Plasma treatment apparatus and plasma treatment method

Abstract

The plasma processing apparatus (1) performs plasma etching on a wafer (16) having an alternating layer of insulating film and a metal-containing film formed on a substrate. The plasma processing apparatus (1) includes: a processing chamber (10) disposed in a vacuum chamber; a sample stage (14) disposed in the processing chamber and on which the wafer is placed; a detection unit (28) for detecting reflected light from light irradiated onto the wafer; a control unit (40) for controlling the plasma processing of the wafer; and an endpoint determination unit (30) for determining the endpoint of etching of the film based on the change in amplitude of vibration in the wavelength direction of the reflected light spectrum. The control unit stops the plasma processing of the wafer upon receiving the endpoint determination from the endpoint determination unit.

Description

Technical Field

[0001] This invention relates to a plasma processing apparatus and a plasma processing method using the same. Background Technology

[0002] Patent Document 1 discloses a technique for precisely detecting the remaining thickness of the film on the object to be etched in order to improve the yield of the etching process. The object to be etched is a wafer having a film structure in which the film to be processed is stacked on a substrate film. Reflected light is generated by irradiating the film structure with light from plasma and reflecting it at the boundaries and interfaces between the films. Since an optical path difference is generated between the reflected light from the substrate film and the reflected light from the film to be processed, interference light is formed. The intensity of the interference light changes as the remaining thickness of the film to be processed decreases with the progress of etching. Therefore, in the technique disclosed in Patent Document 1, the amount of etching of the film to be processed at any time during the wafer processing is calculated by comparing the actual pattern data of the interference light intensity from the wafer obtained during processing with the actual pattern data of the interference light intensity prepared in advance as a reference.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: JP 2016-184638 Summary of the Invention

[0006] Summary of the invention

[0007] The problem that the invention aims to solve

[0008] Patent Document 1 envisions a film formed planarly or on the top layer of a wafer as the film to be etched. In contrast, in semiconductor devices that have advanced to three dimensions, there are processes where one type of film is selectively etched laterally in a multilayer structure (a stacked structure) consisting of two or more layers. For example, in the process of forming the gate electrode of a next-generation 3D-NAND flash memory, a process is included in which the tungsten film is etched laterally (in the horizontal direction relative to the vertical depth direction of the trench) from a fine-width trench with a high aspect ratio formed on a stacked structure of a tungsten film and an insulating film. Previously, the amount of etching was controlled by the etching time for such lateral etching. The amount of etching could be measured by the difference in weight of the wafer before and after etching. However, due to the miniaturization of semiconductor devices, for example, if high-precision etching of the tungsten film at the atomic level is desired, time control has become difficult, and it is considered necessary to determine the endpoint of etching by monitoring the amount of etching.

[0009] Methods for solving problems

[0010] If we were to briefly describe the summary of a representative solution among the inventions disclosed in this application, it would be as follows.

[0011] A plasma processing apparatus performs plasma etching on a wafer with alternating layers of insulating film and metal-containing film formed on a substrate. The plasma processing apparatus includes: a processing chamber disposed within a vacuum chamber; a sample stage disposed within the processing chamber and on which the wafer is placed; a detection unit for detecting reflected light from the wafer; a control unit for controlling the plasma processing of the wafer; and an endpoint determination unit for determining the endpoint of etching of the film based on the change in amplitude of vibration in the wavelength direction of the reflected light spectrum. The control unit stops the plasma processing of the wafer upon receiving the endpoint determination from the endpoint determination unit.

[0012] The effects of the invention

[0013] The effects achieved by the representative solutions disclosed in this application can be briefly described as follows: By monitoring the amount of etching of the film being processed during the process, the endpoint can be determined, thereby improving the yield of the etching process.

[0014] Other topics and new features will become clear from the description in this specification and the accompanying drawings. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the plasma processing device.

[0016] Figure 2 This is a flowchart illustrating a general process for lateral etching of a multilayer film.

[0017] Figure 3 This is a flowchart for determining the endpoint of the lateral etching of the film being processed.

[0018] Figure 4A This is a longitudinal cross-sectional view of the stacked structure before lateral etching.

[0019] Figure 4B This is a longitudinal cross-sectional view of the stacked structure during the lateral etching process.

[0020] Figure 4C This is a longitudinal cross-sectional view of the stacked structure after horizontal etching.

[0021] Figure 5 It is a spectrum detected by irradiating external light onto the stacked structure during lateral etching.

[0022] Figure 6 It is about Figure 5 The spectrum shown indicates the wavelength λ a Light intensity I(λ) a ) and wavelength λ bLight intensity I(λ) b The intensity ratio of (I(λ)) a ) / I(λ b A graph showing the time variation of )).

[0023] Figure 7 It is about Figure 5 The spectrum shown indicates the distribution based on wavelength λ. a Light intensity I(λ) a ) and wavelength λ b Light intensity I(λ) b The amplitude intensity (I(λ)) obtained a )-I(λ b A graph showing the time variation of )).

[0024] Figure 8A It is about Figure 5 The spectrum shown is a first-order differential spectrum obtained by taking the first derivative of the wavelength direction.

[0025] Figure 8B It means Figure 8A The graph shows the time variation of the amplitude intensity of the first differential spectrum.

[0026] Figure 9A It is about Figure 5 The spectrum shown is a second-differential spectrum obtained by performing a second differentiation in the wavelength direction.

[0027] Figure 9B It means Figure 9A The graph shows the time variation of the amplitude intensity of the second differential spectrum. Figure 10 This is a flowchart for determining the endpoint of the lateral etching of the film being processed.

[0028] Figure 11A The detection department measures the spectrum of reflected light from the wafer.

[0029] Figure 11B It is the spectral data used in FFT processing.

[0030] Figure 11C The power spectrum is obtained through FFT processing.

