Abstract:
A high density plasma chemical vapor deposition process including exciting gas mixture to create a plasma including ions, and directing the plasma into a dense region above the upper surface of the semiconductor wafer, heating the wafer using an additional heat source, and allowing a material from the plasma to deposit onto the semiconductor wafer.

Description:
FIELD OF THE INVENTION 
     The present invention relates to methods of making semiconductor devices, and more particularly, to methods using high density plasma chemical vapor deposition. 
     BACKGROUND OF THE INVENTION 
     Chemical vapor deposition has a range of equipment reactor designs, with each producing slightly different types of film quality. Chemical vapor deposition reactors are broadly categorized based upon the reaction chamber pressure regime used during the operations: Atmospheric-pressure chemical vapor deposition (APCVD) reactors and reduced-pressure reactors. The reduced-pressure chemical vapor deposition reactors are of two general types. First, there is low-pressure chemical vapor deposition (LPCVD) reactors where the energy input is thermal. Second, there are plasma-assisted chemical vapor deposition reactors, either plasma enhanced chemical vapor deposition (PECVD) or high-density plasma chemical vapor deposition (HDPCVD) where the energy is partially supplied by a plasma as well as thermally. 
     APCVD generally operates in a mass-transport limited regime. At any given time, there may not be sufficient gas molecules present at the wafer surface for a reaction to occur. Therefore, the reactor must be designed to have optimum reactor gas flow to every wafer in the system. The most common use of APCVD is the deposition of silicon dioxide and doped oxides. These films have been used traditionally as an interlayer dielectric, as a protective overcoat, or to planarize a non-uniform surface. APCVD can be utilized to deposit silicon dioxide with silane typically at a low temperature of about 450 to 500° C. Silicon dioxide can also be deposited with TEOS-ozone at a temperature about 400° C. 
     LPCVD operates at a minimum vacuum of about 4.1 to 5 torr at temperatures ranging between 300 and 900° C. LPCVD reactors typically operate in the reaction-rate limited regime. In this reduced-pressure regime, the diffusivity of the reacting gas molecules increases so that the mass-transfer of the gas to the wafer no longer limits the rate of the reaction. Because of this transfer state, the gas-flow conditions inside the reactor are not important, permitting the reactor design to be optimized for high wafer capacity, for example, wherein wafers can be closely spaced. Films are uniformly deposited on a large number of wafer surfaces as long as the temperature is tightly controlled. LPCVD reactor designs favor a hot-wall reactor type so that the uniform temperature control is achievable of all over a large operating length. 
     Three major types of chemical vapor deposition equipment rely on plasma energy, in addition to thermal energy to initiate and sustain the chemical reaction necessary for chemical vapor deposition. The plasma-assisted chemical vapor deposition reaction necessary to form a film occurs with RF power is use to breakup gas molecules in a vacuum. The frequency of the RF power depends on the application, with a typical frequencies found at about 40 kHz, 400 kHz, 13.56 MHz and 2.45 GHz (microwave power). The molecular fragments or radicals are chemically reactive species and readily bond to other atoms to form a film at the wafer surface. Gaseous byproducts are removed by a vacuum pumping system. The wafer is heated in order to assist the surface reactions and reduced the level of undesirable contaminants such as hydrogen. 
     Plasma-enhanced chemical vapor deposition (PECVD) uses plasma energy to create and sustain the chemical vapor deposition reaction. An important difference between PECVD and LPCVD is the much lower PECVD deposition temperature. For instance, silicon nitride is deposited using LPCVD at 800 to 900° C. On the other hand, silicon nitride is deposited using PECVD at a temperature of about 350° C. The PECVD reactor typically is a cold-wall plasma reactor with the wafer heated in its chuck while the remaining parts of the reactor are unheated. Deposition parameters must be controlled to ensure the temperature gradient does not affect the film thickness uniformity. Cold-wall reactors create fewer particles and require a less downtime for cleaning. 
     High-density plasma chemical vapor deposition (HDPCVD) is a high-density mixture of gases at low pressure that is directed towards the wafer surface in a reaction chamber. The main benefit of HDPCVD is that it can deposit films to fill high aspect ratios with a deposition temperature range of 300-400° C. HDPCVD was initially developed for interlayer dielectric applications, but it has also been used for deposition of ILD- 1 , shallow trench isolation, etch-stop layers, and deposition of low-k dielectrics. The HDPCVD reaction involves a chemical reaction between two or more gas precursors. To form the high-density plasma, a source excites the gas mixture with RF or microwave power and directs the plasma ions into a dense region above the wafer surface. There are different high-density plasma sources, such as electron cyclotron resonance, inductively coupled plasma, and Helicon. Much of the challenge for the use of high-density plasma is related not only to the performance of the plasma source but also to the details of the chamber designs so that the technology works in high-volume wafer fabrication. A particular problem is that the high-density plasma will increase the thermal load to the wafer. This condition leads to high wafer temperatures. As a result, HDPCVD reactors typically include a cooling system for the wafer, which typically includes applying a backside blanket of helium gas to the wafer through access ports in the electrostatic chuck. This action creates a thermally conductive path between the wafer and the electrostatic chuck, thus cooling the wafer and the chuck. 
