JP2004146802A - Inspection method and apparatus for semiconductor wafer testpiece - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an inspection apparatus for holes such as contact holes capable of detecting the change of the bottom face state of the contact holes by detecting a charge transfer occurring in a testpiece. <P>SOLUTION: In the lower part of a wafer testpiece 3, an electrode plate 7 is arranged in parallel with the back of the wafer testpiece 3, and a space (this space is a vacuum) is designed to be provided between the back of the wafer testpiece 3 and the plate 7. Due to this configuration, the back of the wafer testpiece 3 becomes a single side electrode, and a capacitor (capacitance) Cp, in which the plate 7 facing to the back of the wafer testpiece 3 becomes a counterelectrode, is formed. A space distance d between the back of this wafer testpiece 3 and the electrode plate 7 is set so as to obtain a capacitance needed for an integrating circuit structure as a capacitance with dielectric constant being 1 (a vacuum). <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a method for inspecting a semiconductor wafer sample using a charged particle beam such as an electron beam for inspecting the degree of opening of an opening hole such as a contact hole and a via hole formed in a process of manufacturing a semiconductor device and other conditions of the wafer sample. And equipment.

In recent years, semiconductor devices have become more multi-layered, and a contact hole is formed between the lower and upper elements in order to provide conduction between an element formed at the lower part or a silicon substrate and an element formed at the upper part. Then, a conductive material is injected into the contact hole.

The formation of the contact hole, depositing a such oxide film of alumina, which is an insulating material on the bottom of the element or a silicon substrate (S _i O _2), a photoresist thereon. The material coated with the resist is loaded into an exposure apparatus, and a position of a contact hole to be formed is selectively irradiated with light to expose the portion.

(4) The exposed material is subjected to a development process or the like to remove the resist in the exposed portion, and the material is transferred to an etching process. In the etching step, the resist is removed, the portion where the oxide film is exposed is etched, and a large number of contact holes are formed in the oxide film. Thereafter, the resist remaining on the surface of the device material is removed, and a conductive material is injected into the formed contact hole.

By the way, this contact hole must be formed at an accurate position through the oxide film. If this hole is not formed as a complete hole, the manufactured device will eventually be a defective product, causing a decrease in the yield of semiconductor device manufacturing.

Therefore, in the process of forming the contact hole, it is necessary to inspect the opening degree of the contact hole and feed back the result to the manufacturing process that resulted in the poor opening degree to eliminate the cause of the failure. In order to measure the degree of opening of the contact hole, a scanning electron microscope (CD-SEM) having a length measuring function or a method of determining the charge state of the bottom surface of the contact hole using a voltage contrast is used.

In the CD-SEM, an electron beam is irradiated on a sample region where a contact hole is formed, and secondary electrons generated from the sample are detected. The opening diameter of the contact hole is measured based on the detection signal, and the quality of the formed contact hole is determined based on the measured opening diameter.

In the voltage contrast method, an electron beam is scanned in a sample region where a contact hole is formed, secondary electrons generated from the sample are detected, and a detected secondary electron image is displayed using the detection signal as a video signal. As a result, a portion of the contact hole in which the contact hole is accurately formed is not displayed on the screen because the charge is not charged up. On the other hand, in the contact hole where the resist remains at the bottom, charge-up occurs, and this hole portion is displayed brightly on the screen, and the quality of the contact hole can be determined by such a phenomenon.

Such shape observation by CD-SEM and determination of the quality of the opening of the contact hole by the voltage contrast method are performed when the aspect ratio of the contact hole (hole depth / hole opening diameter) is small (about 10/1). Until, can be used.

コ ン タ ク ト By the way, as for the contact holes and the like formed in the chips produced in the semiconductor device production line, the opening diameter of the holes is reduced due to the progress of the production technology. On the other hand, the thickness of the oxide film layer in which the contact hole is formed is several times as large as the conventional thickness. As a result, the aspect ratio in the contact hole is increased.

(4) As the aspect ratio increases, it becomes difficult to measure the bottom surface by CD-SEM measurement by detecting a signal generated at the bottom surface of the contact hole and determining the shape. The reason for this is that the material forming the sample surface is an insulator, and the charged surface beam such as an electron beam causes a charge-up phenomenon due to negative charges on the sample surface.

That is, negative secondary electrons from the bottom surface of the hole are suppressed from going to the outside of the hole by the electric field formed on the negatively charged sample surface. As a result, secondary electrons generated from the bottom surface of the contact hole cannot be sufficiently detected.

Therefore, in the measurement by CD-SEM, in order to detect the signal from the bottom surface of the hole, it is attempted to prevent the charge on the sample surface and take out the signal from the bottom surface of the hole to outside of the hole. However, when the aspect ratio increases, the influence of the electric field applied to the sample surface cannot affect the inside of the hole. Therefore, it has become difficult to detect a signal (for example, secondary electrons) generated from the bottom of the hole and accurately perform measurement as a two-dimensional image.

コ ン タ ク ト In the inspection of a contact hole by the voltage contrast method, among the events occurring at the bottom of the hole, only the signal necessary for determining whether the hole is open or not is used to determine the hole opening degree. This is because when a defect on the bottom surface of the sample occurs, in this case, when a defect in the opening of the oxide film occurs, charges accumulate on the bottom surface of the hole, causing a charge phenomenon.

By observing such a phenomenon, it is possible to determine the defect of the hole. Therefore, it is possible to determine the hole opening / non-opening even in a sample having a large aspect ratio as compared with the CD-SEM. .

However, in the voltage contrast method, since the charge phenomenon at the bottom surface of the contact hole of the sample is observed, it is difficult to determine whether or not the hole is opened before the charge phenomenon occurs. This means that the inspection by the voltage contrast method is suitable for detecting a defect in a hole opening, but is not suitable for device manufacturing process management (inspection of process fluctuation).

