Charged particle beam writing method and charged particle beam writing apparatus
An amount of charge of a substrate is promptly and accurately calculated. A charged particle beam writing method includes a step for virtually dividing a writing region of the writing target substrate in a mesh-like manner and calculating a pattern density representing an arrangement ratio of the pattern for each mesh region, a step for calculating a dose for each mesh region using the pattern density, a step for calculating a charge amount based on a film thickness of the resist film formed on the substrate and the calculated dose by using a predetermined function for charge amount calculation, the function using, as variables, the film thickness of the resist film and the dose, a step for calculating a position shift amount of a writing position from the calculated charge amount, and a step for correcting an irradiation position of the charged particle beam using the position shift amount.
1 . A charged particle beam writing method in which a deflector is caused to deflect a charged particle beam and a pattern is written by irradiating, with the charged particle beam, a substrate on which a resist film is formed, the charged particle beam writing method comprising the steps of:
virtually dividing a writing region of the substrate in a mesh having grid dimensions and calculating a pattern density representing an arrangement ratio of the pattern for each of mesh region;
calculating a dose for each of the mesh region using the pattern density;
calculating a charge amount based on a film thickness of the resist film formed on the substrate and the calculated dose by using a predetermined function for charge amount calculation, the function using, as variables, the film thickness of the resist film and the dose and using, as parameters, a secondary electron yield, a permittivity, a resistivity during beam irradiation, a work function, and a positive-hole residual rate of resist;
calculating a position shift amount of a writing position from the calculated charge amount; and
correcting an irradiation position of the charged particle beam using the position shift amount,
wherein the function for charge amount calculation is independent of dose sensitivity of the resist film.
2 . The charged particle beam writing method according to claim 1 , characterized in that a charge amount is calculated based on a film thickness distribution of the resist film formed on the substrate and the function for charge amount calculation.
3 . The charged particle beam writing method according to claim 1 , characterized in that a resist film thickness measurement is performed on a regular basis,
a resist film thickness of a writing target substrate is estimated based on a change in a resist film thickness of a substrate on which the pattern has been previously written, and
a charge amount is calculated based on an estimated value of the resist film thickness and the function for charge amount calculation.
4 . A charged particle beam writing apparatus in which a deflector is caused to deflect a charged particle beam and a pattern is written by irradiating, with the charged particle beam, a substrate on which a resist film is formed, the charged particle beam writing apparatus comprising:
an emitter emitting the charged particle beam;
a pattern density calculation circuit virtually dividing a writing region of the substrate in a mesh having grid dimensions and calculating a pattern density representing an arrangement ratio of the pattern for each mesh region;
a dose calculation circuit calculating a dose representing a dose for each mesh region using the pattern density;
a storage storing a function for charge amount calculation, the function using, as variables, a film thickness of the resist film and the dose;
a charge amount calculation circuit retrieving the function from the storage, using the function, and calculating a charge amount based on the film thickness of the resist film formed on the substrate and the dose calculated by the dose calculation circuit as variable, and based upon a secondary electron yield, a permittivity, a resistivity during beam irradiation, a work function, and a positive-hole residual rate of resist, as parameters;
a position shift amount calculation circuit calculating a position shift amount of a writing position from the charge amount;
a corrector correcting, using the position shift amount, an irradiation position of the charged particle beam; and
a writer irradiating the corrected irradiation position with the charged particle beam,
wherein the function for charge amount calculation is independent of a dose sensitivity of the resist film.
5 . The charged particle beam writing apparatus according to claim 4 , characterized in that the charge amount calculation circuit calculates a charge amount based on a film thickness distribution of the resist film formed on the substrate and the function for charge amount calculation.
6 . The charged particle beam writing apparatus according to claim 4 , characterized in that the charge amount calculation circuit estimates a resist film thickness of a writing target substrate based on a change in a resist film thickness of a substrate on which the pattern has been previously written, and calculates a charge amount based on an estimated value of the resist film thickness and the function for charge amount calculation.