GB2423633A

GB2423633A - Methods and apparatus for processing wafers

Info

Publication number: GB2423633A
Application number: GB0503688A
Authority: GB
Inventors: Nicholas John; Kevin Powell; David Andrew Tossell
Original assignee: Trikon Technologies Ltd; Aviza Europe Ltd
Current assignee: Trikon Technologies Ltd; Aviza Europe Ltd
Priority date: 2005-02-23
Filing date: 2005-02-23
Publication date: 2006-08-30
Anticipated expiration: 2025-02-23
Also published as: GB2423633B; GB0503688D0

Abstract

A method of processing wafers or batches of wafers sequentially in a vacuum chamber 10. The method involves removing a wafer 25 from a location on a support 11; chemically cleaning particles from the support to form volatile components; and placing the subsequent wafer on the cleaned support. The method is performed without a vacuum break.

Description

BKCDIEFIDBN 188GB

I

Methods and Apparatus for Processing Wafers This invention relates to a method and apparatus for processing wafers or batches of wafers sequentially in a vacuum chamber.

Particularly in the formation of MEMS it is becoming common for wafers to be processed on both sides including features to be etched through the full thickness of a wafer and to be significantly thinned, with the result that flakes or fragments of the wafer are more likely to become deposited on the upper surface of a wafer support. This causes problems when one tries to place the next wafer at the location, particularly, as is very common, if the wafers are clamped.

Problems include: wafer mishandling possibly leading to mechanical breakage and/or poor thermal contact between the water and the support leading to process problems such as resist damage. Currently it tends to be that such incidents cause a subsequent wafer to be mishandled or are discovered on the inspection of the next wafer processed and then the processing chamber has to be opened up, necessitating a time consuming vacuum break, to allow cleaning to take place.

It is also known from US-A-6256 186 to run a short (e.g. 5 sec) etch between wafers to remove polymer film material, which has become deposited on the platen during processing. This material will always be outside the wafer location and can only cause problems if a wafer is misplaced such that it is not entirely at the wafer location on the platen.

According to one aspect the invention consists in a method of processing wafers or batches of wafers sequentially in a vacuum chamber including: removing a wafer from a location on the support; chemically cleaning particles from the support to form volatile components; and placing the subsequent wafer on the cleaned support; the method being performed without a vacuum break.

The particles may be cleaned from the location.

BKCD/EF/DBN.188GB According to a further aspect invention consists in a method of removing particles from a wafer location on a wafer support including performing a chemical cleaning process on the location in the absence of a wafer from the location.

In either aspect the method may further include detecting the presence of particles. For example the detection step may utilise visual recognition apparatus, in which case conveniently the surface of the support at the location may be of a colour contrast visually from the colour of the particles. The cleaning step may be performed in response to the detection of at least one particle and/or the cleaning step may be ended in response to the detection of the absence of particles from the location.

In any of these cases the particles may have a dimension in the range of 100pm to 5mm and in particular 0.5mm to 2mm The method may include the step of assuming the particles are of the same material as the wafer and selecting a cleaning chemistry accordingly.

In any case the platen may be biased during the cleaning step to induce ion bombardment and additionally or alternatively the chemical cleaning step may be plasma assisted. In that case, where there is ion bombardment, the same power source may be used for inducing bias and the plasma.

For silicon wafers, XeF2, CIF3 or SF6 gas may be utilised for the chemical cleaning step with applied plasma if required, which may be regarded as an etch process.

For aluminium or IIIN semiconductors, Cl2 and/or BCL3 would be suitable. For organics, an oxidizing plasma eg 021CF4 mix would be suitable. In general a gas or gas mix - with applied plasma power as appropriate should be chosen by reference to the particulate material to be removed. Where particles are of more than one predominate material type then gas mixes or sequential processes may be selected as appropriate.

In the case of at least SF6 the chamber pressure may be at least about 30mTorr for the cleaning step. Preferably the chamber pressure is in the range of about 3OmTorr to 80mTorr and applied plasma power is required. For BKCD/EF/DBN188GB chemically active gases such as XeF2 and CIF3 no plasma power is required and a pressure of 5-5OTorr is appropriate.

The cleaning step may take between about 1 minute and about 15 minutes and preferably is between about 5 minutes and about 7.5 minutes.

