A process method for direct growth of patterned graphene on integrated circuit chips

Abstract

The application discloses a process method for directly growing patterned graphene on an integrated circuit chip, and comprises the following steps: attaching an ultrathin single-crystal copper foil to the integrated circuit chip by compression as a base material for catalytically growing graphene; performing patterned treatment on the copper foil through a photoetching and etching process; and placing the chip in a three-temperature-zone thermal CVD system to grow graphene, so that the graphene is only grown in the area covered by the copper foil, thereby achieving the purpose of directly growing patterned graphene on the integrated circuit chip. The method provides a new idea for the development of graphene-based integrated circuits, and is beneficial to accelerating the commercialization application process of graphene.

Description

TECHNICAL FIELD

[0001] The present application relates to a novel graphene preparation process, in particular a process method for directly growing patterned graphene on an integrated circuit chip, and belongs to the field of graphene material preparation. BACKGROUND

[0002] As the first discovered two-dimensional material, graphene has many unique properties, such as zero band gap structure, ultra-high carrier mobility, ultra-strong mechanical properties, good thermal conductivity and high light transmittance, etc., and has broad application prospects in the fields of biology, energy, microelectronics, etc. Integrating graphene devices with mainstream CMOS circuits to form a hybrid integrated circuit system with stronger functions has potential application value for the promotion of graphene technology and the development of the microelectronics field.

[0003] At present, graphene needs to go through two processes of transfer and photolithography in the device preparation process. However, the transfer process inevitably causes the rupture, folding and curling of the graphene film, and the introduction of photoresist in the photolithography process often leads to changes in the doping level of graphene. These seriously affect the reliability and yield of microelectronic devices and limit the commercial application process of graphene, a two-dimensional material with excellent performance. To solve this problem, researchers have proposed to pre-prepare a patterned metal sacrificial layer on the target substrate by sputtering, evaporation and other methods. Graphene only grows on the metal sacrificial layer with catalytic effect, and the areas on the substrate not covered by the metal sacrificial layer will not grow graphene. After the growth is completed, the metal sacrificial layer is removed by wet etching, and finally the graphene is directly prepared on the target substrate without transfer and patterned without photolithography. However, using such methods, good quality graphene can usually be grown at 800℃ or above, which exceeds the tolerable temperature of COMS circuits (below 400℃), and graphene cannot be directly prepared on COMS circuits. Therefore, there is an urgent need to develop a process method for directly growing patterned graphene on an integrated circuit chip. SUMMARY

[0004] The present application aims to provide a process method for directly growing patterned graphene on an integrated circuit chip, which can simultaneously solve the problems of transfer-free growth, photolithography-free patterned growth and low-temperature growth of graphene, and realize compatibility with integrated circuit preparation processes.

[0005] The process method for directly growing patterned graphene on an integrated circuit chip provided by the present application adopts the following technical solution:

[0006] The present application adopts single-crystal super-thin copper foil as the substrate for catalytic growth of graphene, and uses a pressing machine to press the copper foil and the target integrated circuit chip under certain temperature and pressure conditions. Then the copper foil attached to the integrated circuit chip is patterned through photolithography and wet etching process. The integrated circuit chip covered with patterned copper foil is placed in a thermal CVD system for low-temperature growth of graphene. Graphene grows only on the patterned copper foil, and no graphene is generated in the area of the chip not covered by the copper foil. After the growth is completed, PMMA is coated on the surface of the chip as a graphene support layer, and then the copper etching solution is used to remove the copper foil covered by the graphene. Due to the protection of the PMMA support layer, the graphene will not be broken, wrinkled or curled during the etching of the copper device. Then the PMMA is washed away, and finally the patterned graphene directly grown on the integrated circuit chip is obtained.

[0007] Specifically, the following steps are included:

[0008] Step 1) Prepare a single-crystal super-thin copper foil. The thinner the copper foil, the shorter the etching time in the subsequent step of preparing the patterned copper foil, which can minimize the impact of etching and is beneficial to the shape retention of the patterned copper foil.