Under such circumstances, it has been attempted to inspect the opening degree of the contact hole by measuring a current flowing through the layer in which the contact hole is formed and flowing through the silicon wafer, that is, an absorption current (for example, And Patent Document 1).

(4) The value of the absorption current changes according to the opening degree of the contact hole. That is, if a contact hole having a good opening degree is formed, the value of the absorption current increases.

On the other hand, if the opening degree of the contact hole is poor, for example, if the resist that has not been removed by etching remains at the bottom of the contact hole, or if the etching is not performed to a sufficient depth in the etching step, the absorption current Is small, and it can be determined from the absorption current value that the formation of the contact hole is insufficient.

Here, the principle of inspecting the opening degree of the contact hole based on the absorption current value will be briefly described. When the sample material is irradiated with an electron beam, secondary electrons, reflected electrons, and the like are generated by their interaction. Depending on the accelerating voltage of the electron beam or the material of the substance, electrons equal to or greater than the number of incident electrons are emitted or accumulated from the substance to the outside of the substance. Change.

Here, when the sample substance is grounded, electrons flow through the substance so as to offset the emission amount of secondary electrons and the like generated by the interaction. That is, if the incident electron current is I _p , the secondary electron current is I _se , the reflected electron current is I _be , and the absorption current is I _ab , the relationship between these currents is expressed by the following equation.

I _p = I _se + I _be + I _ab
I _ab = I _se − (I _be + I _p )
As shown in the above equation, the absorption current I _ab is determined according to the atomic number of the substance on the sample surface irradiated with the electron beam with respect to the total amount I _{p of the} electron beam (charged particle beam) applied to the sample. a reflected electron amount I _bE generated Te is represented by the difference between the secondary electron signal amount I _se generated according to the sample atomic number and the acceleration voltage.
JP 2000-174077 A

In the method of measuring the opening degree of the contact hole by measuring such an absorption current, a method of detecting the absorption current by continuously irradiating a charged particle beam, for example, an electron beam to a measurement region, a method of detecting charged particles in a pulse shape A method of measuring an absorption current by irradiating a beam has been proposed.

When trying to perform high-sensitivity measurement with these measurement methods, it is necessary to increase the amount of current of the charged particle beam to be irradiated if the sensitivity of the detector system is fixed in order to improve the detection sensitivity. is there. However, increasing the irradiation current intensifies the charge-up phenomenon on the sample surface, making it difficult to improve the detection sensitivity.

On the other hand, if the sensitivity of the detector system is to be improved for the purpose of improving the detection sensitivity, a high-sensitivity IV conversion amplifier is required since the current absorbed in the sample is detected. In order to improve the sensitivity of the IV conversion amplifier, the feedback resistance value to the amplifier is generally increased. However, along with this, the influence of the capacitance components existing around the detector and the constituent circuits increases, and as a result, If the signal detection time (response frequency) becomes slow or the resistance value used as the feedback resistor becomes large, the rate of change with respect to temperature becomes large, causing problems such as a decrease in measurement stability.

The present invention has been made in view of such a point, and an object of the present invention is to detect a charge transfer generated in a sample, thereby performing a highly sensitive inspection of a state of a semiconductor wafer sample such as a change in a bottom surface state of a hole. Another object of the present invention is to provide a semiconductor wafer sample inspection method and apparatus which can be performed with high accuracy.

A method for inspecting a semiconductor wafer sample according to the first aspect of the present invention includes irradiating a surface of the semiconductor wafer sample with a charged particle beam, detecting an electron current absorbed by the sample by the irradiation, and based on the absorbed electron current. In a semiconductor wafer sample inspection method for inspecting a wafer sample, electrodes are arranged at predetermined intervals on the back surface of the wafer sample or around the wafer sample, and the current flowing through the electrode capacitively coupled to the wafer sample is detected. The semiconductor wafer is inspected based on the detection signal.

According to the method for inspecting a semiconductor wafer sample according to the second aspect of the present invention, the charged particle beam is scanned in a predetermined two-dimensional area on the surface of the semiconductor wafer sample in which a large number of holes are formed, and is absorbed by the sample by this scanning. In a device for inspecting holes based on the value of the absorbed electron current, electrodes are arranged at predetermined intervals on the back surface of the wafer sample, and the current flowing through the electrodes is detected to detect the wafer current. It is characterized in that a change in surface charge is detected, and a hole opening degree is inspected based on the change in charge on the sample surface.

An inspection apparatus for a semiconductor wafer sample based on the invention according to claim 7 irradiates a surface of the semiconductor wafer sample with a charged particle beam, detects an electron current absorbed by the sample by the irradiation, and detects the electron current based on the absorbed electron current. In a semiconductor wafer sample inspection device that performs wafer sample inspection, electrodes are placed at a predetermined interval on the back surface of the wafer sample or around the wafer sample, and the current flowing through the electrode capacitively coupled to the wafer sample is detected. The semiconductor wafer is inspected based on a detection signal from the detection circuit.

The inspection apparatus for a semiconductor wafer sample based on the invention according to claim 8 scans a charged particle beam in a predetermined two-dimensional region on the surface of the semiconductor wafer sample in which a large number of holes are formed, and is absorbed by the sample by this scanning. In a device for inspecting holes based on the value of the absorbed electron current, electrodes are arranged at predetermined intervals on the back surface of the wafer sample, and the current flowing through the electrodes is detected to detect the wafer current. It is characterized in that a change in surface charge is detected, and a hole opening degree is inspected based on the change in charge on the sample surface.

An inspection apparatus for a semiconductor wafer sample based on the invention according to claim 13 irradiates a surface of the semiconductor wafer sample with a charged particle beam, detects an electron current absorbed by the sample by the irradiation, and detects the electron current based on the absorbed electron current. In a semiconductor wafer sample inspection apparatus for inspecting a wafer sample, electrodes are arranged at predetermined intervals around the wafer sample, and guide pins are provided for adjusting a distance between the wafer sample and the electrode. A detection circuit for detecting a current flowing through an electrode capacitively coupled to the sample is provided, and a semiconductor wafer is inspected based on a detection signal from the detection circuit.

