WO2007088587A1

WO2007088587A1 - Semiconductor measuring apparatus and semiconductor measuring method

Info

Publication number: WO2007088587A1
Application number: PCT/JP2006/301545
Authority: WO
Inventors: Keizo Yamada; Yeong Uk Ko
Original assignee: Topcon Corporation
Priority date: 2006-01-31
Filing date: 2006-01-31
Publication date: 2007-08-09
Also published as: KR101085413B1; JPWO2007088587A1; CN101356635A; KR20080079672A; JP5005551B2; CN101356635B

Abstract

Provided is a semiconductor measuring apparatus which can evaluate complicated fine structures by two-dimensionally scanning the surface of a semiconductor substrate whereupon a fine structure is formed with an electron beam and measuring a substrate current of that time. The semiconductor measuring apparatus is configured to irradiate a semiconductor substrate with an electron beam and obtain an evaluation value of a fine structure formed on the semiconductor substrate from a substrate current induced to the semiconductor substrate by the electron beam. The semiconductor measuring apparatus is characterized in that the apparatus is provided with an evaluating means for obtaining the evaluation value of the fine structure based on the waveform of the substrate current when the waveform of the substrate current is regarded as a differential waveform.

Description

Specification

Semiconductor measuring apparatus and semiconductor measuring method

Technical field

TECHNICAL FIELD [0001] The present invention relates to a semiconductor measurement apparatus and a semiconductor measurement method using an electron beam, and particularly to a measurement technique suitable for evaluating a fine structure such as a contact hole. Background art

[0002] One of the fine structures of semiconductor devices is a contact hole. This contact hole forms part of a wiring structure for electrically connecting, for example, a transistor and another electric element formed in the silicon substrate. As a method for measuring the structure of this contact hole, a method using an electron beam is generally used, and CD SEM is widely known as this type of apparatus.

[0003] According to the above-described CDSEM, the surface of a semiconductor substrate on which a microstructure to be measured is formed is scanned in a line shape with an electron beam, and secondary electrons generated at that time are detected and a fine waveform is obtained from a waveform. Measure the structure. This secondary electron waveform contains information about the edge of the microstructure, and this edge is recognized as a contrast difference.

[0004] On the other hand, in the case of a hole structure with a high aspect ratio, the conventional CDSEM cannot efficiently capture secondary electrons from the inside of the hole, and thus cannot accurately grasp the internal structure of the hole. As a technique for solving such a problem, EBSCOPE using substrate current instead of secondary electrons has appeared (see Patent Document 1).

[0005] According to the above-mentioned EBSCOPE, the surface of the semiconductor substrate is scanned with an electron beam, and the waveform force of the substrate current generated at that time is determined. Here, since the substrate current is induced by the electron beam that has passed through the inside of the hole and reached the semiconductor substrate, this substrate current includes information on the internal structure of the hole. From the current waveform, You can know the internal structure of the hall.

Patent Document 1: Japanese Patent Laid-Open No. 2005-026449

Disclosure of the invention

Problems to be solved by the invention [0006] However, according to EBSCOPE according to the above-described conventional technology, when the hole bottom structure is simple, it is easy to grasp the hole bottom structure from the observed substrate current waveform. There are various residual films such as oxide film and nitride film on the bottom, and the more complicated the structure of the hole bottom, the more complicated the waveform of the observed substrate current. There was a problem that it was difficult to measure the structure of the film correctly.

[0007] An object of the present invention is to provide a semiconductor measuring apparatus capable of correctly measuring the structure of the hole bottom even if the structure of the hole bottom is complicated.

Means for solving the problem

In order to solve the above-described problem, a semiconductor measurement apparatus according to the present invention irradiates a semiconductor substrate with an electron beam, and forms a fine pattern formed on the semiconductor substrate from a substrate current induced in the semiconductor substrate by the electron beam. A semiconductor measurement apparatus configured to obtain an evaluation value of a structure, wherein the evaluation value of the microstructure is obtained based on a waveform of the substrate current when the waveform of the substrate current is regarded as a differential waveform Means are provided.

[0009] In the semiconductor measurement apparatus, the fine structure is a hole, and the evaluation means extracts the waveform force of the substrate current and the edge of the hole.

In the semiconductor measuring apparatus, the evaluation unit calculates an evaluation value of the hole from an edge of the hole.

In the semiconductor measurement apparatus, the evaluation unit extracts a peak force of the waveform of the substrate current and an edge of the hole.

The semiconductor measurement apparatus according to the present invention irradiates a semiconductor substrate with an electron beam, and obtains an evaluation value of a microstructure formed on the semiconductor substrate from a substrate current induced in the semiconductor substrate by the electron beam. The semiconductor measurement apparatus configured as described above includes an evaluation unit that obtains an evaluation value of the microstructure based on an integrated waveform of the substrate current when the waveform of the substrate current is regarded as a differential waveform. It is characterized by.

[0011] In the semiconductor measurement apparatus, the fine structure is a hole, and the evaluation unit extracts the integrated waveform force and an edge of the hole.

In the semiconductor measuring apparatus, the evaluation unit calculates an evaluation value of the hole from an edge of the hole. The semiconductor measurement apparatus according to the present invention irradiates a semiconductor substrate with an electron beam, and obtains an evaluation value of a microstructure formed on the semiconductor substrate from a substrate current induced in the semiconductor substrate by the electron beam. A semiconductor measurement apparatus configured as described above, wherein an equivalent circuit of the microstructure is specified based on a waveform of the substrate current, and an evaluation value of the microstructure is obtained based on a waveform obtained using the equivalent circuit An evaluation means is provided.

