Inductively coupled plasma processing device and etching method thereof

Abstract

An etching method for an inductively coupled plasma processing device, the inductively coupled plasma processing device comprising a reaction chamber, the top of the reaction chamber comprising an insulating window and an inductive coil device located above the insulating window, wherein the center of the insulating window comprises an air inlet nozzle, the reaction chamber further comprising a base, a substrate to be processed is located on the base, the air inlet nozzle is used to input a processing gas into the reaction chamber, and is characterized in that: the processing gas input into the reaction chamber through the air inlet nozzle comprises an etching gas and an inert gas, wherein the etching gas is used to react with the material on the substrate to be processed to etch, and the flow rate of the inert gas is greater than 2 / 3 of the flow rate of the etching gas.

Description

Technical Field

[0001] The present invention relates to the field of semiconductors, and in particular to a plasma processing method applied to an inductively coupled plasma treatment device. Background Art

[0002] Plasma processing devices are widely used in integrated circuit manufacturing processes, such as deposition and etching. Among them, inductively coupled plasma (ICP) devices are one of the mainstream technologies in plasma processing devices. Their principle is to use radio frequency power to drive an inductively coupled coil to generate a strong high-frequency alternating magnetic field, which ionizes the low-pressure reaction gas to produce plasma. Plasma contains a large number of active particles such as electrons, ions, excited atoms, molecules, and free radicals. These active particles can undergo various physical and chemical reactions with the surface of the wafer to be processed, causing the morphology of the substrate to be processed to change, thus completing the etching process.

[0003] Figure 1 A schematic diagram of the structure of an inductively coupled plasma (ICP) reactor is shown. ICP etching equipment uses a magnetic field to couple energy from a radio frequency (RF) power source into a reaction chamber, thereby generating plasma for etching. The inductively coupled plasma reactor includes a vacuum reaction chamber 200, which includes a generally cylindrical metal sidewall 201. An opening 202 is provided in the sidewall for accommodating the entry and exit of a substrate W. An insulating window 217 is provided above the sidewall 201, and an inductive coil 215 is positioned above the insulating window 217. An RF power source 218 applies RF voltage to the inductive coil 215 via an RF matching network 216.

[0004] A liner 220 is provided inside the reaction chamber to protect the inner wall of the reaction chamber from being corroded by plasma. A gas nozzle 203 is provided at one end of the reaction chamber side wall near the insulating window. A gas nozzle 103 can also be provided in the central area of the insulating window 217. The gas nozzle 203 is used to inject the reaction gas into the vacuum reaction chamber 200. The RF power of the RF power source 218 drives the inductor 215 to generate a strong high-frequency alternating magnetic field, so that the low-pressure reaction gas in the reaction chamber is ionized to generate plasma. The processing gas supply device 100 outputs the reaction gas with an adjustable flow rate ratio to the central gas nozzle and the edge gas nozzle 203. A base 210 is provided at the downstream position of the vacuum reaction chamber 200. An electrostatic chuck 212 is provided on the base 210. An electrostatic electrode 213 is provided inside the electrostatic chuck 212 to generate electrostatic suction to support and fix the substrate W to be processed during the process. Plasma contains a large number of active particles, such as electrons, ions, excited atoms, molecules, and free radicals. These active particles can undergo various physical and chemical reactions with the surface of the substrate to be processed, causing the morphology of the substrate surface to change, thus completing the etching process. A biased RF power source 250 applies a biased RF voltage to the base through an RF matching network 252 to control the bombardment direction of the charged particles in the plasma. An exhaust pump 240 is also provided below the vacuum reaction chamber 200 to discharge reaction byproducts from the vacuum reaction chamber and maintain the vacuum environment of the reaction chamber.

