JP2006294627A - Electron beam device and device manufacturing method using this device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electron beam device with a simple structure capable of performing measurement or the like of potential contrast with a high throughput and with high reliability, and a device manufacturing method for manufacturing a device at a good yield using this device. <P>SOLUTION: The electron beam device which irradiates a test piece formed with a pattern by electron beam and evaluates the test piece comprises an electron optical lens barrel 1 housing an electron beam source EG, an objective lens 14, electromagnetic deflectors 11, 12, and a secondary electron beam detector 17. The objective lens 14 is constructed of an upper electrode 18, a center electrode 19, and a lower electrode 20, and furthermore has a control power supply 21 for impressing voltage on the upper electrode, the center electrode 19, and the lower electrode 20. The control power supply 21 impresses a voltage of a certain value to the center electrode 19 and, by performing dynamic focusing by the upper electrode 18, operates so that the objective lens 14 may satisfy focusing conditions. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

Detailed Description of the Invention

TECHNICAL FIELD OF THE INVENTION

  The present invention relates to an electron beam apparatus for evaluating defect inspection, line width measurement, alignment accuracy measurement, etc. of a wafer having a pattern with a minimum line width of 0.1 μm or less, and a device with high yield using the apparatus. The present invention relates to a manufacturing method for manufacturing.

Conventional technology

  2. Description of the Related Art Conventionally, an apparatus that irradiates a sample such as a wafer with an electron beam, detects a secondary electron beam generated from the sample, and performs defect inspection, CD inspection, defect review SEM, alignment accuracy measurement, and the like is known. In particular, it is impossible to evaluate the defects of a sample by applying a charge to charge a pattern and measuring the potential appearing on the surface as a result. Widely done.

  When obtaining the potential contrast of the pattern on the sample in the conventional electron beam device, the resolution of the device without the energy filter for the secondary electron beam is small, but the device with such an energy filter has a small potential resolution. Is known to be measurable. If the objective lens has this energy filter function, there is a problem that the aberration coefficient of the objective lens increases. In addition, in order to correctly align the evaluation place of the sample under the electron optical system, a registration subsystem similar to the drawing apparatus is required, and there is a problem that the entire apparatus becomes large and complicated.

In addition, in the conventional electron beam apparatus, various problems, for example,
About the E × B separator for separating the primary electron beam and the secondary electron beam, it was unclear what structure was simple and desired accuracy could be obtained.
Shot noise is large, and a large beam current is required to obtain the required signal / noise ratio.
There was no electrostatic chuck that can attract the convex wafer flat.
In the overlapping part of the field of view of the primary optical system, there was a place where a dose of 2 times, sometimes 4 times, was given, and there was a possibility that the wafer was destroyed,
It was difficult to secure a space for arranging the scanning deflector between the objective lens and the upper lens.
There was a problem such as.

  The present invention has been proposed in order to solve the above-described various problems, and an object of the present invention is to provide an electron beam apparatus having a simple structure capable of performing high-potential measurement of potential contrast and the like with high reliability. And a device manufacturing method for manufacturing a device with a high yield using the apparatus.

In order to achieve the above object, an electron beam apparatus according to the invention of claim 1 comprises:
An electron beam apparatus for irradiating a sample on which a pattern is formed with an electron beam and evaluating the sample,
An electron optical barrel containing an electron beam source, an objective lens, an electromagnetic deflector and a secondary electron beam detector
The objective lens is composed of an upper electrode, a center electrode and a lower electrode,
A control power supply for applying a voltage to the upper electrode, the central electrode and the lower electrode;
The control power supply is configured to apply a constant voltage to the central electrode and perform dynamic focusing on the upper electrode so that the objective lens satisfies a focusing condition.

An electron beam apparatus according to the invention of claim 2
The control power supply provides three different voltages to the upper electrode as the dynamic focus control,
Measure the signal intensity of the secondary electron beam when the three different voltages are applied, and perform a quadratic function approximation from the signal intensity,
An intermediate value between the voltage value corresponding to the maximum value of the rising slope of the quadratic function and the voltage value corresponding to the maximum value of the quadratic function is used as the voltage of the upper electrode.

