JP2005158642A - Pattern evaluation method, and manufacturing method of device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pattern evaluation method using an electron beam device, having good beam resolution, eliminating the problem of deviation of rotation attitude, capable of inspecting defects of masks with high throughput. <P>SOLUTION: In order to evaluate the pattern of a sample K, an electron beam 2a emitted from an electron gun 37 is made incident on a sample face Ka through an object lens 10. The object lens is composed of a flat plate-shaped electrode 10c having a hole with an optical axis as a center arranged in parallel with the sample face, and an electromagnetic lens 10a having a gap 10b at sample side. In order to inspect the mask, the distances between a plurality of electron beams passed through the mask are magnified by a magnifying lens and converted into an electric signal. The light signal is converted into electric signal by a photomultiplier, and a two dimensional image is formed depending on a scanning signal and the above electric signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for evaluating a wafer or a mask having a pattern with a minimum line width of 0.1 μm or less used for manufacturing a semiconductor device at a high throughput, and a device manufacturing method using such a method. The present invention also provides a method for inspecting a mask having a pattern with a minimum line width of 0.1 μm or less, particularly a stencil mask (a perforated shielding mask) or a membrane mask, used when manufacturing a semiconductor device, with high resolution and high throughput. And a device manufacturing method using a mask inspected by such a method.

  Conventionally, as a mapping type defect inspection apparatus or a pattern evaluation method using a multi-beam, an apparatus and a method using an electromagnetic lens or an electrostatic lens as an objective lens are known. In addition, the conventional stencil mask inspection apparatus scans the back surface of the stencil mask with one narrowed electron beam, detects electrons passing through the stencil mask, forms a transmission image of the stencil mask, and detects defects in the stencil mask. It has a structure to detect.

  Conventional mapping type devices or multi-beam devices using an electrostatic lens as an objective lens have difficulty in obtaining high resolution by increasing the beam current. Furthermore, when an electromagnetic lens is used for the objective lens, the beam is rotated by the objective lens twice in total, that is, the primary beam once and the secondary beam once, so that it is difficult to match the rotation posture of the beam to the reference coordinates. there were. The present invention has been made in view of these problems, and an object of the present invention is to provide a pattern evaluation method that has good beam resolution and that does not cause a problem of deviation in rotational posture.

  Further, the conventional stencil mask inspection apparatus having the above structure has a disadvantage that the throughput (the processing amount in a fixed time) is remarkably small because the entire surface of the stencil mask is scanned with one narrowed electron beam. It is an object of the present invention to provide a method that solves the disadvantages of the prior art and enables a defect inspection of a mask with high throughput.

  The method for evaluating a pattern of the present invention comprises: a. Causing an electron beam emitted from an electron gun to enter a sample surface through an objective lens; b. Directing secondary electrons emitted from the sample to a secondary electron detector; c. Forming a two-dimensional image with the signal from the secondary electron detector; and d. Evaluating the sample based on the two-dimensional image. The objective lens is formed of a perforated flat plate electrode parallel to the sample surface and centered on the optical axis, and an electromagnetic lens having a gap formed on the sample side. If the hole is axially symmetric, the outer shape of the electrode may not be circular as long as it is sufficiently away from the optical axis.

  In the method for evaluating a pattern of the present invention, preferably, the rotation posture of the primary electron beam or the secondary electron around the optical axis is adjusted by changing the excitation current of the electromagnetic lens, and the focusing condition generated thereby The deviation is adjusted by adjusting the voltage between the plate electrode and the sample. The primary electron beam is formed in a rectangular cross section, and the rotation posture is an angle formed by the rectangular beam side and a pattern side on the sample or a reference coordinate axis. Further, the primary electron beam is formed into a multi-beam, and the rotation posture is a multi-beam alignment direction D1, D2 with respect to a reference coordinate axis. The present invention also provides a device manufacturing method characterized by evaluating a wafer in the middle of a process using the pattern evaluation method.

  A method for inspecting a mask of the present invention comprises: a. Scanning one side of the mask based on a scanning signal with a plurality of finely focused electron beams; b. Enlarging the distance between the plurality of electron beams that have passed through the mask with a magnifying lens; c. Converting the expanded electron beam into an electrical signal; d. Forming a two-dimensional image of the mask based on the scanning signal and the electrical signal; e. Converting mask design data into inspection data; and f. A step of comparing the inspection data with the two-dimensional image and performing a defect inspection of the mask.

