Electron beam apparatus

Abstract

PURPOSE: To fix and hold a photomask to an ultra-high heat conductive pallet, to keep the temperature of the whole of the photomask at an arbitrary temperature and uniformly, and to always hold the photomask at a temperature suitable for the reaction of gas in an electron beam device for performing measurement, inspection, or correction by irradiating the photomask with an electron beam.CONSTITUTION: The electron beam exposure apparatus includes an electron beam irradiation system for generating an electron beam, an objective lens for narrowing the electron beam generated by the electron beam irradiation system and irradiating the narrowed electron beam onto a photomask, a scanning system for planarly scanning the electron beam irradiated onto the photomask, and a heat exchange device for holding the photomask at a predetermined temperature, the heat exchange device being fixed to or detachably attached to a surface of the photomask opposite to an electron beam irradiation side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electron beam apparatus for irradiating an electron beam to perform measurement, inspection, or correction. [Background technology]

[0002] Conventionally, photomask repair equipment using electron beams is a device that deposits or etches the desired material on the photomask by colliding the electron beam with a reactive gas adsorbed on the photomask to generate reactive species. Because the number of molecules adsorbed on the photomask is highly dependent on the photomask surface temperature, precise control of the photomask surface temperature is essential for controlling the photomask repair reaction to the desired state and maintaining repair reproducibility.

[0003] Conventional photomask repair devices heat solid reactive gas materials at room temperature to gasify them, then spray them from a nozzle maintained at a high temperature near the photomask, causing the temperature of the photomask to rise due to radiant heat from the nozzle.

[0004] For this reason, heat shield plates and other devices have been used to block the infrared rays emitted from the nozzle, but this has not been sufficient. Because the amount of gas ejected varies, the heat balance is not constant, resulting in the problem of constant temperature fluctuations.

[0005] Furthermore, because the photomask is held in a vacuum with a three-point support structure, the only path for heat conduction from the photomask to the outside is the three-point support area, which creates the problem that the temperature of the photomask other than near the support points cannot be controlled to a desired temperature because heat conduction is localized. DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0006] As mentioned above, conventional photomask repair devices heat solid reactive gas material at room temperature to turn it into gas, and then spray it from a nozzle maintained at a high temperature near the photomask. As a result, the temperature of the photomask rises due to radiant heat from the nozzle, making it impossible to maintain a constant temperature for the photomask.

[0007] Furthermore, because a heat shield plate was used to block the infrared rays emitted from the nozzle, there was a problem in that when the amount of gas ejected changed, the heat balance became unstable, causing temperature changes. Temperature changes (drift) have a negative effect on chemical reactions and mask position drift.

[0008] Furthermore, because the photomask is held in a vacuum with a three-point support structure, the only path for heat to be conducted from the photomask to the outside is the three-point support area, and because heat conduction is localized, there was an issue in that the temperature of the photomask other than near the support points could not be controlled to a desired temperature. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present invention fixes and holds the photomask on an ultra-high thermal conductivity pallet, which is completely different from the conventional stainless steel pallets with poor thermal conductivity, thereby realizing the ability to maintain the temperature of the entire photomask at a desired and uniform temperature and always maintain it at a temperature appropriate for gas reaction.

[0010] The system also has a heat exchanger with a vertical movement mechanism that can contact the entire bottom surface of the photomask pallet when it is transported into the vacuum chamber, and an external chiller is used to achieve precise temperature control.

[0011] In addition, within the chiller's temperature control capacity range, for example, a range of approximately ±50 degrees, precise temperature control of a uniform temperature within the surface of ±0.01 degrees was achieved, allowing for fast arbitrary temperature setting.

[0012] Therefore, the present invention provides an electron beam device for irradiating an electron beam to perform measurement, inspection, or correction, which includes an electron beam irradiation system that generates an electron beam, an objective lens that narrows the electron beam generated by the electron beam irradiation system and irradiates it onto a photomask, a scanning system that performs planar scanning of the electron beam irradiated onto the photomask, and a heat exchanger that is fixed to the surface of the photomask opposite to the side irradiated with the electron beam or is detachable from the surface and maintains the temperature at a predetermined level, and is configured to precisely maintain the temperature of the photomask at a predetermined level to reduce drift.

[0013] In this case, the heat exchanger is provided with a push-up stage on the surface opposite to the photomask, which pushes up and fixes the heat exchanger.

[0014] The heat exchanger circulates a liquid at a predetermined temperature.

[0015] The heat exchanger has a heat pipe attached along the surface opposite to the photomask.

[0016] In addition, the temperature range within the heat exchanger surface is set to within ±0.1°C. [Effects of the Invention]

[0017] The present invention fixes and holds the photomask on an ultra-high thermal conductivity pallet, making it possible to maintain the temperature of the entire photomask at a desired and uniform temperature, and always maintain it at a temperature appropriate for gas reaction, thereby reducing temperature drift.

[0018] In addition, the system is equipped with a heat exchanger with a vertical movement mechanism that can contact the entire bottom surface of the photomask pallet when it is transported into the vacuum chamber, and an external chiller is used to precisely control the temperature, making it possible to control the photomask temperature quickly and precisely.

[0019] Furthermore, precise temperature control using an external chiller allows precise temperature control of a uniform temperature within the wafer of about ±0.01°C within the chiller's temperature control range, for example, a range of about ±50°C, making it possible to quickly set any temperature. This stabilizes the repair reaction and reduces drift in the photomask position. This also indirectly reduces photomask vibration. Example 1

[0020] FIG. 1 shows a configuration diagram of one embodiment of the present invention. This FIG. 1 shows an example of the configuration of one embodiment of a photomask temperature precision control device of the present invention. In this example, a water-cooled temperature control device is configured to maintain the temperature of the photomask 3 at a desired temperature using a high-precision constant-temperature water circulator 32 located outside the vacuum chamber 2, a heat exchanger 24 located inside the vacuum chamber 2, and a water-cooled pipe 31. This will be explained in detail below.

[0021] In FIG. 1, an electron beam 1 is narrowed by an electron gun, focusing lens, and objective lens (not shown), and is irradiated onto a photomask 3 while being scanned in a plane by a deflection device (not shown). The emitted secondary electrons, reflected electrons, or absorbed electrons are detected by detectors (not shown), respectively, to generate an enlarged image on the photomask 3 (see FIG. 11, etc., described later).

