Abstract:
The present invention is directed to improving defect performance in semiconductor processing systems. In specific embodiments, an apparatus for processing semiconductor substrates comprises a chamber defining a processing region therein, and a substrate support disposed in the chamber to support a semiconductor substrate. At least one nozzle extends into the chamber to introduce a process gas into the chamber through a nozzle opening. The apparatus comprises at least one heat shield, each of which is disposed around at least a portion of one of the at least one nozzle. The heat shield has an extension which projects distally of the nozzle opening of the nozzle and which includes a heat shield opening for the process gas to flow therethrough from the nozzle opening. The heat shield decreases the temperature of nozzle in the processing chamber for introducing process gases therein to reduce particles.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   This application is based on and claims the benefit of U.S. Provisional Patent Application No. 60/410,353, filed on Sep. 13, 2002, the entire disclosure of which is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   This invention relates generally to semiconductor processing and, more particularly, to a gas delivery system for a chemical vapor deposition chamber suitable for high density plasma gapfill processing. 
   The fabrication of integrated circuits (ICs) involves performing a number of processes on the substrate, including the deposition of layers on the substrate and filling of gaps in the substrate. To achieve high throughput, it is important to minimize the particles or other contaminants so that more substrates can be processed between cleaning. 
   Chemical vapor deposition (CVD) is a gas reaction process used in the semiconductor industry to form thin layers or films of desired materials on a substrate. Some high density plasma (HDP) enhanced CVD processes use a reactive chemical gas along with physical ion generation through the use of an RF generated plasma to enhance the film deposition by attraction of the positively charged plasma ions onto a negatively biased substrate surface at angles near the vertical to the surface, or at preferred angles to the surface by directional biasing of the substrate surface. 
   The use of high RF power in HDP-CVD results in improved gapfill, particularly for gaps having a width of equal to or less than about 90 nm and an aspect ratio of at least about 4. For example, the source RF power is at least about 10 kW for processing 200 mm substrates and the source RF power is at least about 12 kW for processing 300 mm substrates. The use of high RF power, however, has been shown to cause an increase in particles, resulting in low throughput. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is directed to improving defect performance in semiconductor processing systems. In specific embodiments, the invention relates to decreasing the temperature of nozzles in the processing chamber for introducing process gases therein to reduce particles. The source of particles for high power recipes in plasma CVD chambers has been identified by a combination of modeling and experiments. The source of particles is silane (SiH 4 ) pyrolysis due to an increase in nozzle temperature in the plasma at high source RF power levels. This gas phase particle nucleation mechanism produces hydrogenated Si clusters (e.g., Si 2 H 6 ) as well as SiO 2  particles due to plasma oxidation. Particle SEM plots show spherical particles consistent with gas phase nucleation. 
   Embodiments of the invention improve defect performance in semiconductor processing systems by decreasing nozzle temperatures in the chamber to impede the gas phase particle nucleation mechanism. This is accomplished by placing a heat shield around one or more nozzles of the gas delivery system. The heat shield is typically a hollow, cylindrical member which extends beyond the tip of the nozzle. The heat shield may be made of aluminum oxide or other ceramic materials. 
   In accordance with an embodiment of the present invention, an apparatus for processing semiconductor substrates comprises a chamber defining a processing region therein, and a substrate support disposed in the chamber to support a semiconductor substrate. At least one nozzle extends into the chamber to introduce a process gas into the chamber through a nozzle opening. The apparatus comprises at least one heat shield, each of which is disposed around at least a portion of one of the at least one nozzle. The heat shield has an extension which projects distally of the nozzle opening of the nozzle and which includes a heat shield opening for the process gas to flow therethrough from the nozzle opening. 
   Another embodiment is directed to a heat shield for shielding a nozzle extending into a chamber to introduce a process gas into the chamber through a nozzle opening. The chamber defines a processing region therein and has a substrate support to support a semiconductor substrate for processing in the chamber. The heat shield comprises a hollow member configured to be coupled with the nozzle and having an internal dimension sufficiently large to be disposed around at least a portion of the nozzle. The hollow member has an extension which projects distally of the nozzle opening of the nozzle and which includes a heat shield opening for the process gas to flow therethrough from the nozzle opening. 
