Abstract:
A decoupled capacitive CVD reactor is described, which provides improved CVD capabilities, including processing at lower temperatures, performing alternating deposition and etching steps, and performing in situ cleaning of the chamber, without the need for a remote plasma source. Two RF frequencies are coupled to the susceptor, while the anode is grounded. The high frequency RF source is operated so as to control the plasma density, while the low frequency RF source is operated to control species bombardment on the substrate, so as to control the properties of the film being deposited. Additionally, both RF sources may be controlled, together with selection of gasses supplied to the chamber, to operate the chamber either in deposition mode, partial etch mode, etching mode, or cleaning mode.

Description:
RELATED APPLICATIONS 
     This application claims priority from Chinese Patent Application Serial No. 200810203405.X, which was filed on Nov. 26, 2008, the entire disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Filed of the Invention 
     This invention relates to the art of substrate micro-fabrication and, more particularly, to plasma assisted chemical vapor deposition chamber and processes. 
     2. Related Arts 
     Micro-fabrication of substrates is a well know art employed in, for example, fabrication of semiconductors, flat panel displays, light emitting diodes (LED&#39;s), solar cells, etc. various steps in micro-fabrication include forming thin film using various chemical vapor deposition (CVD) techniques. One such technique is generally referred to as plasma assisted vapor deposition (PECVD). Various chamber technologies have been used for PECVD fabrication, including microwave, inductive, and capacitive sources. In general, conventional chambers are designed so that power is delivered to the plasma from a source that is remote or opposite the substrate. For example, in inductive sources the coil is positioned above the roof of the chamber, while in capacitive sources the RF energy is generally applied to the anode embedded in the showerhead or ceiling of the reactor. The reasoning behind such design relates to preventing species bombardment of the substrate during deposition of the thin film. 
     Another feature of the prior art chambers is the use of remote clean. Since the chambers are used to deposit various materials on the substrate, the materials are also deposited on various parts of the chamber. One problem is that once the deposits on the chamber parts reach a certain thickness level, and partly as a result of thermal cycling of the chamber, the coating flakes off and generates particles that land on the substrate, thereby causing defects. Therefore, it is desirable to clean the chamber from such deposits. One method for cleaning the chamber is the use of plasma etching of the deposits. The most utilized method in the art is that of a remote plasma source, such as Astron®, available from MKS Instruments of Andover, Mass., Litmass® or available from Advanced Energy of Fort Collins, Colo. However, this solution requires attaching additional hardware to the reactor and activation of a plasma source separate from the reactor&#39;s source. 
     A recent problem encountered in the CVD art is that of “pinching.” Due to aspect ration of various structures that need to be CVD filled, as the material is deposited on the sides of the trench it closes the top so as to form voids inside the trench. This is shown in  FIG. 1 , illustrating trench  110  etched in substrate  100 . As shown by contour lines  102 ,  104 , and  106 , as material is CVD deposited onto the substrate, it pinches at the top,  108 , so as to form a seam or void  120 . Even when a seam is generated, after an annealing step it often expands into a void. Such a void is undesirable as is considered a defect. 
     SUMMARY 
     The following summary is included in order to provide a basic understanding of some aspects and features of the invention. This summary is not an extensive overview of the invention and as such it is not intended to particularly identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented below. 
     A decoupled capacitive, i.e., parallel plate, CVD reactor is described, which provides improved CVD capabilities, including processing at lower temperatures, performing alternating deposition and etching steps, and performing in situ cleaning of the chamber, without the need for a remote plasma source. 
     According to certain aspects of the invention, Two RF frequencies are coupled to the susceptor, while the anode is grounded. This structure provides a high density plasma chamber with separate control and efficient tuning of plasma density and species energy. The high frequency RF source is operated so as to control the plasma density, while the low frequency RF source is operated to control species bombardment on the substrate, so as to control the properties of the film being deposited. Additionally, both RF sources may be controlled, together with selection of gasses supplied to the chamber, to operate the chamber either in deposition mode, partial etch mode, etching mode, or cleaning mode. In general, the low frequency RF source is set at a lower power than the high frequency RF source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, exemplify the embodiments of the present invention and, together with the description, serve to explain and illustrate principles of the invention. The drawings are intended to illustrate major features of the exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not drawn to scale. 
         FIG. 1  illustrates a cross section of a CVD fill of a trench, according to the prior art. 
         FIG. 2  illustrates a cross section of a CVD chamber according to an embodiment of the invention. 
         FIGS. 3A-3G  illustrate a process for gap fill using the reactor  200  in an alternating CVD—etch modes. 
         FIG. 4  illustrates another embodiment of the invention, wherein two substrates may be processed simultaneously. 