[0022] The photomask 3 is an example of a sample that is irradiated with the electron beam 1 and scanned across a plane to generate an enlarged image, measure and inspect defects, and further repair defective patterns.

[0023] The vacuum chamber 2 is a vacuum container that houses a photomask 3 and the like in a vacuum.

[0024] The XYZ stage 21 precisely moves the photomask 3 in the X, Y, and Z directions while measuring its length in real time using a laser interferometer (not shown), and is automatically controlled by a system (not shown) so that the electron beam 1 is irradiated at a predetermined position.

[0025] The push-up stage 22 is fixedly mounted on the XYZ stage 21 and presses the heat exchanger 24 against the mask pallet 27 to improve heat conduction.

[0026] The stage control device 31 supplies a control signal to the push-up stage 22, for example by applying a control voltage to a piezoelectric element to move it UP (pushes upward) or DOWN (contracts downward), thereby breaking or making thermal contact.

[0027] The thermally conductive sheet 26 is a sheet with good thermal conductivity, and is a sheet for reducing the thermal resistance between the heat exchanger 24 and the mask pallet. The thermally conductive sheet 26 is pushed upward by the push-up stage 22 through the heat exchanger 24, thereby reducing the thermal resistance.

[0028] The mask pallet 27 precisely fixes the photomask 3 in a predetermined position using a mask fixing device 28. The photomask 3 fixed to the mask pallet 27 is configured to uniformly release heat from the heat exchanger 24 to the outside and maintain a constant temperature over the entire surface (see Figures 2 to 10, etc., described later).

[0029] The water cooling pipe 31 is a pipe for circulating water at a constant temperature through the heat exchanger 24 .

[0030] The constant temperature water circulator 32 circulates water at a constant temperature (for example, room temperature ±0.01°C). Note that the liquid is not limited to water, and any liquid may be used as long as it does not corrode the pipes 31 and can release the heat of the heat exchanger 24 to the outside via the external constant temperature water circulator 32.

[0031] The temperature sensor 29 measures the temperature of the vacuum chamber 2 .

[0032] Next, the configuration and operation of FIG. 1 will be described in detail.

[0033] (1) The constant temperature water circulator 32 is a device that can maintain a temperature of about ±50°C from room temperature with an accuracy of about ±0.01°C. The piping inside the vacuum chamber 2 (such as the water-cooled pipe 31) is made of a material that can withstand oxygen plasma cleaning to prevent water leaks and clean the inside of the vacuum chamber 2, such as a very soft Teflon (registered trademark) composite-coated pipe that does not allow water vapor to pass through, which is used in endoscopes, etc. When cooling to below freezing, an organic solvent such as antifreeze or an ionic liquid with an extremely low vapor pressure may be used instead of water.

[0034] (2) A mask pallet 27 supported by multiple independent Z stages (push-up stages 22) is placed on the XYZ stage 21 to obtain horizontality and a desired WD (working area). A photomask 3 is fixed on the mask pallet 27 by a mask fixing device 28. This mask fixing device 28 also functions as an electrode for biasing the photomask 3. For example, if the photomask 3 is insulating (e.g., a quartz plate) but has a conductive pattern (e.g., a chrome film) inside, the conductive mask fixing device 28 has the function of bridging the external and internal chrome patterns to establish electrical continuity.

[0035] (3) A heat exchanger 24 is placed under the mask pallet 27. A flexible heat-conducting sheet 26 made of silicon rubber or indium containing fillers such as metal, CNT, or graphene is provided on the surface of the heat exchanger 24 to facilitate thermal coupling with the bottom surface of the mask pallet 27. The thermal conductivity is preferably about 5 to 10 W / M degrees. A material with a low vapor pressure that can withstand ultra-high vacuum and oxygen plasma used for cleaning is desirable.

[0036] (4) Because the photomask 3 is frequently replaced with a different photomask for each measurement, the heat exchanger 24 is connected ad hoc to the bottom surface of the mask pallet 27. To achieve this, a push-up stage 22 is provided to raise and lower the heat exchanger 24 in accordance with the timing of photomask 3 replacement. Specifically, it operates as follows: When the mask pallet 27 is not installed on the XYZ stage 21, the heat exchanger 24 on the push-up stage 22 is lowered. On the other hand, when the photomask 3 is fixed to the mask pallet 27 and installed on the XYZ stage 21, the push-up stage 22 rises and presses the heat exchanger 24 against the bottom surface of the mask pallet 27. This pressing ensures good thermal contact and high thermal conductivity.

[0037] (5) The heat generated in the photomask 3 as described above is dissipated to the outside via the heat exchanger 24 and the constant temperature water circulator 32, so that the photomask 3 is maintained at a desired temperature.

[0038] 2 shows an example of a photograph of the heat exchanger of the present invention, which shows an example of a photograph of the heat exchanger (heat exchange device) 24 of FIG.

[0039] In FIG. 2, a water-cooling pipe 31 is the water-cooling pipe of FIG. 1, and is for example a pipe through which water at a constant temperature flows.

[0040] The adhesive layer 27 corresponds to the heat conductive sheet 27 in FIG.

[0041] The heat exchange surface 241 is the heat exchange surface of the heat exchange device 24 and corresponds to the adhesive layer 27 shown in the figure.

[0042] The support fins 242 are used to hold (fix) the heat exchange device 24 .

[0043] Next, the operation of the configuration in FIG. 2 will be described.

[0044] (1) Figure 2 shows an example of a water-cooled heat exchanger 24. The water-cooled pipe 31 is made of copper or brass, which is non-magnetic and has high thermal conductivity. A copper or brass plate is attached to its surface to form the heat exchange surface 241.

[0045] (2) Because the heat exchange surface 241 is hard, if it is left as is, it will result in point contact, resulting in large thermal resistance between it and the mask pallet 27. A flexible heat conduction sheet 27 is provided on the heat exchange surface 241 to keep high thermal conductivity between the mask pallet 27, which is frequently replaced, and the heat exchanger 24. Support fins 242 provided on both sides of the heat exchanger 24 are mechanical components that connect to the push-up stage 22.