   In accordance with still another embodiment, a method of processing semiconductor substrates comprises placing a substrate on a substrate support in a chamber defining a processing region therein; introducing one or more process gases through at least one nozzle which extends into the chamber and which has a nozzle opening for the one or more process gases to flow therethrough; and applying energy in the processing region to perform a process on the substrate. A heat shield is disposed around at least a portion of the nozzle to reduce a temperature rise of the nozzle from the process performed on the substrate. The heat shield has an extension which projects distally of the nozzle opening of the nozzle and which includes a heat shield opening for the process gas to flow therethrough from the nozzle opening. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a simplified diagram of an embodiment of a high density plasma chemical vapor deposition (HDP-CVD) system according to the present invention; 
       FIG. 2  is a simplified cross section of a gas ring that may be used in conjunction with the exemplary HDP-CVD system of  FIG. 1 ; 
       FIGS. 3 and 4  are partial cross-sectional views of a heat shield for a nozzle according to an embodiment of the present invention; and 
       FIG. 5  shows a plot illustrating the time evolution of particles and comparing the experimental results of a CVD system which does not provide heat shields for the nozzles and a CVD system having nozzles with heat shields. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates one embodiment of a high density plasma chemical vapor deposition (HDP-CVD) system  10  in which a dielectric layer can be deposited. System  10  includes a chamber  13 , a vacuum system  70 , a source plasma system  80 A, a bias plasma system  80 B, a gas delivery system  33 , and a remote plasma cleaning system  50 . 
   The upper portion of chamber  13  includes a dome  14 , which is made of a ceramic dielectric material, such as aluminum oxide or aluminum nitride. Dome  14  defines an upper boundary of a plasma processing region  16 . Plasma processing region  16  is bounded on the bottom by the upper surface of a substrate  17  and a substrate support  18 . 
   A heater plate  23  and a cold plate  24  surmount, and are thermally coupled to, dome  14 . Heater plate  23  and cold plate  24  allow control of the dome temperature to within about ±10° C. over a range of about 100° C. to 200° C. This allows optimizing the dome temperature for the various processes. For example, it may be desirable to maintain the dome at a higher temperature for cleaning or etching processes than for deposition processes. Accurate control of the dome temperature also reduces the flake or particle counts in the chamber and improves adhesion between the deposited layer and the substrate. 
   Generally, exposure to the plasma heats a substrate positioned on substrate support  18 . Substrate support  18  includes inner and outer passages (not shown) that can deliver a heat transfer gas (sometimes referred to as a backside cooling gas) to the backside of the substrate. 
   The lower portion of chamber  13  includes a body member  22 , which joins the chamber to the vacuum system. A base portion  21  of substrate support  18  is mounted on, and forms a continuous inner surface with, body member  22 . Substrates are transferred into and out of chamber  13  by a robot blade (not shown) through an insertion/removal opening (not shown) in the side of chamber  13 . Lift pins (not shown) are raised and then lowered under the control of a motor (also not shown) to move the substrate from the robot blade at an upper loading position  57  to a lower processing position  56  in which the substrate is placed on a substrate receiving portion  19  of substrate support  18 . Substrate receiving portion  19  includes an electrostatic chuck  20  that secures the substrate to substrate support  18  during substrate processing. In a preferred embodiment, substrate support  18  is made from an aluminum oxide or aluminum ceramic material. 
   Vacuum system  70  includes throttle body  25 , which houses three-blade throttle valve  26  and is attached to gate valve  27  and turbo-molecular pump  28 . It should be noted that throttle body  25  offers minimum obstruction to gas flow, and allows symmetric pumping, as described in co-pending, co-assigned U.S. patent application Ser. No. 08/574,839, filed Dec. 12, 1995, and which is incorporated herein by reference. Gate valve  27  can isolate pump  28  from throttle body  25 , and can also control chamber pressure by restricting the exhaust flow capacity when throttle valve  26  is fully open. The arrangement of the throttle valve, gate valve, and turbo-molecular pump allow accurate and stable control of chamber pressures from between about 1 milli-Torr to about 2 Torr. 
   The source plasma system  80 A includes a top coil  29  and side coil  30 , mounted on dome  14 . A symmetrical ground shield (not shown) reduces electrical coupling between the coils. Top coil  29  is powered by top source RF (SRF) generator  31 A, whereas side coil  30  is powered by side SRF generator  31 B, allowing independent power levels and frequencies of operation for each coil. This dual coil system allows control of the radial ion density in chamber  13 , thereby improving plasma uniformity. Side coil  30  and top coil  29  are typically inductively driven, which does not require a complimentary electrode. In a specific embodiment, the top source RF generator  31 A provides up to about 8,000 watts (7 kW) of RF power or higher at nominally 2 MHz and the side source RF generator  31 B provides up to 8,000 watts (5 kW) of RF power or higher at nominally 2 MHz. The operating frequencies of the top and side RF generators may be offset from the nominal operating frequency (e.g. to 1.7–1.9 MHz and 1.9–2.1 MHz, respectively) to improve plasma-generation efficiency. 
