Abstract:
A vaporizer head for evenly flowing at low pressure into a processing chamber vaporized precursor compounds for deposition of metal and other layers onto a semiconductor, has a bulb-like body with a center axis, a lengthwise cavity, an input end and an output end. The cavity has an opening for receiving a stream of vaporized precursor compound. There are a plurality of passages for flow of vapor through the head, each passage having a length and a diameter. They extend radially from along and around the cavity like the spokes of a wheel at inclined angles relative to the center axis from the cavity to a tapered output surface of the head. The cavity has a well-like bottom for capturing any droplets or particles of precursor compound and preventing them from leaving the head except as vapor. The plurality of passages have sufficiently large diameters such that there is only a low pressure drop in the vapor flowing through the head.

Description:
FIELD OF THE INVENTION 
     This invention relates to a head for vaporizing solid and/or liquid PRECURSOR compounds and for injecting them as vapor into a processing chamber during chemical vapor deposition onto surfaces of a semiconductor to deposit thin films of materials such as tantalum, tantalum nitride, titanium, etc. 
     BACKGROUND OF THE INVENTION 
     The growth in the use, and usefulness, of semiconductors has been accompanied by the development of new processes and materials for the design and manufacture of semiconductors together with new or improved manufacturing equipment and hardware. Important recent improvements in design and new materials have led to faster speeds of operation and greater densities for very large scale integrated (VLSI) circuits. The use of new materials such as tantalum, titanium, and other metals, has led to the need for more efficient ways of applying them to semiconductor surfaces. 
     A layer or film of a metal such as tantalum, titanium, etc. can be deposited by chemical vapor deposition (CVD) onto exposed surfaces of a semiconductor wafer during processing into VLSIs. For example, a precursor compound of the metal tantalum, namely pentadiethylaminotantalum (PDEAT), can be vaporized under certain conditions of pressure and temperature to obtain a gaseous or vapor phase of the compound which may then be used in CVD processing to form a layer of metal. Precursor compounds of various metals require low pressures (e.g., a Torr or less and elevated temperatures (e.g., roughly 100° C.) to change them into and hold them in vapor phase. This will be explained in greater detail hereinafter. 
     It is desirable that a layer of metal being deposited by CVD on a semiconductor wafer be uniform in thickness. To achieve this, a chemical vapor precursor compound of the metal flowing into a processing chamber where the semiconductor wafer is being processed should be controlled in flow direction and amplitude so that the vapor is evenly distributed and flows uniformly toward the wafer. In addition, because a CVD process step using a precursor compound of a metal such as tantalum, titanium, etc., is typically carried out in a chamber maintained under low pressure conditions (e.g., a Torr or less), the flow of gas vapor into the chamber through a vaporizer head should be impeded as little as possible by the head. The head should have high-flow-conductance so that pressure drop across it is low (e.g., a fraction of a Torr). The gas vapor should also be controlled in temperature as it passes through the head and enters the chamber to prevent condensation of the vapor into droplets or particles. 
     The present invention provides a simple and efficient vaporizer head with improved characteristics which fills these needs. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention in one specific embodiment thereof, there is provided a vaporizer head for low pressure application of vapors of precursor compounds useful in chemical vapor deposition of materials such as titanium, tantalum, etc., onto the surfaces of semiconductors. The vaporizer head comprises a body having a center axis, an outer diameter, an outer surface, an input end, an output end, and a length between the ends. The body defines a cavity along the center axis from the input end to near but not through the output end for receiving a stream of vaporized precursor compound, the cavity having a closed well-like end for containing droplets or particles of condensed precursor compound which may occur. The body also defines a plurality of passages through the head for flow of vapor outward from the cavity through the outer surface, each passage having a length and a diameter and extending radially from the center axis at respective angles relative to the center axis. The plurality of passages have sufficiently large diameters to cause only low pressure drop to vapor flowing through them and to provide dispersion of vapor flowing through the head such that vapor flows evenly onto a semiconductor surface, the head providing a desired operating temperature for the vapor flowing through it. 
     In one specific embodiment the invention is a vaporizer head for applying vapors of precursor compounds useful in chemical vapor deposition of layers of materials onto semiconductors. The head comprises a body having a center axis, an outer diameter, an outer surface, an input end, an output end, and a length between the ends. The body defines a cavity along the center axis from the input end to near but not through the output end for receiving a stream of vaporized precursor compound. The cavity has a closed well-like bottom for containing droplets or particles of condensed precursor compound which may occur. The body defines a plurality of passages through the head for flow of vapor outward from the cavity through the outer surface. Each passage has a length and a diameter and extending radially from the center axis at respective angles relative to the center axis. The plurality of passages have sufficiently large diameters to cause only a pressure drop of less than about a Torr to vapor flowing through them and to provide dispersion of vapor flowing through the head such that vapor flows evenly onto a semiconductor surface. The head provides a desired operating temperature for the vapor flowing through it. 
