KR101928394B1 - Method of measuring resolution of charged particle beam and charged particle beam writing apparatus - Google Patents

Abstract

A method for measuring a resolution of a charged particle beam according to an aspect of the present invention includes the steps of changing a focus position of a charged particle beam in a height direction and scanning a dot mark formed on the substrate with the charged particle beam for each focus position, The method comprising the steps of: detecting reflected charged particles reflected from the dot mark for each focus position; calculating scattered charged particle distribution from the detection result of the reflected charged particles for each height corresponding to the focus position; A step of carrying out a convolution operation of an approximate expression of the beam waveform of the charged particle beam including the aperture angle and the resolution as parameters and a mark shape of the dot mark; And calculating the aperture angle and the resolution.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of measuring a resolution of a charged particle beam and a charged particle beam imaging apparatus using the charged particle beam,

The present invention relates to a method for measuring the resolution of a charged particle beam and a charged particle beam imaging apparatus.

With the increasingly high integration of LSIs, the circuit line width of semiconductor devices is becoming smaller every year. In order to form a desired circuit pattern on a semiconductor device, a high-precision original pattern (mask, or in particular, used in a stepper or a scanner, also referred to as a reticle) formed on quartz is transferred onto a wafer A method of carrying out a reduced transfer onto a recording medium is adopted. A high-precision source pattern is imaged by an electron beam drawing apparatus, so-called electron beam lithography technique is used.

In the electron beam drawing apparatus, various settings such as focusing are performed based on the resolving power of the beam and the opening angle. For example, the electron beam is scanned to irradiate an electron beam onto a dot pattern (metal pattern) on the substrate, the reflected electrons are measured, the beam intensity distribution is calculated from the measurement result, (See, for example, Japanese Patent Application Laid-Open No. 2007-188671 and Japanese Patent Application Laid-Open No. 2007-234263).

In order to improve the drawing accuracy of the electron beam drawing apparatus, it is required to calculate the resolution and aperture angle of the beam with high precision.

The present invention provides a method for measuring the resolution of a charged particle beam and a charged particle beam imaging apparatus capable of accurately obtaining the resolution and aperture angle of the charged particle beam.

A method for measuring a resolution of a charged particle beam according to an aspect of the present invention includes the steps of changing a focus position of a charged particle beam in a height direction and scanning a dot mark formed on the substrate with the charged particle beam for each focus position, The method comprising the steps of: detecting reflected charged particles reflected from the dot mark for each focus position; calculating scattered charged particle distribution from the detection result of the reflected charged particles for each height corresponding to the focus position; A step of carrying out a convolution operation of an approximate expression of the beam waveform of the charged particle beam including the aperture angle and the resolution as parameters and a mark shape of the dot mark; And calculating the opening angle and the resolution.

1 is a schematic view of an electron beam drawing apparatus according to an embodiment of the present invention.
Fig. 2 is a view for explaining the variable shaping of an electron beam.
3 is a flowchart for explaining the beam resolution and the aperture angle measuring method according to the embodiment.
4 is a graph showing an example of scattered electron distribution.
5 is a graph showing an example of a differential waveform of the scattered electron distribution.
6 is a flow chart for explaining the measurement results of the scattered electron distribution and fitting processing of the calculation results.
Fig. 7 is a diagram showing an approximate example of a mark shape.
8 is a view showing an approximate example of a mark shape.
Fig. 9 is a flowchart for explaining a beam resolution and an aperture angle measurement method according to another embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1 is a schematic view of an electron beam drawing apparatus according to an embodiment of the present invention. The drawing apparatus 1 shown in Fig. 1 is a drawing apparatus of a variable mold type provided with a drawing unit 30 and a control unit 10 for controlling the operation of the drawing unit 30. Fig.

The drawing section (30) has an electron lens barrel (40) and a drawing room (50). A blanking aperture 42, a first shaping aperture 43, a second shaping aperture 44, a blanking deflector 45, a shaping deflector 46, An objective deflector 47 and a lens 48 (an illumination lens CL, a projection lens PL, and an objective lens OL) are arranged.