[0031] Figure 12 It is a graph showing the time variation of the power spectrum.

[0032] Figure 13 This is a graph showing the time variation of the peak value of the power spectrum.

[0033] Figure 14 This is a schematic diagram of the plasma processing device.

[0034] Figure 15This is a diagram illustrating the principle of the etching amount measurement method for the comparative example. Detailed Implementation

[0035] exist Figures 4A-4C The diagram schematically illustrates the time-dependent changes caused by plasma etching of a multilayer structure formed on a substrate such as a semiconductor wafer. Figure 4A This is a longitudinal cross-sectional view of the stacked structure before etching. On the substrate film (silicon substrate) 401, a high aspect ratio groove 411 is formed in a multilayer film (stacked structure) consisting of an alternating stacked tungsten film 402 and a silicon oxide film 403 serving as an insulating film. Figure 4B This is a longitudinal cross-sectional view of the stacked structure during the lateral etching process. To etch the tungsten film 402, a fluorine-containing gas is used to form a plasma. A fluorine-containing reactant 404 from the plasma is provided into the tank 411, reacting with the surface of the tungsten film 402 to generate a tungsten-containing reaction product 405. The etching of the tungsten film 402 progresses by removing the reaction product 405 from above. Figure 4C This is a longitudinal cross-sectional view of the etched layered structure.

[0036] The inventors explored a method for monitoring the amount of lateral etching using the intensity of interference light. Details regarding the data acquisition method will be described later. Figures 4A-4C When light from an external light source (external light) is irradiated during the transverse etching of the stacked structure shown, and the reflected light is detected, it is observed that... Figure 5 Such a spectrum (a waveform representing the intensity of light at each wavelength). Figure 5 This indicates the spectrum 5 seconds after the start of horizontal etching (thin solid line), 10 seconds after the start (dashed line), and 15 seconds after the start (thick solid line).

[0037] The intensity of light at each wavelength detected is primarily determined by the intensity of light at each wavelength from the light source illuminating the wafer and the spectral reflectivity of the stacked structure during processing. Before etching begins, as... Figure 4A As shown, the ends of the tungsten film 402 and the silicon oxide film 403 on the side of the groove 411 are aligned. Tungsten has the properties of a metal, and its reflectivity in the ultraviolet to infrared region is approximately 1. Therefore, before etching begins, most of the external light is reflected by the uppermost tungsten film, so the spectrum of the external light is detected approximately unchanged.

[0038] Next, as the lateral etching of the tungsten film 402 progresses, as... Figure 4BAs shown, there exists a region 420 where silicon oxide and tungsten are stacked vertically at their boundaries; and a region 421 where tungsten is removed, i.e., where silicon oxide and vacuum are stacked vertically at their boundaries. In this state, for the vast majority of external light illuminating region 420, the light reflected by the uppermost tungsten film is detected. On the other hand, external light illuminating region 421 is reflected and transmitted according to the refractive index of silicon oxide. Since region 421 has a structure of multiple stacked films, multiple reflections are caused by the silicon oxide films in each layer, resulting in interference light that is detected.

[0039] The intensity of the interference light, such as Figure 5 As shown, the vibrations in the wavelength direction have a period and phase that depend on the material of the multi-reflection film and the thickness of each layer. Since the material of the stacked film constituting region 421 is silicon oxide and vacuum, the period of the vibration of the detected spectrum can be ignored because vacuum has a refractive index of 1. The period of the vibration of the detected spectrum is determined by the thickness of the silicon oxide film stacked in the vertical direction.

[0040] Based on the above, through the analysis of... Figures 4A-4C The spectrum detected by illuminating external light on the stacked structure during the lateral etching process is the sum of the reflected light intensity from region 420 and the interference light intensity from region 421. Furthermore, as the etching process of the tungsten film in the stacked structure progresses, the widths of regions 420 and 421—in other words, the aperture ratio on the wafer surface—change. Therefore, as the lateral etching progresses, the detected spectrum changes due to the change in the ratio of the light intensity from region 420 to the light intensity from region 421. In the process of fabricating the tungsten film in the stacked structure of tungsten and silicon oxide films, because the selectivity relative to the silicon oxide film is very high, the thickness of each layer in the vertical direction of region 421 does not change during the etching process. Therefore, the period and phase of the vibration in the wavelength direction of the interference light from region 421 do not change throughout the etching period.

[0041] According to Figure 5 The progress of lateral etching is estimated by analyzing the spectrum observed in the etching process shown. As a comparative example, the temporal variation of light intensity at a given wavelength is studied. Figure 15 about Figure 5The spectrum shows the temporal variation of light intensity at wavelengths of 515 nm (circular), 574 nm (triangular), and 658 nm (square). As described above, since the periodicity and phase of the vibration in the wavelength direction of the interference light from region 421 remain unchanged throughout the etching process, the light intensity at a specific wavelength is determined based on the ratio of region 420 to region 421 on the wafer surface. Because the intensity of reflected light per unit area from region 420 is greater than the intensity of interference light per unit area from region 421, the light intensity decreases monotonically at each wavelength.

[0042] Theoretically, the progress of etching can be detected by measuring the time-varying intensity at a specific wavelength in the spectrum. However, in practice, various noise components are added to the light intensity detected by the detector, so signal processing, such as time differentiation, is typically performed to separate the signal and noise components. However, in this case, since the signal component monotonically decreases with respect to time, if time differentiation is applied to the light intensity at a given wavelength, the rate of change of light intensity over time remains constant regardless of the etching amount, thus losing the correlation between light intensity and lateral etching amount. Therefore, in order to... Figure 15 The relationship between the estimated lateral etching amount and the signal processing used to remove noise components is limited, thus having a limit to the accuracy surface.