     In an other specific embodiment the invention is a vaporizer head for flowing into a processing chamber vaporized precursor compounds during chemical vapor deposition of metal and other layers onto a semiconductor. The head comprises a body having a center axis, an inwardly tapered lower outer surface, an input end, an output end, and a length between the ends. The body defines a cavity along the center axis and having an opening in the input end for receiving a stream of vaporized precursor compound. The cavity has a closed well-like bottom near the output end for containing droplets and particles of the precursor compound and preventing them from leaving the head except as vapor. The body defines a first plurality of passages for flow of vapor, each passage having a length and a diameter and extending radially from the cavity like the spokes of a wheel at a first inclined angle relative to the center axis from the cavity to the lower outer surface. The body defines a second plurality of passages for flow of vapor, each passage having a length and a diameter and extending radially from the cavity like the spokes of a wheel at a second inclined angle relative to the center axis from the cavity to the lower outer surface. The body defines a third plurality of passages each having a length and a diameter and extending from just above the well-like bottom of the cavity to the output end of the body, the pluralities of passages having sufficiently large diameters to result during operation thereof of only a fraction of a Torr pressure drop to a flow of vapor flowing therethrough. 
     In still an other specific embodiment the invention is an apparatus for chemical vapor deposition onto semiconductor wafers. The apparatus comprises a processing chamber which can be maintained at sub-atmospheric pressure, a platform or susceptor within the chamber for holding a wafer during processing, and a vaporizer head for flowing into the chamber and onto a wafer vaporized precursor compounds for chemical vapor deposition of metal and other films onto the wafer. The head comprises a body having a center axis, an outer surface, input end, and output end, and a length between the ends. The body defines a cavity extending along the center axis with an opening in the input end for receiving a stream of vaporized material. The cavity has a closed well-like bottom end near the output end of the body for collecting droplets and particles of precursor compound and preventing them from leaving the head except as vapor. The body defines a plurality of passages through the head for flow of vaporized material. Each passage having a length and a diameter and extending radially like spokes of a wheel from along and around the cavity at an inclined angle relative to the center axis from the cavity to the outer surface, the plurality of passages having sufficiently large diameters to give pressure drop of a fraction of a Torr to the vaporized precursor compound flowing through them and to provide dispersion of flow through the head such that vaporized precursor compound flows evenly onto a wafer surface. 
     A better understanding of the invention together with a fuller appreciation of its many advantages will best be gained from a study of the following description given in conjunction with the accompanying drawings and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a vaporizer head embodying features of the invention, together with portions (shown schematically) of an apparatus for chemical vapor deposition of materials onto semiconductor wafers; 
     FIG. 2 is a perspective view of the vaporizer head showing the disposition of respective openings and various vapor passages through the head; 
     FIGS. 3A and 3B are sectional views of the vaporizer head taken as indicated in FIG. 2 by the lines  3 A— 3 A and  3 B— 3 B, showing certain dimensional and angular relations of vapor passages through the head; and 
     FIG. 4 is a graph illustrating the relationship of vapor phase versus solid (or liquid) phase of various CVD precursor compounds as a function of pressure and temperature. 
     The drawings are not necessarily to scale. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIG. 1, there is shown an apparatus  10  useful for chemical vapor disposition (CVD) onto semiconductors of various materials in accordance with the present invention. The apparatus  10  comprises a vaporizer head  12  embodying features of the invention and shown in cross-section, a processing chamber  14  (indicated by a dashed-line rectangle), a susceptor (platform)  16 , and a semiconductor wafer  18  positioned on the platform below the head  12 . The chamber  14  is adapted to be maintained at sub-atmospheric pressure during CVD processing of the wafer  18 . During such processing the wafer is heated to an elevated temperature (e.g., about 400° C.) by the platform  16 . The chamber  14  and the platform  16  are well known and are not further described herein. 
     The vaporizer head  12  is hermetically sealed to the top of the chamber  14  by means not shown. The body of the vaporizer head  12  is generally cylindrical and has a center vertical axis  20  which is aligned with a center of the wafer  18 . The head  12  defines a vertical cavity  22 , concentric with the axis  20 , which has a top opening  24  for entrance of vapor, and has a closed well-like bottom end  26 . Radiating outward and angularly downward from the cavity  22  like the spokes of a wheel are a plurality of elongated passages  30 . As will be explained hereinafter, the respective passages  30  are vertically spaced apart and are evenly spaced circumferentially around the center axis  20 . Each passage  30  has a respective input end opening into the cavity  22  as will be further explained shortly, and an output end opening through a tapered side surface  32  of the head  12  and into the processing chamber  14 . Near the bottom end  26  of the cavity  22  are a group of smaller passages  34  which also radiate outward and downward. Each of the passages  34  has an input end opening to the cavity  22  at a location somewhat above the bottom end  26  and an exit opening through a flat bottom surface  36  of the head  12  into the chamber  14 . 