[0009] Step 2) Cut the super-thin copper foil obtained in step 1) to a size close to or slightly smaller than that of the target integrated circuit chip;

[0010] Step 3) Use a pressing machine to press the copper foil and the target integrated circuit chip under certain temperature and pressure conditions. The copper foil is tightly attached to the surface of the chip after pressing and will not fall off;

[0011] Step 4) Prepare a photoresist mask in the area where graphene needs to be grown through photolithography process;

[0012] Step 5) Use copper etching solution to remove the copper in the area not covered by the photoresist mask where graphene does not need to be grown;

[0013] Step 6) Place the chip sample in a three-zone gradient temperature-controlled thermal CVD system for low-temperature growth of graphene. The front temperature zone in the system is set to high temperature for pyrolysis of the carbon source, the middle temperature zone has a temperature between the front and rear temperature zones as a temperature buffer zone, and the rear temperature zone is set to a low temperature zone for graphene growth;

[0014] Step 7) Spin-coat PMMA on the surface of the chip after graphene growth and dry it as a support layer for graphene;

[0015] Step 8) Immerse the chip in a copper etching solution. The etching solution will slowly etch the underlying copper from the edge of the graphene inward through the PMMA layer until the copper is completely removed;

[0016] Step 9) using deionized water to rinse the remaining etching solution on the chip and dry, clean PMMA with acetone and isopropanol, and finally obtain the patterned graphene directly grown on the integrated circuit chip.

[0017] In the above method, the single-crystal super-thin copper foil has a single crystal orientation, which can be any crystal orientation of copper, preferably Cu(111) and Cu(100). The copper foil can be a commercially available single-crystal copper foil or a single-crystal copper foil made by annealing a polycrystalline copper foil;

[0018] The single-crystal super-thin copper foil has a thickness of not more than 10 μm. The copper foil can be a commercially available super-thin copper foil or a super-thin copper foil made by grinding and polishing a thick copper foil;

[0019] The temperature of the press during the pressing process is 300-400℃;

[0020] The pressure of the press during the pressing process is 200-700 Kg / cm 2 ;

[0021] The time for pressing the copper foil and the target integrated circuit chip is 2-10h;

[0022] The copper etching solution is a copper sulfate / hydrochloric acid solution or a ferric chloride solution;

[0023] The working temperature of the copper etching solution is between room temperature and 60℃;

[0024] The thermal CVD system used for low-temperature growth of graphene is a three-zone tube furnace. When growing, the front (gas inlet end) temperature zone of the tube furnace is set to 900-1200℃, the middle temperature zone is set to 500-800℃, and the rear (exhaust end) temperature zone is set to 200-400℃;

[0025] The target integrated circuit chip is placed in the rear low-temperature zone for graphene growth;

[0026] The spin-coating thickness of the PMMA is 300-800nm;

[0027] The baking temperature of the PMMA after spin-coating is 100-150℃, and the baking time is 5-15min;

[0028] After using deionized water to rinse the remaining etching solution on the chip, the baking temperature of the chip is 100-150℃, and the baking time is 10-30min.

[0029] The present application adopts a pressing method to directly fix an ultrathin single crystal copper foil on an integrated circuit chip, completes the patterning preparation of the single crystal copper foil, combines the advantages of low-temperature growth of graphene of the single crystal copper foil and the gradient temperature control means of the multi-temperature zone tube furnace, and finally realizes the direct growth of a patterned high-quality graphene continuous film on the integrated circuit chip below 400 DEG C. The method provides a new idea for the development of graphene-based integrated circuits and is conducive to accelerating the process of graphene truly moving towards commercial application.

[0030] The present application has the following beneficial effects:

[0031] (1) The present application uses single crystal copper as a catalyst for low-temperature growth of graphene, significantly improves the diffusion of carbon atoms on the surface of the catalyst, solves the problems of non-uniformity, discontinuity and many defects of graphene grown at low temperature in the past, and improves the quality of low-temperature growth of graphene;

[0032] (2) The present application uses a pressing process to prepare a single crystal copper catalyst layer, which is simple in process and does not require high-temperature treatment, and has no limitation on the type of substrate;

[0033] (3) The present application uses conventional methane as a carbon source and uses a low-cost three-temperature zone thermal CVD system as a graphene growth device, without the need for special modification of the device, and can avoid physical damage caused by high-energy plasma bombardment on the surface of graphene and integrated circuit chips;

[0034] (4) The present application uses a thermal CVD system gradient temperature control method, which can not only ensure the efficient cracking of the carbon source, but also maintain the graphene growth zone in a low-temperature state;

[0035] (5) The present application ensures that the temperature of the target substrate during graphene preparation is below 400 DEG C throughout, solving the temperature limitation problem of the compatible process of graphene growth and integrated circuit preparation;