(4) An electrode arranged at a predetermined interval on the back surface or side surface of the wafer sample, and means for detecting a capacitance generated between the back surface of the wafer sample and the electrode. As a result, the electric charge moving in the sample is accumulated by the capacitance component formed on the back surface or the side surface of the sample, and this capacitance component is measured by means such as measurement after integration by the Miller integration circuit. Noise can be reduced.

Also, by matching the scanning timing of the charged particle beam with the measurement timing, the measurement result can be determined as a result for each scan field. Further, by measuring after mirror integration, the integration time is lengthened, so that a smaller change in electric charge can be accurately measured.

Furthermore, by performing the charge measurement at the timing when the charged particle beam irradiation to the sample surface is not performed (the blanking period), the signal change in the sample can be measured in a constant state. Then, by comparing the measured data with the irradiation current and comparing the data as signal generation rate data, data comparison independent of the irradiation current amount can be performed.

In addition, the capacitance generated between the electrode that operates as the sample charge detector and the guide pin is significantly smaller than the capacitance generated between the sample and the electrode, or the device operates as a sample charge detector. The capacitance generated between the electrode to be measured and the holder that holds the electrode is significantly smaller than the capacitance generated between the sample and the electrode, so that accurate measurement of the absorption current is possible. In addition, the SN ratio of the measured value was improved, and the measurement of the absorption current with good reproducibility became possible.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a main part of an example of a scanning electron microscope used in the present invention, and FIG. 2 shows a signal detection system and a control system based on the configuration of FIG. In FIG. 1, reference numeral 1 denotes a sample chamber, and an electron optical system column 2 is disposed above the sample chamber 1. An electron gun (not shown) is provided on the upper part of the column 2, and an accelerated electron beam generated from the electron gun is introduced into the sample chamber 1 by a condenser lens and an objective lens (not shown). It is focused on the placed wafer sample 3.

(4) The electron beam is narrowly focused on the sample 3, and a predetermined area on the wafer sample 3 is two-dimensionally scanned by a scanning coil provided in the electron optical column 2. The scanning signal to the scanning coil is supplied from a scanning control circuit controlled by a control device such as a computer.

The wafer sample 3 has an oxide film 5 as an insulating material formed on a silicon wafer 4 to a uniform thickness by using a film forming technique such as vapor deposition or ion plating. Numerous contact holes 6 are formed in oxide film 5. This contact hole 6 is formed, for example, by the following process.

First, a resist is applied to the surface of the oxide film 5, and the wafer sample 3 coated with the resist is set in an exposure apparatus such as a stepper. A predetermined portion of a wafer where a contact hole is to be formed is exposed by this exposure apparatus. The exposed wafer sample 3 is developed, and thereafter, the resist at a predetermined exposed portion is removed, and the unexposed resist is left on the oxide film 5.

(4) The wafer sample 3 from which the resist at the predetermined location has been removed is subjected to an etching process using a plasma etching apparatus or the like. By this etching process, only a predetermined exposed portion is etched, and a large number of contact holes 6 are formed in oxide film 5.

ウ ェ ハ The wafer sample 3 in which the contact hole 6 has been formed in the above-described step is placed in the sample chamber 1. Although not shown in detail, the wafer sample 3 is placed on a sample stage capable of horizontal, vertical movement, rotation, etc., and the wafer sample 3 has a structure insulated from a member supporting the wafer sample. I have.

An electrode plate 7 is arranged below the wafer sample 3 in parallel with the back surface of the wafer sample 3, and a space is provided between the back surface of the wafer sample 3 and the plate 7 (the space in this case is a vacuum). I have to. With this configuration, a capacitor (capacitance) Cp is formed in which the back surface of the wafer sample 3 is a one-sided electrode and the plate 7 facing the back surface of the material wafer 3 is a counter electrode. The distance d of the space between the back surface of the material wafer 3 and the electrode plate 7 is set so that the capacitance required for the integration circuit configuration is obtained as a capacitance having a dielectric constant of 1 (vacuum).

(4) A Faraday cup 8 for measuring a current amount of a charged particle beam, for example, an electron beam applied to a material is provided near an end of the wafer sample 3. Further, an electrode wire 9 is connected to a part of the back surface of the wafer sample 3, and the other end of the electrode wire 9 is connected to a preamplifier described later. The electrode wire 9 is provided through the electrode plate 7, is protected by a shield 10 having the same potential as the electrode plate 7, and keeps the capacitance between the electrode wire 9 from the sample back surface detection terminal and the electrode wire 9 constant. Has a function.

With such a configuration, when the charged particle beam is scanned on the front surface of the wafer sample 3 (or when the current amount of the charged particle beam is measured by the Faraday cup 8), the distance between the back surface of the sample and the electrode plate 7 is set. The function to accumulate electric charge is provided for the capacitor to be used.

Next, the configuration of the signal detection circuit will be described with reference to FIG. Reference numeral 20 denotes a blanker including a blanking electrode 21 and a blanking plate 22, and the charged particle beam passing through the blanker is incident on the scanning coil 11 as a charged particle beam irradiated on the sample 3, and is scanned two-dimensionally. Reference numeral 11 denotes a scanning coil for two-dimensionally scanning the charged particle beam irradiated on the sample 3, and a scanning signal is supplied to the scanning coil 11 from a scanning control circuit 12. By the scanning of the charged particle beam by the scanning coil 11, a capacitance (capacitor) Cc is formed at the bottom of the contact hole according to the state of the bottom.

