Utah-94-721002-System-Manual.pdf - 第162页

mä~ëã~ä~Ä = lñÑç êÇ=fåë íêìãÉåí ë=m ä~ë ã~=qÉÅÜåçäçÖó= System Manual PKPKQ= mb`sa=é~êíáÅäÉë= Please note that once particles have been noticed, all wafers should be examined under a strong light source at various angles …

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Another possible cause of non-uniformity is wafer material - GaAs is less conductive, so large GaAs wafers

show more non-uniformity, which can be counteracted to some degree by increasing the LF frequency,

but there is a trade-off with matching (i.e. reflected power is generally higher at higher frequency). (To

adjust the frequency, Press the Program button - adjust the Frequency - press the Program button again

to run at the new frequency).

For LF power, the PC should be setting (and the generator should be controlling) load power as this is the

power that actually reaches the plasma. The matching is often quite bad for LF, but this doesn't matter

too much as the LF generator increases its power output to compensate and to ensure that the power

delivered to the load (load power) is always as requested.

However, it is advisable to adjust the step-up transformer to minimize reflected power, to avoid

overheating of the LF generator, especially as the RFPP generators will switch themselves off

automatically if reflected power is above 40-50W for self-protection.

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Premature flaking of chamber wall / showerhead material can occur for a number of reasons:

1) For new systems the showerhead may need several deposition/clean cycles before it reaches its

best film adhesion performance. This can be improved by bead blasting the showerhead.

2) Temperature cycling of showerhead / chamber walls can cause flaking, therefore it is important

that chamber walls are set to a stable temperature, e.g. 60C, and that the showerhead cooling

water is flowing properly. It is also important that electrode temperature is maintained at a

constant value as this will also affect showerhead temperature.

3) The system should not be switched off overnight to save power. The system should be left

pumping with electrode maintained at deposition temperature at all times to avoid flaking.

4) Incomplete cleaning during a previous clean cycle can lead to premature flaking.

5) Wiping of chamber and or showerhead with water or IPA can leave residues which subsequently

causes early flake-off of films deposited.

6) Wiping of chamber walls / showerhead with clean room wipes while they are hot can also leave

behind residues which cause premature flaking.

7) Repeated venting of chamber will cause flaking. This one of the main reasons that for a PECVD 80

Plus or a PECVD 800 Plus, it is recommended to clean every 5-10 microns of film, whereas for a

load locked PECVD System 100 running high rate SiO

films, it is not necessary to clean as often.

8) Mixed deposition of oxide, nitride, and oxynitride films can cause increased stresses in deposited

films and hence premature flaking.

9) Changes to standard recipes can also cause increased stress and hence premature flaking.

For a PECVD System100 running high rate oxide we recommend plasma cleaning every 100microns for

best film repeatability. A dry wipe of showerhead and vacuum cleaning of any large particles may also be

required.

For a PECVD 80 Plus or PECVD 800 Plus, it is recommended to clean every 5-10microns of film. Plasma

cleaning may need to be carried out more often if mixing depositions or using a range of electrode

temperatures etc as listed above. A dry wipe of showerhead and vacuum cleaning of any large particles

may also be required.

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Please note that once particles have been noticed, all wafers should be examined under a strong light

source at various angles of incidence, say a microscope light source, to really be sure there are no particles

still present in the wafer. This is by no means a comprehensive list of all the particles, which can occur in a

PECVD process chamber, but is intended as a helpful guide to quickly eliminate the common problems.

Particle descriptions When they most

often occur

Possible causes Remedy/Quick Fix –Test

Small particles less than 5um,

which appear in concentrated,

clusters. These clusters appear

in a pattern, which mirrors

that of the showerhead holes.

They are concentrated mainly

in one focal plane of the

microscope and appear to be

at the bottom of the film.

The first run after a

clean

Running the machine too soon after

the completion of a clean process.

Silane forms particles when it reacts

with residual oxygen in the gas lines

(remember all of the gas line up to the

normally open, hardware interlock

nupro valve is incorporated in the

chamber vacuum and needs to de-gas

at the end of a long clean run).

Wait 30 minutes before

running a deposition process

using Silane after finishing a

clean. Or run pump/purge

cycles with N2 gas.

Small particles less than 5um,

which appear in concentrated,

clusters. These clusters appear

in a pattern, which mirrors

that of the showerhead holes.

They are concentrated mainly

in one focal plane of the

microscope and appear to be

at the bottom of the film.

The first run after a

long period of

machine disuse (say

overnight)

A small leak in the Silane line,

particularly around the mass flow,

allowing a build-up of Silane dust,

which is blown though on to the first

wafer.

Fix the leak in the Silane line.

Flow Silane gas after a

significant period of machine

disuse without a wafer in the

chamber to clear the dust.

Small particles less than 5um,

which appear in concentrated,

clusters. These clusters appear

in a pattern, which may or

may not mirror that of the

showerhead holes.

