JP2002170513A - Aberration correction method in sample evaluation apparatus and semiconductor device manufacturing method - Google Patents

Abstract

(57) [Problem] To provide a method for reducing deflection chromatic aberration, coma aberration, distortion aberration, and deflection trajectory landing angle of a charged particle beam. An electron beam (1) is deflected by a first deflector (2) and turned back by a second deflector (3) to change the position of an intersection (5) at which the deflection trajectory of the electron beam (1) intersects the optical axis (4). Second deflector 3
The electron beam turned back in step irradiates the surface of the sample 6 to generate secondary electrons. The secondary electrons are collected on the optical axis 4 by the objective lenses 7 and 8, and are directed upward on the optical axis in the figure.
The trajectory is deflected by the beam splitter 10 composed of E × B, passes through the trajectory 11, and is collected on the focusing electrode 12. First
By changing the position of the intersection point 5 between the deflector 2 and the second deflector 3, at least one of deflection chromatic aberration, coma aberration, distortion, and the landing angle of the deflection trajectory can be minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sample evaluation using a charged particle beam used for inspection of a mask (a "mask" includes a "reticle" in this specification) and a wafer. (Observation) The present invention relates to an (observation) apparatus, an aberration correction method for reducing the aberration, and a method for manufacturing a semiconductor device having a step of inspecting a mask or a wafer using a sample evaluation apparatus in which the aberration is corrected by the method. .

[0002]

2. Description of the Related Art As the degree of integration required for semiconductor devices increases, it becomes necessary to form a circuit pattern having a minimum line width of less than 100 nm on a wafer, and it becomes impossible to use a conventional optical exposure and transfer apparatus. I have. As a device capable of exposing and transferring such a fine line width pattern at high throughput, a divided particle exposure type charged particle beam exposure apparatus has attracted attention. In the case of using such a charged particle beam exposure apparatus, if a mask serving as a transfer base has a defect or a pattern thereon is not formed as designed, all the wafers formed therefrom include a defect. turn into. Therefore, prior to using the mask, it has been performed to check that the mask is sound. In addition, in order to confirm the soundness of the product wafer, the wafer is also inspected.

Inspection of such a mask has conventionally been performed using a scanning electron microscope, but there has been a problem that it takes about 80 hours to inspect the entire surface of one mask. Therefore, the present inventors have invented an apparatus for inspecting a mask at high speed using a charged particle beam array and detectors corresponding to each array element. This device is disclosed in Japanese Patent Application Laid-Open No. 9-3043.
No. 05. In this method, one detection element is made to correspond to one subfield, and scanning is performed by deflecting and scanning a charged particle beam in the subfield.

[0004]

However, conventionally,
In such an evaluation device, when irradiating the charged particle beam to a place near the optical axis, the aberration is not a problem, but it is attempted to irradiate by scanning the charged particle beam to a place far from the optical axis. In such a case, there is a problem that the deflection aberration becomes large and accurate irradiation cannot be performed.

The present invention has been made in order to solve such a problem. In a sample evaluation apparatus using a charged particle beam, a charged particle beam is scanned to evaluate a place apart from the optical axis. To provide a method for reducing the generated deflection chromatic aberration, coma aberration, distortion aberration, deflection trajectory landing angle (deviation angle (°) from the vertical incidence condition (°)) of the charged particle beam, and to adjust by these methods. It is an object to provide a method of manufacturing a semiconductor device having a step of inspecting a mask or a wafer by using a sample evaluation apparatus.

[0006]

A first means for solving the above-mentioned problem is an apparatus for evaluating a sample using a charged particle beam, which comprises a charged particle beam source, a two-stage deflector, and an objective lens. A method for correcting aberrations of
By adjusting the position where the charged particle beam deflected by the stage deflector intersects the optical axis, deflection chromatic aberration, coma aberration,
At least one of the distortion and the landing angle of the deflection trajectory
An aberration correction method in a sample evaluation device, characterized in that the number of aberrations is reduced.

[0007] The present inventor analyzed the method of correcting an aberration in a device for evaluating a sample using a charged particle beam, which includes a charged particle beam source, a two-stage deflector, and an objective lens. As a result of conducting research, it was found that each of these aberrations and the landing angle changes depending on the position where the charged particle beam deflected by the two-stage deflector intersects the optical axis, and drops sharply at a certain position. According to this finding,
If the adjustment is made based on the position where the charged particle beam deflected by the two-stage deflector intersects the optical axis, one of these aberrations and one of the landing angles can be minimized.
It becomes easy to set one or more to a predetermined value or less.

