JP2007049023A - Electron beam writing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance reliability of an apparatus by preventing the image of a crossover from being formed at an undesired position when driving conditions of a plurality lenses are altered. <P>SOLUTION: Image of electrons emitted from an electron gun is formed on a first aperture by means of first and second electron lenses, a second aperture is irradiated with a beam passed through the first aperture, and a sample is irradiated with a beam shaped by the second aperture. In such an electron beam writing method, a first characteristic curve dependent on the lens drive conditions for forming the image of a crossover on the first aperture, and second characteristic curve dependent on the lens drive conditions for forming the image of a crossover on the second aperture are determined. When the drive conditions of first and second electron lenses are altered so as to alter the current density of a beam with which the sample is irradiated, order for altering the drive conditions of first and second electron lenses is selected such that respective drive conditions of alteration process do not touch the second characteristic curve. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electron beam drawing method, and more particularly to an electron beam drawing method in which a method for changing a driving condition of an electron lens is improved.

  In recent years, various electron beam drawing apparatuses have been used for forming fine patterns such as LSIs. The optical system of this device is composed of an electron gun, various electromagnetic lenses, various aperture masks, various deflectors, etc., and the electrons emitted from the electron gun are focused by the lens, shaped by the aperture, and further on the sample by the deflector. The desired position is irradiated (see, for example, Patent Document 1).

  As a means for changing the current density of the electron beam irradiated on the sample, there is a system for adjusting the current density on the aperture using a two-stage electromagnetic lens. Specifically, a first lens, a second lens, a first aperture (beam limiting aperture), and a second aperture (beam shaping aperture) are arranged in this order from the electron gun side, and the first and second lenses are used. A crossover is imaged on one aperture.

However, this type of method has the following problems. That is, when the excitation conditions for the first and second lenses are changed, the crossover position moves up and down. Even when the crossover is imaged on the first aperture, the crossover may be temporarily imaged on the second aperture in the changing process. When the crossover is imaged on the second aperture, a strong beam is irradiated on the second aperture. The second aperture is generally formed of a material with good workability in order to maintain dimensional accuracy, and heat resistance is not so much considered. For this reason, there arises a problem that the second aperture is melted.
Japanese Patent Laid-Open No. 11-8176

  As described above, in the conventional electron beam drawing method, when the lens driving condition is changed in order to change the current density of the electron beam, a crossover is imaged on the second aperture mask such as a beam shaping aperture. As a result, there is a problem that the second aperture mask is dissolved and deformed.

  The present invention has been made in consideration of the above circumstances. The purpose of the present invention is to form a crossover at a position where it is not desired to form an image when changing the driving conditions of a plurality of lenses. An object of the present invention is to provide an electron beam writing method that can be prevented in advance and can contribute to the improvement of device reliability.

  In order to solve the above problems, the present invention adopts the following configuration.

  In other words, one aspect of the present invention is an electron beam drawing method in which an electron beam emitted from an electron gun is shaped by a plurality of electron lenses and an aperture mask, and the shaped beam is irradiated onto a sample. The first characteristic curve determined by the relationship between the driving condition of the first electron lens and the driving condition of the second electron lens for imaging the crossover at the first position is obtained, and the first characteristic curve that is not desired to be imaged is obtained. A second characteristic curve determined by the relationship between the driving condition of the first electron lens and the driving condition of the second electron lens for forming an image of the crossover at the position 2 is obtained, and the first and second electron lenses are obtained. When changing each driving condition in order to move the driving condition from a predetermined point of the first characteristic curve to a different position, each driving condition in the changing process does not touch the second characteristic curve. First and second electrons And selecting a sequence for changing the lens driving conditions.

  According to another aspect of the present invention, electrons emitted from the electron gun are imaged on the first aperture mask by the first and second electron lenses, and the beam that has passed through the first aperture mask is reflected on the first aperture mask. An electron beam writing method for irradiating on a second aperture mask and irradiating a sample with a beam formed by the second aperture mask, the first for imaging a crossover on the first aperture mask Driving the first electron lens to obtain a first characteristic curve determined by the relationship between the driving condition of the second electron lens and the driving condition of the second electron lens, and to image the crossover on the second aperture mask In order to obtain a second characteristic curve determined by the relationship between the conditions and the driving conditions of the second electron lens, and to change the current density of the beam irradiated on the sample, the driving conditions of the first and second electron lenses The first When changing from a predetermined point of the characteristic curve to a different point, the order of changing the driving conditions of the first and second electron lenses is selected so that each driving condition in the changing process does not touch the second characteristic curve It is characterized by doing.