[0046] Fig. 3 shows an example of a photograph of the push-up stage of the present invention. Fig. 3 shows an example of a photograph of the push-up stage 22 of Fig. 1. The operation of the configuration of Fig. 3 will be described.

[0047] (1) Figure 3 shows an embodiment of the push-up stage 22. In the present invention, two piezoelectric actuators are used corresponding to the two support fins 242 provided on the heat exchanger 24.

[0048] (2) When the photomask 3 is being repaired or measured, the actuator is continuously turned on to push up the heat exchanger 24, which then comes into thermal contact with the mask pallet 27, maintaining the entire surface of the photomask 3 at a constant temperature. If an electromagnetic actuator were used instead of a piezo type, electromagnetic waves would be generated while power is applied, which would affect the electron beam. Therefore, it is desirable to use a piezo type actuator, which does not generate magnetic or electric fields. The stroke should be approximately 1 mm using an expansion mechanism.

[0049] (3) A strain gauge is built into the piezoelectric actuator, and the stroke amount can be measured using only this push-up stage 22. Generally, piezoelectric actuators have hysteresis, so the desired stroke cannot be obtained by simply applying a constant voltage. In this embodiment, the push-up stage 22 obtains the desired push-up amount by feedback-controlling the measured strain amount.

[0050] Fig. 4 shows an example of a photograph of the surface of the mask pallet of the present invention. Fig. 4 is an example of a photograph of the surface of the mask pallet 27 of Fig. 1, and it is clear that the heat conductive sheet 27 is attached to the entire surface (surface). The operation of the configuration of Fig. 4 will be described.

[0051] (1) In the present invention, in order to make the temperature distribution uniform over the entire surface (surface) of the mask pallet 27, the heat conductive sheet 27 is attached over the entire area where the photomask 3 is fixed.

[0052] (2) There are various types of thermally conductive sheets 27. For example, those using graphene sheets exhibit an ultra-high conductivity of 1000 W / M in the horizontal direction along the crystal axis of graphene, while exhibiting thermal conductivity of about 10 W / M in the vertical direction. This means that the thermal conductivity in the horizontal direction is 100 times higher than in the vertical direction, thereby reducing the heat distribution within the surface.

[0053] Fig. 5 shows a photographic example (part 1) of the backside of the mask pallet of the present invention. Fig. 5 is a photographic example of the backside of the mask pallet 27 of Fig. 1, and it is clear that a thermally conductive sheet (graphene sheet) 271 is attached to the entire surface. The configuration of Fig. 5 will be described.

[0054] (1) In the present invention, in order to make the temperature distribution on the entire surface (back surface) of the mask pallet 27 uniform, the heat conductive sheet 27 is attached to the entire surface (back surface) of the area where the photomask 3 is fixed.

[0055] (2) There are various types of thermally conductive sheets 27. For example, those using graphene sheets exhibit an ultra-high conductivity of 1000 W / M in the horizontal direction along the crystal axis of graphene, while exhibiting thermal conductivity of about 10 W / M in the vertical direction. This means that the thermal conductivity in the horizontal direction is 100 times higher than in the vertical direction, thereby reducing the heat distribution within the surface.

[0056] Figure 6 shows a photographic example (part 2) of the backside of the mask pallet of the present invention. In this Figure 6, a heat pipe is used to reduce the heat distribution occurring over the entire surface of the mask pallet 27. The configuration of Figure 6 will be explained.

[0057] (1) In the present invention, the heat pipes 273 are embedded in the mask pallet 27. Conventionally, the mask pallet 27 is made of materials such as non-magnetic stainless steel or titanium, but in the present invention, it may be made of copper or aluminum, which have higher heat transfer capabilities, or other highly thermally conductive materials.

[0058] (2) Heat pipe 273 is a copper or aluminum pipe with good thermal conductivity that has a jagged section called a wick (capillary structure) inside it, allowing capillary action to occur and trapping a small amount of liquid. This structure ensures that the inner wall of heat pipe 273 is always wet with liquid. There is an appropriate liquid depending on the temperature used. A liquid that can evaporate to a certain extent at the temperature used is selected. The optimal liquids for temperatures around room temperature ±30 degrees are water, acetone, or ethanol, and for high temperatures above 100 degrees, there are liquids such as naphthalene.

[0059] (3) Conventional heat conduction in ordinary metals is caused by electrons present in the metal. As is known from electrical resistance, electrons in metals frequently collide while moving through the metal, so their effective movement speed is very slow, and heat is not transferred as quickly as one might think.

[0060] (4) In contrast, Heat Pipe 273 is a technology named in 1963 that utilizes the high-speed movement of evaporating molecules such as water or alcohol inside the pipe. The liquid contained inside evaporates and becomes molecules even at near room temperature. As thermodynamics teaches, the vapor molecules move at a speed comparable to the speed of sound, which is determined by the temperature of the heat pipe, and fly around in all directions inside the heat pipe. Because these molecules have the ability to carry heat, the temperature inside the heat pipe becomes the same in an instant. This speed exceeds that of diamond, which has the highest thermal conductivity. This property is used to cool computer CPUs, etc.

[0061] (5) The temperature within the surface of the photomask 3 or mask pallet 27 can be made uniform by utilizing the property that the entire heat pipe tends to be at the same temperature. A vapor chamber with a structure closer to a flat surface can also be used, utilizing the same principle as a heat pipe. A vapor chamber can be used to create a superheat conductor with a thickness of less than 1 mm.

[0062] (6) In Fig. 6, several heat pipes are arranged symmetrically for ease of understanding, but the entire bottom surface of the mask pallet 27 may be filled with heat pipes 273, or one or more spirally wound heat pipes 273 may be arranged. Naturally, a vapor chamber may also be used.

[0063] 7 shows an example of a photograph of the temperature distribution on the surface of the photomask of the present invention. 7 shows an example of a photograph of the temperature distribution on the upper surface of the photomask 3 of FIG.

[0064] Figure 7(a) shows the temperature photograph distribution on the surface of the photomask without a heat pipe (the gray density in the center is high, indicating a high temperature), while Figure 7(a) shows the temperature photograph distribution on the surface of the photomask with a heat pipe (the gray density is the same in both the center and the periphery, indicating a uniform temperature).

