Patent GB-1325540-A (GB)
Title: Electron beam apparatus
IPC: H03K19/21
Filed: 1969-10-10
Abstract: 1325540 Function generators TEXAS INSTRUMENTS Ltd 2 Oct 1970 [10 Dot 1969] 49919/69 Heading G4G [Also in Division H1] In an electron beam apparatus, especially for exposing a sensitive resist in the manufacture of integrated circuits, wherein the beam is deflected by about 10,000 times the spot diameter over a plane surface, the deflection causes astigmatism and de-focusing due to the focal surface being spherical; these defects are corrected by applying signals proportional to the square of the deflection to the electron lens and signals proportional to the cube of the deflection to an astigmatism correction means. It is shown that the two waveforms to be supplied to the two sets of 4 astigmatism correctors are Œ a 2(X<SP>2</SP> + Y<SP>2</SP>) X (the smaller of | X | and | Y | and a ( | Y | - | X | ) (X<SP>2</SP> + Y<SP>2</SP>) where X and Y are the deflection signals and a is a multiplying factor. If the astigmatism corrector lies partly within the field of a magnetic objective lens which rotates the deflection, the quantities X and Y above should be related to axes which are rotated relative to the deflection axes X<SP>1</SP> and Y<SP>1</SP>. Waveform generating circuit. Fig. 7.- The signals X<SP>1</SP> and Y<SP>1</SP> from the deflection circuits are fed to the rotation circuit 62 which produces outputs X and Y related to rotate axes and includes X and Y preset controls for compensating for any offset in the symmetry along the axes. Circuits 68 and 69 derive | X | and | Y | and provide inputs to a comparator 72, which determines which of its inputs is smaller, and to an exclusive OR gate 77 which determines whether the signs of X and Y are the same or opposite. Multipliers 73 and 74 derive X<SP>2</SP> and Y<SP>2</SP> and combining circuits 78 and 79 combine the inputs to produce the two required outputs mentioned above. The switch 82 allows the two signals to be fed either way to the two astigmatism correctors via amplifiers 80 and 81 which are voltage or current amplifiers according to whether the correctors are electrostatic or magnetic. Axis rotation circuit. Fig. 8.-Four integrated circuit differential operational amplifiers 90-93 are connected as summing circuits with respective feedback resistors 94-97. Each amplifier has a main input resistor such as 98 (to which the Y<SP>1</SP> input is connected) and a pair of subsidiary input resistors such as 102 and 103 which are bridged by a potentiometer such as 110. The rotation control 63 adjusts the wipers of 111 and 112 in one direction and those of 110 and 113 in the opposite direction. The preset controls 64 and 65 shift the zero values of the X and Y waveforms to compensate for lack of symmetry of the objective lens in the two co-ordinate directions. The values of the input resistors of amplifiers 90 and 91 are twice those of the feedback resistors 94 and 95. Amplifying circuit. Fig. 14.-The current through a long-tailed pair 186 and 187 is controlled by the output of a summing amplifier 182, the inputs of which are X<SP>2</SP> and Y<SP>2</SP>. Inputs | Y | and | X | are supplied to the bases of transistors 186 and 187 the outputs of which are fed to a differential amplifier 190 which provides the required output (X<SP>2</SP> + Y<SP>2</SP>) ( | Y | - | X |). The same circuit with the base of transistor 187 earthed is used to derive X<SP>2</SP> from X which is supplied as an input to the amplifier 182 and to the transistor 186 (Fig. 12, not shown).