Chapter 7.7

Centura®Deep Silicon Etch DPS-DT

(centura-dps)

 

1.0         Title

Centura Platform System DPS-DT Etch Chamber Operation Manual

2.0         Purpose

The Centura DPS-DT is a deep silicon etch chamber that is primarily configured to etch high aspect ratio features using a switched gas methodology (TMGM - Time Multiplexed Gas Modulation, aka DRIE - Deep Reactive Ion Etch).

3.0         Scope

The Centura platform is a fully automated, multi-wafer capacity, multi-chamber system. The system consists of a mainframe assembly (loadlocks, transfer chamber, process chambers) and an associated set of remote support equipment (RF power supplies, vacuum pumps, heat exchangers, computers). All wafer handling and processing takes place in the mainframe assembly. Operator interface takes place at the Centura computer terminal located at the front of the system.

TMGM (Time Multiplexed Gas Modulation), also known as Deep Reactive Ion Etching (DRIE), is a switched-gas plasma etch process that is capable of etching high aspect ratio (AR) features in patterned silicon. A standard deep silicon etch process uses the gases SF6 (Sulfur Hexafluoride) and C4F8 (Octofluorocyclobutane) in separate but sequential steps. C4F8  is first deposited conformably upon the substrate for a fixed period of time to provide feature sidewall protection. This step is immediately followed by an SF6  etch step in which an RF bias is furthermore applied to the substrate. This induces etch directionality. By repeating these two steps over and over, high aspect ratio features can be achieved.

The Centura DPS DT chamber is configured for the processing of 6-inch (150 mm) silicon substrates. The plasma is inductively coupled at an RF of 13.56 MHz via a matching unit and coil assembly. Directional energy control is provided by a 400 kHz biasing of the cathode with a separate power supply and independent impedance matching. The cathode bias power may additionally be pulsed by using a pulse generator controlled directly through Applied Material’s software. This option is useful when etching Silicon to buried insulating layers (SOI wafers). The low frequency and pulsed bias option helps to eliminate “notching” or “footing” in silicon structures at the insulator interface. A high voltage polyimide electrostatic chuck secures the substrate within the process chamber during the process. A DTCU, or Dome Temperature Control Unit, heats the dome of the DPS DT chamber thus helping to keep particle contamination at a minimum. Cooling of the cathode and DTCU is provided by a DI (de-ionized) water chiller. Helium gas is used for aiding backside cooling of the substrate. A Throttled Gate Valve (TGV) serves as the mechanism by which chamber pressure is controlled during a typical DRIE switched gas process.

This document provides the following information:

3.1          Specific information about the capabilities, configuration, and proper operating procedures regarding the Centura DPS DT.

3.2          User level troubleshooting.

4.0         Applicable Documents

Revision History

4.1         Silicon Etch DPS DT Chamber Manual (Applied Materials® document)

4.2         Silicon Etch Centura Mainframe (Applied Materials® document)

4.3         Material Safety Data Sheets for the following gases: SF6, O2, Cl2, HBr, CHF3, C4F8, CF4, He, and N2 (copy in Microlab lobby). Note Argon gas is no longer plumbed to the DPS DT chamber.

5.0         Definitions, Process Terminology, Equipment Configuration

Acronyms and other terminology used in this document

5.1         AR: Aspect Ratio (the height to width ratio of a feature)

5.2         Ch A: Chamber A; designation of DPS DT silicon etch process chamber

5.3         Ch B: Chamber B; designation of MxP oxide etch process chamber

5.4         Ch E: Chamber E; designation of the cool down chamber. Note: Ch E not used with current Centura configuration.

5.5         Ch F: Chamber F; designation of flat finder or orienter chamber

5.6         CRT: Cathode Ray Tube

5.7         DPS DT: Decoupled Plasma Source Deep Trench

5.8         DRIE: Deep Reactive Ion Etch

5.9         DTCU: Dome Temperature Control Unit

5.10      ESC: Electrostatic Chuck

5.11      LLA: Loadlock A

5.12      LLB: Loadlock B

5.13      MFC Mass Flow Controller

5.14      MxP: Oxide etch chamber also configured to the Centura cluster platform Note: MxP has a separate operations manual, and a separate qualification is required to use this chamber.