[0013] In the semiconductor measurement apparatus, the fine structure is a hole, and the evaluation unit extracts a waveform force obtained by using the equivalent circuit, and an edge of the hole is extracted.

The semiconductor measurement method according to the present invention irradiates a semiconductor substrate with an electron beam, and obtains an evaluation value of a microstructure formed on the semiconductor substrate from a substrate current induced in the semiconductor substrate by the electron beam. A semiconductor measurement method is characterized in that an evaluation value of the microstructure is obtained based on a waveform of the substrate current when the waveform of the substrate current is regarded as a differential waveform.

The invention's effect

[0015] According to the present invention, it is possible to correctly measure the structure of the hole bottom even if there is a residual film on the hole bottom.

Brief Description of Drawings

FIG. 1 is a configuration diagram of a semiconductor measuring device according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing the flow of operation of the semiconductor measuring apparatus according to the first embodiment of the present invention.

FIG. 3A is a diagram showing a first example of a hole structure (normal structure) to be measured according to the first embodiment of the present invention.

FIG. 3B is a diagram showing a second example of a hole structure (a structure having a gate) to be measured according to the first embodiment of the present invention.

FIG. 3C is a diagram showing a third example of a hole structure (a structure having a floating gate) to be measured according to the first embodiment of the present invention. FIG. 4A] A diagram showing a first example of a waveform of the substrate current observed by the semiconductor measuring device according to the first embodiment of the present invention.

FIG. 4B] A diagram showing a second example of the waveform of the substrate current observed by the semiconductor measuring device according to the first embodiment of the present invention.

FIG. 4C] A diagram showing a third example of the waveform of the substrate current observed by the semiconductor measuring device according to the first embodiment of the present invention.

FIG. 4D is a diagram showing a fourth example of the waveform of the substrate current observed by the semiconductor measuring device according to the first embodiment of the present invention.

FIG. 5A] is an equivalent circuit diagram of the hole structure of the first example according to the first embodiment of the present invention. FIG. 5B] is an equivalent circuit diagram of the hole structure of the second example according to the first embodiment of the present invention. [5C] FIG. 5C is an equivalent circuit diagram of the hole structure of the third example according to the first embodiment of the present invention. FIG. 6A] A differential circuit diagram for explaining the basic principle of the semiconductor measuring device according to the first embodiment of the present invention.

6B] An input waveform diagram of the differentiating circuit for explaining the basic principle of the semiconductor measuring device according to the first embodiment of the present invention.

FIG. 6C is an output waveform diagram of the differentiating circuit for explaining the basic principle of the semiconductor measuring device according to the first embodiment of the present invention.

FIG. 7A is an explanatory diagram of a substrate current generation mechanism (image charge formation period) according to the first embodiment of the present invention.

FIG. 7B is an explanatory diagram of a substrate current generation mechanism (initial tunnel current formation) according to the first embodiment of the present invention.

[7C] FIG. 7C is an explanatory diagram of a substrate current generation mechanism (late tunnel formation) according to the first embodiment of the present invention.

FIG. 7D is an explanatory diagram of the generation mechanism (discharge period) of the substrate current according to the first embodiment of the present invention.

8] Waveform force of substrate current according to the first embodiment of the present invention is an explanatory diagram of the principle of extracting the edge of a contact hole.

FIG. 9 is a flowchart showing a flow of operations of the semiconductor measuring apparatus according to the second embodiment of the present invention. It is

圆 1—

O 10] A flow chart showing the flow of operation of the semiconductor measuring apparatus according to the third embodiment of the present invention.

[11] FIG. 11 is a diagram showing an equivalent circuit of a hole structure which is a measurement target of the semiconductor measurement apparatus according to the third embodiment of the present invention.

FIG. 12 is a characteristic diagram showing a non-linear relationship between the electron beam irradiation amount and the surface potential when an electron beam is irradiated onto the hole structure that is the measurement object according to the third embodiment of the present invention. Explanation of symbols

Electron gun

11 Electron beam source

12 condenser lens

13 Apachiya

14 Deflection electrode

15 Objective lens

20 Vacuum channel

21 ΧΥ Stage

22 Aoi Rei

23 Semiconductor substrate (sample)

24 Secondary electron detector

30 Current measuring device

40 High voltage power supply

100 sequence controller

110 Focus control device

120 Secondary electron image recording device

130 Substrate current waveform recorder

140 Waveform processor

150 Edge extractor

160 Display device 170 Database device

BEST MODE FOR CARRYING OUT THE INVENTION

Next, the best mode for carrying out the present invention will be described with reference to the drawings.

[First embodiment]

FIG. 1 shows the configuration of the semiconductor measuring apparatus according to the first embodiment of the present invention.

This semiconductor measuring apparatus irradiates a semiconductor substrate, which is a measurement object (sample), with an electron beam, measures a substrate current induced by the electron beam, and forms a hole formed in the semiconductor substrate from the substrate current. The basic principle is to obtain an evaluation value of the microstructure such as

As shown in the figure, an electron gun 10 that generates an electron beam EB is attached to an upper portion of a chamber 20 that houses a semiconductor substrate 23 that is a measurement object (sample). The electron gun 10 includes an electron beam source 11, and a high voltage power source 40 is connected to the electron beam source 11. Inside the electron gun 10, a condenser lens 12, an aperture 13, a deflection electrode 14, and an objective lens 15 are arranged in this order along the emission direction of the electron flow from the electron beam source 11. Among these, a deflection control device 50 is connected to the deflection electrode 14 so that the electron beam EB can be deflected with high accuracy. In addition, the energy, current amount, and focus state of the electron beam EB can be arbitrarily controlled.