[0065] As is clear from the photograph in Figure 7, when the heat pipe 273 in Figure 6 is not used (as in Figure 7(a)), if the heat exchanger 24 is placed in the center of the mask pallet to regulate the temperature, the temperature distribution becomes concentric, resulting in a temperature difference of 1 degree or more between the center and the periphery.

[0066] On the other hand, when heat pipes 273 are placed on the mask pallet 27 to achieve uniform heating (as in Figure 7(b)), the non-uniformity of the temperature distribution on the surface of the mask pallet is drastically reduced, making it possible to keep the temperature distribution on the surface of the photomask 3 within ±0.01°C. When the temperature control accuracy of the constant temperature water circulator 32 is ±0.01°C, the average temperature of the photomask 3 is the desired temperature ±0.01°C, and the temperature distribution on the surface is also kept within ±0.01°C. This also makes it possible to suppress drift in the position of the electron beam irradiation point due to thermal expansion of the photomask 3.

[0067] Fig. 8 shows a third example photograph of the rear surface of a mask pallet according to the present invention. Fig. 8 shows an example in which three heat exchanger contact points 276 are provided on the rear surface of a photomask pallet 27 instead of the heat conduction sheet (graphene sheet) 271 shown in Fig. 5.

[0068] 8, as is clear from the drawing, if sufficient uniformity of heat is achieved, similar results can be obtained regardless of where heat exchange takes place at the bottom of the mask pallet 27. For example, by providing heat exchanger 24 at the three Z-axis stages, which was disadvantageous in the past, and bringing it into contact with the mask pallet 27, the temperature of the photomask can be sufficiently controlled.

[0069] 9 shows an example (part 2) of a photograph of the temperature distribution on the surface of the photomask of the present invention. FIG. 9 shows an example of a photograph of the temperature distribution on the top surface of the photomask 3 of FIG.

[0070] Figure 9(a) shows the temperature photograph distribution on the photomask surface without a heat pipe (three areas with high gray density indicate high temperatures), while Figure 9(a) shows the temperature photograph distribution on the photomask surface with a heat pipe (three areas with the same gray density indicate uniform temperatures).

[0071] As is clear from the photograph in Figure 9, the temperature distribution around three points (without heat pipes) is higher at the heat exchanger contact point 276 in Figure 8. On the other hand, when a heat-equalizing pallet is used, the same temperature is obtained across the entire surface of the pallet (with heat pipes).

[0072] 10 shows a flowchart for explaining the operation of the present invention, which is a flowchart for explaining the operation of the entire device shown in FIGS.

[0073] 10, S1 sets the photomask. This involves transporting the photomask 3 fixed to the mask pallet 27 in FIG. 1 into the vacuum chamber 2 and setting it on the XYZ stage 21. At the same time as setting it, the heat exchanger 24 is pressed against the bottom surface of the photomask pallet 27 by the push-up stage 22.

[0074] S2 adjusts the temperature of the photomask by circulating cooling water precisely controlled to a constant temperature using an externally installed water-cooled constant temperature water circulator 32.

[0075] S3 measures the temperature of the photomask 3. The temperature of the photomask 3 may be measured by measuring the temperature of the circulating cooling water, or by using a thermometer installed on the photomask 3 or a non-contact infrared thermometer installed on the top plate or the like.

[0076] In step S4, it is determined whether the measured temperature is the specified temperature. If it is outside the specified temperature range (NO in step S4), the temperature is adjusted in step S2, and the temperature measurement is repeated in step S3. If it is within the specified temperature range (YES in step S4), it has been determined that the temperature is within the specified range, so in step S5 a reactive gas is sprayed, and in step S6 an electron beam is irradiated to correct the pattern on the photomask. Once the mask correction is complete, the push-up stage 22 of the heat exchanger 24 is lowered, and the heat exchanger 24 is removed from the bottom of the mask pallet 27. In this state, the mask pallet 27 is transported outside the vacuum chamber 2 by a transport device, and the mask pallet 27 with the photomask 3 attached is removed from a port.

[0077] As a result of the above, the temperature of the photomask 3 placed in the vacuum chamber 2 is adjusted to a constant value (within ±0.01°C of the specified temperature), the drift of the photomask 3 is reduced to the utmost, and it is now possible to correct the mask pattern with good reproducibility.

[0078] Instead of steps S5 and S6, an image of the pattern on the photomask 3 may be acquired and measured, or the measured value may be compared with a database to inspect whether the pattern is good or bad.

[0079] Next, an application example of the present invention will be described with reference to FIGS.

[0080] Figure 11 shows an example of the overall configuration of a mask repair device using the present invention. This figure shows an application example in which the temperature of the entire surface of the photomask 3 described in Figures 1 to 10 is adjusted with ultra-precision, ensuring stability in mask repair and minimizing drift. This will be explained below.

[0081] (1) A photomask repair system is a device that uses electron beam excitation reactions to perform deposition and etching on the surface of a photomask. It has an electron gun, which is required to irradiate an electron beam with the desired energy and current at the desired position and timing, a blanking device for turning the electron beam on and off, an objective lens for narrowing the electron beam and irradiating it on the photomask, an aberration correction device for correcting the characteristics of the objective lens at low energies to further narrow the electron beam, an electron detection device for detecting secondary electrons and reflected electrons, and an electron beam deflection device for two-dimensionally scanning the electron beam on the photomask. The detected electrons are imaged by a computer, allowing the repair results to be determined.

[0082] (2) The aberration corrector used in this invention is a special device that not only corrects normal spherical aberration but also allows for third-order or higher chromatic aberration correction, so that the electron beam size can be narrowed down to the nm order at low electron beam energies on the order of 100 electron volts. It is also capable of applying a bias voltage to the photomask to change the amount of secondary electrons emitted and the surface potential of the photomask as needed.

[0083] (3) An electron detector is very important for observing the target to be repaired and for confirming the etching or deposition endpoint. It is desirable to use a multi-channel ALD MCP that is resistant to reactive gases and contamination. Photomultiplier or MPPC type scintillator-type electron detectors can also be used.