The preamplifier 13 constitutes a Miller integrating circuit by a capacitance formed between the back surface of the sample 3 and the electrode plate 7. The electrode wire 9 from the back surface of the sample 3 and the incident current signal from the Faraday cup 8 are connected to the + terminal of a preamplifier (differential amplifier) 13, and a shield 10 having the same potential as the electrode plate 7 is Connected to the output side of the operational amplifier 13. The negative terminal of the preamplifier 13 is grounded to the ground of this circuit.

Further, for the capacitance component constituting the Miller integrating circuit, a switch circuit S2 is provided between the input terminal (+ terminal) of the differential amplifier 13 and the output terminal of the differential amplifier 13 in order to reset the integrating circuit. Provided. Furthermore, a switch circuit S1 for grounding the input terminal of the differential amplifier 13 is provided to protect the Miller integrating circuit.

(4) The blanking signal from the scanning control circuit 12 is supplied to the preamplifier control circuit 14. Further, the preamplifier control circuit 14 controls the start and stop of the integration in the Miller integrating circuit (timing control of the switch circuit S2) and the timing of reading data.

In the configurations of FIGS. 1 and 2 described above, the semiconductor circuit formed on the silicon wafer 4 has no direct electrical connection with the wafer constituting the circuit, and is connected by a high resistance or capacitance. Further, as a material constituting the contact hole 6 for measuring the degree of opening (determining the quality of the hole opening), a material having no conductivity is often used. For this reason, when inspecting the contact hole 6, it is difficult to obtain a continuous absorption current accompanying the scanning of the charged particle beam only by irradiating the contact hole 6 with the charged particle beam. Cause difficulties in inspection.

In the embodiment of the present invention shown in FIG. 1 and FIG. 2, attention is paid to the point that the sample to be inspected is capacitively coupled, and the object is achieved by measuring the amount of movement of electric charges by time integration. I have.

(4) In order to prevent charging of the sample surface, it is necessary to shorten the irradiation time of the charged particle beam irradiated on the sample surface. To achieve this, the charged particle beam scans a predetermined area on the sample surface two-dimensionally at regular time intervals. The charged particle beam scanning control system generates a scanning end signal (blanking signal) every time the charged particle beam scans a predetermined area two-dimensionally. In the control of the preamplifier, data reading and refresh timing are controlled based on a blanking signal.

FIG. 3 is a timing chart of such control. FIG. 3A shows the timing of beam scanning. When the signal is at a high level, two-dimensional scanning on the sample by the charged particle beam is performed. When the signal is at a low level, a blanking period of the charged particle beam is set. (B) shows a signal obtained by two-dimensional scanning of the charged particle beam. When the charged particle beam scans the contact hole, an absorption current flows.

FIG. 3C shows the timing of the integration, that is, the timing when the switch circuit S2 is open. As is clear from the figure, integration is performed in synchronization with beam scanning. (D) shows the timing of reading data, and the data is read at the timing of blanking of beam scanning. (E) shows the output data Vo.

In the preamplifier 13, when each contact hole irradiates the wafer with a charged particle beam, charges are accumulated in the contact holes, and the change in the charges is caused by the capacitance formed between the back surface of the wafer and the electrode plate 7. Charge is accumulated. When the charged particle beam has completed scanning over the entire two-dimensional scanning area, the charged particle beam is blanked. The blanking of the charged particle beam stops the supply of new charges from the contact holes, so that the change in the charges in the capacitance portion formed on the back surface of the wafer stops.

(4) During the two-dimensional scanning of the charged particle beam, the switch S2 provided in the preamplifier unit 13 is kept open as described above. As a result, the preamplifier 13 operates as a Miller integrating circuit including the capacitance on the back surface of the wafer and the differential amplifier. When the charged particle beam reaches the blanking state, the output Vo from the Miller integrating circuit is stabilized. The output voltage Vo obtained here is the amount of charge transfer when the charged particle beam scans the contact hole.

(4) After receiving the blanking signal, the preamplifier control circuit 14 instructs the measurement system (data reading circuit 25) to measure the output signal Vo. When the measurement of the output signal Vo is completed, the preamplifier control circuit 14 generates an integrator reset signal and closes the reset switch S2 to refresh the sample back surface capacitance Cp. When the back surface capacitance Cp of the sample is reset, a scanning restart signal of the charged particle beam is instructed to the scanning control circuit 12.

Here, the measured output value can be converted into a current amount by the following calculation from the scanning time (measurement time Δt) and the sample back surface capacity.

Iin = −Vo (Cp / Δt)
Since the amount of signal detection varies depending on the amount of current of the charged particle beam to be irradiated, in order to obtain a correct measurement result, measure the amount of irradiation current before measurement and compare it with the ratio of the measured value to the amount of irradiation current Is desirable. Further, since the amount of charge transfer in the contact hole depends on the secondary electron signal generated from the sample, it is desirable to compare the irradiation current and the measured value when obtaining the measurement result.

Ipr = −Vpr (Cp / Δt)
Iin = −Vo (Cp / Δt)
When the signal generation rate δ is obtained from these two equations, the following is obtained.

δ = 1- (Iin / Ipr)
To summarize the above, the measurement result is equivalent to the following equation.

δ = 1- (Vin / Vpr)
By repeating the above operation, it is possible to obtain a measurement value for each scanning count for the scanning region of the charged particle beam.

FIG. 4 shows another embodiment. In this embodiment, a capacitor Cs having a reference capacitance is provided on the amplifier side as a capacitance constituting the integrator. Further, switches S1 and S2 are provided as reset means of the reference capacitance. The signal detection amplifier does not need to be provided outside the sample chamber, and may be provided near the electrode plate provided on the back surface of the sample.

