The fabricating method of single electron transistor (set) by employing nano-lithographical technology in the semiconductor process

Description of equivalent WO 2007079174 A2

0001Title

0002The fabricating method of Single Electron Transistor (SET) by employing nano-lithographical technology in the semiconductor process

0003This application claims the benefit of provisional U.S. Patent Application Ser. No. 754,614, filed December 30, 2005.

0004Field of the Present Invention:

0005The present invention relates to the fabricating Single Electron Transistor (SET) in nano scale, particularly refers to the fabricating method of SET by employing nano-lithography and etching technology in the semiconductor process with breakthrough of physical limit in the existing facility for fabricating nano-structure so that not only the nano structural SET can be precisely fabricated out but also all the relative position and size, of each nano quantum dot in island electrode, drain electrode, source electrode and gate electrode can be precisely controlled and fabricated under process of room temperature so as to achieve the cost-effective purpose in mass production.

0006Background of the Present Invention

0007The nano-electronic technology is reckoned as the micro-electronic technological core of future new era as it mainly has working current of the nano-electronic component with quantum effect is in the range of several to several tens of electron such that its energy consumption in working operation being very low; Comparing with current micro-electronic component in the semiconductor, not only its energy consumption can be substantially reduced but also the pulse frequency (namely operation speed) is relatively enhanced; Wherein, Single Electron Transistor (SET) is considered as the potential core in the next generation of microprocessor, of which the main operational basis is on the physical effect of Coulomb Blockade Effect and Single Electron Tunnel Effect.

0008In the middle age of the 20^th century, both of the physical effect of Coulomb Blockade Effect and Single Electron Tunnel Effect were already theoretically expected, and the Coulomb Blockade Effect was one of important physical phenomena observed by the solid physics in 1980; When a physical system reduced to reach the nano scale, the charging and discharging process in such system will becomes discrete, namely quantumized. The Charging Energy (Ec) for charging an electron is [e²/2C], where, e is the electric charge of an electron, C is electric capacitance of such physical system; If the smaller is the C, then the greater is the Ec, hence it being called Coulomb Blockade Energy; Under such circumstance of the system, the charging and discharging electron can merely transmitted in one by one electron manner instead of collective group manner; the feature of single electron transmission in individual manner for the nano-scale system is called Coulomb Blockade Effect. Besides, if two quantum points are connected by a "Tunnel Junction" with a "Tunnel Barrier" in between, then a single electron passes from on e quantum point through the Tunnel Barrier and reaches the other quantum point is called "Quantum Tunneling Effect". Tn order to enable an electron tunnel from one quantum point through the Tunnel Barrier and reach the other quantum point, the energy of that electron (eV) must overcome the (Ec) of that electron, namely (eV) > (e/2C), where, C is the electric capacitance of the Tunnel Junction between both of the quantum points. Up to the 80 years of the post 20^th century, people can then successfully fulfill the utilization these effects in the circuit of electronic component under super low temperature; that is later than the theory of which for over several decades; the reason is that the human technology is neither mature enough to form a very tiny electrode nor to precisely position those electrodes. The direct application of the Coulomb Blockade Effect and Single Electron Tunnel Effect is the design and fabrication of the Single Electron Transistor (SET). The characteristic advantage of the SET component is low energy consumption, high temperature sensitivity and easiness of integration so that it is reckoned as one of the most promising new nano components after the micro electronic components.

0009Please refer to FIG 1, the fundamental circuit diagram of the Single Electron Transistor (SET), which had been already published, is a triode of source electrode S, drain electrode D and gate electrode G as well as an island electrode I, which locating between said source electrode S and drain electrode D; For said island electrode I, its electric capacitance is very small and its size is in nano scale relatively and further has Coulomb Blockade Effect of quantum dot QD and Tunnel Junctions at both ends of which; The characteristic of that structure is on the discrete energy level inside of the quantum point so that the electron can only tunnel from the source electrode S quantum point to the drain electrode D quantum point under the condition of lining up the Fermi level of the source electrode S quantum point and the drain electrode D quantum point with the energy level in the quantum point; Thereby, the tunneling electron number for each time can be controlled even up to optimal manner of only one single electron tunneling through each time; Hence, the total performance and yield of the SET is effected by the dl, d2 and d3 as well as size of itself, where, dl is the distance between the source electrode S and the island electrode I, d2 is the distance between the drain electrode D and the island electrode I, and d3 is the distance between the gate electrode G and the island electrode I; For current technology level, it is hard to achieve foregoing requirements; The high fabricating cost other than the technical difficulty aforesaid is the primal reason that SET is still not adopted in mass production by semiconductor and electronics industries.

