July 14, 2016 - 8:01 PM EDT
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Patent Issued for Charged Particle Beam Apparatus (USPTO 9384940)

By a News Reporter-Staff News Editor at Electronics Newsweekly -- A patent by the inventors Fukuda, Muneyuki (Tokyo, JP); Suzuki, Naomasa (Tokyo, JP); Ikegami, Akira (Tokyo, JP); Dohi, Hideto (Tokyo, JP); Enyama, Momoyo (Tokyo, JP); Shojo, Tomoyasu (Tokyo, JP), filed on October 21, 2013, was published online on July 5, 2016, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 9384940 is assigned to Hitachi High-Technologies Corporation (Tokyo, JP).

The following quote was obtained by the news editors from the background information supplied by the inventors: "Various methods are used for defect detection and length measurement and shape evaluation in a formation of a microcircuit such as an LSI. For example, with an optical test device, optical images of the microcircuit are generated and the images are tested for abnormality detection. However, these optical images have resolution that is insufficient to permit identification of very small shape features, and cannot satisfactorily perform distinction between a harmful defect and a harmless defect upon the circuit formation. A target sample of such a measurement and test device has been increasingly miniaturized following technical advancement, and for example, in a process of manufacturing a latest DRAM, a linewidth of a metal wire reaches 40 nm or below, and a logic IC has reached a gate dimension of 20 nm.

"A defect test method by use of an electron beam is provided with sufficient resolution for imaging minute shape features of a contact hole, a gate, and wiring and shape features of a minute defect, and can be further used for classification and detection of a severe defect based on a shade image contrast of the defect shape. Therefore, for measurement and test of the microcircuit, a measurement and a test method putting a charged particle beam into practical use is considerably more advantageous than an optical test method.

"A scanning electron microscope (SEM) as one of charged particle beam apparatuses focuses a charged particle beam emitted from an electron source of a heating type or an electric field discharge type to form a thin beam (probe beam), and scans this probe beam on a sample. Through this scanning, secondary charged particles (secondary electron or reflection electron) are generated from the sample, and providing these secondary charged particles as a luminance signal of image data in synchronization with the scanning of the primary charged particle beam provides a scanned image. In a typical scanning electron microscope, with an extraction electrode between the electron source to which a negative potential has been applied and a grounding potential, the electron emitted from the electron source is accelerated and irradiated to the sample.

"There is a close relationship between resolution of a scanning type charged particle microscope such as the SEM and energy of the charged particle beam. Arrival of the primary charged particle beam with high energy at the sample (that is, great landing energy of the primary charged particle beam) causes the primary charged particle to enter deeply into the sample, thus widening a range of emission of the secondary electron and the reflection electron on the sample. As a result, the range of emission becomes wider than the probe size of the charged particle beam, resulting in remarkable deterioration in observation resolution.

"In contrast, reducing energy of the primary charged particle beam too much in order to reduce the landing energy results in a remarkable increase in the probe size of the charged particle beam due to aberration of an objective lens, deteriorating the observation resolution.

"To perform observation with high resolution, energy of the primary charged particle beam, the landing energy in particular, needs to be appropriately controlled in accordance with an observation target.

"As a technology of controlling the landing energy, a retarding method is widely used. Specifically, with the retarding method, such a potential that decelerates the primary charged particle beam is applied to the sample to reduce the energy of the charged particle beam to desired energy immediately before arrival at the sample. However, as soon as the charged particle beam is inclined towards a sample to be observed, observation with high resolution can no longer be performed.

"Disclosed in Patent Literature 1 is, as a technology of inclining a charged particle beam with respect to a sample to be observed while maintaining high resolution condition of an apparatus, late race on an electron optical orbit in, for example, a method of using focus operation of an objective lens by making the charged particle beam enter to outside of an axis of the objective lens.

"Moreover, disclosed in Patent Literature 2 is a technology of correcting off-axis chromatic aberration occurring when two stages of deflection means adapted to deflect a charged particle beam in mutually opposite directions within a focus magnetic field of an objective lens are provided and the charged particle beam is inclined outside an axis of the objective lens.

"Moreover, disclosed in Patent Literature 3 is a technology of performing correction with a Wien filter in which two stages of deflection means for passage of a charge particle beam through outside of an axis of an objective lens are provided closely to an electron source than the objective lens to thereby reduce resolution deterioration occurring upon inclination of the charged particle.

"Further, disclosed in Patent Literature 4 is a technology of providing, in addition to deflection means within a focus magnetic field of the objective lens, a cup-shaped electrode for beam deceleration between the objective lens and a sample to thereby increase a beam inclination angle.