   A bias plasma system  80 B includes a bias RF (BRF) generator  31 C and a bias matching network  32 C. The bias plasma system  80 B capacitively couples substrate portion  17  to body member  22 , which act as complimentary electrodes. The bias plasma system  80 B serves to enhance the transport of plasma species (e.g., ions) created by the source plasma system  80 A to the surface of the substrate. In a specific embodiment, bias RF generator provides up to 8,000 watts of RF power or higher at 13.56 MHz. 
   RF generators  31 A and  31 B include digitally controlled synthesizers and operate over a frequency range between about 1.8 to about 2.1 MHz. Each generator includes an RF control circuit (not shown) that measures reflected power from the chamber and coil back to the generator and adjusts the frequency of operation to obtain the lowest reflected power, as understood by a person of ordinary skill in the art. RF generators are typically designed to operate into a load with a characteristic impedance of 50 ohms. RF power may be reflected from loads that have a different characteristic impedance than the generator. This can reduce power transferred to the load. Additionally, power reflected from the load back to the generator may overload and damage the generator. Because the impedance of a plasma may range from less than 5 ohms to over 900 ohms, depending on the plasma ion density, among other factors, and because reflected power may be a function of frequency, adjusting the generator frequency according to the reflected power increases the power transferred from the RF generator to the plasma and protects the generator. Another way to reduce reflected power and improve efficiency is with a matching network. 
   Matching networks  32 A and  32 B match the output impedance of generators  31 A and  31 B with their respective coils  29  and  30 . The RF control circuit may tune both matching networks by changing the value of capacitors within the matching networks to match the generator to the load as the load changes. The RF control circuit may tune a matching network when the power reflected from the load back to the generator exceeds a certain limit. One way to provide a constant match, and effectively disable the RF control circuit from tuning the matching network, is to set the reflected power limit above any expected value of reflected power. This may help stabilize a plasma under some conditions by holding the matching network constant at its most recent condition. Other measures may also help stabilize a plasma. For example, the RF control circuit can be used to determine the power delivered to the load (plasma) and may increase or decrease the generator output power to keep the delivered power substantially constant during deposition of a layer. 
   A gas delivery system  33  provides gases from several sources,  34 A– 34 F chamber for processing the substrate via gas delivery lines  38  (only some of which are shown). As would be understood by a person of skill in the art, the actual sources used for sources  34 A– 34 F and the actual connection of delivery lines  38  to chamber  13  varies depending on the deposition and cleaning processes executed within chamber  13 . Gases are introduced into chamber  13  through a gas ring  37  and/or a top nozzle  45 .  FIG. 2  is a simplified, partial cross-sectional view of chamber  13  showing additional details of gas ring  37 . 
   In one embodiment, first and second gas sources,  34 A and  34 B, and first and second gas flow controllers,  35 A′ and  35 B′, provide gas to ring plenum  36  in gas ring  37  via gas delivery lines  38  (only some of which are shown). Gas ring  37  has a plurality of gas nozzles  39  (only one of which is shown for purposes of illustration) that provides a uniform flow of gas over the substrate. Nozzle length and nozzle angle may be changed to allow tailoring of the uniformity profile and gas utilization efficiency for a particular process within an individual chamber. In one embodiment, gas ring  37  has 24 gas nozzles  39  made from an aluminum oxide ceramic. 
   Gas ring  37  also has a plurality of gas nozzles  40  (only one of which is shown), which in a preferred embodiment are co-planar with and the same in length as source gas nozzles  39 , and in one embodiment receive gas from body plenum  41 . Gas nozzles  39  and  40  are not fluidly coupled in some embodiments where it is desirable not to mix gases before injecting the gases into chamber  13 . In other embodiments, gases may be mixed prior to injecting the gases into chamber  13  by providing apertures (not shown) between body plenum  41  and gas ring plenum  36 . In one embodiment, third and fourth gas sources,  34 C and  34 D, and third and fourth gas flow controllers,  35 C and  35 D′, provide gas to body plenum via gas delivery lines  38 . Additional valves, such as  43 B (other valves not shown), may shut off gas from the flow controllers to the chamber. 