         FIG. 5  illustrates yet another embodiment of the invention, wherein four substrates may be processed simultaneously. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the invention provide a plasma processing apparatus that is operable in four modes: CVD, partial etch, etch, and clean modes. In CVD mode the chamber is operated to deposit layers on the substrate. In partial etch mode deposition processing is performed concurrently with partial etch process so as to control the properties of the deposited layer. In etch mode deposition is stopped and the deposited layer is at least partially etched. In clean mode in-situ plasma is used to efficiently clean the chamber. The following are some examples of embodiments of the inventive chamber. 
       FIG. 2  illustrates a cross section of an embodiment of a decoupled capacitive plasma CVD reactor  200  according to an embodiment of the invention. The reactor  200  has a chamber body  205  having a susceptor  225  situated therein and a showerhead  260  opposing the susceptor and also serving as a grounded anode. A gap  210  is formed between the susceptor  225  and the showerhead  260 , where plasma  215  may be ignited and maintained. The pressure inside the chamber is controlled with pump  220 . Due to the design of this chamber, there is no need for a turbo-molecular pump. Rather, a simple mechanical pump may suffice, as the processes in the chamber may be performed at pressures in the range of 50 mTorr to 10 Torr, so as to enable CVD, etch, and clean processes. 
     It should be appreciated that rather than using a showerhead, element  260  may function as a grounded anode only, while gas is delivered using injectors, e.g., from the sidewalls of the chamber  205 . Gas is delivered from gas controller  265 , which may be an array of “gas sticks” in a manner well known in the art, where each gas stick may include filters, mass flow controllers (MFC&#39;s), valves, etc. The controller  265  can be operated to selectively deliver deposition precursor gases, etching precursor gases, and/or cleaning precursor gases. The cleaning gas may or may not be the same as the etching gas. 
     The susceptor includes a heater  230 , which is powered by source  240 . The heater  230  is operable to maintain the substrate at temperatures in the range of about 100° C.-500° C. The susceptor also includes a cathode  235 , which is power by two RF power sources, high frequency  250  and low frequency  255 , fed via frequency match  245 . High frequency source  250  provides RF frequency which may be, e.g., 27 MHz, 60 MHz, 100 MHz, or higher. In general, the high frequency should be 27 MHz or higher. The low frequency may be in the range of hundreds of kilohertz up to 13.56 MHz. For example, it may be set to 400 MHz, 2 MHz, 2.2 MHz, or 13.56 MHz. Applying the RF frequency to the bottom electrode rather than to the top electrode (as is done in the prior art) provides at least the following benefits. Coupling the RF to the bottom electrode enables control of the deposition rate compared to the etch rate, i.e., applying RF power to cause deposition rate to be higher than etch rate. Also, the application of RF power to the bottom electrode enables better dissociation of deposition precursor gas. Also, applying the RF power to the top electrode, as is done in the prior art, causes the plasma to attack the chamber&#39;s ceiling, thereby causing particles. On the other hand, when the RF is applied to the bottom electrode, the plasma does not attack the ceiling of the chamber. 
     Reactor  200  may be operated in a CVD mode to perform, e.g., gap fill process. Gap fill is traditionally done using a high density plasma CVD, HDP-CVD, which utilizes an inductive RF source. However, reactor  200  may perform gap fill by operating the reactor as follows. The pump  220  is operated to maintain a pressure of 1 to 10 Torr in the chamber. A deposition gas which may include silicon-containing gas, an oxygen-containing gas, and a fluent gas, e.g., monosilane (SiH 4 ), molecular oxygen (O 2 ) and helium, or Silane and Ozone, is provided by the gas controller  265  via showerhead  260 . The heater  230  is energized to maintain the substrate at, e.g., 200° C.-400° C. The high frequency source  150  is energized to about 200 W-1000 W, while the bias, i.e., low frequency RF generator  255  is energized to 0-500 W. Notably, as the energy of the bias generator  255  is increased, the reactor  200  is transformed to operate in a partial etch mode. Optionally, argon gas may be added while the reactor  200  operates in a partial etch mode. The argon species can be used to vary the density and/or planarity/conformity of the deposited film. 
     The reactor  200  may also be operated in an etch mode by having controller  280  set operating parameters of the chamber to enable etching. The controller may change the operation modes of, e.g., the pump  220 , the RF generators  250 ,  255 , and the gas controllers. To perform etch, the pump  220  is operated to maintain the chamber at about 50 mT to 2 T. Gas controller  265  is operated to stop injection of deposition gas and instead inject etch precursor gas, e.g., fluorocarbon chemistry with or without argon gas. Also, the RF generators may be operated at different power settings. For example, since the low RF frequency controls the ion bombardments, the power of the RF generator  255  may be increased to cause more ion bombardment of the substrate, thereby increasing ion etch. Notably, the etch mode may be interlaced with deposition mode so as to control the surface texture, planarity and/or conformity of the deposited layer. 