An XY stage 52 and a detector 54, which are movably arranged, are disposed in the painting room 50. A substrate 60 is placed on the XY stage 52. The substrate 60 is, for example, a silicon substrate having a dot mark 62 formed on the surface thereof as a metal mark. The dot mark 62 is in the form of a rectangular parallelepiped (square in plan view), and is made of a metal material such as tungsten or tantalum, which has a reflectance higher than that of silicon. The detector 54 detects the reflected electrons reflected from the dot mark 62 by the irradiation of the electron beam.

The electron beam 49 emitted from the electron gun 41 provided in the electron lens barrel 40 is passed through the blanking deflector 45 and is directed by the blanking deflector 45 to the blanking aperture 42 And in the state of beam-off, the entire beam is deflected so as to be shielded by the blanking aperture 42. [ The beam is turned on in the beam-off state, and then the electron beam 49 passed through the blanking aperture 42 becomes one shot of the electron beam until the beam is turned off.

The electron beam 49 of each shot produced by passing through the blanking deflector 45 and the blanking aperture 42 is directed by the illumination lens 48 to the first shaping aperture 42a having a rectangular opening 43a And irradiated to the plug 43. The electron beam 49 passes through the opening 43a of the first shaping aperture 43 to form a rectangular shape.

The electron beam on the first shaping aperture which has passed through the first shaping aperture 43 is projected onto the second shaping aperture 44 by the projection lens 48 (PL). The position on the first aperture 44 on the second shaping aperture 44 is controlled by the shaping deflector 46. Thus, the shape and dimension of the electron beam passing through the opening 44a of the second shaping aperture 44 can be changed (variable shaping is performed).

The electron beam that has passed through the second shaping aperture 44 is focused by the objective lens 48 and deflected by the objective deflector 47 so that the dots of the substrate 60 on the XY stage 52 The mark 62 is irradiated to scan.

The control unit 10 has a control calculator 12, a control circuit 14, an amplifier 16, and an A / D converter 18. The signal detected by the detector 54 is amplified by the amplifier 16 and converted into a digital signal by the A / D converter 18 and transmitted to the control calculator 12. [

The input / output data of the control calculator 12 or the data being calculated is appropriately stored in a memory (not shown). The control calculator 12 controls the operation of each section of the drawing apparatus 1. [ For example, the control calculator 12 controls the amount of deflection of the blanking deflector 45, the molding deflector 46, and the object deflector 47 via the control circuit 14. [ The control calculator 12 also calculates the resolving power of the electron beam irradiated by the imaging unit 30 and the aperture angle.

A method of measuring the resolution and the aperture angle of the electron beam will be described with reference to the flowchart shown in Fig.

The electron beam is scanned to irradiate the electron beam to move from the front of the dot mark 62 formed on the substrate 60 onto the dot mark 62 (step S1). The beam size of the electron beam is smaller than the width dimension of the dot mark 62. [

The electrons reflected (scattered) from the dot mark 62 by the irradiation of the electron beam are detected by the detector 54 (step S2). The signal detected by the detector 54 is transmitted to the control calculator 12 via the amplifier 16 and the A / D converter 18. [

The control calculator 12 measures the scattered electron distribution from the detection result of the reflected electrons (step S3). For example, the area of the electron beam superimposed (irradiated) on the dot mark 62 with the scanning of the electron beam is gradually increased (first section), then becomes constant (second section) Three sections). Therefore, when the longitudinal axis is the scattering electron amount and the abscissa is the beam position, the scattering electron distribution becomes a waveform that rises in the first section, becomes constant in the second section, and falls in the third section as shown in Fig. 4 . Fig. 4 shows an example of measurement results obtained by setting the number of points to 1024 in the horizontal axis direction.

If this waveform is differentiated, it becomes a waveform such that one hill part and one valley part as shown in Fig. 5 are continuous.

