Patent Application
20110268891
This invention relates to gas delivery devices and process chambers for use in low pressure Atomic Layer Deposition and methods of performing low pressure Atomic Layer Deposition.
The process of Atomic Layer Deposition (ALD) is well known. Essentially it comprises depositing a chemical layer such that a first monolayer is chemically absorbed into the surface of the substrate and then blowing away the excess material using a purge gas, which can also be used to purge the process chamber so that a further monolayer can be laid down, which may be of the same or a different chemistry.
ALD can be performed both at atmosphere and low pressure. At atmospheric pressure, large quantities of gas have to be supplied, because of the ambient pressure to be overcome and the resultant gas flow rates mean that the substrate tends to see a line or cone of a process gas under which it progressively sweeps. In contrast, at low pressures, smaller quantities of gas at slower flow rates can be supplied allowing the gas to diffuse whereby up to the whole of the surface of a substrate can be treated simultaneously. Accordingly for economic and uniformity reasons, there are significant advantages in low pressure ALD, but the very different flow characteristics mean that methods and techniques developed for atmospheric ALD cannot be automatically incorporated into low pressure ALD configurations.
To date, most ALD, whether atmospheric or low pressure operate on single wafers. As with most deposition processes, there is a considerable economic advantage if one can achieve batch processing, provided that uniformity is maintained.
Various approaches have been suggested whereby one might achieve batch ALD. U.S. Pat. No. 6,821,563 is not an untypical example and another approach can be seen in U.S. Pat. No. 7,104,476. Each of these assumes that a wafer will track along a circular path under a variety of process sectors. In this arrangement the processing of the wafers is dictated entirely by the slowest process to be performed and there is little flexibility in use. Further, the injector sectors are divergent and in practice only a small part of the sector is used or there are significant uniformity issues. A not dissimilar arrangement is suggested in 2005/0084610, whilst US 2007/007356 suggests a linear approach.
Another attempt is set out in U.S. Pat. No. 6,902,620. This uses a plurality of shower heads in a single chamber and seeks to separate active process areas by having the intermediate shower heads supplied with an inert gas, where reactions between the process gases may take place. It is far from clear that the arrangement suggested is practical in nature, because it would appear extremely difficult to perform a full diametric argon ‘curtain’ diametrically across the chamber using such a technique.
As far back as 1989, see for example U.S. Pat. No. 4,834,020, linear injectors for CVD have been known in which a gas could be delivered to a process area and then exhausted either side of that process area. Inert or purge gas can be supplied on either side of the process area. The most sophisticated arrangement of this is probably shown in U.S. Pat. No. 6,200,389. It will be noted that “sealing” is only described in the linear direction of travel of the substrates being treated.
From one aspect the invention consists in a gas delivery device for use in low pressure Atomic Layer Deposition at a substrate location including a first generally elongate injector for supplying process gas to a process zone; a first exhaust zone circumjacent the process zone; and a further injector circumjacent the first exhaust gas for supplying purge or inert gas at an outlet surrounding the process zone having a wall for facing the location circumjacent the outlet to define at least a partial gas seal.
For the purposes of this specification a partial gas seal is one in which the leakage is below 10,000 ppm.
The injector preferably has one or more lines of ports and the process area may be between 15 mm and 25 mm in height so as to allow diffusion of the process gas whereby a substrate may effectively see a uniform cloud or mist of process gas.
There may be a plasma area defined by inner and outer purge gas injectors and this may lie within the partial gas seal.
The device may further include a further gas exhaust area circumjacent at the further injector.
From another aspect the invention may include a gas delivery device locatable in the process chamber and having a gas seal around its complete perimeter.
The device may further include a further gas exhaust area circumjacent the further injector.
From a further aspect the invention consists in a low pressure Atomic Layer Deposition apparatus for forming layers on a substrate including a process chamber having at least one gas injector and at least one gas delivery device as defined above and a rotatable support for moving substrates around the chamber and through the gas delivery device process area.
The apparatus may further include a control for rendering the gas delivery device operative or inoperative whereby a substrate can be processed in the process chamber alone or successively by the gas delivery device and the process chamber or vice versa in accordance with the process to be performed on the substrate.
The partial gas seal may at least in part be constituted by a passage of between about 1.5 mm and about 3 mm wide. The passage may be defined, in use, by the distance between the surface of the substrate (e.g. a semi-conductor wafer) and the face of the wall facing the location. Conveniently that wall may extend symmetrically on either side of the outlet or it may extend simply on one side of the outlet, preferably that furthest from the process area.
The partial gas seal may be at least in part constituted by a passage, such as indicated above, of between about 30 mm and about 100 mm in length and particularly conveniently the passage about 60 mm and about 100 mm in length and between about 1.5 and about 3 mm wide. These dimensions may vary somewhat depending on the size of the molecules of the gas or gasses being used as process gasses or purge gasses. They will also be scalable depending on the gas pressures and the pressure drop between the zone and the chamber.
