JPS6319002B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a length measurement method using a charged particle beam.

In the manufacturing process of LSI devices and VLSI devices, pattern inspections such as measuring the line width and line spacing of patterns created on materials are performed. Since the line widths of these patterns reach submicron units, it is impossible to measure them optically.

Therefore, it is conceivable to measure line widths and the like using electron beams or ion beams. That is, by digitally scanning a charged beam over a material and capturing reflected electrons emitted from the material, the edge of the line or the position of the unevenness to be measured is detected, and this detection is performed digitally. Line width and line spacing are measured in relation to target scanning.
However, in general, the material itself has displacements such as warping and unevenness, and the material stage also has similar displacements and backlash during horizontal movement, so work distances may vary within the same material or between materials. As a result, erroneous length measurements are performed. FIG. 1 shows an example of this, in which pattern line widths are measured at different workpiece distances in the same material M, and a pattern P formed at a workpiece distance D is shown. The line width of the pattern P', which has the same line width as the pattern P formed at the workpiece distance D', is calculated by digitally scanning the beam B in the direction of the arrow Q using the deflector DF. When measuring the line width of the pattern P, a value corresponding to the movement (deflection) angle α of the beam from edge to edge of the pattern P is obtained, and the line width of the pattern P' is α'(<α).
A value corresponding to is obtained. However, even if α and α' can be known, the line width cannot be calculated unless the work distances D and D' are known.
Further, it is generally difficult to determine the work distances D and D' with high precision. Therefore, as a result, a measurement error corresponding to (α−α′) occurs even though the same line width is measured. This error is a serious problem when measuring line widths in submicron units.

The present invention was made in view of these points,
This paper relates to a new length measurement method that allows the line width and line spacing of a pattern to be measured without knowing the work distance. That is, two deflectors are provided on the optical axis, above and below, and these deflectors are operated separately to scan the charged particle beam on the material, and in each scan, target information is obtained from the material. The present invention provides a novel length measurement method in which the line width or line spacing of a pattern on a material is calculated based on the value of a scanning signal applied to a deflector when a signal containing a signal is detected.

FIG. 2 shows an embodiment of the present invention. In the figure, reference numeral 1 denotes an electron gun, and an electron beam emitted from the electron gun is focused by electron lenses 2 and 3 onto a material 4 on which a pattern (including patterns such as marks) is formed. Reference numerals 5 and 6 denote deflectors, and at least one pair (for X-direction scanning or Y-direction scanning) is provided on each of the upper and lower sides. Usually, one for scanning in the X direction and one for scanning in the Y direction.
Two pairs are provided for directional scanning. The deflectors 5 and 6 each have a central processing unit (referred to as CPU) 7.
The electron beam is actuated by a digital scanning signal sent from a digital scanning signal generation circuit 8 which is actuated in response to a command from the digital scanning signal generating circuit 8, and causes the material 4 to be scanned with an electron beam. Reference numeral 9 denotes a backscattered electron detector, which detects electrons generated from the material 4 by the scanning.

Now, as shown in Figure 4, the deflector (deflector plate)
The width of the deflection force (by magnetic field or electric field) of D and F' is G, the distance between the deflectors (deflection plates) is H, the acceleration voltage of the electron beam entering the deflector is V _A , the deflector Letting the deflection voltage applied to V _{D be V D} , the beam deflection angle θ can be expressed as θ=G/2H V _D /V _A (1). In this formula, G, H
Since and V _A are known and constant values, the deflection angle θ can be calculated from equation (1) once the deflection voltage is determined.

With this point in mind, the embodiment of FIG. 2 operates as follows.

First, a scanning signal is sent from the scanning signal generating circuit 8 to only the deflector 5 according to a command from the CPU 7, and the beam is caused to scan the material 4 by the deflector 5. At this time, as shown in FIG. 3, the beam is first scanned to the left from the optical axis Z. When the beam crosses the edge of the pattern P ₀ by this scanning, a backscattered electron signal containing information about the edge is input to the CPU 7 via the backscattered electron detector 9. The CPU detects the value (voltage value) V _D1 of the scanning signal when this signal is input, and calculates the deflection angle θ ₁ using the equation (1). Subsequently, only the deflector 6 is operated in the same manner, and the deflection angle θ ₂ is calculated. Now, in FIG. 3, the deflector 5
If the distance between the deflection center O ₁ of the deflector 6 and the deflection center O ₂ of the deflector 6 is A, then the distance l ₁ from the optical axis Z to the left edge of the pattern P ₀ is: l ₁ =Atanθ ₁・tanθ ₂ /tanθ It can be expressed as ₁ −tanθ ₂ ...(2). The CPU 7 calculates l ₁ from the calculated deflection angles θ ₁ and θ ₂ and A (known). Next, in the same manner as above, the beam is scanned from the optical axis Z to the right by the deflector 5, the right edge of the pattern _P0 is detected, and the deflection angle _θ1 ' is calculated.
Next, the beam is scanned in the same manner by the deflector 6, the deflection angle θ ₂ ' is calculated, and the pattern P ₀ is calculated from the optical axis Z.
Distance to the right edge of l ₂ (=Atanθ ₁ ′・tanθ ₂ ′/tan
θ ₂ ′−tanθ ₁ ′) is calculated. Then, the CPU calculates the line width l of the pattern _P0 from the sum of the calculated _l1 and _l2 . In this way, the line width of the pattern can be measured without considering the work distance.

In the above embodiment, the deflector 5 or 6 is
Alternatively, θ ₁ , θ ₁ ′ or θ ₂ , θ ₂ ′ may be calculated by the following, and then θ ₂ , θ ₂ ′ or θ ₁ , θ ₁ ′ may be calculated by the deflector 6 or 5.

Further, the deflectors 5 and 6 may be of a magnetic field type or an electrostatic type.

According to the present invention, the line width or line spacing of the pattern created on the material is calculated based on the above equations (1) and (2), which do not include the work distance.
Even if there is a displacement of the workpiece distance at the measurement location,
Accurate line width, etc. can be measured without any errors. Furthermore, since the deflection angles θ ₁ , θ ₁ ', θ ₂ , and θ ₂ ' can be determined with extremely high precision (for example, 10 ^-4 rad), line widths, etc. can be measured extremely accurately. (Error is about 0.01%) By using two deflectors in this way, it is also possible to determine the distance between the deflector and the material, so for example, even if the material is set at an angle, it is possible to determine the distance between the deflector and the material. It is also possible to determine the distance traveled. That is, since one side A and two angles θ ₁ and θ ₂ of triangles O ₁ , O ₂ , and G in FIG. 3 are known, the spatial position of point G can be determined. Therefore, in this method, the angle of the pattern P ₀ with respect to Z on the measurement surface may be other than a right angle.

[Brief explanation of the drawing]

Fig. 1 shows a length measurement method considered before the present invention, Fig. 2 shows an embodiment of the present invention, and Figs. 3 and 4 are diagrams to supplement the explanation of the operation of the present invention. It is. 4: Material, 5, 6: Deflector, 7: Central processing unit (CPU), 8: Digital scanning signal generation circuit, 9:
Backscattered electron detector, Z: optical axis, P ₀ : pattern.

Claims (1)

[Claims] 1 Two deflectors are provided on the optical axis, above and below, and the charged particle beam is scanned over the material by operating the deflectors separately, and in each scan, target information is acquired from the material. A length measurement method that calculates the line width or line spacing of a pattern on a material based on the value of a scanning signal applied to a deflector when a signal containing the signal is detected.