Microwave and radio frequency compound plasma etching system and method
By using a microwave and radio frequency composite plasma etching system, combining a microwave solid-state source and a radio frequency power source, the problem of etching uniformity in large-size wafers was solved, achieving high-density plasma excitation in the center and edge regions of the wafer, thus improving etching uniformity and etching efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HENAN ORIENTALMATERIALS CO LTD
- Filing Date
- 2026-02-10
- Publication Date
- 2026-06-12
AI Technical Summary
In semiconductor manufacturing, when using microwave-excited plasma etching, it is difficult to guarantee the etching uniformity of large wafers, especially since the plasma density at the wafer edge is significantly lower than that in the center region, resulting in uneven etching.
A microwave and radio frequency composite plasma etching system is adopted. By combining a microwave solid source and a radio frequency power source, high-density plasma is generated in the center and edge regions of the wafer, respectively. By using the design of waveguides and ring source electrodes, the diffusion of plasma in the center is restricted and the plasma density at the edge is increased, so as to achieve uniform etching.
This technology improves etching uniformity in the center and edge regions of large-size wafers. By independently adjusting the gas flow rate and power source, etching efficiency is optimized, thus overcoming the deficiency of insufficient plasma density in existing technologies.
Smart Images
Figure CN122202149A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the semiconductor field, specifically to a microwave and radio frequency composite plasma etching system and method. Background Technology
[0002] Dry etching technology plays a crucial role in semiconductor manufacturing processes. The core principle of this technology is to use gaseous plasma under vacuum conditions to etch the surface of a wafer, selectively stripping away specific materials to precisely replicate the patterned structure carried by photoresist on the thin film surface.
[0003] Among them, etching equipment that uses microwave-excited plasma can generate electron cyclotron resonance through the synergistic effect of microwaves and magnetic fields, thereby producing high-density plasma. The plasma produced has advantages such as high activity, low reaction temperature, and excellent process control precision.
[0004] However, there is a certain distance between the plasma generation region and the wafer, and the plasma needs to diffuse to reach the wafer surface. Moreover, the larger the wafer size, the more difficult it is to ensure the uniformity of plasma diffusion. The plasma density in the edge region of the wafer will be significantly lower than that in the center region, which makes it difficult to achieve ideal etching uniformity on large-sized wafers. Summary of the Invention
[0005] This invention provides a microwave and radio frequency combined plasma etching system and method to solve the technical problem of poor etching uniformity when etching large-size wafers, as mentioned in the background art.
[0006] According to one aspect of the present invention, a microwave and radio frequency composite plasma etching system is characterized in that it comprises:
[0007] The reaction chamber contains bias electrodes that support the wafer.
[0008] Microwave solid-state source, used to generate microwave signals;
[0009] The waveguide has one end connected to a microwave solid-state source to transmit microwave signals, and the other end is fed into the reaction cavity and extends to the bias electrode that carries the wafer inside the reaction cavity. The part of the waveguide inside the reaction cavity is a hollow cylinder.
[0010] An electromagnetic coil is arranged around a waveguide outside the reaction chamber to generate a magnetic field inside the waveguide, so that the reactant gas undergoes electron cyclotron resonance inside the waveguide to generate the first plasma.
[0011] The annular source electrode is coaxially arranged with the portion of the waveguide inside the reaction chamber and parallel to the bias electrode. The annular source electrode surrounds the waveguide.
[0012] The radio frequency power source, electrically connected to the ring source electrode, is used to provide a radio frequency signal to the ring source electrode to generate an electric field between the ring source electrode and the bias electrode, causing the reactant gas to generate a second plasma.
[0013] In one possible implementation, the system further includes a first gas supply unit and a second gas supply unit; the first gas supply unit is connected to a waveguide and is used to supply reaction gas into the waveguide; the second gas supply unit is connected to a reaction chamber and is used to supply reaction gas into the reaction chamber.
[0014] In one possible implementation, the system further includes a control unit configured to: acquire plasma density and electron temperature at different radial positions above the bias electrode; determine the degree of difference between a first plasma generated in the waveguide and a second plasma generated by the annular source electrode based on the plasma density and electron temperature; and adjust at least one of the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit based on the degree of difference to reduce the degree of difference.
[0015] In one possible implementation, the system further includes: a linear motor, which includes a mover and a stator, the stator being fixed to the side wall of the reaction chamber; an electrostatic probe, fixed to the mover of the linear motor; and a control unit electrically connected to the linear motor and the electrostatic probe, the control unit controlling the linear motor to drive the electrostatic probe to move radially above the bias electrode to collect plasma density and electron temperature at different locations.
[0016] In one possible implementation, the microwave signal frequency generated by the microwave solid-state source is 2.45 GHz, and the magnetic flux density generated by the electromagnetic coil is 875 Gs.
[0017] In one possible implementation, the control unit is further configured as follows:
[0018] The electrostatic probe is controlled to collect plasma density and electron temperature at multiple first sampling points in the central region below the waveguide, and plasma density and electron temperature at multiple second sampling points in the edge region below the annular source electrode.