  In the method for inspecting a mask according to the present invention, preferably, the plurality of electron beams are narrowed down by a magnetic lens having a gap on the mask side. The plurality of electron beams are formed by irradiating a plurality of openings with an electron beam generated by a thermionic emission electron gun, and the electron gun is operated under a space charge limiting condition. The plurality of finely focused electron beams irradiate a plurality of openings with an electron beam obtained by thermal field emission of a Zr / O—W (tungsten zirconic acid) Schottky cathode or a transition metal carbide cathode. It is formed as a reduced image of a plurality of openings. The present invention also provides a device manufacturing method using the mask inspected by the above method.

The present invention can provide a pattern evaluation method that has good beam resolution and that does not cause the problem of deviation in rotational posture. In addition, the present invention can provide a method that solves the disadvantages of the prior art and enables inspection of a mask with high throughput. According to the present invention, a defect inspection of a mask can be performed with high resolution. In the inspection method of the present invention, since the LaB ₆ cathode is used under space charge limiting conditions, the S / N ratio is improved by a factor of 4 compared to the Schottky cathode, and the same S / N ratio is obtained with a beam current of 1/16. It is done. Since the number of beams can be 11 to 22, high throughput of 10 times or more can be expected.

  FIG. 1 is a schematic configuration diagram showing an embodiment of an electron optical device 30 used in the pattern evaluation method of the present invention. The electron beam apparatus 30 includes an electron gun 37 including a cathode 1, a Wehnelt 52, a first anode 33, a second anode 34, and a third anode 35. Since the electron gun 37 operates under the space charge limiting condition, the shot noise is reduced to ¼ or less of the amount given by the Schottky theorem. The electron beam 2 a emitted from the electron gun 57 is axially aligned with the condenser lens 48 and the multi-aperture 5 a of the multi-aperture plate 5 by the alignment coils 46 and 47.

  The beam of 4 columns and 4 rows formed by the multi-aperture 5 a is axially aligned with the NA aperture 6 and the reduction lens 7 by the alignment coils 40 and 41. The beam 2b reduced to about 1/10 by the reduction lens 7 is aligned with the objective lens 10 by the octupole electrostatic deflectors 8 and 42, and the multi-beam 2b is focused on the sample K. The objective lens 10 includes an electromagnetic lens 10a and an axially symmetric electrode 10c. The gap 10b of the electromagnetic lens 10a is on the sample side, and the maximum value of the on-axis magnetic field is formed on the sample side of the electromagnetic lens 10a, equivalently lowering the lens principal surface and reducing the aberration coefficient.

  In the electron beam apparatus 30, an axially symmetric electrode 10c to which a positive high voltage is applied is provided at the z position where the on-axis magnetic field is maximized, and aberration is further reduced. The multi-beam 2b scans the sample K two-dimensionally by superimposing a scanning voltage on the axis-aligned electrostatic deflectors 8 and 42. Secondary electrons generated from the sample K are accelerated and focused by an accelerating electric field generated by a negative voltage 68 applied to the sample and a positive voltage 69 of the lens, pass through the objective lens 10 as a thin beam, and E × 1 is deflected to the left in FIG. 1 by the B separators 65 and 66, the interval between the multi-beams is enlarged by the two-stage electrostatic lenses 71 and 72, and detected by the multi-detector 73 including a scintillator and a photomultiplier. That is, it is converted into an optical signal by a scintillator, and this optical signal is incident on a photocathode of a photomal, where photoelectrons are generated, the photoelectrons are amplified by a multistage electrode, and a current signal is generated by a resistor connected between the final electrode and ground. To a voltage signal.

  A two-dimensional image is created in the signal processing circuit 74 based on the output signal of the multi-detector 73, and the image is stored in the memory 75. Magnetic lenses have the problem of rotating the beam instead of having low aberrations. In the multi-beam, if there is a deviation between the arrangement of the multi-beams and the reference coordinate axis, there arises a problem that the interval at which the multi-beam is projected in the y-axis direction is deviated from the equal interval. In the electron beam apparatus 30, if the amount of rotation of the multibeam after passing through the objective lens is too large, if the excitation current of the lens is reduced, and the focusing condition is underfocused, the voltage 69 applied to the electrode 10c is The focusing condition can be matched by lowering. In addition, when there is a rotation shift between the rotation direction of the secondary electron image and the secondary electron detector, the rotation shift can be adjusted by the lens.