{Circle around (2)} By providing a wiring having the same potential as the ground of the amplifier circuit between the electrode plate arranged on the back surface of the sample and the sample stage and isolating it from the stage ground, the SN ratio can be improved. The measurement reference capacitance (Cs) is provided between the input terminal and the output terminal of the preamplifier circuit 13 using the capacitance on the back surface of the sample as a buffer. In this case, the refresh and read timings by S1 and S2 are adjusted. The control may be performed without linking to the ranking operation. FIG. 5 shows a timing chart of each signal in this embodiment.

In the embodiment described above, the charge moving in the sample is accumulated by the capacitance component formed on the back surface of the sample, and this capacitance component is measured by means such as measurement after integration by the Miller integration circuit. In addition, measurement noise can be reduced.

Also, by matching the scanning timing of the charged particle beam with the measurement timing, the measurement result can be determined as a result for each scan field. Further, by measuring after mirror integration, the integration time is lengthened, so that a smaller change in electric charge can be accurately measured.

Furthermore, by performing the charge measurement at the timing when the charged particle beam irradiation to the sample surface is not performed (the blanking period), the signal change in the sample can be measured in a constant state. Then, by normalizing the measured data with the irradiation current and comparing the data as signal generation rate data, it is possible to obtain effects such as data comparison independent of the irradiation current amount.

As a result, the hole inspection apparatus according to the embodiment of the present invention described with reference to FIGS. 1 and 2 can detect a change in the state of the bottom surface of the hole with high sensitivity. However, the design rules of semiconductor devices are rapidly advancing, for example, it is expected that the diameter of contact holes will be reduced and the aspect ratio will continue to increase. Must be performed with high precision.

変 動 Further, variations in parameters due to etching, cleaning, implantation, polishing, and the like in the device manufacturing process and in-plane non-uniformity cause a decrease in the yield of semiconductor products and an increase in defective products due to aging. The problem that is causing the problem is also being miniaturized as in the case of the design rule. For example, it has been pointed out that in the variation of the contact resistance value of the hole, the variation of the level which has not been regarded as a problem so far has a possibility of developing into a serious defect in a future semiconductor product. Therefore, it is required to provide an inspection device with further improved accuracy. Hereinafter, an embodiment of the inspection apparatus with higher accuracy than the embodiment shown in FIGS. 1 and 2 will be described.

Before that, the configuration and operation of the capacitance detection system will be described in some detail. FIG. 6 shows a capacitance component detection system. In the figure, OL is an objective lens, Rw is the resistance between the electrodes in contact with the wafer, Cw is the capacitance of the wafer, Ch is the capacitance between the wafer and the back electrode, and Cs is the capacitance between the back electrode and its constituent base material. . In the absorption current detection system shown in FIG. 6, two kinds of signals Ia and Ib are obtained according to the fluctuation of the capacitance Cw of the wafer and the capacitance Cw between the wafer and the back electrode.

As the absorption current value, the signal Ia obtained from the first detection system Da between the capacitance Cw of the wafer 3, the capacitance Ch between the wafer 3 and the back electrode 7, and the capacitance between the back electrode and its constituent base material A signal obtained by adding the signal Ib obtained from the second detection system Db to Cs with the adder 29 is used. The relational expression is expressed as follows, assuming that the incident electron current is I _p , the secondary electron current is I _se , the reflected electron current is I _be , and the absorption current is I _ab .

_{I ab = I p - (I} se + I be) = Ia + Ib ... (1)
However, in reality, since the wafer is placed on the stage, as shown in the figure, the wafer (including peripheral members such as chambers) is transferred to the stage via the capacitance Cs between the back surface electrode and its constituent base material. Leakage current Is occurs. Therefore, the absorption current value is expressed as follows.

_{I ab = I p - (I} se + I be + Is) = Ia + Ib-Is ... (2)
Here, in the state of FIG. 6, when Ch ≦ Cs and Rw = ∞, the above equation (2) can be rewritten as follows.

_Iab = Ia + Ib-Is = 0 + Small-Large = Negative As a result, the detection ratio of Ia: Ib becomes 0: 100, and the degree of influence of Is increases. If the absorption current is detected in such a state, if Cs is large, Is becomes large, the absolute value of the measured current becomes small, the amplifier must be set to high gain, and if it is relatively very sensitive to noise, etc. I have no choice. Therefore, it becomes difficult to measure the absorption current with high accuracy.

(4) The resistance Rw between the electrodes in contact with the wafer changes depending on the type of the wafer and the difference in the manufacturing process. In the case of high-resistance contact (Rw = ∞), there were cases where current measurement became impossible. Further, the value of Rw changes due to the contact pressure of the wafer, and there has been a problem that the reproducibility of measurement becomes unstable.

To solve such a problem, in the equivalent circuit configuration shown in FIG. 6, the value of the capacitance Cs between the back electrode and its constituent base material may be reduced to a negligible level. In other words, by setting the state of Ch≫Cs, the leak current value Is decreases, and conversely, the measurement current increases, and is less affected by noise. Therefore, it is possible to measure the absorption current with high accuracy. Become.

構成 The configuration of FIG. 7 is a modification of the embodiment of FIG. 6, and the value of Cs is set to a sufficiently small value that can be ignored. Then, the configuration is such that Ia and Ib can be mixed and measured by the same amplifier 30. As a result, it is possible to realize a detection system that ignores the fluctuation of the unstable parameter Rw. Since switches S1 and S2 are provided for each of the Ia signal line and the Ib signal line, Ia, Ib, and Ia + Ib can be selected and detected.

で も In the embodiment shown in FIG. 8, as in the embodiment shown in FIG. 7, the value of Cs is set to a sufficiently small value and can be ignored. Then, Ia and Ib are supplied to separate amplifiers 31 and 32 so that arbitrary signal processing can be performed after amplifying each signal. For example, it is possible to predict Rw by separately measuring Ia and Ib and verifying the ratio.

