JP2008064694A - Interference measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve processing cycle time for measurement by suppressing temperature deterioration of an object to be measured due to adiabatic expansion of air generated when decompressing a vacuum chamber. <P>SOLUTION: An interference measuring instrument is provided with flow passages 110 and 111 for fluidizing temperature regulation water on stages 105 and 106 mounting the object to be measured W<SB>1</SB>and a TS lens 107 in the vacuum chamber 113. The interference measuring instrument supplies the temperature regulation water to the flow passages 110 and 111 by a process for decompressing the vacuum chamber 113 with a vacuum pump 117, and suppresses the temperature deterioration of the object to be measured W<SB>1</SB>and the TS lens 107 by controlling the temperature of the stages 105 and 106. Therefore measurement is enabled at high processing cycle time in highly accurate measurement in a decompression state. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an interference measurement apparatus for measuring the surface shape of optical components such as a reduction projection optical lens and a mirror for a semiconductor exposure apparatus and the wavefront aberration of an optical system with high accuracy.

It is common to use an interferometer as a highly accurate spherical lens and mirror shape measuring method. In recent years, the wavelength of the exposure light source has been shortened to KrF excimer laser (λ = 248 nm), ArF excimer laser (λ = 193 nm), and F ₂ laser (λ = 157 nm) along with miniaturization and higher precision of the semiconductor exposure apparatus. . Furthermore, EUV light (Extreme Ultra Violet: λ = 13.6 nm) has also been used as an exposure light source. The projection optical lens and mirror for these exposure apparatuses are required to have a shape accuracy of 1 to 0.1 nm. In order to perform such highly accurate measurement, control of the measurement environment is important. In particular, in order to perform highly accurate measurement, it is necessary to eliminate air fluctuations. Therefore, it is necessary to measure the object to be measured in a vacuum (reduced pressure) environment.

  However, when the object to be measured is brought into a vacuum (decompressed) environment, the surface temperature of the object to be measured is lowered due to a temperature drop due to adiabatic expansion of air, causing thermal deformation. Therefore, it is usually necessary to measure with sufficient temperature leveling time after making a vacuum (depressurized) environment. The higher the required measurement accuracy, the more this temperature break-in time is required, and more than one day is required at the EUV level.

  For example, a configuration shown in FIG. 4 is known in order to avoid surface deformation due to a temperature drop of an object to be measured due to adiabatic expansion of air during decompression and to improve measurement tact. This has a stocker 1012 in which a plurality of objects to be measured 1008 can be placed in a vacuum chamber 1017 that houses the interference measurement optical system. The interference measurement optical system includes a laser light source 1001, a beam expander 1002, a polarization beam splitter 1003, a reference plane mirror 1005, a vacuum chamber 1007, and a condenser lens 1010. Reference numeral 1008 denotes an object to be measured. The object to be measured 1008 is placed in a reduced pressure environment using the sub-chamber 1018 and the gate valves 1020a and 1020b in advance, and the temperature break-in can be completed while waiting for the order of measurement on the stocker 1012 (see Patent Document 1).

  However, it is necessary to store a certain number of objects to be measured in the vacuum chamber in order to ensure a sufficient temperature adjustment time and increase the measurement tact time. In addition, since the work is performed in a vacuum chamber, it is also necessary to have a mechanism for automatically changing the object to be measured. Therefore, there is an unsolved problem that the size of the vacuum chamber is necessarily increased.

  As other methods for suppressing the influence of air fluctuations, there are known a method of replacing with a He gas whose refractive index is about 1/10 that of air, and a method of bringing the reference surface close to the object to be measured. However, the former requires He filling for each measurement and is costly, and it takes time to fill the measurement space with He, and the latter brings the reference surface very close to each other. Risk of contact. In spherical surface measurement, it is necessary to prepare a reference surface having substantially the same curvature for each curvature of the object to be measured.

Therefore, in general, it is advantageous for high-accuracy measurement to perform measurement in a vacuum (decompression) environment.
Japanese Patent No. 3466707

  In a conventional interference measuring apparatus using a vacuum chamber, the measurement tact becomes very bad because it takes a very long time for the temperature of the object to be measured to stabilize after the object to be measured is in a vacuum (depressurized) environment. . In particular, when performing highly accurate measurement, it is necessary to acclimate the temperature of the object to be measured for a long time.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and suppresses the temperature decrease of the object to be measured due to adiabatic expansion, and improves the measurement tact without increasing the size of the apparatus. It is an object of the present invention to provide an interference measurement apparatus that can perform the above.

  The interference measurement apparatus of the present invention includes a vacuum chamber, an interference optical system for measuring the shape of the object to be measured in the vacuum chamber, and the temperature of the object to be measured by adiabatic expansion of air when the vacuum chamber is depressurized. And a temperature control means for suppressing the decrease.

  By detecting and actively suppressing the temperature drop of the object to be measured during decompression, the temperature break-in time can be shortened and the measurement tact can be improved.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 shows an interference measuring apparatus using a Fizeau interferometer according to the first embodiment, but an interferometer other than a Fizeau type may be used. This interference measuring apparatus has an interferometer body 101 incorporating a laser light source, an interference fringe image acquisition CCD camera, and the like, a beam expander 102 for enlarging the measurement light diameter, and a bending mirror 103 for bending the laser light by 90 degrees. Furthermore, a vacuum window 104 that separates the decompressed environment from the atmosphere, stages 105 and 106 that can perform x, y, z, x tilt, and y tilt, and a TS lens 107 that has a reference spherical surface and converts a transmitted wavefront into a spherical wave are provided. .

Further, a PC 108 for calculating the shape of the object W ₁ on the stage 105 from the acquired interference fringes, and flow paths (piping means) 110 and 111 for temperature adjustment water for adjusting the temperature of the stages 105 and 106 or the holder, Have. The flow paths 110 and 111 are connected to a temperature controller 112 including a chiller for controlling the temperature of temperature-controlled water. A vacuum chamber 113 which incorporates a DUT W ₁ and TS lens 107, a vacuum controller 114 for controlling the pressure in the chamber, the leak valve 115, exhaust valve 116, vacuum pump 117, pressure gauge 118 is connected .

  Laser light emitted from the interferometer main body 101 is widened by a beam expander 102 and bent upward by 90 degrees by a bending mirror 103. Thereafter, the laser light passes through the vacuum window 104 and enters the TS lens 107. In the TS lens 107, a part of the laser beam is reflected on the reference surface in the TS lens 107, and returns to the interferometer body 101 through the same optical path.

The laser light that has passed through the TS lens 107 on the stage 106 is converted into a spherical wave, reflected by the object to be measured W ₁ , and returns to the interferometer body 101 through the same optical path. In the interferometer body 101, the reflected light from the TS lens 107 interferes with the reflected light from the object to be measured W ₁ to form an interference fringe. This interference fringe is acquired by a CCD camera, and the object to be measured W ₁ is obtained by the PC. The shape of is calculated.

After the object to be measured W ₁ is placed in the vacuum chamber 113, the vacuum chamber 113 is evacuated (reduced pressure) by the vacuum pump 117. During this exhausting operation, the air in the vacuum chamber 113 is adiabatically expanded, the temperature in the vacuum chamber 113 is lowered, and the surface temperatures of the object to be measured W ₁ and the TS lens 107 are lowered.

  Normally, in high-accuracy measurement, this temperature drop is restored and left as a temperature break-in until the temperature distribution disappears.However, because of the vacuum environment, there is no heat transfer by air, and the time for the temperature break-in is Longer than the case.

  After reaching the specified pressure, the vacuum controller 114 controls the vacuum pump 117, the leak valve 115, and the exhaust valve 116 so that the specified pressure is reached.

In this embodiment, the temperature break-in time is shortened by flowing the temperature-controlled water through the stage 105, 106 or the holder directly in contact with the object to be measured W ₁ and the TS lens 107. Specifically, when the vacuum chamber 113 is evacuated, the temperature of the object to be measured W ₁ and the TS lens 107 becomes a specified temperature by using the detection value of the object to be measured W ₁ and the temperature sensor 119 attached to the TS lens 107. Thus, the temperature controller 112 controls the temperature of the temperature-controlled water.

As a result, the temperature of the object to be measured W ₁ and the TS lens 107 can be kept constant even during exhaust, and the temperature break-in time after exhaust can be greatly reduced. Furthermore, after the pressure in the vacuum chamber 113 reaches a specified pressure, the temperature controller 112 controls the temperature of the temperature-controlled water so as to maintain a constant temperature, and the measurement is performed in an environment where the temperature is stable. Can do.

By suppressing the temperature drop of the object to be measured W ₁ and the TS lens 107 in the exhaust of the vacuum chamber 113, the temperature break-in time can be shortened, and the measurement tact can be improved despite high-precision measurement.

  FIG. 2 shows an interference measuring apparatus according to the second embodiment. This interference measuring apparatus has an interferometer body 101 incorporating a laser light source, an interference fringe image acquisition CCD camera, and the like, a beam expander 102 for enlarging the measurement light diameter, and a bending mirror 103 for bending the laser light by 90 degrees. Furthermore, a vacuum window 104 that separates the decompressed environment from the atmosphere, stages 105 and 106 that can perform x, y, z, x tilt, and y tilt, and a TS lens 107 that has a reference spherical surface and converts a transmitted wavefront into a spherical wave are provided. .

Further, the PC 108 for calculating the shape of the object to be measured W ₂ on the stage 105 from the acquired interference fringes, and the heat radiating plate 210 which is a heat radiating member disposed in the vicinity of the object to be measured W ₂ and the TS lens 107, respectively. 211 and a temperature controller 212 for controlling these temperatures. The vacuum chamber 113 is connected to a vacuum controller 114 for controlling the pressure in the chamber, a leak valve 115, an exhaust valve 116, a vacuum pump 117, and a pressure gauge 118.

Laser light emitted from the interferometer main body 101 is widened by a beam expander 102 and bent upward by 90 degrees by a bending mirror 103. Thereafter, the laser light passes through the vacuum window 104 and enters the TS lens 107. In the TS lens 107, a part of the laser beam is reflected on the reference surface in the TS lens 107, and returns to the interferometer body 101 through the same optical path. The laser light transmitted through the TS lens 107 on the stage 106 is converted into a spherical wave, reflected by the object to be measured W ₂ , and returns to the interferometer body 101 through the same optical path. In the interferometer main body 101, the reflected light from the TS lens 107 interferes with the reflected light from the object to be measured W ₂ to form an interference fringe. The interference fringe is acquired by a CCD camera, and the object to be measured W ₂ is obtained by the PC. The shape of is calculated.

After the object to be measured W ₂ is placed in the vacuum chamber 113, the vacuum chamber 113 is evacuated (reduced pressure) by the vacuum pump 117. During this exhausting operation, the air in the vacuum chamber 113 adiabatically expands, the temperature in the vacuum chamber 113 decreases, and the surface temperature of the object to be measured W ₂ and the TS lens 107 decreases.

  Normally, in high-accuracy measurement, this temperature drop is restored and left as a temperature break-in until the temperature distribution disappears.However, because of the vacuum environment, there is no heat transfer by air, and the time for the temperature break-in is Longer than the case.

  After reaching the specified pressure, the vacuum controller 114 controls the vacuum pump 117, the leak valve 115, and the exhaust valve 116 so that the specified pressure is reached.

In this embodiment, placing the heat radiating plate 210, 211 in the vicinity of the object W _2, TS lens 107, deprived from the measurement object W ₂ and TS lens 107 surface by a temperature drop caused by the adiabatic expansion of the air during decompression Heat is supplied to the heat sinks 210 and 211. As a result, the break-in time can be shortened. Specifically, after exhausting and after exhausting, the temperature sensor 119 measures the temperature in the vacuum chamber 113 and heats the radiator plates 210 and 211 so that the temperature of the air in the vacuum chamber 113 becomes a specified temperature.

The temperature sensor 119 may directly measure the temperature of the object to be measured W ₂ and the surface of the TS lens 107 instead of the temperature of the air in the vacuum chamber 113. Also in this case, the temperatures of the heat sinks 210 and 211 are controlled so that the temperatures of the object to be measured W ₂ and the TS lens 107 become the prescribed values.

When the temperature change of the object W ₂ to be measured and the TS lens 107 with respect to the exhaust speed is estimated in advance from experiments or calculations, the temperature is further controlled by controlling the temperature of the heat radiation plates 210 and 211 according to the exhaust speed. The break-in time can be shortened. In this way, by actively suppressing the temperature drop of the workpiece W ₂ and the TS lens 107, it becomes possible to shorten the time required for the temperature habituation and improve the measurement tact despite the high-precision measurement. It can be performed.

  FIG. 3 shows an interference measuring apparatus according to the third embodiment. This interference measuring apparatus has an interferometer body 101 incorporating a laser light source, an interference fringe image acquisition CCD camera, and the like, a beam expander 102 for enlarging the measurement light diameter, and a bending mirror 103 for bending the laser light by 90 degrees. In addition, a vacuum window 104 that separates the decompressed environment from the atmosphere, stages 105 and 106 that can perform x, y, z, x tilt, and y tilt, and a TS lens 107 that has a reference spherical surface and converts a transmitted wavefront into a spherical wave are provided. .

Furthermore, a PC 108 for calculating the shape of the workpiece W ₃ on the stage 105 from the acquired interference fringes is provided. The vacuum chamber 113 includes a vacuum controller 114 for controlling the pressure in the chamber, a leak valve 115, an exhaust valve 116, a vacuum pump 117, a pressure gauge 118, and temperature control for controlling the temperature of air (gas) to be leaked. A device 312 is connected.

Laser light emitted from the interferometer main body 101 is widened by a beam expander 102 and bent upward by 90 degrees by a bending mirror 103. Thereafter, the laser light passes through the vacuum window 104 and enters the TS lens 107. In the TS lens 107, a part of the laser beam is reflected on the reference surface in the TS lens 107, and returns to the interferometer body 101 through the same optical path. The laser beam that has passed through the TS lens 107 on the stage 106 is converted into a spherical wave, reflected by the object to be measured W ₃ , and returns to the interferometer body 101 through the same optical path. In interferometer 101 within create an interference pattern to interfere the reflected light from the reflection light and the object to be measured W ₃ from the TS lens 107 to acquire the interference fringe by the CCD camera, the measured object W ₃ by PC108 The shape of is calculated.

After the object to be measured W ₃ is placed in the vacuum chamber 113, the inside of the vacuum chamber 113 is evacuated (depressurized) by the vacuum pump 117. During the exhaust operation, the air in the vacuum chamber 113 is adiabatically expanded, the temperature in the vacuum chamber 113 is lowered, and the surface temperatures of the object to be measured W ₃ and the TS lens 107 are lowered.

  Normally, in high-accuracy measurement, this temperature drop is restored and left as a temperature break-in until the temperature distribution disappears.However, because of the vacuum environment, there is no heat transfer by air, and the time for the temperature break-in is Longer than the case.

  After reaching the specified pressure, the vacuum controller 114 controls the vacuum pump 117, the leak valve 115, and the exhaust valve 116 so that the specified pressure is reached.

In this embodiment, the temperature break-in time is shortened by controlling the temperature of the air supplied from the leak valve 115 during vacuum control. Specifically, after the inside of the vacuum chamber 113 reaches a prescribed pressure, the exhaust flow rate is made constant by the exhaust valve 116, and the flow rate of the sucked air is controlled by controlling the leak valve 115. Maintain the pressure. When the vacuum chamber 113 is evacuated, a temperature drop occurs due to adiabatic expansion of the air. Air that has been raised in temperature by the temperature controller 312 is supplied from the leak valve 115 into the vacuum chamber 113 by an amount necessary to compensate for this temperature drop. . As a result, the temperature drop of the object to be measured W ₃ and the TS lens 107 can be suppressed, and the temperature break-in time can be shortened.

Further, the temperature drop of the object to be measured W ₃ and the TS lens 107 may be suppressed by reducing the pressure while supplying air whose temperature has been increased from the leak valve 115 during the exhaust operation. Even if the time required for decompression is somewhat longer, the break-in time can be significantly shortened, so that the time from the decompression to the start of measurement can be shortened as a whole. Thus actively it becomes possible to reduce the time required to break temperature by suppressing the temperature drop of the measured object W ₃ and TS lens 107, improvement in measurement tact despite accurate measurements It can be carried out.

1 is a schematic diagram illustrating Example 1. FIG. 6 is a schematic diagram showing Example 2. FIG. 6 is a schematic diagram showing Example 3. FIG. It is a schematic diagram which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Interferometer body 102 Beam expander 103 Bending mirror 104 Vacuum window 105, 106 Stage 107 TS lens 110, 111 Flow path 112, 212, 312 Temperature controller 113 Vacuum chamber 115 Leak valve 116 Exhaust valve 117 Vacuum pump 118 Pressure gauge 119 Temperature Sensors 210 and 211 Radiation plate 1001 Laser light source 1002 Beam expander 1003 Polarizing beam splitter 1005 Reference plane mirror 1007 Vacuum chamber 1008 Object to be measured 1010 Condensing lens 1012 Stocker 1018 Subchamber 1010a, 1020b for exchanging workpieces

Claims (4)

  A vacuum chamber, an interference optical system for measuring the shape of the object to be measured in the vacuum chamber, and a temperature control for suppressing a temperature drop of the object to be measured due to adiabatic expansion of air when the vacuum chamber is depressurized. And an interference measuring apparatus.   2. The interference according to claim 1, wherein the temperature control means includes piping means for supplying temperature control water for supplementing the amount of heat taken from the measurement object by adiabatic expansion to the vicinity of the measurement object. Measuring device.   The temperature control means includes a heat radiating member disposed in the vicinity of the object to be measured, and the heat radiating member has an amount of heat necessary to supplement the heat amount taken from the object to be measured by adiabatic expansion. The interference measurement apparatus according to claim 1, wherein the interference measurement apparatus is supplied.   The temperature control means has a mechanism for supplying a gas whose temperature has been increased by an amount necessary for supplying the amount of heat deprived by adiabatic expansion during decompression into the vacuum chamber. The interference measurement apparatus described.

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