JP5362297B2 - Charged particle beam drawing apparatus and charged particle beam drawing method - Google Patents

Description

  The present invention relates to a charged particle beam writing apparatus and a charged particle beam writing method using, for example, a cathode filament.

  In recent years, with the miniaturization of semiconductor devices, miniaturization of mask patterns such as LSIs has been required. A charged particle beam drawing apparatus having an excellent resolution is used for forming this fine mask pattern. In such a charged particle beam drawing apparatus, a thermionic emission electron gun using a cathode filament is used as a charged particle gun. A thermionic emission gun irradiates an electron beam with a predetermined emission current focused by a bias voltage and accelerated by an accelerating voltage. Reference 1 etc.).

  Such an operating condition of the electron gun is usually determined from the relationship between the filament power and the bias voltage with the emission current set to a predetermined value. For example, the relationship (bias saturation characteristic) between the filament power and the bias voltage when the emission current is set to a predetermined value is measured. Then, the filament power at the boundary between the temperature limited region and the space charge limited region, that is, the point at which the bias voltage saturates (bias saturation point) with respect to the change in filament power is obtained, and this filament power is optimally given a predetermined margin Set to operating point.

There is a correlation between filament power and cathode temperature, and these relationships can be measured at individual cathodes to determine the cathode temperature at a set filament power. Usually, the cathode temperature is about 1450 to 1470K, with some variation. When the cathode temperature is high, the cathode evaporates faster, and changes due to heat such as deterioration of the cathode and change of contact state occur, which shortens the life of the cathode. Therefore, the lower the cathode temperature, the longer the life can be achieved (for example, see Patent Document 2).
Japanese Patent Laid-Open No. 5-166481 JP 2006-221983 A

  The current density J of the irradiated electron beam depends on the cathode temperature. When the cathode temperature decreases, the current density J also decreases. Therefore, in order to obtain a desired current density J, it is necessary to control to an appropriate cathode temperature.

  The filament power that determines the cathode temperature is empirically determined by the bias saturation characteristic at the emission current set to a predetermined value. By obtaining the filament power in this manner, even if the cathode temperature varies from about 1450 to 1470 K, variations in the temperature characteristics of the cathode are absorbed, and a desired current density J can be obtained. However, with the demand for miniaturization, the current density J is increasing. Accordingly, the cathode temperature rises, so that the life of the cathode greatly fluctuates due to variations in the cathode temperature.

  Therefore, the present invention seeks a charged particle beam drawing apparatus having a function of obtaining an optimum filament power (cathode temperature) for obtaining a desired current density J, and an optimum filament power for obtaining a desired current density J. An object of the present invention is to provide a charged particle beam writing method capable of performing the above.

  The charged particle beam drawing apparatus according to one embodiment of the present invention focuses electrons emitted by heating a cathode with filament power by using a bias voltage and accelerating using an acceleration voltage to generate a charged particle beam having a predetermined emission current. A charged particle gun for irradiation, a detector installed on the optical axis of the charged particle beam, a detector for measuring the current density of the charged particle beam, and a control unit for controlling the filament power and emission current connected to the detector And the relationship between the current density and the emission current at the bias saturation point where the bias voltage is saturated with respect to the filament power, and the relationship between the filament power and the emission current. A storage calculation unit for calculating an emission current value and a filament power value for A stage for mounting a sample turn is drawn, in a predetermined position on the sample and is characterized by comprising a charged particle beam control system to control the charged particle beam to form a predetermined pattern.

  The charged particle beam drawing apparatus of one embodiment of the present invention preferably includes a determination unit that compares the set current density with the current density detected by the detector, and the determination unit is preferably connected to the detector and the control unit. .

Further, in the charged particle beam drawing method of one embodiment of the present invention, electrons emitted by heating a cathode with filament power are focused by a bias voltage, accelerated by an acceleration voltage, and charged particle beam is generated with a predetermined emission current. Is a charged particle beam writing method in which writing is performed by irradiating a sample on a specimen, and a bias saturation point at which the bias voltage saturates with respect to the filament power is preliminarily determined based on the relationship between the bias voltage, the filament power, and the emission current. Rutotomoni obtained relation between put that off Iramento power and the emission current, the bias voltage as a bias saturation point, by measuring the current density of the charged particle beam in the filament power, and emission current, the current density of the charged particle beam The relationship between emission current and emission current From the relationship between the current density and the emission current, obtains a first emission current values corresponding to the set current density, the relationship between the filament power and emission current, the first filament power value corresponding to the first emission current value It is characterized by calculating | requiring.