An XY stage 21 for supporting the semiconductor substrate 23 and a tray 22 fixed on the XY stage 21 are accommodated in the chamber 20, and the semiconductor substrate 23 is placed on the tray 22. It is placed. The irradiation direction of the electron beam EB emitted from the electron gun 10 is directed to the surface of the semiconductor substrate 23 placed on the tray 22, and by moving the position of the tray 22 by the XY stage 21, The irradiation position of the electron beam EB to the semiconductor substrate 23 can be adjusted.

In addition, a secondary electron detector 24 for detecting secondary electrons, whose surface force is also emitted from the semiconductor substrate 23 when the electron beam EB is irradiated, is provided inside the chamber 120. In addition, an electrode is provided inside the chamber 20 for applying a bias voltage to the semiconductor substrate 23, an electrode is provided, and a voltage applying device for supplying a noise voltage to the electrode is provided outside the chamber 20. It has been. The degree of vacuum inside the chamber 20 is, for example, 10 It is maintained at minus 6 [torr].

Here, in order to irradiate the semiconductor substrate with the electron beam EB irradiated from the electron gun 10 with a position accuracy of the order of nm, the semiconductor is relatively relative to the irradiation axis of the fixed electron beam EB. The position of the substrate 23 is moved by the XY stage 21. As a drive device for the XY stage 21, a Norse motor, an ultrasonic motor, or a piezoelectric element is used. By using high-precision measurement technology such as a laser length measuring instrument and laser scale, the positional accuracy of the semiconductor substrate 23 placed on the XY stage 21 is controlled to about several nm.

A current measuring device 30 is connected to the tray 22, and a substrate current induced in the semiconductor substrate 23 is measured by the current measuring device 30 via the tray 22. The current measuring device 30 includes an AZD converter that AZD converts the measured substrate current value into a digital signal, and outputs the measured value as digital data.

The tray 22 is provided with an electron beam irradiation position measuring device 22A for measuring the irradiation position of the electron beam EB on the semiconductor substrate 23. Electron beam irradiation position measurement device 22A outputs the coordinates of the measured electron beam irradiation position (electron beam irradiation coordinates). The irradiation coordinates of the electron beam obtained by the electron beam irradiation position measuring device 22A are used as parameters for forming a secondary electron image and a substrate current waveform, which will be described later. The coordinate system of the irradiation position of the electron beam EB is not particularly limited.

[0025] In addition, the semiconductor measurement apparatus includes a sequence control apparatus (including a pattern matching engine) 100, a focus control apparatus 110, a secondary electron image recording apparatus 120, a substrate current waveform recording apparatus 130, a waveform processing apparatus 140, and an edge extraction. Device 150, display device 160, and database device 170, which are built on an information processing device such as a computer.

Among these, the sequence control device 100 controls the deflection control device 50 so that the electron beam EB scans the surface of the semiconductor substrate 23 when the substrate current is measured, and the irradiation position of the electron beam on the semiconductor substrate. It controls the pattern matching to adjust the irradiation position of the electron beam EB with high accuracy.

In the present embodiment, the one-dimensional scanning means scanning in a line shape. Also, Two-dimensional scanning means that line-shaped scanning is repeated a plurality of times at regular intervals, and is a concept similar to horizontal scanning and vertical scanning on a television screen, for example.

[0027] Here, a supplementary explanation will be given for pattern matching. The positions of patterns such as holes formed on a semiconductor substrate are slightly different for each semiconductor substrate even in the same lot. In order to adjust this, combined with alignment by the XY stage 21, pattern matching is performed to compare the actual pattern and the reference pattern for each semiconductor substrate so that the actual pattern matches the reference pattern. Shift the irradiation position of electron beam EB. This makes it possible to accurately adjust the irradiation position of the electron beam with an accuracy of several nm for each semiconductor substrate.

[0028] The semiconductor measurement apparatus includes a high-resolution deflection control device 50 for accurately linearly scanning the electron beam EB in order to accurately shift the irradiation position of the electron beam EB in pattern matching, and also performs sequence control. The apparatus 100 includes an image recognition apparatus (including a pattern matching engine) and software for performing pattern matching.

The focus control device 110 controls the focus position of the objective lens 15, and controls the focus amount of the objective lens 15 during measurement to control the focus amount of the electron beam. This is for setting the tip to a desired size and shape. As a method of setting the focus amount of the electron beam EB (focus position of the objective lens 15), the distance of the wafer surface force is obtained optically or electrically, and the focus amount is set based on the distance. A method that sets the amount of focus for the state in which the image obtained by scanning the beam is the clearest or the state force that maximizes the contrast of the secondary electrons, and the image obtained by the substrate current value when the electron beam is irradiated A method such as a method of setting the focus amount can be used for the state where the image becomes the clearest or the state force that maximizes the contrast.

The secondary electron image recording device 120 records an image formed by secondary electrons detected by the secondary electron detector 24. The substrate current waveform recording device 130 stores the waveform of the substrate current value measured by the current measuring device 30 in association with the irradiation coordinates of the electron beam EB at that time. Beam illumination It is read from the shooting position recording device 22A.