     During operation of the apparatus  10  the vaporizer head  12  is raised to a desired temperature (e.g., about 100° C.) by an electric heater  40 , of a type which is commercially available. A source (not shown) supplies precursor material, as indicated by an arrow  42  to a module  44 . The latter may if necessary apply ultrasonic and/or heat energy to the incoming precursor material to ensure that it is properly vaporized as the vapor enters the input opening  24  of the head  12 , as indicated by the arrows  46 . Such vaporized material then flows down the cavity  22 , into respective ones of the passages  30  and  34 , and into the processor chamber  14 , as indicated by the various arrows  48 . As will be explained in greater detail hereinafter, the vaporizer head  12  is configured so that the combined streams of vapor through the passages  30  and  34  flow evenly into the chamber  14  and uniformly down toward the surface of the wafer  18 . The streams of vapor flowing through the passages  30  and  34  are kept at a desired temperature by heat transferred from the vaporizer head  12 , which advantageously is formed from a solid block of aluminum having good heat conductivity. The cavity  22  and the respective passages  30  and  34  are easily machined into the body of the head  12 . 
     The well-like end  26  at the bottom of the cavity  22  remaining acts to collect any droplets or particles which perchance may be present in the vapor stream  46  entering the input opening  24  of the cavity  22 . Stray liquid or solid material collected in the well-like end  26  is quickly vaporized by heat from the head  12  and thus prevented from entering the chamber  14  except as vapor. 
     Referring now to FIG. 2, there is shown a perspective view of the vaporizer head  12 . Output ends of the passages  30  are shown arranged in three vertically spaced-apart circular rows indicated by respective brackets  50 ,  52 , and  54 . The passages  30  in each of the rows  50 ,  52  and  54  are equally spaced angularly relative to the center axis  20 . In the specific example of the vaporizer head  12  shown, the passages  30  are spaced equally by  45  degree angles around the center axis  20  of the body  12 . Thus there are eight passages in each of the rows  50 ,  52 ,  54  for a total of twenty-four passages  30 . The smaller passages  34  are spaced by 90 degree angles and there are four for a total of twenty-eight passages  30  and  34  together. 
     Referring now to FIG. 3A, there is shown a side cross-sectioned view of the vaporizer head  12  taken through the dashed lines  3 A— 3 A of FIG.  2 . It should be noted that though shown smaller, this sectional view of the head  12  is closely similar to that shown in FIG.  1 . As seen in FIG. 3A, there are visible in this view only two passages  30  in the top row  50  and these passages  30  have respective input ends  30 - 1  opening into the cavity  22  just below the top opening  24 . These passages  30  (and the other passages  30  in this view) are formed in the body of the head  12  relative to the center axis  20  at an angle indicated by an arc  60 . Two additional passages  30  in the top row  50 , not visible in FIG. 3A since displaced by an angle of 90 degrees around the center axis  20  relative to those shown, also have respective input ends  30 - 1  opening into the cavity  22  adjacent its top opening  24 . These unseen passages  30  also lie at the same downward angle  60 . 
     As was mentioned previously in connection with FIG. 2, in the specific embodiment of the invention shown herein, the vaporizer head  12  has eight passages  30  with lower exit ends in the upper row  50  all of which exit ends lie along a single circle around the tapered surface  32  of the head  12 . As was just explained, only four such passages  30  have input ends  30 - 1  opening 90 degrees apart into the cavity  22  near its top opening  24 . 
     Referring now to FIG. 3B, there is shown a sectional view of the head  12  taken through a dashed line  3 B— 3 B of FIG.  2 . FIG. 3B is rotated by 45 degrees relative to FIG.  3 A. As seen in FIG. 3B, the passages  30  (two being visible) in the top row  50  have input ends  30 - 2  opening into the cavity  22  below the ends  30 - 1  (FIG.  3 A); and the passages  30  are formed in the body of the head  12  at an angle indicated by an arc  62 . The latter angle is somewhat larger than the angle  60  so that the ends  30 - 2  lie below the ends  30 - 1 . Two additional passages  30  are not visible in FIG. 3B since these lie at 90 degrees relative to the two passages  30  here visible in the top row  50 , also have ends  30 - 2  opening into the cavity  22 . By making the angle  60  in FIG. 3A slightly different from the angle  62  in FIG. 3B, the respective top ends  30 - 1 ,  30 - 2 ,  30 - 3 ,  30 - 4 ,  30 - 5  and  30 - 6  of the twenty-four passages  30  are interspersed at intervals down along the cavity  22  and around the axis  20 . This provides for efficient dispersal of the vapor flowing into the cavity  22 . The four smaller passages  34 , only two of which are visible in FIG. 3A, are formed at an angle indicated by an arc  64  so that the respective top ends  34 - 1  of the passages  34  lie a small distance above the well-like bottom end  26  of the cavity  22 . 
