JP2007531999A - Plasma etch endpoint detection method using VI probe diagnostic method - Google Patents

Abstract

A VI-probe that can provide electrical parameters corresponding to a radio frequency (RF) power source (eg, about 2 MHz, about 27 MHz, or about 60 MHz) for effective monitoring of the plasma processing chamber, and harmonics for each of the electrical parameters Coupled to a processor that can be coupled to and / or included in a commercially available probe product that can be provided and one of the electrical parameters and associated harmonics for endpoint detection for the plasma processing step A plasma processing control system including a controller. The electrical parameters can include voltage, phase and current, and the plasma processing application can be dielectric etching. The system according to embodiments of the present invention is particularly suitable for dielectric etching in a manufacturing environment.
[Selection] Figure 7

Description

  The present invention relates to a method and system for improving semiconductor processing results. In particular, it relates to a method for detecting an end point of dielectric etching.

  The plasma processing system has been in practical use for a long time. For the past several years, plasma processing systems using dielectric coupled plasma sources, electron cyclotron resonance (ECR) sources, capacitive sources, etc. have been put into practical use and have been used in various ways for processing semiconductor substrates and glass panels.

   Typically, multiple deposition (coating) steps and / or etching steps are involved during processing. During the deposition process, the processing material is coated (deposited) on the substrate surface (glass panel or wafer surface). For example, a deposition layer and / or a growth layer including various forms of silicon, silicon dioxide, silicon nitride, metal, and the like are formed on the surface of the substrate. Conversely, etching can also be performed to selectively remove material from certain areas of the substrate surface. For example, etch features such as vias, contacts and / or trenches are formed in the layer of the substrate. Depending on the etching method, chemical action and / or parameters for simultaneously etching and coating the plasma irradiation surface are used.

   The plasma can be generated and / or maintained by various plasma generation methods including, for example, inductively coupled, ECR, microwave and capacitively coupled plasma methods. An exemplary capacitively coupled plasma processing system 150 is illustrated in FIG. Many components of the plasma processing system 150 are conventional, such as the Excellan series of plasma etchers (eg, 2300 Excellan Flex) manufactured and sold by Lam Research Corporation of Fremont, California.

   The plasma processing system 150 shown in FIG. Chamber 100 provides a container that provides a discharge passage utilizing a vacuum pump (eg, “pump”) to process and discharge etch by-products. Chamber 100 is grounded in this exemplary plasma processing system. In the example shown in FIG. 1, the upper electrode 104 that is similarly grounded functions as an etchant source gas (eg, “supply source gas”) supply mechanism. The etchant source gas is introduced into the chamber from the inlet, and is supplied between the upper electrode 104 and the electrostatic chuck (ESC) 108 in the plasma region 102. An electrostatic chuck 108 is provided above the lower electrode 106. A wafer 109 to be processed is mounted on the ESC 108.

   The lower electrode 106 is energized by a radio frequency (RF) delivery system. The RF carrier system includes an RF matching network 110 and an RF power source 118. A V-I probe 112 can be coupled to the output of the RF matching network 110 and measures parameters supplied by the RF power supply 118 for feedback control purposes. In the example of FIG. 1, the RF power source 118 supplies both the lower electrode 106 with a frequency of about 2 MHz and about 27 MHz. When the RF power supply supplies RF power to the lower electrode 106 and the ESC 108, the plasma is ignited and maintained in the plasma region 102 to etch the wafer 109.

   The probe sensor (V-I probe 112) is placed downstream of the RF power source and as close to the ESC as possible. However, how close the ESC can be to install the probe involves maintenance issues. As an example, the V-I probe 112 is about 8 inches to about 9 inches away from the ESC. The V-I probe 112 and digital signal processor (DSP) 114 may also be part of an integrated product. One such commercially available probe product is the VI-PROBE-4100 frequency scan probe, a MKS ENI product from MKS Instruments, Inc. of Andover, Massachusetts. Another such commercial product is Smart PIM, available from Stratum Processware (formerly “Scientific Systems”) of Dublin, Ireland. Each such commercial product can detect voltage, current and phase parameter information at various RF power supply frequencies. Furthermore, each can provide the harmonics of these parameters in a fast Fourier transform (FFT) or other suitable method of DPS. Accordingly, the signal 122 of the plasma processing system 150 can include all relevant harmonics of each parameter measured by the VI probe 112. The etch process module controller 116 uses this information to control the plasma processing steps.