[0084] (4) The end point of the process is determined using the intensity of secondary electrons or backscattered electrons or the output of a mass analyzer. The electron beam column is usually maintained at a vacuum of 10-7 Pa or higher. In addition, apertures and other components are heated to prevent contamination. While the use of corrosion-resistant materials is a natural consideration, the objective lens is equipped with a two-stage differential pumping aperture to prevent reaction gases from flowing into the electron beam column and contaminating it. A TMP installed separately nearby applies strong suction between the two-stage apertures to prevent corrosive reaction gases that may have entered the chamber from entering the column.

[0085] (5) As mentioned above, the apparatus used in this invention is equipped with a powerful differential pumping device at the tip of the objective lens. This device can also be used to create a low vacuum of 10 Pa or more in the chamber itself. Because the electron beam drifts when the sample surface is charged, oxygen or nitrogen gas can be introduced using a gas pipe separate from the reaction gas supply nozzle to achieve a low vacuum that prevents the sample surface from charging during electron beam irradiation. The apparatus is equipped with an electron beam column control device that controls the electron beam column and a high-voltage power supply that controls the electron gun. These are controlled from the PC that controls the entire apparatus.

[0086] (6) The electron beam is generated from an emitter such as a TFE, cold field emitter, or photocathode. The electron gun and column are also equipped with an ion pump to maintain an ultra-high vacuum of 10-7 Pa or higher, or an NEG pump to achieve an ultra-high vacuum. The system also includes an optical microscope for aligning the photomask to the appropriate coordinate system, an XYZ stage for determining the sample position relative to the electron beam irradiation position with nanometer accuracy, a precision sample position measurement device such as a laser interferometer or laser scale, and a photomask temperature control device (described below). The stage employs three independent actuators that adjust the height in the Z direction. Together with multiple height sensors mounted on the top plate, these operate to maintain the electron beam irradiation axis perpendicular to the photomask in real time. This ensures a constant electron beam incidence angle and working distance on the photomask surface. Conversely, they can be set to any angle as needed. This prevents rotation of the electron beam scanning direction and scan width fluctuations due to photomask height fluctuations. The flow of reaction gases can also be maintained constant.

[0087] (7) The system has a vacuum chamber made of low-thermal expansion materials such as pure iron, invar, or superinvar, capable of achieving a vacuum of 10-5 Pa or less so that the electron beam can reach the photomask. A dry pump or turbomolecular pump is used to maintain the desired vacuum level inside the chamber. A vacuum gauge is also provided to measure the chamber vacuum level. To prevent stage drift, the reflectors and bar mirrors that make up the laser interferometer, as well as the sample position control device where the mirrors are located, are made of ultra-low thermal expansion materials with a thermal expansion coefficient of 10 ppb or less. The laser interferometer system is differential. It also has an active vibration isolation system to prevent vibrations from the surrounding environment from being transmitted to the system, and a device that detects sample vibrations with a differential laser interferometer and feeds the results back to the electron beam deflector to stop the electron beam vibration.

[0088] (8) The clean room temperature is maintained at approximately 23°C ± 1°C, but to prevent large fluctuations in the temperature of the mask repair equipment chamber, several environmental temperature control devices with a control capability of ± 0.1°C or less are separately installed within the photomask repair equipment.

[0089] (9) To repair a photomask, it is necessary to accurately irradiate the target repair area with an electron beam to initiate a chemical reaction. The system has a gas supply nozzle system that can supply multiple types of reactive gases to the electron beam irradiation point and its surroundings at the required timing, flow rate, gas pressure, and temperature with high response speed. For example, xenon fluoride gas is used for etching. To prevent spontaneous etching, the system has a forced gas exhaust device that instantly removes unnecessary gas from the electron beam irradiation point at the same time as gas injection, and a deactivating gas supply device such as water vapor that instantly deactivates the reactive gas. These are automatically controlled by a PC.

[0090] (10) The temperature of the gas supplied to the photomask can be controlled individually by the temperature of the gas cylinder and the heater installed in the piping or nozzle. A thermometer is installed in the nozzle to control the temperature so that it is kept above the temperature at which the gas solidifies. The heater is equipped with special wiring and shielding to prevent it from emitting electromagnetic waves.

[0091] (11) When the chamber is under high vacuum, gas molecules are emitted in a straight line from the nozzle and adsorb onto the pattern to be repaired. The moment the gas molecules adsorb, they lose kinetic energy and reach a temperature almost equal to the surface temperature of the photomask. An electron beam collides with these adsorbed molecules, causing a chemical reaction. The amount of molecules adsorbed onto the photomask surface is determined by the surface temperature of the photomask. The optimal photomask temperature varies depending on the reaction. Generally, lowering the photomask temperature increases the adsorption rate of the reactive gas, thereby increasing the reaction rate. On the other hand, lowering the temperature too much can cause the gas to solidify on the photomask surface, resulting in problems such as deposits not reacting sufficiently. In the case of etching, it can also happen that the material that should be removed by etching does not evaporate and can not be removed.

[0092] (12) As described above, the photomask surface temperature affects the repair speed and quality, so as described below, the temperature is precisely controlled to within ±0.1°C of the desired temperature using circulating water or organic liquid cooled to a constant temperature. The photomask surface temperature can be measured directly with an infrared thermometer.

[0093] Fig. 12 shows an example of the configuration of a gas supply device of a mask repair device using the present invention. Fig. 12 shows a detailed configuration example of the parts related to gas supply, such as the gas supply device and gas flow rate control device shown in Fig. 11. This will be explained below.

[0094] (1) Photomask repair uses several types of reactive gases. Reactive gases are broadly divided into etching gases, deposition gases, and pressurized inert gases (carrier gases), and also include purge gases to quickly remove unnecessary reactive gases from the piping, vacuum chamber, and photomask surface.

[0095] (2) Etching gases include xenon difluoride, chlorine, or diketones used in ALE. Etching accelerators include oxygen, NO2, or water vapor. Deposition gases include deposition materials such as trimethylplatinum, tetrakisplatinum, ADDP, Cp2Cr, MeCp2Cr, EtCp2Cr, Cr(acac)3, Cr(TMHD)3, or commonly known organometallic compounds with five-membered rings that easily deposit pure metals, such as tantalum ethoxide, tungsten carbonyl, nickel carbonyl, and chromium carbonyl. Pure metal deposition accelerators include water vapor, oxygen, hydrogen, and ammonia. The gases listed here are examples. Purge gases include nitrogen, oxygen, and rare gases such as argon.