  According to the present invention, a first characteristic curve that is a condition for forming an image of a crossover at a first position and a second characteristic curve that is a condition for forming an image of a crossover at a second position are obtained, When changing the driving conditions of the first and second electron lenses, it is desired to form an image by selecting the order of changing the driving conditions so that each driving condition in the changing process does not touch the second characteristic curve. It is possible to prevent the crossover from being imaged at the second position that is not present. Therefore, it is possible to prevent a crossover from being imaged on a beam shaping aperture mask or the like, thereby causing the aperture mask to be melted or deformed, thereby contributing to improvement in device reliability.

  The details of the present invention will be described below with reference to the illustrated embodiments.

(First embodiment)
FIG. 1 is a diagram showing a main part configuration of an optical system of an electron beam lithography apparatus used in the method of the first embodiment of the present invention.

  In the figure, reference numeral 11 denotes an electron gun. Electrons emitted from the electron gun 11 are focused by a first-stage lens (first electron lens) 21 and a second-stage lens (second electron lens) 22, and are A crossover is imaged on the limiting aperture mask (first aperture mask) 31. The lenses 21 and 22 are electromagnetic lenses, and the focus position can be changed by an excitation current. The beam limiting aperture mask 31 is made of platinum having high resistance to the beam.

  The crossover imaged on the beam limiting aperture mask 31 is irradiated to a beam shaping aperture mask (second aperture mask) 32. The beam shaping aperture mask 32 has, for example, a rectangular opening, and a beam that has passed through the opening is irradiated onto a sample surface (not shown). Further, the beam shaping aperture mask 32 is made of, for example, silicon because high accuracy of the opening dimension is required.

  Note that the material of the beam shaping aperture mask 32 is not necessarily limited to silicon, but it is desirable that the beam shaping aperture mask 32 be easy to work in order to ensure sufficient dimensional accuracy. Further, when the beam shaping aperture mask 32 is formed of platinum in the same manner as the beam limiting aperture mask 31, the plate thickness may be sufficiently reduced in order to maintain high accuracy of the opening dimension.

  In the above configuration, the crossover imaging position changes depending on the excitation conditions of the lenses 21 and 22. FIG. 2 is a diagram showing a relationship between the excitation current of the first-stage lens 21 and the excitation current of the second-stage lens 22 where the crossover is imaged on a predetermined position, for example, the beam limiting aperture 31.

  Now, it is assumed that the excitation currents of the lenses 21 and 22 are set so as to satisfy the relationship shown in FIG. 1, and the crossover imaging relationship is as shown by a solid line in FIG. If the excitation of the first-stage lens 21 is weakened from this state, the imaging relationship represented by the solid line becomes like a one-dot chain line, and the crossover shifts downward. In order to correct this, the excitation of the second-stage lens 22 is strengthened, and a crossover is formed on the beam limiting aperture mask 31 as indicated by the broken line in FIG. Then, as shown in the drawing, the irradiation area on the beam shaping aperture mask 32 becomes small, and as a result, the current density of the beam irradiated on the sample increases.

  FIG. 3 is a diagram illustrating the relationship between the excitation currents of the lenses 21 and 22 for forming a crossover image at a predetermined position. The solid line in the figure is a plot of the relationship between the excitation currents of the lenses 21 and 22 for forming a crossover on the position to be imaged, that is, the beam limiting aperture mask 31 (first characteristic curve). ). The broken line in the figure is a plot of the relationship between the excitation currents of the lenses 21 and 22 for forming a crossover on the beam shaping aperture mask 32 where the image is not desired to be imaged (second characteristic). Curve).

  In the present embodiment, basically, it is used under the condition that a crossover is imaged on the beam limiting aperture mask 31, but in order to change the beam current density on the sample, each of the lenses 21 and 22 is excited. It is necessary to change the area of the beam on the beam shaping aperture mask 32 by changing the conditions. At this time, if the excitation currents of the lenses 21 and 22 are simultaneously controlled, the system becomes complicated and unnecessarily increases in cost. Therefore, it is common to change the excitation current of the other lens after changing the excitation current of one lens. Is.

  Therefore, for example, after the excitation current of the first-stage lens 21 at point A is changed to point B, the excitation current of the second-stage lens 22 is changed from point A to point B. In this case, in the process of setting the excitation current of the first-stage lens 21 to point B, the excitation current value crosses the second characteristic curve, and the crossover is temporarily imaged on the beam shaping aperture mask 32. become. Since the beam shaping aperture mask 32 has low resistance to the beam, if the crossover is imaged in this portion, the aperture mask 32 is melted or deformed.

