JP3364367B2 - Charged beam drawing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charged beam drawing method for drawing a fine pattern such as ULSI on a sample surface.

[0002]

2. Description of the Related Art Conventionally, an electron beam drawing apparatus has been used for drawing a desired fine pattern on a sample surface such as a semiconductor wafer. Among these, the electron beam drawing apparatus in which the beam size is variable has a feature that the drawing throughput is remarkably higher than that of the apparatus of the fixed beam size system.

In the variable-shaped beam electron beam drawing apparatus, it is necessary to adjust the beam size so that the set beam size and the actual beam size match. The beam size is adjusted by first adjusting the sides of the first shaping aperture and the second shaping aperture so as to be parallel to the reference coordinates, as shown in, for example, JP-A-63-237526. The beam current is changed and measured with a Faraday cup or the like. The rotation of the aperture is adjusted so that the increase of the beam current becomes a straight line with respect to the change of the beam size, and the offset amount is obtained from the value which the straight line crosses at the set beam size of zero. Then, correction is performed based on this offset amount so that an actual beam having the set beam size can be obtained.

[0004]

However, in the above-mentioned electron beam drawing apparatus, the electron optical lens barrel (hereinafter referred to as EOS) is used.
It is known that electric charge accumulates in ((Electron Optical System)) (hereinafter referred to as charge-up), and so-called beam drift occurs in which the orbit of an electron beam changes. When beam drift due to charge-up occurs inside the shaping deflector that controls the beam size, the position of the first aperture image on the second shaping aperture drifts, and the actual beam size deviates from the set beam size. . This means that the offset changes as a function of time (hereinafter referred to as offset drift), and this offset drift changes for a very short time and saturates for a short time, and for a few hours, it becomes sloppy. And a slightly varying long-term offset drift. The influence of this offset drift on the drawing pattern becomes more significant as the pattern becomes finer. For example, when the offset drift is 0.01 μm (on the sample surface), the error is 2% (0.01 / 0.5) in the drawing pattern of the 0.5 μm rule, but the fine pattern is 0.1 μm. In the rule drawing pattern, there is an error of 10% (0.01 / 0.1).

If charge-up occurs in the objective lens or in the resist on the sample, the beam size does not change but the beam position changes. In order to eliminate such a beam position error, the electron beam irradiation position is measured at regular intervals during the drawing of the desired pattern and the drift amount is adjusted by adjusting the deflection amount of the electron beam according to the amount of drift. By doing so, it is possible to prevent a decrease in drawing accuracy (see, for example, Japanese Patent Laid-Open No. 5-304080). This method is effective when the drift occurs relatively slowly, but it is difficult to correct the offset drift for a short time. For this reason, so-called dummy irradiation is performed in which a beam is irradiated onto a place outside the material to be drawn and a desired pattern is drawn for a time such that the drift of the beam is relatively stable before drawing the actual pattern.

However, this method has a drawback that the actual beam size during writing cannot be correctly controlled because it has no effect on the drift that changes the beam size. That is, there is a problem that the beam size measured at the time of beam adjustment changes due to the offset drift, and it is unknown how much the beam size is set during writing even if the value becomes stable in time.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a charged beam drawing method which can contribute to improvement of drawing accuracy of a fine pattern.

[0008]

According to a charged beam drawing method of the present invention, a charged beam passing through a first shaping aperture is deflected, and a size of a charged beam passing through a second shaping aperture is controlled to perform variable shaping. In a charged beam drawing method of forming a beam and drawing a desired pattern on a sample by this beam, a step of obtaining an offset drift amount of the charged beam, a step of setting a charged beam size to a target beam size, It is characterized by including a step of correcting the set target beam size in consideration of the offset amount, and a step of drawing based on the corrected target beam size.

The offset drift amount may be updated when the total drawing time exceeds a predetermined value.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a charged beam drawing method according to the present invention will be described below with reference to the drawings.

FIG. 7 is a view showing the arrangement of an electron beam drawing apparatus to which the charged beam drawing method of this embodiment is applied. The electron beam emitted from the electron gun 101 is applied to the first shaping aperture 103 by the condenser lens 102. The image of the first shaping aperture 103 is formed on the second shaping aperture 105 by the projection lens 104. The beam size can be changed by controlling the degree of overlap between the two apertures 103 and 105 by the beam shaping deflector 106. The image formed by the overlapping of the apertures 103 and 105 is the reduction lens 107.
And is reduced by the objective lens 108 to form an image on the sample 109. The beam position on the sample surface is controlled by the main deflector 110. The sample 109 is installed on the movable stage 113 together with the Faraday cup 111 and the beam size measurement mark base 112, and the sample 109 or the Faraday cup 11 is moved by moving the stage.
1 or the beam size measuring mark base 112 can be selected.