  FIG. 2 is a schematic configuration diagram showing a second embodiment of an electron optical device used in the pattern evaluation method of the present invention. In the electron optical device 130 according to the second embodiment, the electron beam 2 a emitted from the electron gun 131 is focused by the condenser lens 132 and illuminates the rectangular opening 133 a of the aperture plate 133. The rectangular shaped electron beam creates a crossover at the NA aperture 134, an irradiation lens 135 creates a rectangular image on the conjugate surface 148 with respect to the primary beam 2 a of the sample surface Ka, and the E × B separators 136 and 137 move to the sample side. It is deflected and a rectangular beam is focused on the sample surface 142 by the two-stage lenses 138 and 139. In this electron optical device, since the secondary beam is given priority, the conjugate surface of the sample surface is formed on the deflection main surface of the E × B separators 136 and 137 by the secondary beam. The conjugate plane of the surface is formed at a position 148 far from the E × B separator.

  The two-stage lenses 138 and 139 are designed so as not to rotate with respect to secondary electrons, but cause some rotation with respect to the primary beam. A slight rotational deviation can be corrected by mechanically rotating the molding opening 133.

  As described above, the greatest merit of combining the first objective lens of the projection type lens system with the magnetic lens having the gap below and the axially symmetric lens as shown in FIG. 2 is that the axial aberration coefficient is several minutes. It is a point which can be made 1 or less. That is, when the electrostatic lens system has a resolution of 100 nm and is limited by axial chromatic aberration, there is a possibility that a resolution of 50 nm or 25 nm can be achieved by using an objective lens pair as an electromagnetic lens pair. .

FIG. 3 is a schematic configuration diagram of an electron beam apparatus used in the mask defect inspection method of the present invention. The electron beam apparatus 50 includes an electron gun 57 including a cathode 1, a Wehnelt 52, and an anode 3. The cathode 1 is obtained by sharpening a single crystal LaB ₆ (polishing into a cone having an angle of 90 degrees) and forming the tip thereof in a spherical portion having a curvature radius of about 15 μm. The Wehnelt 52 is assembled at a position where its lower surface is approximately 0.3 mm from the tip of the cathode 1, and the brightness and emittance of the electron gun 57 are controlled by changing the applied voltage. The electron gun 57 of FIG. 3 is used under operating conditions with high luminance and emittance, and is operated in the space charge limited region.

 The electron beam 2a emitted from the electron gun 57 is focused by the condenser lens 4 and divided into multi-beams 2b by the aperture plate 5 below the condenser lens 4, and then a crossover is formed in the NA aperture 6 of the primary optical system. To do. The aperture plate 5 includes 4 rows and 4 columns of apertures 5a. The multi-beam 2b having passed through the NA aperture 6 is reduced in beam interval and beam diameter by the reduction lens 7, further reduced by the objective lens 10, and reduced to a beam diameter of about 50 nm, and a mask (stencil mask or membrane mask) 12 And is scanned on the mask 12 by the deflectors 8 and 9.

  The objective lens 10 has a lens gap 11 provided on the sample (mask) side, and lowers the axial principal chromatic aberration and spherical aberration by lowering the lens main surface to the sample side. The electron beam 2c that has passed through the unpatterned portion of the mask 12 is magnified by the magnifying lenses 13 and 14 and focused on the detection surface on which the detectors 15 in 4 rows and 4 columns are arranged.

  The electron beam 2 c is controlled so as to always pass through the center of the magnifying lens 14 by the deflector 25 in synchronization with scanning of the mask surface of the mask 12. The transmission electron beam is controlled to enter the corresponding detector 15 by the deflector 23. The mask 12 is detected while being continuously moved in the y direction, and is simultaneously raster scanned in the x direction by the deflectors 8 and 9.