5.15      RF: Radio Frequency

5.16      SOI: Silicon On Insulator

5.17      TGV: Throttled Gate Valve

5.18      TMGM: Time Multiplexed Gas Modulation

Equipment Configuration:

All processes occur in the process chambers. There are two process chambers currently configured to the Centura platform: Ch A (DPS DT), and Ch B (MxP). The following describes other important components currently configured to the Centura platform. 

5.19      Dual Loadlock Chambers

The Centura has two aluminum loadlock chambers. They are referred to as loadlock A (LLA) and loadlock B (LLB). Under normal operating conditions, wafers that are to be processed in Ch A (DPS DT) should be loaded using LLA. Likewise, under normal operating conditions, LLB should be used for loading wafers into Ch B (MxP). (Note: the Mxp chamber is a different etch chamber, and requires a separate qualification procedure). The loadlock chambers serve the purpose of isolating the transfer chamber from atmosphere during wafer cassette loading or unloading. Each loadlock has an automatic platform that raises and lowers the wafer cassette in order to move substrates to or from the transfer chamber. Each loadlock holds one blue 6-inch wafer cassette with a 25-wafer capacity.

5.20      Power Distribution

The source power for the DPS DT plasma is provided by a 2.2 kW RFPP generator (model RF20R). The source generator runs at a frequency of 13.56 Hz. The bias power for the DPS DT chamber is provided by a 100 watt RFPP generator (model LF10A). The bias generator runs at a frequency of 400 Hz. Each source has its own independent RF matchbox. Matchboxes essentially match the load impedance to the source impedance thus maximizing power to the system, and minimizing reflective power.

5.21      Flat Finder Chamber (Ch F)

The wafer orienter chamber; also known as the flat finder chamber or Ch F. This chamber is used to locate the major flat of the wafer so that it can be positioned in the process chamber properly via the wafer handler robot arm. Wafers to be processed always go through Ch F before being placed in any process chamber.

5.22      Transfer Chamber

The transfer chamber isolates the process chambers from the loadlocks during wafer transfer functions. It is also known as the buffer chamber, and essentially “deals” wafers to the processing or flat finder chamber with the wafer handler robot arm. The transfer chamber is held under vacuum and provides a clean neutral environment for wafer transfer to take place.

5.23      Cool Down Chamber (Ch E)

Cooldown chamber. Neither the DPS nor MxP chambers need to make use of Ch E. Thus, this chamber is not used with the current configuration, and is set to an “offline” state by default. (Note: The cool down chamber is primarily used in conjunction with chambers that run relatively high temperature processes such as LPCVD)

5.24      Heat Exchangers

Three separate HX 150 Neslab heat exchangers are used for various cooling applications within the Centura platform. All of the heat exchangers provide closed loop temperature control. Chilled DI water is used as the coolant.

5.25      Gas Cabinet

The gas cabinet is located on the top rear of the centura mainframe. The gas cabinet consists of the following components: MFCs, transducers, tubing valves, regulators, filters, gas detectors, and safety interlock switches. Process gas control and distribution to the process chambers takes place via the gas cabinet. The gases configured for use with the DPS DT are: SF6, O2, Cl2, HBr, He, CHF3, N2, and CF4

5.26      Vacuum Components

The DPS DT chamber uses a Seiko Seiki “mag-lev” turbo pump (model H1303C) to achieve low base pressure. The DPS DT chamber is further backed by a mechanical BOC Edwards QDP 80 stack. The loadlocks also use a separate, but identical mechanical BOC Edwards QDP 80 stack. The buffer chamber is held at a vacuum by a QDP40 BOC Edwards stack.

Software Overview

System operations are accessible through the CRT monitor screen by touching the lightpen to a field on the screen and pressing the lightpen button. This activates the field. There is a hierarchy to the screens and “detail” screens are reached through pulldown menus from the header line. There are 8 main header line fields with the present Centura software/hardware configuration (described below). A schematic of these headers and the pulldown menu hierarchy are shown in Figure 2. Some of the more User-relevant pulldown menu options that can be accessed by selecting these headers are listed as follows:

 

5.27      System header - The more often used options in this pulldown menu include the Login \ Logout option, the Control System screen option, and the Enter Lot Names For screen option.