  The electron beam apparatus according to a third aspect of the invention is characterized in that the control power supply applies a voltage so that a voltage difference between the upper electrode, the intermediate electrode, and the lower electrode is 20 kV or less.

  The electron beam apparatus according to the invention of claim 4 is characterized in that the thickness of the central electrode is 2 mm or less in the optical axis direction.

  The electron beam apparatus according to a fifth aspect of the invention is characterized in that the sample includes a plurality of small regions divided so as not to overlap each other, and only the small regions are evaluated.

  The electron beam apparatus according to claim 6 is such that when the pixel size of the pattern is p and the beam size of the electron beam irradiating the pattern is d, the p and the d are 0.9 <d / p. <1.2 is satisfied.

  A device manufacturing method according to a seventh aspect of the invention is characterized in that a wafer during or after the process is evaluated using the electron beam apparatus according to any one of the first to sixth aspects.

BEST MODE FOR CARRYING OUT THE INVENTION

  FIG. 1 is a diagram schematically showing one embodiment of an electron beam apparatus according to the present invention. In the figure, an electron gun EG comprising a cathode 2, a Wehnelt 3 and an anode 4 is provided inside the electron optical column 1, and a primary electron beam emitted from the electron gun EG passes through a crossover 5 through a first opening. The first aperture plate 6 having a square shaped aperture is irradiated under the conditions created between the plate 6 and the first condenser lens 7. As a result, the primary electron beam is reduced by the first condenser lens 7, and a crossover image 8 is formed in the square opening of the second aperture plate 9. Further, the primary electron beam is reduced by the second condenser lens 10, passes through the E × B separator 13 including the electrostatic deflector 11 and the electromagnetic deflector 12, and then converged by the objective lens 14, A reduced image of a square opening formed in one aperture plate 6 is formed on the wafer 15.

  The secondary electron beam emitted from the wafer 15 by the irradiation of the primary electron beam is accelerated and converged by the objective lens 14, and then deflected to the right side of the figure by the E × B separator 13 to take the trajectory 16. It is detected by the electron beam detector 17. The objective lens 14 has an upper electrode 18, a central electrode 19, and a lower electrode 20, and a required voltage is applied to these electrodes from a control power source 21.

  The E × B separator 13 can be constituted by, for example, a combination of an 8-pole electrostatic deflector and a saddle type electromagnetic deflector, so that the structure is simple and the primary electron beam is not affected. There is an advantage that extra aberration is not generated. Here, even if only an electromagnetic deflector is used instead of the E × B separator, the secondary electron beam can be detected depending on the scanning field of view.

  In order to scan the wafer 15 with the primary electron beam, the primary electron beam is controlled to pass through the track 23 by the electrostatic deflector 11 and the other electrostatic deflector 22. Thus, since the electrostatic deflector 11 of the E × B separator 13 is used as the second stage electrostatic deflector, the space above the objective lens 14 can be used effectively. In addition, considering that it is advantageous that the second stage electrostatic deflector is closer to the objective lens 14, the electrostatic deflector 11 of the E × B separator 13 can be used as a second stage electrostatic deflector. By providing the function, the second stage electrostatic deflector can be arranged at the best position.

  A voltage of −4 kV is applied to the wafer 15 from the control power supply 21. In this case, if the falling speed of the voltage from the control power supply 21 is not set to about 100 V / 10 seconds, for example, the device may be destroyed, and the voltage is gradually applied to the wafer 15.