  The openings 5a in 4 rows and 4 columns of the aperture plate 5 are arranged such that the intervals projected onto the y axis are equal intervals Δy as shown in FIGS. 4A and 4B. The arrangement direction of the openings 5a is indicated by double arrows D1 and D2. The signal detected by the detector 15 is amplified by the signal processing circuit 16, converted into a digital signal, and made into a two-dimensional image 17 a by the image forming circuit 17 together with the signal from the scanning power supply 22. The two-dimensional image 17 a is compared with the inspection data 20 converted from the pattern data 19 by the pattern comparison circuit 18, and the defect 18 a is output to the output device 21. Further, the openings of 4 rows and 4 columns can be arranged in orthogonal directions as shown in FIG. 4A or 4B.

  In the case of a stencil mask, the energy of the electron beam 2b that irradiates the mask 12 can be 1 KeV-20 KeV. In the case of a membrane mask, the energy is scattered when the electron beam passes through the membrane portion. A relatively high energy beam of 10 KeV or higher is suitable so that the amount does not become too large.

The detector 15 can be scanned at a pixel frequency of 500 MHz by using a detector that combines a scintillator with a characteristic of an afterglow time of 1 nanosecond or less and a PMT. However, at that time, an electron gun having a Zr / O-W or TaC cathode is used rather than an electron gun having a LaB ₆ cathode, and electron beams emitted in four directions from these cathodes are irradiated to four openings, Good to do.

Next, the following assumptions are made to estimate the inspection speed.
Pixel size: 0.05μm × 0.05μm
Mask inspection area: 140 mm (y) x 100 mm
Stage turnaround time: 0.5 seconds

1. 16 beams with an electron gun with LaB ₆ cathode,
x-direction field size: 0.05mm
Scan folding time: 5 μs Registration time: 10 seconds Sample loading / unloading time: 20 seconds Flock frequency: 100 MHz
(1) Scanning time:
[140 × 100 / (0.05 × 10 ⁻³ ) ² ] × 10 × 10 ⁻⁹ seconds × [1/16] = 350 seconds (2) Scanning folding time:
(140 / 0.05) × [100 / (16 × 5 × 10 ⁻⁵ )] × 5 × 10 ⁻⁶ seconds = 175 seconds (3) Stage turnaround time:
(140 / 0.05) × 0.5 seconds = 140 seconds (4) Registration + load / unload time = 30 seconds
Total: 695 seconds = 12 minutes
Throughput: 5 sheets / hour

2. An electron gun equipped with a TaC cathode, scanned at 500 MHz, with four beams, the other is the same as 1 above.
(1) Scanning time:
[140 × 100 / (0.05 × 10 ⁻³ ) ² ] × 2 × 10 ⁻⁹ seconds × [1/4] = 280 seconds (2) Scan folding time:
(140 / 0.5) × [100 / (4 × 5 × 10 ⁻⁵ )] × 5 × 10 ⁻⁶ seconds = 700 seconds (3) Stage turnaround time: = 140 seconds (4) Registration + Load unload Time = 30 seconds
Total: 1150 seconds = 19 minutes
Throughput: 3.2 sheets / hour

  Next, a semiconductor device manufacturing method using the electron beam apparatus of the present invention will be described with reference to the flowcharts of FIGS. The electron beam apparatus of the present invention evaluates a wafer during or after the process in the flowcharts of FIGS.

  As shown in FIG. 5, when roughly divided, the semiconductor device manufacturing method manufactures 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. A mask manufacturing process S3, a chip assembling 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 manufacturing of the semiconductor device is the wafer processing process S2. 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. As described above, 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. 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. 6 is a flowchart showing a lithography process which is a sub-process of the wafer processing process of FIG. As shown in FIG. 6, 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.

The schematic block diagram which shows embodiment of the electro-optical apparatus used for the pattern evaluation method of this invention. The schematic block diagram which shows 2nd Embodiment of the electron optical apparatus used for the pattern evaluation method of this invention. The schematic block diagram of the electron beam apparatus used for the defect inspection method of the mask of this invention. 4A and 4B are plan views of multi-apertures of multi-aperture plates that can be used in the electron beam apparatus of FIG. 3, respectively. The flowchart of the method of manufacturing a semiconductor device using the electron beam apparatus of this invention. FIG. 6 is a flowchart showing a lithography process which is a sub-process of the wafer processing process shown in FIG.

