JP2008016324A - Electron beam device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electron beam device capable of adjusting an introducing amount of ozone into a chamber according to material quality of a sample and capable of irradiating a stable electron beam. <P>SOLUTION: The electron beam device to irradiate the electron beam generated from an electron gun onto the sample placed on a stage has an ozone gas introducing means to introduce ozone gas into the chamber in which the electron gun and a stage are housed, and a control means of making the ozone gas introducing means to introduce either ozone-containing gas or oxygen into the chamber according to the material quality of the sample, and of making a gas amount of the ozone-containing gas or oxygen in the chamber constant regardless of the material quality of the sample. The ozone gas introducing means may have an oxygen supply means, an ozone gas forming means to form the ozone containing gas in which the ozone gas and oxygen are constituted to have a prescribed ratio, and may have a gas introducing amount adjusting means to adjust the gas amount introduced into the chamber. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electron beam apparatus, and more particularly to an electron beam apparatus in which ozone is introduced into the apparatus in order to prevent contamination in the apparatus.

  In the manufacturing process of a semiconductor element, observation of a sample with an electron beam apparatus such as an electron microscope and measurement of a line width of a pattern are performed. In the observation and measurement of a sample using an electron beam device, scanning is performed while irradiating the observation portion with an electron beam, and the amount of electrons such as secondary electrons is converted into luminance and displayed on the display device as an image.

  When such an electron beam apparatus is used, a phenomenon occurs in which the optical axis alignment of the electron beam changes with the passage of time, and the measured value of the line width becomes unstable. Such an optical axis alignment shift of the electron beam is considered to occur as follows.

The vacuumed electron beam device contains hydrocarbon (C _x H _x ), and the carbon component of this hydrocarbon adheres to the surface of the component near the electron beam optical axis in the electron column, Contamination is formed. When charges accumulate in this contamination, an electric field is generated due to the difference in the amount of accumulated charges, and the electron beam is deflected by this electric field. As a result, the optical axis alignment of the electron beam varies.

  Various methods for reducing the occurrence of contamination in the electron beam apparatus have been proposed for such problems.

As a technique related to this, Patent Document 1 discloses a method of cleaning the inside of a chamber with ozone in an electron beam exposure apparatus.
JP 09-259811 A

  In the above-described method for preventing the occurrence of contamination in the chamber, the generation of contamination is prevented by injecting ozone into the chamber while operating the apparatus. That is, the ozone in the chamber collides with the electron beam to separate the ozone into oxygen and active oxygen. And it reacts with the contamination which is going to adhere to the surface of each component in a sample or an apparatus with the separated active oxygen, and is evaporated as carbon monoxide gas.

  However, for example, in a sample in which a resist pattern is formed, since the resist pattern changes due to ozone, there is a disadvantage that the length measurement value of the pattern becomes unstable.

  On the other hand, when the sample is affected by ozone gas like a resist, the introduction of ozone gas into the chamber is stopped.

  However, it was confirmed that when the introduction of ozone gas was stopped, the beam current value of the irradiated electron beam changed and it took time to stabilize. When the beam current changes in this way, the amount of secondary electrons generated from the sample changes accordingly, which causes the inconvenience that the length measurement value measured based on the amount of secondary electrons becomes unstable. Further, in order to perform the length measurement stably, it is necessary to wait until the beam current is stabilized, and the throughput of the length measurement process is reduced.

  The present invention has been made in view of the problems of the prior art. An electron beam apparatus capable of adjusting the amount of ozone introduced into the chamber according to the material of the sample and irradiating a stable electron beam is provided. The purpose is to provide.

  In the electron beam apparatus that irradiates a sample placed on a stage with an electron beam generated from an electron gun, the above-described problem is an ozone gas introduction unit that introduces ozone gas into a chamber in which the electron gun and the stage are housed. The ozone gas introducing means introduces either ozone-containing gas or oxygen into the chamber according to the material of the sample, and the amount of ozone-containing gas or oxygen in the chamber is constant regardless of the material of the sample. This is solved by an electron beam apparatus characterized by having a control means.