  On the other hand, the excitation current of the second-stage lens 22 at the point A is changed from the point B to the point B after the excitation current of the first-stage lens 21 is changed from the point A to the point B. In this case, the crossover is not imaged on the beam shaping aperture mask 32 in the process of setting the excitation current of the second-stage lens 22 to the point B. Therefore, it is possible to prevent inconveniences such as a crossover imaged on the beam shaping aperture mask 32 and causing the aperture mask 32 to be melted or deformed.

  When changing the setting from point B to point A, if the setting of the second stage lens is changed after the setting of the first stage lens is changed first, the aperture mask 32 will not be dissolved or deformed.

  As described above, when the excitation current is changed from the point A to the point B of the first characteristic curve, if the excitation current of the second-stage lens 22 is changed first, the beam is crossed on the aperture mask 32 for beam shaping. Over-image formation can be prevented in advance, and the aperture mask 32 can be prevented from being melted or deformed. When the excitation current is changed from point B to point A, if the excitation current of the first-stage lens 21 is changed first, the crossover is imaged on the beam shaping aperture mask 32. It can be prevented beforehand. That is, when the excitation conditions of the lenses 21 and 22 are changed, the order of change is selected based on the first and second characteristic curves, so that the beam shaping aperture mask 32 can be prevented from being melted or deformed. This makes it possible to improve device reliability.

(Second Embodiment)
FIG. 4 is a cross-sectional view showing the configuration of the main part of the optical system of the electron beam drawing apparatus used in the method of the second embodiment of the present invention. The apparatus configuration is basically the same as the apparatus shown in FIG.

  In the first embodiment, a crossover is formed between the first-stage lens 21 and the second-stage lens 22, but in this embodiment, a crossover is formed between these lenses 21 and 22. Instead, the crossover is imaged on the beam limiting aperture mask 31.

  Now, it is assumed that the excitation currents of the lenses 21 and 22 are set so as to satisfy the relationship shown in FIG. 4, and the image formation relationship of the crossover is as shown by a solid line in FIG. From this state, if the excitation of the first-stage lens 21 is weakened, the imaging relationship represented by the solid line moves outward as indicated by the alternate long and short dash line. In this state, since the crossover moves from the beam limiting aperture mask 31 toward the beam shaping aperture mask 32, the excitation of the second-stage lens 22 is strengthened so that the crossover is formed on the beam limiting aperture mask 31. . Then, as indicated by the broken line in the figure, the irradiation area on the beam shaping aperture mask 32 increases, and the current density decreases.

  FIG. 5 is a diagram illustrating the relationship between the excitation currents of the lenses 21 and 22 for forming a crossover image at a predetermined position. The solid line in the figure plots the relationship between the excitation currents of the lenses 21 and 22 for forming a crossover on the position to be imaged, that is, on the beam limiting aperture mask 31. The broken line in the figure plots the relationship between the excitation currents of the lenses 21 and 22 for forming an image of the crossover on the position where the image formation is not desired, that is, on the beam shaping aperture mask 32.

  In the case of the present embodiment as well, as in the first embodiment, after changing the excitation current of the first-stage lens 21 at point A to point B, the excitation current of the second-stage lens 22 is changed from point A to point B. When changing, the crossover is temporarily imaged on the beam shaping aperture mask 32 in the process of setting the exciting current of the first-stage lens 21 to the point B. On the contrary, when the excitation current of the first-stage lens 21 is changed from the A point to the B point after changing the excitation current of the second-stage lens 22 at the A point to the B point, the second stage lens 22 In the process of setting the excitation current to point B, the crossover is not imaged on the beam shaping aperture mask 32.

  As described above, also in this embodiment, when changing the excitation conditions of the lenses 21 and 22, the order of change is selected based on the first and second characteristic curves. By changing the excitation current of the eye lens 22 first, it is possible to prevent inconveniences such as melting and deformation of the beam shaping aperture mask 32. Therefore, the same effect as the first embodiment can be obtained.

(Modification)
In addition, this invention is not limited to each embodiment mentioned above. In the embodiment, the order of changing the excitation currents of the two-stage lenses is changed. However, it is only necessary to prevent the crossover from being imaged on the beam shaping aperture mask in the process of changing the excitation current. The exciting current of the lens may be changed stepwise.

