KR20070020226A - A method of plasma etch endpoint detection using a v-i probe diagnostics - Google Patents

Abstract

A plasma processing control system including a V-I probe for effectively monitoring a plasma processing chamber, where the probe can provide electrical parameters in response to a radio frequency (RF) supply (e.g., about 2 MHz, about 27 MHz, or about 60 MHz), a processor coupled to and/or included with a commercially available probe product that can provide harmonics for each of the electrical parameters, and a controller coupled to the processor that can select one of the electrical parameters and one of the associated harmonics for endpoint detection for a plasma processing step is disclosed. The electrical parameters can include voltage, phase, and current and the plasma processing application can be dielectric etching. A system according to embodiments of the invention may be particularly suited for dielectric etching in a production environment. ® KIPO & WIPO 2007

Description

Plasma etching endpoint detection method using -I probe diagnosis {A METHOD OF PLASMA ETCH ENDPOINT DETECTION USING A V-I PROBE DIAGNOSTICS}

Background of the Invention

FIELD OF THE INVENTION The present invention generally relates to methods and control systems for improving semiconductor processing results, and more particularly, to endpoint detection methods for dielectric etching.

For some time, plasma processing systems have been around. For many years, plasma processing systems using inductively coupled plasma sources, electron cyclotron resonance (ECR) sources, capacitive sources, and the like have been introduced and adopted at various angles to process semiconductor substrates and glass panels.

During processing, a plurality of lamination and / or etching steps are typically encountered. During the lamination step, the material is laminated to the substrate surface (such as the surface of the glass panel or wafer). For example, stacked and / or grown layers comprising various forms of silicon, silicon dioxide, silicon nitride, metals, and the like may be formed on the surface of the substrate. Conversely, etching may be performed to selectively remove material from certain areas of the substrate surface. For example, etched features such as vias, contacts, and / or trenches may be formed in the layer of the substrate. Some etching processes may utilize chemistry and / or parameters to simultaneously etch and deposit films on plasma-facing surfaces.

The plasma may be generated and / or maintained using a variety of plasma generation methods, including inductively coupled, ECR, microwave, and capacitively coupled plasma methods. An example of a plasma processing system in capacitively coupled form is shown in FIG. 1, indicated by general reference numeral 150. Many of the components of the plasma processing system 150 are conventional and are, for example, the Exelan® family (eg, 2300 Exelan® Flex), produced by Lam Research Corporation, Fremont, California. It can be found in the plasma etcher.

In FIG. 1, the plasma processing system 150 includes a chamber 100 that provides an enclosure for the specification and processing of the discharge path using a vacuum pump (eg, “pump”) to discharge the etch byproducts. In this example plasma processing system the chamber 100 is grounded. In the example of FIG. 1, the upper electrode 104, which is also electrically grounded, functions as an etchant source gas (eg, “feed gas”) diffusion mechanism. An etchant source gas is introduced into the chamber through the inlet and diffuses into the plasma region 102 between an electrostatic chuck 108 which is disposed on top of the upper electrode 104 and the lower electrode 106. . The wafer 109 to process can be placed on the ESC 108.

The bottom electrode 106 is energized by a radio frequency (RF) transmission system that includes an RF matching network 110 and an RF power source 118. For feedback control purposes, the V-I probe 112 may be coupled to the RF matching network 110 output to measure a parameter supplied by the RF power source 118. In the example of FIG. 1, the RF power source 118 supplies the lower electrode 106 with both about 2 MHz and about 27 MHz frequencies. When the RF source supplies RF power to the lower electrode 106 via the ESC 108, a plasma for etching the wafer 109 in the plasma region 102 is ignited and maintained.

A probe sensor (VI probe 112) is located downstream of the RF source, generally as close as possible to the ESC. However, there may be a management problem that limits how close the probe can be placed to the ESC. As one example, the VI probe 112 may be spaced about 8 to 9 inches from the ESC. The VI probe 112 and digital signal processor (DSP) 114 may be part of an integrated commercial product. One such commercially available probe product is the VI-PROBE-4100 Frequency Scanning Probe (registered trademark) available from MKS ENI products of MKS Instruments, Inc. with Massachusetts Andover. Another commercial product is SmartPIM ^™ available from Straatum Processware, Ltd (formerly Scientific Systems, Ltd) in Dublin, Ireland. Each such commercial product can detect voltage, current, and phase parameters for various RF source frequencies. In addition, each may provide harmonics for these parameters via fast Fourier transform (FFT) or other suitable method in the DSP. Thus, signal 122 of plasma processing system 150 may include all corresponding harmonics of each parameter measured by VI probe 112. The etch process module controller 116 can then use this information to control one or more plasma processing steps.

