KR100577287B1 - Nondestructive dopant profiler and its frequency modulated rf capacitance sensor - Google Patents

Abstract

The present invention uses a frequency modulation RF capacitance sensor as a capacitive sensing method, and directly measures the capacitance change amount (dC / dV) in the measured sample by non-destructive without cutting the measured sample. Is a non-destructive doping profile measuring device (nano-CV) that can quantitatively extract not only one-dimensional but also two-dimensional and three-dimensional doping profiles by comparing with the capacitance change (dC / dV) calculated through accurate physical modeling. And relates to the RF capacitance sensor of the frequency modulation method applied thereto,

The measuring device includes a nano probe positioned on a surface of a wafer to be measured, an RF capacitance sensor measuring capacitance varying according to a bias voltage applied between the probe and the wafer, and a minute voltage output from the RF capacitance sensor. LIA for measuring a signal, and a computer console for quantitatively extracting a doping profile by comparing the signal output from the LIA and the value calculated through nano-CV modeling. In this case, the RF capacitance sensor is composed of a VCO supply line for supplying the oscillation frequency of the 1.7GHz band, a microstrip resonator, a line for detecting the change in capacitance, and converts the capacitance change in these lines into frequency and again To detect the voltage, an Rf mixer and a frequency demodulation PLL circuit are added to form a detection circuit.

Description

Non-destructive doping profile measuring device and frequency modulated RF capacitive sensor applied to it {NONDESTRUCTIVE DOPANT PROFILER AND ITS FREQUENCY MODULATED RF CAPACITANCE SENSOR}             

1 is a view showing the basic configuration of a typical scanning capacitance microscope (SCM) system

2 is a view schematically showing the configuration of a doping profile measuring apparatus implemented by a preferred embodiment of the present invention

3 is a view showing an example of manufacturing the RF capacitance sensor according to the present invention as a PCB substrate

4 is an equivalent circuit diagram of an RF capacitance sensor used for extracting resonance parameters in a preferred embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

10: probe 20: RF capacitance sensor

21: VCO supply line 22: micro strip resonator

23: detection line (RF stage) 24: voltage controlled oscillator

25: crystal oscillator (TCXO) 26: PLL module for the reference frequency supply

27: Rf Mixer 23: PLL for Frequency Demodulation

30: LIA 40: Computer

The present invention relates to a non-destructive doping profile measuring apparatus for quantitative multi-dimensional doping profile measurement in the semiconductor manufacturing field, and to the RF capacitance sensor of the frequency modulation method applied thereto, according to the miniaturization and speed of the device that did not appear in the conventional micron era In order to consider various influences and predict / analyze these effects, the non-destructive doping profile measuring device that predicts not only one-dimensional and two-dimensional but also three-dimensional doping profiles and frequency modulated RF capacitance sensors applied thereto. It is about.

The current semiconductor technology is rapidly becoming ultra fine, highly integrated and highly functional thanks to the development of micro process technology, and has already entered the world of nanometer (nanometer = 0.001 micron) beyond the existing micron technology. Therefore, in developing next-generation devices, it is necessary to consider various effects of the miniaturization and speed of these devices, which did not appear in the existing micron era, and to predict / analyze these effects in advance. In addition, in order to prepare for the upcoming nano era, the successful development of a technology or device capable of analyzing defects or components of ultra-fine devices must be an essential element technology.

Among these key elements, the doping profile measurement field is to investigate the dopant state injected into the semiconductor not only in the depth direction (1 dimension) but also in the lateral direction (2 dimension) and even in three dimensions. It is an essential technology for characterization.

Until now, the device has been used to measure the device's one-dimensional doping profile using the destructive Secondary Ion Mass Spectrometry (SIMS) analysis device. Accurate control of SIMS depth-profiling conditions, such as ion beam mixing control by ions and sample atoms, is required to improve existing SIMS performance. It is difficult to measure.

Several researches have been conducted to develop the next generation of two-dimensional doping profile measuring devices such as tomographic SIMS, nano-SRP (spreading resistance profiling) and scanning capacitance microscopy (SCM) to replace one-dimensional SIMS measuring devices. Although there are many results in the field of image analysis of dimensional doping profile or quantitative analysis of doping profile, the results are not extracted reproducibly. Among them, the SCM measurement method has excellent sensitivity and high horizontal / vertical resolution (10 nm), so that not only surface analysis such as dopant imaging (e.g., image of effective gate channel length or junction depth) but also two-dimensional doping profile can be obtained. Much research has been done on quantification.