  A common process control for etching in plasma systems is endpoint detection. Conventional methods for determining endpoints include (1) laser interferometry and reflection, (2) emission spectroscopy, (3) direct observation, (4) mass spectroscopy, and (5) time-based prediction. Law, etc. In the conventional plasma processing method, the light emission spectroscopy method or the optical means is the most widely used method by separating the others. For many processing steps, such as applications where the exposed area is about 50% (eg metal), the luminescence method will be successful. However, the effectiveness of this method is limited by the etching rate as well as the total etching area. In particular, optical endpoint detection is generally not very effective in high aspect ratio dielectric etching such as vias. Many such dielectric etches typically have very small exposed areas, perhaps as much as 1% of the total oxidized surface area or dielectric film. As technology for these applications progresses, the reliability of optical methods is increasingly decreasing.

   More recently, parameters from commercial probe systems such as those described above have been used in attempts to detect endpoints. Such methods have generally used specific parameters (typically basic waveforms) for endpoint detection. However, such a method may not be the most sensitive endpoint detection method for different types of etching and / or processing steps. Thus, conventional methods may not be well suited for manufacturing environments. Common problems with traditional methods include the handling diversity of the manufacturing wafer-to-wafer environment as well as the low sensitivity in the limited exposed area etching process steps.

   Therefore, there is a need for a flexible endpoint detection method that can adapt and optimize for different etching steps in the process and that is suitable for the manufacturing environment. In particular, there is a need for a more reliable endpoint detection method for applications such as dielectric etching processing steps.

  According to one embodiment of the present invention, a plasma processing control system includes a VI probe for efficiently monitoring a plasma processing chamber. The probe can provide electrical parameters corresponding to an RF power source (eg, about 2 MHz, about 27 MHz, or about 60 MHz). The plasma processing system further includes a processor coupled to and / or included in a commercially available probe product that can provide harmonics for each electrical parameter, as well as at least one electrical parameter and endpoint detection for the plasma processing application. It includes a controller coupled to a processor that can select one of the associated harmonics. The electrical parameters can include voltage, phase and current, and the plasma treatment can be a dielectric etch. The system according to embodiments of the present invention is particularly suited for dielectric etching in a manufacturing environment.

   In accordance with another embodiment of the present invention, the endpoint detection method may include a general method of performing manufacturing endpoint detection calibration and performing manufacturing environment endpoint detection. The manufacturing endpoint detection calibration execution steps include: (i) performing plasma etching on the sample wafer; (ii) empirically determining a selected harmonic plot to detect the endpoint; and (iii) endpoint. Obtaining a harmonic parameter indicative of The steps of performing manufacturing environment endpoint detection are selected to (i) perform plasma etching on the production wafer, (ii) obtain a selected harmonic plot, and (iii) detect the endpoint. Analyzing the harmonic plot, (iv) continuing plasma etching if an endpoint is not detected, (v) stopping plasma etching if an endpoint is detected, and (vi) post-endpoint processing. Includes steps to perform.

   In the following, these and other features of the present invention will be described in more detail with reference to the accompanying drawings.

  The invention will now be described in detail with reference to an embodiment illustrated in the accompanying drawings. In the following description, numerous specific details are set forth to assist in understanding the present invention. The present invention can be implemented without executing all of them. Descriptions of known techniques are omitted. The features and advantages of the invention will be understood from the drawings and the following description.