[0043] In contrast, in the etching endpoint determination method of this embodiment, the etching amount is accurately measured by utilizing the vibration in the wavelength direction of the spectrum. The structure of the plasma processing apparatus equipped with an endpoint determination unit capable of accurately controlling the etching amount, and its endpoint determination method, will be described below with reference to the accompanying drawings.

[0044] (Plasma processing device)

[0045] exist Figure 1 A schematic structure of the plasma processing apparatus 1 is shown. The plasma processing apparatus 1 includes a processing chamber 10 disposed inside a vacuum container. Above and around the processing chamber 10 are arranged electric field generators such as coaxial cables and antennas (not shown), or waveguides for propagating microwaves, or magnetic field generators such as solenoid coils. High-frequency power is supplied to the electric field generators or magnetic field generators to provide a high-frequency electric field or high-frequency magnetic field into the processing chamber 10.

[0046] Additionally, the top surface of the processing chamber 10 is provided with multiple inlet holes for introducing gas used to process the wafer 16 placed and held on the upper surface of the sample stage 14 into the interior of the processing chamber 10. These inlet holes are connected to a gas introduction mechanism having a gas supply path such as piping (not shown) and a mass flow controller (MFC) disposed upstream thereon.

[0047] The plasma-treated wafer 16 is held on the dielectric mounting surface of the sample stage 14 by electrostatic adsorption. Heat conduction between the wafer 16 and the sample stage 14 is promoted by providing a heat transfer gas, such as He gas, between the back side of the wafer 16 and the mounting surface of the sample stage 14.

[0048] In addition, a turbomolecular pump or other exhaust device is disposed below the vacuum container of the built-in processing chamber 10 to depressurize the internal pressure by exhausting the gas and particles inside the processing chamber 10. The exhaust device is connected to the exhaust port on the bottom surface of the processing chamber 10 disposed below the sample stage 14, and an exhaust regulating valve is disposed in the exhaust pipe between them to change the flow rate or velocity of the exhaust by increasing or decreasing the cross-sectional area of ​​the inner flow path.

[0049] Etching gas is introduced into the processing chamber 10, which is depressurized by the operation of the exhaust device, by a gas introduction mechanism. The pressure inside the processing chamber 10 is adjusted to a pressure suitable for the start of plasma processing by balancing the exhaust volume and the gas supply volume. In this state, a high-frequency electric field or a high-frequency magnetic field is provided. Through interaction, the atoms or molecules of the etching gas are ionized or dissociated, thereby forming plasma 12 in the space above the sample stage 14 inside the processing chamber 10.

[0050] In this embodiment, charged particles in the plasma, as well as particles of highly reactive species that have undergone dissociation, are diffused or guided to the upper surface of the wafer 16, thereby etching (plasma treatment) the film (film to be processed) of the object to be processed in the multilayer film formed on the wafer 16.

[0051] The operation of the plasma processing apparatus 1, including the selection of the type of gas introduced into the processing chamber 10, the amount of gas introduced, the amount of gas exhausted, the ignition, generation, and extinguishing of the plasma 12, the strength and distribution of the electric and magnetic fields used therein, the transport of the wafer 16 and its holding on the sample stage 14, the supply of high-frequency power for forming the bias potential of the electrodes arranged in the sample stage 14, and stopping, is based on command signals from a control unit 40 that is communicatively connected to each device performing each operation. The control unit 40 has the following functions: adjusting the synchronization and timing between each device to obtain the etching process result desired by the user.

[0052] Furthermore, the plasma processing apparatus of this embodiment includes a monitor for measuring the etching amount of the plasma-processed wafer 16 and an endpoint determination unit. Details of these structures will be described later.

[0053] (Horizontal etching process)

[0054] Formed on wafer 16 Figure 4A The laminated film containing a tungsten film is shown in the figure. Figure 2This is a flowchart illustrating the etching process of the laminated film containing a tungsten film formed on wafer 16.

[0055] Step 201: Introduce a fluorine-containing organic gas into the processing chamber 10. Besides C4F8, CHF3, CH2F2, and CH3F, the fluorine-containing organic gas can also be a mixture of these gases diluted with argon, nitrogen, oxygen, etc.

[0056] Step 202: Plasma 12 is generated in the processing chamber 10, providing free radicals (active species) such as CFx generated by activating atoms or molecules of fluorine-containing organic gases to the surface of the wafer 16, which then adheres to the surface of the tungsten film. Here, the tungsten film is not limited to a single tungsten film, but can also be a metal film containing multiple elements including tungsten. For example, it can be a WN film or a WSi2 film. Reactive particles such as free radicals react with the material on the surface of the adhered tungsten film to form a fluorocarbon layer. The thickness of the formed fluorocarbon layer depends on the plasma generation conditions of 12, the temperature of the sample stage 14, and other processing conditions.

[0057] As a component of the fluorocarbon layer formed on the surface of the tungsten film, besides CF x Furthermore, examples could be given of CH4 generated using hydrogen-containing plasma. x F y etc. CH x F y This layer is referred to as a hydrofluorocarbon layer, but here we will also include it, using the term fluorocarbon layer. A self-saturating intermediate layer containing tungsten and fluorine is formed at the boundary between the tungsten film and the fluorocarbon layer. The thickness of the formed intermediate layer varies according to the temperature of the sample stage 14 or the wafer 16 surface. Therefore, the thickness of the intermediate layer is adjusted by controlling the temperature of the sample stage 14.

[0058] Step 203: After the control unit 40 confirms that an intermediate layer of a given thickness has been formed by a detector or by confirming the elapsed time, the flow path cross-sectional area of ​​the pressure-regulating vacuum exhaust pipe is increased by controlling the exhaust regulating valve to increase the exhaust volume, thereby significantly reducing the pressure inside the processing chamber 10 and rapidly exhausting the fluorinated organic gas supplied to the processing chamber 10. This completes the fluorocarbon layer formation process. Alternatively, an inert (rare) gas such as Ar can be supplied to the processing chamber 10 to replace the organic gas and promote its exhaust.

