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Vertex Multi Sensor

Vertex Multi Sensor

Viewing Your Process From Another Angle

The Vertex Multi Sensor measures the ion energy distribution as a function of aspect ratio hitting a surface inside a plasma reactor from multiple locations to analyse the uniformity of ion interactions across a substrate.

The uniformity of Ion energy, Ion flux and bias voltage is also measured from multiple locations.

The angle of ions hitting the bottom of a feature can be determined from the ion energy distribution as a function of aspect ratio which can be measured across a substrate to monitor the uniformity and hence the quality of the etch profile from one side of the substrate to the other.



Features

Substrate Bias Compatible | High RF Bias Resistant |
Easily Installed | High Temperature Resistant


Applications

High Aspect Ratio Processing | Process Uniformity |
Process Development | Equipment Design




Overview

The Vertex Multi Sensor measures the uniformity of the ion energy distribution as a function of aspect ratio. Ion energy uniformity, ion flux uniformity, negative ion uniformity and bias voltage at a surface inside a plasma is provided. The Vertex Multi Sensor is increasingly used in many applications in industry and research where feature profile is of interest, such as plasma etching for larger substrates, ion beams, and plasma sputtering. The Vertex Multi Sensor helps users confirm models, develop new processes and experiments that use plasma and require a uniform process, plasma tool design, plasma characterisation and research.

The Vertex Multi Sensor is housed in a 19" rack mounted electronics unit, vacuum feed-through, and a sensor holder located anywhere inside a plasma or beam chamber. The location can even be a RF or DC powered electrode and can use a replaceable Button Probe sensor. The electronics unit connects to a laptop or a PC and uses the Vertex intelligent software suite. The Vertex Multi Sensor has a number of holder options ranging from 100mm to 450mm and will depend on the user’s application. Users can select a sensor holder assembly to match the size of their substrate holder or their electrode. The sensors are strategically located at different locations across the holder of choice.

The Vertex Multi Sensor analyses the change in plasma input parameters or beam source location in real time, helping users to find the optimum uniformity of ion energy distribution as a function of aspect ratio for their application. The system also takes useful measurements such as bias voltage and the energy and flux of negative ions. While the Vertex System is not used on the process side of plasma manufacturing it has been used to measure side wall pattern in uniform etch processes, beam divergence, elastic scattering to assist with chamber to chamber matching, fault detection, researching new processes, in an offline environment. For the first time, direct measurement of the uniformity of ions through high aspect ratio holes is available with the Vertex System, helping eliminate the need for a trial and error approach - saving time and money.

Plasma Parameters Measured

  • Ion Energy Distribution as a function of Aspect Ratio (Up to 13 Locations)
  • Ion Energy Distribution (Up to 13 Locations)
  • Ion Flux (Up to 13 Locations)
  • Negative Ion (Up to 13 Locations)*
  • Bias Voltage (Average)
  • Edge Profiling (Close to Edge Sensors)

Measurement Functionality

Time Averaged Measurements
This provides an average over time of the ion energy distribution as a function of aspect ratio arriving at the substrate position.

Time Resolved Measurements
This allows the user to synchronise the ion energy distribution measurements with an external synchronisation signal. The user can then obtain detailed information on the ion energy distribution as a function of time or phase through the synchronisation pulse period*. Typically, the pulse period would be on a timescale of milliseconds to microseconds. *Note: in standard energy mode only, for pulsed plasmas, with Vertex mounted on a grounded or floating electrode.

Time Trend Measurements
This allows the user to obtain information on the variation of the ion energy distribution as a function of aspect ratio as time progresses through a particular process. This feature does not require external synchronisation and the timescales involved can be in range of seconds to hours.

Further Product Information

Vertex Electronics Control Unit and Software

Electronics UnitThe user-friendly high energy electronics and software takes accurate and reliable data to provide industry leading ion energy distribution and ion flux measurements. Using intelligent analysis, the optimal plasma parameter measurements are performed easily and repeatedly.

Sensor Holder

The holder is available in various sizes (150mm, 200mm, 300mm, 450mm and Custom Shapes). It sits on a grounded or biased electrode and is used to hold the replaceable Button Probe Sensors. It is available a number of materials including aluminium, anodised aluminium and stainless steel (custom materials are available).

Holder Options

Replaceable Button Probe

Button ProbesThe Vertex Button Probe is a compact Retarding Field Energy Analyser (RFEA) which is designed to support continuous Vertex system operation. When the probe is coated or etched away after a long period of exposure to reactive or insulating plasmas, the sensing element (Button Probe) can easily be replaced. 

Installation

The Vertex is simple to install and requires no adjustments to your plasma chamber. It is a portable system and can be used across a number of different chambers.

