Manual for Alcatel 601 E

Alcatel 601E

Attention Important preliminary notices:

Contents: CMI

  1. Introduction
  2. Equipment description
  3. Standard processes
  4. How to use the system
  5. Metrology
  6. Photos gallery
  7. References

I. Introduction CMI

Alcatel 601 E is a Deep Reactive Ion Etching (DRIE) equipment with high performances, in particular for obtaining high aspect ratio profiles into Silicon (Si).
  1. Some special hardware arrangements provide these performances:
  2. Processes can be separated in 3 specific8 families: pulsed1,2 (Bosch process) and none pulsed at room temperature (continuous process) or cryogenic3,4

The major advantages of this system compared to capacitive coupled reactors (also called RIE: Reactive Ion Etching) are:
  1. Wafer voltage biasing independent from the inductively coupled plasma creation
  2. Creation of a low pressure (0.1 à 20 Pa) and high density (1011 à 1012 cm-3) plasma without reactor walls sputtering
This dissociation between the plasma density (radicals and ions) and the ions energy offers large processes development opportunities.

II. Equipment description CMI

Graphic user Interface

The Alcatel 601 E etcher is totally driven through a very intuitive computer Graphic User Interface (GUI). The only manual handlings are the pluggings/unpluggings of liquid nitrogen to the machine (to thermalise the chuck) and the loadings/unloadings of the wafers into the loadlock. Figure 1 depicts the way recipes are edited. All parameters linked to the etching process are adjustable.

Edition d'une recette de gravure sous le logiciel d'une A601E
Figure 1: Editing of a recipe using the A601E software

Wafer loadlock

The loadlock/transfer arm system is designed in such a way that the process chamber is always under high vacuum during loadings/unloadings procedures of the wafers, which optimizes processes durations.

Processing chamber

Figure 2 shows a global view of the 601 E processing chamber. Main parts are visible: ICP source, diffusion chamber, cryogenic and biasing substrate holder, pumping systems and gas lines. The machine is also fitted with an End Point Detection (EPD) system.

Vue synoptique dun réacteur
Figure 2: Cross-view of 601 E processing chamber

ICP source

ICP source is made with an antenna connected to an RF power supply and wrapped around an alumina cylinder. RF power (2 kW maximum) is coupled to the plasma through an inductive mode. The oscillating current in the antenna at 13.56 MHz induces an electromagnetic field (E/B) in the alumina cylinder. For plasma ignition, some primary electrons collect the E/B field energy (ions are too heavy to get the energy from E/B field). Inelastic collisions between hot electrons and neutrals (injected gas mixture) give ions/electrons pairs. This is the way how the main plasma is created inside the cylinder where the gas mixture and pressure are controlled. A coil surrounding the plasma source gives a permanent magnetic field for a better plasma confinement and to avoid wasting too much charged species.

Diffusion chamber

The diffusion chamber is located between the ICP source and the substrate holder. It is a buffered zone to get better plasma uniformity. Permanent magnets surrounding the chamber limit charged particles wasting on the wall and keep a better plasma density.

Cryogenic substrate holder

The cryogenic substrate holder allows thermalization of 4 or 6 inches (special kit) wafers between -170 °C and room temperature. Substrate holder temperature control is assured via a liquid nitrogen circulation and several heating resistances controlled by a Proportional Integral Derivative (PID) controller. The wafer is fixed onto the substrate holder via a mechanical clamping (ring pressing down the periphery of the wafer). This is compatible with double face etching, the untreated surface not being in contact with the substrate holder. Energy transfers between the wafer and the substrate holder are assured by an helium interface whose pressure is adjustable. The substrate holder biasing is done by a RF generator (500 W maximum), which enables control of the ions mean energy value during the etching process.

Pumping systems

The combination of a 1000 l/s turbo pump and a rough primary pump gives a secondary vacuum of few 10-7 mb without process. In process, the powerful pumping capacity makes possible the use of high gas flow (to enhance etch rate) at a low pressure (few Pa). A secondary turbo pump / primary pump combination is fitted to the machine for load lock pumping.

Gas lines

Injection of gas mixtures is assured by 8 Mass Flow Controllers (MFC): These MFC can be used in pulsed mode with very low response times.

End Point Detection (EPD) system

EPD is a non intrusive technique which enables the detection of different materials transitions during process. It is based on the fluorescence intensity observation of a specific specie (with the use of a optical fiber/photomultiplicator/spectrometer/computer system). The SiF2 molecule, which radiates at 440.5 nm, is usually used because it represents an etch product of Si, SiO2 and Si3N4 etching. The radiation intensity of this molecule is related to the etched material.