  In order to electrostatically hold the wafer 15 by suction, an electrostatic chuck 27 having an electrode plate composed of three electrodes 24 to 26 is provided as shown in FIG. At this time, in order to avoid a discharge between the wafer 15 and the objective lens 14, of the three electrodes 24 to 26, the central electrode 24 corresponding to the central portion of the electrode plate and a part of the periphery of the electrode plate A voltage of 0 V is applied to the first electrode 25 corresponding to the portion, and after the voltage applied to the wafer 15 reaches −4 kV, the second electrode 26 corresponding to the remaining portion around the electrode plate is applied. A voltage of 0V is applied. By using the electrostatic chuck having the structure shown in FIG. 2, even if the wafer is convex upward, the entire surface can be attracted and held flat.

In order to place the wafer 15 on the electrostatic chuck, the wafer 15 is first supplied from the robot 28 to the environment chamber 29 where pre-alignment including rotation of the wafer 15 and placement of the wafer 15 at the correct xy coordinate position is performed. Is done. Next, after the loading chamber 30 is brought to atmospheric pressure, the gate valve 31 is opened to put the wafer 15 into the loading chamber 30. Therefore, after pulling out the loading arm from the loading chamber 30, the gate valve 31 is closed and the loading chamber 30 is evacuated. When the degree of vacuum of the loading chamber 30 becomes 1 × 10 ⁻⁶ Torr or less, the gate valve 32 is opened, and the wafer 15 is attached to the electrode 24 of the electrostatic chuck by a loading arm provided with a part of the electrostatic chuck. -26.

  In FIG. 1, reference numeral 33 indicates a stage for placing the wafer 15, 34 indicates a valve, and 35 indicates an ion pump for exhausting the inside of the lens barrel 1 via the valve 34. It is preferable to magnetically shield the wafer 15 by accommodating the stage 33 on which the wafer 15 is placed in a working chamber (not shown) made of iron as a ferromagnetic material.

  The electron gun EG shown in FIG. 1 is operated under a space charge limited condition by sufficiently increasing the heater voltage or sufficiently increasing the Wehnelt voltage. As a result, if the number of secondary electron beams detected per pixel is 50, evaluation such as defect inspection can be performed with sufficient reliability. Further, if the number of electrons of the secondary electron beam detected per pixel is 100, it is possible to provide a function as a Review SEM. In the case of this Review SEM, the stage 33 is stopped for observation.

Next, the objective lens 14 will be described. In order to control the objective lens 14 so as to satisfy the focusing condition, the voltage applied to the central electrode 19 of the objective lens 14 is set to a predetermined constant value, and the upper electrode 18 Focus is performed. This is realized by the following procedure. First, three different voltages are applied to the upper electrode 18 at a wafer position where a pattern parallel to the x-axis and the y-axis exists, such as a dicing line at a corner of the die. In each of these voltage values, pattern edges parallel to the x direction and the y direction are scanned in the y direction and the x direction, respectively, and the rising slope of the signal intensity of the secondary electron beam at that time is scanned in the y direction and x. Measure against directional scan. For example, rising slopes with respect to scanning in the y direction are a ₁ mV / μm, a ₂ mV / μm, and a ₃ mV / μm, and rising slopes with respect to the x direction scanning are b ₁ mV / μm and b ₂ mV / μm. And b ₃ mV / μm. From these rising slopes, the maximum values of rising slopes a _i mV / μm and b _i mV / μm are obtained by using a quadratic function approximation to the voltage applied to the upper electrode 18. Next, the voltages of the upper electrode 18 giving these maximum values are obtained, respectively, and the voltage of the upper electrode 18 is set to an intermediate value between them.

  In addition, when the voltage of the upper electrode 18 that gives the maximum value of the rising slope is larger than a predetermined value, it is preferable to superimpose a voltage for performing astigmatism correction on the electrostatic deflector 11 of the EB separator 13.

