Patent Application
20240177965
This application claims priority to European Patent Application No. EP22209525, filed Nov. 25, 2022, the entire contents of each are incorporated herein by reference.
The present application relates to shielding the components of an imitation wafer probe used for measuring the incident charged particle current densities and energy distributions arriving at a surface of the probe during plasma processing.
Plasma processing is used extensively in modern industry for a wide range of applications. A well-known example is the manufacture of integrated circuits in the semiconductor industry. Plasma processing is also used in the production of solar panels, flat panel displays, thin film coatings and medical devices, among many others.
The ion current density (ion flux) and energy distribution (IED) of the ions arriving at a 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 glass panel or a variety of alternatives. Wafer and substrate may be used interchangeably through the document but understood to mean any type of substrate to be used in a plasma process. Throughout the process the substrate surface is bombarded by plasma species, including energetic ions, to remove (etch) and/or deposit layers of material to form structures or features on the workpiece surface. Ion impact may drive the etching and deposition directly, or may be used to activate the surface for more reactive plasma species to do the work. For example, in the plasma etching of features in the semiconductor industry the ion flux and associated IED determines important parameters such as etch rate, etch selectivity and etch anisotropy. The IED is therefore a critical plasma parameter to measure, understand and control to ensure optimum process performance.
As the scale-down of transistor critical dimensions continues, tighter control of the IED at the wafer surface is required. Repeatability and uniformity of the IED is critical for optimal process yield. Wafer and substrate integrated IED probes are therefore essential to the advancement of nanotechnology manufactured using plasma processing.
A variety of probes have been developed over many decades to measure the IED in plasma processes. The planar, retarding field analyser (RFA) design is 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 hence determine the IED. An aperture facing the plasma allows a sample of ions into the probe for analysis. A succession of grids are used to a) prevent plasma penetration inside the device, b) repel plasma electrons, c) discriminate ions based on their energies and d) prevent secondary electron emission from the collector electrode. The 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 discrimination grid to give an integral form of the energy distribution. The tabulated ion current versus discriminator grid voltage data is numerically differentiated to determine the IED.
Imitation substrates with embedded sensors have been the subject of numerous inventions. Some of these inventions focus on sensor designs and their construction, while others focus on the electronic control platform for processing, storing and transmitting the sensor data. The electronic platform is either fully integrated into the imitation substrate with its own power supply or is decoupled from the imitation substrate using interconnecting wires which pass through the chamber wall, using vacuum feedthroughs, to the electronic control platform located on the air side.
It is known that the electronics within such sensors and associated circuitry in the substrate must be protected from electromagnetic radiation generated by the plasma process. In prior art designs where the electronic control system and power supply is fully integrated into an imitation wafer probe, undesirable electric field formation can also occur and distort the IED measurements. A Faraday shield is usually provided in such prior art sensors to address these issues.
EP 3968353 discloses an apparatus for obtaining ion energy distribution measurements in a plasma processing system comprising, a substrate for placement in the plasma processing system for exposure to the plasma, an ion energy analyser disposed in the substrate for measuring the ion energy distribution at the substrate surface during plasma processing, the analyser comprising a plurality of grids a rechargeable battery power supply including control circuitry, integrated in the substrate, for supplying voltage to each of the grids and the collector of the ion energy analyser. A Faraday shield is provided encasing the ion energy analyser, the power supply and the control circuitry.
US 2011 0174777 teaches embedding sensors and their corresponding power supplying and controlling electronics directly in a diagnostic wafer in order to facilitate the in-situ measurements of plasma properties during plasma operation. This prior art document also teaches protecting said electronics by means of a Faraday shield.
U.S. Pat. No. 8,104,342 provides an instrument for measuring a parameter comprising a substrate, a plurality of sensors carried by and distributed across a surface of the substrate that individually measure the parameter at different positions, an electronic processing component carried by the substrate surface, electrical conductors extending across the surface connected to the sensors and the electronic processing component, and a cover disposed over the sensors, electronic processing component and conductors.