0010As further shown in FIG 2 through FIG 4, the nano-structure is produced from conventional nano-lithography. The fabricating steps are as below: (A): First layout the expected nano pattern Q on the photomask M, then put said photomask M on the top surface of the substrate 1, which being spread with photo-resist 2 ( as shown in the FIG 2); (B): Pass light beam e through said nano pattern Q on said photomask M so as to have same pattern as said nano pattern Q on said photo-resist 2, which spreads on said substrate 1, by exposure and development to define the nano-aperture 3 structure (as shown in the FIG 3); (C): By means of deposit source device 30, directly deposit deposit material B of gas molecule or atom state on the surroundings and bottom of said nano-aperture 3 (as shown in view X and view Y of the FIG 4); And (D): Finally, selectively remove said photo-resist 2 by solution, thereby forming a nano quantum dot 4 structure on the surface of said substrate 1 (as shown in view Z of the FIG 4). Wherein, the conventional process aforesaid being confined to the precision limit of the existing photolithography such that the current best precise nano-scale can only reach 60—65 run; Hence, the nano-scale of said nano-aperture 3 from photomask M of pattern transferring photolithography is over 60 nm; Thereby, the nano-scale of said nano quantum dot 4 fabricated from these equipment is also over 60 nm relatively; Thus, the physical size limit of said conventional nano-devices of nano-structure is still in the range of over 60 nm; Therefore, how to breakthrough this bottleneck such that making the nano-scale of nano-aperture 3 be smaller becomes the impending crucial technical tough question of all experts in various fields; The solution being subject to the industrial practical feasibility in mass production and cost-effective economical principle so that the choice of means in technical breakthrough becomes more difficult; The scientists who understand the nano-science and the experts who familiarize with nano-technology are all aware of the benefits of working out the devices being smaller than 10 nm or even 1—2 nm, but none of better solution or effective technical breakthrough is proposed, announced or applied.

0011Summary of the Present Invention

0012The present invention originates a fabricating method of Single Electron Transistor (SET) by employing nano-lithographical technology in the semiconductor process with main object is to make use of existing facility of the semiconductor process without any change and alternation or revised design in the accuracy and precision of equipments so that not only the nano structural SET can be precisely fabricated out but also all the relative position, size, constituent and the density of each nano quantum dot in island electrode I, drain electrode D, source electrode S and gate electrode G can be precisely controlled and fabricated under process of room temperature in compatible manner with current existing nano-lithography so as to achieve the cost-effective in mass production.

0013The other object of the present invention is to provide a fabricating method of Single Electron Transistor (SET) by employing nano-lithographical technology in the semiconductor process with processing steps comprising: (a) First deposit the sealing material of gas molecule or atom state on the top-opening of the nano cylindrical pore, which having formed on the substrate, so that the diameter of said top-opening gradually reduce to become a reduced nano-aperture, whose opening diameter is smaller than that of said top-opening; (b) Keep said substrate in horizontal direction, and align the deposit material of gas molecular or atom state to face perpendicularly towards the reduced nano-aperture so that the island electrode nano quantum dot with same diameter as that of reduced nano-aperture is directly deposited n at the expected position on the surface of said substrate of the nano cylindrical pore by means of said deposit material passing through said reduced nano-aperture; (c) Keep the output of the deposit material of gas molecular or atom state in the same direction as before, tilt said substrate rightwards into tilt angle with the reduced nano-aperture as center, the drain electrode nano quantum dot is deposited at the expected right position of said existing island electrode on the surface of said substrate by the deposit material passing through said reduced nano-aperture again; (d) Keep the output of the deposit material of gas molecular or atom state in the same direction as before, tilt said substrate leftwards into tilt angle with the reduced nano-aperture as center, the source electrode nano quantum dot is deposited at the expected left position of said existing island electrode on the surface of said substrate by the deposit material passing through said reduced nano-aperture again; (e) Keep the output of the deposit material of gas molecular or atom state in the same direction as before, rotate said substrate clockwise into rotation angle in coordination with tilt angle θ with said reduced nano-aperture as central axis, the gate electrode nano quantum dot is deposited at the expected front position of said existing island electrode on the surface of said substrate by the deposit material passing through said reduced nano-aperture again; and (f) Finally, By means of solution rinsing (i.e. wet etching) or gas etching (i.e. dry etching), remove said nano cylindrical pore in said photo-resist on said substrate, thereby a SET (Single Electron Transistor) including island electrode nano quantum dot, drain electrode nano quantum dot, source electrode nano quantum dot and gate electrode nano quantum dot with nano-scale is directly fabricated on the surface of said substrate.