[0036] (6) The present application realizes direct patterned growth of graphene by the method of patterning copper foil, so that the graphene is exempted from transfer and photolithography, reducing the damage and contamination of the graphene. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 It is a schematic diagram of pressing the copper foil and the integrated circuit chip using a press at a certain temperature and pressure, wherein 1 is a press, 2 is a copper foil, and 3 is an integrated circuit chip;

[0038] Figure 2 It is a schematic diagram of the copper foil adhering to the integrated circuit chip after pressing;

[0039] Figure 3 It is a schematic diagram of the copper foil pressed on the integrated circuit chip after patterning;

[0040] Figure 4 Figure 1 is a schematic diagram of a patterned copper foil surface on which graphene is grown, wherein 4 is graphene, and 4 / 2 is graphene grown on a copper foil (the upper layer is graphene, and the lower layer is a copper foil);

[0041] Figure 5 Figure 2 is a schematic diagram of patterned graphene grown directly on an integrated circuit chip after the copper foil is etched away;

[0042] Figure 6 Figure 3 is a Raman spectrum of patterned graphene grown directly on an integrated circuit chip; DETAILED DESCRIPTION

[0043] The present application is described in detail below in conjunction with the accompanying drawings and examples.

[0044] The copper atoms in the single-crystal copper have a uniform lattice arrangement, and there are almost no grain boundaries, which is conducive to the movement and diffusion of carbon atoms on the copper catalyst during low-temperature graphene growth, thereby solving the problem of poor quality of graphene grown at low temperatures. In existing reports, the preparation of a single-crystal copper thin film on a substrate requires a high temperature of 900°C or higher, and the substrate is limited to sapphire. The present application uses a pressing method to fix a single-crystal copper foil with good single-crystallinity on an integrated circuit substrate as a catalyst for low-temperature graphene growth. In combination with a multi-temperature zone thermal CDV system gradient temperature control method for growing graphene, a process method for directly growing patterned graphene on an integrated circuit chip is finally realized. The specific implementation steps are as follows:

[0045] Step 1) A commercially available single-crystal copper (Cu(111)) foil is selected as a catalyst for graphene growth, and the thickness of the copper foil is 6 μm;

[0046] Step 2) The copper foil of step 1) is cut into a size of 1.8*2.3 cm 2 , so that its size is slightly smaller than the size of the target integrated circuit chip (2*2.5 cm 2 );

[0047] Step 3) As shown in Figure 1 , a pressing machine 1 is used to press the copper foil 2 and the target integrated circuit chip 3. During the pressing process, the pressing machine presses the copper foil and the target integrated circuit chip substrate with a pressure of 500 kg / cm 2 , and the two are attached. At the same time, the temperature is raised to 350°C at a rate of 10°C / min and maintained for 4 h, argon is introduced into the cavity of the pressing machine, and the cavity pressure is controlled to 10 Pa by a vacuum system. After the pressing is completed, the copper foil is tightly attached to the surface of the chip and will not fall off, as shown in Figure 2 ;

[0048] Step 4) Photolithography is performed on the sample using ultraviolet photolithography technology, so that the area where graphene needs to be grown is covered by photoresist, and the area where graphene does not need to be grown is directly exposed;

[0049] Step 5) Copper outside the photoresist mask is removed using a copper etching solution (ratio: CuSO4·5H2O:HCl:H2O = 10 g:50 mL:50 mL), and the temperature of the etching solution is heated to 55°C during the etching process, and the etching time is 95 s. After etching is completed, the sample is de-glued and cleaned using acetone, ethanol and deionized water in sequence, and the cleaned sample is as shown in Figure 3

[0050] Step 6) The sample is placed in the rear temperature zone of a three-temperature zone gradient temperature control hot CVD system for graphene growth, the front temperature zone of the system is set to 1000°C, the middle temperature zone is set to 750°C, and the rear temperature zone is set to 350°C, the methane flow is 15 sccm, the hydrogen flow is 9 sccm, the gas pressure is 90 Pa, and the growth time is 40 min. The sample after growth is as shown in Figure 4 At this time, graphene has been grown on the area of the sample surface covered with copper foil, and the area of the sample without copper foil has no graphene generated due to the absence of metal catalysis;

[0051] Step 7) PMMA is spin-coated on the surface of the sample on which graphene growth is completed, the spin-coating thickness is 500 nm, and the sample is baked at 120°C for 10 min after spin-coating;

[0052] Step 8) The sample is immersed in a copper etching solution (ratio: CuSO4·5H2O:HCl:H2O = 10 g:50 mL:50 mL) at room temperature for 3 h to remove the copper residue under the graphene;