[0059] Step 204: An oxygen-containing gas is introduced into the treatment chamber 10 as the reaction gas used to remove the fluorocarbon layer and the intermediate layer. The oxygen-containing gas can be a mixture of these gases diluted with argon, nitrogen, or other similar substances, in addition to O2 and O3.

[0060] Step 205: Plasma 12 is generated within the processing chamber 10, providing free radicals (active species) generated by the atoms or molecules of the activated gas to the surface of the wafer 16. As a result, the active species containing oxygen free radicals react with the fluorocarbon layer and the intermediate layer, generating volatile reaction products. Due to their volatility, the reaction products sublimate or detach from the laminated film, thereby being removed from the surface of the tungsten film.

[0061] Examples of reaction products include CO, CO2, and COF. x WF x WO x F y The particles of these reaction products that detach from wafer 16 are discharged from processing chamber 10 through the exhaust action inside processing chamber 10 caused by the operation of exhaust regulating valve and exhaust device, and the resulting flow of particles inside processing chamber 10.

[0062] Step 206: Exhaust the oxygen-containing gas from the processing chamber 10.

[0063] By performing steps 201-206 as a whole in one cycle, the intermediate layer and the fluorocarbon layer are removed together, thereby removing the tungsten film by the corresponding amount of the thickness of these layers.

[0064] (Monitor)

[0065] The plasma processing device 1 in this embodiment is as follows: Figure 1 As shown, a monitor is provided to measure the etching amount, which reflects the depth of the transverse grooves formed by transverse etching in plasma processing. The monitor includes: a light source 18 that emits external light that illuminates the processing chamber 10; a lens 20 disposed on the top surface of the processing chamber 10 that illuminates the wafer 16 inside the processing chamber 10 with the external light from the light source 18 connected by an optical fiber; a lens 26 disposed on the top surface of the processing chamber 10 that receives light reflected from the wafer 16 inside the processing chamber 10; a detection unit 28 connected to the lens 26 by an optical fiber that detects the intensity of the received light; and an endpoint determination unit 30 that determines the endpoint of etching based on the detection signal from the detection unit 28 and based on the etching amount of the wafer 16 in plasma processing. The endpoint determination information determined by the endpoint determination unit 30 and the etching amount calculated based on the detection signal are displayed on the display unit 31.

[0066] External light from the light source unit 18 propagates in an optical fiber and is guided from the top surface of the processing chamber 10 via the lens 20, illuminating the upper surface of the wafer 16 as illumination light 22. Continuous light from ultraviolet to infrared is used as the external light illuminating the wafer 16. Alternatively, a light source emitting a specific wavelength of light may be used, instead of a continuous light source, depending on the endpoint determination method. The reflected light 24 caused by the illumination light 22 illuminating the wafer 16 is focused by the detection lens 26. For example, using... Figures 4A-4C As explained, the reflected light 24 includes reflected light from region 420 and reflected light from region 421. The reflected light 24, focused by lens 26, propagates in the optical fiber and is guided into the detection unit 28.

[0067] The detection unit 28 is equipped with a beam splitter that separates the introduced reflected light into multiple wavelengths, and detects the intensity of the light at each wavelength. When determining the endpoint of etching based on the intensity of a specific wavelength of light, a specific wavelength of light can be selectively detected by using a photodetector and placing a monochromator or similar device before it. Furthermore, when a specific wavelength of light is used as the light source, detection can be performed directly using the photodetector.

[0068] like Figure 1 As shown, lenses 20 and 26 are disposed on the top surface of the processing chamber 10. However, since a gas inlet and a cluster plate for evenly supplying reactive gases to the processing chamber 10 are generally provided directly above the wafer 16, there are cases where lenses 20 and 26 cannot be disposed directly above the wafer 16. In such cases, lenses 20 and 26 are disposed with a distance between them so as not to obstruct the optical paths of the irradiation light 22 and the reflected light 24. In this case, it is desirable to tilt the lenses on the top surface of the processing chamber 10 so that the optical paths of the irradiation light 22 and the reflected light 24 (the optical path of the reflected light 24 is set as the optical path formed by the reflection of the irradiation light 22 on the mirror surface of the wafer 16) are aligned with the optical axes of lenses 20 and 26, respectively.

[0069] Furthermore, if the lens can be positioned directly above the wafer 16, the optical paths of the irradiating light 22 and the reflected light 24 become identical, thus allowing a single lens to be used to construct both lens 20 and lens 26. In this case, the optical axis of the single lens is set to be perpendicular to the wafer 16, the irradiating light 22 irradiates the wafer 16 perpendicularly, and the perpendicularly reflected light 24 is detected.

[0070] Alternatively, the structure can be configured as follows: a group comprising multiple light source units 18, lenses 20 and 26, and a detection unit 28, which performs etching amount detection and endpoint determination at multiple locations along the radial direction of the upper surface of the wafer 16. In this case, the process can be stopped based on a weighted average of the etching amounts detected at multiple locations.

[0071] The detection unit 28 detects the intensity of the reflected light 24 from the wafer 16 and sends the detection signal to the endpoint determination unit 30, which determines the endpoint of the etching of the wafer 16 being etched laterally according to the determination method described later.

[0072] (Method for determining the endpoint of lateral etching)

[0073] Figure 3 This is a flowchart of the endpoint determination unit 30 determining the endpoint of the lateral etching of the processed film on the wafer 16.