[0005] When the plasma treatment effect on the substrate in the plasma reaction chamber of the above structure is uneven in the radial direction, the flow rate input from the processing gas supply device 100 to the edge gas nozzle 203 or the flow rate input to the center nozzle 103 can be adjusted to improve the uniformity. However, the edge gas nozzle 203 provided through the aluminum liner 220 will bring many technical problems. The corrosive processing gas will corrode the air flow duct in the liner 220. The complex shape of the air flow duct and the extremely small inner diameter (the smallest point is <1mm) make it a technical problem to apply a corrosion-resistant coating in these air flow ducts. On the other hand, the air flow duct passing through the liner 220 will also make it more difficult to control the stable temperature of the liner. Therefore, although supplying the processing gas from the side wall of the reaction chamber can improve the uniformity of the plasma treatment, it also brings the problems of complex structure and high manufacturing cost. Summary of the Invention

[0006] The present invention proposes an etching method for an inductively coupled plasma processing device. The inductively coupled plasma processing device includes a reaction chamber, a top portion of which includes an insulating window and an inductive coil device positioned above the insulating window. The insulating window includes a gas inlet nozzle at its center. The reaction chamber also includes a base on which a substrate to be processed is positioned. The gas inlet nozzle is used to input a processing gas into the reaction chamber. The method is characterized in that the processing gas is supplied to the reaction chamber via the gas inlet nozzle, and a plasma is ignited to perform plasma processing on the substrate to be processed. The processing gas input into the reaction chamber includes an etching gas and an inert gas, wherein the etching gas is used to react with the material on the substrate to be processed to etch it, and the flow rate of the inert gas is greater than two-thirds of the etching gas flow rate. The etching method proposed by the present invention can significantly improve the uniformity of plasma processing.

[0007] Preferably, the flow rate of the inert gas is greater than the flow rate of the etching gas.

[0008] The inductor assembly includes first and second inductors, with the first inductor located in the center of the insulating window and the second inductor surrounding the first inductor. When the inert gas flow rate is greater than or equal to twice the etching gas flow rate, and the power input to the first inductor is greater than the power input to the second inductor, etching uniformity can be further improved while simultaneously increasing the etching rate.

[0009] The present invention also proposes an inductively coupled plasma processing device, which includes a reaction chamber, a top of the reaction chamber including an insulating window and an inductive coil device located above the insulating window, wherein the center of the insulating window includes an air inlet nozzle, the reaction chamber also includes a base, and the substrate to be processed is located on the base, the air inlet nozzle is used to input processing gas into the reaction chamber, the air inlet nozzle is connected to a processing gas supply device, and outputs processing gas including etching gas and inert gas into the reaction chamber, wherein the etching gas can react with the surface material of the substrate to be processed; the inductive coil device includes first and second inductive coils, wherein the first inductive coil is located in the central area of the insulating window, and the second inductive coil surrounds the first inductive coil; a controller controls the processing gas supply device so that the flow rate of the inert gas in the processing gas is greater than the flow rate of the etching gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a structural schematic diagram of a plasma processing device in the prior art;

[0011] Figure 2 It is a structural schematic diagram of a plasma processing device of the present invention;

[0012] Figure 3a 、 Figure 3bThis is a graph showing the etching rate distribution at different helium flow rates of the present invention;

[0013] Figure 4 yes Figure 2 The cross-sectional structural diagram of the processing device of the present invention at point X is shown. DETAILED DESCRIPTION

[0014] In semiconductor chip production lines, inductively coupled plasma etcher (ICP) is usually used for etching silicon such as single crystal silicon or polycrystalline silicon due to its low ion energy. The structure of the ICP plasma processor proposed in the present invention is as follows: Figure 2 As shown, Figure 1 The prior art plasma processing device shown has the same basic structure, but the process gas channel is no longer provided in the liner 220, making the liner 220 simple and easy to manufacture, and significantly reducing the manufacturing cost of the entire plasma processing device. The process gas supply device 100 selects the ratio of each component gas from multiple gas storage bottles according to the settings of the process menu, and finally mixes them to form the process gas. The process gas is input into the gas inlet nozzle 103 located below the central area of the insulating window 217 through the gas distributor 101. The gas inlet nozzle includes a first gas nozzle 103a located in the center and a plurality of second gas nozzles 103b arranged around the first gas nozzle 103a. The gas input from the first gas nozzle 103a flows downward, and the gas output from the second gas nozzle 103b flows toward the peripheral area of the reaction chamber. The gas distributor 101 can improve the uniformity to a certain extent by adjusting the flow ratio of the process gas input to the first gas nozzle 103a and the second gas nozzle 103b. The inductor coil at the top of the insulating window includes a first inductor coil 213 located in the central area and a second inductor coil 215 arranged around the central area. An RF power supply 218 outputs RF power to a power divider 214 through a matcher 216. The power divider distributes the power ratio output to the first inductor coil 213 and the second inductor coil 215.