[0019] In one possible implementation, the control unit is further configured as follows:
[0020] The first average density and first average temperature of the central region are calculated based on the plasma density and electron temperature of multiple first sampling points, and the second average density and second average temperature of the edge region are calculated based on the plasma density and electron temperature of multiple second sampling points.
[0021] The comprehensive difference coefficient characterizing the plasma differences between the central and peripheral regions is calculated based on the first average density, the first average temperature, the second average density, and the second average temperature.
[0022] In one possible implementation, the control unit is further configured as follows:
[0023] If the overall difference coefficient is greater than the preset difference threshold, adjust at least one of the following: the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit.
[0024] In one possible implementation, the control unit is further configured as follows:
[0025] The adjustment step size for the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit is determined based on the comprehensive difference coefficient.
[0026] According to another aspect of the present invention, a microwave and radio frequency composite plasma etching method is provided, applied to the above-mentioned microwave and radio frequency composite plasma etching system, the method comprising:
[0027] Obtain plasma density and electron temperature at different radial positions above the bias electrode;
[0028] The degree of difference between the first plasma generated in the waveguide and the second plasma generated by the annular source electrode is determined based on plasma density and electron temperature.
[0029] Based on the degree of difference, at least one of the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit is adjusted to reduce the degree of difference.
[0030] In one possible implementation, the acquisition of plasma density and electron temperature at different radial positions above the bias electrode includes: controlling an electrostatic probe to collect plasma density and electron temperature at multiple first sampling points in the central region below the waveguide, and plasma density and electron temperature at multiple second sampling points in the edge region below the annular source electrode.
[0031] In one possible implementation, determining the degree of difference between the first plasma generated within the waveguide and the second plasma generated by the annular source electrode based on plasma density and electron temperature includes: calculating a first average density and a first average temperature of the central region based on plasma density and electron temperature at multiple first sampling points, and calculating a second average density and a second average temperature of the edge region based on plasma density and electron temperature at multiple second sampling points; and calculating a comprehensive difference coefficient characterizing the plasma difference between the central region and the edge region based on the first average density, the first average temperature, the second average density, and the second average temperature.
[0032] In one possible implementation, the method further includes: adjusting at least one of the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit when the overall difference coefficient is greater than a preset difference threshold.
[0033] In one possible implementation, the above method further includes: determining the adjustment step size of the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit based on a comprehensive difference coefficient.
[0034] In this invention, by using a composite etching structure of microwave solid-state source and radio frequency power source, on the one hand, the plasma generation process excited by microwave solid-state source is confined to a waveguide near the center of the wafer, and the waveguide extends directly to the area above the wafer, reducing the circumferential diffusion diameter of the central plasma and obtaining a high-density, uniform central region plasma on a small circumference; on the other hand, the annular source electrode increases the plasma density in the edge region, making up for the deficiency of insufficient plasma density at the edge of large wafers in the prior art, and achieving uniform etching of the center and edge regions of large wafers. Attached Figure Description
[0035] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings. In the drawings, several embodiments of the invention are illustrated by way of example and not limitation, and like or corresponding reference numerals denote like or corresponding parts, wherein:
[0036] Figure 1 This is a schematic diagram of a microwave and radio frequency composite plasma etching system provided in an embodiment of the present invention;
[0037] Figure 2 This is a schematic diagram of another microwave and radio frequency composite plasma etching system provided in an embodiment of the present invention;
[0038] Figure 3A schematic diagram of another microwave and radio frequency composite plasma etching system provided in an embodiment of the present invention;
[0039] Figure 4 A flowchart of a microwave and radio frequency composite plasma etching method provided in an embodiment of the present invention;
[0040] Figure 5 A flowchart of another microwave and radio frequency composite plasma etching method provided in an embodiment of the present invention. Detailed Implementation
[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Those skilled in the art should understand that the embodiments described below are only some, not all, of the embodiments disclosed. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0042] First, combine Figure 1 The principle of current microwave plasma etching is explained. The microwave generator for plasma-excited etching is a microwave solid-state source. The 2.45GHz microwave emitted by the microwave solid-state source is transmitted to the reaction chamber 102 through the waveguide 100. The reaction chamber is surrounded by electromagnetic coils 101. Electrons undergo cyclotron motion under the action of the electric field generated by the microwave and the magnetic field formed perpendicular to the direction of the electric field. When the microwave frequency is 2.45GHz and the magnetic flux density is 875Gs, electron cyclotron resonance will occur, the collision probability will increase, and thus high-density plasma will be generated.
[0043] However, since the plasma generation area is a certain distance from the surface of wafer 103, it needs to reach the surface of wafer 103 through diffusion. The larger the size of wafer 103, the worse the uniformity of plasma diffusion, and the lower the plasma density is closer to the edge of wafer 103. Therefore, it is difficult to obtain good etching uniformity on a large wafer diameter using microwave-generated plasma etching method. In other words, the current method of using microwave-generated plasma to etch large-size wafers has the technical problem of poor etching uniformity.
[0044] The principles and spirit of the present invention will be explained in detail below with reference to several representative embodiments.
