Shield type device for ion energy analysis of plasma processing

Abstract

To shield components of an imitation wafer probe used to measure the incident charged particle current density and energy distribution reaching the probe's surface during plasma processing.SOLUTION: A device for obtaining ion energy distribution measurements in a plasma processing system comprises a substrate, a plurality of ion energy sensors each having associated control circuitry disposed within the substrate, and a conductive enclosure, arranged within the substrate, enclosing each ion energy sensor and the associated control circuitry such that the substrate at least partially surrounds the conductive enclosure.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This application relates to shielding components of a dummy wafer probe used to measure incident charged particle current density and energy distribution reaching the surface of the probe during plasma processing. [Background technology]

[0002] Plasma processing is widely used in a wide range of applications in modern industry. A well-known example is the manufacture of integrated circuits in the semiconductor industry. Plasma processing is also used in the manufacture of solar panels, flat panel displays, thin film coatings, and medical devices, among others.

[0003] The ion current density (ion flux) and energy distribution (ion energy distribution, IED) of ions arriving at the substrate surface strongly influence the performance of plasma-based processes. In semiconductor manufacturing, the substrate is typically a silicon wafer, while in other industries the substrate may be a glass panel or various alternatives. Wafer and substrate may be used interchangeably throughout this specification, but are understood to mean any type of substrate used in plasma processing. Throughout the process, the substrate surface is bombarded with plasma species, including energetic ions, to remove (etch) and / or deposit layers of material to form structures or features on the workpiece surface. Ion bombardment may directly drive etching and deposition, or may be used to activate the surface for more reactive plasma species to act upon. For example, in plasma etching of features in the semiconductor industry, the ion flux and associated IED determine important parameters such as etch rate, etch selectivity, and etch anisotropy. IED is therefore a key plasma parameter to measure, understand, and control to ensure optimal process performance.

[0004] As transistor critical dimensions continue to shrink, tighter control of IEDs at the wafer surface is required. IED repeatability and uniformity are important for optimal processing yield. Therefore, IED probes integrated into wafers and substrates are essential for the advancement of nanotechnology manufactured using plasma processing.

[0005] Various probes have been developed over the decades to measure IEDs in plasma processing. Planar retarding field analyzer (RFA) designs are well known. In many RFA embodiments, a stack of conductive grids, individually separated by insulators, is used to separate ions based on their energy and thus determine the IEDs. An aperture facing the plasma allows a sample of ions to enter the probe for analysis. A series of grids are used to a) prevent plasma penetration inside the device, b) push back plasma electrons, c) discriminate ions based on their energy, and d) prevent secondary electron emission from the collector electrode. A collector electrode terminates the stack and is used to detect the ion current signal for measurement. The ion current is recorded for each retarding voltage applied to the ion energy discriminator grid to give an integral form of the energy distribution. The tabulated ion current vs. discriminator grid voltage data is numerically differentiated to determine the IEDs.

[0006] Mock boards with embedded sensors have been the subject of many inventions. Some of these inventions focus on the sensor design and its construction, others on the electronic control platform for processing, storing and transmitting the sensor data. The electronic platform is either fully integrated into the mock board with its own power source, or is separated from the mock board using interconnect wires that pass through the chamber wall using vacuum feedthroughs to the electronic control platform located on the air side.

[0007] It is known that the electronics in such sensors and associated circuitry in the substrate must be protected from electromagnetic radiation generated by plasma processing. In prior art designs where the electronic control system and power supply are fully integrated into the mock wafer probe, undesirable electric field formation can also occur and distort the IED measurements. A Faraday shield is typically provided in such prior art sensors to address these issues.

[0008] EP 3968353 discloses an apparatus for obtaining ion energy distribution measurements in a plasma processing system, comprising a substrate placed in the plasma processing system and exposed to plasma, an ion energy analyzer disposed in the substrate for measuring the ion energy distribution at the substrate surface during plasma processing, the analyzer comprising a plurality of grids, a rechargeable battery power supply including a control circuit integrated in the substrate for supplying a voltage to each of the grids, and a collector of the ion energy analyzer. A Faraday shield is provided to house the ion energy analyzer, the power supply and the control circuit.

[0009] US Patent Application Publication No. 2011 / 0174777 teaches embedding sensors and their corresponding power supply and control electronics directly into a diagnostic wafer to facilitate in-situ measurement of plasma characteristics during plasma operation. This prior art document also teaches protecting the electronics with a Faraday shield.

