JPH0817149B2 - Beam adjustment method for electronic beam device - Google Patents

Description

Description: (a) Technical Field of the Invention The present invention relates to a method of aligning an electron beam apparatus for obtaining a maximum beam intensity value.

(B) Background of technology Semiconductor ICs are becoming smaller and higher in density, and pattern formation by electron beam irradiation is used instead of conventional pattern formation by ultraviolet exposure for forming diffusion layers and fine patterns such as conductor patterns. Is being carried out.

That is, in the manufacture of a semiconductor IC, a thin film forming technique and a photo-etching technique (photolithography) are used to form an IC circuit in a multi-layered structure. When contact exposure or projection exposure is performed using a photoresist mask on a photoresist film, Due to the diffraction and scattering of light in conventional ultraviolet irradiation, the pattern accuracy in practice is 1 [μ
m].

On the other hand, when an electron beam is used, its wavelength is about 0.1 [Å] depending on the accelerating voltage.
Since it is shorter than a digit, pattern accuracy of about 0.1 [μm] is possible. Therefore, it is used for forming high-density IC patterns.

A semiconductor substrate (hereinafter, abbreviated as a wafer) on which a semiconductor IC is manufactured is a sliced single crystal rod and has a thickness of about 500 [μm] and a diameter of 3 to 6 [inch]. A large number of IC chips are manufactured on such a wafer, and at the final stage, the wafer is cut into unit chips to produce semiconductor elements.

The present invention relates to a beam adjusting method for an electron beam apparatus used for patterning a large number of IC chips on a wafer.

(C) Prior Art and Problems FIG. 1 is a block diagram of an electron beam exposure apparatus, in which an electron gun composed of a cathode 1, a grid 2 and an anode 3 is provided inside the apparatus held in a high vacuum. The emitted electrons are accelerated by the grid 2 and the anode 3, and the stage 4
A plurality of alignment coils 6 for projecting and drawing on the wafer 5 set in the above, for correcting the projection direction of the electron beam, a plurality of slits 7 for determining the beam shape,
8, a plurality of lenses 9, 10, 11 for converging the beam, an aperture 12 for ensuring the sharpness of the beam, etc. are provided.

The electron beam projected from the potential gun here is slit 7,
It is necessary for the beam to be correctly projected on the beam 8 and the center of the beam thereof to coincide with the center of the aperture 12. For that purpose, it is necessary to correct the projection direction of the beam diameter by the alignment coil 6.

That is, even with a properly set electron gun, the irradiation position of the electron beam projected from now on will be several hundred [μ
It is normal that they are deviated by about [m], and this axis alignment is performed by a plurality of alignment coils 6 having different heights.

Here, at least two sets of alignment coils 6-1 and 6-2 having different distances from the electron gun are required for axis alignment, and each set of alignment coils is orthogonal to each other in the X-direction coil and the Y-direction. It consists of a coil, and each X,
The electron beam is bent by the magnetic field generated by energizing the Y-direction coil to correct the projection direction and align the axes.

Here, as a correction method, the stage 4 on which the wafer 5 is placed is moved so that the Faraday cup 13 provided at this corner is aligned with the axis passing through the slits 7, 8 and the aperture 12, and the Faraday cup 13 is The magnetic field of the alignment coil 6 is adjusted so that the center of the electron beam coincides.

That is, the Faraday cup 13 is grounded through the ammeter 14, but the ammeter 14 is connected to the CPU 16 through the analog digital converter (abbreviated as ADC) 15 and the two-layer alignment coils 6-1 and 6-2. The excitation current to each X, Y coil that composes the signal from CPU16 is register 17, digital analog converter (abbreviated as D
AC) 18 and amplifier 19, and the electron beam to the Faraday cup is automatically adjusted to show the maximum value.

In the conventional automatic adjustment method used here, a plurality of points (≧ 3) are taken at equal intervals as the driving points of the X and Y coils, and the best condition is obtained from the current value at that point.

For example, X that constitutes the upper alignment coil 6-1
For the directional coil, the coil driving current value is set at five points at equal intervals, and the maximum value condition is obtained from the value of the ammeter 14.

Figure 2 shows this result.
If there is no peak value among the 5 points of C, D, and E, add F to compare the 5 points of Rohaniho and repeat this to obtain the best condition for the coil drive current value for the X-direction coil. Then, the same operation was performed for the Y-direction coil, and this was repeated for a plurality of coils to obtain the best condition, and the electron beam was automatically aligned.

However, since a considerable amount of noise is mixed in the detected current, as shown in Fig. 2, the detected current value is affected by noise, making it difficult to detect the peak value. There is a problem that it takes time to find the value, and the peak value obtained for one coil is not always the best value when viewed as the alignment coil as a whole, so detection operation is performed again for all coils. It was necessary to repeat.

