JP2956628B2 - Electron beam writing method and writing apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drawing method and a drawing apparatus using an electron beam, and more particularly to a drawing method and a drawing apparatus capable of improving a drawing pattern position accuracy.

[0002]

2. Description of the Related Art Along with the high integration of semiconductor devices, the circuit structure has been miniaturized. In particular, in recent large-scale integrated circuits (LSIs), the width dimension of wiring and hole patterns constituting the circuit is 0.3 μm or less. For this reason, the pattern position or connection accuracy in the electron beam direct writing used in the fabrication of the reticle (mask), which is the master of the reduced projection exposure pattern, and in the exposure process of the fine dimension pattern, is reduced by 0.04.
It is required to be less than μm. In the electron beam writing method, writing is performed at a desired position by deflecting a beam in conjunction with a sample position on a stage. At this time, the amount of deflection of the electron beam must not exceed a predetermined amount and change unintentionally. However, in reality, small changes are always occurring. This change is temporally divided into the following two. That is, one is a short-period periodic beam vibration, and the other is a beam drift that changes over a long period of time. The former beam vibration may be caused by the influence of a magnetic or electric field or a mechanical vibration in an AC power supply cycle. For example, there is a case where a current of 50 Hz to 60 Hz of electric vibration flows through a transmission line or the like, and the vibration slightly enters the drawing apparatus and is applied to the deflector. On the other hand, the latter beam drift is considered to be caused by charge-up or temperature change due to reflected electrons. Obviously, when these positional changes increase, the positional accuracy of the drawing pattern decreases.

As a method for preventing such a decrease in drawing accuracy, a number of methods have been studied conventionally, and some of them have been implemented. For example, Jpn. J. “Appl. Phys Vo
l.34 "(1995) pp. 6639-6643 describes a method for detecting a beam vibration, storing the beam vibration, and canceling the vibration by subtracting it from the deflection signal. For beam drift, there is widely known a method in which a mark is provided on a stage, the mark position is detected by an electron beam at a certain time or at a certain drawing range, and the drift is sequentially corrected using this position as a new reference position. Further, Japanese Patent Application No. 3-24387 and the drawings propose a method in which a beam drift is developed into a polynomial using time as a parameter, and a correction is made by solving the polynomial.

[0004]

As described above, minute changes in the amount of deflection of an electron beam include short-periodic periodic beam vibration and beam drift that continues to change over a long period of time. Thus, when electron beam writing is actually performed to measure and correct the beam drift, it is noticed that a certain tendency exists. The trend is
In particular, there is a tendency that the drift amount is large in an early stage of drawing, and thereafter changes are small and change slowly. Diagram of beam drift correction amount for each number of stripes (FIG. 5)
This is evident from the above. In an electron beam writing apparatus that divides the writing area of the sample into stripes with a width equal to or less than the deflection range of the electron beam and writes the sample while moving continuously in the longitudinal direction of the stripe, the timing of beam drift correction is set for each stripe. Therefore, the beam drift in one stripe at the start of writing may be 0.04 μm or more. In FIG. 5, the initial beam drift correction amount is 0.045 μm.

As described above, since the drift amount is extremely large in the initial state, in the beam drift correction for each stripe, the pattern position accuracy and the connection accuracy at the stripe boundary are low.
There was a problem that the specification of 0.04 μm could not be satisfied. In particular, in the electron beam lithography system using the continuous moving stage, there is a problem that the drift correction timing is not for each stripe because the correction cannot be performed in time, and the positional accuracy is greatly reduced. An object of the present invention is to solve such a conventional problem and to reduce a temporal change of a drift in a sample writing, thereby improving a writing position accuracy by reducing a beam drift change between drift corrections. An object of the present invention is to provide an electron beam lithography method and a lithography apparatus that can perform the lithography.

[0006]

In order to achieve the above object, the writing method of the present invention provides an electron beam writing method and an electron beam writing apparatus in which the initial beam drift does not affect the writing of a sample. That is, an object having a certain size (hereinafter, referred to as a drift absorbing portion (4)) is placed on a drawing apparatus stage (3) on which a drawing sample (2 in FIG. 2) is mounted. Before drawing on the sample (2), the drift absorbing portion (4) is irradiated with a drawing operation or an electron beam (1) that generates reflected electrons in the same amount as the drawing operation. Then, the mark (5) on the stage (3) is irradiated with the electron beam (1), and the beam drift amount is measured and corrected.
At this time, a certain threshold value is provided, and when the drift correction amount is larger than this threshold value, the drift absorbing unit (4)
After irradiating the top with the electron beam (1), the beam drift amount is measured and corrected. Then, when the beam drift correction amount becomes smaller than the threshold value, writing on the sample (2) is started for the first time. The initial drift is large at the start of irradiation and gradually decreases, so that at some point it always becomes smaller than the threshold.