[0096] (3) The reaction gas generated in the gas supply system is maintained at the desired temperature by a mantle heater or other device. It passes through piping and is then controlled to an appropriate flow rate by a mass flow controller before being injected into the vacuum chamber through a non-magnetic nozzle made of stainless steel or titanium. The nozzle is equipped with a heater, thermometer, and other devices for adjusting the gas temperature. To increase the conductance of the gas supply system and improve the gas supply response speed, a nozzle capable of retaining the gas in a small chamber is used. Gas delivery components within the vacuum chamber are insulated by the chamber vacuum, so they are maintained at the temperature of the heater used to insulate the nearby gas piping. Of course, they can be heated if necessary. When the heated ALD valve is closed, a high vacuum is instantly created inside the nozzle. All gas accumulated in the nozzle is evacuated into the vacuum chamber, quickly creating a high vacuum inside the nozzle. This allows the piping and nozzle to maintain their initial state.

[0097] (4) Reactive gases are often solid or liquid at room temperature. For this reason, the material is placed in a small cylinder whose inner walls have been polished to a mirror finish using electrochemical composite polishing, and the cylinder is heated from the periphery to sublimate and gasify, after which it is introduced into a vacuum chamber for use. The gas supply system includes a heater and temperature control circuit to sublimate the solid source into a gas of the appropriate gas pressure, as well as a pressure sensor or mass flow meter to measure the supply pressure. The controlled temperature range is from room temperature to approximately 200°C, which is the temperature required for gasifying the solid, and it is desirable to control it with an accuracy of about 0.1°C.

[0098] (5) To prevent the material from solidifying midway through the piping leading to the vacuum chamber, a temperature gradient is set up in several stages so that the temperature rises toward the nozzle, and the piping, MFC, and ALD valve are maintained at an appropriate temperature of around 50°C to 200°C. The reaction gas is controlled to an appropriate flow rate by the cylinder temperature and mass flow, etc.

[0099] (6) Several types of reaction gases are used for each process, and each is supplied via multiple pipes. To simplify the system, for gases that do not interact and can be premixed, a mass flow meter is used to set a predetermined flow rate, and the gases are then mixed together through a gas mixer before being supplied. Conventional systems do not achieve uniform gas mixing by simply spraying gases toward the reaction site from multiple nozzles within the chamber. However, this method ensures good gas mixing and stabilizes process results. Furthermore, expensive materials can be introduced in small amounts through the nozzle, while less expensive gases can be introduced throughout the chamber through a low-vacuum port. The gas flow rate introduced through the low-vacuum port is automatically controlled using a mass flow controller or a pressure gauge installed within the chamber. When purifying metals, water vapor, oxygen, hydrogen, or ammonia are often used. Introducing these gases through the low-vacuum port allows for stable delivery of large quantities to the reaction site.

[0100] (7) On the other hand, in the case of gases that interact with each other, it is desirable to have independent gas supply systems for each gas. Each supply system has multiple independent control systems so that the flow rate, pressure, temperature, supply timing, etc. can be digitally controlled using software.

[0101] (8) To simplify maintenance, this equipment is divided into three systems: an etching gas system, a deposition gas system, and a support gas system. A high-speed ALD valve is located near the electron beam column, allowing the appropriate amount of gas to be introduced to the photomask surface in the chamber at the appropriate time. Support gases such as water vapor can also be mixed in midstream if necessary.

[0102] (9) A high-speed switching valve is also incorporated to turn on and off the gas injection onto the photomask surface in a short time of less than a millisecond. The valve can be a solenoid valve, a piezoelectric valve, or an electrostatic valve made with MEMS. The high-speed valve can be located near the electron beam column on the chamber top, or it can be incorporated into the nozzle tip to increase response speed.

[0103] (10) Since each gas material has a different sublimation temperature, each has a means to heat it to the appropriate temperature.

[0104] Figure 13 shows an example of a control screen for the gas supply system of the present invention. The control screen shown in Figure 13, installed on a control panel for integrated automatic control by a PLC, displays the gas cylinder temperature, gas flow rate, gas pipe temperature, the open / close status of each valve, nozzle temperature, and other parameters for controlling the amount of sublimation. Target values ​​and current values ​​are displayed alternately. Control parameter values ​​can be remotely controlled from a PC in accordance with an automatic repair sequence. The above data on the equipment operating status or during the process is all recorded as a log for maintenance purposes.

[0105] (11) Since gases tend to solidify easily, it is natural to heat the valve to prevent them from clogging the pipes, and a mechanism is provided to periodically flow inert gas heated above the sublimation temperature through the pipes to prevent the gas from solidifying. It also has a function to momentarily increase the gas flow rate sharply to flush out the reactive gas.

[0106] (12) Deposition reaction gases have a low vapor pressure of approximately 10 Pa at room temperature, so their supply pressure tends to be lower than that of nitrogen or oxygen, which are gases at room temperature. To compensate for this pressure, an inert gas such as nitrogen, argon, or helium can be used as a booster gas along with the reaction gas. These booster gases generate ions upon collision with the primary electron beam and also function as antistatic gases. The use of booster gas eliminates the need for a nozzle with a small hole like a syringe needle to obtain a locally high-pressure gas flow, as in the past. This allows the use of a gas inlet with a large diameter, thereby reducing the occurrence of problems due to gas solidification. Furthermore, the conductance of the gas supply nozzle can be increased, improving the supply response speed of the reaction gas.

[0107] (13) The carrier gas does not solidify when cooled, but the reactive gas solidifies when cooled. Therefore, by lowering the photomask temperature, the reactive gas accumulates preferentially on the photomask surface, accelerating the reaction.

[0108] (14) Each control device is connected to a control PC that controls the entire system via a local area network or the Internet for remote operation. The control PC is equipped with a status display to show the status of the mask repair device and multiple displays for observing the repaired parts.

