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HD CVD Information and Operating Instructions

High Density Plasma Enhanced Chemical Vapor Deposition (HD PECVD) is an alternative to the conventional methods of the deposition silicon dioxide, silicon nitride and amorphous silicon using PECVD. The advantage of HD PECVD over PECVD is the ability to produce higher quality films at lower temperatures, less than 150C.

 

Contents
  1. Picture and Location
  2. Background
  3. Process Capabilities
    1. Cleanliness Standard
    2. Performance of the Tool
  4. Contact List and How to Become a User
    1. Contact List
    2. Training to Become a Tool User
  5. Operating Procedures
  6. Process Monitoring and Machine Qualification
    1. Tool Qualification Run
    2. Machine Status States
    3. Process Monitoring Results

Picture and Location

 

The tool is located in the B area erroneously labeled 'epi' on the Lab Map.

Background

 

Overview

 

The PlasmaTherm Versaline HDPCVD system is a high density plasma (HDP) deposition system for silicon nitride, silicon oxide and amorphous silicon thin films. The most important characteristic of this system is that the deposition temperatures can be as low as 100 C.

 

What is HDP

In the plasma processing world HDP means having at least 2 sources of plasma power. The first is used to generate the plasma, and is what is called a non-capacitive coupled source, such as inductively coupled (ICP) or ECR coupled, where power is transferred or coupled to the plasma without causing the voltage difference between the plasma and the wafer to be above about 50V.  This first source controls the plasma density (number of ions per cc) in the plasma and thus controls the ions flux (ions per sq cm per sec) bombarding the wafer. The second power source is connected through the wafer chuck/electrode and is capacitive coupled (CCP). This second source is often referred as the bias power in that it is used to control the voltage between the wafer and plasma. This voltage is important between it controls the energy and directionality of the ions bombarding the wafer surface. Thus, with high density plasmas we have the ability to control both ion flux and ion energy independently. Sometimes additional power sources are added to control the energy distribution of the ion for fine control in etching.



HD16

Figure 1



Figure 1 shows the HDP chamber with a 2 MHz RF generator powering the ICP coil and a 13.56 MHz generator for bias power. An addition feature is gas inject at two possible positions. Injection at the top is for gases in which you want a lot of  interact with the plasma, such O2 or N2. While is inject near the wafer surface is for reactive which you do want over fragmentation in the plasma, such as SiH4.


HD17
Figure 2


A typical plasma density for a PECVD system is less than 5E 9 cm-3 while fig 2a shows the dependence of plasma density on the ICP coil power and the bias power to the chuck for the HDP system. We see that the density is in the range of 100x higher than in the PECVD case.  Fig. 2b shows the dependence of bias voltage (ion energy) on ICP power and bias power.  We see that the bias voltage is quite low at high ICP power and low bias power. This  useful getting low damage deposition.

 

 Advantages of HDP Over PECVD Configuration

 

There is a number of advantages in using HDP plasma enhanced CVD compared to standard PECVD. These include: Lower temperature deposition while maintaining high film density, lower H contain, less ion damage and the ability to do hole filling and self planarization.  The high disassociation rates and high ion flux leads to higher density deposition at low temperatures.  The higher density deposition means better film quality at low T than with normal PECVD.  For example, for a PECVD SiNx  film at 150 °C the typical BOE rate is greater than 5,000 while for HDP a BOE rate of 1000 Å/min is typical. Due to the relatively low dissociation efficiency of N2, typical process recipes for SiNx deposition by PECVD use NH3 as the source of nitrogen. Therefore, some portion of hydrogen incorporation from NH3 in deposited SiNx films is inevitable. However, HDPCVD technology enables one to deposit SiNx with a NH3-free recipe because high-density plasma sources have typically one order of magnitude higher ion dissociation efficiency (i.e. ~0.1 % for PECVD and ~1 % for HDPCVD).  This results in much lower hydrogen content in HDP films.



Process Capabilities

Cleanliness Standard

 HD PECVD is a 'All' tool.  By performing a short clean and coat procedure the tool can go from contaminated to clean status.

Performance of the Tool

What the Tool CAN do

  • Deposit low temperature Silicon Dioxide.
  • Deposit low temperature Silicon Nitride.