[0074] In the lateral etching endpoint determination method of this embodiment, the amplitude of the vibration in the wavelength direction of the spectrum during the lateral etching process is considered. Figure 5 In the example, it can be seen that the vibration is more significant in the wavelength range of approximately 500–600 nm, but the amplitude of the vibration in the wavelength direction increases with the length of the etching period. This increase in amplitude is attributed to the vibration originating from region 421 (reference). Figure 4B The proportion of interference light in the reflected light from the wafer increases with the progress of etching. This means that the lateral etching amount can be calculated based on the time variation of the amplitude along the wavelength direction. Therefore, in Figure 3 In the flowchart, two wavelengths of light intensity from the wafer are measured for the multilayer film formed on the wafer as the object of etching. The end point of etching is determined when the intensity ratio of the two wavelengths of reflected light reaches a given set value.

[0075] First, two wavelengths of light intensity are set for the multilayer film formed on the wafer as the target of lateral etching, and the intensity ratio of the reflected light of the two wavelengths at the end point of the etching of the wafer is set (step 301). This setting value is stored in an external storage device such as an HDD (Hard Disk Drive), CD-ROM (Compact Disk-Read Only Memory), or a semiconductor memory device such as RAM (Random Access Memory) or ROM in the control unit 40. The setting value data read by the control unit 40 is sent to the end point determination unit 30, which is configured to communicate with the control unit 40, for use in determining the end point of etching.

[0076] Here, the two wavelengths selected for monitoring are chosen to reflect the time-varying amplitude of the wavelength direction in the ratio of light intensities at those two wavelengths. The greater the change in the ratio of light intensities, the more robust the measurement of noise, etc. Therefore, if... Figure 5 For example, it is desirable to select the wavelength of the peak of the vibration in the wavelength direction of the spectrum near 550 nm and the wavelength of the valley as two wavelengths. In this way, the suitable wavelength varies depending on the material of the stacked structure to be etched, the type of external light source, that is, the spectral characteristics of the external light (irradiation light), and therefore, the two wavelengths to be measured are set according to the stacked structure to be etched.

[0077] The control unit 40 begins wafer processing, and the detection unit 28 detects the spectrum of reflected light from the wafer obtained during processing. The detected spectrum is input to the endpoint determination unit 30 (step 302). Here, the detected intensity of the reflected light can include the intensity of at least two wavelengths set as the etching endpoint condition; it can be the spectrum of continuous light or the intensity of two wavelengths set as the measurement wavelength.

[0078] Next, the endpoint determination unit 30 calculates the intensity ratio (called the measured intensity ratio) for the input light intensity data of the two wavelengths using the same formula as the intensity ratio set in step 301 (step 303).

[0079] Next, the endpoint determination unit 30 compares the measured intensity ratio with the set value (step 304). If the measured intensity ratio is less than the set value, the process returns to step 302. If the measured intensity ratio is determined to be greater than or equal to the set value, the target etching amount is determined to have been reached, and a signal to end the process is sent to the control unit 40 (step 305).

[0080] The control unit 40 receives the process end signal and issues command signals to each mechanism of the plasma processing apparatus 1 to end the process. Specifically, by stopping the generation of the high-frequency electric field or high-frequency magnetic field, the supply of high-frequency power to the electrodes in the sample stage 14 is stopped, thereby extinguishing the plasma 12 and stopping the etching process.

[0081] Afterwards, the electrostatic adsorption of wafer 16 onto sample stage 14 is released, and the wafer is transported outside processing chamber 10 to begin processing the next wafer 16 as needed. At this time, the control parameters of the etching process can be changed according to the wafer. Etching processes on multiple wafers can also be performed without extinguishing the plasma 12.

[0082] exist Figure 6 In China, regarding Figure 5 The spectrum shown indicates the wavelength λ a The light intensity I(λ) at (564nm) a ) and wavelength λb The light intensity I(λ) at (556nm) b The intensity ratio of (I(λ)) a ) / I(λ b The time variation of )). Additionally, in this example, the wavelength λ a (564nm) becomes the vibration peak, wavelength λ b (556nm) becomes the valley of vibration. Thus, the intensity ratio of the two wavelengths was observed to increase monotonically corresponding to the etching time. Therefore, by investigating the intensity ratio of the two wavelengths of reflected light at the time point when the lateral etching amount in the stacked structure of the etched object reaches the desired etching amount and setting it as a threshold, the endpoint of the etching process can be determined. Furthermore, since the temporal change of the intensity ratio of the two wavelengths of reflected light is related to the widths of regions 420 and 421 (see reference...), Figure 4B The change corresponds to the intensity ratio of the reflected light at the two wavelengths, so the etching amount at that time point can be calculated based on the intensity ratio of the reflected light at those two wavelengths. The same applies to the other endpoint determination methods described below.

[0083] exist Figure 3 In this context, the intensity ratio of reflected light with two wavelengths is used as an indicator, but it is not limited to this. The intensity ratio of reflected light with wavelengths greater than two wavelengths can also be used as an indicator. Furthermore, it is not limited to the intensity ratio; the amplitude intensity of vibrations along the wavelength direction of the spectrum can also be used as an indicator. Figure 7 In China, regarding Figure 5 The spectrum shown indicates the distribution based on wavelength λ. a The light intensity I(λ) at (564nm) a ) and wavelength λ b The light intensity I(λ) at (556nm) b The amplitude intensity (I(λ)) obtained a )-I(λ b The amplitude intensity was observed to increase monotonically with time corresponding to the etching time. Therefore, by investigating the amplitude intensity at the point in time when the transverse etching amount in the stacked structure of the etched object reaches the desired etching amount and setting it as a threshold, the endpoint of the etching process can be determined.

[0084] Furthermore, the above example illustrates how the endpoint of etching can be determined based on the spectrum (light intensity) detected in the detection unit. However, the first or second derivative of the wavelength direction of the spectrum can also be used for determination.

[0085] Figure 8A Yes Figure 5 The spectrum shown is obtained by taking the first derivative along the wavelength direction (called the first derivative spectrum). Figure 8BThe time variation of the amplitude intensity of the first differential spectrum is shown. Furthermore, the amplitude intensity is calculated here as the difference between the wavelength of the peak (560 nm) and the wavelength of the valley (554 nm) of the first differential spectrum.