[0008] A second means for solving the above problems is as follows.
The first means, wherein an electrode which is axially symmetric with respect to the optical axis is provided between the objective lens and the sample, and a position where the charged particle beam deflected by the two-stage deflector intersects the optical axis is adjusted. In addition, by adjusting the voltage applied to the electrode,
The present invention is characterized in that at least two of deflection chromatic aberration, coma aberration, distortion aberration, and deflection trajectory landing angle are reduced (claim 2).

In the first means, the adjusting means may include
Therefore, if the position where the deflected charged particle beam intersects the optical axis is determined, the deflection chromatic aberration, coma aberration, distortion, and the landing angle of the deflection trajectory are also determined. Therefore, a trade-off problem arises if two or more of these are to be reduced.

In this means, by changing the voltage applied to the electrode provided between the objective lens and the sample, the deflection chromatic aberration with respect to the position where the deflected charged particle beam intersects the optical axis,
Since the relative relationship between coma aberration, distortion aberration, and the landing angle of the deflection trajectory can be changed, the position where the deflected charged particle beam intersects the optical axis, which minimizes these, is defined as deflection chromatic aberration, coma aberration, distortion aberration, At least two of the landing angles of the deflection trajectory can be set at the same position or close to each other. Therefore, at least two of them can be reduced.

A third means for solving the above-mentioned problem is as follows.
The first means or the second means, wherein the position, size, applied voltage or structure of the electrode of the electrostatic lens is adjusted to obtain at least one of a deflection chromatic aberration, a coma aberration, and a landing angle of a deflection trajectory. It is characterized in that two are reduced (claim 3).

In this means, by adjusting the position, size, applied voltage or structure of the electrode of the electrostatic lens, the deflection chromatic aberration, coma aberration and deflection trajectory with respect to the position where the deflected charged particle beam intersects the optical axis are adjusted. Since the relative relationship of the landing angles can be changed, it is easy to find a position where the deflected charged particle beam intersects the optical axis, which further increases one degree of freedom and reduces at least two of them. Become. Some of the aberrations include distortion, which can be easily corrected by a signal given to the deflector. If the deflection chromatic aberration and coma are reduced by the present means, the entire aberration can be reduced.

A fourth means for solving the above-mentioned problem is as follows.
In any one of the first means to the third means, the sample evaluation device reverses secondary electrons generated from the sample surface through the objective lens along the trajectory of the charged particle beam,
The evaluation is performed by deflecting the trajectory of the secondary electron by a beam splitter on the way, and the secondary electron is guided to the opposite side of the objective lens by using the convex lens function of the objective lens. (Claim 4).

In this means, secondary electrons emitted from the sample surface in each direction are converged by the convex lens action of the electromagnetic field formed by the objective lens, and are guided to the opposite side of the sample through the objective lens. Therefore, 2 used for evaluation
The number of secondary electrons can be increased, and the S / N ratio for detection can be improved.

[0015] A fifth means for solving the above problems is as follows.
In any one of the first means to the fourth means, all of the electrodes provided between the deflector, the objective lens, and the objective lens of the target sample evaluation apparatus are provided as an electrostatic type. (Claim 5).

In this means, since all of these devices are of the electrostatic type in which control is performed by an electric field, the size of the device can be reduced.

A sixth means for solving the above-mentioned problem is:
A semiconductor device comprising a step of inspecting a mask or a wafer using a sample evaluation apparatus in which aberration is reduced by the aberration correction method according to any one of the first to fifth means. (Claim 6).

In this means, since the mask and the wafer are inspected by using the sample evaluation apparatus having small aberration of the charged particle beam, an accurate inspection can be performed, and therefore, the semiconductor device having a fine pattern can be inspected. Inspection is possible even if there is any, and a defective product is not missed.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a main part of an example of a sample evaluation device to which an adjustment method according to an embodiment of the present invention is applied. In FIG. 1, 1 is an electron beam, 2 is a first deflector, 3 is a second deflector, 4 is an optical axis, 5 is an intersection of the optical axis and the electron beam, 6 is a sample, 7 and 8 are objective lenses (electrode electrodes). ), 9 are electrodes, 10 is a beam splitter, 11 is a secondary electron orbit,
12 is a focusing electrode, 13 is a scintillator, 14 is a light guide, and 15 is a shield cylinder.

