Multi-electron beam focusing device and control method

Abstract

The present invention discloses a multi-electron beam focusing device and a control method. The multi-electron beam focusing device comprises a thermal or cold field emission cathode electron source and a grid for generating electron beams, a beam splitter for splitting the electron beams, an accelerating lens for increasing the energy of the electron beams, a phase-decontrast lens for increasing the quality of the electron beams, a high-resolution objective lens array for each electron beam spot, an electron beam deflector for fine-tuning the electron beam position, and a beam gate for controlling the passage of the electron beams, so as to facilitate accurate control of the electron beams. Therefore, a larger number of electron beams can be accommodated on a wafer of the same area to achieve simultaneous exposure, thereby improving the accuracy and speed in integrated circuit processing applications.

Description

Technical Field

[0001] The present invention relates to the field of high-precision semiconductor processing, and in particular to a multi-electron beam focusing device and a control method. Background Art

[0002] Integrated circuit performance, such as computing speed and storage density, has always followed Moore's Law in the past. In the past few decades, it has become faster and stronger, which has also driven the continuous development of chip processing technology and the development of higher resolution processing technology. Until now, high-yield and high-precision patterning processing equipment has always been the core equipment of the semiconductor industry. Currently, advanced chip processing requires 30 to 50 exposure processes, and the cost of the entire exposure process accounts for about 1 / 3 of the cost of integrated circuit processing. Because the lithography machine can meet the needs of industrial production, it has developed into the only choice of exposure equipment in the current semiconductor processing industry.

[0003] Multi-beam electron beam exposure machine still has a huge market prospect. The realization of multi-beam electron beam is as follows:

[0004] One is to use a single electron emission source to generate an electron beam, which is divided into multiple beams by an aperture array and then focused by a single electron optical system. Its advantage is that the electron beams are generated from the same emission source, and the problems of current density and brightness unevenness are relatively small. Its significant disadvantage is that the uneven spatial field distribution of the focusing element makes it very difficult to focus the electron beam, and it is also difficult to make the beam spot of each electron beam uniform.

[0005] Another way to form multiple electron beams is to use multiple single electron beam systems to form an array. Its advantage is that each electron beam is a separate module, which is independent of each other and can be controlled individually. Due to the modular design, a large number of modules can be arbitrarily spliced ​​after a single module is completed. At the same time, since each module only contains a single electron beam, its electron optical design is also more concise and effective, the electron beam quality is higher, and the beam spot size that can be achieved is less than 5nm. However, with this solution, the number of electron beams depends entirely on the size of a single module. The size of a single module found in the literature is 2 cm * 2 cm, so only 16 electron beams can be accommodated on a 4-inch wafer. Increasing the electron beam can only reduce the size of a single module, but it is foreseeable that there is limited room for improvement using this technical route.

[0006] The third method is to replace the beam splitter with an electron emission array to generate multiple electron beams, such as a thermal field emission cathode array and a photocathode array. Compared with a single electron source, the emission current of the cathode array is distributed on a larger plane, the Coulomb effect is greatly reduced, the current density of a single electron beam is larger, and a higher electron beam energy can also be used. In experiments, good results can also be obtained using a cathode array. However, in a production environment, the electron beam exposure machine needs to work continuously and stably for a long time, and has high requirements on the emission ability and consistency of the cathode. Thermal cathodes such as coated barium tungsten cathodes have been used and tested for a long time, and have more advantages in uniform emission and life, and also meet the requirements of brightness and emission current. The photocathode array has not yet been used in the production line and needs further verification.

[0007] The fourth type is that a single electron emission source is divided into multiple beams by a beam splitter, and then focused by a micro-electron optical array. Mapper also adopts this technical route. In order to realize the concept of "patterned beam" and increase the total electron beam current, Mapper uses a total of 650,000 electron beams. The electron optical system array contains 13,000 units, each of which is used to focus 7*7=49 electron beams. To achieve a massive number of electron beams, it is necessary to overcome the difficulties of electron transmission focusing, especially to obtain small beam spots of 49 sub-electron beams within the limited focusing capacity of the micro unit, which is very difficult to achieve. Summary of the invention

[0008] In order to overcome the deficiencies of the prior art, the present invention provides a multi-electron beam focusing device, which can solve the difficulties in generating, transmitting and focusing multiple electron beams.