  FIG. 3 is a graph showing a change in axial chromatic aberration when the thickness of the central electrode 19 of the objective lens 14 is changed in the vicinity of the optical axis. The half-angle of the aperture of the beam on the sample surface is 30 milliradians. The voltage difference between the upper electrode 18 and the central electrode 19 and the voltage difference between the central electrode 19 and the lower electrode 20 were both adjusted to be 20 kV or less. In this state, the line 41 indicates the axial chromatic aberration when the voltage that causes the filtering action of the secondary electron beam is applied to the lower electrode 20, and the line 42 indicates the voltage at which the axial chromatic aberration coefficient is minimized. The axial chromatic aberration in the state applied to the electrode 20 is shown.

  The axial chromatic aberration represents the amount of beam blur due to the energy width. Therefore, assuming that the axial chromatic aberration is ΔCc, the axial chromatic aberration coefficient is Cc, and α represents the half aperture angle of the beam on the sample surface,

[Equation 1]
ΔCc = Cc (ΔV / V) α
Holds. Therefore, ΔCc is an aberration generated per unit (energy width / beam energy) per unit aperture half angle.

From the graph of FIG.
(1) When the thickness of the central electrode 19 is 2 mm or less, the focusing condition of the primary electron beam is satisfied only under a condition in which a voltage that causes a filtering action of the secondary electron beam is applied to the lower electrode 20;
(2) When the thickness of the central electrode 19 is 1.5 mm or less, the axial chromatic aberration coefficient can be greatly reduced under the condition that a voltage that causes the filtering action of the secondary electron beam is applied to the lower electrode 20. ,
(3) When the thickness of the center electrode 19 is 1.0 mm or less, the axial chromatic aberration is 100 nm or less, and is most preferable.
I understand.

  FIG. 4 is a diagram for explaining an alignment mechanism that measures the direction of the dies on the wafer 15. In the figure, reference numeral 51 is a dicing line, 51 'is one of the sides in the y direction of one dicing line 51, 52 is a test via provided on the dicing line 51, 53 is The field of view of the electron optical system when the stage 33 is at the first position, and 54 is the position of the electron optical system when the stage 33 is moved by the unit length in the y direction from the first position and placed at the second position. The field of view 55 indicates the chip area.

  Therefore, in order to correct the deviation between the direction in which the dies are arranged and the direction in which the stage 33 moves in the y direction, first, one side 51 ′ of one dicing line 51 extending in the y direction within the field of view 53 of the electron optical system. , And the position of the side 51 ′ in the x direction in the field of view 54 of the electron optical system, respectively, and then the difference between these positions is divided by the unit length in the y direction. . Thereby, a deviation angle between the direction in which the dies are arranged and the moving direction of the stage 33 in the y direction is calculated. Accordingly, when the stage 33 is continuously moved in the y direction, the stage 33 may be moved in the x direction so as to correct the deviation angle.

  In FIG. 4, a chip region 55 surrounded by adjacent dicing lines parallel to the y-axis and adjacent dicing lines parallel to the x-axis is an evaluation target. By doing so, since the beam irradiation is not performed twice on the chip region 55, there is no possibility of damaging the device oxide film or the like if the irradiation amount is kept below a predetermined value.

  FIG. 5 is a graph showing changes in various parameters when d / p is taken on the horizontal axis when the beam size of the primary electron beam is d and the pixel size is p. A graph 61 is a curve showing the value of MTF, and shows how the contrast decreases when the beam dimension d is large (when observing with a so-called blurred beam). A graph 62 is a curve representing the beam current of the primary electron beam. When axial chromatic aberration is dominant, the beam current is proportional to the fourth power of the beam diameter. That is, the graph 62 is a straight line that rises to the right with an inclination of 4: 1. A graph 63 is a curve showing the square of the MTF value. Note that MTF is an abbreviation for Modulation Transfer Function and represents the degree of deterioration of signal contrast when the odor structure is scanned with a blurred beam.