Gas treatment before drainage

Downstream the pumping system, outlet gases are treated before being drained. A M150 ² Gas reactor column² from EDWARDS collects toxic compounds  such as chlorine or fluorine through absorption in a cartridge tank heated between 450°C and 550°C.

III. Standard processes at CMI CMI

Table 1 gives an overview of the different standard processes available on 601 E at CMI. A photos gallery is given in section VI to illustrate the processes.

Attention
Materials to be etched and TemperatureProcess name
Mask material
Selectivity to maskMaterial etch rate
(µm/min)
End Point Detection
Remarks
SiO2 at 20°CSiO2PR» 10.34YES
Transfer of mask sidewalls into the material
Si3N4 at 20°CNitrure_1PR» 0.850.26YES
Transfer of mask sidewalls into the material
Nitrure 1 : fluoro-carbonated chemistry (C2F6)
Nitrure 2: fluorine chemistry (SF6).
Nitrure_2» 10.16
Si "isotropic" at 20°C
Note : Process developed to free structures when silicon is the sacrificial layer
Si_releasePR
SiO2
>100
>200
Vlateral » 5
If thin layer
NOIsotropic etching
Si_isoslowVvertical » 0.5
Vlateral » 0.25
Si "anisotropic" deep etching. Bosch processes at 20°C
Note : pulsed processes: alternated etching and passivation steps, anisotropic etching, rough sidewalls + polymers.
Si_ambiant1PR
SiO2
> 100
> 200
6 to 9NOProcess optimized for small apertures (typically less than 100 µm)
Si_ambiant2> 200
> 400
7 to 10Process optimized for big apertures (typically more than 50 µm)
Si_ambiant3> 50
> 100
3 to 5Process optimized to minimize sidewalls roughness for etching depth inferior to 100 µm
Si "anisotropic" thin layer at 20°CSi_optoPR
SiO2
> 201 to 2YES
Continuous process: simultaneous etching and passivation, anisotropic etching, smooth sidewalls covered with polymers
PR: Photo Resist

Table 1: standard etching processes available on 601 E

IV. How to use the system CMI

Preliminary remark: wafers with PR as etching mask MUST have an Edge Bead Removal (EBR), unless agreement with CMI staff
  1. Login on the 601 E on zone 2 computer.
  2. Login on 601 E computer (username: 1, password: 1).
  3. Select your process (refer to Standard processes at CMI). Go to "edition" and select the process in the right list. Select the etching steps and hit "modify". Check the parameter "etching time" and if necessary modify it (and only this parameter) to match your needs.
  4. Edition d'une recette de gravure sous le logiciel d'une A601E

    It is strictly forbidden to modify parameters (gaz, working pressure, power,...) but the "etching time", unless agreement with CMI staff.
  5. Substrate holder thermalization:
  6. Load the wafer to be etched (check mask compatibility with selected process and cleanliness of backside), validate an EPD program if required and start the process.
  7. If etching silicon, it is advised to prime the processing chamber especially when previous process was SiO2 or SiN etching.
  8. When the process is over, check the results (refer to "V. Metrology" part)
  9. Repeat the procedure to etch other wafers
  10. Once all your processes are finished, put the equipment on stand-by mode. To do so :

V. Metrology CMI

Optical Microscope

Mechanical profiler

Mechanical profiler in zone 4 (alpha-step) gives accurate step measurements in the range 0.1µm to 2mm. The system does not work when the aspect ratio becomes too high; the stylus cannot reach the bottom.

Interferometry

Spectro-reflectometer (Nanospec) in zone 3 gives accurate thickness measurements for transparent layers (SiO2 or Si3N4 for example) on Si. This metrology is useful to estimate etching selectivity. However, it is not suitable for thickness less than 10nm.

Scanning Electron Microscope (SEM) and Focus Ion Beam (FIB)

SEM LEO 1550 in zone 1 is a very powerful tool to study profiles after etching (verticality, roughness, depth, selectivity...). It is very often necessary to cleave the wafer to get a full etching characterization. When it is not possible to destroy the wafer, a local cross section can be performed with FIB.

VI. Photo gallery CMI

Deep etching using a pulsed room temperature process (Si ambiant):
photo MEB (vue en coupe) dune gravure profonde réalisée avec le procédé ambiant pulsé, observation de tranchés pour différentes ouvertures (test CMI).
Figure 3: SEM image (cross view) of a deep etching realized using a pulsed room temperature process, observation of various aperture sizes (test CMI).