[0086] Similarly, Figure 9A Yes Figure 5 The spectrum shown is obtained by taking a second derivative along the wavelength direction (called the second-differential spectrum). Figure 9B The time variation of the amplitude intensity of the second differential spectrum is shown. Furthermore, the amplitude intensity is calculated here as the difference between the wavelength of the peak (544 nm) and the wavelength of the valley (552 nm) of the second differential spectrum.

[0087] Thus, for either the first-order or second-order differential spectrum, it can be confirmed that the amplitude increases with increasing etching time. Therefore, it is possible to... Figure 3 The flowchart follows the same process, determining the endpoint of the etching process based on either the first or second derivative spectrum. An example of determination by amplitude is also given, but it can also be determined based on the spectral intensity ratio at two wavelengths. In this case, since either the first or second derivative spectral value could potentially be zero, it is desirable to avoid wavelengths where the derivative value is zero and instead select the two wavelengths representing the peaks and valleys of the vibrations that constitute the derivative spectral value.

[0088] use Figures 10-13 To further illustrate other methods for determining the endpoint. For example... Figure 5 As shown, the spectrum of reflected light from the stacked structure vibrates along the wavelength direction. Thus, by performing a Fast Fourier Transform (FFT) on the periodic spectrum, all frequency components in the spectrum can be represented as a power spectrum (power density at each frequency). As mentioned above, due to the increased amplitude intensity of the spectrum caused by the lateral etching process of the tungsten film in the stacked structure, the peak value of the power spectrum corresponding to the vibrational frequency along the wavelength direction of the spectrum also increases. Therefore, the lateral etching process can become... Figure 4C The peak intensity value corresponding to the vibration frequency in the wavelength direction of the reflected light spectrum at the desired time point of the film structure is used as the threshold value to determine the end point of etching.

[0089] Figure 10 This is a flowchart of the endpoint determination unit 30 determining the endpoint of the lateral etching of the processed film on the wafer 16.

[0090] First, the following pre-settings are performed. The vibrational frequency of the spectrum of the reflected light, which becomes the endpoint condition for etching, and the peak value of the power spectrum corresponding to the vibrational frequency that becomes the endpoint condition for etching the wafer are set (step 1001). Additionally, the range of wavelengths used in calculating the power spectrum within the spectrum detected by the detection unit is set (step 1002). By limiting the range of the spectrum used in calculating the power spectrum to the region where the vibrations in the frequency direction caused by the interference light are significant, determining the corresponding peak value becomes easier. Furthermore, the number of sampling points for the FFT is set (step 1003). These setting values ​​are also related to... Figure 3 The process is similarly stored in the storage device of the control unit 40 and sent to the endpoint determination unit 30 for use in determining the endpoint of etching.

[0091] The control unit 40 begins wafer processing, and the detection unit 28 detects the spectrum of reflected light from the wafer obtained during processing. The detected spectrum is input to the endpoint determination unit 30 (step 1004). Alternatively, before proceeding to step 1005, the light intensity data for each wavelength, i.e., the spectrum, can be transformed into light intensity data for each wavenumber (the reciprocal of the wavelength), and then processed after step 1005. It is known that performing an FFT on the spectrum transformed into light intensity data for each wavenumber improves the accuracy of the FFT.

[0092] Next, the endpoint determination unit 30 performs spline interpolation processing on the light intensity data within the wavelength range set in step 1002 for the spectrum, and obtains the number of sampling points of the FFT set in step 1003 for the spectrum that has undergone spline interpolation processing (step 1005). At this time, sampling is performed so that the sampling interval becomes equal.

[0093] Next, the endpoint determination unit 30 multiplies the sampled data obtained in step 1005 by an FFT window function (step 1006). An example using a Hamming function as the window function is shown here, but other window functions can also be used considering the shape of the spectrum within the wavelength range set in step 1002. Alternatively, if the window function multiplication is not required, step 1006 can be skipped, and the process can proceed to step 1007.

[0094] Next, the endpoint determination unit 30 performs FFT processing to calculate the power spectrum of each frequency (step 1007).

[0095] Next, the endpoint determination unit 30 reads the power spectrum value (peak value) at the vibration frequency set in step 1001 for the power spectrum obtained in step 1007 (step 1008).

[0096] Next, the endpoint determination unit 30 compares the power spectrum value read in step 1008 with the set value set in step 1001 as the endpoint of wafer etching (step 1009). If it is determined that the power spectrum value read is insufficient to reach the set value, the process returns to step 1004. If it is determined that the power spectrum value read is above the set value, the target etching amount is determined to have been reached, and a signal to end the process is sent to the control unit 40 (step 1010).

[0097] use Figures 11A-11C To explain Figure 10 The processing in the flowchart. Figure 11A The detection unit detects the spectrum of reflected light from wafer 16, which is a wavelength range of approximately 200–850 nm. Next, the obtained spectral data is input to the endpoint determination unit 30, and spectral data within the wavelength range used in the etching endpoint determination process is extracted according to the settings in step 1002. Here, 500–700 nm is set as the wavelength range used. Figure 11B The spectral data for this wavelength range is shown in bold solid lines. Spline interpolation is performed on this spectral data to generate data with the number of sampling points in the wavelength direction following the set value in step 1003. This generates spectral data by multiplying the spline-interpolated sampled data by a Hamming function. Figure 11B The spectral data obtained in step 1006 (spectral data multiplied by the Hamming function) is shown in the image with a thin solid line. In step 1007, an FFT is performed on the spectral data multiplied by the Hamming function to obtain... Figure 11C The power spectrum is shown. In this example, the peak value of the power spectrum (peak value = 340) can be seen at sampling point (horizontal axis) 12. This sampling point (horizontal axis) 12 corresponds to the vibrational frequency in the wavelength direction of the spectrum. Furthermore, a larger value at the sampling point indicates a shorter period of vibration in the wavelength direction of the spectrum. Additionally, the magnitude of the peak value (power spectrum intensity) corresponds to the amplitude of the vibration in the wavelength direction visible in the spectrum before the FFT processing.