Measuring Parameters

Aspect Ratio Range 0.5 to 20
Aspect Ratio Resolution 0.5
Ion Energy Range 2000 eV - Vdc
Ion Current 1 mA DC max
Ion Flux Ranges 0.01 - 50 (A/m²)
IEDF Resolution ± 1 eV nominal

Probe Bias Conditions

Max RF Bias Voltage 1 kV peak-to-peak
Max DC Bias Voltage -1940 V
Bias Frequency Range (Time Averaged Measurements) 100 kHz to 80 MHz
Bias Frequency Range (Time Resolved Measurements) 0 Hz to 100 kHz
Time Resolution 100 µs

*for pulsed plasmas with Vertex mounted on a grounded or floating electrode

RFEA Probe

Number of Sensors Up to 13
Probe Configuration 4-grid
Button Probe Diameter 33 mm
Holder Diameter 150 mm, 200 mm, 300 mm, 450 mm and custom shapes
Holder Thickness 5 mm
Max Operating Temperature 200º C
Mounting RFEA Probe holder mounted on electrode
Probe Enclosure and Holder Material Aluminium, anodized aluminium, stainless steel* and ceramic (Al2O3)*
RFEA Probe Cable Length 650 mm standard (custom available)

*on request

Feed-Through Assembly

Flange Type CF40 (custom available)

Control Unit Electronics

Grid Voltage Range -2 kV to +2 kV
Current Range 100 pA to 2.4 mA
Connectivity USB 2.0

Application Software

Operating System Windows 2000 / XP / Vista / Windows 7 / Windows 8

Operating Parameters

Pressure (Pascal) 0 to 40 Pa*
Pressure (Torr) 0 to 300 mTorr*
Density Ranges(for Ar at 3 eV) Low: 1.2 x 1012 to 7.4 x 1015 | Std: 2.0 x 1013 to 1.2 x 1017 | High: 2.7 x 1014 to 1.6 x 1018 (m-3)
Gas Reactivity Inert to highly reactive

*dependent on ion mean free path

The Vertex Multi Sensor used in Plasma Etching applications

Ion velocity distribution measurement through high-aspect ratio holes using the Semion system

Abstract

Plasma etching and filling of high aspect-ratio (AR) structures is becoming more difficult at each new semiconductor technology node for several reasons. Ion bombardment of the sidewalls of the feature (due to the angular distribution of ion energies) complicates etching profile control. Also, ion loss on the sidewall reduces ion flux to the bottom of the feature. Ions are directed to the substrate with an angular spread due to the ion thermal velocity at the sheath edge. The thermal velocity causes ions to have a velocity component parallel to the substrate surface while the sheath electric field accelerates the ion toward the substrate in the perpendicular direction. As a result, the ion arrives at the surface at off-normal incidence.

VE02: Ion velocity distribution measurement through high-aspect ratio holes using the Semion system

Ion energy and ion flux measurements through high-aspect ratio holes using the Vertex system

Abstract

High aspect ratio (AR) etching is a key process in integrated circuit (IC) fabrication. The manufacture of a 3D NAND memory stack requires structures with an AR > 50 to be created. The key challenge is to create bow-free, straight profiles with minimal twisting. Transport of ions and neutrals to the bottom of these structures can be limited by sidewall shadowing. In particular, ion bombardment of feature sidewalls complicates etching profile control while ion loss to the sidewall reduces ion flux to the bottom of the feature. Only ions with a relatively narrow angular spread, relative to normal incidence, will reach the bottom of high AR features. Ions are accelerated toward the substrate by the sheath electric field perpendicular to the substrate surface. However, ions have some thermal velocity when entering the sheath and therefore have an energy component parallel to the substrate surface. The ratio of the perpendicular to parallel components of the ion energy vector determines the angular distribution.

VE01: Ion energy and ion flux measurements through high-aspect ratio holes using the Vertex system

Ion angular distribution measurement with a planar retarding field analyser

Abstract

In this application note, we present a novel method which can be applied to a planar retarding field energy analyser (RFEA) for the measurement of ion angular distributions. Ion energy and angular ion distributions play a critical role in plasma assisted etching and conformal deposition processes. Ion impact at wider angles may be required for better step coverage in certain sputter deposition and ion implantation processes while large angle ion impact can be detrimental to anisotropic etch processes. In the early 80’s, Stenzel et al 1, 2 developed a directional RFEA where particles are geometrically filtered through a micro-capillary plate prior to energy analysis. The high aspect ratio (AR) of the holes/channels in the plate allowed them to select particles within a geometric acceptance angle. The Vertex RFEA design has a variable AR, controlled using a potential difference between two grids (see application noteVE02). A variable AR controls the ion angular spread passing through the sensor for detection. The Vertex product produces a plot of ion energy distribution versus AR.