 

What the Tool CANNOT do

  • Process wafers with sticky surfaces.  They stick to the clamp.
  • At this point we do not have a procedure for samples that are not full 100mm in wafers.  Pocket wafers may be an option.

 

Process Monitoring

 

Contact List and How to Become a User

Contact List

The following people make up the Tool Quality Circle:

  • Process Staff: Nancy Latta
  • Maintenance: Elmer Enriquez
  • Super-Users: None yet, Please apply!

 

Training to Become a Tool User

 Consult the training calendar for the training session which is most convenient to attend.  Contact the appropriate staff member.

Read the training materials.

Shadowing a qualified user prior to the training session is highly recommended and will speed up your understanding of the tool.

 

 

Introduction



Machine Specifications

 

The following gases are plumbed to the tool;

  • N2 a - (top) is used either as a flush or process gas for SiNx, SiO and Etchback process sequences
  • N2 b - not used
  • N2 c - not used
  • N2 d- (electrode)
  • Ar - (top) is used in SiNx, a_Si-H, and SiO process sequences
  • O2 - (top) is used in SiO and Etchback process sequences
  • SiH4 - (electrode) is used in SiNx, a_Si_H and SiO process sequences
  • SF6 - is used ib the Etchback process sequences

 

 

System Components

 

  • Load Lock
  •  Reaction Chamber
  •  Process Monitor/Control Computer
  •  Mechanical Pumps –  located in basement.
  • Heat exchanger – located next to the tool

 

 

 General Information on Plasma Therm Versaline Software

 

At SNF there are four Plasma Therm Versaline etch and deposition systems and they share a common software platform.  Differences between them will be noted in the operating instructions.  Here's a link to information about the software system.

 

Please keep in mind that the description may be centered on the etchers, not the dep tool.  Much of the information, however, is common to all the Versaline based tools.

 A process sequence is a recipe that is made up of several process steps.  Here is the default process step for the HDPCVD system. It gives information like gases, min/max flows, set points for RF, etc.  Be warned that once you change a value in a process steps that value will be changed for all the steps with the same name.  To be safe, if you copy a step be sure to give it a unique name.

 

Operating Instructions for HD PECVD

 

  1.  Enable 'hdpcvd'.
  2. Check the accumulated film thickness of the chamber by looking in the logbook.  Perform an Etchback and Coat if the accumulation is about 3.5um thick, or if you want to keep your samples CMOS clean.  See How to run Etchback and Coat.
  3. Check that the system is in PRODUCTION Mode. You can tell by looking at the top of the screen.  If it is MAINTENANCE Mode you will need to go to Maintain/Mode and chose PRODUCTION All Chambers.
  4. In 'Jobs/Jobs Start' select the desired recipe in the Recipe Section, for ex., HDP SiO2.
  5. To change the time in the Dep Step go to 'Editors/Sequence Editor'.  Click on the bold step name, for ex., 4: Ox4 Dep Step.  In the pop up menu chose Edit This Step.  This will put you in the Step Editor and you may change the Process Time Set Point.
  6. Complete the change by clicking the Save button to the right of the screen.  Be aware that the steps are in a library shared by many process sequences (recipes) so you will have changed all the recipes that use that step.  Contact the responsible staff member if you want to change any parameter except Time.
  7. Verify the change by going back to the Sequence Editor and looking at the step.
  8. In the 'Jobs/Start Jobs' screen Vent the load lock.
  9. When vented place the wafer on the carrier taking care to align the flat perfectly.  Failure to do so will cause you to lose the wafer in the chamber.
  10. Pump the load lock.
  11. Chose 'Vent After Job'.  The system will load, process, unload and vent the LL.
  12. If 'Process in PM. No Transfer' is chosen you will need to manually load and unload the wafer into the chamber.   To do that; 1) go to 'Maintain/Mode' and put the system into MAINTENANCE 2) go to 'Maintain/Transport' and click on Transfer Material 3) once the wafer is in the chamber go back to 'Maintain/Mode' and put all chambers into PRODUCTION.
  13. Start the recipe by clicking Start in 'Jobs/Job Start'.
  14. Monitor the process of the recipe by looking at the parameters on the right side of the screen.
  15. At the completion of the run unload the wafer from the LL.  If using 'Process in PM. No Transfer' see section above.
  16. Continue with next wafer or if you are finished pump LL.
  17. Record results on logsheet.  It is important to keep a running total of the chamber film thickness so estimate your deposition thickness if you need to.
  18. Disable.