Where there is no detection system, the cleaning step may take place between every wafer or batch of wafers or it may take place after a predetermined number of wafers being processed. However, as the dropping of particles from the wafer is a generally unpredictable event it is preferred that there is either a detection system or the operator makes an inspection between each wafer.

The method may include clamping each wafer to the support for processing in which case a support may include an electrostatic chuck.

It will be appreciated that by using chemical means to remove the particles, they can essentially be converted into volatile components that can be pumped out of the chamber without the need for a vacuum break.

From a further aspect there is provided apparatus for cleaning particles from a substrate support including a vacuum chamber containing a support defining a substrate location; a detection system for detecting particles on the substrate support at the substrate location; and chemical cleaning apparatus for cleaning the support without a vacuum break in response to the detection of particles.

Although the invention has been defined above it is to be understood that it includes any inventive combination of the features set out above or in the

following description.

The invention may be performed in various ways as specific embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic view of an "RIE" type apparatus for performing one embodiment of the invention; and Figure 2 is a graph correlating the initial surface area of test particles and their etch rate.

BKCDIEF/DBN 188GB Referring to Figure 1, a vacuum chamber 10 contains a wafer support 11, having a wafer location A and being driven by an RF supply 12, and a gas inlet 13 communicating with a shower head 14 for process gas. The chamber 10 also has an outlet 15, controlled by valve 16, to enable a pump 17 to evacuate it and to take away volatile gases. The gas inlet supply is controlled by a valve 18 and the apparatus includes a controller 19 which controls valve 16 and 18 and pump 17 in response to a visual recognition system 20, which can observe the wafer location A through a window 21 by means of a sensor 22 and a suitable computing facility at 23. A wafer handling device is schematically indicated at 24 for introducing and removing wafers 25 from the location A through a gate 26.

As will be indicated in more detail below the controller 19 also controls the wafer handling apparatus 24 and is responsive to the visual recognition system 20.

In one embodiment, this system comprises a window in the wall or ceiling of the chamber with an optical imaging apparatus that monitors the state of the support surface. This optical imaging apparatus may comprise a camera, a source of illumination and a control system with pattern recognition capability.

The source of illumination may comprise an external light source, or it may comprise a plasma, initiated by applying power from a source to a suitable gas in the process chamber. In this latter embodiment, the action of illumination may be combined with an action of cleaning of the chamber or an action of declam ping of a wafer.

In a second embodiment, the presence of fragments on the support may be inferred by detecting the absence of these fragments from the processed wafer, for example by comparing an image of the processed wafer to a reference image.

The subsystem that detects the presence of fragments on the support may also be used to determine the endpoint of the fragment removal process, or a separate endpoint system may be used to determine the completion of the fragment removal operation, or the process may be operated for a predetermined length of time, according to the size or number of fragments to be removed.

BKCD/EF/DBN.188GB In one embodiment, the subsystem that detects or infers the presence of fragments on the support may make a record of this fact for future analysis.

L x W x H Initial mass Initial surface Disappearance Sample # (mm) (mg) area (mm2) time (s) 1 6.0 x 4.0 x 0.18 10.2 51.6 330 2 15.0 x 1.5 x 0.18 9.6 51.0 400 3 2.5 x 1.1 x 0.18 1.2 6.8 310 4 2.5 x 0.5 x 0.19 0.6 3.6 435 2.0 x 0.8 x 0.19 0.7 4.2 220 6* 13.5 x 5.2 x 0.65 107.1 164.9 1340 7 9.0 x 5.5 x 0.65 74.6 117.8 1085 8 6.0 x 3.9 x 0.65 35.7 59.7 990 9 3.5 x 3.0 x 0.66 16.1 29.6 757 7.0 x 1.6 x 0.65 16.9 33.5 762 11 5.0 x 1.0 x 0.65 7.6 17.8 610 12 1.6 x 1.6 x 0.62 3.7 9.1 522 * Sampie coated with oxide on one face Table 1. Dimensions and disappearance times of silicon fragments removed using a SF6 plasma etch.

Example

The Applicants have demonstrated the effectiveness of this method in removing silicon fragments.