  In the electron beam apparatus according to the above aspect, the ozone gas introduction unit includes an oxygen supply unit, an ozone gas generation unit that generates an ozone-containing gas composed of ozone gas and oxygen at a predetermined ratio, and an amount of gas introduced into the chamber. It is also possible to have a gas introduction amount adjusting means for adjusting the gas.

  Further, in the electron beam apparatus according to the above aspect, the control means causes the ozone gas generation means to generate ozone gas from oxygen supplied by the oxygen supply means, and the gas introduction amount adjustment means includes the ozone gas and oxygen. The amount of ozone-containing gas may be made constant and introduced into the chamber. When the sample is a resist, the control unit causes the ozone gas generation unit to stop generating ozone gas, and the gas introduction amount. The amount of oxygen supplied from the oxygen supply means to the adjusting means may be made constant and introduced into the chamber.

  In the present invention, ozone-containing gas or oxygen gas is introduced into the chamber according to the material of the sample placed on the stage in the electron beam apparatus. When the sample is damaged by ozone gas, the introduction of the ozone gas is stopped, and at the same time, the same amount of oxygen as the introduced ozone gas is introduced. Thereby, the pressure in the chamber becomes constant before and after the replacement of the sample, the pressure in the vicinity of the cathode of the electron gun is not changed, and the sample can be irradiated with a stable electron beam.

  Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, an electron beam size measuring device will be described as an example of the electron beam device.

  First, the configuration of the electron beam dimension measuring apparatus will be described. Next, the configuration of the ozone gas introduction device will be described. Next, a process for stably irradiating an electron beam when the introduction of ozone gas is stopped will be described. Next, a modified example of the ozone gas introducing device will be described, and finally, the effect of the present invention will be described using the beam current characteristics.

(Configuration of electron beam size measuring device)
FIG. 1 is a configuration diagram of an electron beam dimension measuring apparatus according to the present embodiment.

  The electron beam size measuring apparatus 100 includes an electronic scanning unit 10, a signal processing unit 30, a display unit 40, and a control unit 20 that controls the electronic scanning unit 10, the signal processing unit 30, and the display unit 40. Broadly divided. Among these, the electronic scanning unit 10 includes an electron column (column) 15 and a sample chamber 16. In addition, a preliminary exhaust chamber 42 is connected to the sample chamber 16 via a gate 41, and an ozone gas introduction device 50 is connected via an MFC 52.

  The electron column unit 15 includes an electron gun 1, a condenser lens 2, a deflection coil 3, and an objective lens 4, and the sample chamber 16 includes an XY stage 5 and a sample support unit 6.

  A motor (not shown) for moving the XY stage 5 and a vacuum pump (not shown) for maintaining the inside of the sample chamber 16 in a predetermined reduced pressure atmosphere are connected to the sample chamber 16.

  An electron beam 9 irradiated from the electron gun 1 is irradiated to the sample 7 on the XY stage 5 through the condenser lens 2, the deflection coil 3 and the objective lens 4.

  The amount of secondary electrons or reflected electrons emitted from the sample 7 after being irradiated with the electron beam 9 is detected by an electron detector 8 composed of a secondary electron control electrode, a scintillator, and the like, and the detected amount in the signal processing unit 30. Is converted into a digital quantity by an AD converter, further converted into a luminance signal, and displayed on the display unit 40. The electronic deflection amount of the deflection coil 3 and the image scan amount of the display unit 40 are controlled by the control unit 20.

  The control unit 20 is composed of a microcomputer and stores a program for executing length measurement.

  The control unit 20 controls the ozone gas introduction device 50 to adjust the amount of ozone gas introduced into the sample chamber 16 according to the material of the sample carried into the sample chamber 16.

(Configuration of ozone gas introduction device)
FIG. 2 shows a block configuration diagram of the ozone gas introducing device 50.

  The ozone gas introduction device 50 includes an oxygen cylinder 60 that stores oxygen as a raw material for generating ozone, a discharge unit 51 that generates ozone from oxygen, and an MFC (mass flow) that controls the amount of gas introduced into the sample chamber 16. Controller) 52 and an ozone treatment device 53 that exhausts a part of a mixed gas (ozone-containing gas) of ozone and oxygen generated through the discharge unit 51.