[0045] According to one aspect of the present invention, a microwave and radio frequency combined plasma etching system is provided, such as... Figure 2 As shown, the above-mentioned microwave and radio frequency composite plasma etching system includes:
[0046] The reaction chamber 1 is equipped with a bias electrode 12 that supports the wafer 11.
[0047] Microwave solid-state source 2, used to generate microwave signals;
[0048] The waveguide 3 is connected at one end to the microwave solid-state source 2 to transmit microwave signals, and at the other end it is fed into the reaction cavity 1 and extends to the top of the bias electrode 12. The part of the waveguide 3 inside the reaction cavity 1 is a hollow cylinder.
[0049] An electromagnetic coil 4 is arranged around a waveguide 3 outside the reaction chamber 1 to generate a magnetic field inside the waveguide 3, so that the reaction gas undergoes electron cyclotron resonance inside the waveguide 3 to generate the first plasma.
[0050] The annular source electrode 5 is coaxially arranged with the portion of the waveguide 3 inside the reaction chamber 1 and parallel to the bias electrode 12. The annular source electrode 5 is arranged around the waveguide 3.
[0051] The radio frequency power source 6 is electrically connected to the ring source electrode 5 and is used to provide radio frequency signals to the ring source electrode 5 to generate an electric field between the ring source electrode 5 and the bias electrode 12, so that the reaction gas generates a second plasma.
[0052] Understandably, the aforementioned microwave and radio frequency composite plasma etching system no longer relies on a single plasma source and diffusion to cover the entire wafer area. Instead, it integrates the microwave solid-state source 2 and the radio frequency power source 6 into a single etching system. Based on this, two coaxially arranged but independently operating plasma excitation regions are introduced: one inside the waveguide 3 located above the central region of wafer 11, where the first plasma is excited; and another region corresponding to the area above the edge region surrounding the central region of wafer 11 and below the annular source electrode 5, where the second plasma is excited. This provides high-density plasma sources for different radial regions of wafer 11 (the circular central region and the annular edge region), thereby addressing the edge density attenuation problem caused by long-range plasma diffusion from a single microwave source.
[0053] It should be noted that the plasma excitation function in the central region of the above system is jointly achieved by the microwave solid-state source 2, the waveguide 3, and the electromagnetic coil 4. The microwave solid-state source 2 generates a stable microwave signal with a frequency of 2.45 GHz, which is transmitted through the waveguide 3. The waveguide extends directly into the interior of the reaction chamber 1, with its end opening suspended at a predetermined distance directly above the wafer 11 or the bias electrode 12. The electromagnetic coil 4 is applied to the periphery of the waveguide 3 outside the reaction chamber 1, generating a steady-state magnetic field with an intensity of approximately 875 Gauss, perpendicular to the microwave electric field. When the reactive gas is introduced from the sidewall of the waveguide, the gas molecules enter the confined cylindrical space containing the microwave and magnetic field. Within this region, electrons undergo cyclotron resonance under the combined action of the electromagnetic field, gaining extremely high energy, thereby undergoing efficient and violent collisional ionization with the gas molecules, directly generating a highly active, high-density first plasma below the exit of the waveguide 3. (See details below.) Figure 3 .
[0054] In one possible implementation, the distance between the lower exit of the waveguide 3 and the wafer 11 is 50 to 100 mm.
[0055] Furthermore, by strictly confining the electron cyclotron resonance process within the waveguide 3 and limiting the distance between the lower outlet of the waveguide 3 and the wafer 11, the radial diffusion of the first plasma to the surrounding areas can be reduced, thereby forming a concentrated and uniform plasma cluster (first plasma) above the central region of the wafer 11.
[0056] Furthermore, to simultaneously etch and compensate for the annular region at the wafer edge, thus mitigating poor etching uniformity due to insufficient plasma diffusion to the wafer edge, a coaxial annular source electrode 5 is fitted around the periphery of the waveguide 3. This annular source electrode 5, together with the bias electrode 12 below, forms an annular parallel-plate capacitor structure, driven by an independent radio frequency power source 6. When radio frequency power is applied to the annular source electrode 5, an electric field is generated in the annular region between it and the bias electrode 12. The reactive gas introduced into this region is broken down under the influence of the strong electric field, forming a second plasma, namely radio frequency plasma. (See details...) Figure 3 .
[0057] It should be noted that although the plasma generation method relying on the parallel plate capacitor principle has better etching uniformity than the electron cyclotron resonance method, its plasma density is directly coupled to ion energy. For the plasma generation method relying on the parallel plate capacitor principle, to generate high-density plasma, it is necessary to increase the power fed into the plasma. In other words, the radio frequency power source limits the plasma density it generates. In this embodiment, the source electrode is set as a ring and is only responsible for exciting the second plasma above the ring edge region of the wafer. Under the premise that the maximum operating power of the radio frequency power source 6 remains unchanged, the significant reduction in electrode area means a significant increase in power density (power per unit area), thereby enabling the excitation of high-density plasma in this specific ring region to compensate for the edge etching uniformity of wafer 11.