Now, FIG. In the embodiment shown in FIG. 2, the electrodes 7 are arranged on the back surface of the wafer sample 3 at predetermined intervals, and the change in the charge on the surface of the wafer sample is determined by the current flowing through the electrode 7 capacitively coupled to the wafer sample 3. Is configured to be detected by measuring. The same effect can be achieved by using an electrode 35 arranged around the wafer sample 3 so as to surround the wafer sample 3 as shown in FIG. 9 as an electrode for detecting the amount of absorption current of the wafer sample 3.

In FIG. 9, the distance L between the electrode 35 and the wafer sample 3 is maintained at a constant value. The absorption current generated by irradiating the wafer sample 3 with the electron beam, that is, the electric charge accumulated in the sample, operates as a detector due to the spatial distance between the electrode 35 and the sample 3 and the capacitance due to vacuum. It is detected by the electrode 35. The signal detected by the electrode 35 is supplied to an amplifier 36. The coupling capacitance that determines the detection sensitivity of the electrode depends on the dielectric constant of the sample itself and the distance between the sample 3 and the electrode 35 serving as a detector.

In the embodiment shown in FIG. 10, four guide pins G1 to G4 for finely adjusting the position of the sample are provided in order to maintain the distance between the sample 3 and the electrode 35 at a predetermined value L. One end of each guide pin is in contact with the side of the wafer sample 3, and by slightly moving the guide pin in the direction of the arrow in the figure, the distance between the sample 3 and the electrode 35 can be finely moved. , And the distance between the sample 3 and the electrode 35 is maintained at a predetermined value L. As a result, the coupling capacitance Ch between the sample 3 properly set on the stage and the electrode 35 is prevented from fluctuating due to a change in the distance between the sample and the electrode.

(4) Each guide pin is formed of a conductive member, and the other end of each guide pin is connected to the amplifier 37. As a result, the charge from the sample 3 is supplied to the amplifier 37 via each guide pin. The signal amplified by the amplifier 37 is supplied to a data processing device 39 and a data determination processing unit 40 via a measuring device 38. The signal detected by the electrode 35 is supplied to a measuring device 38 via an amplifier 36.

In this embodiment, since the guide pins G1 to G4 are configured to contact the sample 3, it is possible to directly measure the charge in the sample. Furthermore, since the signal from the guide pin and the signal from the electrode 35 can be separately detected, the data processing device 39 and the data determination processing unit 40 can also determine the state of the wafer sample 3 such as charging. Can do it. Of course, the detection signal from the electrode 35 and the signals detected by the guide pins G <b> 1 to G <b> 4 can be added by the measuring instrument 38, and the added value can be used as the total charge measured in the sample 3 to be inspected.

When the signal from the electrode 35 operating as the sample charge detector is 0, the back surface of the sample is in contact with the electrode plate 7 shown in FIG. 1, for example, or the guide pins are in contact with the sample around the sample. Can be determined. Conversely, when the signal from the electrode 35 is other than 0, it can be determined that the guide pin contact portion on the back surface of the sample or around the sample has contact resistance.

Further, since the detection signal is processed by the data processing device 39 and various determinations are made by the data determination processing unit 40 based on the processing result, for example, the detection signal from the electrode 35 as a sample charge detector is output. When the detection signal is detected immediately after the irradiation of the charged particle beam and the detection value becomes 0 thereafter, it can be determined that the sample 3 is formed of a substance having a high dielectric constant.

で は In the embodiment of the present invention shown in FIG. 10, the following inspection can be further performed. That is, when the signal from the electrode 35 serving as the sample charge detector is 0, it can be determined that the guide pins G1 to G4 are in contact with the back surface of the sample 3 or the peripheral portion of the sample 3. Conversely, when the signal from the electrode 35 serving as the sample charge detector is other than 0, it is determined that the contact portions of the guide pins G1 to G4 have contact resistance on the back surface of the sample 3 or on the peripheral portion of the sample 3. can do.

These determinations are made by the signal processing system shown in FIG. 10 as follows. That is, after the signals detected by the electrodes 35 and the signals detected by the guide pins G1 to G4 are amplified by the amplifiers 36 and 37, respectively, the current amount of each signal is measured by the measuring instrument 38. The current values of the two signals measured by the measuring device 38 are stored in the data processing device 39, and the stored data is supplied to the data determination processing unit 40. The data processing determination processing unit 40 determines whether the sample 3 is in contact with the guide pin, for example, based on the two types of current value data of the signal detected by the electrode 35 and the signal detected by the guide pins G1 to G4. It is determined whether or not the guide pin contact portion has contact resistance. The determination result is printed out by a printer (not shown) or displayed on a display device such as a liquid crystal display.

In the configuration of FIG. 10, a signal from the electrode 35 serving as a sample charge detector is supplied to the measuring device 38 via the amplifier 36, and a signal corresponding to the sample charge is detected. In the configuration shown in FIG. 10, when the sample 3 is irradiated with a charged particle beam such as an electron beam, a current signal of a predetermined value or more is detected immediately after the irradiation of the beam, and then the detected value may become zero.

FIG. 11 shows such a detection signal waveform, in which the horizontal axis represents time (t) and the vertical axis represents current value. In the detection signal waveform diagram, the sample is irradiated with the charged particle beam at time T1, and the sample charge detection signal sharply rises simultaneously with the irradiation of the charged particle beam. The time from the time T1 to the time T2 when the maximum value of the detection signal is detected is a signal rise time t1. The detection signal sharply rises to the maximum value, but after the maximum value, decreases relatively slowly, and becomes zero at time T3. The time from the time T2 to the time T3 is a signal fall time t2.

As in the waveform shown in FIG. 11, when the signal rises at the same time as the irradiation of the charged particle beam and the detection signal becomes 0 thereafter, it is determined that the sample 3 is formed of a substance having a high dielectric constant. be able to. This determination is made in the data determination processing unit 40.