Common process control for etching applications in plasma systems is endpoint detection. Conventional methods for detecting endpoints include: (1) laser interferometer and reflection coefficient; (2) optical emission spectroscopy; (3) direct observation; (4) mass spectroscopy; And (5) time-based prediction. To date, optical emission spectroscopy or optical means are most widely used in conventional plasma processing approaches. For many processing steps, such as applications (eg, metals) where the area exposed is about 50%, optical emission can play a good role. However, the sensitivity of this approach is limited by the etch rate and the total area etched. In particular, optical endpoint detection is generally not robust to dielectric etch of high aspect ratios, such as vias. Many such dielectric etches typically have very low exposure areas, such as only about 1% of the total surface area of the oxide or dielectric film. The optical approach is less reliable at the technical scale for these applications.

More recently, the use of parameters from commercially available probe systems described above has been used in attempts to detect endpoints. In general, such an approach has used certain parameters, typically fundamental wave waveforms, for endpoint detection. However, such an approach may not be the most sensitive endpoint detection method for different types of etching and / or processing steps. Thus, known approaches may be inadequate for the production environment. Common problems with known approaches include handling variation in the per wafer wafer production environment and low sensitivity of the etch process step of narrow exposed areas.

There is a need for a flexible endpoint detection method that can be adapted and optimized for the different etching steps of the process and is suitable for the production environment. In particular, some applications, such as dielectric etch process steps, require more reliable endpoint detection methods.

Summary of the Invention

According to one embodiment of the present invention, a plasma processing control system is capable of providing electrical parameters in response to a radio frequency (RF) supply (eg, about 2 MHz, about 27 MHz, or about 60 MHz), A VI probe for efficiently monitoring the plasma processing chamber, a processor coupled to and / or incorporated in commercially available probe products to provide harmonics for each of the electrical parameters, and coupled to the processor to provide endpoint detection for plasma processing applications. And a controller capable of selecting one or more of the electrical parameters and one or more of the corresponding harmonics. Electrical parameters can include voltage, phase, and current, and the plasma processing application can be a dielectric etch. The system according to an embodiment of the present invention may be particularly suitable for dielectric etching in a production environment.

According to another embodiment of the present invention, a method for detecting an endpoint may include a general method of performing a manufacturing endpoint detection calibration and performing a production environment endpoint detection. Performing a manufacturing endpoint detection calibration includes: (i) performing a plasma etch on the sample wafer; (ii) empirically determining a selected harmonic plot to detect an endpoint; And (iii) obtaining a harmonic parameter indicative of the endpoint. Performing production environment endpoint detection includes: (i) performing a plasma etch on the production wafer; (ii) obtaining a selected harmonic plot; (iii) analyzing the selected harmonic plots to detect endpoints; (iv) continuing the plasma etching if no endpoint is detected; (v) stopping plasma etching if an endpoint is detected; And (vi) performing the activity after any endpoint.

These and other features of the present invention are described in more detail with reference to the accompanying drawings in the following detailed description of the invention.

Brief description of the drawings

In the drawings of the accompanying drawings the invention is illustrated by way of example and not by way of limitation, like reference numerals designate like elements.

1 is a cross-sectional view of a conventional plasma processing system having a V-I probe.

2 is a flow chart of a manufacturing lab endpoint detection calibration method according to one embodiment of the invention.

3 is a flow diagram of a production environment endpoint detection method according to one embodiment of the invention.

4 is a graph of a voltage harmonic waveform for endpoint detection in accordance with an embodiment of the invention.

5 is a graph of phase harmonic waveforms for endpoint detection in accordance with an embodiment of the invention.

6 is a graph of current harmonic waveforms for endpoint detection in accordance with an embodiment of the invention.