   In embodiments where flammable, toxic, or corrosive gases are used, it may be desirable to eliminate gas remaining in the gas delivery lines after a deposition. This may be accomplished using a 3-way valve, such as valve  43 B, to isolate chamber  13  from delivery line  38 A and to vent delivery line  38 A to vacuum foreline  44 , for example. As shown in  FIG. 1 , other similar valves, such as  43 A and  43 C, may be incorporated on other gas delivery lines. Such 3-way valves may be placed as close to chamber  13  as practical, to minimize the volume of the unvented gas delivery line (between the 3-way valve and the chamber). Additionally, two-way (on-off) valves (not shown) may be placed between a mass flow controller (“MFC”) and the chamber or between a gas source and an MFC. 
   Referring again to  FIG. 1 , chamber  13  also has top nozzle  45  and top vent  46 . Top nozzle  45  and top vent  46  allow independent control of top and side flows of the gases, which improves film uniformity and allows fine adjustment of the film&#39;s deposition and doping parameters. Top vent  46  is an annular opening around top nozzle  45 . In one embodiment, first gas source  34 A supplies source gas nozzles  39  and top nozzle  45 . Source nozzle MFC  35 A′ controls the amount of gas delivered to source gas nozzles  39  and top nozzle MFC  35 A controls the amount of gas delivered to top gas nozzle  45 . Similarly, two MFCs  35 B and  35 B′ may be used to control the flow of oxygen to both top vent  46  and oxidizer gas nozzles  40  from a single source of oxygen, such as source  34 B. The gases supplied to top nozzle  45  and top vent  46  may be kept separate prior to flowing the gases into chamber  13 , or the gases may be mixed in top plenum  48  before they flow into chamber  13 . Separate sources of the same gas may be used to supply various portions of the chamber. 
   In the embodiment shown in  FIGS. 1 and 2 , remote microwave-generated plasma cleaning system  50  is provided to periodically clean deposition residues from chamber components. The cleaning system includes a remote microwave generator  51  that creates a plasma from a cleaning gas source  34 E (e.g., molecular fluorine, nitrogen trifluoride, other fluorocarbons or equivalents) in reactor cavity  53 . The reactive species resulting from this plasma are conveyed to chamber  13  through cleaning gas feed port  54  via applicator tube  55 . The materials used to contain the cleaning plasma (e.g., cavity  53  and applicator tube  55 ) must be resistant to attack by the plasma. The distance between reactor cavity  53  and feed port  54  should be kept as short as practical, since the concentration of desirable plasma species may decline with distance from reactor cavity  53 . Generating the cleaning plasma in a remote cavity allows the use of an efficient microwave generator and does not subject chamber components to the temperature, radiation, or bombardment of the glow discharge that may be present in a plasma formed in situ. Consequently, relatively sensitive components, such as electrostatic chuck  20 , do not need to be covered with a dummy wafer or otherwise protected, as may be required with an in situ plasma cleaning process. 
     FIGS. 3 and 4  show a heat shield  100  which can be used to shield the nozzle  102  from the heat generated in the CVD chamber by plasma or other energy applied to perform a process in the CVD chamber. The nozzle  102  may be any one of the nozzles  39 ,  40  shown in  FIG. 2 . The proximal end  104  of the nozzle  102  is connected to the gas ring  37  ( FIG. 2 ), and the remaining portion of the nozzle  102  is subject to the temperature rise from the energy generated in the chamber. The distal end  106  of the nozzle is typically tapered into a tip, and includes a distal nozzle opening through which one or more process gases flow into the chamber. Due to the low thermal mass at the nozzle tip, the distal end  106  of the nozzle typically experiences the greatest temperature rise due to the energy applied in the chamber. It is desirable to shield the portion of the nozzle  102  exposed inside the chamber, including the distal end  106  of the nozzle. 
   As shown in  FIGS. 3 and 4 , the heat shield  100  is configured to be disposed around at least a portion of the nozzle  102 , desirably around the entire portion of the nozzle  102  that is exposed in the chamber. The heat shield  100  is typically made of a ceramic material, such as alumina or aluminum oxide, aluminum nitride, silicon carbide, or the like. In specific embodiments, the heat shield  100  and the nozzle  102  are made of the same material, such as aluminum oxide, Al 2 O 3 . The heat shield  100  as shown is a separate piece that is coupled to the nozzle  102 , for example, by a threaded connection  110  or the like. Such a heat shield  100  can be conveniently retrofitted onto nozzles in existing CVD chambers. In other embodiments, the heat shield may be formed integrally with the nozzle. 