Also, as shown in FIG. 12, when it is known that the dielectric film 45 is formed on the surface of the sample 3 to be inspected, when a signal as shown in FIG. 11 is detected, the dielectric film 45 on the sample surface is detected. It can be determined that the thickness is large. The dielectric constant of this dielectric film can also be determined by the maximum value Sm of the detection signal, and by measuring various samples and comparing the maximum value of the detection signal at the time of measurement for each sample, various values can be obtained. The magnitude of the dielectric constant of the sample can be known.

比較 Such comparison of the dielectric constant of each sample can be performed by the rise time t1 of the detection signal. That is, the rise time t1 becomes shorter as the sample has a higher dielectric constant. The comparison of the dielectric constant of each sample can be performed by the fall time t2 of the detection signal. That is, the fall time t2 becomes shorter as the sample has a higher dielectric constant. Further, the comparison of the dielectric constant for each sample can be performed based on the half width W of the detection signal. That is, the half value width W of the detection signal becomes smaller as the sample has a higher dielectric constant.

Next, a method for determining whether an insulating film is formed on the back surface of the sample 3 or the sample contact surface of the guide pin, and the thickness of the insulating film when the insulating film is formed will be described. When making this determination, the configuration shown in FIG. 10 is used. First, when a signal is detected by both the electrode 35 serving as a sample charge detector and the guide pins G1 to G4, it is determined that an insulating film is formed on the back surface of the sample or the sample contact surface of the guide pin. it can.

In determining the thickness of the insulating film formed on the sample surface, the determination can be made based on the ratio between the signal intensity detected by the electrode 35 and the signal intensity detected by the guide pin. That is, it can be determined that the larger the ratio of the signal intensity detected by the electrode 35, the thicker the insulating film. When obtaining the absolute value of the thickness of the insulating film, the relationship between the ratio of the signal strength and the thickness of the insulating film is stored in a table format in advance, and the ratio of the two signal strengths is actually measured during an inspection. And the thickness of the corresponding insulating film may be read from the stored table.

By the way, the detection signal from the electrode 35 and the signals detected by the guide pins G1 to G4 were amplified by amplifiers 36 and 37, respectively, and then added by a measuring device 38. The added value was measured in the sample 3 to be inspected. It has been described earlier that it can be used as the total charge. By comparing this total charge amount with the total amount of current of the charged particle beam irradiated on the sample when measuring the total charge amount, the film pressure of the dielectric film on the surface of the sample 3 to be compared is estimated. Can be.

Next, the sample 3 is irradiated with a charged particle beam, the total charge is measured for a certain period of time, and a change rate R of the total charge within the measurement time is obtained. FIG. 13 shows the time change of the rate of change R of the total charge, and the charged particle beam is irradiated on the sample at time T1. The change rate of the total charge amount after the irradiation of the charged particle beam is measured, and when the change rate R becomes equal to or less than a predetermined threshold value S (T4), the measurement of the change rate is terminated.

When the rate of change R becomes equal to or less than a predetermined threshold value S (T4), the total electric charge is collected and stored, and the total electric charge obtained by a similar method using a standard sample or various different samples is obtained. A comparison with the amount is made. This comparison processing is performed in the data determination processing unit 40, and various items of the sample 3 can be inspected.

FIG. 14 shows another embodiment of the present invention. After the detection signal from the electrode 35 and the signals detected by the guide pins G1 to G4 are amplified by amplifiers 36 and 37, respectively, To supply. In the imaging processing unit 46, luminance and contrast are adjusted so that the two types of signals can be used as video signals.

The video signal subjected to the signal processing in the imaging processing unit 46 is supplied to a display device 47 such as a cathode ray tube or a liquid crystal display, so that the display device 47 displays the two-dimensional charged particle beam in a specific region of the sample 3. Based on the scanning, a surface image of the sample based on the signal detected by the electrode 35 is obtained. Further, a surface image of the sample can be obtained in the same manner by using the signals detected by the guide pins G1 to G4 as the video signals. Of course, a surface image of the sample can be obtained in the same manner by using a signal obtained by adding a signal detected by the electrode 35 and a signal detected by the guide pins G1 to G4 as a video signal. The image obtained in this manner detects charge transfer occurring in the sample and is based on the detection signal, so that a change in the state of the bottom surface of the hole can be visualized with high accuracy.

FIG. 3 shows a wafer sample and a plate electrode arranged in a sample chamber according to the present invention. FIG. 2 is a diagram illustrating an example of a circuit that measures capacitance in the configuration of FIG. 1. FIG. 3 is a timing chart of the measurement circuit of FIG. 2. FIG. 2 is a diagram illustrating another example of a circuit for measuring capacitance in the configuration of FIG. 1. FIG. 5 is a timing chart of the measurement circuit of FIG. 4. FIG. 3 is a diagram illustrating an example of an equivalent circuit for measuring electric charge absorbed by a sample. FIG. 9 is a diagram illustrating another example of an equivalent circuit for measuring the electric charge absorbed by the sample. FIG. 9 is a diagram illustrating another example of an equivalent circuit for measuring the electric charge absorbed by the sample. FIG. 9 is a diagram showing another embodiment of the present invention in which electrodes operating as a sample charge detector are arranged around a sample. FIG. 10 is a diagram showing an embodiment of the present invention that enables fine adjustment of a sample position in the configuration shown in FIG. 9. FIG. 5 is a diagram showing a time change of an absorption current value when a charged particle beam is irradiated on a sample. FIG. 5 is a diagram illustrating an embodiment in which signal processing is performed when a dielectric film is formed on a sample surface. FIG. 4 is a diagram showing a change rate curve of a total charge amount when a sample is irradiated with a charged particle beam. FIG. 4 is a diagram illustrating an embodiment in which a sample image is displayed based on an absorption current of the sample.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Electron gun 2 Blanking electrode 3 Deflection electrode 4 Aperture 5 Knife edge 6 Detector 7 Device control unit 8 Data control unit 9 Blanking amplifier 10 DA conversion amplifier 11 Preamplifier 12 Signal processing unit 13 Correction table 14 Adder 15 Position Correction circuit