However, compared to the field of dopant imaging, standardized measurement methods for quantitative analysis of the three-dimensional effects at the mask edges and edges and the unplanarization of the doping profile due to the reduction of device isolation area have to be solved. Due to the problem, it is not presented yet.

Current SCM technology is destructive because it measures the cross section of the measurement sample and is too sensitive to the environment around the measurement due to the complexity of the sample preparation process and the depletion layer capacitance generated by the tiny SCM probe. Problems such as lack of reproducibility, difficulty in interpreting accurate SCM measurement data, and verifying accuracy of SCM modeling remain challenges.

The present invention is a system that can directly measure in the actual structure, not the test structure, to ensure reliability and reproducibility through a non-destructive method, and to accurately quantify the doping profile by analyzing the measurement results accurately.

1 is a diagram illustrating a configuration of an existing SCM measuring apparatus.

As shown in FIG. 1, the conventional SCM system uses an AFM as a platform, and a UHF capacitance sensor 2 for processing an electrical signal and a conductive probe (Pt / Ir plating) at the bottom of the AFM cantilever 1 and It is composed of DSP LIA (Lock-In Amplifier) (3) which can measure very fine signal.

In the above, the UHF capacitance sensor 2 is composed of an oscillator, an LC resonator, and a detection circuit, and finds a minute signal using the resonance state of the system. Since the LC resonator is directly connected to the probe at the bottom of the AFM cantilever 1, the overall resonant frequency of the system is determined by the parasitic capacitance between the probe and the measuring wafer 4. When AC bias is applied to the measurement wafer 4 in this state, the depletion layer capacitance due to depletion layer generation changes, so that the resonance frequency of the system is changed, and this minute amplitude change is detected using a detection circuit.

Briefly, the operation of attaching the UHF capacitance sensor 2 to the AFM cantilever 1 determines the total resonant frequency of the system, which is determined by the parasitic capacitance between the probe and the measured sample. When only the dc bias is applied, the value of the depletion layer capacitance generated in the semiconductor is too small to obtain an absolute value. Accordingly, the signal is modulated by applying an ac bias to the measurement sample to obtain the amount of change in capacitance while the dc bias is applied. At this time, since only the capacitance change dC that varies between the probe and the measurement sample by the applied ac bias voltage is modulated by dV (change of the ac bias voltage), only the actual modulated value regardless of parasitic capacitance or ambient noise You can get it. LIA (3) is used to obtain these values. Accordingly, the measurement result is a change in capacitance with respect to the applied ac bias, that is, dC / dV.
In FIG. 1, AFM (Automatic Force Microscopy) is a device that shows surface information of a sample by measuring attraction or repulsive force between the probe and the sample (4), which is located under the AFM cantilever (1) Proximity of the probe to the surface of the sample 4 to take advantage of the force between the atoms of the probe results in a pull or push force depending on the distance between them. When the probe is attached to a curved object such as a diving board called the AFM cantilever 1, the AFM cantilever 1 is easily released by the force acting between the atoms of the probe and the atoms of the sample 4.
If the degree of the AFM cantilever 1 is known, the contour of the sample 4 can be identified. At this time, the degree of 측정 is measured through the angle reflected by shooting a laser (laser) on the AFM cantilever (1), at this time using a photodiode (Photodiode). The X and Y scanners are used to measure the sample 4 while moving in the X direction or the Y direction, and the topography of the surface is photographed through a feedback loop. The Z scanner is used to position the probe in the Z direction.

As a result, the conventional SCM technique is destructive because it measures the cross section of the measurement sample, and there is a problem that the preparation process of the sample is complicated.

In addition, the image by the conventional SCM system is sensitive to changes due to the movement of the flow charge and the humidity of the surroundings even when a constant dc bias is applied, there is a problem that can not secure the reproducibility of the image.

The present invention has been made to solve the above problems of the prior art, the object of which is not a special test structure to predict not only the measurement of one-dimensional, two-dimensional doping profile but also three-dimensional doping profile, not the actual three-dimensional structure To provide a non-destructive doping profile measuring device that can be applied directly to the RF capacitance sensor applied to the frequency modulation method applied thereto.

In addition, another object of the present invention is to measure the change in capacitance (dC / dV) directly on the wafer, and compare the multi-dimensional doping profile by comparing the value of the change in capacitance (dC / dV) calculated through accurate physical modeling The present invention provides a non-destructive doping profile measuring apparatus which can be quantitatively extracted, and an RF capacitance sensor of a frequency modulation method applied thereto.