7 illustrates an implementation involving a plurality of V-I probes, in accordance with an embodiment of the invention.

Detailed description of the invention

Hereinafter, the present invention will be described in detail with reference to some preferred embodiments as shown in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and / or structures have not been described in order not to unnecessarily obscure the present invention. The features and advantages of the invention may be more clearly understood by the drawings and the following description.

As mentioned above, V-I probes can be used to measure current, voltage, and phase parameters. In addition, harmonics for each may be determined through signal processing (eg, DSP 114 of FIG. 1). These harmonics, including fundamental waves or first harmonics, can be considered in the endpoint detection method according to the embodiment of the present invention. In addition, these methods are applicable to different frequency selections, for example, as provided by the RF power source 118 of FIG. Methods in accordance with embodiments of the present invention enable the selection of specific parameters and corresponding harmonics that are best suited for endpoint detection at a given RF frequency. For example, in certain embodiments, a second harmonic of the voltage parameter for the about 2 MHz RF signal can be used to reliably detect the endpoint. The method of selecting such frequencies, harmonics, and parameters for optimal endpoint detection for a particular application is described in more detail below.

According to the embodiment of the present invention, a manufacturing end point detection calibration method and a production environment end point detection method are provided. In general, the manufacturing endpoint detection calibration method may enable the selection of optimal harmonics and parameters for endpoint detection at a given frequency. In addition, the production environment endpoint detection method may enable process control of endpoint detection for various process steps in a production environment.

In a manufacturing lab environment, the general method according to embodiments of the present invention may be as described below. Test etching of a plurality of wafers (eg, 2 to 100) may be performed. Each of the available harmonics (including the fundamental) may be reviewed to determine which harmonics for which parameter at the endpoint provide the optimal signature. In addition, to allow for processing variations in the manufacturing environment, an appropriate wafer must be selected for test etching. For example, a “nominal” process wafer may be selected to achieve optimal zeroing of the detection margin.

Referring to FIG. 2, a flow diagram of a manufacturing lab endpoint detection calibration method in accordance with one embodiment of the present invention is shown, indicated by general reference numeral 200. The flow may begin at start 202. Next, the substrate of the test wafer or sample wafer may be etched for a predetermined time (step 204). Next, the end point time of the etching can be determined, for example, by means of independent means (step 206). One way to empirically determine the endpoint for a sample wafer is to perform Scanning Electron Microscopy (SEM) analysis on the etched location of the sample wafer. Predetermination of these endpoints may enable "pin pointing" of the endpoint detection time for each harmonic plot. Thus, there may be some manner of endpoint determination (eg, SEM analysis of a sample wafer), and then the observation of all possible plots empirically determining which manner can provide the best correlated endpoint indicator. May exist.

Next, decision box 208 may return the flow to step 204 if no endpoint time is detected. Alternatively, the flow may proceed to etch the new substrate after the endpoint time and record the V-I probe signal (step 210). Next, for a given RF frequency, a harmonic plot including parameters of voltage, current, and phase can be analyzed and compared to determine the most sensitive signature of the endpoint near the known endpoint time. Next, an endpoint harmonic algorithm can be defined (step 214). Of course, in some applications, the first harmonic or fundamental wave waveform may be best suited for endpoint detection in accordance with an embodiment. In one embodiment, a second harmonic for the voltage parameter at about 2 MHz supply has been found to provide optimal endpoint detection for dielectric etch applications. Step 214 may also include selecting a mathematical way to find the endpoint from the selected harmonics (ie, “algorithm”). Such possible algorithms or methods are described in more detail below. In one embodiment, the selected algorithm and harmonic / parameter combination can be programmed, for example, in software located in the etch process module controller 116 of FIG. 1. Referring again to FIG. 2, the flow may continue by etching the new substrate (step 216). Next, the endpoint precision can be verified by independent means (step 218). The flow may end at 220.