The focus position of the electron beam is moved in the height direction (z direction) to acquire the scattered electron distribution of the z coordinate of n points (n is an integer of 2 or more) (steps S1 to S5). For example, a differential waveform as shown in Fig. 5 is obtained for each z coordinate.

It is also preferable to adjust the optical system so that the size of the beam does not change when the focus position is moved. Since the intensity of the beam is also to be fitted, it is preferable not to change the sensitivity of the detector 54 every time the focus position is moved.

Next, the fitting process (step S6) will be described with reference to the flowchart shown in Fig.

The resolution (? (Z)) of the electron beam for each z coordinate when the opening angle of the electron beam is? And the focus deviation at the time of measurement is b is expressed by the following equation (1).

When the beam position is x and the half of the beam size is h, the beam waveform can be expressed by the following approximate expression (Equation 2).

From this approximate expression, a beam waveform for each z coordinate is obtained by using the beam resolution () and the beam opening angle alpha (step S61). Further, assuming that the dot mark 62 is a rectangular parallelepiped, the mark shape is obtained using the mark height, mark position, and mark width as fitting parameters (step S62). The beam waveform obtained in the step S61 and the mark shape obtained in the step S62 approximate the shape to, for example, 1024 points along the horizontal axis in accordance with the measurement results of the steps S1 to S5.

The control calculator 12 performs a convolution operation between the beam waveform obtained in the step S61 and the mark waveform obtained in the step S62 to calculate the scattered electron distribution for each z coordinate (step S63). Convolution operations can be performed, for example, as follows. First, a frequency component of a beam waveform and a mark shape (for example, approximate to a shape of 1024 points) is obtained by FFT. Next, the complex conjugate of the frequency component of the beam waveform and the frequency component of the mark shape is multiplied for each frequency component. Then, inverse FFT is performed on the result.

(The sum of the squares of the differences of the scattering electron intensities for each measurement point in the horizontal axis direction) is obtained by fitting the measurement results of the n scattering electron distributions obtained in steps S1 to S5 to the calculation result of the convolution operation (step S65 )). While the error is small (step S66_Yes), the fitting parameters are updated (changed) (step S67), and steps S61 to S65 are repeated. And? And? (B) when the error becomes small (the error becomes minimum) are obtained. Accordingly, the aperture angle and resolution of the electron beam can be calculated at the same time.

As described above, according to the present embodiment, the scattered electron distribution for each of the z-coordinates in which the focus position is moved in the z-direction is measured, and the beam opening angle alpha and the resolution () The aperture angle? And the resolution? Can be obtained with high precision.

The control calculator 12 controls the imaging unit 30 so that b, which minimizes the resolution, becomes the focus position.

The shape of the mark of the dot mark 62 is assumed to be a rectangular parallelepiped, but the shape of the mark is not necessarily a rectangular parallelepiped by the processing accuracy of the dot mark 62 or deterioration due to irradiation of the electron beam to the dot mark 62 Do not. For this reason, it is preferable to consider also the parameter relating to the mark shape as the fitting parameter.

For example, as shown in Fig. 7, assuming that the half of the mark height is A, the mark position is o, the mark width is w, and the mark deterioration degree (for example, the radius of curvature of both edges of the dot mark upper surface in the beam scanning direction) delta 1 and delta 2, the mark shape can be approximated by the following expression (3). In addition, the negative range of the value of Equation 3 is zero.

The control calculator 12 performs the convolution operation of the beam waveform of the above-described equation (2) and the mark shape of the equation (3), and fits the measurement results of n scattered electron distributions to the calculation result. The fitting parameters are a total of nine of σ (b), α, h and b in the beam waveform and A, о, w, δ1 and δ2 in the mark shape.