An electron beam 1 emitted from an electron gun (not shown) is converged by a condenser lens (not shown), deflected by a first deflector 2 and turned back by a second deflector 3 to obtain an electron beam. The position of the intersection 5 where the deflection trajectory of the line 1 intersects the optical axis 4 can be changed. Two objective lenses 7 and 8 are provided on the sample 6 side of the second deflector 3, and an electrode 9 symmetrical with respect to the optical axis 4 is provided on the sample 6 side.

The electron beam returned by the second deflector 3 irradiates the surface of the sample 6 to generate secondary electrons. The secondary electrons are collected on the optical axis 4 by an objective lens composed of two pairs of electrodes 7 and 8, are directed upward on the optical axis in the figure, and are deflected by the beam splitter 10 composed of E × B, Then, the light passes through the orbit 11 and is collected on the focusing electrode 12. Then, the light enters the scintillator 13, is converted into an optical signal, and is guided by the light guide 14 to the photomultiplier tube. The shield tube 15 is a metal tube for preventing the voltage of the secondary electron detector from leaking into the passage of the primary electrons.

In this sample evaluation apparatus, a plurality of such optical systems are arranged in an array so that a plurality of regions can be evaluated at the same time. In addition, the first deflector 2, the second deflector 3, the objective lenses 7, 8 and the electrodes 9 are all of an electrostatic type that is controlled by voltage, thereby reducing the size of the apparatus.

An example in which such an apparatus is adjusted according to the embodiment of the present invention will be described below. In each case, the sample was set to the ground potential, and a voltage of +20 V was applied to the focusing electrode 12 and a voltage of 20 KV was applied to the scintillator 13.

First, the cathode voltage of the electron gun is -500 V, the objective lens 7 has +3.724 KV, and the objective lens 8 has +10 KV.
And the electrode 9 was set to the ground potential. The maximum field of view of the electron beam was 1 mm, and the half angle of convergence was 2 mrad. The energy of the electron beam was 10 KeV ± 0.2 eV. In this state, the first deflector 2 and the second deflector 3 were operated to change the intersection point 5 between the optical axis 4 and the electron beam 1, and the aberration and the change in the landing angle were investigated by simulation. here,
The voltages of the electrodes (objective lenses) 7 and 8 were such that the primary electron beam was focused on the sample.

FIG. 2 shows the result. In FIG. 1, A is the field curvature aberration, B is the deflection astigmatism, C is the axial chromatic aberration, D
Denotes spherical aberration, E denotes distortion, F denotes a landing angle, G denotes deflection chromatic aberration, and H denotes coma. The horizontal axis is the distance (mm) between the intersection point 5 and the sample 6, and the left vertical axis is the magnitude of each aberration.
(nm, logarithmic scale), the vertical axis on the right side is the landing angle (°, logarithmic scale). However, among the aberrations, the field curvature aberration A and the deflection astigmatism B are 1/10 times, and the distortion E is 1/10.
The figure multiplied by 0 is shown.

As is apparent from the drawing, when the distance between the intersection point 5 and the sample 6 is set to 21 mm, the coma is 0.1 nm or less. When this distance is 25.2 mm, the deflection chromatic aberration is 0.25 nm or less. This distance is 25.5mm
In this case, the landing angle was 0.02 °. When this distance is 29 mm, the distortion is 70 nm. As described above, by changing the position where the deflection trajectory of the electron beam 1 intersects the optical axis 4, one of the coma, the deflection chromatic aberration, the landing angle, and the distortion can be minimized. Further, when the distance is about 25.3 mm, both the deflection chromatic aberration and the landing angle can be set to very small values.

FIG. 3 shows that the voltage applied to the objective lens 7 is 3.53.
The simulation results are shown under the same conditions as when the data shown in FIG. 2 was collected, except that the voltage was changed to 5 KV and the voltage applied to the electrode 9 was changed to -100 V. Each coordinate and A to H indicate the same as those in FIG. 2, and the magnification of each data is also the same as in FIG. Here, I indicates the fifth-order aberration before dynamic correction, and J indicates the fifth-order aberration after dynamic correction.

A comparison between FIG. 2 and FIG. 3 shows that the distance between the intersection point 5 which gives the minimum value of coma, deflection chromatic aberration, landing angle and distortion is changed as shown in Table 1. I understand.