Referring now to FIG. 3, a flow diagram of a production environment endpoint detection method in accordance with one embodiment of the present invention is shown, indicated by general reference numeral 350. The flow can begin at start 300. First, the wafer may be loaded (step 302). Next, etching may begin on the wafer (step 304). Next, the substrate may be etched (eg, of the production wafer) while monitoring the V-I probe signal (step 306). Next, the V-I signal can be measured (step 308) and analyzed (step 310). The analysis can include the use of conventional algorithms to detect endpoints from the plot. Also, any methods that can be used in conventional optical detection methods, including methods such as slope change detection, amplitude comparison, or multivariate techniques that combine multiple signals (eg, voltage and phase). Standard techniques of may be used. In addition, a time window may be included in the detection method in which the time range in which the end point is expected can be effectively emphasized in the harmonic plot. More details of end point detection from the plot are backed out with reference to FIG. 4.

In FIG. 3, after step 310, if an endpoint has not yet been detected, decision box 312 may advance the flow to step 314 where etching may continue. Thereafter, the flow from step 314 can proceed to step 308. If an endpoint is detected, post-endpoint activity, such as etching or other chemical activity or any other processing activity, for any additional period of time may be performed (step 316). The flow may end at step 318.

There are a number of possible process recipes and wafer stack combinations that can be used in accordance with embodiments of the present invention. An example of the recipe used for the testing method according to the embodiment of the present invention is shown in the following table. 4 to 6 show corresponding harmonic waveforms and will be described in detail below.

Referring to FIG. 4, a graph of voltage harmonic waveforms for endpoint detection in accordance with an embodiment of the present invention is shown, indicated by the general reference numeral 400. This is an example waveform snapshot showing the possibility of using a fundamental or second harmonic plot for endpoint detection. As noted above, a general method may be to determine optimal harmonics for a parameter (eg, voltage, current, or phase) at a given RF frequency. In general, properties that may make one waveform preferred over another include the largest amplitude change near the endpoint and repeatable and reproducible properties per wafer. Such repeatability is an important characteristic for the production environment.

In FIG. 4, waveform 402 shows a first harmonic (ie, fundamental wave) plot of the voltage parameter for an RF frequency of about 27 MHz. From this graph, an end point corresponding to the area 406 can be determined. One way to make this decision is an algorithm that involves filtering to find troughs and possibly smoothing minor variations (higher frequencies). In addition, as discussed above, a delay factor may be used to form a "bracket" or window near the end point because it may not be expected to appear before or after a particular point in time. Other possible methods include using the amplitude difference, differential function, ratio, or any other standard technique of the signal. For example, the etch process module controller 116 of FIG. 1 may perform filtering and identification of valleys for endpoint detection, as programmed by software control. In FIG. 4, waveform 404 shows a second harmonic plot of the voltage parameter for an RF frequency of about 2 MHz. Similarly, the waveform exhibits a characteristic for detecting an endpoint, as shown. Thus, according to embodiments of the present invention, waveform 402 or waveform 404 may be effectively selected and used for endpoint detection.

Referring now to FIG. 5, a graph of phase harmonic waveforms for endpoint detection in accordance with an embodiment of the present invention is shown, indicated by general reference numeral 500. Waveform 502 shows a first harmonic (ie, fundamental wave) plot of the phase parameter for an RF frequency of about 27 MHz. From this graph, as shown, an endpoint can be detected. Waveform 504 shows a second harmonic plot of the phase parameter for an RF frequency of about 2 MHz. As observed from the figure, the endpoint determination may be more difficult for the second harmonic of the phase parameter of about 2 MHz than the fundamental wave plot of the phase parameter of about 27 MHz. Thus, other parameters and / or harmonics may be selected to determine the endpoint for the about 2 MHz RF supply.

Referring now to FIG. 6, a graph of current harmonic waveforms for endpoint detection in accordance with an embodiment of the present invention is shown, indicated by general reference numeral 600. Waveform 602 shows a second harmonic plot of the current parameter for an RF frequency of about 2 MHz. From this graph, as shown, an endpoint can be detected. Thus, each of the parameters of voltage, phase, and current may have harmonics suitable for endpoint detection in accordance with embodiments of the present invention. In other applications, other parameters and / or harmonics may provide the optimal endpoint detection plot.