For example, the Gauss-Newton method can be used as the least squares method. In this case, since the square error does not necessarily decrease every execution of the ignition formula including the influence of the numerical calculation error, when the fitting parameters are updated in the ignition formula, the fitting parameters before the update and the fitting parameters after the update are equally divided And the point at which the square error is minimized is used as the next fitting parameter. The calculation of the squared error and the updating of the fitting parameters are repeated to obtain? And? (B) when the error becomes minimum. Accordingly, the aperture angle and resolution of the electron beam can be calculated at the same time. Since the dot mark shape is also considered as a fitting parameter, the opening angle? And the resolution? Can be obtained with higher precision.

The parameters may be changed in proportion to the amount by which the square error is reduced when the parameters are slightly changed by using the most rapid method (the fastest descent method) instead of the Gauss-Newton method. Alternatively, fitting parameters may be obtained such that the error is minimized by other least squares methods.

The fitting object may be a scattering waveform itself, or a differential waveform or a second derivative waveform of a scattering waveform (step S64 in Fig. 6). In the case of using the differential waveform, the fitting parameters are obtained so that the square error (the sum of the difference between the differential of the scattered electron intensity for each measurement point in the horizontal axis direction and the difference of the differential of the result of the convolution operation) is minimized. The same applies to the case of using a second derivative waveform.

It is not necessary to assume that the mark shape is a rectangular parallelepiped. For example, it may be assumed that the shape of the mark is a rectangular concave-convex shape, and that the cross-sectional shape is any other shape than the rectangular shape as shown in Fig.

In the above embodiment, the optical system is adjusted such that the beam size does not change when the focus position is moved for the measurement of the scattered electron distribution. However, it is difficult to adjust the beam size to be zero. For this reason, it is preferable to consider the beam size change also as a fitting parameter.

In the above embodiment, the scattered electron distribution is measured using one dot mark 62 formed on the substrate 60, but the scattering electron distribution is measured using the plurality of dot marks 62 to improve the fitting accuracy .

A method for measuring the scattering electron distribution with a plurality of dot marks 62 and measuring the resolution and aperture angle of the electron beam by fitting the beam size variation will be described with reference to the flowchart shown in Fig.

An electron beam is irradiated to one of the dot marks 62 (m is an integer of 2 or more) formed on the substrate 60 by scanning the electron beam, and the scattered electron distribution is obtained by detecting the reflected electrons S11 to S13). Subsequently, the focus position of the electron beam is moved in the height direction (z direction) to acquire the scattered electron distribution of the z coordinates of n points (n is an integer of 2 or more) (steps S14 and S15). The processing in steps S11 to S15 is the same as the processing in steps S1 to S5 in Fig. The scattering electron distribution of the z coordinates of the n points is acquired sequentially for the m dot marks 62 (steps S16 and S17).

As described later, the change in the size of the beam is also considered as the fitting parameter. The adjustment of the optical system is performed so that the beam size does not change when the focus position is shifted in the measurement of the scattered electron distribution. In addition, the sensitivity of the detector 54 is not changed.

The fitting process (step S18) is the same as the process shown in Fig. However, since the beam size variation is also a fitting parameter, h (z) = k (z) * h (0) in the above-described equation (2). It is assumed that the beam intensity is inversely proportional to the square of the beam size, i.e., the beam intensity at the coordinate z is 1 / (k (z)) ² times the beam intensity at z = 0.

It is also assumed that the focus deviation (b) at the time of measurement in the formula (1) is the number of the dot portions (m) of the dot mark 62 and the approximate expression of the mark shape shown in the expression (3) m).

The moving distance of the focus position in the vicinity of z = 0 may be made smaller than the other area for the purpose of improving the focus deviation (b) precision at the time of measurement.

A convolution operation of a beam waveform and a m-shaped mark approximate expression in which a plurality of defocus (b) and a beam size (h (z)) of z = 0 in Equation To calculate the scattering electron distribution per unit area. Then, an error is obtained by fitting the measurement result of the scattering electron distribution obtained in the steps S11 to S17 to the calculation result of the convolution operation. The fitting parameters are updated to obtain the opening angle? And the resolution? (B) at which the error becomes minimum.

