Method for estimating cathode lifetime of electron gun, and electron beam writing apparatus

1 . A method for estimating a cathode lifetime of an electron gun comprising:

recording a change amount, per unit temperature increase of a cathode of an electron gun which emits an electron beam, with respect to a parameter value relating to the electron beam which changes with usage time of the cathode, to be recorded in relation to the usage time of the cathode each time a temperature of the cathode is changed; and

estimating a lifetime of the cathode by one of estimating a time obtained by adding a predetermined time to a time at which the change amount recorded a plurality of times becomes lower than a prescribed value as the lifetime of the cathode, and estimating, using an approximate line obtained by a line approximation function using a plurality of the change amounts recorded each time the temperature of the cathode was changed, a time at which the approximate line indicates that the change amount becomes zero as the lifetime of the cathode, and

outputting an estimated lifetime.

2 . An electron beam writing apparatus comprising:

a recording circuit configured to perform recording according to claim 1 ;

an estimation circuit configured to estimate a lifetime according to claim 1 ;

an output circuit configured to output, at a time of an end of the lifetime estimated is approaching, information indicating that the lifetime is coming to the end soon; and

a writing mechanism configured to include an electron gun which emits an electron beam and to write a pattern on a sample by using the electron beam.

3 . A method for estimating a cathode lifetime of an electron gun comprising:

recording a change amount, per unit temperature increase of a cathode of an electron gun which emits an electron beam, with respect to a value obtained by differentiating a sample surface current at a position on a sample surface irradiated with the electron beam, by an emission current of the electron beam, to be recorded in relation to a usage time of the cathode each time a temperature of the cathode is changed; and

estimating a lifetime of the cathode by one of estimating a time obtained by adding a predetermined time to a time at which the change amount recorded a plurality of times becomes lower than a prescribed value as the lifetime of the cathode, and estimating, using an approximate line obtained by a line approximation function using a plurality of the change amounts recorded each time the temperature of the cathode was changed, a time at which the approximate line indicates that the change amount becomes zero as the lifetime of the cathode.

4 . An electron beam writing apparatus comprising:

a recording circuit configured to perform recording according to claim 3 ;

an estimation circuit configured to estimate a lifetime according to claim 3 ;

an output circuit configured to output, at a time of an end of the lifetime estimated is approaching, information indicating that the lifetime is coming to the end soon; and

a writing mechanism configured to include an electron gun which emits an electron beam and to write a pattern on a sample by using the electron beam.

5 . A method for estimating a cathode lifetime of an electron gun comprising:

recording a change amount, per unit temperature increase of a cathode of an electron gun which emits an electron beam, with respect to a bias voltage to be applied to a Wehnelt electrode of the electron gun, to be recorded in relation to a usage time of the cathode each time a temperature of the cathode is changed; and

estimating a lifetime of the cathode by one of estimating a time obtained by adding a predetermined time to a time at which the change amount recorded a plurality of times becomes lower than a prescribed value as the lifetime of the cathode, and estimating, using an approximate line obtained by a line approximation function using a plurality of the change amounts recorded each time the temperature of the cathode was changed, a time at which the approximate line indicates that the change amount becomes zero as the lifetime of the cathode, and

outputting an estimated lifetime.

6 . An electron beam writing apparatus comprising:

a recording circuit configured to perform recording according to claim 5 ;

an estimation circuit configured to estimate a lifetime according to claim 5 ;

an output circuit configured to output, at a time of an end of the lifetime estimated is approaching, information indicating that the lifetime is coming to the end soon; and

a writing mechanism configured to include an electron gun which emits an electron beam and to write a pattern on a sample by using the electron beam.

7 . A method for estimating a cathode lifetime of an electron gun comprising:

recording a change amount, per unit temperature increase of a cathode of an electron gun which emits an electron beam, with respect to a sample surface current of the electron beam at a position on a sample surface irradiated with the electron beam, to be recorded in relation to a usage time of the cathode each time a temperature of the cathode is changed; and

estimating a lifetime of the cathode by one of estimating a time obtained by adding a predetermined time to a time at which the change amount recorded a plurality of times becomes lower than a prescribed value as the lifetime of the cathode, and estimating, using an approximate line obtained by a line approximation function using a plurality of the change amounts recorded each time the temperature of the cathode was changed, a time at which the approximate line indicates that the change amount becomes zero as the lifetime of the cathode, and

outputting an estimated lifetime.

8 . An electron beam writing apparatus comprising:

a recording circuit configured to perform recording according to claim 7 ;

an estimation circuit configured to estimate a lifetime according to claim 7 ;

an output circuit configured to output, at a time of an end of the lifetime estimated is approaching, information indicating that the lifetime is coming to the end soon; and

a writing mechanism configured to include an electron gun which emits an electron beam and to write a pattern on a sample by using the electron beam.

9 . A method for estimating a cathode lifetime of an electron gun comprising:

recording a change amount, per unit temperature increase of a cathode of an electron gun which emits an electron beam, with respect to a current density of the electron beam at a position on a sample surface irradiated with the electron beam, to be recorded in relation to a usage time of the cathode each time a temperature of the cathode is changed; and

estimating a lifetime of the cathode by one of estimating a time obtained by adding a predetermined time to a time at which the change amount recorded a plurality of times becomes lower than a prescribed value as the lifetime of the cathode, and estimating, using an approximate line obtained by a line approximation function using a plurality of the change amounts recorded each time the temperature of the cathode was changed, a time at which the approximate line indicates that the change amount becomes zero as the lifetime of the cathode, and

outputting an estimated lifetime.

10 . An electron beam writing apparatus comprising:

a recording circuit configured to perform recording according to claim 9 ;

an estimation circuit configured to estimate a lifetime according to claim 9 ;

an output circuit configured to output, at a time of an end of the lifetime estimated is approaching, information indicating that the lifetime is coming to the end soon; and

a writing mechanism configured to include an electron gun which emits an electron beam and to write a pattern on a sample by using the electron beam.