For systems that provide RF power to both the top and bottom electrodes, the VI-probe may be provided with only the bottom electrode, or only the top electrode, or each of the two electrodes. 7 shows an alternative implementation in which the upper power electrode 704 is provided to the V-I probe 732 and the corresponding DSP 734. The lower power electrode 708 is provided to the V-I probe 712 and the DSP 714. The upper power electrode 704 also includes an RF matching network 730, an RF power source 728, and an upper electrode insulator 738 for insulating the upper electrode 704 from the grounded chamber 700. Components are provided. In the implementation of FIG. 7, the endpoint signal can be measured from a V-I probe 712, a V-I probe 732, or both V-I probes.

While the invention has been described in terms of some preferred embodiments, there are alternatives, modifications, and equivalents that fall within the scope of the invention. For example, although there are three parameters of voltage, phase, and current in the exemplary embodiment, any suitable number of parameters and / or parameter combinations may be employed. In addition, different harmonics may be desirable, may vary depending on the system or application, and may be empirically determined for different systems or applications. Similarly, more phase system harmonics may be possible as the V-I probe system improves, and such possible harmonics are also within the scope of the present invention. As another example, harmonic plots such as the fifth, sixth, seventh, etc. may provide the most effective endpoint detection in accordance with embodiments of the present invention. As another example, while the RF frequencies of about 2 MHz, about 27 MHz, and about 60 MHz have been described as exemplary RF frequencies, any other RF frequency or suitable form of frequency applicable to a plasma processing system or the like may be employed. . It will be appreciated that there are a number of alternative ways of implementing the systems and methods of the present invention. Accordingly, the following appended claims are intended to be construed to include all such substitutes, modifications, and equivalents as fall within the true spirit and scope of the present invention.

Claims (22)

A probe coupled to an electrode of a plasma processing chamber and a radio frequency (RF) generator, the probe configured to provide data pertaining to a plurality of electrical parameters when energy is supplied to the RF generator; A processor coupled to the probe and configured to provide a plurality of harmonics for each of the plurality of electrical parameters; And And a controller coupled to the processor and configured to select any one of the plurality of electrical parameters and any one of the plurality of harmonics for endpoint detection of a plasma processing step. The method of claim 1, And the RF generator provides a frequency of about 2 MHz. The method of claim 1, The RF generator providing a frequency of about 27 MHz. The method of claim 1, The RF generator providing a frequency of about 60 MHz. The method of claim 1, And the plurality of electrical parameters comprises a voltage. The method of claim 1, And the plurality of electrical parameters comprises a phase. The method of claim 1, And the plurality of electrical parameters comprises a current. The method of claim 5, And said plurality of harmonics comprises first and second harmonics. The method of claim 6, And said plurality of harmonics comprises first and second harmonics. The method of claim 7, wherein And said plurality of harmonics comprises first and second harmonics. The method of claim 1, And any one of the plurality of harmonics is other than a first harmonic. The method of claim 1, And the plasma processing step comprises dielectric etching. A method of detecting an endpoint for a plasma processing step of a plasma processing chamber, comprising: Receiving first data identifying predetermined electrical parameters and predetermined harmonics of the predetermined electrical parameters; Providing a plasma processing control system, wherein the plasma processing control system, A probe coupled to an electrode of a plasma processing chamber and a radio frequency (RF) generator, the probe configured to provide second data belonging to a plurality of electrical parameters when energy is supplied to the RF generator; And A processor coupled to the probe and configured to provide a third jitter from the second data, the third data belonging to a particular harmonic for a particular electrical parameter of the plurality of electrical parameters, the specific electrical parameter being Providing the plasma processing control system comprising the processor, wherein the particular harmonic is of the same type as the predetermined electrical parameter and the particular harmonic is of the same order as the predetermined harmonic; And Employing the third data for the detection. The method of claim 13, The first data further comprises a parameter identifying a predicted endpoint characteristic at the given harmonic of the given electrical parameter. The method of claim 14, And said predetermined harmonic is other than a first harmonic of said predetermined electrical parameter. The method of claim 15, The RF generator providing a frequency of about 2 MHz. The method of claim 15, The RF generator providing a frequency of about 27 MHz. The method of claim 15, The RF generator providing a frequency of about 60 MHz. The method of claim 15, And the plurality of electrical parameters comprises a voltage. The method of claim 15, And the plurality of electrical parameters comprises a phase. The method of claim 15, Wherein the plurality of electrical parameters comprises a current. The method of claim 13, And the plasma processing step comprises an electrical etch.

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