[0109] (15) The observation display allows for in-situ observation of the repair process using secondary electrons generated during the process. It also has an observation means for checking the relative positions of the nozzle and sample. This can be achieved by placing a small camera module inside the vacuum chamber or through an observation window installed in the chamber. A fiberscope used in endoscopes can also be used. A pixel count of 5 million or more is desirable. In addition to visible light cameras, sensors using thermopiles or infrared cameras can also be used to measure and control the temperature of the reaction area in real time.

[0110] (16) A bias voltage can be applied to the photomask. In the case of an EUV mask, a conductive film for electrostatic chucking is provided on the back of the mask, so a voltage can be applied to that film. If there is no conductive film on the back of the mask, the metal part of the mask support mechanism on which the mask is mounted can be used as a bias electrode. If necessary, a needle-shaped electrode can be brought into contact with the metal film on the surface of the mask to establish electrical continuity.

[0111] (17) The bias voltage applied to the photomask changes the trajectory and quantity of secondary electrons emitted from the sample, making it one of the process parameters that affect the electron beam excitation process. The bias can be DC, AC, or high-frequency RF. These bias voltages are synchronized with electron beam control or gas control. For example, when a positive potential is applied to the photomask, the secondary electrons remain at the bottom of the pattern created on the photomask. This means that electron excitation reactions are more likely to occur at the bottom. On the other hand, when a negative potential is applied to the photomask, the generated secondary electrons scatter in all directions, causing reactions in places other than the bottom of the pattern. Since the two reactions occur at different locations, the shape at the end of the process differs. The property of changing the reaction location depending on the voltage applied to the photomask can also be used to control the sidewall shape.

[0112] Figure 14 shows the configuration of another embodiment of the present invention. In Figure 14, the temperature of the photomask 3 is set to a desired temperature in order to achieve a desired state of gas adsorption. This embodiment is characterized in that the reaction between the electron beam and the gas is carried out in a gas reservoir 42 that is surrounded on its periphery to prevent the gas from escaping to the surrounding area, in order to quickly bring the gas temperature into thermal equilibrium.

[0113] In the repair device of this example, the distance between the bottom of the objective lens and the photomask is only about 1 mm. Therefore, the reaction gas diffuses and floats in the space between the two lenses. This alone creates a certain amount of diffusion resistance (pressure loss), but the pressure loss is further increased by shielding.

[0114] In FIG. 14, a temperature adjusting device 41 adjusts the temperature of the photomask 3 to a predetermined temperature.

[0115] The gas reservoir 42 allows the gas injected from the gas inlet pipe 45 to remain inside the gas reservoir surrounded by the gas blocking plate 43 .

[0116] The gas shielding plate 43 is for blocking the release of the reaction gas accumulated in the gas reservoir chamber 42 into the chamber. It may be ring-shaped or may have a gap in the middle.

[0117] The reactive gas / carrier gas 44 is a supply source that supplies reactive gas and carrier gas.

[0118] The gas introduction pipe 45 introduces the reaction gas / carrier gas into the gas reservoir chamber .

[0119] The objective lens is used to narrow the electron beam and irradiate it onto the photomask 3 , and also to perform planar scanning using a scanning deflection system (not shown) to generate an enlarged image on the photomask 3 .

[0120] The low vacuum gas inlet 46 is a source for introducing gas for low vacuum.

[0121] Next, the configuration of FIG. 14 will be described.

[0122] (1) In Figure 14, reactive gas 44 is expensive, costing as much as 10,000 yen per gram, and there is a desire to minimize its usage in order to reduce the running costs of the equipment. Since frequent gas cylinder replacement increases equipment downtime and reduces cost performance, there is also a desire to reduce the frequency of gas cylinder replacement.

[0123] (2) For example, the repair area typically performed with one photomask 3 is no more than a few square microns. Even if a chromium film with a thickness of 1 micron is deposited on an area of ​​a few square microns, its weight is on the order of picograms.

[0124] (3) The amount of chromium contained in 1 cc of organic chromium gas is on the order of milligrams, which is an astronomically large value compared to the ideal amount of material required to repair one photomask 3.

[0125] (4) Conventional repair equipment performs repairs while continuously flowing gas at a flow rate of the order of 1 sccm. In other words, in conventional repair equipment, it is highly likely that most of the introduced reactive gas is not utilized but is instead released into the vacuum chamber and exhausted. This embodiment discloses a method for reducing this significant waste to the utmost. This will be explained in detail using Figure 15.

[0126] 15 is a flowchart for explaining the configuration of another embodiment of the present invention, which is a flowchart for explaining the operation of the configuration of FIG.

[0127] In Figure 15, S11 closes the gas reservoir. This closes the gas reservoir chamber 42 in Figure 14 described above. To do this, the photomask 3 is moved on the XYZ stage so that the electron beam is irradiated at the desired position, and then raised toward the top plate in the Z direction to contact the gas shielding plate 43 located around the electron beam irradiation point. When the mask is not being corrected, there is a gap of about 1 mm between the gas shielding plate 43 and the photomask 3, allowing the photomask 3 to move freely. During correction, the photomask 3 is pushed up to eliminate this gap. To prevent scratches caused by contact with the gas shielding plate 43, a chemically inert and flexible material is used for the gas shielding plate 43. For example, Teflon sponge, which is softer than glass, can be used. When the Teflon sponge is brought into contact with the surface of the photomask 3, the area around the electron beam irradiation point is surrounded by the Teflon sponge, creating a gas reservoir. The smaller the volume of the gas reservoir, the less gas consumption there is.

[0128] By bringing the photomask into contact with the material that constitutes the top plate in this way, it becomes possible to absorb the energy caused by resonance of the stage, and this also produces the secondary effect of preventing vibration and drift of the photomask.

[0129] In step S12, gas is introduced. This is done by introducing gas into the gas reservoir 42 through the gas inlet pipe 45 shown in Figure 14 (because the gas reservoir is under vacuum, gas is automatically drawn in from the outside). The gas required for repair is introduced into the gas reservoir 42. For etching, xenon fluoride can be used, and for deposition, organometallic materials such as trimethyl platinum, MeCp2Cr, or chromium carbonyl can be used. By using the gas reservoir 42, the introduced reactive gas does not escape into the vacuum chamber outside the gas reservoir 42, thereby achieving extremely low reactive gas consumption.

