JP6548374B2 - Charged particle beam system for low vacuum - Google Patents

Description

  The present invention relates to a low vacuum charged particle beam device using a retarding voltage.

  Semiconductor devices are shrinking every year according to Moore's law, and cutting edge devices are trying to cut the minimum feature size of 20 nm for mass production devices. In order to realize a small feature size, an exposure technique capable of forming a smaller pattern is required.

  Conventionally, a laser beam with a wavelength of 193 nm has been used for exposure, but since it has already far exceeded the limit that can be resolved optically, in recent years exposure technology utilizing EUV light with a wavelength of 13.5 nm is vigorously promoted ing.

  This technology is a technology said to be from Japan, but has been researched and developed for practical use in ASML etc. from 10 years ago. Although the exposure system main body optical system is almost complete, the current EUV exposure system can not obtain the light source power of 100 W to 200 W required for economical mass production, so it can not be used for 20 nm generation exposure It was skipped.

  Instead, a so-called double or triple exposure technique is used in actual production sites, which can realize smaller feature sizes by repeating the existing 193 nm wavelength exposure process multiple times. In principle, it is possible to make a pattern as small as possible by repeating immersion lithography using a laser beam with a wavelength of 193 nm multiple times, but it is necessary to have an alignment accuracy on the order of nm higher than the conventional one. It is known that the large roughness etc. coming from the large molecular structure of the chemically amplified resist repeatedly becomes the limitation of the exposure process. At present, double patterning that repeats the exposure process twice, which is said to be an economic limit, is put to practical use, and a memory device with a relatively simple structure is used to achieve 20 nm to 16 nm lines and spaces. It is done.

  Not only simple memory devices but also CPUs and logic devices need to be reduced in size to expand their functions and reduce their power consumption. Since logic devices utilize complex patterns that do not repeat, considerable complexity of patterns is required to make logic devices with double or triple exposure. A very complicated calculation is required to divide a pattern that can be originally realized by one exposure into patterns on two photomasks so that it can be used by multiple exposures. Depending on the pattern, the required result may not be obtained due to divergence of division calculation.

  In order to avoid these complexities, lithography facilitation technology called "Complementary Lithography", mainly proposed by Intel, is being used. This exposure method is characterized by using a pattern obtained by reducing a complicated logic circuit into a simple L & S pattern such as a memory circuit. In this way, the complicated logic device pattern is limited to the process of cutting the L & S pattern and its lines that are most easily exposed, so there is no need for complicated pattern division calculation, and the process is simple. The top is said to go to about 8 nm.

  On the other hand, as described above, when the 193 nm exposure technology is extended, the photomasks used for it will increase by the number of exposures for each layer, and more mask inspection and precise dimension measurement will be required than ever before. Become. For example, in double patterning, since two photomasks are sequentially stacked and used, the absolute position accuracy and alignment accuracy of the lines formed on the mask between the two masks are more important than ever. Optical correction for exposing finer patterns is also complicated and precise. A mask or the like using inverse lithography is used up to high-order diffraction height, so the pattern size used for correction is smaller.

  Although electron microscope technology is essential in order to determine whether these masks are made with the correct dimensions, in order to obtain a high-resolution image, the sample surface is irradiated with electrons of small beam spot size, and signals are obtained. Although it is necessary to detect the electrons, it is essential that the sample surface be charged so as not to adversely affect the irradiated electron beam and the signal electrons.

  Conventionally, in order to reduce the aberration of the electron beam optical system, a retarding method is used. In this method, once the energy of the electron beam is increased to several tens of KV, the electron beam is narrowed using an electron optical system, and the energy of the electrons is reduced to 1 KV or less by the reverse bias applied to the sample. It is a method to irradiate. As the energy of the electron beam increases, the wavelength becomes shorter, and the beam size can be narrowed to a smaller size, and the image resolution is improved. However, when a semiconductor device or the like is directly observed with a high energy electron beam, it has been found that high energy electrons cause a semipermanent action on the semiconductor to damage the device. In order to prevent this, the CDSEM for semiconductors uses a retarding method to reduce the electron beam energy at the time of irradiation while narrowing down the beam size.

  The retarding method is characterized in that since the sample to be measured can be subjected to any reverse bias voltage, the energy of the irradiation electron beam can be adjusted so that the secondary electron emission efficiency becomes 1. When the secondary electron emission efficiency is 1, since the number of incident electrons and the number of electrons coming out of the sample are equal, charge accumulation does not occur on the surface of the sample, and thus it is said that it is resistant to charge up.

  However, if the sample is made of pure quartz and the photomask or nanoimprinting template, the potential is different between the sample support and the surface of the photomask used to apply the voltage, so the secondary electron emission efficiency is adjusted to 1 It is extremely difficult to do. Therefore, in some cases, it is known that the image becomes white and can not be observed. In addition, when charges are accumulated sparsely near the sample surface due to the process, the surface potential of the sample differs depending on the place, and the optimum point of the irradiation energy can not be found, and the lettering method is powerless.

  On the other hand, by controlling the atmosphere of the vacuum chamber to a low vacuum of 1 Pa or less, positive and negative ions are positively generated by electron beam irradiation to prevent excess charge from accumulating on the sample surface, which is quartz. It is known that electron beam observation can be stably performed.

  If the aberration reduction effect by retarding, the secondary electron emission efficiency adjustment effect, and the surface charge accumulation prevention effect by low vacuum can be realized simultaneously, electron beam observation becomes very stable for any sample.

  However, in order to realize a low vacuum, a gas is introduced into the vacuum, so when a high voltage for retarding is applied to the sample, the gas is ionized between the pole piece and a discharge occurs, causing the device or sample to It is known that a failure occurs such as breakage, and there is a problem that the retarding method can not be adopted as it is.