  The output side of the oxygen cylinder 60 and the input side of the discharge unit 51 are connected via an MFC 54. The output side of the discharge unit 51 is connected to the ozone treatment device 53 and also connected to the sample chamber 16 via the MFC 52. These parts are connected by a conduit 61.

  The discharge unit 51 includes two electrodes 55, an oscillator 56 connected to the electrode 55, and an on / off switch 57 of the oscillator 56.

  Oxygen supplied from the oxygen cylinder 60 is supplied to the discharge unit 51 via the MFC 54. A high-frequency high-frequency signal is applied between the electrodes 55 of the discharge unit 51 from the oscillator 56 to generate a discharge between the electrodes 55. A part of the oxygen supplied from the oxygen cylinder 60 is ozonized when passing between the electrodes 55.

  By controlling the voltage applied to the electrode 55 of the discharge unit 51, the amount of ozone generated is controlled. Here, the ratio of ozone gas to oxygen is set to be 1: 9.

  A part of the mixed gas (ozone-containing gas) of ozone gas and oxygen generated by the discharge unit 51 is introduced into the sample chamber 16 through the MFC 52, and most of the other part is sent to the ozone processing device 53. After the ozone treatment device 53 performs a treatment for returning the ozone gas to oxygen, it is exhausted to the atmosphere.

  The flow rate of the ozone-containing gas is controlled by the MFC 52, and a predetermined amount of ozone-containing gas is introduced into the sample chamber 16.

  Since ozone introduced into the sample chamber 16 is an unstable substance, it is decomposed into oxygen and active oxygen over time. The decomposed active oxygen and organic substance C which is a causative substance of contamination are combined and evaporated. As a result, as shown in FIG. 3A, the organic substance C present on the sample is removed from the surface of the sample as shown in FIG. 3B.

  After introducing the ozone-containing gas, the sample is carried into the sample chamber 16. First, the gate 43 is opened, and the sample is carried into the preliminary exhaust chamber 42. Next, the preliminary exhaust chamber 42 is evacuated, and when the degree of vacuum is the same as that of the sample chamber 16, the gate 41 is opened and the sample chamber 16 is loaded.

  The control unit 20 determines whether or not the introduction of the ozone-containing gas is continued depending on the material of the sample to be carried in. If the sample is not a material that is affected by deformation such as ozone, the ozone-containing gas is continuously introduced.

  On the other hand, when the sample is a resist made of an organic material, oxygen is introduced instead of introducing the ozone-containing gas because the pattern is affected by ozone. The introduction of oxygen is performed by stopping the discharge in the discharge unit 51 in the ozone gas introduction device 50. By stopping the discharge, ozone is not generated from oxygen, but passes through the discharge unit 51 in the state of oxygen and is introduced into the sample chamber 16 via the MFC 52.

  The ratio of ozone and oxygen of the ozone-containing gas introduced into the sample chamber 16 is set to 1: 9. However, the ratio is not limited to this, and the ratio of the voltage applied to the electrode 55 in the discharge unit 51 is adjusted to 2 You may make it change like pair 8 or 3-7. For example, when the amount of contamination increases in the column 15 or the sample chamber 16 due to long-term use, the ratio of the ozone-containing gas is set to 3 to 7, and then from 2 to 8 to 1 to 9. It may be changed.

(Process to stably irradiate an electron beam when the introduction of ozone gas is stopped)
As described above, the gas introduced into the sample chamber 16 is switched to the ozone-containing gas or the oxygen gas depending on the material of the sample placed on the XY stage in the sample chamber 16. The reason why it can be stabilized regardless of the material is described below.

  Conventionally, an ozone-containing gas is introduced into the sample chamber 16 and the column 15 or stopped depending on the material of the sample. The reason why the introduction of the ozone gas is stopped is that the resist is damaged by the ozone gas introduced to eliminate contamination.

  However, it was found that when the introduction of the ozone-containing gas was stopped, the beam current of the electron beam applied to the sample changed greatly compared to the case where the ozone-containing gas was introduced.