[0058] In summary, by using the design of a composite plasma excitation source consisting of a microwave solid-state source 2 and a radio frequency power source 6, the plasma generation process excited by the microwave solid-state source 2 is confined within the waveguide 3 near the center of the wafer 11. At the same time, the waveguide 3 extends directly to the area above the wafer 11, reducing the first circumferential diffusion diameter of the plasma at the center and obtaining a high-density, uniform plasma in the central region on a small circumference. On the other hand, the annular source electrode 5 increases the plasma density in the edge region, compensating for the deficiency of insufficient plasma density at the edge of large wafers in the prior art, and achieving uniform etching of the center and edge regions of large wafers.
[0059] In one possible implementation, the system further includes a first gas supply unit 71 and a second gas supply unit 72;
[0060] The first gas supply unit 71 is connected to the waveguide 3 and is used to supply reaction gas into the waveguide 3;
[0061] The second gas supply unit 72 is connected to the reaction chamber 1 and is used to supply reaction gas into the reaction chamber 1.
[0062] It should be noted that the first gas supply unit 71 and the second gas supply unit 72 can be composed of a gas supply chamber and a gas flow meter. The gas flow rate of the first gas supply unit 71 to the waveguide 3 or the gas flow rate of the second gas supply unit 72 to the reaction chamber 1 can be controlled by controlling the gas flow meter.
[0063] In one possible implementation, the sidewalls of the reaction chamber 1 and the waveguide 3 have through holes, so that the gas paths of the first gas supply unit 71 and the second gas supply unit 72 can form gas paths with the interiors of the reaction chamber 1 and the waveguide 3 through the through holes, thereby transmitting gas into the reaction chamber 1 and the waveguide 3.
[0064] Specifically, the first gas supply unit 71 is connected to the waveguide 3 and is responsible for injecting the reactive gas into the electromagnetic field region inside the waveguide 3; the second gas supply unit 72 is connected to the main body of the reaction chamber so that reactive gas exists in the outer annular region between the annular source electrode 5 and the bias electrode 12. Furthermore, the flow rate, ratio, and even composition of the two gases can be independently adjusted according to different requirements for the first and second plasmas, thereby optimizing the etching efficiency of the two regions respectively. For example, by adjusting the flow rate ratio of the two gases, the difference in plasma density between the center and the edge can be directly compensated or balanced, avoiding the etching unevenness caused by pre-consumption or uneven mixing of the reactive gas during long-path transport.
[0065] In one possible implementation, the system further includes a control unit 8, which is configured to:
[0066] The plasma density and electron temperature at different radial positions above the bias electrode 12 were obtained;
[0067] The degree of difference between the first plasma generated in waveguide 3 and the second plasma generated by the annular source electrode is determined based on plasma density and electron temperature.
[0068] Based on the degree of difference, at least one of the power of microwave solid-state source 2, the power of radio frequency power source 6, the flow rate of first gas supply unit 71, and the flow rate of second gas supply unit 72 is adjusted to reduce the degree of difference.
[0069] It should be noted that the aforementioned control unit 8 can be a central processing unit, microcontroller, FPGA, DSP, edge computing device, or other computing device capable of performing logic calculations and artificial neural network calculations.
[0070] In one possible implementation, the aforementioned microwave and radio frequency combined plasma system further includes:
[0071] Linear motor 91, the linear motor includes a mover 91a and a stator 91b, the stator 91b is fixed to the side wall of the reaction chamber 1;
[0072] An electrostatic probe 92 is fixed to the mover 91a of the linear motor 91;
[0073] The control unit 8 is electrically connected to the linear motor 91 and the electrostatic probe 92. The control unit 8 controls the linear motor 91 to drive the electrostatic probe 92 to move radially above the bias electrode 12 in order to collect plasma density and electron temperature at different locations.
[0074] In one possible implementation, the control unit 8 is further configured as follows:
[0075] The electrostatic probe 92 is controlled to collect the plasma density and electron temperature at multiple first sampling points in the central region below the waveguide 3, and the plasma density and electron temperature at multiple second sampling points in the edge region below the annular source electrode 5.
[0076] In one possible implementation, the control unit 8 is further configured as follows:
[0077] The first average density and first average temperature of the central region are calculated based on the plasma density and electron temperature of multiple first sampling points, and the second average density and second average temperature of the edge region are calculated based on the plasma density and electron temperature of multiple second sampling points.
[0078] The comprehensive difference coefficient characterizing the plasma differences between the central and peripheral regions is calculated based on the first average density, the first average temperature, the second average density, and the second average temperature.
[0079] It should be noted that, for the central region, the control unit 8 calculates the first average density and the first average temperature based on the plasma density and electron temperature of multiple first sampling points, as shown in the following formula:
[0080] The average density of the central region is: ;
[0081] The average temperature in the central area is: ;
[0082] in, The number of the first sampling points in the central region. The plasma density at the first sampling point, The electronic temperature is the temperature of the first sampling point.
[0083] Similarly, control unit 8 calculates the second average density and the second average temperature for the edge region, as shown in the following formula:
[0084] The average density of the edge region is: ;
[0085] The average temperature of the edge region is: ;
[0086] in, The number of second sampling points in the edge region. The plasma density at the second sampling point, The electronic temperature at the second sampling point.