[0010] U.S. Patent No. 8,104,342 provides an apparatus for measuring a parameter comprising a substrate, a plurality of sensors carried by and distributed across a surface of the substrate for individually measuring parameters at different locations, an electronic processing component carried by the substrate surface, conductors extending across the surface connected to the sensors and the electronic processing component, and a cover disposed over the sensors, the electronic processing component and the conductors.

[0011] WO 2007 / 130790 describes a process condition measuring device for measuring process conditions in a processing system processing workpieces of standard dimensions, the device comprising a first conductive substrate portion, a second conductive substrate portion and an electrical circuit interposed between the first and second conductive substrate portions, the first and second conductive substrate portions being electrically connected to each other to form a conductive body having at least one dimension equal to a dimension of the workpiece being processed by the processing system.

[0012] Some real production wafers are known to develop non-uniform charge accumulation across their surface. The DC bias potential induced by the RF power supply to the wafer may also be non-uniform across the wafer surface, resulting in non-uniform IEDs at different points on the wafer. The formation of a conductive body (to provide a shield) in the dummy wafer probe forces a uniform charge distribution across the surface and makes the DC bias potential the same at all points where the shield is an equipotential surface. Thus, an IED measured locally in the presence of such a shield may be a distorted version of the true IED at that location on the real production wafer.

[0013] In such known configurations, the RF current is forced to flow around the outside of the continuous shield and not through the wafer, which can also be problematic for some applications.

[0014] The shielding provided by prior art dummy board probes has several shortcomings. These shortcomings need to be addressed. Summary of the Invention

[0015] The present teachings describe an apparatus or dummy wafer probe for obtaining ion energy distribution measurements in a plasma processing system, comprising: a substrate; a plurality of ion energy sensors, each having an associated control circuit disposed within the substrate; and a conductive housing, disposed within the substrate, enclosing each ion energy sensor and the control circuit such that the substrate at least partially surrounds the conductive housing.

[0016] The substrate may be conductive or non-conductive.

[0017] The device may further comprise an insulating layer between the substrate and the conductive housing.

[0018] The substrate may be semiconductive. Optionally, the substrate is silicon.

[0019] The device may further comprise a semiconductor cover over the surface of the substrate. The semiconductor cover may be made of silicon.

[0020] Optionally, an ion energy sensor measures the energy distribution at a first surface of the substrate, and a cover is provided on a second surface of the substrate opposite the first surface.

[0021] The device may further include an RF antenna disposed in the substrate exterior to the conductive housing.

[0022] Optionally, the RF antenna is connected to a control circuit.

[0023] The RF antenna may be provided at the periphery of the substrate in a non-conductive or semi-conductive area.

[0024] Each ion energy sensor and associated control circuitry may be provided on a circuit board. [Brief description of the drawings]

[0025] The present application will now be described with reference to the accompanying drawings. [Figure 1] 1 shows an overview of a system for use with a dummy wafer probe in accordance with the present teachings. [Diagram 2] 1 shows an array of sensors for measuring IEDs distributed across the surface of a dummy wafer probe. [Figure 3(a)] 1 illustrates a first embodiment of a shielded device (dummy wafer probe) according to the present teachings. [Figure 3(b)] 13 shows another embodiment of a shielded device. [Figure 4] 1 illustrates a further embodiment of a shielded device according to the present teachings. [Diagram 5] 13 shows another embodiment of a shielded device. [Figure 6] 1 illustrates a further embodiment of a shielded device according to the present teachings. [Figure 7] 1 shows a perspective view of a circuit board for use in a shielded device of the present teachings. Detailed Description of the Drawings

[0026] FIG. 1 shows an overview of a system 100 capable of measuring the ion energy distribution arriving at the surface of a dummy wafer probe 101 surface during plasma processing. In this particular figure, the diagnostic system 100 includes a dummy wafer probe 101 with an integrated ion energy sensor and control electronics including battery power and wireless communication. The diagnostic system further includes a docking station 102 with an integrated wireless transponder 103 to allow charging, configuration, and data retrieval of the dummy wafer probe 101. The docking station 102 includes an Ethernet connection for communicating with a host PC 104. Application software is provided to display and analyze retrieved data. The application software provides a control panel for scheduling experiment assignments. An advanced programming interface (API) is also provided to allow direct interaction between the docking station and the factory control software.