[0009] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0010] A multi-electron beam focusing device, the system comprises an electron beam emission source, a beam splitter, an accelerating lens, a phase-contrast lens, an objective lens array, an electron beam deflector and a beam gate which are sequentially arranged along the electron beam emission direction;

[0011] The electron beam generated by the electron beam emission source is sequentially split by a beam splitter, an accelerating lens is used to increase the energy of the electron beam, a phase-defocusing lens is used to eliminate phase difference to improve the quality of the electron beam, an objective lens array is used to focus the beam spot of each electron beam to improve the resolution, and an electron beam deflector is used to fine-tune the position of the electron beam, and then a beam gate is used to control the conduction or shutdown of the electron beam.

[0012] As a preferred technical solution of the present invention, the electron beam emission source includes a cathode electron source for generating an electron beam and a grid for emitting the electron beam, and the cathode electron source is arranged in the grid.

[0013] As a preferred technical solution of the present invention, the cathode electron source includes but is not limited to a tungsten metal needle tip with zirconium oxide plated on the surface.

[0014] As a preferred technical solution of the present invention, the beam splitter is provided with a plurality of beam splitting microholes arranged in an array, and the surface of the beam splitter is coated with a graphite layer.

[0015] As a preferred technical solution of the present invention, a high-voltage electrostatic field is applied to the accelerating lens.

[0016] As a preferred technical solution of the present invention, the number of electron beam deflectors corresponds one-to-one to the split electron beams, and the multi-electron beam focusing device also includes a first processor for controlling the working state of the electron beam deflectors, and the first processor is electrically connected to the electron beam deflectors through a data bus.

[0017] As a preferred technical solution of the present invention, the electron beam deflector includes a first bias electrode, a second bias electrode, a third bias electrode, a fourth bias electrode and a digital-to-analog conversion module. The four bias electrodes are respectively placed in four circuit layers, and each bias electrode is electrically connected to the first processor through the digital-to-analog conversion module and the data bus.

[0018] As a preferred technical solution of the present invention, four bias electrodes are surrounded to form a ring structure.

[0019] As a preferred technical solution of the present invention, the number of beam gates corresponds one-to-one to the split electron beams, and the multi-electron beam focusing device also includes a second processor for controlling the working state of the beam gates, and the second processor is electrically connected to the beam gates through a photoelectric transmission module.

[0020] As a preferred technical solution of the present invention, the beam gate includes a first beam gate electrode, a second beam gate electrode and a photoelectric transmission module. The two beam gate electrodes are respectively placed in two circuit layers, one of which is grounded and the other is a bias voltage. All beam gates have the same bias voltage. The beam gate is electrically connected to the second processor through the photoelectric transmission module.

[0021] The present invention also provides an electron beam control method, characterized in that it comprises the following steps:

[0022] An electron beam is generated and emitted by an electron beam emission source;

[0023] The electron beam is split by a beam splitter and directed to an accelerating lens;

[0024] The energy of the electron beam is increased by the accelerating lens so that the electron beam is accelerated to the achromatic lens;

[0025] The phase difference is eliminated by the dephaser lens to improve the quality of the electron beam;

[0026] The beam spot of each electron beam is focused by using an objective lens array, thereby reducing the electron beam spot radius and improving the resolution of electron beam exposure;

[0027] After the electron beam deflector fine-tunes the position of the electron beam, the beam gate controls whether the electron beam is emitted outward.

[0028] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0029] The multi-electron beam focusing device of the present invention is that the electron beam generated by the electron beam emission source is sequentially split by a beam splitter, an accelerating lens is used to increase the energy of the electron beam, a phase-defocusing lens is used to eliminate the phase difference to improve the quality of the electron beam, an objective lens array is used to focus the beam spot of each electron beam to improve the resolution, and after the electron beam position is fine-tuned by an electron beam deflector, the electron beam is turned on or off by a beam gate, thereby improving the resolution of the electron beam. In addition, each electron beam has a dedicated electron optical system, a deflection system and a beam gate, so as to facilitate the precise control of the electron beam, so that a larger number of electron beams can be accommodated on a wafer of the same area to achieve simultaneous exposure, thereby improving the accuracy and speed in integrated circuit processing applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a principle framework diagram of the generation, transmission and focusing system of multiple electron beams of the present invention;