  The present invention solves these problems, and in addition to being able to apply a target retarding voltage stably even in a low vacuum state where it is possible to neutralize the charge of a sample scanned by charged particles, The object is to make it possible to irradiate a sample with charged particles of landing energy.

  Therefore, the present invention uses a retarding voltage for detecting the secondary charged particles or reflected charged particles emitted at that time by scanning while irradiating the sample while decelerating the charged particles to be irradiated to the sample by the retarding voltage. In the charged particle beam apparatus, the charged particle beam source for generating charged particles, the acceleration voltage for accelerating the charged particles generated by the charged particle beam source, and the charged particles accelerated by the acceleration voltage are finely narrowed to the sample surface. An objective lens to be irradiated, a deflection scanning system for narrowly scanning charged particles to be irradiated by narrowly narrowing the sample surface with the objective lens on the sample surface, and emission when planarly scanned while finely charged charged particles are irradiated to the sample A vacuum chamber for providing a detector for detecting charged particles on the high vacuum side, storing the sample, holding the sample at a predetermined low vacuum, and neutralizing the charge On the low vacuum side, and a hole located at the center between the low vacuum side and the high vacuum side, facing the low vacuum side to connect the first aperture and the high vacuum side to connect the second aperture The first aperture is applied with a retarding voltage to decelerate charged particles that are accelerated and accelerated by an accelerating voltage and decelerated charged particles are irradiated to the sample to decelerate the charged particles, and finely narrowed charged particles are sampled. The secondary charged particle or the reflected charged particle emitted when the plane scan is performed while irradiating to the second hole and the hole of the second aperture center in the opposite direction, and the second hole The next charged particle or the reflected charged particle is detected by the detector.

  At this time, the space between the first aperture and the second aperture is differentially pumped.

  In addition, the diameter of the hole in the center of the first aperture and the second aperture is arbitrarily set to 0.005 to several mm.

  In addition, a decelerating voltage is applied to the first aperture so that the energy of the charged particle beam to be irradiated to the sample is in the range of several hundred volts to several kilovolts.

  Further, a retarding voltage of several kilovolts to several tens of kilovolts is applied to the first aperture.

  Also, the first aperture is connected to the lower pole of the objective lens and the second aperture to the upper pole of the objective lens so that the space between the first aperture and the second aperture is differentially pumped. .

  In addition, the first aperture and the second aperture are connected by a high-resistance material to reduce the influence of discharge due to contamination or the like.

  Further, a cylindrical electrode is provided on the charged particle beam source side of the second aperture, and a booster voltage is applied to further accelerate the charged particle beam accelerated by the accelerating voltage.

  Further, instead of applying the retarding voltage to the first aperture, the retarding voltage is applied to the second aperture, or the retarding voltage is applied to both the first aperture and the second aperture.

  Also, a voltage for attracting secondary charged particles or reflected charged particles is applied to the detector.

  In addition to being able to apply the target retarding voltage stably even in a low vacuum state where the charge of the sample scanned by charged particles can be neutralized, the present invention applies charged particles of low landing energy to the sample. It can be irradiated.

 In addition, the retarding voltage is adjusted to minimize the generation of charge on the surface of the sample, and the charge that has been generated by all means is a positive generated by separating the gas in a low vacuum state. It can be neutralized and removed with a negative charge. As a result, the charge (charge) generated on the sample can be removed from the sample having any surface state, and a high resolution image can be observed, acquired, and measured.

  In the present invention, a charged particle beam source, an accelerating voltage for accelerating charged particles, an objective lens for narrowing charged particles finely and irradiating the sample surface, a deflection scanning system, and a detector are provided on the high vacuum side. A vacuum chamber is provided on the low vacuum side to hold the low vacuum to neutralize the charge, and a first aperture and a second aperture are provided in connection between the low vacuum side and the high vacuum side, Is applied to the sample to decelerate the charged particle beam by applying a retarding voltage to decelerate the charged particle which is accelerated by the acceleration voltage and decelerated finely narrowed charged particle, and irradiate the sample while irradiating the finely narrowed charged particle to the sample. The secondary charged particle or reflective charged particle emitted when scanned is caused to travel in the opposite direction of the hole in the center of the first aperture and the hole in the center of the second aperture, and the secondary charge particle or the reflected that has been traveled Charged particles In addition to being able to apply the target retarding voltage stably even in a low vacuum state where it is possible to detect the charge by the detector and neutralize the charge of the sample scanned by the charged particles, charged particles of low landing energy It was realized to irradiate the sample.

  FIG. 1 shows a block diagram of one embodiment of the present invention. FIG. 1 shows the entire structure, and shows an example of the configuration of one embodiment in the case of electrons having a negative charge among charged particle beams. The case of positively charged ions also has a similar configuration corresponding to positive charges. Hereinafter, the case of an electron having a negative charge will be described in detail as an example.

  In FIG. 1, an electron gun 1 generates electrons, and for example, an extraction voltage is applied to a sharp-pointed emitter (which may be heated) to extract electrons, which are accelerated by an acceleration voltage. It is a known one that emits primary electrons.

  The primary electrons 2 are primary electrons emitted from the electron gun 1 and accelerated by a voltage (anode voltage 21) applied to an anode (anode) not shown. The energy generates several kilovolts to several tens kilovolts as needed. The energy of the primary electron 2 is not exactly the anode voltage 21 but an initial velocity (several eV) before being accelerated by the anode voltage of the primary electron 2 is added to this, but this is a small value Therefore, the anode voltage 21 will be described below as the energy (voltage) of the primary electron 2 in order to simplify the description.

  The condenser lens 3 is a known one that focuses the primary electrons 2 emitted from the electron gun 1.

  The blanking electrode 4 is for passing or blocking the primary electrons 2 emitted from the electron gun 1, and a voltage is applied to the parallel plate to deflect the primary electrons 2 for blanking. It is a known one that irradiates outside the hole of the aperture 5 to substantially block the primary electron 2.