   In the embodiment shown, the heat shield  100  has a hollow, cylindrical body, which has an internal dimension sufficiently large to be placed around the nozzle  102 . The internal cross-section of the heat shield  100  desirably is slightly larger than the external cross-section of the nozzle  102 , as seen in  FIG. 4 . In the specific embodiment, the gap or spacing between the heat shield  100  and the nozzle  102  is smaller than the thickness of the heat shield  100 . The heat shield  100  includes a heat shield opening  114  through which the process gas flows from the nozzle opening. The heat shield  100  preferably includes an extension  120  which projects distally of the nozzle opening at the distal end  106  of the nozzle  102 . The length of the extension  120  should be sufficiently large to shield the distal end  106  of the nozzle  102  from the heat in the chamber. The length of the extension  120  should not be so large as to have an adverse effect on the process being performed, such as the uniformity of a layer being formed on the substrate. Moreover, an excessively long extension  120  may produce additional particles. In some embodiments, the length of the extension  120  is between the radius of the nozzle and the diameter of the nozzle  102 . In a specific embodiment, the length of the extension  120  is about 0.25 inch, the heat shield  100  has a length of about 1.97 inches, an outer diameter of about 0.635 inch, and a thickness of about 0.153 inch. As shown in  FIGS. 1 and 2 , the nozzles ( 39 ,  40 ) are disposed around the substrate support. Heat shields  100  may be placed around some or all of the nozzles. In some embodiments, the nozzles and heat shields  100  are configured such that the heat shield openings  114  are disposed radially outwardly of the periphery of the substrate. That is, if the heat shields  100  are projected vertically downward onto the plane of the substrate, the heat shields  100  do not overlap with the substrate. 
   Although the heat shield  100  as shown has a uniform circular cross-section with a uniform thickness, it is understood that other configurations, shapes, and thickness profiles may be employed in different embodiments. 
   The heat shield  100  keeps the nozzle temperature relatively low to provide improved particle performance. This allows high power operation in a plasma CVD chamber, for instance, for improved gapfill capability. Due to the improved defect performance, the use of the heat shield allows multi-x clean to be run, thereby improving the throughput of the substrate processing system. 
     FIG. 5  shows a plot illustrating the time evolution of particles and comparing the experimental results of a CVD system which does not provide heat shields for the nozzles and a CVD system having nozzles with heat shields. The CVD system is similar to the one shown in  FIGS. 1 and 2 , and the heat shields  100  of  FIGS. 3 and 4  are placed on the nozzles  39 ,  40  disposed around the periphery of the substrate. The particles included in the plot are greater than about 0.16 μm in size. The process involves gapfill of a shallow trench isolation (STI) on a 300 mm silicon substrate having a trench width of about 110 nm and an aspect ratio of about 4:1 by depositing a USG layer from SiH 4 , H 2 , and O 2 . The pressure in the chamber is about 4 mTorr. 
   The first three experiments were conducted without the heat shield. The source power levels for the top SRF generator ( 31 A) and the side SRF generator ( 31 B) are about 6 kW and 4 kW for the first test, about 7 kW and 4 kW for the second test, and about 7 kW and 5 kW for the third test. As shown in  FIG. 5 , the particle counts climb rapidly after about 80 seconds at rates that range from about 50 to about 116 particles per second. 
   The particles increase at a substantially lower rate when the heat shield is used. The two tests employ top and side SRF power levels of about 6 kW and 4 kW, and about 7 kW and 5 kW, respectively. The rates of particle count increase for the two tests, respectively, are about 1 and about 5 particles per second after about 80 seconds, and are about 5 and about 9 particles per second after about 120 seconds. 
   The present invention is applicable to various processes including STI, IMD (inter-metal dielectric), PSG (phosphosilicate glass), FSG (fluosilicate glass), and the like. In addition to improved gapfill, the invention allows multi-x clean resulting in improved throughput by as much as about 50%. The use of the heat shields results in improved particle performance, thereby allowing high power operation in a plasma CVD chamber, for instance, for improved gapfill capability. 
   It is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments will be apparent to those of skill in the art upon reviewing the above description. By way of example, the present invention may extend to other types of thermal as well as plasma deposition chambers and to other processes for processing substrates. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.