       FIGS. 3A-3G  illustrate a process for gap fill using the reactor  200  in an alternating CVD—etch modes. In  FIG. 3A  a first layer  302  is deposited by operating the reactor  200  in a CVD mode. Then, the reactor  200  is operated in an etch mode so as to partially etch layer  302 . As shown in  FIG. 3B , the layer naturally tends to etch preferentially at the corners  304 , so as to widen the opening to the gap. A further deposition step then follows to further fill the gap, as shown in  FIG. 3C . As the corners  304  become close again, the reactor is reverted to etch mode, so as to partially etch the deposited layer and open the corners  304 , as shown in  FIG. 3D . As shown in  FIG. 3E , the gap is almost totally filled, at which time the reactor is reverted to etch so as to planarize the top of the deposited layer, as shown in  FIG. 3F . Further deposition and etch processes can be used to provide a planar surface, as shown in  FIG. 3G . 
     In an alternative embodiment, partial etch is continuously performed together with the CVD, so that the corners  304  are continuously bombarded and etched. For this process, the reactor is operated in partial etch mode, wherein the controller sets the chamber&#39;s operating parameters such that deposition gas is supplied to the chamber and the heater is energized to deposition temperature. The high frequency source is energized to generate plasma at density controlled for deposition, while the bias power is slightly energized, e.g., 100-300 W to generate low level bombardment of the substrate. Optionally, argon gas is added to the deposition gas to enhance sputtering of the substrate so as to physically etch the corners  304 . 
     Once processing is completed, the substrate may be removed and the chamber may be operated in a cleaning mode by having the controller set various operating parameters to perform in-situ chamber cleaning. For example, during cleaning mode the chamber is operated by energizing the high RF source to generate plasma using cleaning gas, such as, e.g., HF, F2, C2F6, COF2, etc. During cleaning mode, the low frequency bias generator  255  may be kept off, or energized to a low level, so as to minimize ion bombardment of the interior parts of the chamber. On the other hand, the pump  220  may be energized to reduce the pressure in the chamber to below 1 T. 
       FIG. 4  illustrates another embodiment of the invention, wherein the chamber body  405  is divided into two processing zones  410 ,  412 , by partition  414 . The two zones  410 ,  412  are fluidly coupled to pump  420 . Each zone has a susceptor  425 ,  427  and showerhead  460 ,  462 . Each susceptor includes a heater,  430 ,  432  and an electrode  435 ,  437 . The electrodes  435 ,  437  are coupled to high RF source  450  and its related impedance match  445 , and to low RF bias  455  and its related impedance match  447 . Each showerhead is coupled to gas source controller  465  and includes an electrode  464 ,  466  that is grounded. Each zone can be operated in CVD mode, partial etch mode, etch mode, and clean mode, similar to the modes described above. 
     As can be understood from the above description, using the parallel plate structure with dual frequency fed from the susceptor creates a planar plasma source that can be easily extended to any required area, while maintaining relatively uniform plasma distribution. Therefore, this structure can be easily extended to large substrate sizes, so as to fabricate, for example, LCD displays and thin-film solar panels. Also, this structure can operate at pressure regimes, e.g., 2-5 Torr range, that do not require turbo molecular pumps, but can be maintained using a simple mechanical pump, thereby lowering costs and complexity. 
     Another thing to note is that for the reactor described herein there is no need for an electrostatic (ESC) chuck. Rather, a simply susceptor may be used. On the other hand, the susceptor should be operable at high temperature, higher than conventional ESC chuck. The level of temperature of the chuck would depend on the frequency of the high frequency plasma source. The temperature requirements of the susceptor can be relaxed as the frequency of the source is increased. For example, the temperature of the susceptor may be reduced if the source is at 100 MHz or above, as opposed to when the source operates at, say 27 MHZ. 
       FIG. 5  illustrates yet another embodiment of the invention, wherein four substrates may be processed simultaneously. Reactor  40  has chamber body  45  and lid  100 . The lid has four showerheads  105 , which also serve as anodes coupled to ground. When the lid  100  is closed over the body  45 , four processing zones, each having a susceptor  44 , are created for processing four substrates simultaneously. Each susceptor also includes a cathode embedded therein. Each cathode is coupled to a high frequency RF generator  10  and low frequency RF generator  12 , via match  14 . A mechanical pump  62  is provided to control the pressure in the four processing zones, via evacuation slits  55 . The substrates are delivered and removed from the chamber via valve  22 . At central coupling  51  a rotary robot arm is situated (not shown as not to obscure other elements) which is used to accept substrates from valve  22  and place the substrates in the respective processing zone. 
     It should be understood that processes and techniques described herein are not inherently related to any particular apparatus and may be implemented by any suitable combination of components. Further, various types of general purpose devices may be used in accordance with the teachings described herein. It may also prove advantageous to construct specialized apparatus to perform the method steps described herein. The present invention has been described in relation to particular examples, which are intended in all respects to be illustrative rather than restrictive. Those skilled in the art will appreciate that many different combinations of hardware, software, and firmware will be suitable for practicing the present invention. Moreover, other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. Various aspects and/or components of the described embodiments may be used singly or in any combination in the server arts. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.