0014Brief Description of Drawings

0015FIG. 1 is the fundamental circuit diagram of the Single Electron Transistor (SET).

0016FIG. 2 is the perspective illustrative view showing the photo-mask and substrate according to conventional pattern transferring photolithography of nano-lithography process.

0017FIG. 3 is the cross sectional view taken on the line A-A of FIG. 2.

0018FIG. 4 is the illustrative flow chart showing the fabrication of nano-quantum-dot structure according to nano-lithography in the conventional semiconductor process.

0019FIG. 5 is the perspective illustrative view showing the formation of nano-cylindrical-pore according to nano-lithography in the conventional semiconductor process.

0020FIG. 6 is the illustrative flow chart showing the formation of reduced nano-aperture on the top of nano-cylindrical-pore according to the present invention.

0021FIG. 7 is the cross sectional illustrative view showing the completion of reduced nano-aperture on the top of nano-cylindrical-pore according to the present invention.

0022FIG. 8 is the operation illustrative view showing the formation of nano-quantum-dot for growing into SET on the surface of the substrate according to the present invention.

0023FIG. 9 is the illustrative flow chart showing the fabrication of nano-quantum-dot for the source electrode of the SET on the surface of the substrate according to the present invention.

0024FIG. 10 is the illustrative flow chart showing the fabrication of nano-quantum-dot for the drain electrode of the SET on the surface of the substrate according to the present invention.

0025FIG. 11 is the illustrative flow chart showing the fabrication of nano-quantum-dot for the island electrode of the SET on the surface of the substrate according to the present invention.

0026FIG. 12 is the illustrative flow chart showing the fabrication of nano-quantum-dot for the gate electrode of the SET on the surface of the substrate according to the present invention.

0027FIG. 13 is the illustrative view showing the completion of all the nano-quantum-dots for fabrication of the SET on the surface of the substrate according to the present invention.

0028FIG. 14 is the illustrative view showing the fabrication of nano-rod for the drain electrode of the SET on the surface of the substrate according to the present invention.

0029FIG. 15 is the illustrative view showing the fabrication of nano-rod for the source electrode of the SET on the surface of the substrate according to the present invention.

0030FIG- 16 is the illustrative view showing the fabrication of nano-rod for the gate electrode of the SET on the surface of the substrate according to the present invention. FIG. 17 is the illustrative view showing the completion of nano-quanrum-dot for island-electrode, nano-rod for drain-electrode, nano-rod for source-electrode and of nano-rod for gate-electrode of the SET on the surface of the substrate according to the present invention.

0031FIG. 18 is the first illustrative operation view showing the fabrication in widening process on the end of nano-rod for the drain-electrode of the SET according to the present invention.

0032FIG. 19 is the second illustrative operation view showing the fabrication in widening process on the end of nano-rod for the drain-electrode of the SET according to the present invention.

0033FIG. 20 is the first illustrative operation view showing the fabrication in widening process on the end of nano-rod for the source-electrode of the SET according to the present invention.

0034FIG. 21 is the second illustrative operation view showing the fabrication in widening process on the end of nano-rod for the source-electrode of the SET according to the present invention.

0035FIG. 22 is the illustrative view showing the completion of widening process on each end of the nano-rod for the drain-electrode, the source-electrode and the gate-electrode of the SET on the surface of the substrate according to the present invention.

0036Detailed Description of the Preferred Embodiment

0037Please refer to FIG 5, the existing nano cylindrical pore 10 is fabricated from conventional process in accordance with the build-up or build-down method; The minimum size of said conventional nano cylindrical pore 10 is 60 ran or 60 ran over; The alternative fabricating process can be anyone of the photolithography, nano-imprinting, Molecular Beam Epitaxy (MBE), and Metal-Organic Vapor phase Chemical Deposition in Epitaxy (MOVCD) to achieved the implement; However, the ways of these conventional technologies aforesaid are not to be detailed described here as their feature and know-how being not aspired after or sought for by the present invention.