They appear in many different

focal planes of the

microscope, at regular

intervals throughout the film.

Every run A leak in the gas in-let assembly or a

severe leak in the Silane line.

Plasma forming behind the

showerhead or in the gas inlet

assembly.

Leak check chamber and gas

line. If both less than 1mT

per minute contact Oxford

service department and give

this description. If greater

than 1 mTorr per minute

take apart gas inlet assembly

and clean O-rings and PTFE

part.

First run after a clean Residual particles not etched during

the cleaning process

Vacuum the chamber inside,

this is necessary periodically

after cleaning. It may be a

good idea to cool the

chamber first to prevent risk

of injury with the hot table.

After a power failure

or other reason

which caused a

significant drop in

table temperature

When the lower electrode cools

deposited film, particularly around the

edges, cracks and is blown on to the

wafer during subsequent deposition

runs.

Clean the chamber.

After a certain

amount of deposition

on the chamber, but

it varies when they

occur.

If you are depositing films of many

different chemistries and stresses,

particularly those with high stress,

then the film will flake off much

earlier than expected.

Clean more regularly.

Flakes or larger non-metallic

particles

After a certain

amount of deposition

but it seems to be

getting less and less

after every clean.

The films are not adhering to the

showerhead very well. Someone has

cleaned the showerhead using solvent,

leaving behind a residue that is giving

poor adhesion for the deposited films.

The showerhead has become dirty and

the clean process is unable to clean it –

the showerhead is ready for its

periodic maintenance.

Bead blast the showerhead.

Metal particles, which shine

under normal clean room light

and are greater than 20um in

maximum dimension.

Mostly all the time Showerhead holes may be lighting-up

or the showerhead holes have become

damaged due to normal wear and

tear.

Bead blast the showerhead.

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Particle descriptions When they most

often occur

Possible causes Remedy/Quick Fix –Test

Particles or marks, which

appear randomly on the

wafer, but look as if they are

underneath the film.

Every run The wafer has been cleaned using

solvents, which have not been

properly washed off with de-ionised

water.

Use a fresh wafer straight

from a new box.

As part of the regular maintenance of the system the showerhead (and doughnut ring) must be bead

blasted. This is the only Oxford Instruments Plasma Technology approved way of cleaning a showerhead.

The use of solvents and ultra-sonic baths is strongly discouraged. Scrubbing with Scotchbrite is also not

recommended. OIPT will not be able to support you if you use these alternative cleaning methods and still

experience problems the problems described in the above table with showerhead particles.

Recommended bead blasting specification:

Bead blast using alumina powder (aluminium oxide beads) of 180 grit size or less - maybe 120. Do not use

any solvents. Clean the showerhead after bead blasting using compressed air only. Hold the showerhead

up to the light to check that none of the holes are blocked by any grit from the bead blasting. Clean out

holes with paper clip or similar if blocked.

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PECVD showerhead holes can become enlarged during use. This is caused during high-power processing

(on an 80 Plus this is typically during plasma cleaning). Any holes, which have slightly sharper edges, will

form an intense discharge over the hole (due to the high fields generated by the sharper edges). This can

be seen as a 'bright spot' in the plasma located over the hole during the clean process.

This can cause some erosion of the hole and widening of the hole opening (on the outlet side only).

Eventually, the bright spot burning itself out, i.e. the erosion removes the sharp edges and hence the

bright spot no longer occurs at that hole. This may happen for several holes during the initial run-up of

the system, until the showerhead 'stabilises' itself.

The bright spot may also result in some black/brown polymer deposition around the holes which, can

cause premature flake-off of deposited films. It is recommended that the showerhead is bead-blasted

clean to remove such residues.

The bright spots should not be observed during low power (<50W) 80 Plus deposition processes. If they

are, it is recommended that the showerhead is plasma cleaned and bead-blasted cleaned until the bright

spots are eliminated. If bright spots are still present then it may be necessary to obtain a replacement

showerhead.

The effect of the enlarged holes on the deposition results should be minimal, since they only enlarge the

outlet of the hole, hence they do not affect the gas flow.

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Oxford Instruments Plasma Technology has integrated its optical emission spectroscopy (OES) end-point

detector with the mä~ëã~ä~Ä=standard PC 2000 operating software. This provides a real-time display of

detector signal, and allows for automatic process end-point detection or user terminated end-point.

Part No. 81-12-70

The end-point detector is a fixed, single wavelength detector with a narrow bandpass optical filter and

high sensitivity photodiode. The kit includes a KF40 process window and detector mount assembly.

The system monitors the 704 nm wavelength (atomic fluorine) emission. This fluorine is consumed while

the deposited material in the chamber is clearing and rises at endpoint, indicating the completion of the

chamber plasma cleaning process. An example of clearing a thick film (100um) deposition is shown in the

following graph.

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