In addition, another object of the present invention is to use a non-destructive doping profile that can measure a more accurate and reproducible doping profile using the RF capacitance sensor having a newly designed operating frequency of 1.7GHz band by modifying the operating frequency and detection characteristics The present invention provides a profile measuring device and an RF capacitance sensor of a frequency modulation method applied thereto.

In addition, another object of the present invention is a non-destructive doping profile measuring device and a frequency modulation method applied to the non-destructive method to apply the frequency modulation (frequency modulation) method as a capacitance detection method to improve the capacitive sensing ability It is to provide a capacitance sensor.

According to a first aspect of the present invention for achieving the above object, the nano-probe positioned on the surface of the wafer to be measured, and the electrical characteristics (capacitance) vary depending on the bias voltage applied between the nano-probe and the wafer The nano-capacitance sensor for measuring and outputting different voltage signals accordingly, the LIA (Lock-In Amplifier) for measuring the minute voltage signal output from the RF capacitance sensor, and receives the signal output from the LIA nano CV The present invention provides a non-destructive doping profile measuring apparatus including a computer which quantitatively extracts a doping profile by comparing with a value calculated through modeling.

In this case, according to an additional feature of the present invention, the RF capacitance sensor is composed of a VCO supply line for supplying the oscillation frequency of 1.7GHz band, a micro strip resonator, a detection line for detecting the capacitance change, these lines It is preferable that the circuit is composed of a detection circuit including an Rf mixer and a frequency demodulation PLL for detecting a change in capacitance through a frequency difference.

On the other hand, according to a second aspect of the present invention for achieving the above object, in the RF modulation sensor of the frequency modulation method applied to the non-destructive doping profile measuring device for quantitative multi-dimensional doping profile measurement,

It consists of a VCO supply line for supplying the oscillation frequency of 1.7GHz band, a microstrip resonator, and a detection line for detecting the change of capacitance, and the detection circuit connected to the detection line includes the inside of the wafer according to the bias applied to the semiconductor. Frequency applied to a non-destructive doping profile measuring device comprising an Rf mixer for detecting a change in capacitance generated by a frequency difference and a PLL for frequency demodulation converting an output value of the Rf mixer into a change in voltage. The present invention provides a modulated RF capacitance sensor.

In this case, according to an additional feature of the present invention, the frequency supply module includes a voltage controlled oscillator (VCO) for supplying a variable oscillation frequency in the 1.7 GHz band and a crystal oscillator (TCXO) for supplying a constant reference frequency in the 1.7 GHz band; It is preferable to include a PLL module for supplying a reference frequency.

The above objects and various advantages of the present invention will become more apparent from the preferred embodiments of the present invention described below with reference to the accompanying drawings by those skilled in the art.

Hereinafter, a preferred embodiment according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a view schematically showing the configuration of a doping profile measuring apparatus implemented by a preferred embodiment of the present invention, Figure 3 is a view showing an example of manufacturing an RF capacitance sensor according to the present invention as a PCB substrate 4 is an equivalent circuit diagram of an RF capacitance sensor used for extracting resonance parameters in a preferred embodiment of the present invention.

2 and 3, reference numeral 10 denotes a probe positioned on a surface of a wafer to be measured, and 20 denotes a probe that is different from each other according to electrical characteristics between the probe 10 and the wafer. An RF capacitance sensor outputs a voltage signal, and 30 denotes a lock-in amplifier (LIA) for measuring a change in capacitance by measuring a minute voltage signal output from the RF capacitance sensor 20 (40). ) Denotes a computer that receives a signal output from the LIA 30 and creates a doping profile.

In the above, the RF capacitance sensor 20 detects the VCO supply line 21, the microstrip resonator 22, and the capacitance change as the frequency difference, as shown in FIG. 3, to supply the oscillation frequency in the 1.7 GHz band. It consists of a detection line 23 for the purpose of being connected to the RF mixer. In this case, the frequency supply module provided to the RF mixer input includes a voltage controlled oscillator (VCO) 24 for supplying a variable oscillation frequency in the 1.7 GHz band and a crystal oscillator (TCXO) 25 for supplying a constant reference frequency in the 1.7 GHz band. ) And a PLL module 26 for supplying a reference frequency.

As the detection circuit connected to the detection line 23, an Rf mixer 27 and a frequency demodulation PLL 28 were used.

In general, the width of the line in the micro strip preference means the impedance, so the wider the width, the smaller the impedance, the narrower the impedance, the larger the impedance. In addition, the length of the line is designed to be proportional to the wavelength, such as 1/4, 1/8 of the wavelength.

The RF capacitance sensor 20 according to the present invention is designed to detect a very small capacitance change even in a high concentration region of 10 ¹⁸ cm ^-3 or more by increasing the operating frequency, and to detect the capacitance change of the depletion layer. Frequency modulation is applied instead of amplitude modulation.