In this method, it is desirable that the amount of reflected electrons from the drift absorbing portion (4) is substantially the same as that of the sample (2). Therefore, if the object (4) is made of an object having the same electron reflectance as that of the drawing sample (2) and the amount of electrons irradiated per unit time is the same as that at the time of drawing, the effect is large. That is, only in the initial period when the beam drift correction amount is large (for example, only the portion near the number of stripes 0 in FIG. 5), the object is different from the sample (2) but has the same material and shape as the sample. By writing on the sample (2) after writing on the sample (2), it is possible to reduce the beam drift change between drift corrections when writing on the sample (2), thereby improving the writing position accuracy. Can be. In particular, in an electron beam writing apparatus that divides the writing area of the sample (2) into stripes with a width equal to or less than the deflection range of the electron beam and writes the sample while moving the sample continuously in the longitudinal direction of the stripe, the width is limited to the deflection range. The effect is great when writing is performed with a pattern that is larger than the length and the same length as the writing in the drift absorbing portion whose length is equal to or larger than the writing range of the sample. By using the method and apparatus described above, it is possible to completely prevent the influence of the beam drift at the initial stage of writing on the sample, which has conventionally lowered the writing position accuracy and connection accuracy.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a flowchart of a drawing method showing one embodiment of the present invention, and FIG. 2 is a side sectional view of a drawing apparatus showing one embodiment of the present invention. In a conventional apparatus, at the start of writing, a reflected electron from a sample is rapidly generated by beam irradiation in an electron beam apparatus which has not changed until then. Therefore, the reflected electrons collide again with the optical system, the detector, and the like in the electron beam writing apparatus, and the electrons that collide with the poorly-conductive portion of the electron beam stay there, causing charge-up. When the charge-up amount increases, a new electric field is generated, which may change the trajectory of the electron beam deflecting and irradiating the sample. The beam drift amount in the initial stage of writing tends to change depending on the degree of vacuum and the use time of the apparatus, and the drift amount is not constant. For this reason, it is extremely difficult to predict and correct this. Therefore, an electron beam writing method and apparatus of the present invention have been proposed. As shown in FIG. 2, the electron beam writing apparatus according to the present invention includes an electron source section 10 for generating and accelerating an electron beam, and a forming section for transmitting an aperture while converging and deflecting the electron beam emitted from the electron source section 10. 11
An objective lens unit 12 for imaging the electron beam passing from the molding unit onto the sample 2; and a deflector 6 for deflecting the electron beam.
A stage 3 on which the sample 2 is placed and movable in two vertical directions in the sample plane, a detector 7 for detecting the amount of electrons reflected from the sample 2, and a drift correction mark for performing beam irradiation positioning 5 is provided.

The detailed operation of the present invention will be described below with reference to FIGS. First, the sample 2 is placed on the stage 3 in the vacuum sample chamber to prepare for writing, as in the case of the conventional writing (step 101 in FIG. 1). Subsequently, the drift absorber 4 of the present invention is irradiated with an electron beam to draw a predetermined pattern (step 102). Next, stage 3
To move the electron beam 1 onto the drift correction mark 5.
Is scanned by the deflector 6, and the reflected electron detector 7 detects the amount of reflected electrons on the mark. At this time, the mark position can be detected from the position of the laser interferometer 8 and the amount of deflection of the electron beam. Then, by examining the change in the mark position from a certain point in time, the beam drift amount can be detected. That is, although the beam actually drifts, the amount of drift is measured by viewing the drift as a change in the mark position.

Then, the obtained beam drift amount (Δ
A value (−Δx, −Δy) obtained by inverting the sign of (x, Δy) is given to the deflector 6 as a drift correction amount (step 10).
3). In the present invention, a certain threshold value is provided for the drift correction amount. If the drift correction amount is equal to or larger than the threshold value (step 104), the stage 3 is moved to the drift absorbing section 4 again, and the electron beam 1 is irradiated to draw a predetermined pattern (step 102). The drift correction amount is determined and correction is performed (step 103). This operation is repeated until the drift correction amount becomes equal to or less than the threshold. Then, if the drift correction amount becomes equal to or less than the threshold value (step 10).
4), actual drawing of the sample is started (step 105). Although omitted in the flow of FIG. 1, as will be described later, even during the writing of the sample, a certain time or the writing area
Detect beam drift every time (stripe) ends,
By repeating the sequential correction, the pattern connection accuracy and the position accuracy are improved.

FIG. 3 is a perspective view of the periphery of a stage of an electron beam writing apparatus according to the present invention. This shows a state in which chromium called a reticle 2 for a reduced projection exposure apparatus is mounted on a stage 3 of an electron beam lithography apparatus as a sample, and a quartz plate on a sputtered mirror surface is mounted. The reticle 2 has a thickness of about 6.4 mm and a size of 150 mm square. Now, a semiconductor pattern is drawn on the reticle surface with a drawing area of about 130 mm square. This pattern has a position accuracy of 0.04 μm and a connection accuracy of 0.03 μm.
In the connection accuracy, since a connection error between the divided stripes between patterns is generally large, the error tolerance is indicated as the accuracy. Further, when a plurality of deflectors are provided in one drawing apparatus and writing is performed in an optimum combination according to the deflection range and the speed, the connection accuracy is shown for each deflection range of each deflector. On the stage, a reticle cut out to a width of 10 mm and a length of 150 mm separately from the sample is placed as a beam drift absorbing portion 4 in the longitudinal direction in the Y direction. This reticle has a quartz plate on a mirror surface on which chromium has been sputtered, and is the same as sample 2 in material and thickness (about 6.4 mm). This drawing apparatus is capable of drawing while continuously moving in the Y direction, and has a maximum deflection area of 2 mm.