[0027] A four-chamber plasma processing system 105 is also shown in FIG. 1. This is one of many different types of plasma processing systems and is used simply to illustrate the functionality of the dummy wafer probe 101 according to the present teachings. The plasma processing system 105 can have one or more interconnected processing chambers 106. Each processing chamber 106 includes a vacuum pump for evacuating the chamber, a gas flow control for setting the processing recipe, a vacuum gauge and transducer for adjusting the processing operating pressure, a power delivery mechanism for exciting the chemical recipe into a plasma state, and a pedestal for holding the substrate during processing. A load lock chamber 108 with a robotic transfer mechanism 107 is used to transport substrates to and from the processing chambers. Substrate batches are delivered to the load lock chamber 108 through a cassette or FOUP.

[0028] The dummy probe 101 is placed in the docking station 102 and communication is established through application software on the host PC 104. The battery power on the wafer probe 101 is charged, stored data is retrieved, and the next experimental assignment is scheduled to prepare the wafer probe 101. The dummy wafer probe 101 is then placed in an available slot in the Front Opening Universal Pod (FOUP) and then delivered to the load lock chamber 108. The robot arm 107 transports the dummy wafer probe 101 to the processing chamber 106 and positions it on the processing pedestal in preparation for plasma exposure. With the chamber 106 already under vacuum, the process recipe is configured and the plasma is ignited. Once the plasma is formed, plasma species begin to bombard the wafer probe 101 and samples of it enter the probe's 101 sensor for analysis. If the on-board pressure sensor reports that the high voltage application threshold has been reached, the analysis proceeds at the time configured in the scheduler. This safety mechanism prevents accidental application of high voltage at atmospheric pressure, which could destroy the sensor by electrical arcing. If the pressure threshold is met, the wafer probe 101 is activated at the scheduled time. Appropriate voltages are applied to all grids and collectors, and the collector currents are recorded as a function of ion discrimination potential by a microcontroller (MCU) (not shown), and the resulting data is stored in memory. The wafer probe 101 returns to sleep mode until the next scheduled measurement, at which point the process is repeated. Once the assignment is complete, the plasma process can be terminated to allow the wafer probe 101 to be retrieved from the process pedestal using a robotic arm that transports the wafer probe back through the load lock chamber 108 to the FOUP. The user removes the wafer probe 101 from the FOUP and places it back in the docking station 102 for data retrieval, recharging, and scheduling the next experimental assignment.Alternatively, the wafer probe can transmit sensor data in real time from its location within the processing chamber to the docking station using known wireless communication devices and methodologies.

[0029] It should be understood that the wafer probe 101 according to the present teachings is not limited to use in a system such as that shown in FIG. 1, and that any suitable system may be selected.

[0030] The configuration of the wafer probe 101 will now be described in more detail. In a preferred embodiment, the wafer probe 101 is fabricated on a substrate to mimic a standard semiconductor workpiece. The wafer probe may also be fabricated from silicon, ceramic, metal, glass or any other material to mimic other types of substrates used in plasma processing and may have the same shape as a standard substrate with substantially the same dimensions and weight. The general configuration of the dummy wafer probe 101 is shown in FIG. 2, which shows an array of sensors 201 distributed across the surface of the semiconductor wafer probe 101. In particular, FIG. 2 shows a plan view of the wafer probe 101 with nine sensors 201, which are used to measure the ion energy distribution at the substrate surface of the wafer probe 101. The dummy wafer probe 101 may comprise a single sensor 202 (at any location) or may comprise multiple sensors 201 spatially distributed.

[0031] It can be seen that the sensor 201 may comprise alternating layers of planar, parallel conductive metal grids and insulators, the grids being systematically electrically polarized to filter out plasma electrons, separate positive ions based on their energy, suppress secondary electron emissions, and collect the ion current for measurement. The sensor is embedded in the substrate of the dummy after probe 101. The sensor configuration shown in EP 3968353. However, it should be understood that the particular configuration of the sensor 201 used with the dummy wafer probe 101 is not the focus of this application, and any suitable sensor configuration may be used. Rather, the present teachings provide improved techniques for shielding the sensor and associated electronics within the substrate of the dummy probe 101.

[0032] With reference to FIG. 3(a), a first embodiment of a shielded apparatus (dummy wafer probe) for obtaining ion energy distribution measurements in a plasma processing system is provided. The apparatus 300 includes a non-conductive substrate 301. A number of circuit boards 302 are provided within the apparatus 300, i.e., within the substrate 301. Each circuit board 302 includes a sensor 303 (such as a known grid stack) and associated control circuitry 304. As known to those skilled in the art, an aperture is fabricated in the plasma-facing surface of the substrate 301, constituting the top surface of the apparatus. In one embodiment, the substrate is a silicon wafer with a diameter of 100 mm, 150 mm, 200 mm, 300 mm, or 450 mm, although any other material, geometry, or dimensions can be used in the manufacture of the wafer probe as required by the application. The control circuitry includes an on-board power source, such as a rechargeable battery, and any other circuitry required for the operation of the apparatus 300. An antenna can also be provided to charge the battery and to communicate with a docking station.