Highlight of the microloading effect:
photo MEB (vue en coupe) dune gravure profonde réalisée avec le procédé ambiant pulsé pour la fabrication dun microactionneur (projet LPMO réalisé par Ch. Edouard)
Figure 4: SEM image (cross view) of a deep etching realized using a pulsed room temperature process for a micro-actuator fabrication (LPMO project done by Ch. Edouard)

photo MEB (vue tiltée) dune gravure profonde réalisée avec le procédé ambiant (test CMI)
Figure 5: SEM image (tilted view) of a deep etching realized using a room temperature process (test CMI)

photo MEB (vue tiltée) dune gravure profonde réalisée avec le procédé ambiant (test CMI)
Figure 6: SEM image (tilted view) of a deep etching realized using a room temperature process (test CMI)

photo MEB (vue en coupe) dune gravure profonde réalisée avec le procédé ambiant pulsé pour la fabrication dun micro réseau
Figure 7: SEM image (cross view) of a deep etching realized using a pulsed room temperature process for micro-grating fabrication.

photo MEB (vue en coupe) du fond dune gravure profonde au travers d'un substrat réalisée avec le procédé ambiant pulsé débouchant sur une membrane de SiO<sub>2</sub> (test CMI)
Figure 8: SEM image (cross view) of a pattern bottom through a substrate opening on a SiO2 membrane (test CMI). Done with a pulsed room temperature process.

photo MEB (vue en coupe) d'une mico-buse en SiO<sub>2</sub> obtenue avec un moule Si (succession de deux gravures profondes dans Si de diamètres différents) et libérée par une gravure anisotrope de SiO<sub>2</sub> suivie d'une gravure isotrope du Si
Figure 9: SEM image (cross view) of a SiO2 micro-nozzle obtained with a Si mold (2 succesive deep etchings of different diameters in silicon) and released by an  anisotropic etching of SiO2 followed by an isotropic etching of Si

photo MEB (vue en coupe) d'un trou conique au travers d'un substrat Si, projet Microshutters Colibrys S.A., Neuchâtel,CH.
Figure 10: SEM image (cross view) of a cone-shaped hole through a Si substrate, project of Microshutters6 Colibrys S.A., Neuchâtel,CH.

photo MEB d'une vue 'tiltée' d'une gravure anisotrope d'une couche épaisse de polySi réalisée avec le procédé ambiant continu, projet Microshutters Colibrys S.A. , Neuchâtel, CH.
Figure 11: SEM image (titlted view) of an anisotropic etching of a thick polySi layer realized with a continuous process at room temperature, project  of Microshutters6 Colibrys S.A. , Neuchâtel, CH.

photo MEB (vue en coupe) d'une gravure anisotrope dans Si réalisée avec le procédé ambiant continu, projet Optosimox, EPFL-DE/MET, Lausanne, CH.
Figure 12: SEM image (cross view) of an anisotropic etching in Si  d'une gravure anisotrope dans Si realized with a continuous process at room temperature, project of Optosimox7, EPFL-DE/MET, Lausanne, CH.

photo MEB (vue en coupe) d'un réseau dans Si de gravures profondes réalisées avec le procédé cryogénique (test CMI). Mise en évidence du 'microloading effect'
Figure 13: SEM image (cross view) of  Si gratings deep etching realized with the cryogenic process (test CMI). Highlight of the "microloading effect"

VII. References CMI

  1. J.K. Bhardwaj, H. Ashraf, Proc. SPIE, 2639, 224 (1995).
  2. A. Schilp, M. Hausner, M. Puech, N. Launay, H. Karagoezoglu, F. Laermer, "Advanced etch tool for high etch rate deep reactive ion etching in silicon micromachining production environment" Proceeding MST 2001, Dusseldorf.
  3. M. Puech, Ph. Maquin, Applied Surface Science 100/101, 579 (1996).
  4. S. Aachboun, P. Ranson, C. Hibert and M. Boufnichel, J. Vac. Sci. Technol. A 18(4), Jul/Aug 2000.
  5. C. Hibert, S. Aachboun, M. Boufnichel, and P. Ranson, J. Vac. Sci. Technol. A 19(2), Mar/Apr 2001.
  6. G. Perregaux, S. Gonseth, P. Debergh, JP. Thiébaud and H. Vuilliomenet, "Arrays of addressable high-speed optical microshutters", Proceedings MEMS 2001, pp. 232-235.
  7. P. Dainesi, A. Küng, M. Chabloz, A. Lagos, Ph. Flückiger, A. Ionescu, P. Fazan, M. Declerq, Ph. Renaud and Ph. Robert, IEEE Photonics Technology Letters, vol.12, N°6, pp. 660-662, June 2000.
  8. C. Hibert and Ph. Flückiger, "Deep anisotropic etching of Si using low pressure high density plasma. Presentation of complementary techniques and their application in microtechnology", ISPC 15 (International Symposium of Plasma Chemistry), Orléans, june 2001.