[0098] Figure 12 express Figure 5 The power spectrum shows its temporal variation at various time points (5, 10, and 15 seconds after the start of the etching process). At each time point (5 seconds later: solid black line; 10 seconds later: dashed line; 15 seconds later: solid gray line), a peak in the spectrum can be observed at sampling point 12. Figure 13 Show Figure 12 The peak values ​​of the power spectrum at various times are shown in relation to the time interval. It can be seen that the peak values ​​increase with increasing etching time. Therefore, it is possible to... Figure 10 The flowchart describes a process that uses the power spectrum of the spectrum to determine the endpoint of the etching process.

[0099] In addition, as mentioned above, Figure 12The horizontal axis and Figure 5 The vibrational frequency in the wavelength direction of the reflected light spectrum is shown. This vibrational frequency corresponds to the thickness of the silicon oxide film in the stacked structure. Therefore, since a change in the peak position of the power spectrum during etching indicates a change in the thickness of the silicon oxide film, defective wafers can also be identified. For the same reason, the uniformity of the silicon oxide film thickness in the film structure can be estimated based on the waveform near the peak position of the power spectrum.

[0100] The above describes an example of the etching endpoint determination method in this embodiment. The embodiments described above are merely examples of some of the implementation methods of the present invention, and the implementation methods of the present invention are not limited to those described above, and various modifications can be made.

[0101] For example, in a plasma processing apparatus, the plasma generated during plasma processing emits light. This light from the plasma (called plasma light) has a different spectrum depending on the processing gas, but it includes wavelengths in the ultraviolet to visible light region, overlapping with the wavelength region of the external light spectrum. Therefore, if external light used for etching amount monitoring is applied during plasma emitting light, the effect of plasma emitting light is included in the amount of light detected in the detection unit. Specifically, in the detection unit 28, in addition to detecting the reflected light of the irradiation light (external light), plasma light and the reflected light of the plasma light from the wafer are also detected. In this case, since the amplitude of the wavelength direction vibration of the reflected light of the irradiation light (external light) and the reflected light of the plasma light increases with the progress of etching, the etching amount can be calculated and the endpoint determined according to the principle of this embodiment. However, the time variation in the amount of plasma light emitted, relative to the wavelength direction vibration in the spectrum of the interference light, becomes background noise, which may reduce the signal-to-noise ratio (S / N ratio).

[0102] As a method to suppress the decrease in the S / N ratio, a detection unit is provided at a location where interference light from the wafer is not being detected (e.g., the side of the processing chamber 10) to primarily detect the amount of plasma light emitted. The etching amount and endpoint determination can then be performed after eliminating the time-varying factors of the plasma light. Alternatively, increasing the luminous intensity of the light source 18 is considered. This increases the ratio of the intensity of interference light based on external light to the intensity of interference light based on plasma light, thereby suppressing the decrease in the S / N ratio caused by the time-varying amount of plasma light emitted. For example, when an LED is used as the light source (external light source), illumination light with an intensity several to ten times that of the plasma light can be irradiated onto the wafer. Both methods can also be used in combination.

[0103] Furthermore, in plasma processing device 1, through Figure 2In the case of plasma etching using plasma processing as shown, by periodically irradiating external light without causing plasma generation, the etching amount can be calculated and the endpoint determined unaffected by the plasma light. Specifically, in Figure 2 No plasma is generated during the venting process in step 206. Alternatively, no plasma is generated during the removal of reaction products in step 205. Therefore, by irradiating the wafer with external light during the period in step 206 or step 205 when no plasma is generated, and detecting the reflected light, the etching amount can be calculated and the endpoint determined without being affected by plasma light.

[0104] Furthermore, the external light source (light source unit) is not limited to LEDs. The wavelength bands in the interference light obtained by irradiating the wafer with external light exhibiting significant vibrations in the wavelength direction vary depending on the material and structure of the stacked structure to be etched. Therefore, by using a corresponding light source, the etching amount can be monitored with high precision. For example, xenon lamps, halogen lamps, etc., can also be used as the light source unit 18.

[0105] Conversely, when the vibrations of the interference light in the wavelength direction of the spectrum are strong within the emission band of the plasma light, the etching amount can be calculated by detecting the reflected light from the wafer without using an external light source. Figure 14 The structure of the plasma processing apparatus 1b in this case is shown. Figure 14 In the plasma processing apparatus 1b shown, in order to eliminate the time variation factor of plasma light, a detection unit 52, which mainly detects the emission amount of plasma light, is provided on the side of the processing chamber 10, thereby improving the accuracy of endpoint determination. Regarding... Figure 1 The plasma processing apparatus 1 shown has the same structure and is indicated by the same reference numerals. The lens 51 mainly focuses the plasma light, and the intensity of the plasma light is measured by the detection unit 52. By eliminating the influence of time variation in the intensity of the plasma light, the etching amount is calculated and the endpoint is determined, thereby improving the accuracy of the etching process.

[0106] In addition, in this embodiment, with Figures 4A-4C The example shown is a multilayer structure containing a tungsten film, but it can also be applied to multilayer structures where the film to be processed is a metal film. For example, the same etching amount monitoring can be performed on multilayer structures where Ni, Co, Mo films or their oxide films are used as the film to be processed. In addition, the insulating film of the multilayer structure is not limited to silicon oxide films, but can also be an insulating film such as a silicon oxynitride film.