[0031] The waveform processing device 140 shapes the waveform of the substrate current value to remove unnecessary noise components. The edge extraction device 150 extracts the contact hole edge from the waveform-shaped substrate current waveform, and calculates an evaluation value related to the shape of the contact hole. The display device 160 displays the evaluation value. The database device 170 stores the evaluation values calculated by the edge extraction device 150 in a database.

Next, the operation of the semiconductor measurement apparatus will be described along the flow shown in FIG. Here, a contact hole will be described as a measurement target.

First, alignment of the electron beam EB and the semiconductor substrate 23 is performed under the control of the sequence controller 100. That is, the position coordinate of the hole to be measured is specified with respect to the control system of the XY stage 21 holding the semiconductor substrate 23, the XY stage 21 is moved, and the center of the hole is set at the irradiation position of the electron beam EB. Match roughly. Then, the electron beam EB is irradiated while scanning two-dimensionally, and pattern matching is performed by comparing the image of secondary electrons generated at that time with the template image, and the amount of deviation between the center of the template image and the center of the hole Is calculated. This deviation amount is input to the deflection controller 50, and the irradiation position of the electron beam EB is shifted so that the irradiation position of the electron beam EB is accurately aligned with the center of the hole to be measured.

When the above alignment is completed, the following series of processes (steps S 11 to S 14) for calculating the evaluation value of the substrate current force hole are executed under the control of the sequence control device 100.

First, the substrate current waveform is acquired by irradiating the semiconductor substrate 23 with the electron beam EB (step Sl l). That is, a predetermined region on the surface of the semiconductor substrate 23 is two-dimensionally scanned by the electron beam EB with reference to the hole center. In this two-dimensional apparatus, the electron beam EB is irradiated perpendicularly to the surface of the semiconductor substrate 23, the focus position of the objective lens 15 is controlled so that the tip of the electron beam EB has a desired size, and the deflection control device By applying a control voltage to 50, one-dimensional scanning is repeated at regular intervals and at a constant speed (for example, 10 one-dimensional scannings are performed at regular intervals). The semiconductor substrate irradiated with the electron beam EB by this scanning Secondary electrons and reflected electrons are generated from a minute region on the surface of the substrate 23, and a substrate current is induced in the semiconductor substrate 23.

The substrate current induced in the semiconductor substrate 23 by the above-described scanning is measured by the current measuring device 30 and converted into an electric signal having a necessary dynamic range. This electrical signal is immediately sampled and converted to a digital signal with the required resolution so that the signal quality is not degraded. For example, the resolution of this digital signal is 16 bits and its sampling frequency is 400 MHz. In parallel with the above-described measurement of the substrate current, the irradiation position of the electron beam EB is measured by the electron beam irradiation position measuring device 22A.

The measurement value of the substrate current obtained by scanning the electron beam EB in this way includes information on the structure of the bottom surface of the hole, and the measurement coordinates (electron beam) measured by the above-described electron beam irradiation position measuring device. As a waveform information expressed as a function of measurement time (irradiation time of electron beam EB) or digitally recorded on a substrate current waveform recording device 130 (for example, a memory or a hard disk).

On the other hand, secondary electrons generated from a minute region on the surface of the semiconductor substrate 23 by the above-described scanning are detected by the secondary electron detector 24. The secondary electrons can be detected by using a well-known photomultiplier, multichannel plate, or simple electrode to directly collect secondary electrons and use them as current signals. Here, the important thing is that a relationship in which the amount of secondary electrons detected by the secondary electron detector 24 is proportional to the amount of secondary electrons actually generated can be obtained. The output value of the secondary electron detector 24 is set to be exactly proportional to the number of input electrons. As a result, secondary electrons are detected linearly from the small signal region to the large signal region.

[0037] On the other hand, in ordinary SEM, the secondary electron is expressed for the purpose of expressing it as a binary image, so that the detected value has a large difference between when there is a signal and when there is no signal. It is set! That is, the detection value is set to 0 when very few electrons are input to the detector, and the amplifier has nonlinear characteristics that generate a large detection value when electrons exceeding a certain threshold are input. It has become.

[0038] The measurement value of the secondary electrons obtained by the above-mentioned scanning includes information on the surface structure of the semiconductor substrate 23, and the measurement coordinates (electricity) measured by the electron beam irradiation position measurement device 22A. Digital information is recorded in the secondary electron image recording device 120 (for example, a memory or a hard disk) as image information expressed as a function of a child beam irradiation position) or a measurement time (electron beam EB irradiation time).

Also, the backscattered electrons that have generated micro-region forces on the surface of the semiconductor substrate 23 are detected by a backscattered electron detector (not shown), and the backscattered electron image obtained from the detected value is digitally recorded on a backscattered electron image recording device (not shown). Is done.

Note that secondary electrons and reflected electrons can be distinguished by differences in energy and emission direction, but depending on the type of detection device, they can be handled together without being distinguished. In addition, for each of the secondary electron detector 24 and the backscattered electron detector (not shown), a plurality of units may be arranged. In such a case, information shall be recorded independently according to the number of detectors. Is desirable. Of course, each of the secondary electron detector 24 and the backscattered electron detector (not shown) may be arranged one by one.

[0040] The waveform of the substrate current measured as described above is shaped by the waveform processing device 140 in order to remove unnecessary noise and high frequency components. Examples of the waveform processing include moving average filter processing, waveform processing for removing a specific frequency, or filter processing for extracting only a signal of a specific frequency. These waveform shaping processes can be performed in hardware or software.