  Further, when the first and second characteristic curves have special shapes as shown in FIG. 6, when the point A is changed to the point D, the second characteristic is simply selected by selecting the change order of the excitation current. It is inevitable to touch the curve. In such a case, as indicated by A → B → C → D in the figure, the excitation current may be changed stepwise and the order of change may be changed as appropriate. The point is that the first characteristic curve determined by the excitation conditions of the first and second stage lenses for imaging the crossover at the first position to be imaged and the second position not to be imaged. If there is a second characteristic curve determined by the excitation conditions of the first and second lenses for imaging the crossover, the excitation conditions in the changing process do not touch the second characteristic curve. What is necessary is just to set the order which changes the excitation conditions of the 1st step | paragraph and the 2nd step | paragraph lens.

  Further, the position where the crossover is not desired to be imaged is not necessarily limited to the position on the beam shaping aperture mask, but may be a position where it is desired to avoid irradiation of a focused beam having a high current density.

  In the embodiment, an electromagnetic lens is used as the electronic lens, but an electrostatic lens can also be used. In this case, the applied voltage may be changed instead of the excitation current. Further, the electron lens whose driving conditions are to be changed is not necessarily limited to two stages, and may be three or more stages.

  In addition, various modifications can be made without departing from the scope of the present invention.

The figure which shows the principal part structure of the optical system of the electron beam drawing apparatus used for the method of 1st Embodiment. The figure which shows the relationship between the excitation current of a 1st lens, and the excitation current of a 2nd lens in which a crossover is imaged in a predetermined position. The figure which shows the relationship of the excitation current of each lens in order to image a crossover on the 1st, 2nd aperture mask in the structure of FIG. The figure which shows the principal part structure of the optical system of the electron beam drawing apparatus used for 2nd Embodiment method. FIG. 5 is a diagram showing a relationship between excitation currents of respective lenses for forming a crossover on the first and second aperture masks in the configuration of FIG. 4. The figure for demonstrating the modification of this invention.

Explanation of symbols

11 ... electron gun 21 ... first stage lens (first electron lens)
22 ... Second stage lens (second electron lens)
31 ... Aperture mask for beam limiting (first aperture mask)
32 ... Aperture mask for beam shaping (second aperture mask)

Claims (5)

An electron beam writing method in which an electron beam emitted from an electron gun is shaped by a plurality of electron lenses and an aperture mask, and the shaped beam is irradiated onto a sample,
Obtaining a first characteristic curve determined by the relationship between the driving condition of the first electron lens and the driving condition of the second electron lens for imaging the crossover at the first position to be imaged;
Obtaining a second characteristic curve determined by the relationship between the driving condition of the first electron lens and the driving condition of the second electron lens for forming an image of the crossover at the second position where the image is not desired to be imaged;
When the driving conditions of the first and second electron lenses are changed in order to move the driving conditions from a predetermined point of the first characteristic curve to different positions, the driving conditions of the changing process are the second driving conditions. An electron beam writing method comprising: selecting an order of changing driving conditions of the first and second electron lenses so as not to contact the characteristic curve. The electrons emitted from the electron gun are imaged on the first aperture mask by the first and second electron lenses, the beam that has passed through the first aperture mask is irradiated onto the second aperture mask, and the second An electron beam writing method for irradiating a sample with a beam formed with an aperture mask of
Determining a first characteristic curve determined by a relationship between a driving condition of the first electron lens and a driving condition of the second electron lens for forming an image of the crossover on the first aperture mask;
Obtaining a second characteristic curve determined by the relationship between the driving condition of the first electron lens and the driving condition of the second electron lens for imaging the crossover on the second aperture mask;
When changing the driving conditions of the first and second electron lenses from a predetermined point of the first characteristic curve to a different point in order to change the current density of the beam irradiated onto the sample, each of the changing processes An electron beam drawing method, wherein the order of changing the driving conditions of the first and second electron lenses is selected so that the driving conditions do not contact the second characteristic curve.   The first aperture mask is made of a material having better beam resistance than the second aperture mask, and the second aperture mask is made of a material that is more workable than the first aperture mask. The electron beam drawing method according to claim 2, wherein:   3. The electron beam writing method according to claim 2, wherein the first and second aperture masks are formed of the same material, and the second aperture mask is formed thinner than the first aperture mask.   The electron beam drawing method according to claim 1, wherein the change of the driving conditions of the first and second electron lenses is divided into multiple stages.

Images