[0107] Explanation of reference numerals in the attached figures

[0108] 1, 1b: Plasma processing device; 10: Processing chamber; 12: Plasma; 14: Sample stage; 16: Wafer; 18: Light source unit; 20, 26, 51: Lens; 22: Irradiation light; 24: Reflected light; 28, 52: Detection unit; 30: Endpoint determination unit; 31: Display unit; 40: Control unit; 401: Base film; 402: Tungsten film; 403: Silicon oxide film; 404: Reaction seed; 405: Reaction product; 411: Tank.

Claims

1. A plasma processing apparatus for performing plasma etching on a wafer having a multilayer film on which an insulating film and a metal-containing film to be processed are alternately stacked in a vertical direction. The plasma processing device is characterized by having: A processing chamber located within a vacuum container; A sample stage disposed within the processing chamber and on which the wafer is placed; A detection unit that detects the reflected light from the wafer when light irradiates the wafer; A control unit that controls the plasma processing of the wafer; and An endpoint determination unit determines the endpoint of the lateral etching of the film being processed based on the change in amplitude of vibrations in the wavelength direction of multiple wavelength spectra detected from the reflected light. The control unit accepts the endpoint determination made by the endpoint determination unit to stop the plasma processing of the wafer.

2. The plasma treatment apparatus according to claim 1, characterized in that, The plasma processing device has the following features: Light source; and The first lens and the second lens are disposed on the top surface of the processing chamber. Light from the light source is incident on the wafer through the first lens, and the reflected light received by the second lens is detected by the detection unit.

3. The plasma treatment apparatus according to claim 2, characterized in that, The control unit, at a time when no plasma is generated in the processing chamber, causes light from the light source to irradiate the wafer.

4. The plasma treatment apparatus according to claim 1, characterized in that, The plasma processing device has the following features: A lens disposed on the top surface of the processing chamber. The plasma light generated in the processing chamber is irradiated onto the wafer, and the reflected light received by the lens is detected by the detection unit.

5. The plasma treatment apparatus according to claim 1, characterized in that, When the intensity ratio of the reflected light at the first wavelength to the reflected light at the second wavelength is greater than or equal to a given set value, the endpoint determination unit determines that the etching of the film being processed has reached its endpoint. The first wavelength and the second wavelength are respectively set as the peak and valley wavelengths of the vibration in the wavelength direction of the spectrum of the reflected light.

6. The plasma treatment apparatus according to claim 1, characterized in that, When the difference between the intensity of the reflected light at the first wavelength and the intensity of the reflected light at the second wavelength reaches or exceeds a given set value, the endpoint determination unit determines that the etching of the film being processed has reached its endpoint. The first wavelength and the second wavelength are respectively set as the peak and valley wavelengths of the vibration in the wavelength direction of the spectrum of the reflected light.

7. The plasma treatment apparatus according to claim 1, characterized in that, The endpoint determination unit calculates the differential spectrum of the reflected light spectrum after performing one or two differential processing in the wavelength direction, and determines the endpoint of etching the film being processed based on the change in the amplitude of the vibration in the wavelength direction of the differential spectrum.

8. The plasma treatment apparatus according to claim 1, characterized in that, The endpoint determination unit calculates the power spectrum of the reflected light spectrum, and determines the endpoint of etching the film being processed when the peak value of the power spectrum corresponding to the vibration frequency of the vibration in the wavelength direction of the reflected light spectrum is above a given set value.

9. The plasma treatment apparatus according to claim 1, characterized in that, The insulating film is a silicon oxide film, and the film being treated is a tungsten film.

10. A plasma processing method, using a plasma processing apparatus, performing plasma etching on a wafer having a multilayer film on a substrate having an insulating film and a metal-containing film alternately stacked in a vertical direction, wherein the film to be processed is said to be plasma etched. The plasma processing apparatus includes: A processing chamber located within a vacuum container; A sample stage configured within the processing chamber and on which wafers are placed; Optical detection department; A control unit that controls the plasma processing of the wafer; and An endpoint determination unit that determines the endpoint of plasma etching of the wafer. The plasma treatment method is characterized in that... The photodetector detects the reflected light from the wafer as light irradiates the wafer. The endpoint determination unit determines the endpoint of the lateral etching of the film being processed based on the change in amplitude of vibrations in the wavelength direction of the spectrum of multiple wavelengths detected from the reflected light. The control unit accepts the endpoint determination made by the endpoint determination unit to stop the plasma processing of the wafer.

11. The plasma treatment method according to claim 10, characterized in that, The plasma processing device is equipped with a light source. The control unit, at a time when no plasma is generated in the processing chamber, causes light from the light source to irradiate the wafer.

12. The plasma treatment method according to claim 10, characterized in that, When the endpoint determination unit determines that the etching of the film being processed has reached or exceeded a given set value, either the intensity ratio of the reflected light at the first wavelength to the intensity of the reflected light at the second wavelength, or the difference between the intensity of the reflected light at the first wavelength and the intensity of the reflected light at the second wavelength. The first wavelength and the second wavelength are respectively set as the peak and valley wavelengths of the vibration in the wavelength direction of the spectrum of the reflected light.

13. The plasma treatment method according to claim 10, characterized in that, The endpoint determination unit calculates the differential spectrum of the reflected light spectrum after performing one or two differential processing in the wavelength direction, and determines the endpoint of etching the film being processed based on the change in the amplitude of the vibration in the wavelength direction of the differential spectrum.

14. The plasma treatment method according to claim 10, characterized in that, The endpoint determination unit calculates the power spectrum of the reflected light spectrum, and determines the endpoint of etching the film being processed when the peak value of the power spectrum corresponding to the vibration frequency of the vibration in the wavelength direction of the reflected light spectrum is above a given set value.

15. The plasma treatment method according to claim 10, characterized in that, The insulating film is a silicon oxide film, and the film being treated is a tungsten film.

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