Claims (19)

In a semiconductor wafer sample inspection method of irradiating a charged particle beam to a surface of a semiconductor wafer sample, detecting an electron current absorbed by the sample by the irradiation, and inspecting the wafer sample based on the absorbed electron current, An electrode is arranged at a predetermined interval on the back surface or around the wafer sample, a current flowing through the electrode capacitively coupled to the wafer sample is detected, and a semiconductor wafer is inspected based on the detection signal. Inspection method for semiconductor wafer samples. A charged particle beam is scanned in a predetermined two-dimensional area on the surface of a semiconductor wafer sample on which a large number of holes are formed, and an electron current absorbed by the sample is detected by this scanning. In a device for inspecting, the electrodes are arranged at a predetermined interval on the back surface of the wafer sample, and the change in the charge on the surface of the wafer sample is detected by detecting the current flowing through the electrodes. And a method for inspecting a semiconductor wafer sample, wherein an opening degree of a hole is inspected. 3. The method for inspecting a semiconductor wafer sample according to claim 1, wherein mirror integration is performed based on a signal from the wafer sample and a signal from the electrode. The charged particle beam blanking period is provided between the charged particle beam scanning periods, and the capacitance generated between the wafer sample and the electrode is refreshed during the blanking period. Inspection method for semiconductor wafer samples. The semiconductor wafer sample according to any one of claims 1 to 4, wherein a blanking period of the charged particle beam is provided during a scanning period of the charged particle beam, and an output signal is taken out from the Miller integration circuit during the blanking period. Inspection method. 6. The apparatus according to claim 1, further comprising a measuring device for measuring a current amount of the charged particle beam applied to the wafer sample, and determining a ratio of a capacitance generated between the wafer sample and the electrode to the measured current amount. An inspection method for a semiconductor wafer sample according to any one of the above. In a semiconductor wafer sample inspection apparatus that irradiates a charged particle beam onto the surface of a semiconductor wafer sample, detects an electron current absorbed by the sample by the irradiation, and inspects the wafer sample based on the absorbed electron current, An electrode is arranged at a predetermined interval on the back surface or around the wafer sample, and has a detection circuit for detecting a current flowing through the electrode capacitively coupled to the wafer sample, based on a detection signal from the detection circuit. And a semiconductor wafer sample inspection apparatus for inspecting a semiconductor wafer. A charged particle beam is scanned in a predetermined two-dimensional area on the surface of a semiconductor wafer sample on which a large number of holes are formed, and an electron current absorbed by the sample is detected by this scanning. In a device that inspects the wafer, the electrodes are arranged at a predetermined interval on the back surface of the wafer sample, the change in the charge on the wafer sample surface is detected by detecting the current flowing through the electrodes, and based on the change in the charge on the sample surface. And a semiconductor wafer sample inspection apparatus for inspecting a hole opening degree. 9. The semiconductor wafer sample inspection apparatus according to claim 7, further comprising a circuit that performs a mirror integration based on a signal from the wafer sample and a signal from the electrode. 10. A control circuit for providing a blanking period of a charged particle beam between scanning periods of a charged particle beam and refreshing a capacitance generated between a wafer sample and an electrode during the blanking period. 2. The semiconductor wafer sample inspection apparatus according to claim 1. 11. The semiconductor according to claim 7, further comprising a control circuit for providing a blanking period of the charged particle beam during a scanning period of the charged particle beam and extracting an output signal from the Miller integration circuit during the blanking period. Wafer sample inspection device. 12. The method according to claim 7, further comprising a measuring device for measuring a current amount of the charged particle beam applied to the wafer sample, wherein a ratio of a capacitance generated between the wafer sample and the electrode to the measured current amount is obtained. An inspection device for a semiconductor wafer sample according to any one of the above. In a semiconductor wafer sample inspection apparatus that irradiates a charged particle beam onto the surface of a semiconductor wafer sample, detects an electron current absorbed by the sample by the irradiation, and inspects the wafer sample based on the absorbed electron current, Electrodes are arranged at predetermined intervals around the periphery, equipped with guide pins for adjusting the distance between the wafer sample and the electrodes, and provided with a detection circuit for detecting the current flowing through the electrodes capacitively coupled to the wafer sample. And a semiconductor wafer sample inspection apparatus for inspecting a semiconductor wafer based on a detection signal from the detection circuit. 14. The apparatus for inspecting a semiconductor wafer sample according to claim 13, wherein the guide pin is formed of a conductive material, and can directly measure a charge amount in the sample. The capacitance generated between an electrode that operates as a sample charge detector and a guide pin is significantly smaller than the capacitance generated between a sample and an electrode. The inspection device for a semiconductor wafer sample according to any one of the above. The capacitance generated between the electrode operating as the sample charge detector and the guide pin is set to be 1/10 or less of the capacitance generated between the sample and the electrode. Item 16. An inspection device for a semiconductor wafer sample according to item 15. The capacitance generated between the electrode operating as the sample charge detector and the holding table holding the electrode is significantly smaller than the capacitance generated between the sample and the electrode. An apparatus for inspecting a semiconductor wafer sample according to claim 13. The capacitance generated between the electrode that operates as the sample charge detector and the holder that holds the electrode must be set to 1/10 or less of the capacitance generated between the sample and the electrode. The inspection apparatus for a semiconductor wafer sample according to claim 17, wherein: 19. An apparatus according to claim 13, further comprising a device for detecting a current from each of an electrode operating as a sample charge detector and a guide pin, and determining a state of the sample based on two types of detection signals. Inspection equipment for semiconductor wafer samples.

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