[0087] Furthermore, referring to the following formula, the control unit 8 calculates the difference between the first average density and the second average density (density difference rate) and the difference between the first average temperature and the second average temperature (temperature difference rate).
[0088] Density difference rate: ;
[0089] Temperature difference rate: ;
[0090] Furthermore, the control unit 8, based on the aforementioned density difference rate... Temperature difference rate The comprehensive difference coefficient, which characterizes the overall difference, is determined using the following formula:
[0091]
[0092] in, The comprehensive difference coefficient, , These are the weighting coefficients. .
[0093] Understandably, it can be determined based on specific process requirements. , The numerical value, for example, considering the significant impact of plasma density on the etching rate in the etching process, can be selected... 0.6 It is 0.4.
[0094] In one possible implementation, the control unit 8 is further configured as follows:
[0095] If the overall difference coefficient is greater than the preset difference threshold, adjust at least one of the following: the power of the microwave solid-state source 2, the power of the radio frequency power source 6, the flow rate of the first gas supply unit 71, and the flow rate of the second gas supply unit 72.
[0096] The specific adjustment methods are as follows:
[0097] like (The average density of the central area) is less than (The average density of the edge region) indicates that the plasma density in the central region is low. In this case, increasing the power of the microwave solid-state source 2 and the gas flow rate through the first gas supply unit 71 increases the microwave power, thereby enhancing the electron cyclotron resonance intensity in the central region and increasing the first plasma density. The increased gas flow rate also increases the amount of reacting gas, raising the collision probability and further enhancing the first plasma density in the central region. Furthermore, reducing the power of the radio frequency power source 6 and the gas flow rate through the second gas supply unit 72 can suppress the generation of the second plasma in the edge region, thereby reducing... and The differences between them;
[0098] like Greater than This indicates that the plasma density in the central region is high. In this case, increasing the power of the radio frequency power source 6 and the gas flow rate through the second gas supply unit 72 increases the radio frequency power, thereby strengthening the electric field intensity in the edge region and increasing the second plasma density. The increased gas flow rate also increases the amount of reactant gas, raising the collision probability of the reactant gas in the edge region and further enhancing the second plasma density there. Alternatively, reducing the power of the microwave solid-state source 2 and the gas flow rate through the first gas supply unit can suppress the generation of the first plasma in the central region, thereby reducing... and The differences between them;
[0099] like (The average temperature in the central area) is less than (The average temperature of the edge region) indicates that the temperature of the central region is low. In this case, increasing the power of the microwave solid-state source 2 increases the microwave power, thereby increasing the electron kinetic energy and raising the temperature of the central region. Simultaneously, decreasing the power of the radio frequency power source reduces the electron kinetic energy of the edge region, thus achieving... and The reduction of the differences between them;
[0100] like Greater than This indicates that the temperature in the central region is high. In this case, increasing the power of the RF power source 6 increases the RF power, thereby increasing the electron kinetic energy and thus raising the temperature in the annular edge region. Simultaneously, decreasing the power of the microwave solid-state source 2 reduces the electron kinetic energy in the central region, thereby achieving… and The difference between them has decreased.
[0101] In one possible implementation, the control unit 8 is further configured as follows:
[0102] The adjustment step size for the power of microwave solid-state source 2, the power of radio frequency power source 6, the flow rate of the first gas supply unit 71, and the flow rate of the second gas supply unit 72 is determined based on the comprehensive difference coefficient.
[0103] In one possible implementation, the system further includes a bias source 13 and an exhaust pump 14, wherein the bias source 13 is electrically connected to the bias electrode 12 and is used to provide a radio frequency signal to the bias electrode 12, and the exhaust pump 13 is used to evacuate the reaction chamber 1.
[0104] Through the above embodiments, the microwave and radio frequency composite plasma etching system, by using a composite etching structure of microwave solid source 2 and radio frequency power source 6, on the one hand, confines the generation process of the first plasma excited by microwave solid source 2 within a waveguide near the center of the wafer, and at the same time extends the waveguide directly to the area above the wafer, reducing the circumferential diffusion diameter of the first plasma in the central region, thereby obtaining a high-density and uniform first plasma in the central region on a small circumference; on the other hand, the annular source electrode 5 increases the second plasma density in the edge region, making up for the deficiency of insufficient plasma density at the edge of large wafers in the prior art, thereby improving the uniformity of etching large wafers.
[0105] According to another aspect of the present invention, a microwave and radio frequency (RF) composite plasma etching method is provided. This microwave and RF composite plasma etching method can be implemented using the aforementioned microwave and RF composite plasma etching system, such as... Figure 4 As shown, the above-mentioned microwave and radio frequency combined plasma etching method includes:
[0106] S102, obtain the plasma density and electron temperature at different radial positions above the bias electrode;
[0107] S104, based on plasma density and electron temperature, determine the degree of difference between the first plasma generated in the waveguide and the second plasma generated by the annular source electrode;
[0108] S106, based on the degree of difference, at least one of the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit is adjusted to reduce the degree of difference.