Next, a charged beam drawing method using this electron beam drawing apparatus will be described below.

Before specifically explaining the charged beam drawing method, an offset drift for changing the beam size will be described. The measurement result of this offset drift is shown in FIG.
Shown in. When the electron beam blocked by the blanking aperture (not shown) is applied to the blanking electrode (not shown) by the voltage application (or the voltage release) to reach the sample 109, the beam shaping deflector 10
6 Charge accumulates inside and eventually becomes saturated. The charge accumulated in the deflector 106 causes a change in the trajectory of the beam directed onto the sample. The state of this variation can be known by measuring the beam current with the Faraday cup 111 installed on the movable stage 113. The measurement result shown in FIG. 8 plots the beam current with respect to the time axis, and shows how the shape of the beam formed by the beam forming deflector 106 changes after the blanking is released. It can be seen from FIG. 8 that in the electron beam writing apparatus to which the writing method of the present embodiment is applied, the offset drift is almost saturated within a few minutes, and then very slowly increases little by little. On the other hand, when the blanking is applied again, the accumulated charge reaches almost zero over almost the same time, and then completely reaches zero over time.

On the other hand, since the net time for irradiating the sample surface 109 with the beam for adjusting the beam size is several seconds, the beam shaping deflector 106 is used during this time.
Almost no charge is accumulated inside, and offset drift does not occur. However, once the drawing is started, the beam is reflected on the sample 10 by repeating blanking / unblanking.
Irradiation is performed on the 9th surface, but since the blanking time is extremely short, it is effectively equivalent to irradiating the beam on the sample 109 at all times, and the offset drift is almost saturated in a few minutes, and then the Gradually increase to.

Therefore, in order to accurately manage the beam size at the time of writing, it is necessary to correct the short-time offset drift that occurs at least for a certain period of time, and to correct the long-term offset drift when high accuracy is required. It turns out that is necessary.

FIG. 3 shows the first shaping aperture image 2 when the beam size is set to zero assuming that there is no offset drift for a short time even after drawing after the beam size adjustment.
3 shows the positional relationship between the second shaping aperture 8 and the second shaping aperture 8. Since the beam size is zero, there is no optical overlap between the two apertures, and the sample 109 is not irradiated with the electron beam.

However, in general, when writing is started after beam adjustment, offset drift occurs as described above, so that the dimensions of ΔX and ΔY are set even though the beam dimension is set to zero as shown in FIG. Is generated, and the sample 109 is irradiated with the electron beam. Therefore, the short-time offset drifts of ΔX and ΔY are obtained in advance (for the obtaining method, refer to the patent application invented by the present inventor and filed on the same day by the present applicant). Next, the beam size is adjusted in consideration of these drift amounts,
That is, when the offset drift as shown in FIG. 4 occurs, the beam position is previously shifted to the positions of −ΔX and −ΔY (see FIG. 5). As a result, the first shaping aperture image 2 becomes the correct position (ΔX, ΔY) = (0, 0) (the position shown in FIG. 3) after the offset drift, and the target beam size is obtained at the time of drawing. Note that, here, for ease of understanding, the first shaping aperture image 2 is
Although it was explained that they are shifted by -ΔX and -ΔY without overlapping with the shaping aperture 8, the beam size or beam position is measured by the Faraday cup as the amount of the electron beam generated by the overlapping of the first and second apertures reaching the sample surface. Then do.

In practice, first, the short-time offset drift amount is obtained as described above (see step F1 in FIG. 1). Next, the first shaping aperture image is superimposed on the second shaping aperture to form a beam of size X × Y (see step F2 in FIG. 1). Next, the beam size is adjusted in consideration of the calculated offset drift amount (ΔX, ΔY) for a short time (see step F3 in FIG. 1). That is (X-Δ
The beam size is determined to be (X) × (Y−ΔY) (see FIG. 2). Whether or not the corrections of ΔX and ΔY have been performed correctly can be confirmed from the increase / decrease in the amount of current measured on the sample surface and the deflector sensitivity that controls the position of the first shaping aperture image.
Then, drawing is performed (see step F4 in FIG. 1).