5.28      Wafer header - Among several other options, this pulldown menu consists of the Monitor Wafers screen, the Monitor Handler screen, and the Load \Unload A option.

5.29      Ch A  header - This pulldown menu includes Monitor Process, Monitor Chamber, and Monitor Gas Panel screen options for the DPS DT process chamber.

5.30      Ch B header - This pulldown menu consists of the Monitor Process, Monitor Chamber, and Monitor Gas Panel screen options for the MxP process chamber. Note: Ch B has a separate operations manual, and a separate qualification is required to use this chamber.

5.31      Ch E header - This pulldown menu not used with current configuration. Ch E is offline.

5.32      Ch F header - This pulldown menu includes the same options as listed for the Ch A pulldown menu.

5.33      Program header - The important User-relevant options in this pulldown menu include the Wafer Sequencing, Process Programs, and Lot\Sequence Control screen options.

5.34      Misc header - The most User-relevant option in this pulldown menu is the Vacuum Service Screen.

6.0         Safety

6.1         RF Power

This system, like many other dry etching systems, uses high-power radio-frequency (RF) energy to generate a plasma. Avoid touching or otherwise disturbing RF cables at all times.

6.2         UV Radiation

Ultraviolet light is generated in the etch chamber during normal operation. UV-opaque “caps” are placed over all chamber ports to block this radiation. No UV light should be observable to the User at any time.

6.3         Automatic Loadlock (LLA, LLB)

Users must be aware of moving loadlock doors and components at all times. !!! Moving parts can crush or cut !!! Be aware that the cassette handler in the loadlock swings out and down automatically. Keep away from loadlock doors during automatic loading or unloading. Keep away chairs or other items that would potentially interfere with the loadlock doors or cassette handler at all times.

6.4         Emergency Stop Button

Red button located on front panel of tool. Pressing this button will cut power to the entire system. Use this button only if person or equipment is in harm’s way - e.g. earthquake, flood, or for any other dire circumstance.

7.0         Statistical/Process Data

(under construction…)

8.0         Available Processes, Process Notes

8.1         The Centura DPS DT is a six-inch compatible wafer system. Please contact Matt Wasilik regarding the potential processing of a different size substrate at this time. 

8.2         Standard Recipes: The Centura DPS DT chamber has been extensively characterized by process staff. A wide range of recipes have been developed, including standard 30:1 aspect ratio silicon etch processes. All of the standard recipes on DPS are password protected. They are permanent, and may not be modified. Contact staff (Matt Wasilik) concerning current state of process at centura. Requests for new, permanent recipes specialized for your application welcomed.

8.3         Variable Recipes: The recipe entitled DPS VARIABLE is a User-modifiable recipe. For the time being, all parameters in this recipe are open to modification by Users. Please contact staff about questions that may arise concerning editing process parameters. Note that there are no default parameters for the recipe DPS VARIABLE. WYSIWYG!

8.4         Thick Wafer Cassette:  A special thick wafer cassette is availble for processing handle bond pairs. It is kept on the shelf across from the machine at all times. Only one thick wafer pair at a time may be loaded with this special cassette. Place the handle pair in the large designated slot, and load the cassete into load lock as normal. The wafer mapping routine will apply a red “flag” to the wafer on the terminal screen. This “excessive thickness” flag may be ignored, and the wafer may be processed as normal. Be sure to place the thick wafer cassette back when finished. Contact staff for further details.

Conditioning Recipe: The recipe CONDITION 1 is highly recommended to be run just prior to actual processing, as it helps to both clean and “season” the chamber ultimately promoting more stable results. It consists of three basic steps: an SF6 clean, an Oxygen plasma clean, and a standard switched gas process. Use a bare, clean, 6 inch silicon wafer when running CONDITION 1. For further information please contact Matt Wasilik.