[0109] In one possible implementation, step S102 above includes:
[0110] The electrostatic probe is controlled to collect plasma density and electron temperature at multiple first sampling points in the central region below the waveguide, and plasma density and electron temperature at multiple second sampling points in the edge region below the annular source electrode.
[0111] It should be noted that step S102 above is used to acquire plasma data at different locations in the space above the wafer. This step can be performed by... Figure 1 This is achieved by using a linear motor 91 to drive an electrostatic probe 92. For example, through... Figure 1 The control unit 8 commands the linear motor 91 to drive the electrostatic probe 92 to move radially above the wafer 11 and stop at multiple pre-set sampling positions.
[0112] It should be noted that the aforementioned sampling locations are divided into two groups. One group is located directly below the waveguide outlet, corresponding to multiple first sampling points in the central region of the first plasma interaction. The other group is located below the annular region covered by the annular source electrode, corresponding to multiple second sampling points in the peripheral region (annular edge region) of the second plasma interaction. At each sampling point, the electrostatic probe collects the current-voltage characteristic curve and feeds the data back to the control unit 8. The control unit 8 calculates the plasma density and electron temperature at that point using electrostatic probe diagnostic theory, thereby realizing the aforementioned step S102 to obtain the plasma density and electron temperature at different radial positions above the bias electrode.
[0113] After obtaining the plasma density and electron temperature at different radial positions above the bias electrode, the above step S104 is performed to determine the degree of difference between the first plasma generated in the waveguide and the second plasma generated by the annular source electrode based on the plasma density and electron temperature.
[0114] Specifically, see Figure 5 The above step S104 includes steps S104-1 to S104-2:
[0115] S104-1, calculate the first average density and first average temperature of the central region based on the plasma density and electron temperature of multiple first sampling points, and calculate the second average density and second average temperature of the edge region based on the plasma density and electron temperature of multiple second sampling points;
[0116] S104-2, calculate the comprehensive difference coefficient characterizing the plasma difference between the central region and the edge region based on the first average density, the first average temperature, the second average density, and the second average temperature.
[0117] For step S104-1 above, the first average density and first average temperature of the central region are calculated based on the plasma density and electron temperature of multiple first sampling points, and the second average density and second average temperature of the edge region are calculated based on the plasma density and electron temperature of multiple second sampling points. It should be noted that, for the central region, its first average density and first average temperature are calculated based on the plasma density and electron temperature of multiple first sampling points, as shown in the following formula:
[0118] The average density of the central region is: ;
[0119] The average temperature in the central area is: ;
[0120] in, The number of the first sampling points in the central region. The plasma density at the first sampling point, The electronic temperature is the temperature of the first sampling point.
[0121] Similarly, the second average density and second average temperature are calculated for the edge region, as shown in the following formula:
[0122] The average density of the edge region is: ;
[0123] The average temperature of the edge region is: ;
[0124] in, The number of second sampling points in the edge region. The plasma density at the second sampling point, The electronic temperature at the second sampling point.
[0125] Understandably, by calculating the average density and temperature of the central region and the average density and temperature of the edge region through the above step S104-1, random errors or local anomalies (such as interference from a micro-dust particle) that may exist in single-point measurements are eliminated, and a large amount of data is compressed into the above four values, simplifying the subsequent calculations. Furthermore, it should be noted that plasma density characterizes ion flux and mainly affects the etching rate; while electron temperature affects the proportion of high-energy electrons and is closely related to the dissociation efficiency of reactive groups and the probability of device surface damage. Calculating and evaluating them separately, it can be determined that the main reason for etching non-uniformity lies in the difference in plasma density and the difference in plasma activity.
[0126] Furthermore, after calculating the first average density and first average temperature of the central region based on the plasma density and electron temperature of multiple first sampling points through the above step S104-1, and calculating the second average density and second average temperature of the edge region based on the plasma density and electron temperature of multiple second sampling points, the above step S104-2 is performed to calculate the comprehensive difference coefficient characterizing the plasma difference between the central region and the edge region based on the first average density, first average temperature, second average density, and second average temperature.
[0127] It should be noted that the differences between the first and second average densities, as well as the differences between the first and second average temperatures, can be determined first. Then, the aforementioned comprehensive difference coefficient can be calculated. As mentioned earlier, plasma density characterizes ion flux and primarily affects the etching rate; while electron temperature affects the proportion of high-energy electrons and is closely related to the dissociation efficiency of reactive groups and the probability of device surface damage. Determining these individual differences separately allows us to identify the main cause of etching non-uniformity as the difference in plasma density and plasma activity, thereby determining the overall difference.
[0128] For example, refer to the following formula to first calculate the difference between the first average density and the second average density (density difference rate) and the difference between the first average temperature and the second average temperature (temperature difference rate).
[0129] Density difference rate: ;
[0130] Temperature difference rate: ;
[0131] Furthermore, based on the aforementioned density difference rate Temperature difference rate The comprehensive difference coefficient, which characterizes the overall difference, is determined using the following formula:
[0132]
[0133] in, The comprehensive difference coefficient, , These are the weighting coefficients. .
[0134] Understandably, it can be determined based on specific process requirements. , The numerical value, for example, considering the significant impact of plasma density on the etching rate in the etching process, can be selected... 0.6 It is 0.4.
[0135] For example, in applications requiring high etching rates and stringent damage control, settings can be configured... 0.8 The value is set to 0.2 to give greater attention to density differences.
[0136] Understandably, this can be achieved by introducing preset weighting coefficients. , And perform linear weighting to adjust the above density difference rate Temperature difference rate The final comprehensive difference coefficient is calculated. The comprehensive difference coefficient is a value between 0 and 1, where 0 represents that the central region and the edge region are completely consistent, and the larger the value of the comprehensive difference coefficient, the worse the uniformity.
[0137] Furthermore, the comprehensive difference coefficient value calculated in real time can be compared with a predetermined difference threshold. For example, if the comprehensive difference coefficient is less than the difference threshold, it means that the current uniformity is within the allowable range, and the existing process parameters should be maintained; while if the comprehensive difference coefficient is greater than the difference threshold, it indicates that the non-uniformity has exceeded the allowable range, and the etching process parameters need to be adjusted.
[0138] That is, after performing step S104 above, and determining the degree of difference between the first plasma generated in the waveguide and the second plasma generated by the annular source electrode based on plasma density and electron temperature, if the comprehensive difference coefficient used to characterize the degree of difference is greater than a preset difference threshold, then at least one of the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit is adjusted.
[0139] The specific adjustment methods are as follows:
[0140] like (The average density of the central area) is less than The average density of the edge region indicates a low plasma density in the central region. In this case, increasing the microwave solid-state source power and the gas flow rate through the first gas supply unit increases the microwave power, which in turn strengthens the electron cyclotron resonance intensity in the central region, thus increasing the plasma density. The increased gas flow rate also increases the amount of reactive gas, raising the collision probability and further enhancing the plasma density in the central region. Furthermore, reducing the power of the radio frequency power source and the gas flow rate through the second gas supply unit can suppress the generation of edge plasma, thereby reducing... and The differences between them;
[0141] like Greater than This indicates a high plasma density in the central region. In this case, increasing the power of the radio frequency power source and the gas flow rate through the second gas supply unit will enhance the radio frequency power, thereby increasing the electric field strength in the edge region and consequently raising the plasma density. The increased gas flow rate also increases the amount of reactant gas, raising the probability of collisions with the reactant gas in the edge region and further enhancing the plasma density there. Alternatively, reducing the power of the microwave solid-state source and the gas flow rate through the first gas supply unit can suppress plasma generation in the central region, thus reducing... and The differences between them;
[0142] like (The average temperature in the central area) is less than (The average temperature of the edge region) indicates that the temperature of the central region is low. In this case, increasing the power of the microwave solid-state source increases the microwave power, which in turn increases the electron kinetic energy, thus raising the temperature of the central region. Simultaneously, decreasing the power of the radio frequency power source reduces the electron kinetic energy of the edge region, thereby achieving... and The reduction of the differences between them;
[0143] like Greater than This indicates that the temperature in the central region is high. In this case, increasing the power of the radio frequency power source increases the radio frequency power, which in turn increases the electron kinetic energy, thus raising the temperature in the annular edge region. Simultaneously, reducing the power of the microwave solid-state source lowers the electron kinetic energy in the central region, thereby achieving... and The difference between them has decreased.
[0144] The above implementation method can actively compensate for the impact of uniformity differences caused by cavity wear, gas batch differences or power fluctuations, thereby improving the reliability of the process.
[0145] In one possible implementation, the above method also includes:
[0146] The adjustment step size for the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit is determined based on the comprehensive difference coefficient.
[0147] It is understood that, for step S106 above, based on the degree of difference, at least one of the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit is adjusted to reduce the degree of difference. The adjustment range of the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit is not fixed, but is determined according to the magnitude of the above comprehensive difference coefficient, and is positively correlated.
[0148] Specifically, one or more threshold ranges for the comprehensive difference coefficient are preset. For example, when the comprehensive difference coefficient value just exceeds the difference threshold but is less than the first reference difference threshold, it is judged as a slight deviation. At this time, a small adjustment step size (such as micro power being fine-tuned by 1%) will be used for correction to avoid process oscillation or overshoot caused by excessively rapid parameter changes.
[0149] For example, if the value of the comprehensive difference coefficient exceeds the first reference difference threshold but is less than the second reference difference threshold, it indicates that the plasma state difference between the central region and the edge region is relatively serious. In this case, a larger adjustment step size (such as 5%) can be used to adjust the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit.
[0150] For example, if the overall difference coefficient exceeds the second reference difference threshold, it indicates that the plasma state difference between the central region and the edge region is extremely significant. In this case, a larger adjustment step size (such as 10%) can be used to adjust the power of the microwave solid-state source, the power of the RF power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit. This allows for faster intervention, enabling the process state to quickly return to a uniform range.
[0151] In addition, more precise settings can be made by combining the physical characteristics and process windows of each parameter. For example, a relatively small base step size can be used for a fast-responding RF power source to prevent instability, while a slightly larger step size can be set for a gas flow system with greater inertia to ensure the adjustment effect.
[0152] Through the above implementation method, by determining the adjustment step size of the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit based on the comprehensive difference coefficient, highly robust process control is achieved in the complex multivariable coupled plasma etching process.
[0153] The aforementioned microwave and radio frequency combined plasma etching method first obtains the plasma density and electron temperature at different radial positions above the bias electrode. Then, based on the plasma density and electron temperature, the degree of difference between the first plasma generated within the waveguide and the second plasma generated by the annular source electrode is determined. Finally, based on the degree of difference, at least one of the following is adjusted: the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit, to reduce the degree of difference. This overcomes the deficiency of insufficient plasma density at the edge of large-size wafers in existing technologies, thereby improving the uniformity of etching large-size wafers.
[0154] The above-described preferred embodiments of the present invention are provided as examples, but it will be apparent to those skilled in the art that such embodiments are provided merely by way of example. Many modifications, alterations, and alternatives will occur to those skilled in the art without departing from the spirit and intent of the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in the practice of the invention. The appended claims are intended to define the scope of protection of the invention and therefore cover the modular compositions, equivalents, or alternatives within the scope of these claims.
Claims
1. A microwave and radio frequency composite plasma etching system, characterized in that, include: The reaction chamber contains bias electrodes that support the wafer. Microwave solid-state source, used to generate microwave signals; A waveguide, one end of which is connected to the microwave solid-state source to transmit microwave signals, and the other end is fed into the interior of the reaction cavity and extends to the top of the bias electrode. The portion of the waveguide inside the reaction cavity is a hollow cylinder. An electromagnetic coil is arranged around the waveguide outside the reaction chamber to generate a magnetic field inside the waveguide, so that the reactant gas undergoes electron cyclotron resonance inside the waveguide to generate a first plasma. A ring-shaped source electrode is coaxially arranged with a portion of the waveguide within the reaction chamber and parallel to the bias electrode, the ring-shaped source electrode being arranged around the waveguide; A radio frequency power source, electrically connected to the ring source electrode, is used to provide a radio frequency signal to the ring source electrode to generate an electric field between the ring source electrode and the bias electrode, thereby causing the reactant gas to generate a second plasma.
2. The system according to claim 1, characterized in that, The system also includes a first gas supply unit and a second gas supply unit; The first gas supply unit is connected to the waveguide and is used to supply the reaction gas into the waveguide; The second gas supply unit is connected to the reaction chamber and is used to supply the reaction gas into the reaction chamber.
3. The system according to claim 2, characterized in that, The system also includes a control unit, which is configured to: The plasma density and electron temperature at different radial positions above the bias electrode were obtained; The degree of difference between the first plasma generated in the waveguide and the second plasma generated by the annular source electrode is determined based on the plasma density and electron temperature. Based on the degree of difference, at least one of the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit is adjusted to reduce the degree of difference.
4. The system according to claim 1 or 3, characterized in that, The system also includes: A linear motor, comprising a mover and a stator, wherein the stator is fixed to the side wall of the reaction chamber; An electrostatic probe is fixed to the mover of the linear motor; The control unit is electrically connected to the linear motor and the electrostatic probe. The control unit controls the linear motor to drive the electrostatic probe to move radially above the bias electrode in order to collect plasma density and electron temperature at different locations.
5. The system according to claim 1, characterized in that, The microwave signal frequency generated by the microwave solid-state source is 2.45 GHz, and the magnetic flux density generated by the electromagnetic coil is 875 Gs.
6. A microwave and radio frequency combined plasma etching method, characterized in that, Applied to the system as described in claims 1 to 5, the method comprises: Obtain plasma density and electron temperature at different radial positions above the bias electrode; The degree of difference between the first plasma generated in the waveguide and the second plasma generated by the annular source electrode is determined based on the plasma density and the electron temperature. Based on the degree of difference, at least one of the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit is adjusted to reduce the degree of difference.
7. The method according to claim 6, characterized in that, The process of obtaining the plasma density and electron temperature at different radial positions above the bias electrode includes: The electrostatic probe is controlled to collect plasma density and electron temperature at multiple first sampling points in the central region below the waveguide, and plasma density and electron temperature at multiple second sampling points in the edge region below the annular source electrode.
8. The method according to claim 6 or 7, characterized in that, The determination of the degree of difference between the first plasma generated within the waveguide and the second plasma generated by the annular source electrode, based on the plasma density and electron temperature, includes: The first average density and first average temperature of the central region are calculated based on the plasma density and electron temperature of multiple first sampling points, and the second average density and second average temperature of the edge region are calculated based on the plasma density and electron temperature of multiple second sampling points. A comprehensive difference coefficient characterizing the plasma difference between the central region and the edge region is calculated based on the first average density, the first average temperature, the second average density, and the second average temperature.
9. The method according to any one of claims 6 to 8, characterized in that, The method further includes: If the overall difference coefficient is greater than a preset difference threshold, adjust at least one of the following: the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit.
10. The method according to claim 9, characterized in that, The method includes: The adjustment step size for the power of the microwave solid-state source, the power of the radio frequency power source, the flow rate of the first gas supply unit, and the flow rate of the second gas supply unit is determined based on the comprehensive difference coefficient.