  The blanking aperture 5 is provided with a small hole on the axis, and is known to block when the primary electron 2 is deflected by the blanking device 4.

  The electron detector 6 has a hole through which the primary electrons 2 pass at the center, and a detection surface for detecting secondary electrons and reflected electrons around the hole, and a predetermined high voltage as necessary. Is applied to attract the secondary electrons for detection. An electron detector 6 in which a cylindrical electrode is provided inside the electron detector 6 and a negative voltage is applied to it, and the secondary electrons emitted from the sample 12 and the reflected electrons reflected further are arranged around the axis It may have an action to repel the detection surface of.

  The deflector 7 is a known device that deflects the primary electrons 2 and planarly scans the primary electrons narrowed by the objective lens 8 on the sample 12.

  The booster electrode 17 is an electrode to which a booster voltage 22 is applied, and accelerates (or decelerates as necessary) the energy of the primary electron 21 having the anode voltage 21, or generates a primary electron 2 with a retarding voltage described later. When decelerating the lens, it is made to travel as close to the retarding electrode as possible to the initial acceleration voltage to suppress the reduction of aberration due to the objective lens etc. by the deceleration, or the booster electrode 17 here. The accelerator voltage 22 is accelerated (or decelerated) to the voltage 22 applied thereto.

  The objective lens 8 narrows the primary electrons 2 and irradiates the surface of the sample 12.

  The vacuum chamber 9 is a container which holds the sample 12 and the like in a low vacuum, and is a known one which is evacuated by an evacuation system (not shown).

  The pressure sensor 10 is a sensor that detects a low vacuum in the vacuum chamber 9.

  The differential exhaust aperture 11 is a two-stage differential exhaust aperture, and the differential exhaust aperture (lower, first) 11 is provided on the side facing the sample 12 on the low vacuum side, and the surface is on the high vacuum side. The differential exhaust aperture (upper, second) 11 is provided on the side to provide a space between the low vacuum side and the high vacuum side. This space is evacuated (differential evacuation) with an evacuation system (not shown) as necessary. The aperture may be provided with an electron transmitting thin film such as an oxide film, a ticker film, a carbon film or the like. Typical sizes of differential exhaust apertures range from 0.005 mm to several mm. Differential exhaust aperture is a technology that provides a place that has two or more vacuum levels in one device, and requires a high vacuum, and an environment where an electron detector such as an electron gun or MCP can operate is a low vacuum chamber. Provide with the environment.

  The sample 12 scans a plane while narrowing down and irradiating primary electrons 2, detects emitted secondary electrons and reflected electrons, and generates an image (eg, photomask, silicon wafer, GaAs wafer, etc.) It is a template for nanoimprinting, a plastic sheet or the like. When a predetermined voltage (sample voltage 24) is applied to the sample 12, the sample 12 and the XY stage 13 are insulated by an insulator (insulation plate) not shown.

  The XY stage 13 precisely moves the sample 12 in the X direction and the Y direction, and is a known one that moves the position precisely while measuring the position in real time by a laser interferometer (not shown).

  The TMP 14 is a turbo molecular pump and is an example of an exhaust system for evacuating from oil-free atmospheric pressure to high vacuum, and here, the vacuum chamber 9 is set to a predetermined pressure (for example, from atmospheric pressure to 1 Pa, further necessary). (Evacuate to high vacuum) according to

  The mass flow controller 15 causes the gas from the GAS 16 to flow into the vacuum chamber 9 so that the vacuum in the vacuum chamber 9 becomes the pressure specified based on the pressure information in the vacuum chamber 9 from the pressure sensor 10. To adjust.

  The GAS 16 is a cylinder storing high purity gas to be introduced into the vacuum chamber 9 such as N 2 or O 2.

  An anode voltage 21 is a voltage applied to an anode electrode (not shown) in the electron gun 1 to accelerate the primary electrons 2.

  The booster voltage 22 further accelerates (or decelerates) the primary electrons 2 with the booster voltage 22 to reduce the influence of the aberration by the objective lens 8 (reduces by the accelerated voltage), and makes the first-order beam narrower on the sample 12 It is a voltage applied to squeeze the electrons 2.

  The retarding voltage 23 is a voltage that decelerates the primary electrons (or primary electrons) 2 accelerated by the booster voltage 22 and is usually a low energy primary electron of several hundreds V to 2 KV in the sample 12. It is for planar scanning while irradiating and for high resolution. In addition, according to the sample 12, you may make it a low voltage or a high voltage. It is desirable to set the retarding voltage to such a voltage that charge-up of the sample does not occur.

  The sample voltage 24 is a voltage applied to the sample 12, and is usually 0V. As necessary, the difference between the retarding voltage 23 and the sample voltage 24 is the energy (voltage) of the primary electrons for irradiating the sample 12, so that the energy (voltage) for irradiating the sample 12 is appropriate. The sample voltage 24 may be set to an arbitrary voltage instead of 0V.

  The operation under the above configuration will be briefly described.

  (1) The sample 12 is fixed to the XY stage 13, the vacuum chamber 9 is evacuated by the TMP 14, and the gas from the GAS 16 is vacuum chamber 9 by the mass flow 15 so that the pressure detected by the pressure sensor 10 becomes a predetermined pressure. Adjust the amount to flow into the Thereby, the inside of the vacuum chamber 9 is maintained at a predetermined low vacuum state (for example, 1 to 100 Pa).

  (2) Simultaneously with (1), the high vacuum side of the upper part of the differential exhaust aperture 11 is evacuated to a high vacuum by a high vacuum exhaust system (not shown).