Since the change in the size of the beam is also used as a fitting parameter, the fitting object can be fitted with high precision even if the scattering electron distribution itself is not a differential waveform of the scattering electron distribution. In addition, it is possible to precisely fit the scattered electron distribution even at a position where z is large.

Further, since the mark deterioration degrees? 1 and? 2 are used as the fitting parameters, they can be used for the measurement of the scattered electron distribution even when the dot marks 62 on the substrate 60 deteriorate.

In the above embodiment, the electron beam having the beam size smaller than the width dimension of the dot mark 62 is irradiated to the dot mark 62. However, since the scattered electron distribution is calculated from the dot mark and the beam shape, But an electron beam having a larger beam size than the width dimension of the dot mark 62 may be irradiated.

The function of the control calculator 12 may be configured by hardware or software. In the case of constituting by software, a program for realizing at least some functions may be stored in a recording medium such as a CD-ROM and read by a computer having an electric circuit and executed.

Although the drawing apparatus for irradiating an electron beam has been described in the above embodiment, it may be irradiated with another charged particle beam such as an ion beam. The drawing apparatus is not limited to the variable mold type, and may be a multi-beam drawing apparatus that irradiates a plurality of beams at one time.

Further, the present invention is not limited to the above-described embodiment, and can be embodied by modifying the constituent elements within the scope of the present invention without departing from the gist of the present invention. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments. For example, some constituent elements may be deleted from the entire constituent elements shown in the embodiments. In addition, components extending over different embodiments may be appropriately combined.

Claims (10)

Changing the focus position of the charged particle beam in the height direction and scanning the dot mark formed on the substrate with the charged particle beam for each of the focus positions,
Detecting reflected charged particles reflected from the dot mark for each focus position;
Calculating a scattered charged particle distribution for each height corresponding to the focus position from the detection result of the reflected charged particles;
Performing a convolution operation of an approximate expression of the beam waveform of the charged particle beam including the aperture angle and resolution of the charged particle beam as parameters and a mark shape of the dot mark;
A step of calculating the opening angle and resolution by fitting the scattered charged particle distribution for each height and the calculation result of the convolution operation
And measuring the resolution of the charged particle beam. The method according to claim 1,
Wherein the shape of the mark is represented by an approximate expression including a height, a width, a degree of deterioration, and a position as parameters. 3. The method of claim 2,
Wherein the degree of deterioration is a radius of curvature of the edge of the dot mark. The method according to claim 1,
Wherein adjustment of the optical system is performed so that the size of the beam is not changed when the focus position of the charged particle beam is changed in the height direction. 5. The method of claim 4,
Wherein the sensitivity of the detector for detecting the charged charged particles is not changed when the focus position of the charged particle beam is changed in the height direction. The method according to claim 1,
Wherein a plurality of dot marks are formed on the substrate, each dot mark is scanned with a charged particle beam for each focus position, and the scattered charged particle distribution is calculated from the detection result of the reflected charged particles. How to measure. The method according to claim 1,
Wherein the approximate expression of the beam waveform of the charged particle beam includes a change in the size of the charged particle beam in a height direction as a parameter. The method according to claim 1,
Wherein the aperture angle and the resolution are calculated by fitting the derivative of the scattered charged particle distribution and the derivative of the calculation result of the convolution operation. An imaging unit for changing the focus position of the charged particle beam in the height direction and scanning the dot mark formed on the substrate for each of the focus positions with the charged particle beam,
Calculating a scattered charged particle distribution from the detection result of the charged particles reflected from the dot mark for each height corresponding to the focus position, calculating a scattered charged particle distribution of the beam waveform of the charged particle beam including the aperture angle and the resolution of the charged particle beam as parameters A control calculator for calculating an aperture angle and a resolution by fitting an approximate expression and a mark-shaped convolution operation of the dot mark, fitting the scattered charged particle distribution for each height and the calculation result of the convolution operation,
And a charged particle beam imaging device. 10. The method of claim 9,
Wherein the mark shape is represented by an approximate expression including a height, a width, a degree of deterioration, and a position as parameters.

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