Explanation of symbols

  1: cathode, 5: multi-aperture plate, 3: anode, 4: condenser lens, 5: multi-aperture plate, 5a: multi-aperture, 6: NA aperture, 7: reduction lens, 8: axis alignment and scanning deflector (1 scanning deflector), 9: second scanning deflector, 10: electromagnetic lens for objective lens, 10c: axially symmetric electrode, 10b: lens gap, 10d: lens power supply, 11: gap, 12: mask to be inspected (stencil mask) , Membrane mask), 13: first magnifying lens, 14: second magnifying lens, 15: detector (scintillator + PMT detector), 16: signal processing circuit, 17: image forming circuit, 18: comparator, 19: pattern Data: 20: Data converter, 21: Defect output device, 22: Scanning power supply, 23: Deflector, 25: Deflector, 33: First anode, 34: Second anode, 35: Third ano 40, 41, 46, 47: Axis alignment coil, 42: Scanning deflector and axis alignment deflector, 48: Condenser lens, 52: Wehnelt, 65: Electrostatic deflector for E × B, 66: E × B Electromagnetic deflector, 68: Negative power source, 69: Positive power source, 71: Magnifying lens, 72: Second magnifying lens, 73: Secondary electron detector, 74: Signal processor, 75: Pattern memory, 130: Electron beam Device: 131: electron gun, 132: sensor lens, 133: field aperture, 134: NA aperture, 135: irradiation lens, 136: 8-pole deflector for E × B, 137: deflection coil for E × B, 138: first 2 objective lens, 139: first objective lens, 140: lens gap, 141: axially symmetrical electrode, 143: magnifying lens, 144: magnifying lens, 145: FOP window with scintillator, 146: optical lens, 147 : TDI camera, 148: conjugate plane of sample with respect to primary beam, D1, D2: alignment direction, K: sample (wafer), Ka: sample plane.

Claims (10)

A method for evaluating a pattern,
a. Making the electron beam emitted from the electron gun enter the sample surface through the objective lens;
b. Directing secondary electrons emitted from the sample to a secondary electron detector;
c. Forming a two-dimensional image with the signal from the secondary electron detector; and d. Evaluating the sample based on the two-dimensional image,
The objective lens is formed of a perforated flat plate electrode parallel to the sample surface and centered on the optical axis, and an electromagnetic lens having a gap formed on the sample side.   The rotational attitude around the optical axis of the primary electron beam or secondary electron is adjusted by changing the excitation current of the electromagnetic lens, and the deviation of the focusing condition caused thereby is obtained by changing the voltage between the plate electrode and the sample. The method of claim 1, wherein the adjustments are combined.   3. The method according to claim 2, wherein the primary electron beam has a rectangular cross section, and the rotation posture is an angle formed by the rectangular beam side and a sample pattern side or a reference coordinate axis.   The method according to claim 2, wherein the primary electron beam is formed into a multi-beam, and the rotation posture is an alignment direction of the beams of the multi-beam with respect to a reference coordinate axis.   5. A device manufacturing method, wherein a wafer in the middle of a process is evaluated using the pattern evaluation method according to claim 1. A method for inspecting a mask,
a. Scanning one surface of the mask based on the scanning signal with a plurality of narrowed electron beams;
b. A step of magnifying a distance between a plurality of electron beams that have passed through the mask with a magnifying lens;
c. Converting an electron beam having an increased interval into an electrical signal;
d. Forming a two-dimensional image of the mask based on the scanning signal and the electrical signal;
e. Converting mask design data into inspection data; and f. Comparing the inspection data with the two-dimensional image and performing a defect inspection of a mask.   7. The method according to claim 6, wherein the plurality of electron beams are narrowed down by a magnetic lens having a gap on the mask side.   7. The method of claim 6, wherein the plurality of electron beams are formed by irradiating a plurality of apertures with an electron beam generated by a thermionic emission electron gun, and the electron gun is operated under a space charge limited condition. .   The plurality of narrowed electron beams irradiate a plurality of apertures with an electron beam obtained by thermal field emission of a Zr / O—W Schottky cathode or a transition metal carbide cathode, and the plurality of apertures are reduced. 7. The method of claim 6, wherein the method is formed as an image.   10. A device manufacturing method using a mask inspected by the method according to any one of claims 6 to 9.

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