dilution of phosphoric acid and hydrogen peroxide mixed in proportion, the mixing ratio is phosphoric acid: hydrogen peroxide: water = 1: 1: 9, and the corrosion rate is

Fig. 2 shows the process flow diagram of the controllable removal of graphene-metal contact area residual optical photoresist provided by the present invention, comprising the following steps: the graphene grown by CVD method is transferred to the target substrate, and the graphene is automatically formed on the graphene surface Assemble an organic layer, and then deposit an inorganic layer to form a double-layer protective layer; after two optical lithography, the residual photoresist on the surface of the inorganic layer is removed by plasma, and then the protective layer is corroded controllably by using an etching solution. The purpose of controlled removal can be achieved.

The present invention is illustrated by specific examples below, but those skilled in the art understand that the present invention is not limited thereto, and any improvements and inventions made on the basis of the present invention are within the protection scope of the present invention. The experimental methods described in the following examples, unless otherwise specified, are conventional methods; the reagents and materials, unless otherwise specified, can be obtained from commercial sources.

Embodiment 1. Using polystyrene as the organic layer and metallic nickel as the inorganic layer as the double-shielding layer, the controllable removal of the residual optical photoresist in the double-layer graphene-metal contact area.

Specific steps are as follows:

Step 1: Grow a single layer of uniform graphene on the surface of copper foil by CVD method, spin-coat PMMA photoresist on the surface of graphene and heat and bake to cure the photoresist, and then place the copper sheet with graphene and PMMA into a copper etching solution, etch away the copper and transfer it to a silicon dioxide semiconductor substrate with a 300 nm insulating layer.

Step 2: Spin-coat a layer of 9912 photoresist with a thickness of 1.4 μm on the surface of a 300nm SiO ₂ /Si substrate spread with graphene (transferred twice), after exposure (light intensity 5, time 15s), development (40s ), primer, acetone degumming, and graphene active area patterning.

Step 3: self-assemble a layer of 10nm-thick organic film polystyrene (concentration 5%) on the surface of the patterned graphene by self-assembly as a mask layer, and dry at 100°C.

Step 4: Deposit metallic nickel on the surface of the polystyrene film with a thickness of 10 nm by electron beam evaporation technology.

Step 5: Spin coat a layer of AZ5214 reverse photoresist on the surface, expose, reverse, flood, develop, and make source and drain metal.

Step 6: use phosphoric acid: hydrogen peroxide: water ratio of 1:2:5 to corrode metal nickel, corrosion time is 1h, and use organic film corrosion solution cyclohexane to corrode 20nm; the organic film in the graphene-metal contact area is controlled Clean to ensure that there is no residual photoresist on the surface of the contact area.

Fig. 3 is the optical picture in the clearing process in embodiment 1, and the optical picture illustration of Fig. 3, after depositing metallic nickel (a figure), corrodes metallic nickel (b figure), corrodes polystyrene (c figure) photoetching pattern keeps Complete, the color change shows that the protective layer is completely corroded, and Figure d shows that there is almost no residual photoresist and protective layer residue in the contact area.

Fig. 4 is the atomic force microscope atomic force microscope (AFM) figure of bilayer graphene-metal contact region after corrosion mask layer in embodiment 1, the atomic force of bilayer graphene-metal contact region behind the corrosion mask layer of Fig. 4 The micrograph shows that the height of the graphene-metal contact area is 3.9nm, indicating that there is almost no glue residue on the graphene surface, and the graphene surface is complete.

Fig. 5 is the electrical characteristic of the graphene field effect transistor (FET) in embodiment 1, and the transfer curve of the graphene back gate device of Fig. 5 shows that the Dirac point of the device is around 0V, and the leakage current reaches the milliampere level.

Embodiment 2, using polystyrene as the organic layer, metal nickel as the inorganic layer as the double shielding layer, controllably removes the residual optical photoresist in the graphene-metal contact area.

The specific steps are similar to those in Example 1, but in step 3, the thickness of polystyrene is 20nm, and the corrosion rate is 1nm/min; in step 4, the thickness of metal nickel is 20nm, and the corrosion rate is 1nm/min.

Fig. 6 is the optical photo in the removal process in embodiment 2, and the optical photo of Fig. 6 shows that the corrosion rate of the protective layer plays a decisive role in maintaining the integrity of the photolithography pattern, and the corrosion rate is too fast, which causes relatively obvious capillarity, resulting in photoresisting. Lack of engraved graphics.

Embodiment 3, using polyethylene as the organic layer and metal nickel as the inorganic layer as the double shielding layer, controllably removes the residual optical photoresist in the graphene-metal contact area.