Preferably the pressure in the process area is not more than about +/−0.25 Torr (±30 Pa) than the 1 Torr pressure in the chamber. (1 Torr˜133.3 Pa)
The velocity of the gas at the further injector may be at least about 50 m/s. The velocity or flow rate should not exceed the exhaust capabilities of the gas delivery system.
From a still further aspect the invention consists in a method of performing low pressure Atomic Layer Deposition in the process chamber including a gas delivery device having a full perimeter seal to define a separate process area from the process chamber and a rotatable support for moving substrates around the process chamber and through the process area wherein, in the method, the substrates are, during at least part of the method, processed both in the chamber and the process area.
For example, the gas delivery device may be switched off during one or more rotations of the support. This enables the substrates, e.g. semi-conductor wafers, to be exposed to a process gas in the process chamber for a desired period and then to have subsequent processing in the process area. This is a particularly useful way of processing wafers in a batch, when the process times are significantly unequal. Thus a process gas may be supplied to the process chamber or a purge gas, for removing excess deposition, may be supplied to the chamber, in which case the gas delivery device may perform the other process or processes.
As there is a full seal around the gas delivery device, cross-contamination between the processes should not occur.
Although the invention has been defined above, it is to be understood it covers any inventive combination of the features set out above or in the following description.
The invention may be performed in various ways and specific embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:
As will be described in more detail below, the injector device 15 of the injector 13 has a central element for supplying a process gas and this element is effectively 360° sealed from the main process chamber 11, in the sense that gas can neither come in from the process chamber to the central process area of the gas delivery device 15 nor can process gas escape from the device 15 into the process chamber 11. As is indicated schematically by the arrow A, the process chamber contains a rotatable support of the type that is well-known in the art on which substrates 16, such as semi-conductor wafers, can sit and be rotated around the chamber to pass under the gas delivery device 15. A control 17 is provided for rendering the gas delivery device 15 operative or inoperative and the control may also control other aspects of the apparatus 10, such as the rate of rotation of the support and the operation of the load lock 12.
The process chamber 11 may be provided with one or more process gas inlets, one of which is schematically illustrated at 18.
In use, wafers may be introduced onto the support in a batch and rotated around the chamber 11. Depending upon the chemistry which is intended, the chamber 11 may contain a purge gas, at least at some stages of the process, and the gas delivery device 15 may or may not be operative at different stages of the process.
By way of example, TiN can be deposited by first treating the surface of the substrate 16 with NH3 and then subsequently being exposed to TiCl4. The usual exposure to NH3 is over a second, whilst an exposure of less than 0.1 seconds to TiCl4 is required. This can very conveniently be achieved in the chamber 11 by switching the gas delivery system off initially; supplying NH3 to the process chamber 11 for the desired period and then switching on the gas delivery device 15 to supply TiCl4. It will often be possible to balance the timing within one rotation for example by altering the concentration of the TiCl4. In this case the NH3 could be left on permanently. The wafers may be rotated during all stages to make sure that one does not lie beneath the gas delivery system 15 during the first part of the process or the support can be static with a gap corresponding to the gas delivery device 15.
Such large exposure disparities are difficult to accommodate with the apparatus described in the prior art. However, it will equally be appreciated that the apparatus of the present invention can equally well accommodate processes where the deposition periods for gas is similar. The apparatus can also be used with the process chamber 11 may be filled with purge gas to remove excess material when the substrate 16 emerges from the gas delivery devices 15.
In
The nature of the gas delivery device 15 is shown in more detail in
In use, wafers pass from, say right to left, from the chamber 11 beneath a portion of the wall 25 underneath the argon curtain created by the inlet 26, past the exhaust 23 through the process area 22 and then continue outwardly until they reach the chamber 11 again.
It will be understood that the majority of the TiCl4 is exhausted by the surrounding exhaust 23. Any which diffuses beyond the exhaust 23 then has to pass down a passage 27 where it is likely to be captured by the argon curtain created by inlet 26 and driven back towards the exhaust 23. By making the width of the passage as small as is viable without risking damage to the wafers or creating excessive drag, the likelihood of any molecules escaping down the passage is significantly reduced. The length of the passage is also a relevant factor. Another factor is the rate of flow of the argon through the outlet 26.
As far as the NH3 is concerned the same criteria of passage dimension and air curtain reduced the likelihood of diffusion from the chamber through to the process area 22. Even if molecules get to the left hand end of the passage 27 they will likely be exhausted by the exhausts 23.
In certain circumstances it may only be necessary for the passage to extend between the argon inlet and the chamber 11. This would be particularly true if only low flow rates of the gas into the process area where required and essentially the passage was simply trying to prevent ingress of NH3.
As can be seen in
The wafer then passes out of the device 15 still continuing in the same direction.
As can be seen in
The designs of
It will be understood that the principals of the gas delivery device 15 illustrated and described with reference to
| Number | Date | Country | Kind |
|---|---|---|---|
| 0816186.1 | Sep 2008 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2009/001731 | 7/13/2009 | WO | 00 | 3/9/2011 |
| Number | Date | Country | |
|---|---|---|---|
| 61081463 | Jul 2008 | US |