   As mentioned above, the V-I probe can be used to measure current, voltage and phase parameters. Further, each harmonic can be determined through signal processing (eg, DSP 114 in FIG. 1). These parameters, including the basic parameters or the first parameters, can be considered in the endpoint detection method according to an embodiment of the present invention. Further, these methods can accommodate different frequencies, such as provided by the RF power supply 118 of FIG. The method according to an embodiment of the present invention allows selection of specific parameters and associated harmonics for endpoint detection at a given RF frequency. For example, in certain embodiments, a second harmonic of a voltage parameter for an RF signal of about 2 MHz can be used for reliable detection of the endpoint. The method of selecting frequency, harmonics and parameters for best endpoint detection for a specific application is described in further detail below.

   According to embodiments of the present invention, a manufacturing endpoint detection calibration method and a manufacturing environment endpoint detection method are provided. In general, manufacturing endpoint detection calibration methods provide selection of the best harmonics and parameters for a given frequency for endpoint detection. Furthermore, the manufacturing environment endpoint detection method provides process control of endpoint detection for various processing steps of the manufacturing environment.

   In a manufacturing research environment, a general method according to an embodiment of the present invention is as follows. Test etching of the wafer (eg 2 to 100) can be performed. Each of the available harmonics (including the basic ones) is examined, and it can be determined by examining which harmonic to which parameter provides the best identifier (signature) at the endpoint. In addition, suitable wafers for test etching must be selected to provide process diversity in the manufacturing environment. For example, a “nominal” processing wafer can be selected to optimize the detection margin.

   In FIG. 2, a flow diagram of a manufacturing research endpoint detection calibration method according to an embodiment of the present invention is shown at 200. This flow diagram can begin at start step 202. Next, the substrate of the test wafer or sample wafer can be etched for a predetermined time (step 204). Next, the etch endpoint time can be determined by an independent means, eg, an “empirical” determination means (step 206). One method of empirically determining the sample wafer endpoint is scanning electron microscope (SEM) analysis at the sample wafer etch location. Thus, by determining the end point in advance, the end point detection time in each harmonic plot can be determined by “pin point”. Thus, there can be a predetermined endpoint determination method (eg, SEM analysis of sample wafers), and there is an observation of all available plots to empirically determine which provides the optimal correlation endpoint indicator. it can.

   Next, if the endpoint time has not been detected, decision box 208 can return the process to step 204. Otherwise, the new substrate is etched beyond the endpoint time and the VI probe signal is recorded (step 210). Next, a harmonic plot for a given RF frequency including voltage, current and phase can be analyzed and compared to determine the most sensitive endpoint identifier near the known endpoint time. Yes (step 212). Next, an endpoint harmonic algorithm can be defined (step 214). Of course, in some embodiments, the first harmonic or basic waveform may be most suitable for endpoint detection according to the embodiment. In one embodiment, the second harmonic for a voltage parameter of about 2 MHz was supposed to provide the best endpoint detection for dielectric etching. Further, step 214 may include selecting a mathematical method (or “algorithm”) for selecting an endpoint from the selected harmonics. Possible algorithms or methods are described in detail later. In one embodiment, the selected algorithm as well as the harmonics / parameter combination can be programmed, for example, by software in the etch process module controller 116 of FIG. Returning to FIG. 2, the process continues with etching the new substrate (step 216). Next, the end point accuracy is confirmed by an independent means (step 218). The process ends at step 220.

  FIG. 3 is a flow diagram 350 of manufacturing environment endpoint detection according to an embodiment of the present invention. The process can begin at start 300. First, a wafer is mounted (step 302). Next, wafer etching is started (step 304). Next, the substrate (eg, production wafer) is etched while monitoring the VI probe signal. Next, the V-I signal is measured (step 308) and analyzed (step 310). Analysis includes endpoint detection from plots using conventional algorithms. In addition, methods such as changes in slope detection, intensity comparison, or any standard technique used in conventional optical detection methods can be used, including multivariate techniques that combine multiple signals (eg, voltage and phase). In addition, a time window may be incorporated into the detection method to effectively highlight the time range over which the endpoint is expected on the harmonic plot. Endpoint detection from the plot is described in further detail with respect to FIG.