  (3) Here, since the two-stage differential exhaust aperture 11 of the present invention having a hole in the center is provided between the low vacuum side and the high vacuum side, both (the low vacuum side and the high vacuum Side and) can hold the desired vacuum respectively, and the present invention also allows the retarding voltage 23 to be below the differential exhaust aperture 11 (below (or above, or both) closer to the sample 12). In order to perform planar scanning while applying, decelerating, and making the energy of primary electrons 2 low energy to irradiate the sample 12, (1) influence of aberration by the objective lens 8 (aberration of the primary electrons 2 makes aberration (2) The high-resolution image can be acquired by irradiating the sample 12 with the narrowly focused primary electrons 2 to reduce the influence of the increase of Light the surface In order to emit a secondary electron from the very surface of the sample 12 and obtain a high resolution signal while planarly scanning, and (3) to irradiate the primary electron 2 to the sample 12 placed in a low vacuum state It is striking that it collides with the gas in the low vacuum and separates to generate positive and negative charges, which can neutralize the charge generated on the sample 12 and reduce (or eliminate) the influence of the charge on the sample 12 An effect is obtained.

  This will be sequentially described in detail with reference to FIGS. 2 to 10 below.

  FIG. 2 shows a block diagram (detail) of one embodiment of the present invention.

  (A) of FIG. 2 shows a block diagram (detail), and (b) of FIG. 2 shows the energy (voltage KV) of the primary electron 2. In FIG. 2, since the primary electron 2, the deflector 7, the objective lens 8, the sample 12, the XY stage 13 and the like are the same as those of the same numbers in FIG.

  In FIG. 2A, the differential exhaust aperture (lower) 11 and the differential exhaust aperture (upper) 11 are connected to the lower pole of the objective lens 8 through the insulator 18 as shown in the figure. And a retarding voltage 23 (e.g. -9 KV) is applied.

  The vacuum chamber 9 is held in a low vacuum state, here, for example, 100 Pa. The low vacuum state is desirably determined by conducting experiments in the range of 1 Pa to 100 Pa and further atmospheric pressure. When the pressure is smaller than 1 Pa, the probability of collision with the gas becomes too small when planar scanning while irradiating the sample 12 with primary electrons 2 of low energy, and the gas is separated to have sufficient positive and negative charges. Because the charge on the surface of the sample 12 is difficult to neutralize, it is sufficient to determine the optimum value by experiment. Although the high vacuum side is 1 mPa in this example, the present invention is not limited to this, and it is sufficient that the vacuum is usually higher than 100 mPa.

  The booster electrode 17 applies a booster voltage 22 (for example, 10 KV) to apply a voltage for accelerating the primary electrons 2. A booster electrode 17 for accelerating the primary electrons 2 is provided inside the pole piece constituting the objective lens 8, whereby the energy of the primary electrons 2 is decelerated by the decelerating voltage before entering the objective lens 8. Can be prevented or the energy of the primary electrons 2 can be increased. For example, when a voltage of 10 KV is applied to this electrode, the primary electrons 2 emitted from the electron gun 1 at 8 KV are accelerated to 10 KV and enter the objective lens 8, and two apertures are continuous at the tip of the objective lens 8. A differential exhaust aperture 11 is supported by an insulator 18.

  In order to avoid discharge, it is preferable to increase the degree of vacuum where high voltage is applied so that a large amount of gas ions are not generated. Of course, it is preferable to subject the material to a vacuum heat treatment in advance to perform a degassing treatment. The pressure between the two apertures constituting the differential exhaust aperture 11 is intensely drawn by a vacuum pump such as TMP, and the pressure difference between the two apertures, that is, the degree of vacuum of the vacuum chamber 9 and the differential exhaust aperture 11 The upper part of can realize a vacuum difference of 3 orders of magnitude. For example, when the periphery of the sample 12 is 100 Pa, 0.1 Pa can be realized on the electron source side of the differential exhaust aperture 11. In this case, the space above the differential exhaust aperture 11 has a high vacuum, and a normal gas discharge is unlikely to occur, so that a vacuum isolation voltage of several KV or more can be realized with a gap of 1 mm. On the other hand, the degree of vacuum on the side close to the vacuum chamber 9 under the differential evacuation aperture 11 can be maintained in a low vacuum state of about 1 Pa to 100 Pa. According to Paschen's law, under certain conditions, discharge can be avoided even in a low vacuum state to apply a certain high voltage, but in the present embodiment, discharge can be prevented even when a higher voltage is applied.

  In order to avoid discharge, it is also important not to cause a high potential difference in the low vacuum part. In this embodiment, in the conventional SEM structure, electrical control is performed so that the potential between the differential exhaust aperture 11 which is likely to cause discharge and the sample 12 becomes the same. In this way, no high voltage is applied between the tip of the differential exhaust aperture 11 in a low vacuum state and the sample 12, so in principle no discharge occurs. On the other hand, a high voltage (retarding voltage 23) necessary for the retarding effect is applied to the differential exhaust aperture 11 and the sample 12. For example, the energy (voltage) of the primary electrons 2 emitted from the electron gun 1 is 8 KV, and is accelerated to 10 KV (booster voltage 22) by the booster electrode 17, and the potential of the differential exhaust aperture 11 and the sample 12 is -9 KV. If set, the landing voltage to the sample 12 can be 1 KV. On the other hand, the potential difference between the differential exhaust aperture 11 and the sample 12 is 0 KV and no discharge occurs. Since the high voltage is applied only to the high vacuum side, the above-mentioned potential difference can be sufficiently sustained by taking measures against creeping discharge in the normal high vacuum.

  According to the above method, the retarding voltage 23 can be applied while maintaining the peripheral pressure of the sample 12 in the vacuum chamber 9 in a low vacuum state, and the retarding method further changes the energy of the primary electrons 2 to further enhance the second order. Since the efficiency of electron emission can be changed, conditions can be created in which no charge is accumulated on the surface of the sample 12. The retarding method can not make the charge accumulation of all parts of the sample 12 zero, but the non-zero part separates the gas in the low vacuum state of the present invention to generate positive and negative ions. By letting the charge on the sample 12 be neutralized and removed, it is possible to observe and measure the sample 12 with a very high degree of stability.

