CN102507875A - Method for quickly and nondestructively measuring thickness and band structure of graphene film - Google Patents

Abstract

The invention belongs to the technical field of semiconductor integrated circuit manufacturing, in particular to a method for rapidly and non-destructively measuring the thickness and energy gap of graphene films. The present invention first utilizes ellipsometry to obtain the ellipsometric data of the film; then establishes a suitable theoretical model according to the structure of the measured film, analyzes and fits the obtained ellipsometric data, and obtains the thickness and energy band of the measured graphene film structure. The invention greatly simplifies the complexity of the thickness test of the ultra-thin film in the past, reduces the difficulty of using other technical processes, and has important application value in the manufacture of large-scale integrated circuits after 22 nanometers.

Description

A rapid and non-destructive method for measuring the thickness and band structure of graphene films

technical field

The invention relates to a method for measuring the thickness and energy band structure of a graphene film, in particular to a method for rapidly and non-destructively measuring the energy band structure of a graphene film applied in the manufacture of large-scale integrated circuits after 22 nanometers, belonging to the manufacture of semiconductor integrated circuits technology field.

Background technique

With the continuous development of semiconductor technology, the continuous extension and depth of Moore's Law has made the size of silicon-based integrated circuit devices closer and closer to its physical limit. The international semiconductor development roadmap ITRS has planned MOSFET materials and processes in 16nm feature size technology, among which the most important thing in MOSFET is the selection and control of the gate oxide layer, such as TiO ₂ , aluminum-doped titanium oxide, hafnium oxide, oxide Zirconium et al. However, how to conduct non-destructive and rapid quality assessment of ultra-thin films (physical thickness <10 nm), especially the measurement of energy band structure, is an important issue.

Establishing a rapid and non-destructive nanoscale quality assessment method for ultra-thin films based on optical methods combined with physical calculations is one of the important factors to improve the process yield of large-scale integrated circuits after 22 nm.

Contents of the invention

The object of the present invention is to propose a method for fast and non-destructive measurement of graphene film thickness and energy band structure with wide surface area and high measurement accuracy, so as to solve the band structure measurement and thickness fitting in the process of adjusting the energy gap.

The method for fast and non-destructive measurement of graphene film thickness and energy gap proposed by the present invention is based on optical methods combined with physical calculations. The specific steps include:

Provide the graphene film that needs to be measured;

Utilize ellipsometry to obtain the ellipsometric data of described graphene film;

Establish a suitable theoretical model according to the structure of the graphene film;

On the basis of the established theoretical model, the obtained ellipsometric data are analyzed and fitted to obtain the energy band structure analysis of the graphene film.

Further, the graphene thin film is several layers of ultra-thin films such as reduced graphene oxide film (FRGO) and GO. The said theoretical model is a Lorentz oscillator model.

Based on the theoretical basis of density functional (DFT) simulation calculations, the present invention selects a suitable model (such as the Lorentz oscillator model), and uses ellipsometry to detect the defect energy levels in ultra-thin graphene films, and provides a Non-destructive and non-contact probing methods for studying band structure gradients in graphene thin films. Non-destructive and non-contact optical detection can break through the limitations of all current process conditions, and can be directly integrated on graphene film growth equipment such as ALD or CVD, so that the energy gap can be monitored and controlled in situ.

The present invention greatly simplifies the complexity of previous graphene thin film energy gap change testing, reduces the difficulty of using other technical processes, and can significantly increase the detection speed compared with other technical means, and is of great importance in the manufacture of large-scale integrated circuits after 22 nanometers. Value.

Description of drawings

Figure 1 shows the structure of the graphene film measured by ellipsometry.

Figure 2(a)(c) is the experiment (solid line) and fitting curve of the ellipsometric parameters of GO and FRGO films, (b)(d) is the refractive index n and extinction coefficient k obtained from the fitting of GO and FRGO .

Figure 3 shows (a) (c) the experimental and fitting curves (points) of the ellipsometric parameters of GO and FRGO thin films, (b) (d) the refractive index n and extinction coefficient k obtained from the fitting of GO and FRGO .

Fig. 4 is a diagram showing the change of energy band structure during the reduction process of graphene oxide.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. The method for measuring the energy gap gradient of graphene thin films proposed by the present invention can be applied to the measurement of electronic energy gaps of graphene thin films such as FRGO and GO. What is described below takes the detection of energy gap changes before and after the reduction of GO thin films as an example. process flow.

First, a SiO ₂ thin film 102 is grown on a silicon substrate 101 , and then GO or FRGO is transferred onto the SiO ₂ to form a thin film 103 , as shown in FIG. 1 .