Subsequently, the edge extraction device 150 also extracts the edge of the hole with respect to the waveform force of the substrate current (step S12). In other words, the edge extraction device 150 extracts an edge of a hole from the above-described substrate current waveform using an edge extraction algorithm, and converts the extracted edge coordinate value into the XY coordinate system. This embodiment has a feature in the principle of the edge extraction algorithm, and details thereof will be described later.

[0042] Further, the edge extraction device 150 applies a circle approximation function or an ellipse approximation function to the converted XY coordinate values (step S13), and performs curve fitting using the least square method. In other words, the edge coordinates of the current waveform described above correspond to the edge coordinates of the hole, and the shape of the edge of the hole is reproduced by connecting the coordinate values of the edge of the substrate current waveform obtained by one-dimensional scanning. be able to.

[0043] Therefore, by applying an approximation function to the above-mentioned edge coordinate values, Mathematical expression of dimensional shape. Specifically, an approximate function of, for example, a circle or an ellipse is applied to the above-described converted edge coordinate value, and the approximation function is set so that the error between the approximate function value and the edge coordinate value is minimized. Fitting various parameters that specify This represents the two-dimensional shape of the hole. If such an approximate function is used, the hole shape is accurately maintained even if the relative positions of the holes are deviated. Therefore, even if an alignment error occurs, the effect on the measured value of the hole can be kept small. . It should be noted that what kind of function is adopted as the approximate function is appropriately determined by the design pattern force of the hole to be measured.

[0044] Further, the edge extraction device 150 calculates the evaluation value of the hole shape by using the above approximate function to which the parameter is fitted (step S14). For example, the hole evaluation value includes the hole diameter, hole center position, hole inclination angle, hole rotation angle, hole roundness, hole distortion, edge roughness, and the like. When an elliptic function is used as an approximate function, the major axis, minor axis, focus, distortion, rotation, etc. of the ellipse are calculated. These values are displayed on a display device 160 such as a computer display or stored as digital data in a database device 170.

Next, the principle of the edge extraction algorithm in the edge extraction device 150 will be described in detail. This edge extraction algorithm is based on obtaining an evaluation value of the fine structure based on the waveform of the substrate current when the measured waveform of the substrate current is regarded as a differential waveform. The edge extracting device 150 is configured.

FIG. 3 shows a cross-sectional structure of a contact hole that is a measurement target of the semiconductor measurement apparatus.

Here, FIG. 3A shows a cross-sectional structure of a normal contact hole HA. As shown in the figure, an interlayer insulating film F is formed on the main surface of the silicon substrate S via an oxide film, and a contact hole HA is formed so as to penetrate the interlayer insulating film F. . The silicon substrate S is exposed at the bottom of the hole HA. Normally, a P-type or N-type diffusion layer is formed on the silicon substrate S, and this diffusion layer has conductivity.

FIG. 3B shows a cross-sectional structure of the contact hole HB formed on the gate G. The gate G is a control electrode that constitutes a MOS transistor, and the gate G is very thin. A gate oxide film GOX of nm order is formed, and a silicon substrate S exists below it. The gate G and the silicon substrate S are insulated from each other by the gate oxide film GOX and are not connected in a direct current.

[0048] FIG. 3C is a force showing the cross-sectional structure of the contact hole formed on the gate G2. This example is a floating gate (electrically isolated) used in flash memory or the like that has attracted attention in recent years. Gate) structure. That is, an insulator ONO for accumulating charges exists under the gate G2, and a normal gate G1 exists under the insulator ONO. Under the gate G1, there is a silicon substrate S through a gate oxide film GOX. This floating gate structure is a structure in which the gate G shown in FIG. 3B is stacked. In other words, the insulating film is characterized in that two layers of gates are formed with the electrode interposed therebetween.

[0049] The contact holes HA to HC shown in FIGS. 3A to 3C, respectively, have a very large aspect ratio, but a conventional SEM cannot measure the shape of the hole bottom. In the semiconductor measurement apparatus of the embodiment, the electron beam EB that is narrowly focused is irradiated so as to hit the bottom of the holes HA to HC, and the shape (size) of the hole bottom is determined from the change in the substrate current induced in the silicon substrate S at that time. Is identified.

[0050] FIGS. 4A to 4D show the waveform of the substrate current actually observed in this manner.

Here, FIG. 4A shows the waveform of the substrate current when the electron beam EB is irradiated on the hole structure shown in FIG. 3A, and an N-type diffusion layer is formed on the surface of the silicon substrate S corresponding to the bottom of the hole. It is a waveform when it is. FIG. 4B shows the waveform of the substrate current when the electron beam EB is irradiated to the hole structure shown in FIG. 3A. A P-type diffusion layer is formed on the surface of the silicon substrate S corresponding to the bottom of the hole. ing. 4C shows the substrate current when the electron beam EB is irradiated to the hole structure shown in FIG. 3B, and FIG. 4D shows the substrate current when the electron beam EB is irradiated to the hole structure shown in FIG. 3C. Is

Next, the reason why each waveform shown in FIGS. 4A to 4D is observed will be described.

FIG. 5A shows an electrical equivalent circuit of the normal contact hole HA shown in FIG. 3A. The equivalent circuit of the contact hole HA is composed of the resistance R1 of the silicon substrate S, and the irradiated electron beam EB flows to the silicon substrate S through the resistance R1. Therefore, silicon Regardless of whether the diffusion layer formed on the surface of the substrate S is N-type or P-type, when the normal contact hole HA is irradiated with the electron beam EB, as shown in Fig. 4A and Fig. 4B In addition, a trapezoidal substrate current waveform is obtained.