  FIG. 4 shows changes in the beam current of the electron beam when the ozone-containing gas is introduced and when it is stopped. As shown in FIG. 4, the beam current value of the electron beam differs greatly between when the ozone-containing gas is introduced and when it is stopped. While the ozone is being introduced, the value is stable at about 4.5 [pA] (A in FIG. 4), but from the time when the ozone introduction is stopped, the value is as shown in FIG. 4B. The beam current rises and changes to stabilize at about 5.3 [pA] after 7 [h].

  The partial pressure of ozone around the cathode of the electron gun changes by switching between introduction and stop of the ozone-containing gas. The work function of the metal constituting the cathode is considered to be affected by the partial pressure of ozone around the cathode. The change in the work function value due to the change in the ozone partial pressure is considered to change the beam current as a result.

The pressure in the sample chamber 16 when ozone is present is about 10 ⁻³ Pascal. On the other hand, the pressure in the sample chamber 16 when ozone is not present is about 10 ⁻⁴ Pascal. As described above, the present inventor changes the partial pressure of ozone around the cathode of the electron gun, that is, the amount of ozone, by changing the pressure in the sample chamber 16 and the column 15 with or without ozone gas, and the beam current is changed. I found it unstable.

  Therefore, in order to stop the introduction of the ozone gas and not to change the pressure in the sample chamber 16 and the column 15, it was considered to introduce oxygen instead of the ozone gas. The amount of oxygen to be introduced is the same as that of ozone gas, and the amount of gas in the sample chamber 16 and the column 15 is the same when ozone gas is introduced and when oxygen is introduced.

  In the ozone gas introduction device 50, oxygen is ozonized by generating discharge between the electrodes 55 of the discharge unit 51 and passing oxygen between the electrodes 55. Therefore, oxygen is introduced into the sample chamber 16 by turning off the voltage applied between the electrodes 55 of the discharge unit 51 so that this discharge does not occur.

  As a result, even when the introduction of ozone gas into the sample chamber 16 and the column 15 is stopped, the pressure in the sample chamber 16 and the column 15 does not change, so that the beam current of the electron beam becomes unstable. Can be prevented.

  Since oxygen has a weaker oxidizing power than ozone, the increase in oxygen does not increase sample damage.

  As described above, in the electron beam apparatus according to the present embodiment, the ratio of ozone and oxygen introduced into the sample chamber 16 is determined according to the material of the sample placed on the stage in the sample chamber 16, and the introduced gas. The amount is constant. As a result, the pressure in the sample chamber 16 and the column 15 becomes constant, and the pressure in the vicinity of the cathode of the electron gun is not changed, so that it is possible to irradiate the sample with a stable electron beam.

  Next, an introduction gas switching method in the electron beam apparatus of the present embodiment will be described with reference to the flowchart of FIG. Here, it is assumed that an ozone-containing gas is introduced into the sample chamber 16 and the column 15.

  First, in step S11, the material of the sample carried into the sample chamber 16 is determined. If the sample is a resist, the process proceeds to step S12. If the sample is not a resist, the process proceeds to step S13.

  In the next step S12, the power supply of the discharge unit 51 of the ozone gas introduction device 50 is turned off. Thereby, ozone is not generated in the ozone gas introduction device 50, and oxygen is introduced into the sample chamber 16.

  On the other hand, in step S13, since it is determined in step S11 that the sample is not a resist, there is no problem even if ozone gas is introduced into the sample chamber 16. Therefore, the power supply of the discharge unit 51 of the ozone gas introduction device 50 is kept on, and ozone is generated to introduce the ozone-containing gas into the sample chamber 16.

  In the next step S <b> 14, the sample is carried into the sample chamber 16.

  In the next step S15, it is determined whether or not the sample processing, for example, the length measurement processing is completed. When the process is finished, the process proceeds to the next step S16. When the process is not finished, the process waits until the process is finished.

  In the next step S <b> 16, the sample is carried out from the sample chamber 16.

  In the next step S17, it is determined whether or not the processing for all the samples has been completed. If all the processes are not completed, the process returns to step S11 to continue the present process, and if all the processes are completed, the present process is terminated.

(Modification)
In the above embodiment, the generation of ozone gas is controlled by turning on and off the power supply of the discharge unit 51 of the ozone gas introduction device 50.