  In the charged particle beam writing method of one embodiment of the present invention, the current density when the first emission current value and the first filament power value are measured is measured, and the measured current density does not reach the set current density In this case, it is preferable to adjust the emission current to be the second emission current value, and obtain the second filament power value corresponding to the second emission current value from the relationship between the filament power and the emission current.

  In the charged particle beam drawing method of one embodiment of the present invention, it is preferable to finely adjust the current density by controlling the amount of lens excitation with respect to the irradiated charged particle beam.

  ADVANTAGE OF THE INVENTION According to this invention, in a charged particle beam drawing apparatus and a charged particle beam drawing method, it becomes possible to obtain | require optimal filament electric power in order to obtain a desired current density.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a conceptual diagram of a thermionic emission type electron beam drawing apparatus which is a charged particle beam drawing apparatus of the present embodiment. As shown in the drawing, in the electron gun 10, a cathode 11 from which electrons are emitted is connected to a filament supply power source 13 for heating the cathode 11 via a filament 12 to constitute a filament circuit.

  A Wehnelt 14 having an opening below the cathode 11 and converging and controlling electrons emitted from the cathode 11 is disposed so as to surround the cathode 11 and the filament 12. A bias power supply 15 for applying a bias voltage to the cathode 11 is connected to the Wehnelt 14 to constitute a bias circuit.

  An anode 16 is disposed below the Wehnelt 14 and grounded. An acceleration voltage is applied between the cathode 11 and the anode 16 and an acceleration power source 17 for supplying an emission current is connected to the filament circuit and the bias circuit.

  The filament supply power source 13 and the bias power source 14 are connected to a control unit 18 for controlling the filament power and the emission current. Further, the control unit 18 stores a relationship between parameters, and is connected to a storage calculation unit 19 for calculating an emission current value and a filament power value from a set current density J.

  Below the electron gun 10, an electron beam control system 21 including an excitation lens for controlling the irradiated electron beam 20 is installed, and a stage on which a sample to be drawn is placed (see FIG. Not shown) is installed. A detector 22 for measuring the current density J is also installed on the stage. The detector 22 is connected to the control unit 18 via a determination unit 23 that determines whether or not the measured current density J falls within the specifications.

  Using such an electron beam drawing apparatus, the optimum emission current and filament power in the cathode 11 to be used are set prior to drawing.

  As shown in the flowchart in FIG. 2, first, the emission current is set to 120 to 150 μA, for example, and the relationship between the filament power and the bias voltage (bias saturation characteristics) is measured. The filament power is obtained from the applied voltage and current value applied from the filament supply power source 13. These are plotted as shown in FIG. 3 to obtain the bias saturation point at each emission current (step 1). At this time, the bias saturation point is a point at which the bias voltage becomes 99.6% of the bias voltage when the filament power is infinite. Then, the relationship between the emission current and the filament power at the bias saturation point is plotted (step 2).

  Next, the current density J is measured by irradiating the detector 22 with the electron beam 20 under the condition at each bias saturation point, and the relationship between the emission current and the current density J is plotted as shown in FIG. 4 (step 3). .

  Then, as shown in FIG. 5, the filament power and the current density J at each bias saturation point are superimposed using the emission current as a parameter (step 4). The relational data of these parameters is stored in the storage calculation unit 21.

  Next, a target value of the current density J is set (step 5), and based on the stored relational data of each parameter, an emission current value at the set current density J is obtained in the storage calculation unit 19 (step 6). A filament power value corresponding to the emission current value is obtained (step 7).

  The detector 22 is again irradiated with the electron beam 20 with the emission current value and the filament power value obtained in this way, and the current density J is actually measured (step 8). The determination unit 23 determines whether the measured current density J is within specifications such as ± 10% of the target value (step 9). If not within specifications, the emission current is adjusted (step 10), and the filament power is obtained again (step 7). At this time, the current density J may be finely adjusted by adjusting the lens excitation amount in the control system 21. On the other hand, if it is within the specifications, actual drawing is started under the conditions (step 11).

First, the inside of the electron beam drawing apparatus including the electron gun 10 is depressurized to about 10 ⁻⁶ Pa. Filament power is supplied to the cathode 11 from the filament supply power source 13, and electrons are emitted from the cathode 11.