     The HDPCVD oxide process usually uses silane as the silicon precursor and oxygen as the oxygen precursor. Argon is added in the process to enhance the sputtering etch effect. HDPCVD can also deposit PSG and FSG by reacting with phosphorus and silicon tetrafluoride. 
     Problems in this sputtering are continued to challenge those skilled in the art.  FIG. 1  illustrates a high sputter rate process in which molecules  10  such as silicon dioxide are sputtered into a trench  12  to fill the trench and form a silicon dioxide layer  14 . As illustrated in  FIG. 1 , in a high sputter rate process, the silicon dioxide molecules  10  often bounce off of the corner defining the trench  12  and tend to stick to the sidewalls  16  defined in the trench  12 . As a result, as illustrated in  FIG. 2 , a birds peak  18  tends to develop along the sidewall  16  of the trench. Eventually, sidewall birds peaks  18  converge on each other creating a void  20  in the trench as illustrated in  FIG. 3 . 
       FIG. 4  illustrates a relatively low sputter rate process in which molecules  10 , such as silicon dioxide are sputtered into a trench  12 . However, in this process because the sputter rate is relatively low, the molecules  10  do not tend to stick to the sidewalls  16  of the trench, but tend to fall towards the bottom  22  of the trench  12 . However, even using a relatively low sputter rate process, it&#39;s difficult to control the process without producing voids in the trench.  FIG. 5  illustrates a void  20  formed in the trench when the deposition to sputter ratio is about 10 for silicon dioxide being deposited in the trench.  FIG. 6  illustrates a void  20  that develops when the deposition to sputter ratio is increased to about 20 for silicon dioxide being deposited in the trench. 
     The present invention provides alternatives to the prior art. 
     SUMMARY OF THE INVENTION 
     One embodiment of the present invention includes a high-density plasma chemical vapor deposition process including exciting a gas mixture to create a plasma compromising ions and directing the plasma into a dense region above the upper surface of a semiconductor wafer, heating the wafer using an additional heat source, and allowing material from the plasma to deposit on to the semiconductor wafer. 
     On another embodiment of the invention the semiconductor wafer includes a layer having an opening therein and wherein the material is deposited into the opening. 
     On another embodiment of the invention the material is deposited into a trench in the semiconductor wafer to form a shallow trench isolation structure. 
     Another embodiment of the invention includes a high-density plasma chemical vapor deposition process including exciting a gas mixture to create a plasma comprising ions and directing the plasma into a dense region above the upper surface of a semiconductor wafer and wherein the plasma includes a sputter etchant comprising at least one of helium and hydrogen ions and allowing a material in the plasma to be deposited on the upper surface of the wafer. 
     Another embodiment of the invention includes a high-density plasma chemical vapor deposition reactor comprising a chamber, a chuck, and a heating means in the chuck. 
     Another embodiment of the invention includes a high-density plasma chemical vapor deposition reactor comprising a chamber, a source for exciting a gas mixture, a chuck for supporting a wafer and an additional heater in the chamber to supply heat to the semiconductor wafer. 
     Other embodiments of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIGS. 1-3  illustrate a high sputter rate silicon dioxide deposition process of the prior art. 
         FIGS. 4-6  illustrate a low sputter rate silicon dioxide deposition process of the prior art. 
         FIG. 7  illustrates one embodiment of the present invention including a high-density plasma chemical vapor deposition process. 
         FIG. 8  illustrates one embodiment of the present invention including a high-density plasma chemical vapor deposition reactor. 
         FIG. 9  illustrates one embodiment of the present invention including an alternative high-density plasma chemical vapor deposition reactor. 
         FIG. 10  illustrates one embodiment of the invention including a semiconductor wafer chuck having a first electrical resistance heating element and a second electrical resistance heating element in the chuck. 
         FIG. 11  illustrates one embodiment of the present invention including a semiconductor wafer chuck including a fluid passage defined therein for providing a heating gas and/or liquid for heating a semiconductor wafer on the chuck. 
