DIGILEM - Interferometric Endpoint Detector & Thin Film Monitor

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Introduction

Ellipsometry
Applications
Basic Principles
Ex-Situ UVISEL
In-Situ UVISEL
Optical Set-up
PZ 2000
PQ Ruby
Software

Process Control
DIGISEM
DIGILEM
DIGITWIN
PlasmaScope
MULTISEM
User Guide

Process Applications

EPD at Interfaces

EPD at Depths

Optical Emission Spectroscopy

Thicknesses, refractive indices and absorption constants

Depth Targeting for MEMS

III-V Process Control

Flat Panel Display Film Thickness

Thin dielectric and transparent film

Real-time process monitoring

Ultra-thin gate oxide (UTGO) layer thicknesses

Pulsed Plasma Monitoring

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Interferometric Endpoint Detector and Thin Film Monitor

Interferometry

Interferometry is a powerful technique that can be used for endpoint detection of planar layer and trench etching, or deposition. The technique involves illuminating the surface of a sample (typically a wafer) and measuring the reflected intensity.

The system may be used as a simple reflectometer, in which case interfaces between materials with different refractive indices can be detected by the resultant step change in the reflectivity signal.

More often however, interferometry is used. For suitable samples and hardware configurations, as the sample is etched or deposited the reflectivity signal oscillates in a sinusoidal manner due to constructive and destructive interference. Once a period of interference has been observed the etch/deposition rate can be calculated. The etch/deposition can then be stopped at a pre-set depth. Additionally interfaces can also be detected by the changes or even absence of interferometry.

Jobin Yvon has considerable experience in appropriate hardware selection and process parameter optimisation and our application scientists will work with you to obtain a reliable process solution.

DIGILEM Configurations.

DIGILEMs are available in a variety of configurations with different optical set-ups to enable the optimum performance for different processes.

We offer three basic configurations:

DIGILEM – Camera;

Enables the measurement to be made with a microspot. Ideal for complex patterned wafers. Available with laser diode sources with various wavelengths. 670 nm is ideal for most silicon processes and 905 nm is especially suited for III-V processes.

DIGILEM – Twin Spot;

This is a development of the camera system and allows two separate spots to be placed on the wafer, one on the open area the other on the resist. This provides accurate depth control of trench etches in excess of 500 µm and is ideal for controlling many MEMs processes.

DIGILEM – Tilt;

Permits interferometry over a large area (typically 30 mm diameter). This system is especially flexible and can be configured to use a variety of wavelengths from the UV, visible to the IR to match the optical and geometric properties of the structure. This type of solution is particularly suitable for regular structures or planar wafers.

Applications

Typical applications of the DIGILEM systems include:

In-Situ Real time control of:

Plasma etch and deposition process endpoints

Endpoint at a specified layer thickness

Endpoint at a given remaining layer thickness

Endpoint at a predetermined trench depth

Endpoint of planarisation processes

Real time monitoring of:

Etch and deposition rates

Process selectivity

The DIGILEM is particularly suitable for the following application areas

Microelectronic:

Sub-micron trench etching of silicon, poly silicon, resist... for DRAM, microprocessors, logic and flat panel displays

Optoelectronics:

GaAs, AlGaAs, InP ... for telecommunication products, CCD sensors. The DIGILEM-Camera system with a 905nm laser is ideally suited for this type of process.

Microsystems:

Micro motors, micro pumps, hard disk heads and other MEMs applications. The DIGILEM-Twin Spot has been developed specially for this application

DIGILEM - Camera

The Jobin Yvon DIGILEM includes a compact interferometer that integrates a laser source, signal detector and a CCD camera with an associated illuminator in a compact head. This camera is controlled by an electronics unit that includes a computer with full software control of the acquisition.

The camera produces a microspot on the wafer surface 20 – 60 µm in diameter, depending on the wafer to camera distance. This spot can be positioned accurately anywhere on the wafer using a manual or motorised XY translation stage and a digital image of the wafer surface provided by the integrated CCD camera. The motorised stage can work in conjunction with the image of the wafer surface and a pattern recognition program for real time pattern specific etching.

The camera is available in two versions with different wavelength laser diodes. The standard 670 nm red laser version is suitable for most applications. However the 905 nm infra red camera has distinct advantages for III-V applications.

Click on picture for a diagram of the camera head

Click on picture for the relationship between spot size and window to sample distance

Schematic Diagram of DIGILEM-Camera System

DIGILEM-twin spot

The DIGILEM-Twin Spot system is a development of the Jobin Yvon DIGILEM-Camera arrangement described above. It therefore has the same general specifications except that the system replaces the standard camera with our patented twin spot camera.

The system has been designed for real time in-situ control of MEMS applications including the measurement of large feature and deep trench etch rates. It can also be used for endpoint control on etches with an etch depth in excess of 500 µm. Measurements are performed using two separate laser beams that can be positioned accurately (one in the trench the other on the mask) using a manual or motorised XY stage. This process can be automated using pattern recognition software, a real time digital CCD image of the wafer surface and a motorised XY stage.

The twin spot camera system takes advantage of the highly developed software platform associated with other members of our process control range. This includes real time process control, user programmable steps, high sensitivity endpoint algorithms, data management, numerical etch rate fitting methods and reprocessing facilities for off line endpoint algorithm optimisation. Additionally the software is compatible with the Bosch process.

DIGILEM-Tilt

The minimum controllable etch depth is directly related to the wavelength of light used. As layer thicknesses continually reduce the advantages of using UV light become more significant. Camera systems generally contain components which do not transmit UV light so Jobin Yvon have developed a Tilt Head which when combined with a suitable light source and detector provides a interferometry system which can cover the 220-850 nm wavelength range. Various sources and detectors are offered so a solution can be tailored to your specific requirements. Automated wavelength selection is available so multiple processes requiring different wavelengths can be catered for with no user interaction, simply select the required wavelength in the endpoint step setup.

The tilt head produces a relatively large spot on the wafer, typically 3 cm diameter. Therefore it lends itself to unpatterned or regularly patterned samples and can therefore be used as an alternative to a camera system for these processes.

SPECIFICATIONS

DIGILEM-Camera

Wavelength : 670 nm or 905 nm (others on request)

Magnification : standard x 50, optional x 120

Camera to wafer distance: 50 mm to 700 mm

Spot size : 20 - 120 microns depending on camera to wafer distance.

Solid state detector

Camera dimensions (h x l x L), 231mm x 71 mm x 111 mm

16 mm x 16 mm manual XY translation stage

Options

25mm x 25 mm motorised XY translation stage

Remote camera lens focus and motorised XY stage adjustment by joystick control

Pattern recognition system for automated microspot positioning

Frame grabber for displaying the video image directly on the PC monitor with high resolution

DIGILEM-Twin spot

Specifications as standard system except:

Distance between spots : 160 - 560 microns depending on wafer to camera distance, nominal value is approximately 240µm at a distance of 230 mm

DIGILEM-Tilt head

Spectral range, 220 nm - 850 nm

Spot size : 3 cm