FIG. 4 is a diagram of a beam drift correction amount when drawing by the method of the present invention, and FIG. 5 is a diagram of a beam drift correction amount drawn by a conventional method for comparison. In drawing, first, the stage 3 was moved, and the beam was scanned on the drift correction mark 5 to determine the origin of the beam drift. Then, the stage was moved to the beam drift absorber 4. Next, while the stage 3 was continuously moved in the Y direction on the drift absorbing portion 4, writing with a deflection width of 2 mm and the same pattern density as the sample writing was performed. After this drawing, the stage 3 was moved to detect the amount of drift correction, which was 0.043 μm. In this drawing, since the threshold value of the drift correction amount was set to 0.030 μm, the drawing was performed again by the beam drift absorption unit 4. After this drawing, when the drift correction amount was detected, it was 0.023 μm. Since this value is equal to or smaller than the threshold value, drawing of the sample 2 was started next. Sample 2 had 65 stripes, and the beam drift was corrected every time one stripe was drawn. The correction amount was 0.030 μm or less as shown in FIG. In addition, both the pattern position error and the connection error variation after drawing
It was 0.030 μm or less. FIG. 5 shows the drift correction amount when the sample 2 is drawn by the conventional method without drawing by the beam drift absorption unit 4. As is clear from this example, the beam drift correction amount after writing the first stripe is as large as 0.045 μm, and the pattern position error and the connection accuracy variation when measured after writing are 0.04 μm.
That's all. In FIG. 5, the beam drift correction amount after the second stripe writing is also 0.032 μm.
In order to write the target sample 2, the first drift correction is performed by the beam drift absorption unit 4, and if the writing of the sample 2 is started after the second drift correction, the drift correction amount becomes equal to or less than the threshold value.

In this embodiment, after the writing operation is performed by the beam drift absorbing section 4, the change in the irradiation position of the electron beam is obtained, and after the value becomes equal to or less than a predetermined value, the writing of the sample 2 is performed. However, if it is known that if the irradiation is performed for a certain period of time and the drift correction amount is equal to or less than the threshold value without applying the above-described determination each time, the beam drift absorption unit 4 It goes without saying that the writing of the sample 2 can be started immediately after performing the writing operation for a certain period of time.

[0014]

As described above, according to the writing method and the writing apparatus of the present invention, the drift in the initial stage of writing does not affect the writing of the sample, so that the positional accuracy and connection accuracy of the written pattern are improved. This has the effect.

[Brief description of the drawings]

FIG. 1 is an operation flowchart of an electron beam writing method according to an embodiment of the present invention.

FIG. 2 is a side sectional view of an electron beam writing apparatus showing one embodiment of the present invention.

FIG. 3 is a detailed perspective view around a stage of the electron beam writing apparatus of the present invention.

FIG. 4 is a diagram showing a beam drift correction amount when writing is performed by the method of the present invention.

FIG. 5 is a diagram showing a beam drift correction amount when writing is performed by a conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electron beam, 2 ... Sample, 3 ... Stage, 4 ... Drift absorption part, 5 ... Drift correction mark, 6 ... Deflector, 7
... A backscattered electron detector, 8 a laser interferometer, 10 an electron source section, 11 a molding section, 12 an objective lens section.

Continuation of the front page (56) References JP-A-10-22195 (JP, A) JP-A-7-142321 (JP, A) JP-A-7-86143 (JP, A) JP-A-63-308317 (JP) , A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01L 21/027 G03F 7/20

Claims (4)

(57) [Claims] An electron beam drawing method for irradiating an electron beam on a sample while deflecting the sample to draw a desired pattern, the method comprising: irradiating an electron beam on a position different from the sample to perform a drawing operation; An electron beam writing method, wherein writing is performed on the sample. 2. An electron beam writing method for irradiating an electron beam on a sample while deflecting the electron beam and writing a desired pattern, after irradiating the electron beam to a position different from the sample to perform a writing operation, An electron beam writing method, comprising: obtaining a change amount of the irradiation position of the electron beam; and starting writing of the sample after the change amount of the beam position becomes equal to or less than a predetermined value. 3. An electron source section for generating an electron beam and accelerating the generated electron beam, a forming section for transmitting an aperture while converging and deflecting the electron beam emitted from the electron source section; An objective lens unit that forms an image of the passed electron beam on a sample, a deflector that deflects the electron beam onto the sample, a stage on which the sample is mounted and movable in two vertical directions in the sample plane, An electron beam lithography system having a detector for detecting the amount of electrons reflected from the sample and a mark for performing beam irradiation positioning, wherein the stage can be irradiated with an electron beam and has the same material composition as the sample. An electron beam writing apparatus characterized by providing an object. 4. The electron beam writing apparatus according to claim 3, wherein said object has a width not less than a deflection range of an electron beam and a length not less than a drawing range of a sample.