  When shot noise is dominant, the S / N ratio of the signal output from the secondary electron detector 17 is as follows:

[Equation 2]
S / N = MTF (N / 2) ^1/2 ∝MTF (i) ^1/2
It is represented by Therefore, in order to maximize the S / N ratio, (MTF) ² i may be maximized. (MTF) ² i is the product of the value shown by the graph 62 and the value shown by the graph 63, and becomes an upwardly convex curve represented by the graph 64. From this graph 64,
(1) When d / p≈1.1, the S / N ratio is maximized.
(2) When 1.0 <d / p <1.15, the S / N ratio is almost the same as the maximum value.
(3) When 0.9 <d / p <1.2, the S / N ratio is a sufficiently large value.
I understand that.

    Next, the semiconductor device manufacturing method of the present invention will be described with reference to FIGS. The semiconductor device manufacturing method of the present invention evaluates a wafer during or after the process using the above-described evaluation apparatus. A general semiconductor device manufacturing method will be described below with reference to the flowcharts of FIGS.

  As shown in FIG. 6, the semiconductor device manufacturing method is roughly divided into a wafer manufacturing step S1 for manufacturing a wafer, a wafer processing step S2 for performing processing necessary for the wafer, and a mask required for exposure. It comprises a mask manufacturing process S3, a chip assembly process S4 that cuts out chips formed on the wafer one by one and enables operation, and a chip inspection process S5 that inspects the completed chip. Each of these steps includes several sub-steps.

  Among the processes described above, the process that has a decisive influence on the manufacture of semiconductor devices is a wafer processing process. This is because in this process, the designed circuit pattern is formed on the wafer and a large number of chips that operate as a memory or MPU are formed.

  Thus, it is important to evaluate the processing state of the wafer executed in the sub-process of the wafer processing process that affects the manufacture of the semiconductor device, and the sub-process will be described below.

  First, a dielectric thin film that forms an insulating layer is formed, and a metal thin film that forms a wiring portion and an electrode portion is formed. Thin film formation is performed by CVD, sputtering, or the like. Next, the formed dielectric thin film and metal thin film and the wafer substrate are oxidized, and a resist pattern is formed in the lithography process using the mask or reticle created in the mask manufacturing process S3. Then, the substrate is processed according to the resist pattern by dry etching technique or the like, and ions and impurities are implanted. Thereafter, the resist layer is peeled off and the wafer is inspected.

  Such a wafer processing process is repeated for the required number of layers, and a wafer before being separated for each chip in the chip assembly process S4 is formed.

  FIG. 7 is a flowchart showing a lithography process which is a sub-process of the wafer processing process of FIG. As shown in FIG. 7, the lithography process includes a resist coating process S21, an exposure process S22, a developing process S23, and an annealing process S24.

  In the resist coating step S21, a resist is coated on the wafer on which the circuit pattern is formed by using CVD or sputtering, and in the exposure step S22, the coated resist is exposed. Then, in the developing step S23, the exposed resist is developed to obtain a resist pattern, and in the annealing step S24, the developed resist pattern is annealed and stabilized. These steps S21 to S24 are repeated for the required number of layers.

In the semiconductor device manufacturing method of the present invention, by using the electron beam apparatus described in relation to FIG. 1 in the chip inspection step S5 for inspecting a completed chip, even a semiconductor device having a fine pattern, Since an image with reduced distortion, blur, etc. can be obtained, defects on the wafer can be reliably detected. Note that the processing apparatus in which the electron beam apparatus is disposed in the vicinity may be any processing apparatus as long as it performs processing that requires evaluation.
〔The invention's effect〕

As described above, as described from one embodiment of the electron beam apparatus according to the present invention and the device manufacturing method using the apparatus, the present invention
(1) Since the dimension of the electrode of the objective lens can be set to a value having a filter effect on the secondary electron beam, the axial chromatic aberration coefficient can be reduced.
(2) Registration can be performed in a very short time, and since registration can be performed even during wafer evaluation, throughput is not affected.
(3) Since an E × B separator that separates the secondary electron beam from the primary optical system can be obtained with a simple structure, the aberration of the primary electron beam can be easily calculated.
(4) Shot noise can be reduced to 13% of the TFE electron gun.
(5) Even an upwardly convex wafer can chuck the entire surface flatly.
(6) There is no fear of destroying the device, particularly the gate oxide film.
(7) Dynamic focusing can be performed with the objective lens electrode at a voltage close to ground.
(8) The S / N ratio of the output from the secondary electron detector can be set to a maximum value or a value close thereto.
(9) The E × B separator and the scanning deflector can be arranged at optimum positions.
There are exceptional effects such as.