(D) Object of the Invention It is an object of the present invention to provide a beam adjusting method for an electron beam apparatus capable of performing accurate axis alignment in a short time operation.

(E) Configuration of the invention The object of the present invention is to measure the intensity of the electron beam at five or more discrete and evenly spaced points for driving the coils for each alignment coil, and make a quadratic curve a least squares approximation to obtain a maximum value. And the value of the alignment coil can be determined accordingly.

(F) Example of the Invention The present invention is the same as measuring the intensity of the electron beam under each of a plurality of driving conditions at discrete points for each coil constituting the alignment coil. The best condition is obtained by approximation. Thirteenth
The figure shows this method, and shows the state in which the measurement result of FIG. 2 is approximated to the quadratic curve of y = a (x−b) ² + c (1) by the method of least squares. If the value of b is obtained, this value becomes the best condition for driving the coil.

The process of measuring the intensity of the electron beam at discrete 2n + 1 measuring points and obtaining the b value of the equation (1) from the measured data will be described below.

First, in the x-axis (alignment coil drive current value) in FIG. 3, discrete and equally spaced 2n + 1 (n is a natural number of 2 or more) measurement points are set. For example, when n = 2, five measurement points −2, −1,0,1,2 are set. Each measurement point has a corresponding coil drive current value.
Replace the measurement point on the x-axis with the coil drive current value -2, -1,0,
By expressing the integer values 1, 2 centered at 0 at equal intervals, the calculation of the least-squares approximation is facilitated as described later.

To obtain the value of b in equation (1), Is equivalent to finding the value of b such that takes the minimum value.

Here, f (xi) is the detected current value (measured value) y: a (xi-b) ² + c (3) at the measurement point i.

Next, in order to find the minimum value of Φ, the extreme value of Φ is found. That is, ∂Φ / ∂a = 0 (4) ∂Φ / ∂b = 0 (5) ∂Φ / ∂c = 0 (6) A, b, and c are satisfied.

When the formula (3) is expanded, y = axi ² −2abxi + ab ² + c (7) is obtained, but for simplification, A = a (8) B = −2ab (9) C = ab ² + c If we put (10), equation (7) can be expressed as follows.

y = Axi ² + Bxi + C (11) When the equation (11) is substituted into the equation (2) and the equation (5) is calculated, Becomes

By taking the measurement point i as ..., -2, -1,0,1,2, ... And then Then, the equation (12) becomes B · T ₂ −P ₁ = 0 …… (18). Similarly, when formulas (4) and (6) are calculated, A · T ₄ + C · T ₂ −P ₂ = 0 …… (19) A · T ₂ + C (2n + 1) −P ₀ = 0 …… (20) When A, B, and C are obtained by using equations (18), (19), and (20) as simultaneous equations of three elements, the following is obtained.

Then, B, C, A obtained by the equations (21), (22) and (23)
The value of b can be obtained by substituting the value of into the equations (8), (9), and (10).

By obtaining the above processing for each coil using a computer, the axis of the alignment coil can be accurately aligned.

(G) Effect of the Invention In the present invention, as an electron beam axis alignment method using an alignment coil in an electron beam exposure apparatus, conventionally, the best condition is obtained by repeatedly measuring the increase and decrease of the measured value with a plurality of points at equal intervals as measurement points. However, in the case of the present invention, the peak value is obtained by approximating the quadratic curve to the least squares, and the implementation of the present invention enables accurate and quick axis alignment.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the configuration of an electron beam apparatus, FIG. 2 is a relational diagram between a coil drive current and a detected current in a conventional axis alignment method, and FIG. 3 is an explanation of a quadratic curve according to the present invention. It is a figure. In the figure, 6,6-1,6-2 are alignment coils, 7,8 are slits, 1
2 is the aperture and 13 is the Faraday cup.

Claims (1)

[Claims] 1. An electron gun for emitting an electron beam, a stage provided with a sensor for irradiating the electron beam and measuring the beam intensity of the electron beam, and an electron beam emitted from the electron gun for the stage. A beam adjusting method for an electron beam device having a deflecting means for deflecting the electron beam so as to irradiate the electron beam to a predetermined position above, wherein the measurement is performed at discrete intervals of 2n + 1 (n is a natural number of 2 or more) or more. At this point, the intensity of the electron beam is measured by using the sensor, and the obtained measured values at 2n + 1 points or more are approximated to a quadratic curve by least squares to obtain a position where the beam intensity has a maximum value, and the position A beam adjusting method for an electron beam apparatus, wherein the deflection amount of the deflecting means is adjusted so that the electron beam is irradiated onto the beam.