[0031] Figure 2 is a schematic diagram of the electron source and beam splitter of the present invention;

[0032] Figure 3 is a top view of the electron beam bias electrode of the present invention;

[0033] Figure 4 is a side view of an electron beam bias electrode of the present invention;

[0034] Figure 5 is a schematic diagram of a control circuit of an electron beam deflector of the present invention;

[0035] Figure 6 is a top view of the electron beam gate electrode of the present invention;

[0036] Figure 7 is a side view of an electron beam gate electrode of the present invention;

[0037] Figure 8 is a schematic diagram of a control circuit for an electron beam gate of the present invention;

[0038] Fig. 9 It is a schematic structural diagram of the objective lens array of the multi-electron beam focusing device of the present invention.

[0039] Wherein: 1, electron beam emission source; 11, cathode electron source; 12, grid; 2, beam splitter 3, accelerating lens; 4, phase-decontrast lens; 5, objective lens array; 6, electron beam deflector; 61, first bias electrode; 62, second bias electrode; 63, third bias electrode; 64, fourth bias electrode; 7, beam gate; 71, first beam gate electrode; 72, second beam gate electrode DETAILED DESCRIPTION

[0040] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0041] Please refer to Figure 1-8 As shown, the present invention provides a multi-electron beam focusing device, which includes an electron beam emission source 1 for generating electron beams, a beam splitter 2 for splitting the electron beams, an accelerating lens 3 for increasing the energy of the electron beams, a phase-decontrast lens 4 for improving the quality of the electron beams, a high-resolution objective lens array 5 for each electron beam spot, an electron beam deflector 6 for fine-tuning the electron beam position, and a beam gate 7 for controlling the passage of the electron beams. The beam gate 7 and the electron beam deflector 6 are both connected to a control circuit, which can control whether a single electron beam is deflected and turned on and off, so as to facilitate accurate control of the electron beams. Therefore, a larger number of electron beams can be accommodated on a wafer of the same area to achieve simultaneous exposure, thereby improving the accuracy and speed in integrated circuit processing applications.

[0042] In precision electron beam optical systems, since the electromagnetic fields of adjacent units in a micro-electron optical array are not completely isolated, the influence of surrounding units must be fully considered during design. If multiple electron beams need to be transmitted in a single unit, the entire spatial field of the unit must be accurately calculated. At the same time, since the entire optical system itself is small in size and has relatively weak focusing ability, its design is much more difficult. Fig. 9 As shown, the objective lens array 5 is a micro objective lens array, with a small gap between the two objective lenses. Each electron beam is focused by a corresponding objective lens, and no electron beam passes through the gap between the objective lenses. The present invention uses an independent micro-electron optical unit to focus each electron beam, which can simplify the design and obtain a smaller electron beam spot. For example, when a beam splitting array of 100 rows and 100 columns is used, Figure 2 As shown, a single focusing unit can focus an electron beam current of 0.2 microamperes to a beam spot of a few nanometers.

[0043] In an optional embodiment, the electron beam emission source 1 includes a cathode electron source 11 and a grid 12, and is emitted from a metal surface under an external electric field force of a grid voltage. In this embodiment, the thermal field emission cathode electron source or the cold field emission cathode electron source includes but is not limited to a tungsten metal needle tip with a surface coated with zirconium oxide, and other electron emission materials may also be used.

[0044] The beam splitter 2 is provided with a plurality of beam splitting microholes arranged in an array, and the surface of the beam splitter 2 is coated with a graphite layer, which is located on the emission side of the electron beam emission source 1 of the beam splitter 2. A high-voltage electrostatic field is applied to the accelerating lens 3, and the voltage is 15KV, so that the energy of the electrons after the beam splitting is enhanced.

[0045] The number of the electron beam deflectors 6 corresponds to the split electron beams. The multi-electron beam focusing device also includes a first processor for controlling the working state of the electron beam deflectors 6. The first processor is electrically connected to the electron beam deflectors 6 via a data bus.