  FIG. 3 shows an example of the relationship between the aperture size and the degree of vacuum according to the present invention. The condition of the horizontal axis in the figure is the degree of vacuum in the vacuum chamber 9 and represents Pa. Apertures on the vertical axis represent the upper and lower sides of the differential exhaust aperture 11 in FIGS. 1 and 2, the chamber represents the vacuum chamber 9 on the low vacuum side, and the MCP chamber represents the MCP chamber on the high vacuum side (electrons Represents the space in which the detector exists.

For example, the lower right: Above the aperture: 0.25 mmΦ
・ Aperture lower: 0.5mmΦ
Chamber: 95 Pa
・ MCP room: 1.3 × 10 ^-3
Were obtained in the experiment. That is, when the hole on the differential exhaust aperture 11 in FIGS. 1 and 2 is 0.25 mm mm and the hole on the lower side is 0.5 mm 、, the vacuum degree of the vacuum chamber 9 (low vacuum side) is 95 Pa (about 100 Pa) The degree of vacuum of the MCP chamber (high vacuum side) is 1.3 × 10 ^-3 (about 1 mPa). The distance between the lower and upper holes is several mm.

  As described above, by arranging the differential exhaust aperture 11 having two stages of holes between the low vacuum side and the high vacuum side as shown in FIGS. 1 and 2, the degree of vacuum on the low vacuum side is 100 Pa. It has been found that the degree of vacuum on the high vacuum side can be maintained at 1 mPa when it is set, and it can be configured to have no problem in practical use. In the low vacuum state, 100 Pa to 1 Pa (1 Pa causes primary electron 2 to collide with the gas, the probability of separation into positive and negative ions decreases, and the lower limit at which the charge on the surface of sample 12 can be neutralized. Equivalent).

  FIG. 4 shows an example of a relationship curve (Paschen curve) of the vacuum degree and the discharge voltage according to the present invention. The horizontal axis represents p · d (Torr · cm), and the vertical axis represents the discharge start voltage (V). 133 Pa = 1 Torr.

  In FIG. 4, when the electrode spacing is 1 mm at 1 Torr, the pd product is 1 Torr × 0.1 cm = 0.1, and when the horizontal axis is 0.1 in the vertical direction, the discharge start voltage (V) is 1000 or more From the fact that it is clear that there is a withstand voltage of 1000 V or more.

  Therefore, it is found that the discharge start voltage in the vacuum chamber 9 in a low vacuum state of 1 Torr (133 Pa) is 1000 V or more at 1 mm intervals, and 2 mm in the case of the sample voltage 24 of several hundred V to 2 KV of the present invention. It turns out that there should be a degree interval.

  FIG. 5 shows a block diagram of another embodiment of the present invention.

  (A) of FIG. 5 shows a configuration diagram (details), and (b) of FIG. 5 shows the energy (voltage KV) of the primary electron 2. In FIG. 5, since the primary electron 2, the deflector 7, the objective lens 8, the sample 12, the XY stage 13 and the like are the same as those in FIGS. 1 and 2, the description will be omitted.

  In FIG. 5A, the differential exhaust aperture (bottom) 11 is fixed to the tip (pole piece) of the lower pole of the objective lens 8 through the insulator 18 as shown in FIG. Is applied.

  The differential exhaust aperture (upper) 11 is fixed to the booster electrode 17 at the tip of the upper pole of the objective lens 8 as shown, and a booster voltage 22 applied to the booster electrode 17 is applied. An electron detector 6 (MCP or an electron detector such as a small and thin avalanche diode) is mounted around the central hole of the differential exhaust aperture (upper) 11.

  The operation under the above configuration will be described.

  (1) In FIG. 5, the upper and lower differential exhaust apertures 11 are electrically separated by the insulating or high-resistance material, respectively, and different voltages are applied. In this case, the differential exhaust aperture (upper) 11 has a booster voltage 22 The retarding voltage 23 was applied to the differential exhaust aperture (bottom) 11. In particular, by applying the retarding voltage 23 to the differential exhaust aperture (bottom) 11 supported by the insulator 18 and applying the same voltage (or a voltage of several hundred V to 2 KV) to the sample 12, the differential It is possible to prevent discharge between the exhaust aperture (bottom) 11 and the sample 12 or the like.

  (2) Further, the retarding method is characterized in that the effect of the aberration of the objective lens 8 can be reduced as the decelerating electric field (decelerating electric field by the retarding voltage 23) used for retarding is closer to the surface of the sample 12. Therefore, in FIG. 5, it is desirable to arrange the position where the primary electrons 2 decelerate as the lower differential exhaust aperture (lower) 11 at a portion as close to the surface of the sample 12 as possible. By arranging the differential exhaust aperture (bottom) 11 to which the retarding voltage 23 is applied as shown in FIG. 5 as close as possible to the sample 12, the influence of the objective lens 8 on the aberration is reduced as much as possible. Even if the energy of the primary electrons 2 incident on the sample 12 is reduced, the primary electrons 2 can be narrowed finely.

  (3) Furthermore, an electron detector 6 for detecting secondary electrons or reflected electrons is disposed in a ring-shaped portion outside the central hole of the upper differential exhaust aperture (upper) 11, for example, a PIN diode, The APD (avalanche diode) is disposed in this portion, or the differential exhaust aperture (upper) 11 is manufactured itself. Then, by applying a voltage of 10 KV or more between the sample 12 and the electron detector 6, electrons irradiated to the sample 12 at a low acceleration voltage generate secondary electrons, and the secondary electrons are After passing through the center hole of the differential exhaust aperture (bottom) 11, it is accelerated by the voltage applied to the differential exhaust aperture (top) 11, collides with the electron detector 6, amplifies and detects, and the electron efficiently It is possible to detect Here, the semiconductor electron detector 6 is so thin and small that it can be easily arranged in a ring-shaped part outside the central hole of the differential exhaust aperture (top) 11. Of course, without being limited to the drawing, the electron detector may be arranged at another place where electrons can be detected.

