I 2
METHOD FOR EPITAXIALLY GROWING THIN FILMS means is provided to vaporize the mercury for introduction at
v,.-, ,„„,.,„. ~ „„ ,„,« ,„» ^ the upstream end of the reaction chamber. Individually con
BACKGROUND OF THE INVENTION trolla^le heatmg means fa provjded at ... region/along
The present invention relates to the formation of semicon- tne reaction chamber for volatilizing source materials of cad
ductor bodies by vapor deposition and particularly to a ^ mium, and tellurium, and in the region surrounding the growth
method and apparatus for epitaxially vapor growing thin film site. Cooling means at the growth site is used to control the
materials of mercury, cadmium, and tellurium. temperature of a vapor growing substrate and in combination
with the heating means establishes a sharp temperature
DESCRIPTION OF THE PRIOR ART gradient in the vicinity of the substrate to provide rapid coolIn prior processes for producing crystalline film materials ln&
from vapors of the elements and compounds of mercury, cad- The foregoing and other objects, features and advantages of mium and tellurium, as well as other II-VI elements, it was the invention will be apparent from the following more parthought that the presence of other vapor reactants were ticular description of preferred embodiments of the invention, required to obtain growth and stoichiometric ratio control. In 15 as illustrated in the accompanying drawings, such processes it was common to include halogen or halogen BR,EF DESCRIPTION OF THE DRAWINGS compound vapors which produced a chemical disproportiona
tion reaction and which acted as a transport agent for the FIG. 1 is a cross-sectional view of an apparatus for epitaxi
vapor phase reactants to the growth site on a seed crystal or ally growing thin films in accordance with the present inven
substrate. In such processes, the transport agent vapor con- 20 tion;
densed to some degree with the principal reactants. This FIG. 2 is a cross-sectional view of a portion of the deposi
tended to contaminate the end product film resulting in loss of tion site mechanism showing the means for cooling a deposi
purity and prevented the production of films having precise tion substrate;
stoichiometric ratios. FIG. 3 is an isometric view of the cooling cap of FIG. 2,
25 showing the detail structure for using thermocouple tempera
SUMMARY OF THE INVENTION ture measurement;
The broad object of the present invention is to provide an FK>. 4 is an isometric view of the cooling probe of FIG. 2; improved process for expitaxially growing films from vapors of FI(3- 5 is a graph showing the operational conditions for elements and compounds of materials in the H-VI valence epitaxially growing films according to this invention; and groups. FIG. 6 is a three-dimensional graph for showing the operaIt is a specific object to provide a process for epitaxially tional conditions for the practice of the present invention.
growing thin film crystals having the formula Hg,llx,Cd(x)Te INSCRIPTION OF THF PRFFFRRFD FMRODIMFNTS
where x is greater than zero and less than 1, and which has DESCRIPTION OF THE PREFERRED EMBODIMENTS
greater purity and homogeneity. 35 Referring to FIGS. 1-4, a film growing apparatus comprises
It is a further specific object to provide a process for grow- a cyiindrical quartz reaction chamber 10 closed at one end by
ing monocrystallme epitaxial films of very precise a transparent quartz wall 11 fused to the inner wall of chamber
stoichiometric ratio from vapors of mercury, cadmium, and ,0 The other end of fte chamber 10 is inwardly tapered to
tellurium elements or compounds receive a ^ st 12 outwardly tapered to coact with
The above, as well as other objects of th,s invents are 4Q thechamber to produce an airtight taper joint 13. The stopper
readily achieved by vaporizing the film producing reactant u has a ho,,ow mward, extendi f ,4 to which is „.
materials in predetermined stoichiometric quant.ties m a ... a cyiindricai cap 15. A substrate crystal 16 is
chamber devoid of any other reactants. In the specific system he)d fa Qn
for making epitaxial films having ternary combinations of mer- ... * ^ u an inf , rt J ,£ Wmle » „, Fone
cury, cadmium, and tellurium, the mercury vapor, in addition Ac .. ,_. , ..... , .. „ ..
/ . , • • f u ji j r-. i 45 clip 17 is shown, additional clips as well as other means may
to being a combining reactant of the end product film, also , F ., , ... . . . .. . '.
6 , 6 . *" ., , be provided, if necessary, to insure good thermal contact of
serves as the transport agent. In carrying out the process, the .. , ^ • , *, , j. L j r
vapors of mercury, cadmium, and tellurium arc mixed in a th* s"bst[f 16 *>* <*P /f totennedmte the ends of
reaction chamber and maintained in the vapor phase at tem- chambe; ,10 are P°rts *8 and " ^'ch are «>nn^d to form
peratures which effectively prevent preferential binary com- 50 a. d°S<.ed lo°,P, Wlth C^amber '?' When sto.pper,.1u !' u ...
binations. This mixture is then rapidly cooled proximate the tlon- fi"8elu14 e*tends inwardlv to a position slightly beyond
growth site to the point of supersaturation causing a ternary Port 18' The chamber ls evacuated by means of suitable
reaction to occur whereby the film grown has the same vacuun? svstem 21 connected through pipe 22 opened and
stoichiometric ratio established by the composition ratio in closed by valve 23.
the vapor phase. By eliminating the halogens or other dispro- 55 The ^f'10". chamber 10 is designed to have separately
portionation reactant vapors, and by using the vapor of one of controlled heating zones A, B, and C, and these are provided
the constituent reactants, namely mercury, as the carrier, by sultable induction windings 24, 25, and 26 connected to
epitaxial films were obtained having superior intrinsic proper- suitable regulated power supplies 27,28, and 29, respectively,
ties. Preferably, the process is carried out dynamically. This is A fourth heatln8 means comprises induction coil 30 wound on
done by flowing mercury vapors through successive zones of 60 conduit 20 proximate inlet port 19 and connected to a
an evacuated chamber where vaporization of the other reac- separate regulated power supply 31.
tants occurs and to the deposition site. Mercury is vaporized Means for temperature regulating the substrate 16 com
from a liquid source and excess mercury is condensed ad- Prises metallic cylindrical heat sink 32 located within the hol
jacent the condensation reaction region and returned to the low core of finger 14 and means for supplying cooling air
liquid source. 65 thereto which comprises a hollow metal probe 33 connected
The mercury recycling and redistribution acts to dynami- by P'Pe 34 '° an air coolant source 35. The probe 33 and pipe
cally flow the mercury through the reaction chamber causing 34 are designed to be readily removable from finger 14 in
the reactant mixture to move more rapidly through the mixing order that stopper 12 may be removed from chamber 10 in
and cooling zones to the growth site. preparation for the vapor growth operation. As best seen in
To achieve this dynamic system for epitaxially growing Hg 70 FIGS. 2 and 4, the heat sink 32, when in position at the far end
Cd Te film, the furnace apparatus is equipped with a separate of finger 14, makes surface contact with the probe finger 14
recirculating conduit connected to opposite ends of the reac- and through cap IS to substrate 16. The cooling probe 32 has
tion chamber where vapor generation, mixing and film grow- a conical point 36 with plural apertures 37, When in position,
ing take place in a multitemperature zone. A supply of mercu- the point of cylinder 36 makes contact with the inside of heat
ry is provided in liquid form in the return conduit. Heating 75 sink 32, and when heat sink 32 is made preferably of silver, the