Fragments with maximum dimensions ranging from 2mm to 15mm and masses from 0.5mg to 100mg were placed on the support, using an oxide- coated wafer as a carrier. This carrier is resistant to the etching action, and was used for convenience in the study. It does not form part of the invention.

The fragments were then exposed to a plasma formed from SF6 gas, with additional power applied to the support in accordance with a first embodiment of the invention. The time taken for these fragments to disappear are recorded in Table 1. The plot in Figure 2 shows that these disappearance times are correlated with the exposed surface area of the fragment, and can be interpreted with a constant etch rate of approximately I 5pm/min acting at all surfaces.

The presence of an oxide coating on one surface of one of the fragments did not significantly inhibit the removal operation.

BKCD/EF/DBN 188GB The chamber used in this study was a specialised deep silicon etch tool which had a helicon type plasma source above the wafer, but it will be appreciated that the invention can be applied in any chamber capable of supporting an etching environment. For example Reactive Ion Etch (RIE), Inductively Coupled Plasma (ICP), diode, triode, microwave, remote and in fact any plasma source/chamber configuration suitable for etching wafers or layers upon a wafer. Similarly, although this study was restricted to removal of silicon fragments using a plasma formed from SF6 gas, it will be appreciated that appropriate changes to the etching environment will allow fragments or particles of many other materials to be removed by the methods encompassed in this invention.

Where SF6 is used as a process gas the following conditions have been used: 500sccm SF6 - (a lower flow rate may be acceptable) to 80mTorr chamber pressure - (a pressure of >30mTorr is probably

acceptable).

3kW RF source - (lower powers may be acceptable).

75W bias (200mm) and 30W for a 150mm diameter wafer were used.

Claims

BKCD/EFIDBN.188GB Claims 1. A method of processing wafers or batches of

wafers sequentially in a vacuum chamber including: removing a wafer from a location on a support; chemically cleaning particles from the support to form volatile components; and placing the subsequent wafer on the cleaned support; the method being performed without a vacuum break
2. A method as claimed in claim I wherein the particles are cleaned from the location.
3. A method of removing particles from a wafer location on a wafer support including performing a chemical cleaning process on the location in the absence of a wafer from the location.
4. A method as claimed in any one of the preceding claims including detecting the presence of particles.
5. A method as claimed in claim 3 wherein the detection step utilises visual recognition apparatus.
6. A method as claimed in claim 5 wherein the surface of the support at the location is of a colour which contrast visually from the colour of the particles.
7. A method as claimed in any one of claims 4 to 6 wherein the cleaning step is performed in response to the detection of at least one particle.
8. A method as claimed in any one of claims 4 to 7 wherein the cleaning step is ended in response to the detection of the absence of particles from the location.
9. A method as claimed in any one of the preceding claims wherein the particles have a dimension in the range of 100 micrometers to 5 millimeters.
10. A method as claimed in any one of the preceding claims including assuming the particles are of the same material as the wafer and selecting a cleaning chemistry accordingly.

BKCD/EFIDBN.188GB
Ii. A method as claimed in any one of the preceding claims wherein the platen is biased during the cleaning step to induce ion bombardment.
12. A method as claimed in any one of the preceding claims wherein the chemical cleaning step is plasma assisted.
13. A method as claimed in any one of the preceding claims wherein SF6 gas is utilised for the chemical cleaning step.
14. A method as claimed in claim 13 wherein the gas is SF6 the chamber pressure is at least about 30mTorr for the cleaning step.
15. A method as claimed in claim 14 wherein the chamber pressure is in the range of about 3OmTorr to about 80mlorr.
16. A method as claimed in anyone of Claims I to 11 wherein CIF3 or XeF2 are utilised for the chemical cleaning step.
17. A method as claimed in any one of the preceding claims wherein the cleaning step takes between about 1mm and about l5mins.
18. A method as claimed in claim 16 wherein the cleaning step is between about 5mins and about 7.5mins.
19. A method as claimed in any one of the preceding claims wherein each wafer is clamped to the support for processing.
20. A method as claimed in claim 18 wherein the support includes an electrostatic chuck.
21. Apparatus for cleaning particles from a substrate support including a vacuum chamber containing a support defining a substrate location; a detection system for detecting particles on the substrate support at the substrate location; and chemical cleaning apparatus for cleaning the support without a vacuum break in response to the detection of particles.