By the way, the amount of the short-time offset drift described above gradually increases as the operating time of the electron beam drawing apparatus increases. FIG. 6 shows how the short-time offset drift increases with respect to the number of operating days. This is the result of an experimental investigation on whether to do it. This is a plot of the beam size variation after 3 minutes have elapsed since the beam irradiation was started on the sample surface after the beam size adjustment. It is considered that this increase variation is caused by the carbon contamination adhering to the inside of the deflector gradually increasing with the time of use, but with the current EOS, this contamination cannot be suppressed to zero. As can be seen from FIG. 6, since the short-time offset drift gradually increases, it is necessary to timely measure the offset drift amount and update the correction value (see steps F5 and F6 in FIG. 1). That is, when the integrated value of the drawing time is less than or equal to the predetermined value, the drawing is continued, and when it exceeds the predetermined value, the offset drift amount is obtained again, and the above is repeated. As a result, a charged beam drawing method that is stable and reliable even when the dimensional accuracy is always high can be provided.

On the other hand, the long-term offset drift also gradually increases, though slightly. Therefore, when it is necessary to accurately control the beam dimension at the time of drawing, the long-term offset drift amount is also measured and the method described above is used. Similarly, the beam size must be set to a value different from the adjusted size.
In this way, it is possible to perform drawing with extremely accurate beam size control during drawing.

In the drawing method described above, offset drift occurs due to the charges accumulated inside the beam shaping deflector. Therefore, in order to correct this offset drift, it is necessary to saturate the electric charge and substantially saturate the offset drift. For this purpose, it should be clearly stated that it is indispensable to charge up the inside of the deflector by irrelevant to the original drawing, for example, dummy drawing, or drawing that does not require accuracy even if it is related.

[0022]

According to the present invention, the amount of drift that occurs after beam size adjustment is measured, and the beam size is adjusted to include this value, so that the actual size of the beam at the time of writing can be managed correctly. it can. Therefore, extremely accurate pattern drawing can be performed. Further, the offset drift amount is measured at every moment, the drift amount is updated, and the beam adjustment is performed, so that it is possible to provide a stable and highly reliable drawing method with higher drawing accuracy (dimensional accuracy).

[Brief description of drawings]

FIG. 1 is a flowchart showing a drawing procedure of a drawing method according to the present invention.

FIG. 2 is a diagram for explaining adjustment of a beam dimension by the drawing method of the present invention.

FIG. 3 is a schematic diagram showing the positional relationship between the first shaping aperture image and the second shaping aperture when the beam dimension is set to zero when there is no beam drift after the beam dimension adjustment.

FIG. 4 is a schematic diagram showing that the positional relationship between the first shaping aperture image and the second shaping aperture changes even if the beam dimension is set to zero due to a beam drift at the time of drawing after the beam dimension adjustment.

FIG. 5 is a schematic diagram showing a positional relationship between the first shaping aperture image and the second shaping aperture when the beam drift is shifted in advance.

FIG. 6 is a graph showing experimental results showing that the short-time offset drift increases as the number of working days increases.

FIG. 7 is a schematic configuration diagram of an electron beam drawing apparatus.

FIG. 8 is a diagram showing measurement results of offset drift.

[Explanation of symbols]

2 First shaping aperture 2a First shaping aperture image at the start of drawing 2b Target first shaping aperture image 8 Second shaping aperture image 101 electron gun 102 Condenser lens 103 First forming aperture 104 projection lens 105 Second Forming Aperture 106 beam shaping deflector 107 Reduction lens 108 Objective lens 109 sample surface 110 Main deflector 111 Faraday Cup 112 Beam size measurement mark stand 113 movable stage

─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-7-74071 (JP, A) JP-A-6-188180 (JP, A) JP-A-61-49420 (JP, A) JP-A-7- 122471 (JP, A) JP-A-9-63933 (JP, A) JP-A-5-166708 (JP, A) JP-A-5-304080 (JP, A) JP-A-63-237526 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/027 G03F 7/20 G03F 9/00

Claims (3)

(57) [Claims] 1. A variable shaped beam is formed by deflecting a charged beam that has passed through a first shaping aperture and controlling the size of the charged beam that has passed through a second shaped aperture to form a variable shaped beam on a sample. In the charged beam drawing method for drawing a desired pattern, the step of obtaining a short-time offset drift amount of the charged beam, the step of setting the dimension of the charged beam to a target beam dimension, and the obtained short-time offset drift amount In consideration of the above, a charged beam drawing method comprising: a step of correcting the set target beam size and a step of drawing based on the corrected target beam size. 2. The charged beam drawing method according to claim 1, wherein the short-time offset drift amount is updated when an integrated value of drawing times exceeds a predetermined value. 3. The charged beam drawing method according to claim 1, wherein the drawing is performed after the charged beam reaches the sample surface or on a stage on which the sample is placed for a certain period of time or longer. .