VE03: Ion angular distribution measurements with a planar retarding field analyser

The Vertex Multi Sensor used in HiPIMS Plasma applications
Coming soon
The Vertex Multi Sensor used in Ion Beam Plasma applications
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The Vertex Multi Sensor used in PECVD applications
Coming soon
The Vertex Multi Sensor used in Space Plasma applications
Coming soon
The Vertex Multi Sensor used in Plasma Sputtering applications
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The Vertex Multi Sensor used in Dusty Plasma applications
Coming soon

Overview

The incoming ions have an energy component in the X direction perpendicular to the sampling aperture EI and an energy component in the Y direction EII parallel to the sampling aperture

Incoming Ion Angle

Variable Aspect Ratio

The aspect ratio determines if the EII energy component is such that the ion gets collected at the aperture electrodes or passes through the apertures for detection at the collector of the RFEA.

Incoming Ion Angle

Variable Aspect Ratio Using a Variable Bias

The electric field applied in the EI direction determines if the EII energy component is such that the ion gets collected at the aperture electrodes or passes through the apertures for detection at the collector of the RFEA.

Incoming Ion Angle

Aperture Between Grid 2 and Grid 3

Incoming Ion Angle

Theory

The RFEA is designed to have electric fields in the X direction only, it is a planar system with all grids parallel to each other. The discriminator potential at G2 is used to separate ions with different energy and acts only on the EI component of the incoming ion. The EII component of the ion energy is unaffected by the electric fields inside the sensor. At any location inside the sensor the EII component of the ion energy is identical to the EII energy component of the ion as it entered the sensor through the sampling aperture.

By varying the potential difference between G2 and G3, the acceptance angle for which ions can enter the sensor is varied.

AR selection aperture

The aperture between grid 2 and grid 3 is designed to have a specific geometrical AR. Figure 3 shows a schematic representation of the aperture used to measure IEDs at the bottom of features with different ARs. The physical geometrical aperture is fixed with AR (l/w) of 0.5. The effective geometrical AR for positively charged ions can be varied by applying a potential difference (ΔV) between grid 2, which covers the entrance plane of the aperture, and grid 3, which covers the exit plane of the aperture.

Grid 2 is biased to discriminate ions based on their energy. In other words, grid 2 is used to select ions with a specific energy. As a result, the selected ions have close to zero energy when they cross grid 2 i.e. the process of selecting the ions of a particular energy involves the application of a retarding field that reduces the ion energy to almost 0 eV. In order to change the effective geometrical AR, we need to determine the ion trajectory through the aperture in terms of velocity (ν) rather than energy. The kinetic energy of the ion is equal to ½mν². Since the AR is effectively a ratio between ν⊥ and ν∥ then the ion mass (m) can be eliminated and

v∥ = √E∥

s⊥ = √(e∆V)

where the energy E has units of eV. The ion’s position (s) within the aperture (relative to the entrance plane) is given by Newton’s second law of motion, assuming the ion’s initial velocity in the perpendicular direction is zero

s∥ = v∥t

s⊥ = ½a⊥t²

The time taken for an ion to reach the aperture exit plane, in terms of its perpendicular acceleration, is √(2l/a⊥) . The perpendicular velocity at the exit plane v⊥=a⊥ t=√e∆V and therefore the perpendicular acceleration is e∆V/2l. An expression for the perpendicular position can be written as

s⊥ = (e∆V/4l)t²

The position of the ion in the parallel direction, in terms of its parallel energy, is √(E∥)t. The perpendicular position can now be written in terms of the parallel position

s⊥² = (e∆V/4lE∥)s∥²

Solving for the ion’s parallel position with respect to the exit plane gives

s∥² = 4E∥l²/e∆V

Using basic geometric considerations, the AR is v⊥/v∥ or √(E⊥/E∥). In the same reference frame, any ion with s∥>1 will hit the side wall of the aperture. Solving for s∥=1 and substituting E⊥/AR² for E∥ gives the equivalent geometrical AR for the ion energy selected by grid 2 and the potential difference applied between grid 2 and grid 3

AR = 2l/w√E⊥/e∆V

The software user interface (UI) allows the user to select an AR (or series of ARs) and the algorithm automatically selects ions with specified energy and applies the appropriate ΔV to keep AR constant for the duration of a specified AR scan.

Ion energy distribution as a function of aspect ratio

This graph shows the ion flux and IEDs measured for different ARs, using the technique outlined above. These measurements were taken at the powered electrode in a capacitively coupled parallel plate reactor. The driving frequency was 13.56 MHz, the working gas was oxygen and the pressure was 0.5 Pa. The drop in ion flux and the change in shape of the IED as the AR is increased is seen as expected. This implementation of the variable AR method is more convenient than the method described by Cunge et al.

Coming soon

Ion Energy Distribution as a function of Aspect Ratio

Coming soon


Ion energy distribution function

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