  In FIG. 3, if no endpoint has been detected after step 310, decision box 312 can return the process to step 314 where etching continues. The process from step 314 can then proceed to step 308. If an endpoint has been detected, an endpoint post-process such as etching for a specified additional time or performing another chemical process or other process can be performed (step 316). The process ends at step 318.

  There are many combinations of processing methods and wafer stacks that can be used in embodiments of the present invention. An example for use in a test method according to an embodiment of the present invention is shown in the following table. 4 to 6 show related harmonic waveforms, which will be described in detail later.

  FIG. 4 shows a graph 400 of voltage harmonic waveforms for endpoint detection according to an embodiment of the present invention. This is an exemplary waveform that illustrates the possibility of using either a basic or second harmonic plot for endpoint detection. As mentioned above, a common method is to determine the best harmonics of a parameter (eg, voltage, current or phase) at a given RF frequency. In general, features that make one waveform preferred over another include maximum intensity changes with respect to the endpoints, as well as those that can be repeated and reproduced from wafer to wafer. This repeatability is one of the important features for the manufacturing environment.

   In FIG. 4, waveform 402 shows a first harmonic (ie, basic) plot of voltage parameters for an RF frequency of about 27 MHz. From this graph, the endpoint corresponding to region 406 can be determined. One way to make this determination is an algorithm for looking for troughs, possibly including a filtering step to smooth out minor operations (higher frequencies). As described above, the delay factor is unlikely to occur before or after a predetermined point in time, so the delay factor can be used to "bracket" or form a window around the endpoint. Other possible methods include the use of intensity differences in signals, derivatives, ratios or any other standard technique. The etch process module controller 116 of FIG. 1 can perform trough filtering and identification for endpoint detection, eg programmed by software control. In FIG. 4, waveform 404 shows a second harmonic plot of voltage parameters for an RF frequency of about 2 MHz. Similarly, as shown in the figure, the waveform indicates a feature for endpoint detection. Thus, in an embodiment of the present invention, an endpoint can be detected by effectively selecting and using either waveform 402 or waveform 404.

   FIG. 5 shows a graph 500 of phase harmonic waveforms for endpoint detection according to an embodiment of the present invention. Waveform 502 shows a first harmonic (ie basic) plot of the phase parameter for an RF frequency of approximately 27 MHz. As shown, the endpoint can be determined from this graph. Waveform 504 shows a second harmonic plot of phase parameters for an RF frequency of about 2 MHz. As can be seen, the second harmonic of the approximately 2 MHz phase parameter would be more difficult to determine the endpoint than the basic plot of the approximately 27 MHz phase parameter. Accordingly, another parameter and / or harmonics may be selected to determine an endpoint for about 2 MHz RF.

   FIG. 6 shows a graph 600 of current harmonic waveforms for endpoint detection according to an embodiment of the present invention. Waveform 602 shows a second harmonic plot of current parameters for an RF frequency of about 2 MHz. As shown, the endpoint can be determined from this graph. Thus, the voltage, phase and current parameters can each have harmonics suitable for endpoint detection according to embodiments of the present invention. In other examples, other parameters and / or harmonics may provide the best endpoint detection plot.

   In systems that provide RF power to the upper and lower electrodes, the VI-probe can be provided with only the lower electrode, only the upper electrode, or each of the two electrodes. FIG. 7 shows another embodiment, where the VI-probe 732 and associated DSP 734 are provided with an upper electrode 704. A lower electrode 708 is provided for the VI-probe 712 and the DSP 714. The upper electrode 704 is also provided with associated components including an RF matching network 730, an RF power source 728, and an electrode insulator 738 for isolating the upper electrode 704 from the ground chamber 700. In the embodiment of FIG. 7, the endpoint signal can be measured from the V-I probe 712, the V-I probe 732, or both V-I probes.