[0033] To protect the sensors and associated circuitry, a conductive housing 305 is provided surrounding each circuit board 302. It can be seen that the substrate 301 at least partially surrounds each conductive housing 305.

[0034] In order to measure the uniformity of ion energy and ion flux, it is important to ensure that the distributed sensors 303 are electrically isolated from each other. Therefore, the sensors 303 are advantageously shielded independently using a conductive enclosure for each sensor 303. This ensures that the sensors and associated circuitry are electrically isolated from each other. This allows each sensor 303 to accurately detect what is happening at its respective location without being affected by an artificially created continuous shield surrounding the device, which may not be representative of the real situation. That is, the absence of an artificially created continuous shield surrounding the device results in more accurate sensor measurements.

[0035] In the embodiment of Figure 3(a), the electrically shielded sensor 303 (and associated circuitry) is provided within a non-conductive substrate, which replicates the conditions "seeing" by the non-conductive substrate during processing.

[0036] Referring to Fig. 3(b), this shows the embodiment of Fig. 3(a), where only a single circuit board 302 with a single sensor 303 is provided on the board 301 of the apparatus 306. This variation of the embodiment of Fig. 3(a) also ensures that the sensor 303 can detect exactly what is happening at its location. No artificially created continuous shield surrounding the entire device / apparatus is provided, so that this cannot interfere with the sensor measurement.

[0037] 4, which illustrates another embodiment of a shielded apparatus 400 for obtaining ion energy distribution measurements in accordance with the present teachings. A conductive substrate 401 is provided having embedded therein a circuit board 402 having a sensor 403 and associated circuitry 404. Also shown is a conductive housing 405 that surrounds the sensor 403 and associated circuitry 404. Additionally, an insulating layer 406 is provided between the conductive housing 405 and the conductive substrate 401.

[0038] In this embodiment, if a conductive substrate 401 is used, it is important to break the naturally formed continuous electrical shield that may form around the conductive substrate 401. In particular, for conductive substrates, the rf potential across the surface of the substrate may be non-uniform. To ensure that a true measurement of the plasma conditions at the sensor location is achieved, the conductive housing 405 (sensor shield) should be insulated from the conductive substrate 401. This is achieved by installing an insulating layer 406 between the conductive housing 405 and the conductive substrate 401 to break the continuity of the conductive housing 405, as shown in FIG. 4.

[0039] Although the embodiment of Figure 4 is shown with only one circuit board 402 having a sensor 403 and associated circuitry 404, the embodiment is not so limited and multiple circuit boards may be provided, as described with respect to the embodiment of Figure 3(a).

[0040] 5 illustrates another embodiment of an apparatus 500 of the present teachings. As previously described, a substrate 501 is provided having circuit boards 502 therein. Sensors 503 and electronic circuitry 504 are provided on the circuit board 502. A conductive housing 505 surrounds each circuit board 502.

[0041] The substrate 501 is formed from undoped silicon. As previously mentioned, the substrate 501 of the device 500 according to the present teachings can be fabricated from silicon. In the case of the previously mentioned conductive substrates, these can be formed from doped silicon. However, for silicon-based substrates, it is advantageous from a manufacturing standpoint to avoid the need to dope the silicon to make it conductive. Silicon is considered a semiconductor (neither a conductor nor an insulator). Germanium or other semiconductor materials can also be used.

[0042] In the undoped silicon substrate embodiment of Figure 5, a silicon cover 506 is also provided on the bottom side of the substrate 501, i.e., the silicon cover 506 is provided on the opposite side of the substrate from where the plasma is detected by the sensor 503. This is useful when the silicon substrate based apparatus 500 is used in semiconductor manufacturing processes, since the machine handles silicon wafers. It is therefore desirable to build a dummy wafer probe where all exposed surfaces are made of silicon. This minimizes the risk of contamination of the machine by the wafer probe.

[0043] A silicone cover or a cover formed from another material may also be used with the other embodiments described herein, i.e., a cover may be provided on the underside of any of the devices described herein.