  FIG. 6 shows a second embodiment block diagram (part 2) of the present invention.

  (A) of FIG. 6 shows a configuration diagram (details), and (b) of FIG. 6 shows the energy (voltage KV) of the primary electron 2. In FIG. 6, since the primary electron 2, the deflector 7, the objective lens 8, the sample 12, the XY stage 13 and the like are the same as those in FIGS. 1, 2 and 5, the description will be omitted.

  In FIG. 6A, the differential exhaust aperture (upper) 11 and the differential exhaust aperture (lower) 11 are fixed by the high resistance material 19 as shown, and the differential exhaust aperture (upper) 11 Is fixed to the illustrated booster electrode 12 mounted inside the tip of the upper pole of the objective lens 8. A booster voltage 22 applied to the booster electrode 17 is applied to the differential exhaust aperture (upper) 11. On the other hand, a retarding voltage 23 is applied to the differential exhaust aperture (bottom) 11 as shown. A retarding voltage 23 is applied to the sample 12 (or held at 0 V).

  The operation under the above configuration will be described.

  (1) In FIG. 6, the voltages of the two apertures constituting the differential exhaust aperture 11 disposed near the center of the objective lens 8 can be separately controlled. The differential aperture (upper) 11 and the differential exhaust aperture (lower) 11 are made of a conductive material and function as independent electrodes. In FIG. 6, the differential exhaust aperture (upper) 11 applies a booster voltage 22 The differential exhaust aperture (bottom) 11 applies a retarding voltage 23.

  (2) According to experiments, it is known that it becomes difficult to cause a vacuum discharge by continuously supplying a minute current between the differential exhaust aperture (upper) 11 and the differential exhaust aperture (lower) 11 That is, by passing a minute current, the electric field portion on the surface or in the vicinity becomes smooth, reducing the phenomenon that the electric field strength becomes extremely high locally, and generation of a trigger minute discharge (local discharge) It is expected that large vacuum discharge can be suppressed as a result. Of course, in actual use, it is desirable to perform discharge conditioning by applying a voltage higher than that actually used in advance to improve discharge resistance characteristics.

  (3) Therefore, in the present invention, the two electrodes (upper and lower differential exhaust apertures 11) are connected by a high resistance material 19 exceeding 10 MΩ. By so doing, when a high voltage is applied between the two electrodes, microampere-order microcurrents will always flow, and a large potential gradient will be prevented from locally occurring, improving the discharge resistance characteristics. .

  FIG. 7 shows a configuration diagram (part 3) of another embodiment of the present invention.

  FIG. 7A shows a configuration diagram (detail), and FIG. 7B shows the energy (voltage KV) of the primary electron 2. In FIG. 7, the primary electron 2, the deflector 7, the objective lens 8, the sample 12, the XY stage 13 and the like are the same as those in FIGS. 1, 2, 5 and 6, and thus the description is omitted. Do.

  In (a) of FIG. 7, the retarding electrode 221 is fixed to the tip of the lower electrode of the objective lens 8 via the high resistance material 19, and applies a retarding voltage 22.

  The differential exhaust aperture (upper) 11 and the differential exhaust aperture (lower) 11 are fixed to a booster electrode 17 disposed at the tip of the upper pole of the objective lens 8, and a booster voltage 22 is applied. The electron detector 6 fixes a diode in the form of a ring outside the central hole of the differential exhaust aperture (bottom) 11 (as in FIG. 6).

    The operation under the above configuration will be described.

  (1) In FIG. 7, an electrode (retarding electrode 221) for applying the retarding voltage 23 is fixed to the tip of the pole piece of the lower pole of the objective lens 8 through the high resistance material 19. The differential exhaust aperture 11 is fixed to the tip of the pole piece of the upper pole of the objective lens 8, and the upper part from this part is kept high vacuum. Since the differential exhaust aperture 11 is fixed by the high-resistance material 19, a minute current is always flowing even in a space (low vacuum space) which is not in a high vacuum, and therefore discharge is difficult to occur. Furthermore, according to Paschen's law, the discharge voltage can be increased by appropriately taking the space and pressure between the retarding electrode 221 and the differential exhaust aperture (bottom) 11. However, since the retarding electrode 221 is in a low vacuum state, it is desirable to avoid a voltage difference of several tens of KV or more. It is desirable to use a titanium material which is said to have discharge resistance as the retarding electrode 221. The surface of the retarding electrode 221 may be covered with an organic or inorganic thin film such as a very thin pressure-resistant plastic to improve the discharge resistance.

  (2) In FIG. 7, the differential exhaust aperture (bottom) 11 is made of a PIN diode or APD that is the electron detector 6, or the ring shape of the outer periphery of the differential exhaust aperture (bottom) 11 without a hole. A PIN diode or an APD can be placed in the part of. A large potential difference is generated between the surface of the sample 12 and the differential exhaust aperture (bottom) 11. Therefore, secondary electrons and reflected electrons generated by the primary electrons 2 irradiated to the surface of the sample 12 with low energy are accelerated by the potential difference, and are incident on the PIN diode or APD that is the electron detection device 6 to be amplified and detected. Ru. Since the electron amplification factor of these devices is proportional to the energy of incident electrons, sufficient amplification can be obtained.

  FIG. 8 shows a configuration diagram (part 4) of another embodiment of the present invention.