0038Please refer to FIG. 5 through FIG 13, the process steps of the fabricating method of Single Electron Transistor (SET) by employing nano-lithographical technology in the semiconductor process in the present invention comprise:

0039(a): First deposit the sealant, sealing material A of gas molecule or atom state on the top-opening 11 of the nano cylindrical pore 10, which having formed on the photo-resist 2 of the substrate 1 (as shown in view B-B of the FIG. 5), so that the diameter of said top-opening 11 gradually reduce to become a reduced nano-aperture 20, whose opening diameter is smaller than that of said top-opening 11 (as shown in view g of the FIG 6 and FIG 7);

0040(b) Keep said substrate 1 in horizontal direction, and align the deposit material B of gas molecular or atom state to face perpendicularly towards the reduced nano-aperture 20 so that the island electrode I nano quantum dot 40 with same diameter as that of reduced nano-aperture 20 is directly deposited n at the expected position on the surface of said substrate 1 of the nano cylindrical pore 10 by means of said deposit material B passing through said reduced nano-aperture 20 (as shown in the FIG 9);

0041(c) Keep the output of the deposit material B of gas molecular or atom state in the same direction as before, tilt said substrate 1 rightwards into tilt angle 01 with the reduced nano-aperture 20 as center, the drain electrode D nano quantum dot 50 is deposited at the expected right position of said existing island electrode I on the surface of said substrate 1 by the deposit material B passing through said reduced nano-aperture 20 again (as shown in the FIG 10 and cross section view 2-2 of the FIG 10);

0042(d) Keep the output of the deposit material B of gas molecular or atom state in the same direction as before, tilt said substrate 1 leftwards into tilt angle Θ2 with the reduced nano-aperture 20 as center, the source electrode S nano quantum dot 60 is deposited at the expected left position of said existing island electrode I on the surface of said substrate 1 by the deposit material passing through said reduced nano-aperture 20 again (as shown in the FIG 11 and cross section view 3-3 of the FIG 11);

0043(e) Keep the output of the deposit material B of gas molecular or atom state in the same direction as before, rotate said substrate 1 clockwise into rotation angle Φ in coordination with tilt angle θ with said reduced nano-aperture 20 as central axis, the gate electrode G nano quantum dot 70 is deposited at the expected front position of said existing island electrode I on the surface of said substrate 1 by the deposit material B passing through said reduced nano-aperture 20 again (as shown in the FIG 12 and cross section view 4-4 of the FIG 12);

0044(f) Finally, By means of solution rinsing (i.e. wet etching) or gas etching (i.e. dry etching), remove said nano cylindrical pore 10 in said photo-resist 2 on said substrate 1, thereby a Single Electron Transistor (SET) including island electrode I nano quantum dot 40, drain electrode D nano quantum dot 50, source electrode S nano quantum dot 60 and gate electrode G nano quantum dot 70 with nano-scale is directly fabricated on the surface of said substrate 1 (as shown in the FIG 13 and whose top- view).

0045Wherein, if said tilt angle θl in step (c) equals tilt angle Θ2 in step (d), then the distance d2 will equal dl (as shown in the FIG 13); Besides, d3 is controlled by the magnitude of said rotation angle Φ (as shown in view 4-4 of the FIG 12), Hence, by means of easily controllable positioning in the 01,02 and Φ, then each of dl, d2 and d3 for source electrode S nano quantum dot 60, drain electrode D nano quantum dot 50 and gate electrode G nano quantum dot 70 between common island electrode I nano quantum dot 40 can be, together along with the density required per unit area, precisely achieved; Where,dl is the distance between said source electrode S nano quantum dot 60 and said island electrode I nano quantum dot 40, d2 is the distance between said drain electrode D nano quantum dot 50 and said island electrode I nano quantum dot 40, d3 is the distance between said gate electrode G nano quantum dot 70 and said island electrode I nano quantum dot 40.,(as shown in the FIG 13); Further, if each nano quantum dot is even required to have different material respectively such as semiconductor, metal and the like, they can be met by only selecting matched different deposit material B so that the present invention indeed has high total effect and low cost in consequence of not only applicable field and expansion is rather comprehensive but also all the process involved can be performed under the room temperature.

0046Moreover, the foregoing procedure of steps (b), (c), (d) and (e) are not mandatory in order sequence without flexibility; for example, if step (c) is taken as initial step to finish the drain electrode D nano quantum dot 50, then other island electrode I nano quantum dot 40, source electrode S nano quantum dot 60 and gate electrode G nano quantum dot 70 can also be subsequently finished with same result as foregoing procedure by approprirately control and adjust the each tilt angle θ and the rotation angle Φ .