   While the invention has been described in terms of a number of preferred embodiments, modifications are possible within the scope of the invention. For example, although the exemplary embodiment lists three parameters: voltage, phase, and current, any suitable number of parameters and / or combinations of parameters can be utilized. Further, depending on the system, other harmonics may be preferable, and the other system and usage may be determined empirically. Similarly, as the V-I probe system is improved, more phase system harmonics can be utilized, and thus such available harmonics are within the scope of the present invention. As yet another example, fifth, sixth, seventh, etc. harmonic plots may provide the best endpoints according to embodiments of the present invention. Although RF frequencies of about 2 MHz, about 27 MHz, and about 60 MHz are listed as examples, other RF frequencies or suitable types of frequencies may be utilized in plasma processing systems and the like. There are many other variations on the implementation of the system and method of the present invention. The appended claims include all modifications within the scope of the present invention.

FIG. 1 is a schematic sectional view of a conventional plasma processing system using a VI probe. FIG. 2 is a flow diagram of a manufacturing laboratory endpoint detection calibration method according to one embodiment of the present invention. FIG. 3 is a flow diagram of a manufacturing environment endpoint detection method according to one embodiment of the present invention. FIG. 4 is a voltage harmonic waveform diagram for endpoint detection according to one embodiment of the present invention. FIG. 5 is a phase harmonic waveform diagram for endpoint detection according to one embodiment of the present invention. FIG. 6 is a current harmonic waveform diagram for endpoint detection according to one embodiment of the present invention. FIG. 7 illustrates a configuration involving multiple VI probes according to one embodiment of the present invention.

Claims (22)

A plasma processing control system comprising:
Designed to provide data relating to a plurality of electrical parameters when the radio frequency (RF) generator is activated, electrodes of a plasma processing chamber and a probe coupled to the radio frequency (RF) generator;
A processor coupled to the probe and designed to provide a plurality of harmonics for each of the plurality of electrical parameters;
A controller coupled to the processor and designed to select one of the plurality of electrical parameters as well as one of a plurality of harmonics for endpoint detection of a plasma processing step;
Including system. The system of claim 1, wherein the RF generator provides a frequency of approximately 2 MHz. The system of claim 1, wherein the RF generator provides a frequency of approximately 27 MHz. The system of claim 1, wherein the RF generator provides a frequency of approximately 60 MHz. The system of claim 1, wherein the plurality of electrical parameters includes a voltage. The system of claim 1, wherein the plurality of electrical parameters includes a phase. The system of claim 1, wherein the plurality of electrical parameters includes current. 6. The system of claim 5, wherein the plurality of harmonics includes first and second harmonics. The system of claim 6, wherein the plurality of harmonics includes first and second harmonics. 8. The system of claim 7, wherein the plurality of harmonics includes first and second harmonics. The system according to claim 1, wherein the predetermined harmonic of the plurality of harmonics is other than the first harmonic. The system of claim 1, wherein the plasma processing step includes a dielectric etching step. An endpoint detection method for a plasma processing step in a plasma processing chamber comprising:
Receiving first data identifying a given electrical parameter and a given harmonic of the given electrical parameter;
A probe designed to provide second data regarding a plurality of electrical parameters upon activation of the RF generator, coupled to an electrode of the plasma processing chamber and a radio frequency (RF) generator;
Designed to provide, from the second data, third data relating to specific harmonics for specific electrical parameters of the plurality of electrical parameters, the specific electrical parameters being of the same type as the given electrical parameters, A processor coupled to the probe, wherein the specific harmonics are in the same order as the given harmonics;
Providing a plasma processing control system comprising:
Using the third data for detection;
Including methods. 14. The method of claim 13, wherein the first data further includes a parameter that identifies an expected endpoint feature in a given harmonic of the given electrical parameter. 15. The method of claim 14, wherein the given harmonic is other than a first order harmonic of the given electrical parameter. The method of claim 15, wherein the RF generator provides a frequency of approximately 2 MHz. The method of claim 15, wherein the RF generator provides a frequency of approximately 27 MHz. The method of claim 15, wherein the RF generator provides a frequency of approximately 60 MHz. The method of claim 15, wherein the plurality of electrical parameters includes a voltage. The method of claim 15, wherein the plurality of electrical parameters includes a phase. The method of claim 15, wherein the plurality of electrical parameters includes current. The method of claim 13, wherein the plasma treatment step includes a dielectric etching step.

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