WO 2007/130790 describes a process condition measuring device for measuring a process condition in a processing system that processes workpieces of standard dimensions, comprising a first conductive substrate portion, a second conductive substrate portion, an electrical circuit interposed between the first conductive substrate portion and the second conductive substrate portion, and the first and second conductive substrate portions electrically connected together to form an electrically continuous body that has at least one dimension that is equal to a dimension of a workpiece processed by the processing system.
Some real production wafers are known to develop non-uniform charge build up across the surface. The DC bias potential induced by RF power delivery to the wafer can also be non-uniform across the wafer surface, resulting in non-uniform IED's at different points on the wafer. The formation of an electrically continuous body (to provide a shield) in an imitation wafer probe forces a uniform charge distribution across the surface and forces the DC bias potential to be the same at every point, where the shield becomes an equipotential surface. Therefore, the locally measured IED in the presence of such a shield can be a distorted version of the true IED at that location on a real production wafer.
With such known configurations, RF current is forced to flow around the outside of the continuous shield and not through the wafer. This can also be a problem for some applications.
There are a number of shortcomings with the shielding provided by the prior art imitation substrate probes. There is a need to address these shortcomings.
The present teachings describe an apparatus or imitation wafer probe 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 in the substrate, and a conductive enclosure disposed in the substrate and surrounding each ion energy sensor and control circuitry such that the substrate at least partially surrounds the conductive enclosure.
The substrate may be conductive or non-conductive.
The apparatus may further comprise an insulating layer between the substrate and the conductive enclosure.
The substrate may be semi-conducting. Optionally, the substrate is silicon.
The apparatus may further comprise a semi-conducting cover on a surface of the substrate. The semi-conducting cover may be made from silicon.
Optionally, the ion energy sensor measures energy distribution at a first surface of the substrate and the cover is provided at a second surface of the substrate opposite to the first surface.
The apparatus may further comprise an RF antenna disposed in the substrate outside of the conductive enclosure.
Optionally, the RF antenna is connected to the control circuitry.
The RF antenna may be provided at the periphery of the substrate in a non-conductive or semi-conductive region.
Each ion energy sensor and associated control circuitry may be provided on a circuit board.
The present application will now be described with reference to the accompanying drawings in which:
A four chamber plasma processing system 105 is also shown in
The imitation probe 101 is placed in the docking station 102 and communication is established through the application software on the host PC 104. The battery power supply on the wafer probe 101 is charged, stored data retrieved and the next experimental assignment scheduled to prime the wafer probe 101. The imitation wafer probe 101 is then placed in an available slot in a Front Opening Universal Pod (FOUP) which is subsequently delivered to the load lock chamber 108. The robotic arm 107 transports the imitation wafer probe 101 to the processing chamber 106 and positions it on a processing pedestal in preparation for plasma exposure. With the chamber 106 already under vacuum, the process recipe is configured and plasma ignited. When plasma is formed, plasma species begin to bombard the wafer probe 101, a sample of which enters the sensors of the probe 101 for analysis. Analysis proceeds at the times configured in the scheduler if the on-board pressure sensor reports that the threshold for high voltage application has been met. This safety mechanism prevents the accidental application of high voltage at atmospheric pressure, which could destroy the sensor due to electrical arcing. If the pressure threshold has been met, the wafer probe 101 is activated at the scheduled time. The appropriate voltages are applied to all the grids and collector, the collector current is recorded as a function of ion discrimination potential by a microcontroller (MCU), not shown, and the resultant 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. When the assignment is completed, the plasma process may be terminated to allow retrieval of the wafer probe 101 from the processing pedestal using the robotic arm which transports the wafer probe back through the load lock chamber 108 to the FOUP. The user extracts the wafer probe 101 from the FOUP and places it back in the docking station 102 for data retrieval, recharging and scheduling of the next experimental assignment. Alternatively, it is possible for the wafer probe to transmit the sensor data in real-time to the docking station, from its location inside the processing chamber, using known wireless communication apparatus and methodology.