[0046] like Figure 4 As shown, the electron beam deflector 6 includes a first bias electrode 61, a second bias electrode 62, a third bias electrode 63, a fourth bias electrode 64 and a digital-to-analog conversion module. The four bias electrodes are arranged in a ring structure. The four bias electrodes are respectively placed in four circuit layers. Each bias electrode is electrically connected to the first processor through the digital-to-analog conversion module and the data bus.

[0047] Fine-tuning of the electron beam spot position is achieved through an electron beam deflector. Due to the large number of electron beams, even the most ideal electron beam optical system cannot minimize the spot size of all electron beams, so each electron beam optical system needs to be equipped with a separate electron beam deflector. The electron beam deflector uses electrostatic deflection to adjust the position of the electron beam by changing the deflection voltage. Configuring multiple deflection electrodes can achieve a good deflection effect, which are stacked in different circuit layers. Each deflection electrode needs to be able to be configured individually, and the voltage value to be configured is transmitted to the front-end processing circuit through the data bus, and becomes a bias voltage after digital-to-analog conversion. The maximum bias voltage is determined by the required deflection amount.

[0048] The number of the beam gates 7 corresponds to the split electron beams one by one. The multi-electron beam focusing device further includes a second processor for controlling the working state of the beam gates 7. The second processor is electrically connected to the beam gates 7 through a photoelectric transmission module.

[0049] In this embodiment, the beam gate 7 includes a first beam gate electrode 71, a second beam gate electrode 72 and a photoelectric transmission module. The two beam gate electrodes are respectively placed in two circuit layers, one of which is grounded and the other is a bias voltage. All beam gates 7 have the same bias voltage. The beam gate 7 is electrically connected to the second processor through the photoelectric transmission module.

[0050] In order to increase the yield of the electron beam exposure machine, in the multi-electron beam focusing device of the present invention, each electron beam is equipped with an independent beam gate to block or pass the electron beam to form a pattern of the wafer to be processed. The function of the electron beam beam gate is relatively simple. In the blocked state, it is only necessary to deflect the electron beam position outside the electron beam aperture, so only a single electrode is needed, and all electrodes can use the same bias voltage, so the circuit design is much simpler than the deflector. However, the biggest difficulty of the beam gate is that it requires high-speed dynamic response, and its total data bandwidth is the product of the exposure frequency of the electron exposure machine and the number of electron beams. In order to increase the scanning speed, the beam gate needs to work at high speed to operate each sub-electron beam. The present invention uses multiple optical fibers for signal distribution, and the number of unit arrays responsible for each optical fiber is determined by the bandwidth of the data processor, generally dozens to hundreds of arrays, such as a unit array of 10 rows and 10 columns. The control data of the unit array is transmitted in serial mode, and when it reaches the beam gate, it undergoes serial-to-parallel conversion, and simultaneously drives the corresponding number of beam gate array units to turn on and off.

[0051] Based on the above-mentioned multi-electron beam focusing device, the present invention also provides an electron beam control method, which comprises the following steps:

[0052] S10, an electron beam is generated by an electron beam emission source and emitted;

[0053] S20, splitting the electron beam through a beam splitter and directing it toward an accelerating lens;

[0054] S30, increasing the energy of the electron beam by an accelerating lens so that the electron beam is accelerated and directed toward an aberration lens;

[0055] S40, improving the quality of the electron beam by eliminating the phase difference through the phase-decontrast lens;

[0056] S50, focusing the beam spot of each electron beam by using the objective lens array, reducing the beam spot radius of the electron beam, and improving the resolution of electron beam exposure;

[0057] S60, after the electron beam deflector finely adjusts the position of the electron beam, the beam gate controls whether the electron beam is emitted outward.

[0058] In the electron beam control method of the present invention, the steps of electron beam generation, transmission and focusing are as follows:

[0059] 1. The electron beam is generated by a single tungsten metal needle tip with zirconium oxide coating on the surface. After the tungsten metal needle tip is heated, the energy of the free electrons is greater than the work function and then emitted from the metal surface under the external electric field force of the gate voltage. The gate voltage is between 50-100V. If the gate voltage is too large, the electron beam will easily collide with the beam splitter to generate unnecessary secondary electrons. Moreover, a voltage of 50-100V can make the cathode life exceed 1000 hours, the current density has good uniformity, the current intensity is about 5mA, and it has the ability to work continuously and stably for a long time. After the electrons are emitted, they are divided into 10,000 electron beams by a miniature 100*100 beam splitter. The diameter of the circular hole in the beam splitter is 15 microns, and the distance between the centers of adjacent circular holes is 22 microns. Figure 2 As shown, each electron beam carries a current of 0.2 microamperes, so that a nanometer-scale spot can be obtained during subsequent focusing.