0047Additionally, the sub-steps of performing said step (a) aforesaid in forming the reduced nano-aperture 20 on the top-opening 11 of the nano cylindrical pore 10 comprise (as shown in FIG 6):

0048(1):. First firmly place said substrate 1 on the tilt-rotary console R with capability of 3-D tilt and rotation and adjust said tilt-rotary console R in tilt angle 0(as shown in view a of the FIG 6), namely the included angle value of the central line of said top-opening 11 of said nano cylindrical pore 10 and the output direction of said deposit source device 40 is (90°-0); so that said sealing material A of gas molecule or atom state can partially deposit on the end rim of said top-opening 11 of said nano cylindrical pore 10 (as shown in view a of FIG 6 and corresponding view marked with A); and

0049(2): Let said tilt-rotary console R keep in tilt angle θ inclination, and gradually rotate it one complete rotation (as respectively shown in view b, c, d, e₅ f and each of corresponding lateral views of the FIG 6), thereby a reduced nano-aperture 20 with diameter being smaller than that of said top-opening 11 is formed on said top-opening 11 of said nano cylindrical pore 10 by deposition of said sealant, sealing material A of gas molecule or atom state (as shown in view g and corresponding lateral view of the FIG 6).

0050In aforesaid sub-step (2), the rotational number of said tilt-rotary console R can be increased so as to get smaller orifice diameter in said reduced nano-aperture 20; Besides, the size of the orifice diameter in said reduced nano-aperture 20 can be real-time monitored by membrane thickness meter to serve as basis in control the rotational speed of said tilt-rotary console R; Thus, the expected subsequent nano-structure of said island electrode I nano quantum dot 40, drain electrode D nano quantum dot 50, source electrode S nano quantum dot 60 and gate electrode G nano quantum dot 70 in various specifications can be conformed in consequence of the expected size of the orifice diameter in said reduced nano-aperture 20 can be achieved in this way. Furthermore, the output of said deposit material B of gas molecule or atom state in step (a) aforesaid is supplied by said deposit source device 30; In order to regulate said deposit material B of gas molecule or atom state to pass through said reduced nano-aperture 20 in manner of straight line path, a collimator Y can be installed between said deposit source device 30 and said reduced nano-aperture 20 (as shown in the FIG 8) so that the moving direction of said deposit material B of gas molecule or atom state becomes more coherent; Thus, the reliability of said island electrode I (nano quantum dot 40, drain electrode D nano quantum dot 50, source electrode S nano quantum dot 60 and gate electrode G nano quantum dot 70 forming on the surface of said substrate 1 is enhanced.

0051Please further refer to FIG 14 through FIG 17, in order to enable the drain electrode D nano quantum dot 50 to compatibly connect with other electronic components or conducting wire, the size of which should be expanded or widened by gradually increasing rightwards tilt angle Θ4 in foregoing step (c) so that a bar-shaped of drain electrode D nano rod 50a is gradually deposited and formed by letting deposit material B of gas molecular or atom state continuously passing through reduced nano-aperture 20 (as shown in the FIG 14 and view 5-5 of the FIG 14); Likewise, the leftwards tilt angle 05 in the foregoing step (d) can be further gradually increased so that a bar-shaped of source electrode S nano rod 60a is gradually deposited and formed by letting deposit material B of gas molecular or atom state continuously passing through reduced nano-aperture 20 (as shown in the FIG 15 and view 6-6 of the FIG 15); For the foregoing step (e), the tilt angle θ can be further gradually increased in coordination with the rotation angle Φ so that a bar-shaped of gate electrode G nano rod 70a is gradually deposited and formed by letting deposit material B of gas molecular or atom state continuously passing through reduced nano-aperture 20 (as shown in the FIG 16 and view 7-7 of the FIG 16); Through fabricating process of foregoing steps, the SET (Single Electron Transistor) with compatibility in connection with other electronic components or conducting wire can be successfully obtained.

0052Please further refer to FIG 18 through FIG 22, in order to widen the end of each nano-rod for drain electrode D nano rod 50a, source electrode S nano rod 60a and gate electrode G nano rod 70a respectively, the rotation anglesΦl, Φ2, Φ3 and Φ4 in foregoing steps (c), (d) and (e) can be gradually increased in controllable adjustment manner so that a SET including widened end of each nano-rod in drain electrode D nano rod 50a, source electrode S nano rod 60a and gate electrode G nano rod 70a respectively is successfully obtained.

0053In conclusion, adopting the fabricating method of Single Electron Transistor (SET) in the present invention, by means of adjusting suitable tilt angle θ, rotation angle Φ and diameter of the reduced nano-aperrure, all the position, size, constituent and the density of each nano quantum dot in island electrode I, drain electrode D, source electrode S and gate electrode G can be precisely controlled and fabricated under process of room temperature in compatible manner with current existing nano-lithography so that it becomes very simple and cost-effective in mass production as well as technical breakthrough in the fabricating process and technology of the SET (Single Electron Transistor); Thus, the present invention not only conforms to the industrial application and exploitation but also possesses the essential criteria of patentability of novelty, non-obviousness and practical advancement in practical use.