(Table 1)

[Table 1]

According to FIG. 3, the distance giving the minimum value of the coma aberration and the distance giving the minimum value of the deflection chromatic aberration are close to each other. In addition, referring to FIG.
It can be seen that when the distance between them is 22.4 mm to 23.5 mm, the coma aberration and the deflection chromatic aberration can be simultaneously made smaller than the axial chromatic aberration C, which is an uncorrectable amount.

Although not shown, it has been found that when the voltage applied to the electrode 9 is +30 V, the landing angle and the deflection chromatic aberration can be almost simultaneously reduced to zero. Thus, for example, even when the energy distribution of the electron beam is as large as 1 eV and the convergence half angle is as small as 1 mrad, the landing angle and the deflection chromatic aberration can be improved.

Even if the inner diameter and length of the electrode 9 and the distance to the sample 6 are changed instead of the voltage applied to the electrode 9, each aberration, landing angle, and distance between the intersection point 5 and the sample 6 are similarly calculated. Relationship can be changed.

Also, by adjusting the positions, dimensions, applied voltages or structures of the electrodes of the electrostatic lens, the relationship between the aberration, the landing angle, and the distance between the intersection point 5 and the sample 6 can be changed. Can be.

In the optical system shown in FIG. 1, a voltage of +10 KV is applied to the objective lens 8 as described above, and the sample surface 6 is grounded. A deceleration electric field for the electron beam 1 is generated.
Therefore, the electron beam incident on the sample has low energy of 500 V, and can have chromatic aberration and diffraction aberration at 10 KV.

The voltage applied to the objective lens 7 is about
Since it is a relatively small value of 3.5 to 3.7 KV, the beam splitter 10 using ExB can deflect the secondary electron orbit with a relatively low voltage. This makes it possible to create a condition in which the electron beam 1 travels straight with a small magnetic field.

FIG. 4 is a diagram showing the envelope of the trajectory of secondary electrons emitted in a direction of ± 89 ° at an initial velocity of 10 eV from a point 1 mm away from the optical axis. What is shown by the broken line is the equipotential surface. The voltage of the objective lens 7 is 4 KV, the voltage of the objective lens 8 is 10 KV, and the sample 6 is grounded. FIG. 4 shows that all electrons are guided to the opposite side of the objective lens from the sample by the convex lens action of the objective lenses 7 and 8.

Hereinafter, an embodiment of a method for manufacturing a semiconductor device according to the present invention will be described. FIG. 5 is a flowchart illustrating an example of a semiconductor device manufacturing method according to an embodiment of the present invention. The manufacturing process of this example includes the following main processes. Wafer manufacturing process for manufacturing a wafer (or wafer preparing process for preparing a wafer) Mask manufacturing process for manufacturing a mask used for exposure (or mask preparing process for preparing a mask) and a process for inspecting the manufactured mask Necessary for wafer Wafer processing process for performing various processing processes Chip assembly process for cutting out chips formed on a wafer one by one and making them operable Chip inspection process for inspecting the resulting chips Each of these processes is further divided into several sub-processes Consists of

Among these main steps, the main step that has a decisive effect on the performance of the semiconductor device is the wafer processing step. In this step, designed circuit patterns are sequentially stacked on a wafer to form a large number of chips that operate as memories and MPUs. This wafer processing step includes the following steps. A thin film forming step (using CVD, sputtering, etc.) for forming a dielectric thin film, a wiring portion, or a metal thin film for forming an electrode portion to be an insulating layer (using CVD or sputtering, etc.) An oxidation process for oxidizing the thin film layer or the wafer substrate A lithography process of forming a resist pattern using a mask (reticle) in order to selectively process etc. An etching process of processing a thin film layer or a substrate according to a resist pattern (for example, using a dry etching technique) An ion / impurity implantation diffusion process Resist stripping step Inspection step of inspecting the processed wafer Further, the wafer processing step is repeated by a necessary number of layers to manufacture a semiconductor device that operates as designed.

FIG. 6 is a flowchart showing a lithography step which is the core of the wafer processing step shown in FIG. This lithography step includes the following steps. A resist coating step of coating a resist on a wafer on which a circuit pattern has been formed in the preceding step An exposing step of exposing the resist A developing step of developing the exposed resist to obtain a resist pattern Stabilizing the developed resist pattern The above-described semiconductor device manufacturing process, wafer processing process, and lithography process are well known, and will not require further explanation. In the present embodiment, a sample evaluation apparatus using a charged particle beam is used in the step of inspecting a mask and the step of inspecting a wafer, and the sample evaluation apparatus is adjusted by the adjustment method of the present invention. . Therefore, an accurate inspection can be performed, so that even a semiconductor device having a fine pattern can be inspected, and a defective product is not missed.