It is possible to easily extract the edge of the hole from such a trapezoidal substrate current waveform. For example, using the threshold method and the maximum gradient method, in the slope region of the waveform that forms the trapezoid in the substrate current waveform, the coordinates when the waveform crosses a predetermined threshold value, or the maximum slope of the waveform in each slope region Define the coordinates indicating the value as the edge of the hole and extract the required number of edges. The circle shape, ellipse approximation, or straight line approximation is applied to the extracted edge to extract the shape of the hole. On the other hand, as shown in FIGS. 3B and C, in the hole structure where the gate or floating gate exists at the bottom of the hole, the obtained substrate current waveform must be trapezoidal as shown in FIGS. 4C and 4D. .

FIG. 5B shows an electrical equivalent circuit of the contact hole HB shown in FIG. 3B. A gate G exists at the bottom of the contact hole HB. This electrical equivalent circuit is composed of one capacitor C1 formed of a gate G that also has a polysilicon force, a gate insulating film GOX, and a silicon substrate S, and a resistor R1 that the silicon substrate S has. And the resistor R1 are connected in series. The capacitor C 1 and the resistor R1 form a time constant circuit, and this time constant is determined by the product of the capacitance value of the capacitor C1 and the resistance value of the resistor R1. Therefore, the Hall structure in this case is equivalent to a circuit having a time constant proportional to the capacitance value of the capacitor C1 and the resistance value of the resistor R1. Here, other parasitic CR components are ignored for convenience of explanation.

FIG. 5C shows an electrical equivalent circuit of the contact hole HC shown in FIG. 3C. As shown in FIG. 3C, the bottom of the contact hole HC has a gate G2, an insulating film ONO, and a gate. Gl, gate oxide GOX, and silicon substrate S exist. As shown in FIG. 5C, the hole structure includes two gates, a gate G2 and a gate G1, and two insulating films, a gate oxide film GOX and a nitride film ONO. The two electrodes and the two insulating films form capacitors CI and C2 connected in series. The silicon substrate S forms a resistor R. These capacitors CI, C2 and resistor R1 are connected in series.Therefore, the hole structure in this case is the capacitance value and resistance of resistor R1 when capacitors CI, C2 are directly connected. This is equivalent to a circuit having a time constant composed of a resistance value.

Here, as shown in FIG. 6A, generally, when a capacitor C and a resistor R are connected in series, a differentiation circuit is obtained. When a rectangular waveform as shown in FIG. 6B is input to the differentiating circuit, the rectangular waveform is differentiated, and a differential waveform having a component proportional to the amount of inclination of the rectangular waveform is output as shown in FIG. 6C. The Here, since the input rectangular waveform has both positive and negative slopes at the rise and fall, an output having both positive and negative values can be obtained.

That is, according to the differentiating circuit, a current that flows in both plus and minus is generated from a rectangular current waveform that flows in one direction. This waveform is unidirectional if there is a differential circuit in the hole structure of the measurement object, regardless of the time constant of the measurement object or the force affected by the scanning speed of the electron beam EB irradiated for measurement. Even if only the current flowing through is supplied, both positive and negative currents are observed. Therefore, it can be seen from the waveforms shown in FIGS. 4C and 4D that the equivalent circuit of the hole structure shown in FIGS. 3B and 3C includes a differentiation circuit.

Here, as shown in FIGS. 3B and 3C described above, the generation mechanism of the substrate current in the case where the gate exists at the bottom of the hole and the silicon substrate S is exposed will be described.

Fig. 7A shows the state of charge redistribution that occurs in the initial stage (image charge formation period) when the measurement target is irradiated with the electron beam EB. In the figure, the electron beam EB scans at a constant speed toward the left side force and right side of the figure.

[0058] When the irradiation position of the electron beam EB reaches the contact hole to be measured and the gate G existing at the bottom of the hole is irradiated with the electron beam EB, secondary electrons are generated from the surface of the gate G, Image charge ICG is induced on the substrate side by the charge remaining on the surface. The amount of image charge ICG accumulated is determined by the capacitance value of the capacitor formed by gate G and gate oxide film GOX. V and substrate current IK are observed as the image charge ICG is formed. The current at this time is expressed by the following equation.

1 = 1 (l-exp (-AA))

0

t: time constant

FIG. 7B shows the next stage of the image charge formation period described above. In this example, The thickness of the mono-acid film is about 10 nm. As time elapses after irradiation of the electron beam EB begins, charges accumulate on the electrode of the gate G, and the potential of the gate G rises in proportion to the amount of irradiation current. Then, as shown in FIG. 7C, when the potential of the gate G exceeds, for example, about 10 V, the electric field E at that time becomes lOMVZcm, and the tunnel current IT starts flowing in the gate oxide film GOX having a thickness of about lOnm. , The charge moves. At this time, a tunnel current IT is generated so that the surface potential is constant, and as a result, the surface potential is kept constant. The tunnel current IT at this time is also observed as the substrate current IK. The current at this time is expressed by the following equation. I = AE ² exp (-B / E)

FIG. 7D shows the state of charge transfer when the scanning position of the electron beam EB deviates from the contact hole to be measured and the irradiation of the electron beam EB to the measurement object is completed. In this state, the supply of electrons by the electron beam EB is lost, and as a result, charges accumulated in the region sandwiched between the gate G, the gate oxide film GOX, and the silicon substrate S are discharged. During this discharge process, a tunnel current IT flows in the opposite direction to the charge accumulation process shown in FIG. 7C. The current at this time is expressed by the following equation.