4 is an equivalent circuit diagram of an RF capacitance sensor used in a circuit simulation to determine the resonant frequency in the micro strip resonator 22. Here, the resonance parameters were extracted by simulating changes in the characteristics of the substrate, the length of the resonator, the wire length from the end of the resonator to the output terminal, and the parasitic capacitance.

In FIG. 4, two parallel capacitance models connected to the resonator are equivalent circuits that assume parasitic capacitance existing between the probe and the measurement wafer and capacitance due to semiconductor depletion, and the total capacitance of the system is 0.1pF. Calculated.

In addition, the wire connecting the RF capacitance sensor and the nano probe is assumed to be 0.0025cm in diameter, and the impedance of the resonator is open, so the impedance is 50GΩ.

In the above, the Rf mixer 27 receives signals having different frequencies f1 and f2 and multiplies the two signals in the mixer circuit and outputs the result. At this time, signals having various frequency components are output. The signal types considered mainly include the frequency components f1 and f2 of each input signal, the sum (f1 + f2) and the difference (f1-f2) frequencies of these input signals. It is a component, and among these signals, only a desired frequency can be selected using a filter. Rf mixer 27 used in the present invention outputs a frequency change (Δf) according to the change in the depletion layer capacitance (ΔC), the frequency range that can be used at the input terminal is 1MHz to 2500MHz, which can be obtained at the output stage The frequency range was a frequency mixer with electrical specifications up to DC-500MHz.

In addition, the frequency demodulation PLL 28 is a feedback circuit composed of a phase detector, a loop filter, and a voltage controlled oscillator (VCO), and serves to lock or synchronize a received signal. In the present invention, the frequency change Δf corresponding to the change in the depletion layer capacitance ΔC output from the Rf mixer 27 is input and converts the output value into a change in voltage ΔV.

While the invention has been shown and described with respect to particular embodiments, it will be appreciated by those skilled in the art that various modifications and changes can be made without departing from the spirit and scope of the invention as set forth in the appended claims. Anyone can grow up easily.

As described above, the non-destructive doping profile measuring apparatus of the present invention and the frequency modulation RF capacitance sensor applied thereto measure the change amount of capacitance (dC / dV) directly on the wafer and calculate it through accurate physical modeling. Compared with the value of the capacitance change (dC / dV), the multi-dimensional doping profile can be extracted quantitatively.

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In addition, it is possible to measure a more accurate and reproducible doping profile by using an RF capacitance sensor having an operating frequency of 1.7GHz band by modifying the operating frequency and sensing characteristics.

In addition, by applying a frequency modulation method as a capacitive sensing method has the effect of improving the capacitive sensing capability.

Claims (4)

An nano-capacitance sensor for measuring a nano-probe positioned on the surface of the wafer to be measured, an electrical characteristic (capacitance) which varies according to a bias voltage applied between the nano-probe and the wafer, and outputting a different voltage signal accordingly; Computer for quantitatively extracting doping profile by comparing LIA (Lock-In Amplifier) for measuring minute voltage signal output from RF capacitance sensor and receiving signal output from LIA and comparing with calculated value through nano CV modeling Non-destructive type doping profile measuring apparatus, characterized in that comprises a. The method of claim 1, The RF capacitance sensor is composed of a VCO supply line for supplying an oscillation frequency in the 1.7 GHz band, a micro strip resonator, and a line for detecting a change in capacitance. A non-destructive doping profile measuring device comprising: an Rf mixer and a frequency demodulation PLL for detection. In the frequency modulation RF capacitance sensor applied to the non-destructive doping profile measuring device, It consists of a VCO supply line for supplying the oscillation frequency of 1.7GHz band, a microstrip resonator, and a detection line for detecting the change of capacitance, and the detection circuit connected to the detection line includes the inside of the wafer according to the bias applied to the semiconductor. A non-destructive doping profile measuring device comprising an Rf mixer for detecting a change in capacitance generated by a frequency difference and a PLL for frequency demodulation converting an output value of the Rf mixer into a change in voltage. RF capacitance sensor applied to the frequency modulation method. The method of claim 3, wherein The frequency supply module includes a voltage controlled oscillator (VCO) for supplying a variable oscillation frequency in the 1.7 GHz band, a crystal oscillator (TCXO) for supplying a constant reference frequency in the 1.7 GHz band, and a PLL module for supplying a reference frequency. RF capacitance sensor of the frequency modulation method applied to the non-destructive doping profile measuring apparatus.

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