[0060] 2. Each electron beam is then accelerated to a higher energy under the electric field force of the acceleration voltage. The stronger the energy carried by the electrons, the stronger the exposure capability and the higher the yield of the exposure machine. However, too high electron beam energy will also require the focusing and deflection circuits to work at a higher voltage, which will bring greater design difficulties. Therefore, the acceleration voltage is selected to be 15 kilovolts.

[0061] 3. After each electron beam passes through the corresponding dephasing electrostatic lens and focusing lens array, the energy dispersion of the electron beam becomes smaller, while the electron beam is focused and the beam spot becomes smaller. The spatial electromagnetic field of the sub-unit of the micro-electron optical array is calculated by the finite element method, and the unit field is extended to the neighboring units through the periodic boundary method. The overall spatial field is then used to accurately calculate the movement of the electron beam in the micro-electron optical array. The structural parameters and voltage of the electron optical system are finally obtained through a large number of simulations and optimizations to obtain the smallest beam spot. The results show that a 0.2 microampere 15 kilovolt electron beam can be focused to a beam spot of 10 nanometers.

[0062] 4. Due to the spatial distribution of electrons, it is impossible for the electron optical system to keep all electrons in the optimal focusing state, so it is necessary to fine-tune its configuration. Therefore, after the electron optical array, each electron beam can be fine-tuned in position and beam spot size through an independent deflector. The electron deflector consists of 4 electrodes, which can be loaded with different voltage values ​​in 4 circuit layers. Its structure is as follows: Figure 3 , Figure 4 As shown. The set voltage value is sent by the control program, reaches the corresponding electron deflector circuit through the bus system, undergoes digital-to-analog conversion, and then is obtained by the amplifier. The voltages of the four electrodes have different polarities and various voltage combinations can deflect the electrons to any position in the center hole. The corrected voltage value will be stored and used as a correction parameter, such as Figure 5 shown.

[0063] 5. In the application of electron beam exposure machine, it is necessary to expose various patterns, which is achieved by controlling the on and off of the electron beam, that is, the beam gate, such as Figure 6 , Figure 7 As shown. After passing through the electron beam deflector, each sub-electron beam is in the correct state. If the beam gate is not biased, the electron beam passes normally and exposure is implemented. If the beam gate is biased, the electron beam is deflected and cannot pass through the center hole, and exposure cannot be performed. Since the beam gate has only two states, on and off, there is no need to finely select the deflection voltage, so all beam gates share the same operating voltage. In this case, a multi-channel optical fiber signal distribution system is used to transmit the on / off signal to each control circuit using a photoelectric conversion circuit. Calculated at an exposure frequency of 10MHz and the number of 10,000 electron beams, the data bandwidth is 100Gb. When 100 optical fibers are used, the data bandwidth of each is 1Gb. Each optical fiber transmits a single 10*10 array data in serial, and after serial-to-parallel conversion, it simultaneously drives the on and off of the 10*10 array units, as shown Figure 8 shown.

[0064] The present invention splits the electron beam, then applies voltage to the accelerating lens to accelerate the electrons, uses a phase-decontrast lens to eliminate the phase difference to improve the quality of the electron beam, and then uses a micro-objective lens array to focus the beam spot to improve the resolution before emitting it. It is used for the exposure of integrated circuits, improves the precision of integrated electronic products, and reduces the cost of the optical system.

[0065] The implementation methods of the present invention are not limited to this. According to the above-mentioned embodiments of the present invention, by using conventional technical knowledge and customary means in the field, without departing from the above-mentioned basic technical ideas of the present invention, the above-mentioned preferred embodiments can also make other various forms of modification, replacement or combination, and the other embodiments obtained all fall within the scope of protection of the present invention.