1 is a diagram schematically showing one embodiment of an electron beam apparatus according to the present invention. It is a top view which shows an example of the electrostatic chuck used in the electron beam apparatus of FIG. It is a graph which shows the relationship between the thickness of the center electrode of the objective lens provided in the electron beam apparatus of FIG. 1, and axial chromatic aberration. It is a figure for demonstrating the registration method and to-be-evaluated area | region in the electron beam apparatus of FIG. It is a figure which shows the logarithmic curve which shows the relationship of the beam current, MTF, and S / N ratio with respect to the beam diameter / pixel dimension in the electron beam apparatus of FIG. 3 is a flowchart of a method for manufacturing a semiconductor device by applying the electron beam apparatus according to the present invention. 7 is a flowchart showing a lithography process that is a sub-process of the wafer processing process shown in FIG. 6.

Explanation of symbols

  1: barrel, 2: cathode, 3: Wehnelt, 4: anode, EG: electron gun, 5: crossover, 6: first aperture plate, 7: first condenser lens, 8: crossover image, 9: second aperture plate, 10: second condenser lens, 11: electrostatic deflector, 12: electromagnetic deflector, 13: E × B separator or electromagnetic deflector, 14: objective lens, 15: wafer 16: secondary electron orbit, 17: secondary electron detector, 18: upper electrode, 19: center electrode, 20: lower electrode, 21: control power source: 22: electrostatic deflector, 23: deflection orbit, 24, 25, 26: Electrode, 27: Electrostatic chuck, 28: Robot, 29: Environment chamber, 30: Loading chamber, 31, 32: Gate valve, 33: Stage, 3 : Valve, 35: ion pump,

Claims (7)

An electron beam apparatus for irradiating a sample on which a pattern is formed with an electron beam and evaluating the sample,
An electron optical barrel containing an electron beam source, an objective lens, an electromagnetic deflector and a secondary electron beam detector
The objective lens is composed of an upper electrode, a center electrode and a lower electrode,
A control power supply for applying a voltage to the upper electrode, the central electrode and the lower electrode;
The electron beam apparatus according to claim 1, wherein the control power source applies a constant value voltage to the central electrode and performs dynamic focusing on the upper electrode so that the objective lens satisfies a focusing condition. The electron beam apparatus according to claim 1,
The control power supply provides three different voltages to the upper electrode as the dynamic focus control,
Measure the signal intensity of the secondary electron beam when the three different voltages are applied, and perform a quadratic function approximation from the signal intensity,
An electron beam apparatus characterized in that an intermediate value between a voltage value corresponding to the maximum value of the rising slope of the quadratic function and a voltage value corresponding to the maximum value of the quadratic function is used as the voltage of the upper electrode. 3. The electron beam apparatus according to claim 1, wherein the control power supply applies a voltage so that a voltage difference among the upper electrode, the intermediate electrode, and the lower electrode is 20 kV or less. An electron beam device. The electron beam apparatus according to any one of claims 1 to 3, wherein the thickness of the central electrode is 2 mm or less in the optical axis direction. 2. The electron beam apparatus according to claim 1, wherein the sample includes a plurality of small areas divided so as not to overlap each other, and only the small areas are evaluated. 2. The electron beam apparatus according to claim 1, wherein when the pixel size of the pattern is p and the beam size of the electron beam that irradiates the pattern is d, p and d are 0.9 <d / An electron beam apparatus satisfying p <1.2. A device manufacturing method, wherein a wafer during or after the process is evaluated using the electron beam apparatus according to claim 1.

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