1 = 1 exp (-A / t)

0

[0061] As can be seen from the above, when an insulating film such as a gate oxide film GOX exists under the gate electrode at the bottom of the hole, a complex current waveform is observed. It is possible to interpret the structure of That is, when there is an insulator under the gate G, the gate G, the insulator, and the silicon substrate S form a differential circuit, so that the observed waveform is regarded as a differential waveform, and this waveform force can also grasp the hole structure. Is possible.

For example, the waveform of the substrate current shown in FIG. 8 has two peaks P1 and P2, which correspond to the differential waveform obtained by the differentiation circuit shown in FIG. 5B described above. Therefore, if we consider that this peak P1 and peak P2 are obtained by differentiating the waveform observed when there is no insulator such as a gate at the bottom of the hole, each peak corresponds to the edge of the hole. The hole diameter CD can be calculated as the hole evaluation value from the interval between these peaks P1 and P2.

[0063] In addition, a plurality of edges are obtained from a plurality of substrate current waveforms obtained when the electron beam EB is scanned two-dimensionally with respect to a single hole. For these multiple edges, circular approximation, elliptical By applying an approximate function corresponding to a circular approximation or other shapes, the shape of the bottom of the hole can be evaluated from the measured substrate current waveform. In this case, in order to obtain the absolute size of the hole, it is only necessary to calibrate the measured value by performing the same measurement in advance for the hole whose size is divided in advance.

[0064] In general, the gate oxide film does not function as a complete capacitance as described above. That is, when a certain amount of charge accumulates in the gate electrode and the surface potential rises, a tunneling current flows through the gate oxide film, so a differential waveform different from a pure capacitance is observed. . Therefore, a more accurate method for determining the edge of the hole is to extract the waveform of the region where the gate oxide film functions as a pure capacitor from the components that make up the observed waveform, and then calculate the waveform force derivative. Therefore, the exact hole edge can be extracted. Or, conversely, by adjusting the electron beam dose as small as possible, there is a method of measuring in a state where the structure composed of the gate electrode, the gate insulating film, and the silicon substrate functions as a pure capacitor. .

[0065] When a normal hole is a measurement target, a force that produces a trapezoidal waveform as the substrate current waveform. The waveform force is differentiated as one method for extracting the edge of the hole. The place where the differential value shows the maximum value is extracted as the edge of the hole. The shape of the hole is evaluated by applying a circle approximation, an ellipse approximation or another approximate curve to the multiple edges obtained as described above.

[0066] [Second Embodiment]

FIG. 9 shows an operation flow of the semiconductor measuring apparatus according to the second embodiment of the present invention. The apparatus configuration of this embodiment is basically the same as that of the first embodiment described above, but the principle of the edge extraction algorithm is different. That is, the edge extraction algorithm of the present embodiment is based on obtaining an evaluation value of the fine structure based on the integrated waveform of the substrate current when the waveform of the substrate current is regarded as a differential waveform. Such an evaluation means is configured as an edge extraction device 150, for example.

[0067] The operation flow of the present embodiment shown in FIG. 9 includes step S22 related to waveform integration processing, step S23 related to filtering, instead of step S12 of the operation flow of the first embodiment shown in FIG. Step S24 related to edge detection. Figure 9 shows Steps common to the steps shown in FIG. 2 are given the same reference numerals.

In this embodiment, since the waveform obtained in step S 11 is a differential waveform, it is integrated once and returned to the original waveform (step S 22). After that, necessary components are extracted from the integrated waveform using a filter that extracts components corresponding to the bottom of the hole as required (step S23). For example, the differential waveform contains high-frequency components or low-frequency components that are unnecessary for estimating the size of noise and holes, so these are removed as appropriate to obtain a waveform that correctly reflects the bottom of the hole.

[0069] The current waveform obtained by integrating in this way is the same as the waveform obtained by measuring the normal contact hole HA as shown in FIG. To extract edges (step S24). As this edge extraction algorithm, all algorithms commonly known in mathematics such as threshold value method, differentiation method, Sobel method, Laplacian method can be used. The following is the same as in the first embodiment (steps S13 and S14).

[0070] [Third Embodiment]

FIG. 10 shows an operation flow of the semiconductor measuring apparatus according to the third embodiment of the present invention. In FIG. 10, steps that are the same as those shown in FIG. 9 are given the same reference numerals.

The apparatus configuration of the present embodiment is basically the same as that of the first or second embodiment described above. In the operation, the apparatus includes step S32 relating to inverse calculation, and the waveform of the substrate current obtained in step S11. Based on the above, it is essential to identify an equivalent circuit of a fine structure and obtain an evaluation value of the fine structure based on the waveform obtained by using this equivalent circuit. Composed.

To describe in detail, first, an equivalent circuit (parameter values are not set) is prepared in advance, which represents in detail the hole structure to be measured including the gate structure and the control gate structure. For example, a specific component of the capacitor formed by the gate electrode is also incorporated in the equivalent circuit.

Here, the equivalent circuit of FIG. 11 is as shown in FIG. 12 formed by a gate electrode by incorporating a zener diode ZD into the equivalent circuit of the Hall structure of FIG. 3B. It expresses the nonlinearity that is a specific component of a simple capacitor. In FIG. 11, R2 is the resistance component of the gate. The Zener diode ZD is also called a constant voltage diode. When the voltage across the diode reaches a constant voltage, current flows through the diode and keeps the voltage across the diode constant. By using such a precise equivalent circuit, the measurement object can be expressed more accurately by a mathematical expression. By solving the equation expressing this equivalent circuit, the measured substrate current waveform can be converted into the substrate current waveform indicated by a normal contact hole.