[0040]

As described above, according to the first aspect of the present invention, deflection chromatic aberration, coma aberration,
It becomes easy to minimize one of the distortion aberration and the landing angle of the deflection trajectory, or to set two or more to a predetermined value or less.

According to the second and third aspects of the present invention, it is easy to reduce at least two of deflection chromatic aberration, coma, distortion, and the landing angle of the deflection trajectory.

In the invention according to claim 4, the number of secondary electrons used for evaluation can be increased, and the detection performance can be improved. In the invention according to claim 5, the device can be downsized. In the invention according to claim 6, even a semiconductor device having a fine pattern can be inspected and a defective product is not missed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a main part of an example of a sample evaluation device to which an adjustment method according to an embodiment of the present invention is applied.

FIG. 2 is a diagram illustrating an example of a relationship between aberration and a landing angle with respect to a distance between an intersection of an optical axis and a deflection trajectory of an electron beam and a sample surface.

FIG. 3 is a diagram showing another example of the relationship between aberration and landing angle with respect to the distance between the intersection of the optical axis and the deflection trajectory of the electron beam and the sample surface.

FIG. 4 is a diagram illustrating an example of a trajectory of a secondary electron emitted from a sample surface.

FIG. 5 is a flowchart illustrating an example of a semiconductor device manufacturing method according to an embodiment of the present invention.

FIG. 6 is a flowchart showing a lithography process.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electron beam, 2 ... First deflector, 3 ... Second deflector, 4 ... Optical axis, 5 ... Intersection of optical axis and electron beam, 6 ... Sample, 7, 8 ... Objective lens, 9 ... Electrode, 10 ... Beam splitter, 11 ... 2
Secondary electron orbit, 12: focusing electrode, 13: scintillator, 1
4 ... Light guide, 15 ... Shield tube

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H01L 21/66 H01L 21/66 J

Claims (6)

[Claims] 1. An apparatus for evaluating a sample using a charged particle beam, comprising: a charged particle beam source, a two-stage deflector, and an objective lens, wherein the method comprises the steps of: A sample characterized by reducing at least one of deflection chromatic aberration, coma aberration, distortion aberration, and deflection trajectory landing angle by adjusting the position where the charged particle beam deflected by the deflector intersects the optical axis. An aberration correction method in the evaluation device. 2. The aberration correcting method according to claim 1, wherein an electrode symmetrical with respect to an optical axis is provided between the objective lens and the sample, and the electrode is deflected by the two-stage deflector. By adjusting the position where the charged particle beam intersects the optical axis and adjusting the voltage applied to the electrode, it is possible to reduce at least two of deflection chromatic aberration, coma aberration, distortion aberration, and the landing angle of the deflection trajectory. A method for correcting aberrations in a sample evaluation apparatus. 3. A method for correcting aberration in a sample evaluation apparatus according to claim 1 or 2, further comprising: adjusting a position, a size, an applied voltage or a structure of an electrode of the electrostatic lens, to thereby obtain a deflection chromatic aberration. A method for correcting aberrations in a sample evaluation apparatus, wherein at least two of the following parameters are reduced: coma aberration and landing angle of a deflection trajectory. 4. One of claims 1 to 3
The method for correcting aberrations in the sample evaluation device according to the item, wherein the sample evaluation device reverses secondary electrons generated from the sample surface through the objective lens along the trajectory of the charged particle beam, and a beam splitter on the way. The aberration is evaluated by deflecting the trajectory of the secondary electron, and using the convex lens function of the objective lens to guide the secondary electron to the opposite side of the objective lens from the sample. Correction method. 5. The method according to claim 1, wherein
The method for correcting aberrations in a sample evaluation apparatus according to any one of the first to third aspects, wherein the deflector, the objective lens, and the electrodes provided between the objective lens and the sample of the target sample evaluation apparatus are all of an electrostatic type. A method for correcting aberrations in a sample evaluation apparatus, characterized in that: 6. A sample evaluation apparatus in which the aberration is reduced by the aberration correction method according to claim 1,
A method for manufacturing a semiconductor device, comprising a step of inspecting a mask or a wafer.