[0015] When etching silicon materials, the primary etching gas used can be SF6, or it can also include Cl2. To assist in ion bombardment, a small amount of inert gas, such as argon or helium, is often added. Typical process gas parameters are SF6 / Cl2 / He gas flow rates of 60 sccm / 240 sccm / 100 sccm, respectively. However, when etching with these parameters, even after adjustment using the aforementioned gas flow distributor 101 and power distributor 214, ideal etching uniformity cannot be achieved. The applicant's research has discovered that because the reaction chamber liner lacks independent gas flow channels and only has the gas nozzle 103 at the center of the insulating window 217, the etching gas ejected from the second gas nozzle 103b within the reaction chamber is difficult to diffuse to the peripheral areas. Even increasing the gas flow rate from the second gas nozzle has little effect. The inability of the etching gas to quickly reach the edge areas also results in the etching gas dissociating into a small amount of plasma in the process gas below, even if the input power of the second coil 215 is increased. This fails to effectively compensate for the uneven distribution of the final etching rate due to the uneven gas distribution.

[0016] Based on the above-mentioned limited gas inlet structure, the inventors have developed a plasma processing method that uses process component adjustment to achieve the best etching rate and etching uniformity. The new etching method proposed by the present invention includes, on the basis of keeping the flow rate of the etching gas SF6 / Cl2 basically unchanged at 300sccm, significantly increasing the flow rate of the inert gas (He) to 200sccm or above 300sccm. The significantly increased He gas can be introduced into any nozzle 103a / 103b in the gas inlet nozzle 103, and then the He gas molecules with extremely small molecular weight quickly diffuse to the peripheral area of the reaction chamber, so that the plasma concentration distribution curve generated by the He gas molecules is complementary to the plasma concentration generated by the ionization of the etching gas (SF6 / Cl2) molecules. Ultimately, even if the concentration of etching gas molecules in the edge area is slightly lower, the plasma concentration is higher, making these etching gas molecules more active, compensating for the etching speed difference between the edge area and the central area due to the small amount of etching gas. The etching rate is mainly affected by the concentration of the etching reactants. In the prior art, helium is only used as a component of physical bombardment, so a small flow rate is sufficient to achieve downward bombardment. However, it is not recognized that increasing the helium flow rate to the extent defined in the present invention can change the role of helium in the etching process. Although helium does not directly react with the silicon material below, high-flow helium gas entering the gas nozzle 103 located in the center of the reaction chamber can form a higher concentration plasma at the periphery of the reaction chamber, thereby compensating for the etching rate below. In order to further enhance the effect of the invention, more helium can be input into the reaction chamber through the nozzle 103b in the air inlet nozzle, which helps the helium to quickly diffuse to the edge area of the reaction chamber. Therefore, the process gases flowing through 103a and 103b in the air inlet nozzle 103 have different helium contents, wherein the helium content in 103b is higher than that in 103a, but the helium content in the total process gas still needs to be maintained at more than 2 / 3.

[0017] The inventors further discovered that Figure 3a The figure shows a comparison of the etching rate distribution curves under different helium flow rates when the etching gas is maintained at a stable flow rate. The horizontal axis is the position area, extending from the center of the substrate (X = 0) to the periphery to the edge of the substrate (x = 150mm), and the vertical axis is the etching rate in angstroms per minute (A / m). It can be seen from the figure that as the helium flow rate increases, the etching rate in the edge area of the substrate rises rapidly, while the etching rate in the center area slowly decreases, reaching a new uneven distribution in which the etching rate in the center area is lower than the etching rate in the edge area. Figure 3a and 3bAs shown, in the prior art, a helium flow rate of approximately 100 sccm is typically selected, resulting in an etch rate uniformity of 6.1% (the difference in etch rate between different regions on the substrate). This uniformity improves to 4.9% at a helium flow rate of 200-300 sccm, and to 4.1% at a helium flow rate of 500 sccm. Further increasing the flow rate to 600 sccm increases the uniformity to 7.5%, but this distribution is completely opposite to the prior art's high-center-low-edge distribution, with the etch rate being higher at the edges and lower at the center.