The specific steps are similar to Example 1, but step 3 uses polyethylene as an organic mask layer with a thickness of 20nm and an etching rate of 1nm/min. In step 4, the thickness of metal nickel is 20nm and the etching rate is 1nm/min.

Fig. 7 shows the electrical characteristics of the graphene field effect transistor in Example 3. The transfer curve in Fig. 7 shows that the corrosion rate is too fast and the performance of the device is not good.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. a method for controlled removing Graphene-Metal contact regions residual optical photoresist, is characterized in that, comprising:

Step 1: at graphenic surface self assembly one deck organic layer, then deposit the double shielding layer of one deck inorganic layer as Graphene;

Step 2: spin coating one deck photoresist on the double shielding layer of Graphene, exposes photoresist, reverses, generally to expose to the sun and development operation, forms the figure prepared needed for metal electrode;

Step 3: adopt O ₂the photoresist of inorganic layer remained on surface is removed by plasma, wet etching is adopted to fall the inorganic layer of Graphene-Metal contact regions again, and use organic corrosion liquid to carry out controlled removing to the organic film of Graphene-Metal contact regions, ensure Graphene-Metal contact regions surface noresidue photoresist.

2. the method for controlled removing Graphene-Metal contact regions residual optical photoresist according to claim 1; it is characterized in that; the double shielding layer of Graphene described in step 1 comprise can controlled dissolving organic layer and treatment surface can remain the inorganic layer of photoresist; directly contact with photoresist in order to avoid Graphene; wherein, inorganic layer protection O ₂plasma treatment remains the Graphene sample of photoresist, and organic layer can controlled dissolving and make litho pattern obtain perfect maintenance, with the photoresist in controlled removing graphene field effect transistor technique.

3. the method for controlled removing Graphene-Metal contact regions residual optical photoresist according to claim 1, is characterized in that,

Organic layer described in step 1 selects the solubility parameter between photoresist to differ comparatively large, can form dense film at graphenic surface, and can by the organic polymer polystyrene regulating rate of dissolution to reach controlled dissolving;

Inorganic layer described in step 1 is that select can alkali resistance solution corrosion, is easy to again the metallic nickel of dissolving acid etchant solution.

4. the method for controlled removing Graphene-Metal contact regions residual optical photoresist according to claim 3, it is characterized in that, described organic layer forms dense film at graphenic surface, and film thickness is 5nm ~ 30nm; Described inorganic layer adopts the thickness of electron beam evaporation or magnetron sputtering technique deposition to be the metal nickel dam of 10 ~ 30nm.

5. the method for controlled removing Graphene-Metal contact regions residual optical photoresist according to claim 1, it is characterized in that, Graphene described in step 1 is grown by chemical vapour deposition technique (CVD), adopts matrix etching method that Graphene is transferred to target substrate.

6. the method for controlled removing Graphene-Metal contact regions residual optical photoresist according to claim 1, it is characterized in that, photoresist described in step 2 is reversal photoresist, wherein:

This reversal photoresist is AZ glue, and etching condition is: photoresist thickness is 1.2 ~ 1.7 μm, ultraviolet ray intensity 3 ~ 6,4 ~ 7 seconds time for exposure, reverses 110 ~ 120 DEG C, generally exposes to the sun 50 ~ 70 seconds, develops 40 ~ 70 seconds;

This reversal photoresist is AZ5214, and etching condition is: photoresist thickness is 1.4 μm, ultraviolet ray intensity 5,5 seconds time for exposure, reverses 115 DEG C, generally exposes to the sun 65 seconds, develops 60 seconds.

7. the method for controlled removing Graphene-Metal contact regions residual optical photoresist according to claim 1, is characterized in that, adopt O described in step 3 ₂the photoresist of inorganic layer remained on surface is removed by plasma, and process conditions are O ₂flow 20 ~ 60sccm, power 30 ~ 60W, etch period 1 ~ 5 minute.

8. the method for controlled removing Graphene-Metal contact regions residual optical photoresist according to claim 7, is characterized in that, in described process conditions, and O ₂flow 40sccm, power 20W, etch period 3 minutes.

9. the method for controlled removing Graphene-Metal contact regions residual optical photoresist according to claim 1, it is characterized in that, wet etching is adopted to fall the inorganic layer of Graphene-Metal contact regions described in step 3, corrosive liquid is for being weakly acidic mixed solution, this weakly acidic mixed solution is the dilution of phosphoric acid and the hydrogen peroxide mixed in proportion, and corrosion rate is

10. the method for controlled removing Graphene-Metal contact regions residual optical photoresist according to claim 9, it is characterized in that, the dilution of the described phosphoric acid that mixes in proportion and hydrogen peroxide, mixed proportion is phosphoric acid: hydrogen peroxide: water=1: 1: 9, and described corrosion rate is