"In addition, disclosed in Patent Literature 5 is an invention in which an orbit of a primary beam is caused by a deflector or a movable diaphragm to pass through outside of an axis and controlling its off-axis orbit to cancel aberration occurring on the objective lens at time be beam inclination by use of aberration of another lens."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "Technical Problem

"Resolution of a charged particle beam image is affected by a probe diameter of the charged particle beam, and to acquire a scanned image with high resolution, the probe diameter needs to be reduced. However, reducing the probe diameter requires strong beam reduction through shortening a focal point of the objective lens. To focus the beam on the sample with a short focal point, an objective lens is required which has strong lens operation accordingly. In case of an objective lens of a magnetic field type which focuses a beam by leaking the magnetic field to an optical axis of the primary charged particle beam, the amount of excitation needs to be increased in order to strengthen the lens operation.

"The amount of a magnetic flux flowing through a magnetic path of the objective lens is restricted by magnetic saturation. Saturated magnetic flux density of the magnetic path is almost determined by a magnetic material forming the magnetic path. Therefore, even if the amount of magnetic flux passing through the magnetic path increases, the magnetic flux that cannot be accepted by the magnetic path leaks from somewhere in the magnetic path, as a result of which lens operation is not great enough to follow the increase in the amount of excitation. Especially in a case where acceleration voltage of the charged particle beam is increased to form a probe beam with high energy, there may arise a situation that the beam itself cannot be focused. Thus, it is impossible to provide, adjacently to the magnetic path of the objective lens, deflection means adapted to deflect a charged particle beam within a magnetic field for focus by the objective lens by use of the conventional technologies as described in Patent Literature 1 to 3.

"Moreover, resolution of the charged particle beam apparatus is defined by the probe diameter of the beam, and a decrease in energy of the charged particle beam results in an increase in the probe diameter and thus resolution deterioration due to the chromatic aberration as described above. Therefore, with the retarding method, effect of the aberration can be more reduced by bringing a deceleration position of the charged particle beam closer to the sample. Thus, upon apparatus designing, a work distance of the objective lens is designed to be as small as possible. However, it is impossible to achieve physical contact between the objective lens and the sample, and thus there is limitation on the method of reducing the effect of aberration through work distance reduction. In particular in case of the retarding method, there is a great potential difference between a sample (or a sample stage) and the objective lens, and a too small work distance raises a risk of sample breakage due to discharge. Therefore, the apparatus cannot be fabricated by use of the conventional technologies as described in Patent Literature 1 to 3. Further, the cup-shaped electrode as described in Patent Literature 4 cannot be provided between the sample and the objective lens.

"As described above, a focal point of the objective lens for aberration suppression has become increasingly shorter, and compared to on-axis aberration, aberration occurring upon beam inclination has increased. Thus, it is difficult of cancel the aberration occurring upon the beam inclination with another lens shown in Patent Literature 5. For example, even only a small change in the beam inclination requires a large change in the amount of aberration occurring on another lens. Further, a great change in an axis of the beam needs to be made. An operation of adjusting the aberration and the axis requires repeated monitoring and setting changes, which takes much time. Further, aberration required for cancelling the aberration may not be created by another lens.

"It is an object of the invention to provide a charged particle beam apparatus capable of measuring samples with high resolution at a given inclination angle.

"Solution to Problem

"To address the object of the present invention, one embodiment refers to a charged particle beam apparatus irradiating a primary charged particle beam to a sample loaded on a stage to detect secondary charged particles generated by the irradiation,

"wherein the charged particle beam apparatus includes a beam tilt lens having a function of focusing the primary charged particle beam on the sample and inclining the primary charged particle beam onto the sample at a given angle,

"the beam tilt lens

"is a member with a hollow inside provided along a region surrounding the primary charged particle beam,

"has a gap for a pole piece at a bottom aperture end on a side opposing the sample, and

"further includes: a yoke magnetic path member characterized by having a lens coil therein;

"a solenoid coil arranged in a manner such as to surround the pole piece at the central aperture end of the yoke magnetic path member from outside;

"a lens coil power source supplying current to the lens coil to control a focus position of the primary charged particle beam; and

"a solenoid coil power source supplying current to the solenoid coil to control an inclination angle of the primary charged particle beam, and

"the solenoid coil has an upper end arranged on a side surface of the yoke magnetic path member and has a lower end arranged between the pole piece tip of the yoke magnetic path member and the sample.

"Advantageous Effects of Invention

"The present invention can provide a charged particle beam apparatus capable of measuring a sample with high resolution at a given inclination angle."

URL and more information on this patent, see: Fukuda, Muneyuki; Suzuki, Naomasa; Ikegami, Akira; Dohi, Hideto; Enyama, Momoyo; Shojo, Tomoyasu. Charged Particle Beam Apparatus. U.S. Patent Number 9384940, filed October 21, 2013, and published online on July 5, 2016. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=9384940.PN.&OS=PN/9384940RS=PN/9384940

Keywords for this news article include: Electronics, Magnetic Flux, Technology Companies, Hitachi High-Technologies Corporation, Semiconductor Equipment and Materials Companies.

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