[0018] For this purpose, the inventors have proposed another preferred embodiment, which increases the flow rate of helium to more than twice that of the etching gas (more than 600 sccm). At this time, the etching rate is higher in the edge area and lower in the center area. Through the adjustment of the power divider 214, the RF power input to the central inductor 213 is increased from 40% of the total power output of the matcher 216 to more than 50%, or more than 60%. Since the etching gas itself is more concentrated in the central area above the substrate, increasing the corresponding RF power input can immediately increase the etching rate in the central area, and finally obtain a uniform etching rate distribution (etching rate uniformity is less than 4%). At the same time, the overall etching rate is also increased from 1400 A / m to more than 1600 A / m. As shown in FIG. Figure 3b As shown, curve 290 is the etching rate curve when the helium flow rate is 600 sccm and the power of the first RF coil is increased to 55%. Therefore, the plasma etching process of the present invention can achieve higher plasma etching rate uniformity in an inductively coupled reactor equipped with only a single gas inlet nozzle, while also increasing the average etching rate.

[0019] The inductor device of the present invention can be as follows Figure 2 The flat-plate inductor coil shown may also be in other shapes, such as a dome shape, or have a concave center and convex edges. Any coil structure that can independently adjust the concentration ratio between the center and edge areas in the plasma processing chamber below can be applied to the embodiments of the present invention.

[0020] The first inductor coil 213 and the second inductor coil 215 are used to control the plasma concentration parameters of the first processing area Sc located at the center and the second processing area Se located at the periphery. Figure 4 Shown Figure 2A schematic cross-sectional view of a plasma processor at point X shows a dividing line L between the first and second inductors, dividing the reaction space below into two processing regions. The dividing line L can be located midway between the outermost portion of the first inductor 213 and the innermost portion of the second inductor 215, or it can be closer to the first or second inductor. The electromagnetic field generated by the first inductor 213 dominates the plasma concentration in the first region Sc within the inner portion of the dividing line L. Correspondingly, the electromagnetic field generated by the second inductor 215 dominates the plasma concentration in the region Se between the outer portion of the dividing line and the inner wall 220. In conventional plasma processing, the inductor structure and dimensions of a plasma processor are relatively fixed. The area ratio of Sc to Se is R, and the RF power P1 and P2 input to the first and second inductors are positively correlated with the area ratio R. The RF power ratio (P1 / P2) input to the first and second inductors is typically between 1.2 and 1.5R. Excessively high or low RF power ratios can lead to uneven plasma concentration distribution. Because conventional process parameters result in a distribution where the central region's etching rate is higher than that of the peripheral regions, unevenness is typically addressed by increasing input power P2 or decreasing input power P1, further reducing the power ratio. In the present invention, due to the large amount of inert gas introduced into the reaction chamber, this unique situation occurs where the central etching rate is lower than the peripheral etching rate. Therefore, the power P1 input to the central region Sc needs to be greater than the power P2 input to the peripheral regions to compensate for the significantly different etching rate distribution curve from the prior art due to the large amount of inert gas introduced. Therefore, the RF power ratio between the first and second inductor coils in the present invention needs to be greater than 2.5R to meet process uniformity requirements, far exceeding the adjustment range of conventional processes. For example, if the first inductor coil occupies 1 / 4 of the cross-sectional area of the plasma processing space and the second inductor coil occupies 3 / 4, the ratio R is 1 / 3. In this case, under conventional processes, the power ratio (P1 / P2) input to the first and second inductor coils needs to be around 0.4-0.5, meaning that the first inductor coil at the center receives 28.5% of the RF power, and the second inductor coil at the peripheral receives 71.5% of the RF power. However, after adopting the present invention, the RF power ratio parameter of the first and second inductor coils needs to reach 2.5×1 / 3=0.83 or above, that is, P1 needs 45.4% and P2 needs 54.6% of RF power to meet the requirement of etching rate uniformity.

[0021] The second inductor 215 can be further divided into multiple sub-inductors, each with independent input power control, such as input power P21 for the first sub-coil and P22 for the second sub-coil. As long as the ratio of P1 to the sum of the two sub-coil powers (P21 + P22) is greater than 2.5R, the etching rate uniformity can be relatively improved, ultimately achieving the objectives of the present invention. This is a variant embodiment of the present invention.