     Referring now to FIG. 4 there is shown a graph  70  illustrating the relationships of vapor phase to solid phase (or liquid) of CVD precursor compounds as a function of temperature versus pressure. The horizontal axis of the graph  70  indicates temperature in degrees Centigrade (° C.), and the vertical axis indicates pressure in Torr and is non-linear. The graph  70  has a first line  72  along which a precursor material such as tetradimethylaminotitanium (TDMAT) is in vapor phase. When the temperature or pressure moves sufficiently to the left or up in the graph  70  away from the line  72 , the material returns to a solid (or liquid) state. For a given precursor material (e.g., TDMAT), when being used in CVD processing there are conveniently employed an operating value of temperature, and an operating value of pressure, such as indicated at a point  73  on the line  72 . In the case of TDMAT, the temperature at point  73  may be about 50° C. and pressure about one-half TORR. The graph  70  has a second line  74  indicating vapor phase relationship of a second precursor material, namely pentaethylmethylaminotantalum (PEMAT) and a point  75  indicating operating values of temperature and pressure. Similarly, the graph  70  has a line  76  and an operating point  77  for pentadiethylaminotantalum (PDEAT), and a line  78  and an operating point  79  for pentadimethylaminotantalum (PDMAT). 
     It is apparent from the graph  70  that each of the various precursor compounds illustrated, when employed in CVD processing in the apparatus  10 , requires a low chamber pressure. Such material at normal atmospheric temperature and pressure is a solid (or liquid) but it can be made to change phase into vapor at suitably low pressure and elevated temperature. It is delivered, as indicated by the arrows  46 , to the vaporizer head  12  (see FIG. 1) It is desirable therefore in order to prevent the vapor from returning to solid (or liquid) phase in passing through the head  12  that such vapor not be significantly impeded in its flow. Thus, the head  12  should have high-flow-conductance, i.e., the pressure drop through it be small (e.g., a fraction of a Torr). The head  12  should also maintain the vapor at a desired operating temperature (e.g., the temperature at point  73  on the line  72  of the graph  70 ) as the vapor passes within and through the head  12 . The head  12  is easily maintained at a desired temperature by the heater  40 . 
     In the specific embodiment of the invention illustrated herein, the vaporizer head  12  is somewhat bulb-shaped. The diameter of the larger passages  30  through the head is about 0.20 inch and the diameter of the smaller passages  34  is about 0.10 inch. The lengths of the passages  30  and  34  are much longer than their respective diameters. Because the passages  30  and  34  through the head  12  are relatively large, plasma-excited gas can pass through the head  12 . This makes it possible to place a source for plasma excitation above the entrance  24  in the head  12  and outside of the chamber  14 . The diameter of cavity  22  is about one-half inch and it extends down along the axis  20  to near (but not through) the bottom  36  of the head  12 . The diameter of the upper part of the head  12  is about three inches, and its lower part tapers to about 1.5 inch diameter at the bottom  36 . The length of the head  12  from the top entrance  24  to the bottom  36  is about four inches. The angle  60  (FIG. 3A) is about 28°, the angle  64  slightly larger, and the angle  62  (FIG. 3B) about 35°. During CVD processing a flow of vaporized precursor material (e.g., TDMAT) in the range from about 2 to 10 standard cubic centimeters per minute (SCCM) mixed with about 100 to 200 SCCM of argon was passed through the head  12  (maintained at desired temperature) into the chamber  14  where the pressure was a Torr or less (see FIG.  4 ). The temperature of the wafer  18  was about 400° C. and it was positioned about one-half inch from the bottom  36  of the head  12 . The processing cycle lasted several minutes. 
     The above description is intended in illustration and not in limitation of the invention. Various changes or modifications in the vaporizer head  12  embodying features of the invention may occur to those skilled in the art and can be made without departing from the spirit or scope of the invention as set forth herein and as defined by the accompanying claims. For example, the invention is not limited to use with only the precursor materials mentioned but is useful with other CVD precursor materials. Still further, it is not limited to a particular set of dimensions or diameter of a vaporizer head, or to the particular numbers, sizes and angles of the passages  30  and  34 , as described above, or to a particular material or method of manufacture for a vaporizer head.