It should be appreciated that the wafer probe 101 in accordance with the present teachings is not limited for use in the system as shown in
The configuration of the wafer probe 101 will now be described in more detail. In the preferred embodiment the wafer probe 101 is fabricated on a substrate to mimic the standard semiconductor work piece. It may be manufactured using silicon, ceramic, metal, glass or any other material to mimic the types of substrates used in plasma processing, and may have the same geometry as a standard substrate with substantively the same dimensions and weight. The general configuration of the imitation wafer probe 101 is shown in
The sensors 201 may comprise alternating layers of planar, parallel, conductive metal grids and insulators, the grids being electrically polarised in a systematic way to filter out plasma electrons, separate positive ions based on their energy, suppress secondary electron emission and collect ion current for measurement. The sensors are embedded in the substrate of the imitation after probe 101. The sensor configuration shown in EP 3968353. However, it should be appreciated that the specific configuration of the sensors 201 used with the imitation wafer probe 101 is not the focus of the present 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 imitation probe 101.
Turning to
To protect the sensors and associated circuitry, a conductive enclosure 305 is provided surrounding each circuit board 302. It can be seen that the substrate 301 at least partially surrounds each conductive enclosure 305.
In order to measure ion energy and ion flux uniformity, it is important to ensure the distributed sensors 303 are electrically isolated from each other. Therefore, it is advantageous for the sensors 303 to be independently shielded using a conductive enclosure for each sensor 303. This ensures the sensors and associated circuitry are electrically isolated from each other. This in turn allows each sensor 303 to detect exactly what is happening at its respective location without being influenced 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.
In the embodiment of
Turning to
Turning to
In this embodiment, when a conductive substrate 401 is used, it is important to break the naturally formed continuous electrical shield, which could form around the conductive substrate 401. In particular, in the case of a conducting substrate, the rf potential across the surface of the substrate can be non-uniform. To ensure that a true measurement of the plasma conditions at the sensor location is achieved, the conductive enclosure 405 (sensor shield) should be isolated from the conductive substrate 401. This is achieved by installing the insulating layer 406 between the conductive enclosure 405 and the conductive substrate 401 to break the continuity of the conductive enclosure 405 as shown in
While the embodiment of
The substrate 501 is formed from undoped silicon. As previously mentioned, the substrate 501 of the apparatus 500 in accordance with the present teachings can be manufactured from silicon. For the previously described conductive substrates, these can be formed from doped silicon. However, for silicon based substrates, it is advantageous from a manufacturing point of view to avoid the need to dope the silicon to make it conductive. Silicon is considered a semiconductor (neither conductor nor insulator). Germanium or another semiconductor material can also be used.
In the undoped silicon substrate embodiment of
A silicon cover or a cover formed from another material may also be used with the other embodiments described herein. That is, a cover may be provided on the underside of any of the apparatuses described herein.
An RF (loop) antenna 606 is also provided in the non-conducting substrate 601. The antenna is connected back into the control circuitry 604 within the conductive enclosure 605. This antenna 606 is used for communicating data off the apparatus 600 in real-time while the plasma is running, where digitised sensor measurements can be encoded onto the antenna by switching it on and off to modulate the power flow into the chamber at a very low level. This modulation can be sensed on the power feed line.
Although only one rectangular loop antenna 606 is shown in the cross-section view of
While the apparatus if
For certain applications, it is desirable to centralise all circuitry (and power supplies), while the sensors are distributed at various locations around the wafer. For this embodiment, the conductive enclosure needs to surround the circuitry and all sensing elements in one continuous shield. This would have the configuration of a circular disk in the centre (housing the circuitry) and extending out on spokes to each sensor position. The antenna would circumnavigates the edge of the wafer.
RF antennas (loops) for real time communication cannot be installed in conducting material (conducting substrate) as commonly used in known imitation wafer probes.
RF current must be allowed to flow through the wafer cross-section (from bottom to top) to activate the antennas. The RF antenna may also be provided in a semi-conductive region of the substrate.
With reference to
The invention is not limited to the embodiment(s) described herein but can be amended or modified without departing from the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 22209525 | Nov 2022 | EP | regional |