[0053] Step 9) The sample is rinsed with deionized water to remove the remaining etching solution and baked at 150°C for 10 min, and the sample is cleaned with acetone and isopropanol in sequence to remove PMMA, and finally patterned graphene directly grown on an integrated circuit chip is obtained, as shown in Figure 5

[0054] We use Raman spectroscopy to characterize the quality of the patterned graphene directly grown on the integrated circuit chip obtained in the embodiment of the application. Figure 6 For the Raman spectrum of graphene, three characteristic peaks of graphene can be clearly observed, namely D peak (~1350 cm -1 ), G peak (~1580 cm -1 ) and 2D peak (~2700 cm -1 ), which indicates that graphene is successfully prepared. The ratio of D peak to G peak (I D / I G ​​) is about 0.1, indicating that the grown graphene contains a small amount of defects, the ratio of 2D peak to G peak (I 2D / I G ) is about 1, indicating that the graphene is close to bilayer graphene. In summary, it can be known from the above that the process method provided by the application can successfully grow patterned graphene on an integrated circuit chip. Figure 6

[0055] The embodiments described in the application are only for exemplary purposes, and are not used to limit the protection scope of the application, and other alternatives, changes and improvements can be made by those skilled in the art within the scope of the application, so the application is not limited to the above embodiments, but only limited to the claims.​

Claims

1. A process method for direct growth of patterned graphene on an integrated circuit chip, the process method comprising: The method comprises the following steps: ​ Step 1) preparing a single-crystal super-thin copper foil, the thinner the copper foil, the shorter the etching time in the subsequent step of preparing a patterned copper foil, so that the etching can be avoided and the shape of the patterned copper foil can be preserved; Step 2) cutting the super-thin copper foil obtained in step 1) to have a size close to or slightly smaller than that of a target integrated circuit chip; Step 3) pressing the copper foil and the target integrated circuit chip under certain temperature and pressure conditions by using a pressing machine, so that the copper foil is tightly attached to the surface of the chip and will not fall off after the pressing is completed; Step 4) preparing a photoresist mask in a region where graphene is needed to be grown by using a photolithography process; Step 5) removing the copper in a region other than the photoresist mask where graphene is not needed to be grown by using a copper etching solution; Step 6) placing the chip sample in a three-temperature-zone gradient temperature control thermal CVD system to grow graphene at a low temperature, the front temperature zone in the system is set to a high temperature for pyrolyzing a carbon source, the middle temperature zone has a temperature between the front and rear temperature zones and is used as a temperature buffer zone, and the rear temperature zone is set to a low temperature zone for growing graphene; Step 7) spin-coating PMMA on the surface of the chip on which the graphene growth is completed and drying the PMMA to serve as a support layer of the graphene; Step 8) immersing the chip in a copper etching solution, the etching solution will slowly etch the underlying copper from the edge of the graphene through the PMMA layer until the copper is completely removed; Step 9) cleaning the chip with deionized water to remove the residual etching solution and drying the chip, and using acetone and isopropyl alcohol to clean the PMMA, so that a patterned graphene directly grown on the integrated circuit chip is finally obtained; The single-crystal super-thin copper foil is a copper foil with a single crystal direction, the crystal direction is any crystal direction of copper, and the thickness is not more than 10 μm; The single-crystal copper foil for catalytically growing graphene is attached to the integrated circuit chip by using a pressing machine; The temperature of the press during the pressing process is 300-400 °C, and the pressure applied by the press is 200 - 700 Kg / cm 2 ; The pressing time of the copper foil and the target integrated circuit chip is 2-10 h; The copper etching solution is a copper sulfate / hydrochloric acid solution or a ferric chloride solution; The working temperature of the copper etching solution is between room temperature and 60 ℃; The thermal CVD system for growing graphene at a low temperature is a three-temperature-zone tube furnace, when growing, the temperature of the front temperature zone of the tube furnace is set to 900-1200 ℃, the temperature of the middle temperature zone is set to 500-800 ℃, and the temperature of the rear temperature zone is set to 200-400 ℃; The spin-coating thickness of the PMMA is 300-800 nm; The drying temperature of the spin-coated PMMA is 150 ℃, and the drying time is 10 min.

2. The process method of claim 1, wherein: After the chip is cleaned with deionized water to remove the residual etching solution, the drying temperature of the chip is 100-150 ℃.

3. The process for direct growth of patterned graphene on integrated circuit chips according to claim 1 or 2, wherein: After the chip is cleaned with deionized water to remove the residual etching solution, the drying time of the chip is 10-30 min.

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