Reflow chamber and process

Coating apparatus – Work holders – or handling devices – Gripper or clamped work type

Reexamination Certificate

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Details

C118S503000, C156S345420, C204S298110, C204S298150, C024S457000, C269S287000

Reexamination Certificate

active

06299689

ABSTRACT:

BACKGROUND OF THE INVENTION
Thin film deposition is essential to the manufacture of solid state electronic devices. By layering various materials (i.e., films) on a wafer in a prescribed pattern, a solid state electronic device is formed.
Within the semiconductor device industry there is an ever present trend for more complex multi-layer structures and smaller device dimensions. In order to reduce the lateral device area of storage capacitors, for example, high aspect ratio (i.e., high depth to width ratio) features (e.g., steps, trenches and vias) have become prevalent. Such features possess large side wall surface areas which allow lateral device dimensions to shrink while maintaining constant capacitor area (and thus a constant capacitance).
When depositing a film over a high aspect ratio feature, material tends to deposit near the top surface (i.e. the surface nearest the deposition material source or target) of the feature and to prevent subsequently deposited material from reaching the feature's lower surfaces, causing variations in deposition layer thickness including voids (areas containing no deposition material). Accordingly, much attention has been directed to formation of continuous conformal films within high aspect ratio features, and/or to continuous filling of high aspect ratio features (e.g., aluminum planarization).
As described in “Aluminum Planarization for Advanced Via Applications,”
European Semiconductor
, February 1996, a preferred technique for achieving aluminum planarization is known as the high temperature flow process (i.e., reflow). Aluminum reflow typically begins with deposition of a thick film of aluminum that is deposited on a wafer at relatively low wafer temperatures (e.g., less than 150° C.). The wafer is then transferred to a reflow chamber and heated to a temperature at which the aluminum film flows (i.e., a reflow temperature). A temperature of 570° C. is conventionally required to supply aluminum with sufficient energy to cause the aluminum to flow. At this temperature solid phase diffusion and surface tension transport aluminum across the wafer's surface, and transport aluminum from the top region of surface features to the bottom of surface features (i.e., top down filling).
Although conventional reflow methods can produce adequate filling of many types of surface features, reflow is unfeasible for small feature applications. Thus, for small feature applications a more costly and time consuming process known as cold/hot sequential deposition (having wafer temperatures in the range of 430-475° C.) must be employed.
Moreover, both conventional reflow and cold/hot sequential deposition processes experience degraded film properties caused by contaminants (water vapor, O
2
, etc.) which desorb from chamber surfaces, from process kit parts, or from the wafer itself during the planarization process. These contaminants enter the chamber atmosphere and are pumped therefrom. Over time fewer contaminants desorb, however, water is often the last contaminant to desorb, and can break into hydrogen and oxygen. Free oxygen is highly reactive and tends to bond with the film (e.g., aluminum) causing the film to surface passivate (e.g., tying up dangling bonds and reducing the surface energy of the film). Surface passivation degrades the film's ability to flow (i.e., degrades surface mobility), thus encouraging void formation. In addition to degrading surface mobility of the film, oxygen and hydrogen, because they have very low atomic weights, are extremely difficult to pump from the chamber. These contaminants remain in the chamber, producing an increase in chamber base pressure which causes the film to have poor crystal orientation and film purity. The poor crystal orientation and film purity result in resistivity and reflectivity deterioration. Thus contaminants which desorb from processed wafers can increase chamber base pressure, and consequently, cause incomplete feature filling due to decreased surface mobility.
Accordingly, a need exists for an expeditious and cost effective method and apparatus for planarizing films at relatively low temperatures, and for a method which resists the adverse affects of desorbed contaminants.
SUMMARY OF THE INVENTION
The present invention provides an improved reflow method and apparatus that significantly improves film quality, and reduces chamber downtime. Specifically, the inventive reflow process comprises introducing, into a reflow chamber, a material which is at least as reactive as the material of the film to be reflowed (i.e., the reflow material). For convenience a material that is at least as reactive as the reflow material is referred to herein as a gettering material.
Preferably the gettering material is sputter deposited while an object (e.g., a wafer) having a reflow material film thereon is shielded from gettering material deposition. The reflow material film is heated and reflows at a lower temperature (as compared to conventional reflow temperatures) because the surface mobility of the film is not degraded since desorbed contaminants react with the gettering material (which deposits on chamber surfaces, on process kit parts, and/or is present in the chamber's atmosphere), rather than reacting with the reflow material film. Preferably sputtering of the gettering material occurs during film heating and before contaminant desorption. However, gettering material may be deposited at anytime during the reflow process as long as it does not interfere with the deposited film being reflowed and/or, alternatively may be deposited on the chamber surfaces and on the process kit parts prior to introducing the wafer to the chamber.
Contaminants which desorb from the wafer, the film, the process kit parts and/or from chamber surfaces tend to react with the gettering material rather than with the reflow material for the following reasons:
1) because the surface area of gettering material within the chamber (e.g., chamber and process kit part surfaces coated with gettering material) is much greater than the surface area of the reflow material film;
2) because the gettering material present in the chamber's atmosphere is in a more energetic state (e.g., a plasma state) and is therefore more likely to react than the solid phase reflow material;
and/or
3) because the gettering material (e.g., titanium) whether in a solid, liquid or gas phase is preferably more reactive than the reflow material (e.g., aluminum).
Thus with use of the present invention the film absorbs fewer, if any, contaminants. Film reflow is more effective and superior surface feature filling is achieved. Because contaminants react with the gettering material rather than remaining in the chamber's atmosphere, the inventive reflow chamber experiences a lower rate of rise in pressure during reflow than do conventional reflow chambers. A lower chamber pressure is therefore maintained during the inventive reflow process and causes the reflowed film to exhibit improved characteristics as compared to conventionally reflowed films (e.g., smoother surface, greater wafer to wafer sheet resistance/surface resistivity uniformity, etc.).
Finally, following an idle period, a chamber that employs the inventive reflow process can be pumped down from sputtering pressure to its base pressure faster (e.g., in as little as two minutes, depending on the pump rate) than chamber's that employ conventional reflow processes. Faster pump down is possible because the gettering material deposited on the process kit parts and on the chamber's surfaces absorbs airborne contaminants, reducing the number of airborne contaminants that need to be pumped from the chamber's atmosphere in order to return the chamber to its base pressure. Additionally, gettering material in the chamber's atmosphere reacts with airborne contaminants to produce larger molecules which are more easily pumped from the chamber. In fact, following an idle period the inventive reflow process reduces downtime by more than an order of magnitude, allowing signifi

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