Additional Information

 

How to Do an Etchback and Coat

Etchback and coat is done to clean the chamber of accumulated films when the thickness reaches about 3.5um.  It is also done when a user wants to put the chamber into clean state in order to maintain clean status.

 

Endpoint detection is used to ensure complete etching of the chamber.  A short SiN deposition follows to 'seal' the chamber walls.

 

  1. Load the recipe Etchback.
  2. Load the sapphire cleaning wafer.  Endpoint will not be achieved if a Si or SiO2 wafer is used.
  3. Run the recipe in 'Process in PM. No Transfer' mode.  A description on how to do that can be found in pt. 12 of the Operating Instructions.  You are doing this so that the wafer does not travel in and out of the chamber for the two recipes you will be running.
  4. Start the recipe.
  5. Turn on the endpoint computer using the Windows key on the keyboard.  A toolbar ribbon will appear on the bottom of the screen.  Click on P1 endpoint to bring up the endpoint window.  Click on the green Start button.
  6. End point is achieved when the white line (fluorine) has reached 16,000 in the chart and the blue line (derivative) has reached 0 for a minute.  The recipe may go to a flush step once those conditions have been meet.
  7. If the recipe fails at stopping you will need to manually stop it.  Go to 'Jobs/Jobs Adjust' and click on the Next Step button.  This will advance the recipe safety. 

 

Wafer Alignment During Loading

 

The wafer must be perfectly aligned on the loading arm in order to ensure that it is lined up on the chuck correctly.  If it is not you run the risk of losing your sample in the chamber, or worse breaking your wafer.

  • The flat should be snuggly aligned on the loading arm.
  • If you remove the wafer from the chamber always vent the load lock and verify that the wafer is aligned on the loading arm.
  • Failure to do this may cause wafer breakage.

 

Processing Transparent Wafers

 

Special care must be taken when processing transparent (quartz, pyrex or glass) wafers.  Here is a procedure on how to do it.

 

Trouble Shooting and Alarm Recovery

 

 

How to continue after a process fault on the HDPCVD system

 

When a process stops due to a fault during a deposition run where SiH4 is flowing, it is best to 
skip the faulty step and go on to the flush step to purge out the chamber. To this do, follow these 
three steps. 

1. Click on the red fault message at the top of the screen.

2. Click on Skip-Step on the right of the fault window.

3. Go back to the Job-Start/Adjust window and click on Next Step of the right of this screen.


If the fault occurs before the SiH4 begins to flow, you can just abort the process.

From Jim McVittie, Dec 2012

 

Process Monitoring and Machine Qualification

Tool Qualification Run

 

Frequency

Quals are run after major repairs to the system, when a labmember reports a variance from normal results and on a routine basis.

 

Procedure

 We have been using the standard SiO recipe for 26 secs.  This is because at this point it is the recipe we know the most about.  Labmembers should feel free to contact the responsible staff member to suggest a more relevent recipe.

 

Recipe conditions are;

<to be written>

Responsibility

 Quals may be run by concerned labmembers before running critical processes or as a measure of tool functionality.  Staff members will run quals as needed or requested.

 

Recommendation to users with critical processes

 It would be wise to run the qual before committing valuable samples to the deposition.

Machine Status States

Red:

Yellow:

Green:

 

Process Monitoring Results


Results from recipe SiO;


Date
Deposition Rate
A/sec
 Deposition Rate
A/min
Time in Secs
Include 6sec
Light Strike Step
Thickness
in A
Within a wafer
Uniformity %
Comments
8/30/12 27.34  1640 146 3991 1.24 Courtesy of Scott Lee
12/7/12 27.0  1620 26 702 ~1.0
Courtesy of Jim Kruger
1/9/13 26.99  1619 26 701.7 ~1.0
Courtesy of Jim Kruger




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