[0022] According to the description of the working principle of the present invention, it can be seen that the etching method of the present invention can also be applied to Figure 2 In the various etching processes in the inductively coupled reactor shown, as long as there is uneven distribution of etching gas from the center to the edge, the method of the present invention can be used to increase the helium flow rate, obtain a plasma concentration distribution curve with a higher edge concentration, and ultimately obtain a more uniform etching rate distribution. For different etching processes, such as when etching a silicon oxide material layer, the etching gas can be a fluorocarbon such as C4F8 or a fluorocarbon hydrogen such as CHF3, etc., mixed with other auxiliary gases such as oxygen and other halogen gases such as bromine for etching, and a large amount of small molecule inert gas is introduced at the same time so that the etching rate has a uniform distribution on the substrate. The flow rate of the inert gas needs to reach more than 2 / 3 of the total amount of the etching gas, and preferably needs to be greater than the total flow rate of the etching gas or even reach 2 times or more, and then combined with increasing the power input to the central inductor coil, it is possible to achieve improved etching uniformity while increasing the etching rate.

[0023] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. An etching method for an inductively coupled plasma processing apparatus, the inductively coupled plasma processing apparatus comprising a reaction chamber, the top of the reaction chamber comprising an insulating window and an inductive coil device positioned above the insulating window, wherein a gas inlet nozzle is positioned at the center of the insulating window, the reaction chamber further comprising a base on which a substrate to be processed is positioned, the gas inlet nozzle being used to introduce a processing gas into the reaction chamber, characterized in that: The processing gas is supplied to the reaction chamber through a gas inlet nozzle, and plasma is ignited to perform plasma treatment on the substrate to be processed. The processing gas input into the reaction chamber includes an etching gas and an inert gas, wherein the etching gas is used to react with the material on the substrate to be processed to etch, and the flow rate of the inert gas is greater than or equal to twice the flow rate of the etching gas; The gas inlet nozzle includes a first gas inlet nozzle located in the center, and a plurality of second gas inlet nozzles surrounding the first gas inlet nozzle, wherein the gas output by the second gas inlet nozzles is ejected toward the edge area of the substrate below, and a gas distributor controls the gas flow composition or flow ratio input to the first and second gas inlet nozzles; The inductor device includes first and second inductors, wherein the first inductor is located in the central area of the insulating window, and the second inductor surrounds the first inductor; The power input to the first inductor coil is greater than the power input to the second inductor coil.

2. The etching method according to claim 1, wherein: The material on the substrate is crystalline silicon, and the etching gas includes fluorine-containing gas and chlorine-containing gas.

3. The etching method according to claim 1, wherein: The material on the substrate is a silicon oxide compound, and the etching gas includes a fluorocarbon compound or a fluorohydrocarbon compound.

4. The etching method according to claim 1, wherein: The flow rate of the inert gas is greater than the flow rate of the etching gas.

5. An inductively coupled plasma processing apparatus, comprising a reaction chamber, a top of the reaction chamber comprising an insulating window and an inductive coil device located above the insulating window, wherein a gas inlet nozzle is located at the center of the insulating window, the reaction chamber further comprising a base, a substrate to be processed being located on the base, the gas inlet nozzle being used to input a processing gas into the reaction chamber, The gas inlet nozzle is connected to a processing gas supply device to output processing gas including etching gas and inert gas into the reaction chamber, wherein the etching gas can react with the surface material of the substrate to be processed; The inductor device includes first and second inductors, wherein the first inductor is located in the center of the insulating window, and the second inductor surrounds the first inductor; The power input to the first inductor is greater than the power input to the second inductor; a controller for controlling the processing gas supply device so that the flow rate of the inert gas in the processing gas is twice the flow rate of the etching gas; The air inlet nozzle includes a first air inlet nozzle located in the center and multiple second air inlet nozzles surrounding the first air inlet nozzle. The gas output by the second air inlet nozzles is sprayed toward the edge area of the substrate below. A gas distributor controls the air flow composition or flow ratio input to the first and second air inlet nozzles.

6. The plasma processing apparatus according to claim 5, wherein: The first inductor coil is used to control the plasma concentration of the first processing area below, and the second inductor coil is used to control the plasma concentration of the second processing area, wherein the horizontal cross-sectional area ratio of the first and second processing areas is R, and the controller makes the RF power P1 input to the first inductor coil more than 2.5R times the RF power P2 input to the second inductor coil.

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