JPS58223247A - Setting method for brightness of electron gun - Google Patents

Abstract

PURPOSE:To stabilize the brightness of an electron gun and improve the working ratio of an electron beam plotting device by detecting all beam current when used and controlling all beam current so that the current value can match the preset current value to the desired brightness based on the measurement result. CONSTITUTION:The operation temperature of a cathode 2 is held at 1,500 deg.C or more. In this status, the brightness of an electron gun is measured by applying proper bias between the cathode 2 and a Wehnelt electrode 4 and all beam current in this case is measured. Then all beam current for the brightness is measured in the same way by properly varying the bias and these types of information are stored in the CPU9. Furthermore, when the electron gun is used actually, a bias resistor 8 is varied so that the detected current value by an ammeter 10 can match the preset current value to the desired brightness stored in the CPU9. As a result, the brightness of an electric gun 1 can easily and stably be set to the desired size.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for setting the brightness of an electron gun used for electron beam lithography quality.

[Technical background of the invention and its problems]

In electron beam lithography equipment, high brightness of the electron gun is required to enable high-speed lithography, and high-precision lithography is required. To make this possible, stabilization of brightness is required. The electron gun used in an electron beam lithography system is usually formed into a three-electrode structure consisting of a cathode, a Wehnelt electrode, and an anode.
Has it become brighter recently? For measurement purposes, single crystal lanthanum hexapolide (LaB6) is used at 1° with the cathode. In this type of electron gun, the brightness changes greatly due to slight changes in cathode temperature, bias voltage, etc. Hence the stabilization of brightness? To measure it, find the actual brightness r during use, and this brightness will be the desired level. L
Various conditions must be set again.

Brightness of electron gun? To find this, it is necessary to measure the diameter of the electron beam on the drawing surface using the sharp edge method, and also to measure the current value, but these measurements are very complicated and the time required for the measurement is short. do not have. Also, as mentioned above, the brightness changes greatly due to slight changes in cathode temperature, bias, etc., so the above measurements should be performed every time these conditions change. There is a need to do. For this reason,
Stabilization of electron gun brightness? Does the operation rate of the electron beam lithography system decrease when trying to measure it? Figures 1 (a) to (c) show LaB with a tip curvature of 15 (μm).
6 candos? Brightness, temperature, and bias of the electron gun used↓
In the temperature dependence of brightness β shown in Figure 1(a), which is a characteristic diagram showing the relationship between n and total beam current, n,
I Bt 6 Bg means bias resistance, 0 to A where B+<Bg<”s, and Tl + Tt e Ts are the temperatures at which the respective brightness is maximum.1g1The bias of brightness β shown in Figure (b) T1mT1 in dependence.

T is the same as that in FIG. 3A, and the bias at which the brightness is maximized is approximately the same regardless of temperature. In the total beam current dependence of the brightness β shown in Fig. 1(C), 'r,s T1
+'r is the same as that in (&) and (b) of the same figure, and the total beam current at which the brightness is maximum increases as the temperature increases. As can be seen from Fig. 1 (a) to (,), the brightness β depends on the temperature and bias as parameters.
It is a higher-order function of the total beam current, and furthermore its shape is dependent on each parameter, hence the required brightness, temperature, bias.

It is difficult to determine it uniquely from any of the total beam currents. Also, although only an example is shown here, there is considerable variation in each curve from the cathode.
What brightness conditions do you need? It was even more difficult to ask than Eli.

[Purpose of the invention]

The purpose of the present invention is to improve the brightness of an electron gun using a single crystal LaB6 cathode. Brightness stabilization can be easily determined? [Summary of the Invention] The present invention provides a method for setting the brightness of an electron gun, which can be used to measure the brightness of an electron beam, and which can contribute to improving the operation rate of an electron beam lithography system. In the method of setting the brightness of a gun, the axial direction of the cathode is set to v<1oo> or <310>, the cathode tip is machined into a flat surface with a diameter of 70 [μm] or more, and the cathode operating temperature is r1500 [°C] or more. The brightness of the total beam current flowing through the cathode is measured in advance, and the total beam current is detected during use, and this detected current value matches the set current value for the desired brightness based on the measurement results. ↓ This is a method to make the total beam current dependent on the 0 °C condition mentioned above, i.e. the axial orientation (100).

<310>, cathode tip diameter 70 [μm] or more.

The cathode operating temperature is 1500 (°C). When an electron gun is used under the above conditions, the dependence of brightness on temperature and bias will undergo complex changes similar to those shown in Figure 1 (a) and (b) above. ?, and some variation is seen, but a very simple relationship is obtained when looking at the dependence of brightness on the total beam current. Figure 2 is a characteristic diagram showing this result, and the curve P in the figure is the cathode tip plane. The diameter of the area is 70 [μ?n
]2 Curve Q is a curve (μ*L), curve R is 150 (p
m) (7) field 4yr.