  (A) of FIG. 8 shows a configuration diagram (details), and (b) of FIG. 8 shows the energy (voltage KV) of the primary electron 2. In FIG. 8, the primary electrons 2, the deflector 7, the objective lens 8, the sample 12, the XY stage 13, etc. are the same as those in FIG. 1, FIG. 2, FIG. 5, FIG. I omit explanation.

  In (a) of FIG. 8, the booster electrode 171 is an electrode that is cylindrically arranged around the axis and applies a booster voltage 22 as illustrated.

  The differential exhaust aperture (upper) 11 and the differential exhaust aperture (lower) 11 are fixed to a booster electrode 171 disposed at the tip of the upper pole of the objective lens 8 as shown in FIG. Is applied.

    The lower electrode 31 is for applying a retarding voltage 23 to decelerate the energy of the primary electron 2, and here, the tip of the lower electrode of the objective lens 8 is shown via an insulator at the tip of the lower electrode. As shown in FIG. 8, a retarding voltage 23 is applied to the ring-shaped and flat electrode.

  The operation under the above configuration will be described.

  (1) In FIG. 8, as a method of applying a decelerating voltage (retarding voltage 23) to the primary electrons 2 emitted from the electron gun, between the sample 12 and the pole piece of the lower pole of the objective lens 8 Since it is easy to be discharged if a large potential difference is generated in the low vacuum state, a retarding voltage 23 is applied to the low vacuum region, which causes a voltage difference below the discharge limit which can be calculated by Paschen's law. Since a high potential difference is allowed in the high vacuum region created by the differential exhaust aperture 11, a large voltage is applied to that location. Alternatively, a high discharge withstand voltage can be provided by applying Paschen's law to the contrary and using a low vacuum of over 300 Pa. At this time, in order to avoid lowering of the high vacuum on the side where the electron gun is located, the aperture size should be smaller, or an electron transmission film such as a very thin nitride film, carbon film, metal or semiconductor film should be used for the aperture It is also possible to shut off the low vacuum.

  (2) For example, the primary electrons 2 incident on the objective lens 8 are accelerated to, for example, 8 KV by the booster voltage 22. The voltage of the lower electrode 31 fixed via the insulator to the tip of the lower pole piece that has passed through the objective lens 8 is -6 KV (retarding voltage 23), and decelerates to 2 KV at a stretch. The voltage of the sample 12 is -7 KV (sample voltage 24) and is further decelerated by 1 KV. By thus decelerating in multiple stages, while passing through the objective lens 8 with high energy, between the sample 12 and the lower electrode 31 fixed to the tip of the pole piece of the lower pole of the objective lens 8 via an insulator. Can be maintained at a voltage below the discharge limit. In order to decelerate the energy of the primary electron 2 just before the sample 12, the influence of the reduction of the aberration of the objective lens 8 is minimized, and the finely focused primary electron 2 is irradiated to the sample 12 to obtain a high resolution image It is possible to

  FIG. 9 shows a fifth embodiment of the present invention.

  (A) of FIG. 9 shows a configuration diagram (details), and (b) of FIG. 9 shows the energy (voltage KV) of the primary electron 2. In FIG. 9, the primary electron 2, the deflector 7, the objective lens 8, the sample 12, the XY stage 13 etc. are the same as those of the same numbers in FIG. 1, FIG. 2, FIG. 5, FIG. Description is omitted because it exists.

  In (a) of FIG. 9, the moderation electrode 32 schematically shows a state in which the portion of the pole piece at the tip of the lower electrode of the objective lens 8 is electrically isolated by the insulator 32 and connected by the small magnetic reluctance. Is shown. By configuring in this manner, the pole piece at the tip of the lower pole of the objective lens 8 can have substantially the same magnetic characteristics as in the case where it is not insulated with an insulator, and the tip portion is electrically isolated and retarded It can be used as a decelerating electrode 32 for applying a voltage.

  The operation under the above configuration will be described.

  (1) In FIG. 9, the pole piece of the lower pole of the objective lens 8 is a magnetic material such as pure iron or permalloy, and is made of a metal and a conductive material. Therefore, it can be used as an electrode. In FIG. 5, the pole piece at the tip of the lower pole of the objective lens 8 is divided and electrically isolated from each other, so that the tip portion of the pole piece is used as a retarding electrode (deceleration electrode 32).

(2) Thereby, the tip part (deceleration electrode 32) of the lower pole of the objective lens 8 is electrically insulated, and the retarding voltage 23 is applied to this tip part. For example, the primary electrons 2 incident on the objective lens 8 with an energy of 8 KV are decelerated to 2 KV by the voltage of -6 KV applied to the decelerating electrode 32. For example, if a voltage of -7 KV (sample voltage 24) is applied to the sample 12, the primary electrons 2 are finally irradiated to the sample with an energy of 1 KV.
In this way, the retarding method can be performed while avoiding the discharge.

  FIG. 10 shows a sixth embodiment of the present invention.

  (A) of FIG. 10 shows a configuration diagram (detail), and (b) of FIG. 10 shows the energy (voltage KV) of the primary electron 2. In FIG. 9, the primary electron 2, the deflector 7, the objective lens 8, the sample 12, the XY stage 13 and the like have the same numbers as in FIG. 1, FIG. 2, FIG. 5, FIG. Since it is the same as in FIG.

  In (a) of FIG. 10, the insulator 35 covers a portion to which a voltage existing in a low vacuum state is applied with an insulator and electrically insulates it so that it is difficult to cause a discharge breakdown.

  The operation under the above configuration will be described.