 

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8.5         Available DPS-DT Chamber Process Gases

 

  

                                       

 

 

 

 

 

 

Table 1

8.6         Materials

As of November 2007, the following materials are allowed in DPS DT: Any standard photoresist spun on wafer from SVGcoat1 or 2, SVG3, or SVG6; silicon, silicon nitride (stoichiometric or low stress), and silicon oxide (thermal or LPCVD). An exposed area of silicon must always be present to etch on the substrate. Exposed metals are not allowed in the DPS DT chamber. Please consult Centura process staff for more details about specific allowable materials for respective processes in the DPS DT.

9.0          Operation

The Centura system runs on Applied Materials’ proprietary software. System operations are accessible through the CRT monitor screen at the front of the system. Commands are performed by touching the lightpen to the appropriate field on the screen, and then pressing the lightpen button. This activates the field, and either the command is executed or a pulldown menu with further “field” options appears. There is a hierarchy to the screens and detail screens are reached though pulldown menus from the header line. The software allows the User to load pre-existing process recipes, load and unload the substrate, run a process, and vent the load lock.

9.1         Logging into the System

All qualified Users of Centura will be required to chose User names and passwords for the Centura system software. The Centura system software restricts User names to 8 digit characters. Passwords are restricted to 4 digits.

9.1.1          Enable the DPS DT chamber on the Microlab WAND (equipment name is: centura-dps).

9.1.2          The CRT monitor at the front of the system will turn ON. The default login screen for Centura appears in Figure 1.

9.1.3          Use the lightpen to select the Enter User Name: field. An alphanumeric keypad pulldown menu will appear. Enter your User name using the lightpen and select ENTER.

9.1.4          Use the lightpen to select the Enter Password: field. Enter your User password using the lightpen and again select ENTER.

9.1.5          Use the lightpen to select the Processing field. A Log In Complete message should appear on the screen. The User is now logged in to the system, and may proceed with running a process.

9.2     Viewing a Recipe

To view a recipe’s parameters, use the lightpen to select the Program header, followed by the Process Programs option. The Process Recipe Directory screen should appear with a list of process recipes. Use the lightpen to select the arrow keys at the bottom left hand corner of the screen to scroll up or down the recipe list.

9.2.1          Once the desired recipe has been located in the list, select it with the lightpen. A process recipe screen should appear on the monitor showing the gas flows, pressure, and times in the steps of the recipe.

9.2.2          Select the More Step Info field to view the RF parameters, pulsing parameters, as well as the number of cycles in each recipe step.

9.2.3          Selecting the Header/Exchange field will display all of the auxiliary information of the recipe. This includes Helium backside wafer cooling pressure, ESC dechuck voltage, and other specific items. Select the Edit Steps field to return to the process recipe screen.      

9.3         Running a Process in Manual Mode

The Centura platform is a sophisticated system designed primarily for production-level wafer throughput. Running a sequence of multiple wafers entails running the system in automatic mode. Nevertheless, in an R&D environment such as that of The UCB Microlab, it is also convenient for Users to have the option of running wafers in manual mode as well (there have been documented incidents where by attempting to run wafers in automatic mode has proved troublesome). It is recommended that Users with long (1hr+), deep silicon etch applications use manual mode. Use the following directions to run a process in manual mode:

9.3.1          When the tool is not being used, by default the loadlocks should be in a pumped down state. LLA is used for processing wafers in the DPS chamber. Use the lightpen to select the Wafer header on the menu screen, and then select the Monitor Wafers option. The screen shown in Figure 3 should appear.

9.3.2          Use the lightpen to select Wafer again, followed by selecting Load/Unload A. The LLA field should read …Venting… It generally takes 2-3 minutes to vent the loadlock.

9.3.3          Once the loadlock has vented, the wafer cassette handler will automatically lower and swing out towards the User. Do not touch any of the moving components until this procedure is complete. When the green field on the loadlock screen reads: Can remove cass, it is then okay to remove the wafer cassette.

9.3.4          Carefully pick up the blue wafer cassette using both hands and place it on top of a tech wipe on the table opposite the Centura mainframe.