[0073] A waveform simulating the original waveform is obtained using the above-described equivalent circuit (step S32). Specifically, this parameter is obtained by inversely calculating each parameter of the equivalent circuit so that the waveform obtained using the equivalent circuit prepared in advance matches the waveform actually observed in step S11. Identify each parameter. Next, filtering is performed on the waveform obtained using the equivalent circuit with the specified parameters (step S23), and the edge extraction method is applied to extract the edge and obtain the evaluation value of the hole ( Steps S12 to S14).

[0074] In the above description, since the hole structure shown in Fig. 3B is taken as an example, the waveform obtained by the equivalent circuit is a force that becomes a differential waveform. Generally, the content of the equivalent circuit varies depending on the hole structure. The waveform obtained by the equivalent circuit also changes. Therefore, in step S12 of this embodiment, edge detection is performed by applying an appropriate edge extraction algorithm to the waveform obtained using the equivalent circuit. That is, if the waveform obtained using the equivalent circuit is a differential waveform, the same edge extraction algorithm as in the first embodiment is applied, and if it is a trapezoidal waveform, the same conventional power as in the second embodiment is applied. A known edge extraction algorithm may be applied.

[0075] While the embodiments of the present invention have been described above, the embodiments of the present invention can be modified without departing from the spirit of the present invention. For example, in the above-described embodiment, the force described in the case where a gate is present at the bottom of the hole as an example may be any member that is present at the bottom of the hole. Moreover, the member does not need to be present on the entire bottom surface of the hole, but may be present on a part of the bottom of the hole.

In the above-described embodiment, the present invention is a semiconductor measuring device and a semiconductor measuring method. However, the present invention is not limited to this. Semiconductor inspection equipment, semiconductor inspection methods, semiconductor analysis equipment, semiconductor analysis methods, semiconductor analysis equipment, semiconductor analysis methods, semiconductor evaluation equipment, semiconductor evaluation equipment, semiconductor manufacturing equipment, semiconductor manufacturing equipment It may be expressed as a method or the like.

Industrial applicability

INDUSTRIAL APPLICABILITY The present invention is useful for a semiconductor device or an apparatus used for inspection, analysis, manufacturing, measurement or evaluation in a manufacturing process thereof, and a semiconductor device manufacturing method. For example, the present invention is used in the fields of inspection techniques, analysis techniques, measurement techniques, evaluation techniques, and semiconductor device manufacturing apparatuses and methods that use a method of irradiating a semiconductor substrate such as a wafer with an electron beam or ion beam. Can do.

Claims

The scope of the claims

[1] A semiconductor measuring apparatus configured to irradiate a semiconductor substrate with an electron beam and obtain an evaluation value of a microstructure formed on the semiconductor substrate from a substrate current induced in the semiconductor substrate by the electron beam. There,

A semiconductor measuring apparatus comprising: an evaluation unit that obtains an evaluation value of the microstructure based on a waveform of the substrate current when the waveform of the substrate current is regarded as a differential waveform.

[2] The microstructure is a hole,

The semiconductor measuring apparatus according to claim 1, wherein the evaluation unit extracts an edge of the hole from a waveform of the substrate current.

3. The semiconductor measuring apparatus according to claim 2, wherein the evaluation means calculates an edge force of the hole and an evaluation value of the hole.

4. The semiconductor measurement apparatus according to claim 2, wherein the evaluation unit extracts a peak force of the waveform of the substrate current and an edge of the hole.

[5] A semiconductor measuring apparatus configured to irradiate a semiconductor substrate with an electron beam and obtain an evaluation value of a fine structure formed on the semiconductor substrate from a substrate current induced in the semiconductor substrate by the electron beam. There,

A semiconductor measuring apparatus comprising: an evaluation unit that obtains an evaluation value of the microstructure based on an integrated waveform of the substrate current when the waveform of the substrate current is regarded as a differential waveform.

[6] The microstructure is a hole,

6. The semiconductor measurement apparatus according to claim 5, wherein the evaluation unit extracts an edge of the integrated waveform force of the hole.

7. The semiconductor measuring apparatus according to claim 6, wherein the evaluation means calculates an edge force of the hole and an evaluation value of the hole.

[8] A semiconductor measuring apparatus configured to irradiate a semiconductor substrate with an electron beam and obtain an evaluation value of a fine structure formed on the semiconductor substrate from a substrate current induced in the semiconductor substrate by the electron beam. There,

Evaluating means for identifying an equivalent circuit of the microstructure based on the waveform of the substrate current and obtaining an evaluation value of the microstructure based on a waveform obtained using the equivalent circuit A semiconductor measuring device.

[9] The microstructure is a hole,

9. The semiconductor measurement apparatus according to claim 8, wherein the evaluation means extracts a waveform force obtained by using the equivalent circuit.

10. The semiconductor measuring apparatus according to claim 9, wherein the evaluation means calculates an edge force of the hole and an evaluation value of the hole.

[11] A semiconductor measurement method for obtaining an evaluation value of a fine structure formed in a semiconductor substrate from a substrate current induced in the semiconductor substrate by irradiating an electron beam to the semiconductor substrate,

An evaluation value of the microstructure is obtained based on a waveform of the substrate current when the waveform of the substrate current is regarded as a differential waveform.