  In this modified example, ozone and oxygen are generated individually, and the ratio of ozone and oxygen is determined by adjusting the amount of opening of a valve connected to a device that supplies each gas. Then, the amount of gas is controlled by MFC, and a mixed gas of ozone and oxygen is introduced into the sample chamber 16.

  FIG. 6 is a block diagram of an ozone gas introducing device 50a of this modification. The ozone gas introduction device 50 a includes an oxygen cylinder 72, an ozone generator 71, an oxygen valve 74, an ozone valve 73, and an MFC 52.

  Adjustment of the ozone valve 73 and the oxygen valve 74 is performed by the controller 20 determining the material of the sample, and when the sample is affected by ozone, the ozone valve 73 connected to the ozone generator 71 is closed and the oxygen cylinder 72 is set. Only the oxygen is introduced into the sample chamber 16 by maintaining or increasing the opening ratio of the connected oxygen valve 74. Further, when the sample is not affected by ozone, the opening ratio of the ozone valve 73 connected to the ozone generator 71 and the opening ratio of the oxygen valve 74 connected to the oxygen cylinder 72 are set to predetermined values, for example, ozone. The opening ratio of the valve 73 and the opening ratio 74 of the oxygen valve are set to 1: 9.

  The ratio of the mixed gas of ozone gas and oxygen introduced into the sample chamber 16 is set to 1: 9. However, the ratio is not limited to this, and the ratio of the mixed gas is set to 2: 8 or 3: 7 by adjusting the valve. You may make it change to. For example, when the amount of contamination increases in the sample chamber 16 and the column 15 due to long-term use, the ratio of the mixed gas is changed to 3 to 7, and then changed from 2 to 8 to 1 to 9. You may make it make it.

(Beam current characteristics)
FIG. 7 is a diagram showing changes in the beam current when the introduction of gas is controlled by controlling the power supply of the discharge unit 51 and the MFC 52 of the ozone gas introduction device 50. In FIG. 7, the horizontal axis represents time, and the vertical axis represents the value of the beam current on the stage. In FIG. 7, the beam when transitioning to three states, a state where oxygen is introduced into the sample chamber 16, a state where ozone-containing gas is introduced, and a state where introduction of ozone-containing gas is stopped is performed. It shows the change in current.

  First, in a state where oxygen is introduced (A in FIG. 7), the value is almost constant (4.4 to 4.5 [pA]) although there is some change. From the state in which oxygen is introduced, the power source of the discharge unit 51 is turned on at time t 2 to generate ozone, and ozone gas is introduced into the sample chamber 16. The amount of gas introduced into the sample chamber 16 was constant before and after t2. As can be seen from FIG. 7, the beam current does not change greatly from the time of switching, and is a substantially stable value (4.5 to 4.6 [pA]) (B in FIG. 7).

  Next, at time t3, the valve 58 of the ozone gas introduction device 50 was closed, and the introduction of the ozone-containing gas was stopped. Immediately after the introduction of the ozone-containing gas was stopped, the beam current started to increase and stabilized at 5.3 [pA] at about 6 [h] (C in FIG. 7).

  Next, at time t4, the valve 58 of the ozone gas introduction device 50 was opened, and the introduction of the ozone-containing gas was started by controlling the MFC 52. Immediately after the introduction of the ozone-containing gas, the beam current began to decrease (D in FIG. 7).

  The partial pressure of ozone around the cathode of the electron gun is changed by switching between introduction and stop of the ozone-containing gas at time points t3 and t4 in FIG. The work function of the metal constituting the cathode is considered to be affected by the partial pressure of ozone around the cathode. The change in the work function value due to the change in the ozone partial pressure is considered to change the beam current as a result.

  As can be seen from the beam current values before and after time t2 in FIG. 7, the beam current is increased by keeping the amount of gas introduced into the sample chamber 16 and the column 15 constant and the pressure in the sample chamber 16 and the column 15 constant. Can be stabilized.

  As described above, in the electron beam apparatus according to the present embodiment, the ratio of ozone and oxygen of the gas introduced into the sample chamber 16 is determined according to the material of the sample placed on the stage in the sample chamber 16 and introduced. Keep the amount of gas to be constant. For example, in the case of a resist that is deformed by ozone, the gas introduced into the sample chamber 16 is only oxygen, and the amount of oxygen introduced is the same as the ozone-containing gas that has been introduced. As a result, the pressure in the sample chamber 16 and the column 15 becomes constant, and the pressure in the vicinity of the cathode of the electron gun is not changed. Therefore, a stable electron beam is applied to the sample without changing the work function of the metal constituting the cathode. Irradiation is possible.

  In this embodiment, the electron beam size measuring device is described as an example of the electron beam device. However, the present invention is not limited to this, and can be applied to a device that performs processing by irradiating an electron beam. It is also possible to apply.

It is a block diagram of the electron beam dimension measuring apparatus used by embodiment of this invention. It is a block diagram of the ozone gas introduction apparatus in the electron beam dimension measuring apparatus which concerns on FIG. It is a figure explaining the principle by which contamination is suppressed. It is a figure which shows the change of the beam current of an electron beam when an ozone containing gas is introduced and when it stops. It is a flowchart which shows the introduction gas switching method of an electron beam dimension measuring apparatus. It is a block diagram of the ozone gas introduction apparatus which concerns on a modification. It is a figure which shows the beam current characteristic of an electron beam.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electron gun, 2 ... Condenser lens, 3 ... Deflection coil, 4 ... Objective lens, 5 ... XY stage, 6 ... Sample support part, 7 ... Sample, 8 ... Electron detector, 9 ... Electron beam, 10 ... Electron scanning , 15 ... Electronic column (chamber), 16 ... Sample chamber (chamber), 20 ... Control unit, 30 ... Signal processing unit, 40 ... Display unit, 50 ... Ozone gas introduction device, 51 ... Discharge unit (discharge device, Ozone gas generating means), 52, 54 ... MFC (gas introduction amount adjusting means), 53 ... ozone treatment device, 55 ... electrode, 56 ... oscillator, 57 ... switch (switching switch), 60 ... oxygen cylinder, 61,75 ... conduit 71 ... ozone supply unit, 72 ... oxygen supply unit, 73 ... ozone valve, 74 ... oxygen valve, 100 ... electron beam size measuring device.

Claims (7)

In an electron beam apparatus that irradiates a sample placed on a stage with an electron beam generated from an electron gun,
Ozone gas introduction means for introducing ozone gas into the chamber in which the electron gun and the stage are housed;
Depending on the material of the sample, the ozone gas introduction means introduces either ozone-containing gas or oxygen into the chamber, and the amount of ozone-containing gas or oxygen in the chamber is constant regardless of the material of the sample. And an electron beam apparatus characterized by comprising: The ozone gas introducing means is
Oxygen supply means;
Ozone gas generating means for generating an ozone-containing gas composed of ozone gas and oxygen in a predetermined ratio;
The electron beam apparatus according to claim 1, further comprising: a gas introduction amount adjusting unit that adjusts an amount of gas introduced into the chamber.   The control means causes the ozone gas generation means to generate ozone gas from the oxygen supplied by the oxygen supply means, and causes the gas introduction amount adjustment means to make the amount of ozone-containing gas composed of the ozone gas and oxygen constant, The electron beam apparatus according to claim 2, wherein the electron beam apparatus is introduced into the chamber.   When the sample is a resist, the control unit stops the ozone gas generation unit from generating ozone gas, causes the gas introduction amount adjustment unit to keep the amount of oxygen supplied from the oxygen supply unit constant, and The electron beam apparatus according to claim 2, wherein the electron beam apparatus is introduced into the electron beam apparatus.   The electron beam apparatus according to claim 3, wherein the ozone-containing gas has a ratio of ozone gas to oxygen of 1: 9.   The electron beam apparatus according to claim 3, wherein the control means continuously changes the ozone content of the ozone-containing gas. The ozone gas generation means includes a discharge device that generates ozone from oxygen;
A changeover switch for turning on and off the power supplied to the discharge device;
5. The control unit according to claim 3, wherein the control unit causes the ozone gas generation unit to turn on the changeover switch to generate ozone gas and turn off the changeover switch to stop generation of ozone gas. 6. Electron beam equipment.

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