9.3.5          Wafers can now be loaded carefully using 6-inch wafer vacuum wand or tweezers. When loading wafers into the cassette, ensure that the wafers are correctly placed, and not cross-loaded (e.g. half of wafer in slot 4, half in slot 5). Ensure that the wafer flat is facing up, and that the bottom of the substrate is facing the “H-bar” portion of the cassette. The top of the substrate, or the side to be processed, should be facing away from the H-bar.

9.3.6          Gently place the wafer cassette back into the loadlock handler. The H-bar of the wafer cassette should point towards the Centura mainframe, opposite the User. The LLA field on the screen for should now read Ready For Load.

9.3.7          If the LLA field on the screen does not read Ready For Load, the cassette needs to be reset. Gently lift the wafer cassette up and then place back down again to reset system. The virtual wafers on the screen should disappear and the LLA field should read Ready For Load. Do not attempt to load wafers until this is the case.

9.3.8          Verify that the loadlock field on the screen reads: Ready For Load, and that there are no wafers shown in the wafer cassette field on the monitor screen.

9.3.9          Check that the System header field is white. This verifies that the system is in manual operating mode (see Figure 4 for a listing of header field colors and their meanings). Alternatively, use the lightpen to select the field System followed by Control System. The system state field should read manual.

9.3.10      Use the lightpen to select Wafer and Monitor Wafers to obtain the Monitor Wafer Screen.

9.3.11      Use the lightpen to select Wafer and Load/Unload A. LLA should then read ...Busy… The loadlock cassette handler should swing up and into the loadlock, and the door of the loadlock will close. A Pumping/Mapping message will be displayed in the LLA field, and automatic wafer mapping will occur as the loadlock is pumped down. Automatic mapping is the process where by the wafers that were placed in the wafer cassette are detected and subsequently displayed on the monitor screen. When the loadlock has reached the pumpdown stage, the loadlock field will read: Unload/Run, and the wafers that were loaded in the cassette should appear (virtually) in the respective wafer cassette slots on the screen. The User should verify that the quantity and position of the wafer(s) is accurate. The color of the virtual wafer(s) should appear white, which indicates that the wafer has not yet been processed (see Figure 5 for more information regarding virtual wafer colors and meanings).

9.3.12      Use the lightpen to select the desired wafer to be processed, then select Source for move. The selected wafer should blink, indicating it is waiting for a destination. Use the lightpen to select the virtual Ch F position on the monitor, and the Destination for move option. Note: *All* wafers must *first* be directed to Ch F. It is critical that the orienter chamber find the flat of the wafer before it can be loaded into a process chamber.

9.3.13      Note at this stage that the wafer will be designated a identification name by the software. The name correlates with the loadlock and cassette position from which it originated e.g. a wafer loaded from LLA and wafer cassette-slot 3 would automatically be designated LA: 3. Once the flat has been found, the virtual wafer should turn purple in color. It is good practice to physically view the wafer inside the orienter chamber to ensure that it is indeed the correct wafer to be processed.

9.3.14      Using the lightpen select the wafer in Ch F and Source for move. The wafer on the monitor screen should turn white and blink.

9.3.15      Select the Ch A position using the lightpen and Destination for move. The transfer robot arm will automatically place the wafer into the DPS chamber. The wafer should then appear inside the chamber as a purple color on the screen schematic.

9.3.16      Select System and Control System using the lightpen.

9.3.17      The Control System Screen will depict which recipe has been selected for both Ch A and Ch B under the column Wafer Process. A different recipe can be loaded by selecting the recipe name with the lightpen. A pulldown menu of all available recipes will be displayed. Select the desired recipe from the pulldown menu once, and then again to confirm as it appears in the Wafer Process column.

9.3.18      Select Run and Run Process on Wafer in chamber using the lightpen. The Ch A header will turn green, and the process will commence.

9.3.19      Select the Ch A header and the Monitor Process option. All of the recipe process parameters are displayed in real time. The Status field should initially be yellow and read: Stable Flow/ Pressure, then turn green and read: Chuck Wafer. The final status should be green in color and read: