Electron Beam Lithography

This invention relates to electron beam lithographies and particularly to an electron beam apparatus suitable for uniformly exposing the area to be exposed, by an electron beam.

In a conventional electron beam lithography, when the electron beam is blanked, a voltage is applied to electrostatic electrodes provided at a position along the electron beam path in synchronism with a lithographing signal, to thereby deflect the electron beam out of the opening of an aperture plate provided in the electron beam path. In addition, when the electron beam is irradiated on a sample, thereby exposing it, the voltage to the electrostatic electrodes is removed in synchronism with the lithographing signal so that the electron beam is released from the blanked state and passed through the opening of the aperture plate to the sample for a predetermined time. Thereafter, the electron beam is again blanked in synchronism with the image signal, thereby making a desired exposure on the sample.

The amount of electron beam irradiated on the sample with respect to time will be described with reference to FIGS. 5(a), 5(b) and 5(c).

When exposure is made at a predetermined point c on the sample by a beam spot of 4 .mu.m.times.4 .mu.m size, the electron beam is moved as indicated by A, B and C (see FIG. 5(b)) in synchronism with a blanking voltage signal V (see FIG. 5(a)), stops at point c for time t.sub.b and again is moved as indicated by C, B and A, completing the exposure. FIG. 5(b) shows the situation in which the beam is moved on the sample. At this time, the amounts of charge, Q.sub.a and Q.sub.b irradiated at points a and b can be expressed as follows:

where J is the current value.

Therefore, the difference between the amounts of charge irradiated on points a and b is expressed as

If the amount of charge at point a is assumed to be the optimum exposure condition, the amount of charge at point b is .DELTA.Q short for exposure. Thus, when it is developed through a process, the size at point c is smaller than 4 .mu.m. On the other hand, when the sensitivity of the photoresist is increased, the optimum exposure condition Q.sub.a decreases and as a result the rate of .DELTA.Q to Q.sub.a is large. Thus, insufficient exposure will greatly increase the dimensional error.

Accordingly, it is an object of this invention to provide an electron beam lithography apparatus capable of uniforming exposure of a sample by an electron beam.

According to this invention, there is provided an electron beam lithography apparatus comprising means for generating an electron beam, means for shaping the electron beam, means for focusing the shaped electron beam on a sample to form an image thereon, means for permitting the focused electron beam to scan the sample, and means for deflecting the electron beam to thereby blank and unblank the same, wherein the electron beam is deflected in one direction to be blanked, unblanked and blanked in turn.

FIG. 1 schematically shows an electron beam lithography apparatus to which this invention is applied.

FIG. 2 is a circuit diagram of a main part of one embodiment of this invention.

FIGS. 3(a), 3(b) and 3(c) are diagrams to which reference is made in explaining the operation of an electron beam lithography apparatus according to this invention.

FIG. 4 is a diagram to which reference is made in explaining the effect of the electron beam lithography apparatus according to this invention.

FIGS. 5(a) and 5(b) are diagrams to which reference is made in explaining the operation of a conventional electron beam lithography apparatus.

FIG. 6 is a diagram to which reference is made in explaining the drawbacks of the conventional electron beam lithography apparatus.

FIG. 1 schematically shows the construction of an embodiment of an electron beam lithography apparatus according to this invention. Referring to FIG. 1, there is shown an electron gun 1, which emits an electron beam 2. This electron beam 2 passes through a shaping aperture 4 and through shaping lenses 3 and 3' by which the beam is shaped to be rectangular in cross-section. The rectangular-shaped electron beam 2 is further shaped by a shaping aperture 4' and passed through a blanker 10 to a projecting lens 5. The electron beam 2 passed through the projecting lens 5 is deflected to scan the surface of a sample 6 by a deflector 9.

There is also shown a CPU 7, which produces data and supplies it to a lithographing signal generating portion 8. A certain signal from the image signal generating portion 8 is supplied to the blanker 10 as a blanking voltage. Another certain signal from the generator portion 8 is supplied to the deflector 9, thereby deflecting the electron beam to scan the surface of the sample 6.

The voltage applied to the blanker 10 is generated by a circuit 8 which constitutes the image signal generating portion 8 and constructed as shown in FIG. 2. In FIG. 2, a high-level or low-level signal is supplied to terminals D.sub.A and D.sub.B and the terminal D.sub.A is connected to the gate of a switching transistor 12. This switching transistor 12 is connected in series with a resistor R.sub.1. One end of the series circuit on the resistor side is grounded and the other end of the series circuit on the transistor side is supplied with a voltage of -2 V. The terminal D.sub.B is connected to the gate of a switching transistor 13. This transistor 13 is also connected in series with a resistor R.sub.2. One end of the series circuit on the resistor side is grounded, and the other end thereof is supplied with a voltage of -V. One electrostatic electrode 11A of the blanker 10 is connected to the junction between the switching transistor 12 and the resistor R.sub.1 and to the junction between the switching transistor 13 and the resistor R.sub.2. The other electrostatic electrode 11B is connected to the other end of the series circuit of the transistor 13 and the resistor R.sub.2, or supplied with the voltage of -V.

When in this circuit arrangement of FIG. 2 a high-level signal is supplied to the terminal D.sub.A and a low-level signal to the terminal D.sub.B, the electrostatic electrodes 11A ad 11B provides a blanking voltage of -V/2 at the mid point, .alpha. between the electrodes (the blanking voltage is expressed by the voltage difference between the electrodes 11A and 11B). Thus, the electron beam is deflected to pass along the orbit of O, or blanked as shown. Then, when a low-level signal is supplied to the terminal D.sub.A and a high-level signal to the terminal D.sub.B, the blanking voltage at point .alpha. becomes 0 V, so that the beam is deflected to take the orbit of P, or making exposure as shown. At this time, the electron beam moves on the sample as indicated by F, G and H in FIG. 3(b). For the exposure of the next area K, the blanking voltage is changed as +V/2, 0 V and -V/2, thereby deflecting the electron beam so that it moves in the areas I, J, K. L and M on the sample as shown in FIG. 3(c), thus K being exposed.

FIG. 3(a) shows the change of the blanking voltage relative to the signal level applied to the terminals D.sub.A and D.sub.B.

The amounts of charge, Q at exposure points c and d within F can be expressed as

Thus, the amounts of change at points c and d are equal to each other as shown in FIG. 4. When the optimum exposure condition is Q.sub.e (=Q.sub.d), the maximum amount of deviation at point e from Q.sub.e is

This value is half the amount in the prior art. Therefore, the areas F and K are equally exposed, and hence the dimensional error can be reduced.

As described above, the electron beam lithography apparatus of the invention is constructed to deflect the electron beam in one direction, thereby blanking, unblanking and blanking it in turn. Thus, the surface of the sample can be uniformly exposed by the electron beam.