  Electrons radiated from the cathode 11 are controlled by a predetermined bias voltage applied to the Wehnelt 14 by the bias power source 15 and are focused at a crossover point immediately below the Wehnelt 14 to form an electron beam 20. An acceleration voltage of, for example, 50 kV is applied between the cathode 11 and the anode 16 by the acceleration power source 17, and the electron beam 20 is accelerated toward the anode 18.

  Further, the accelerated electron beam 20 is shaped and adjusted so that the electron beam control system 21 irradiates a predetermined position on the sample on which the pattern is drawn by being placed on the stage. The shaped and adjusted electron beam 20 is controlled by a stage drive system, and is irradiated onto the sample to draw a predetermined pattern.

  In this way, the optimum emission current value and filament power value can be obtained. Then, by optimizing the filament power value, the life of the cathode can be extended by about 20%.

  In this embodiment, an electron beam is used as a charged particle beam, but the present invention is not limited to an electron beam, and other charged particle beams such as an ion beam can also be used. In the case of using an ion beam, Ar + ions are formed by collision of thermoelectrons generated at the cathode with Ar gas or the like introduced into the ion gun. The formed Ar + ions are accelerated in the same manner as the electron beam, irradiated onto the sample, and a predetermined pattern is drawn. At that time, the filament power can be adjusted to an optimum value in order to obtain a desired current density J.

  In addition, this invention is not limited to embodiment mentioned above. Various other modifications can be made without departing from the scope of the invention.

1 is a conceptual diagram of a thermionic emission type electron beam drawing apparatus of one embodiment of the present invention. The flowchart which sets the optimal emission current and filament electric power in 1 aspect of this invention. FIG. 6 is a graph showing the relationship between filament power and bias voltage in one embodiment of the present invention. The figure which shows the relationship between the emission current and filament electric power in 1 aspect of this invention. The figure which shows a filament electric power and current density J as an emission current parameter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electron gun 11 ... Cathode 12 ... Filament 13 ... Filament supply power 14 ... Wehnelt 15 ... Bias power supply 16 ... Anode 17 ... Acceleration power supply 18 ... Control part 19 ... Memory | storage calculating part 20 ... Electron beam 21 ... Electron beam control system 22 ... Detector 23 ... judgment part

Claims (5)

A charged particle gun that irradiates a charged particle beam of a predetermined emission current by focusing electrons emitted by heating the cathode with a filament power with a bias voltage and accelerating with an acceleration voltage;
A detector installed on the optical axis of the charged particle beam for measuring the current density of the charged particle beam;
A controller connected to the detector for controlling the filament power and the emission current;
Connected to the controller, stores the relationship between the current density and the emission current at a bias saturation point where the bias voltage is saturated with respect to the filament power, and stores the relationship between the filament power and the emission current. A memory calculation unit for calculating an emission current value and a filament power value for drawing from the current density;
A stage on which a sample on which a pattern is drawn is placed;
A charged particle beam drawing apparatus comprising: a charged particle beam control system that controls the charged particle beam to form a predetermined pattern at a predetermined position on the sample.   2. The determination unit according to claim 1, further comprising a determination unit that compares the set current density with a current density detected by the detector, the determination unit being connected to the detector and the control unit. Charged particle beam lithography system. Electron emitted by heating cathode with filament power is focused by bias voltage, accelerated by acceleration voltage, and charged particle beam writing is performed by irradiating the sample with a charged particle beam with a predetermined emission current A method,
Previously, the bias voltage, the filament power, and the relationship between the emission current, obtain the relation of the bias voltage is said filament power before Symbol filament power that put the bias saturation point to be saturated with respect to the said emission current And measuring the current density of the charged particle beam at the bias voltage, the filament power, and the emission current that become the bias saturation point, thereby obtaining a relationship between the current density of the charged particle beam and the emission current. Seeking
From the relationship between the current density and the emission current, a first emission current value corresponding to a set current density is obtained,
A charged particle beam drawing method, wherein a first filament power value corresponding to the first emission current value is obtained from the relationship between the filament power and the emission current. Measure the current density when the first emission current value and the first filament power value,
If the measured current density does not reach the set current density, the emission current is adjusted to a second emission current value,
4. The charged particle beam writing method according to claim 3, wherein a second filament power value corresponding to the second emission current value is obtained from the relationship between the filament power and the emission current.   5. The charged particle beam drawing method according to claim 3, wherein the current density is finely adjusted by controlling an excitation amount of a lens with respect to the irradiated charged particle beam.

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