[0044] 6 illustrates a further embodiment of an apparatus 600 for obtaining ion energy distribution measurements in a plasma processing system. The apparatus includes a non-conductive substrate 601 and a plurality of circuit boards 602. As previously described, each circuit board 602 includes a sensor 603 and associated control circuitry 604. A single conductive housing 605 encloses the plurality of circuit boards 602 such that substrate 601 is not within the conductive housing 605.

[0045] An RF (loop) antenna 606 is also provided in the non-conductive substrate 601. The antenna is connected back to control circuitry 604 in a conductive housing 605. This antenna 606 is used to communicate data from the apparatus 600 in real time while the plasma is running, and digitized sensor measurements can be encoded onto the antenna by switching the antenna on and off to modulate the power flow into the chamber at very low levels. This modulation can be sensed on the power supply lines.

[0046] Although only one rectangular loop antenna 606 is shown in the cross-sectional view of Figure 6, multiple loop antennas 606 can be provided. As many as 100 connected loops can be provided just around the wafer edge. Furthermore, the loop antenna can be divided into several sections that can be switched in and out of the device.

[0047] Although the device of FIG. 6 is shown with multiple circuit boards 602, only a single circuit board may be provided with one or more loop antennas.

[0048] In certain applications, it is desirable to centralize all the circuitry (and power), but the sensors are distributed at various locations around the wafer. For this embodiment, a conductive housing is required to surround the circuitry and all the sensing elements in one continuous shield. This has the configuration of a circular disk at the center (which houses the circuitry) and extending on spokes to each sensor location. The antenna goes around the edge of the wafer.

[0049] RF antennas (loops) for real-time communication cannot be placed on conductive materials (conductive substrates) as is commonly used in known imitation wafer probes. RF current must be able to flow through the wafer cross section (bottom to top) to activate the antenna. RF antennas can also be provided in semiconductor areas of the substrate.

[0050] Referring to FIG. 7, this shows a perspective view of a conductive housing 700 of the aforementioned circuit board and associated sensor that can be embedded in the substrate of any of the devices described herein. The sensor is shown located within a raised section 701 and having an aperture 702 on its top surface. The apertures 702 form an array fabricated on the top surface of the conductive housing. The top surface of 702 is exposed to the plasma and may be flush with the top surface of the substrate assembly. Alternatively, the top surface of 702 may be located just below the top layer of the substrate, where a matching array of apertures is formed and constitutes the plasma-facing surface of the wafer probe. Plasma species can enter the sensor through 702 for analysis. The sampling aperture 702 may be less than a millimeter in diameter and must provide sufficient opening area to deliver adequate charged particle flux for detection. The aforementioned control circuitry or any other components required for operation of the dummy wafer probe may be provided in a cavity in section 703 of the circuit board and sensor housing 700. The shape and scale of the conductive housing 700 shown in FIG. 7 in which the sensor stack and circuitry are disposed are for illustrative purposes only. The conductive housing 700 can take any suitable form factor.

[0051] The invention is not limited to the embodiments described herein, which can be amended or modified without departing from the scope of the invention.

Claims

1. 1. An apparatus for obtaining ion energy distribution measurements in a plasma processing system, comprising: A substrate; a plurality of ion energy sensors each having associated control circuitry disposed within the substrate; a conductive housing disposed within the substrate, the conductive housing enclosing each ion energy sensor and associated control circuitry such that the substrate at least partially surrounds the conductive housing.

2. The device of claim 1 , wherein the substrate is non-conductive.

3. The device of claim 1 , wherein the substrate is electrically conductive.

4. The device of claim 3 further comprising an insulating layer between the substrate and the conductive housing.

5. The device of claim 1 , wherein the substrate is semiconductive.

6. The device of claim 5 , wherein the substrate is silicon.

7. The apparatus of claim 5 or 6, further comprising a semi-conductive cover on a surface of the substrate.

8. The device of claim 7 , wherein the semiconductive cover is silicon or germanium.

9. 8. The apparatus of claim 7, wherein the ion energy sensor measures an energy distribution at a first surface of the substrate, and a cover is provided on a second surface of the substrate opposite the first surface.

10. The device of claim 2 , further comprising an RF antenna disposed within the substrate outside the conductive housing.

11. The apparatus of claim 10 , wherein the RF antenna is connected to the control circuit.

12. The device of claim 10 , wherein the RF antenna is disposed within the non-conductive substrate.

13. An apparatus according to any preceding claim, wherein each ion energy sensor and associated control circuitry is provided on a circuit board.

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