Claims

1. A multi-electron beam focusing device, characterized in that: It comprises an electron beam emission source (1), a beam splitter (2), an accelerating lens (3), a phase-decontrast lens (4), an objective lens array (5), an electron beam deflector (6) and a beam gate (7) which are sequentially arranged along the electron beam emission direction; The beam splitter (2) is provided with a plurality of beam splitting microholes arranged in an array, and the surface of the beam splitter (2) is coated with a graphite layer, which is located on the emission side of the electron beam emission source 1 of the beam splitter 2; A high-voltage electrostatic field with a voltage of 15KV is applied to the accelerating lens (3) to enhance the energy of the electrons after beam splitting; The electron beam generated by the electron beam emission source (1) is sequentially split by a beam splitter (2), the energy of the electron beam is increased by an accelerating lens (3), the phase difference is eliminated by an anti-phase lens (4) to improve the quality of the electron beam, the beam spot of each electron beam is focused by an objective lens array (5) to improve the resolution, and the position of the electron beam is finely adjusted by an electron beam deflector (6), and then the electron beam is turned on or off by a beam gate (7); The number of the electron beam deflectors (6) corresponds to the number of the split electron beams. The multi-electron beam focusing device further comprises a first processor for controlling the working state of the electron beam deflectors (6). The first processor is electrically connected to the electron beam deflectors (6) via a data bus. The electron beam deflector (6) comprises a first bias electrode (61), a second bias electrode (62), a third bias electrode (63), a fourth bias electrode (64) and a digital-to-analog conversion module, wherein the four bias electrodes are arranged in a ring structure, the four bias electrodes are respectively placed in four circuit layers, and each bias electrode is electrically connected to the first processor via the digital-to-analog conversion module and a data bus; each bias electrode can be configured individually, and a voltage value to be configured is transmitted to a front-end processing circuit via the data bus, and becomes a bias voltage after digital-to-analog conversion; The number of the beam gates (7) corresponds one-to-one to the split electron beams, and the multi-electron beam focusing device further comprises a second processor for controlling the working state of the beam gates (7), and the second processor is electrically connected to the beam gates (7) via a photoelectric transmission module; The beam gate (7) comprises a first beam gate electrode (71), a second beam gate electrode (72) and a photoelectric transmission module. The two beam gate electrodes are respectively placed in two circuit layers, one of which is grounded and the other is biased. All beam gates (7) have the same bias voltage. The beam gate (7) is electrically connected to the second processor via the photoelectric transmission module, so that each electron beam is equipped with an independent beam gate to block or pass the electron beam, and the signal is distributed via the photoelectric transmission module. The control data of the unit array responsible for each photoelectric transmission module is transmitted in a serial manner, and when it reaches the beam gate (7), it undergoes serial-to-parallel conversion, and simultaneously drives the corresponding number of beam gates to turn on and off. After passing through the electron beam deflector (6), each sub-electron beam is in a correct state. If the beam gate (7) is not biased, the electron beam passes normally and exposure is performed. If the beam gate (7) is biased, the electron beam is deflected and cannot pass through the center hole, and exposure cannot be performed.

2. The multi-electron beam focusing device according to claim 1, characterized in that: The electron beam emission source (1) comprises a cathode electron source (11) for generating an electron beam and a grid (12) for emitting the electron beam, wherein the cathode electron source (11) is arranged in the grid (12).

3. The multi-electron beam focusing device according to claim 2, characterized in that: The cathode electron source (11) comprises a tungsten metal needle tip with zirconium oxide plated on the surface.

4. An electron beam control method for a multi-electron beam focusing device as claimed in claim 1, characterized in that: The steps include: An electron beam is generated and emitted by an electron beam emission source; The electron beam is split by a beam splitter and directed to an accelerating lens; The energy of the electron beam is increased by the accelerating lens so that the electron beam is accelerated to the achromatic lens; The phase difference is eliminated by the dephaser lens to improve the quality of the electron beam; The beam spot of each electron beam is focused by using an objective lens array, thereby reducing the radius of the electron beam spot and improving the resolution of electron beam exposure; After the electron beam deflector fine-tunes the position of the electron beam, the beam gate controls whether the electron beam is emitted outward.

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