         FIG. 12  illustrates a semiconductor device including a shallow trench isolation feature formed according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     Referring now to  FIG. 7 , one embodiment of the present invention includes a high-density plasma chemical vapor deposition process  24 . The plasma and a high-density plasma chemical vapor deposition process is a high-density mixture of gases at low pressure (a few mTorr or less) that is directed towards a semiconductor wafer surface in a reaction chamber. To form the high-density plasma, a source excites the gas mixture with, for example, RF or microwave power and directs the plasma ions into a dense region above the semiconductor wafer surface. There are different high-density plasma sources, such as electron cyclotron resonance, inductively coupled plasma, and Helicon that can be used according to the present invention. The high-density plasma chemical vapor deposition process uses a simultaneous deposition and etching action that is the basis for the ability to accomplish high aspect ratio gap fills with typically dielectric material without any voids. Although hereto forth, high-density plasma chemical vapor deposition processes have used relatively heavy bombardment species such as argon, the present invention includes a light bombardment species  26 , such as helium or hydrogen. In one embodiment of the invention, only a light bombardment species is utilized. However, it is within the scope of the present invention to use a combination of heavy bombardment species such as argon and light bombardment species such as helium and/or hydrogen. The light bombardment species are used in the etching process and produce less heat in comparison to heavy bombardment species. One embodiment of the present invention includes the use of an additional heater to heat the semiconductor wafer during the high-density plasma chemical vapor deposition process. In one embodiment, the semiconductor wafer is heated to a temperature equal to or greater than 600° C. In another embodiment of the invention the semiconductor wafer is heated to a temperature greater than 600° C. In another embodiment of the invention, the semiconductor wafer is heated to a temperature greater than 650° C. 
     Referring now to  FIG. 8 , a high-density plasma chemical vapor deposition reactor  30  is illustrated that include a reaction chamber  32 , inductive coils  34 , source RF  36  and bias RF  37 . The chamber  32  includes sidewalls  82  and a dome  84 . A semiconductor wafer chuck  40  is provided on which a semiconductor wafer  42  is supported. A fluid passage  44  is provided to the chuck, which may be utilized for a cooling gas such as helium or may be used for a heating material such as a hot gas or liquid to heat the wafer  42  according to one embodiment of the invention. In one embodiment of the invention a heater  48  is provided on at least one of the sidewalls  82  and/or dome  84  of the chamber  32 . The heater  48  may include at least one of a hot gas heat exchanger and a hot liquid heat exchanger. The reactor  30  produces a plasma  46  over the upper surface of a semiconductor wafer  42 . 
     Referring now to  FIG. 9 , another embodiment of the present invention includes a high-density plasma chemical vapor deposition reactor  50 , which includes a chamber  32  having sidewalls  82  and a dome  84 . This embodiment includes a microwave source  54  located in the dome  84 . Magnetic coils  52  are provided around the chamber  32  and produce a magnetic field line  90  that directs a plasma  46  produced in the chamber  32 . The reactor  50  includes a bias RF  92 , and a semiconductor wafer chuck  40  for supporting the semiconductor wafer  42 . A fluid passage  44  is provided to the chuck  40  for supplying a cooling fluid such as helium, or in one embodiment of the present invention supplying a heating fluids such as a gas or liquid to the chuck to heat the semiconductor wafer  42 . An additional heater  48  is provided on at least one of the sidewalls  82  and/or dome  84  of the chamber  32 . The heater  48  may include at least one of a hot gas heat exchanger and a hot liquid heat exchanger. 
     Referring to  FIG. 10 , one embodiment of the present invention includes a semiconductor wafer chuck  40 , which includes a first electrical resistance heating element  56  positioned near the periphery of the chuck  40 . Optionally, a second electrical resistance heating element  58  is provided near the interior of the chuck  40 . The first and second electrical resistance heating elements  56 ,  58  are separately controlled to prevent hotspots in the chuck  40  and a semiconductor wafer. 
     Referring now to  FIG. 11 , an alternative embodiment of the present invention includes a semiconductor wafer chuck  40  including a fluid passage  80  through which a heating fluid such as a gas or hot liquid may flow to heat the semiconductor wafer during the high-density plasma chemical vapor deposition process. 
     Referring now to  FIG. 12 , a semiconductor device  60  is provided including a p+ silicon substrate  62  and an overlying p− epitaxial layer  64  in which a n-well  66  and a p-well  68  have been formed. A liner oxide  70  may be formed over the upper surface of the epitaxial layer  64  and the n-well  66  and the p-well  68 . A nitride layer  72  may selectively cover portions of the semiconductor device. A silicon dioxide layer is deposited using a high-density plasma chemical vapor deposition process according to the present invention to form shallow trench isolation features  74 . 
     A gas mixture is introduced into the high density plasma chemical vapor deposition reactors and excited using one of a RF and/or microwave power source. The gas mixture may include any of a variety of materials including, but not limited to silane, oxygen, and a light bombardment species including at least one of helium and hydrogen. Alternatively, the gas mixture may include tetraethylorthosilicate.