[0130] However, because the amount of reactant gas introduced is small, it is difficult to prevent charging using only the reactant gas. Therefore, it is desirable to simultaneously introduce a large amount of inexpensive gases into the gas reservoir chamber 42 to create a low vacuum inside the chamber 42 to prevent charging, which can cause electron beam drift (the electron beam collides with the gas, generating positive and negative ions, which neutralize the charge and prevent charging). Therefore, a low vacuum of several to several tens of Pa can be achieved inside the gas reservoir by simultaneously flowing a carrier gas such as oxygen, nitrogen, or argon or an inert dilution gas along with the reactant gas. To facilitate the creation of a low vacuum, the vacuum chamber itself can also be filled with nitrogen, oxygen, or an inert gas such as argon or helium to create a low vacuum. A low vacuum around the gas reservoir can further reduce the amount of reactant gas leaking from the gas reservoir into the chamber.

[0131] In step S13, the mask temperature is adjusted to adsorb the gas. This is done by using temperature control device 52 to create a state of thermal equilibrium between photomask 4 and the reactive gas present in the space of gas reservoir chamber 42, so that a desired amount of reactive gas is stably adsorbed onto the photomask surface. If the photomask temperature is high, the amount of gas adsorption is small, and if the photomask temperature is low, the amount of gas adsorption is large.

[0132] In step S14, an electron beam reaction is performed. This is performed by irradiating the surface of the photomask 3 with the gas adsorbed thereon with an electron beam. The reaction is deposition or etching depending on the adsorbed gas.

[0133] In step S15, the gas reservoir chamber is opened. Since the reaction has ended, in order to bring the surface of the photomask 3 into a neutral state, the photomask 3 is lowered to create a gap between the gas shielding plate 43 and the surface of the photomask 3, and the gas accumulated in the gas reservoir chamber 42 is released, completing the process. At this time, a cleaning gas or the like may be introduced to clean the surface of the photomask 3.

[0134] By following the above steps, it is possible to establish thermal equilibrium early and to minimize the amount of gas required to modify the pattern on the photomask 3. Furthermore, if an electron-transparent film with a thickness on the order of nanometers, such as graphene or silicon nitride film, is provided instead of the differential aperture, the amount of reaction gas sucked out from the differential pumping mechanism will be zero, making it possible to further reduce gas consumption. If it is completely closed, it will be difficult to introduce the reaction gas itself, so it is desirable to allow a moderate amount of leakage.

[0135] In the examples, an example of blocking the reaction gas is shown, but it is sufficient to prevent the gas from escaping from the gas reservoir into the chamber. Therefore, by using a spacer that narrows the gap as much as possible between the gas supply nozzle or the bottom surface of the objective lens and the photomask, a large pressure loss can be created, and it is also possible to prevent the expensive reaction gas from escaping into the chamber. [Brief explanation of the drawings]

[0136] [Figure 1] FIG. 1 is a configuration diagram of an embodiment of the present invention. [Figure 2] 1 is a photographic example of a heat exchanger according to the present invention. [Figure 3] 1 is a photographic example of a push-up stage according to the present invention. [Figure 4] 1 is a photographic example of the surface of a mask pallet according to the present invention. [Figure 5] 1 is a photograph (part 1) of the backside of the mask pallet of the present invention. [Figure 6] 10 is a photograph (part 2) of the backside of the mask pallet of the present invention. [Figure 7]1 is a photograph showing an example of the temperature distribution on the surface of a photomask of the present invention. [Figure 8] 10 is a photograph (part 3) of the backside of the mask pallet of the present invention. [Figure 9] 2 is a photographic example (part 2) of the temperature distribution on the surface of the photomask of the present invention. [Figure 10] 1 is a flowchart illustrating the operation of the present invention. [Figure 11] 1 is a diagram showing an example of the overall configuration of a mask repair apparatus using the present invention; [Figure 12] 1 shows an example of the configuration of a gas supply device of a mask repair device using the present invention. [Figure 13] 10 is an example of a control screen for the gas supply system of the present invention. [Figure 14] FIG. 10 is a diagram illustrating the configuration of another embodiment of the present invention. [Figure 15] 10 is a flowchart illustrating the configuration of another embodiment of the present invention. [Explanation of symbols]

[0137] 1: Electron beam 2: Vacuum chamber 20:Fixed stand 21:XYZ Stage 22: Push-up stage 23:Support 24: Heat exchange device (heat exchanger) 241: Heat exchange surface 242: Support fin 25:Support 26: Thermal conductive sheet 27: Mask Palette 271: Graphene sheet 272: Ultra-high heat transfer material 273, 275: Heat pipe 276: Heat exchanger contact point 28: Mask fixing device 29:Temperature sensor 3: Photomask 31: Water cooling pipe 32: Constant temperature water circulation device 41: Temperature control device 42: Gas chamber 43: Gas shielding plate 44: Reactant gas / carrier gas 45: Gas inlet pipe 46: Low vacuum gas introduction

Claims

1. In an electron beam device that irradiates an electron beam to perform measurement, inspection, or correction, an electron beam irradiation system for generating an electron beam; The electron beam generated by the electron beam irradiation system is narrowed and irradiated onto a photomask, and an objective lens is then a scanning system that scans the electron beam irradiated onto the photomask in a plane; a heat exchanger that is fixed to the surface of the photomask opposite to the electron beam irradiation side or that is detachable from the surface and maintains the temperature at a predetermined level; Equipped with The electron beam device is characterized in that the temperature of the photomask is precisely maintained at a predetermined temperature to reduce drift.

2. 2. The electron beam apparatus according to claim 1, wherein the heat exchanger is provided with a push-up stage on the opposite surface of the photomask for pushing up and fixing the photomask.

3. 3. The electron beam apparatus according to claim 1, wherein said heat exchanger circulates a liquid at a predetermined temperature.

4. 4. The electron beam apparatus according to claim 1, wherein the heat exchanger has a heat pipe attached along the opposite surface of the photomask.

5. 5. An electron beam inspection apparatus according to claim 4, wherein the temperature range within the surface of the heat exchanger is set to ±0.1°C.

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