It shows. As can be seen from this figure, all of the curves increase monotonically, and if the temperature of the LaB6 cathode is 1500 [℃] or higher, there is almost no difference in temperature, and the curve closely matches the curve in Figure 2. Axial orientation is <100>, <31
0), then no significant difference is observed.0 Thus, if LaB and cathode r are used under the above conditions, the brightness of the electron gun can be uniquely determined from the total beam current, which is very easy to measure.

Note that when the diameter of the cathode tip plane region is 70 μm smaller, the dependence of the brightness on the total beam current is as shown in Fig. 1 (
0 similar to that shown in C) Furthermore, even if the diameter is 70 [μm] or more, if the axis orientation is other than <100> or <310>, a more complicated change τ will occur. Therefore, the axial direction, cand tip diameter, cand temperature, etc. must meet the conditions described above.

〔Effect of the invention〕

According to the present invention, what is the brightness of the electron gun? It can be easily measured and the brightness can be easily set to a desired level. Therefore, the brightness of the electron gun can be stabilized, and the drawing process can be made into a single line. And brightness stabilization? Because it can be done easily and in a short time, it contributes to improving the operation rate of electron beam lithography equipment and throughput. play.

[Embodiments of the invention]

Figure 3 is a schematic diagram showing the electron gun and its control system used in one embodiment of the present invention.
The electron gun consists of a cathode 2, a heater 3, a Wehnelt electrode 4, and an anode 5. The heater 3 of the electron gun 1 is connected to a power source 6 for heating the cathode. Further, the axial direction of the cathode 2 is set to <100>, and the tip is processed into a flat surface with a diameter of 90 [μm]. A high-voltage power supply 7 with the illustrated polarity is connected between the Wehnelt electrode 4 and the anode 5, and a bias resistor 8 is connected between the cathode 2 and the Wehnelt electrode 4. The resistance value of this bias resistor 8 can be varied based on control commands from the CPU 9. In addition, 10 in the figure is the total beam current flowing through the cathode 2? An ammeter for detection, 11 indicates the sample.

With this ↓ configuration, first the operating temperature of cathode 2 'k1
Maintain the temperature above 500 [℃], and in this state, connect the cathode to
Is it possible to apply an appropriate bias voltage between Wehnelts and adjust the brightness using a well-known method? It was measured. And the total beam current at this time? It was detected with an ammeter 10. Next, change the bias r as appropriate and do the same as above to calculate the detected value of the total beam current with respect to the brightness? It was measured. This result is the curve Q shown in FIG. 2 above. Then, this curve is calculated by the least squares method as follows:
It is approximated by the following formula.

Luminance β[AArJ-str)=AIt”+BIt”+C
It+D-・S(1)where, It is the magnitude of the total beam current, A, B.

C and D are coefficients, and according to the experiments conducted by the present inventors, they were defined as shown in the following table according to the diameter of the tip of the cand.

The information specified in this table is stored in the fzcPU 9, and when the electron gun is actually used, the current value detected by the ammeter 10 matches the set current value for the desired brightness stored in the CPU 9. The resistance value of resistor 8 is varied. This makes it possible to easily and stably set the brightness r of the electron gun 1 to a desired level.

It should be noted that the present invention is not limited to the embodiments described above, and the gist of the invention is not limited to the embodiments described above. Various modifications can be made without departing from the scope. For example, the tip plane of the LaB cathode is not limited to a circular shape, but has an area equal to or larger than a circle with a diameter of 70 [μm]? If it has one, it may be rectangular.

[Brief explanation of drawings]

Figures 1 (a) to (c) are detailed explanations of the conventional problems: What is the relationship between brightness, temperature, bias, and total beam current?
2 is a characteristic diagram showing the relationship between the brightness of the electron gun and the total beam current according to the method of the present invention, and FIG. 3 is a characteristic diagram showing the electron gun control system used in an embodiment of the present invention. FIG. 1...electron gun, 2...single crystal LaI3. cathode, 3
°°° heater, 4°°° Wehnelt electrode, 5... anode, 6... cathode heating power supply, 7... high voltage power supply, 8... bias resistor, 9... CPU, 10...・
Ammeter, 11...sample. Applicant's agent Patent attorney Suzue Takehiko

Claims (2)

[Claims] (1) What is the brightness of a three-electrode electron gun with a cathode temperature of single crystal lanthanum to xaporide? In the setting method, the axial direction of the force node k<100) or <31
o) and the cathode tip diameter is 70 [μm].
Processed into a flat surface with a cathode operating temperature of 11soo.
(℃) or more, and the brightness relative to the total beam current flowing to the cathode above? Detect the total beam current during use, and find out whether this detected current value matches the set current value for the desired brightness based on the measurement results. A method for setting brightness of an electron gun characterized by controlling. (2) Said total beam current? Is the means for controlling the Wehnelt bias of the electron gun? Is it something that can be changed? A method for setting brightness of an electron gun according to claim 1.