  (1) In FIG. 10, the differential exhaust aperture (upper) 11 and the differential exhaust aperture (lower) 11 for dividing the low vacuum region and the high vacuum region exist in the center of the objective lens 8. The upper part of the differential exhaust aperture (upper) 11 is maintained at a high vacuum of 1 mPa or more, and the differential exhaust aperture (lower) 11 to the side of the vacuum chamber 9 is maintained at a low vacuum of about 100 Pa. Alternatively, contrary to common sense, a low vacuum of over 300 Pa may be applied as Paschen's law teaches by providing a thin film in the lower aperture. On the other hand, the tip end portions of the upper and lower poles of the pole piece of the objective lens 8 are electrically insulated and divided, whereby the booster electrode 17 and the reduction electrode 36 are respectively configured.

  (2) In FIG. 10, the booster electrode 17 and the reduction electrode 36 are in a low vacuum state, and when exposed to a low vacuum, the location is likely to be discharged. Therefore, in FIG. 10, the booster electrode 17 and the reduction electrode 36 are respectively covered with the insulator 35 to make it difficult to discharge.

  (3) For example, if 10 KV is applied to the booster electrode 17 as being higher than the energy of the primary electron 2, the primary electron 2 enters the objective lens 8 at 10 KV. It decelerates by the decelerating voltage (retarding voltage, for example -8 KV) applied to the pole piece (deceleration electrode 36) of the lower pole electrically isolated from the surrounding pole piece at the point of exiting the objective lens 8 . Further, a potential of -9 KV (sample voltage 24) is applied to the sample 12, and finally the primary electrons 2 are irradiated to the sample 12 with an energy of 1 KV.

  When an electrode such as the deceleration electrode 36 is covered with a dielectric such as the insulator 35 to make it difficult to discharge, the electric field is reduced to about 1 / 分 の of the dielectric constant ε, but it becomes difficult to discharge. (Insulator) is determined by experiment and its optimum configuration is applied. As the insulator, an inorganic film such as an oxide film or glass, or an organic material such as a fluorine resin can be used. Since it is important that the insulators be covered with a material with sufficient breakdown voltage on the surface of the electrode, it is not necessary to fill all the space between the electrodes, and depending on the material, the electrode is covered with a thin film of about 100 microns or more. The pressure resistance of It is desirable to round the tip of the electrode to avoid electric field concentration.

It is a block diagram of one Example of this invention. It is a block diagram (detail) of one embodiment of the present invention. The present invention is an example of the relationship between the aperture size and the degree of vacuum. It is an example of a related curve of the degree of vacuum and discharge voltage of the present invention. It is a block diagram of another Example of this invention. It is another Example block diagram (2) of this invention. It is another Example block diagram (3) of this invention. It is another Example block diagram (4) of this invention. It is another Example block diagram (the 5) of this invention. It is other Example structure FIG. (6) of this invention.

1: Electron gun 2: Secondary electron 3: Condenser lens 4: Blanking electrode 5: Blanking aperture 6: Electron detector 7: Deflector 8: Objective lens 81: Pole piece 9: Vacuum chamber 10: Pressure sensor 11: Differential exhaust aperture 12: Sample 13: XY stage 14; TMP
15: Mass flow 16: GAS
17: booster electrode 18: insulator 21: anode voltage 22: booster voltage 23: blanking voltage 24: sample voltage 31: lower electrode 32, 36: deceleration electrode 33, 34: insulator

Claims (7)

Charged particle beam apparatus using a retarding voltage for decelerating the charged particles to be irradiated to the sample by the retarding voltage and irradiating and scanning the sample while detecting secondary charged particles or reflected charged particles emitted at that time In
A charged particle source for generating charged particles;
An accelerating voltage that accelerates charged particles generated by the charged particle beam source;
An objective lens for narrowing down the charged particles accelerated by the acceleration voltage and irradiating the sample surface with the charged particles;
A deflection scanning system for making the charged particle irradiated narrowly focused on the sample surface with the objective lens flatly scanned on the sample surface;
Providing a detector for detecting secondary charged particles or reflected charged particles emitted when planarly scanning while irradiating the sample with the finely narrowed charged particles on the high vacuum side;
A vacuum chamber is provided on the low vacuum side for housing the sample and holding the sample at a predetermined low vacuum, and neutralizing the charge.
A hole is formed in the center between the low vacuum side and the high vacuum side, the first aperture facing the low vacuum side and the second aperture facing the high vacuum side. Set up
Said first aperture, with said accelerated at an acceleration voltage finely focused charged particle by applying a negative retarding voltage to the sample to decelerate the decelerating the charged particle beam for irradiating the sample Charging using a retarding voltage, characterized in that secondary charged particles or reflected charged particles emitted when planarly scanning while irradiating the sample with the finely narrowed charged particles are detected by the detector. Particle beam equipment.   The charged particle beam device using a retarding voltage according to claim 1, wherein a space between the first aperture and the second aperture is differentially pumped.   The first aperture is connected to the lower pole of the objective lens and the second aperture to the upper pole of the objective lens, and the space between the first aperture and the second aperture is differentially pumped. The charged particle beam apparatus using the retarding voltage according to any one of claims 1 to 2, characterized in that.   The high resistance material is connected between the first aperture and the second aperture, and the influence of the discharge due to the contamination etc. is reduced to any one of claims 1 to 3. Charged particle beam device using a retarding voltage of   A cylindrical electrode is provided on the charged particle beam source side of the second aperture, and a positive booster voltage is applied to further accelerate the charged particle beam accelerated by the acceleration voltage. The charged particle beam apparatus using the retarding voltage in any one of claim | item 4.   Instead of applying the negative retarding voltage to the first aperture, the negative retarding voltage is applied to the second aperture, or the negative aperture is applied to both the first aperture and the second aperture. The charged particle beam apparatus using the retarding voltage according to any one of claims 1 to 5, wherein a retarding voltage is applied.   The charged particle beam device using a retarding voltage according to any one of claims 1 to 6, wherein a voltage for attracting secondary charged particles or reflected charged particles is applied to the detector.

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