Next, the ellipsometric data of GO and FRGO thin films were obtained by ellipsometry, and the spectra of GO and FRGO thin films are shown in the solid lines in Figure 2(a)(c).

Next, establish a theoretical model, here we use the classic Lorentz oscillator model for analysis. The complex permittivity described by the Lorentz oscillator can be expressed as:

This is the Lorentz model. In the formula, ε _∞ is the high-frequency dielectric constant, which corresponds to the value of the permittivity at high energy in the far ultraviolet, ε ₁ is the real part of the complex permittivity, and ε ₂ is the imaginary part of the complex permittivity. A _i is the weight factor of oscillation, C _i is the center energy, ν _i is the damping coefficient, E is the photon energy, A _i , C _i , ν _i are unknown quantities, and the unit is eV. The value of the weight factor A _i represents the proportion of the vibrator i in the entire oscillation system, and the central energy C _i can have different meanings in different systems. The refractive index n and extinction coefficient k of the material can be obtained from the complex permittivity:

。

.

Next, the obtained ellipsometric data are analyzed and fitted on the basis of the established Lorentz model. Use 2-5 order oscillators to minimize the deviation between the fitting variance and the measured value. The fitting results are shown in Figure 3. The graphs (a) and (c) correspond to GO and FRGO respectively. The solid line in the figure represents the ellipse of the experimental measurement. Offset values Δ and Ψ, solid points are obtained by fitting according to the Lorentz oscillator model. It can be seen that the fitting value is in good agreement with the experimental value, and the electronic defect level parameters obtained after fitting are shown in Table 1.

Due to the coverage of different groups, the energy gaps of GO are 1.8 eV, 2.1 eV, and 2.8 eV, as shown in Figure 4. According to the definition of A _i in the Lorentz model, it can be considered that it represents the probability of electronic states with different coverages of different groups in GO. From the above table, we can see that A4, which represents the probability of the electronic state, is dominant in the sample, indicating that in the sample GO thin film, the coverage corresponding to 1.8 eV is the most probable, and the coverage corresponding to 2.8 eV also occupies a certain weight . A3 remains at a small level, indicating that the coverage corresponding to 2.1 eV is almost non-existent. For FRGO, except for the characteristic energy level of exciton oscillation of 4.6 eV and the plasmon oscillation level of π bond of 4.7 eV, 0.02 eV is a very heavy oscillator, which represents the energy of the in-band transition of FRGO obtained by fitting.

As mentioned above, many widely different embodiments can be constructed without departing from the spirit and scope of the present invention. It should be understood that the invention is not limited to the specific examples described in the specification, except as defined in the appended claims.

Table 1

go FRGO d (nm) 9.08±0.049 4.10±0.027 _ε∞ 3.2217±0.0017 2.903±0.069 A ₁ 2.0215 2.5334±0.094 C ₁ (eV) 2.8032±0.133 4.6002±0.032 A ₂ 1.4385±0.0051 2.697±0.061 C ₂ (eV) 5.0031±0.0762 0.02±0.005 A ₃ 0.4366±0.0037 0.0955±0.004 C ₃ (eV) 2.1493±0.064 4.7±0.047 A ₄ 6.8171±0.2475 C ₄ (eV) 1.8325±0.052

Claims (3)

1. a method for measuring graphene film thickness and energy band structure, is characterized in that concrete steps are: (1) Provide the ultra-thin graphene film that needs to be measured; (2) Obtaining the ellipsometric data of the graphene film by ellipsometry; (3) establishing a suitable theoretical model according to the structure of the graphene film; (4) Analyzing and fitting the obtained ellipsometric data on the basis of the established theoretical model to obtain the thickness and energy band structure of the graphene film. 2. the method for measuring graphene film thickness and energy gap according to claim 1, is characterized in that, described ultra-thin film is the graphene oxide film of several layer reductions. 3. the method for measuring graphene thin film thickness and energy gap according to claim 1, is characterized in that, described theoretical model is Lorentz oscillator model; The complex dielectric constant described with Lorentz oscillator model is expressed as:

In the formula, ε _∞ is the high-frequency dielectric constant, which corresponds to the value of the permittivity at high energy in the far ultraviolet, ε ₁ is the real part of the complex permittivity, ε ₂ is the imaginary part of the complex permittivity; A _i is The weight factor of oscillation, C _i is the center energy, ν _i is the damping coefficient, E is the photon energy, A _i , C _i , ν _i are unknown quantities, and the unit is Ev; the value of the weight factor A _i indicates that the vibrator i is in The proportion of the entire oscillating system; the complex refractive index of the material is obtained from the complex permittivity: .

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