United States Patent
`
`[19]
`
`Gat
`
`4,331,485
`[11]
`[45] May 25, 1982
`
`
`
`[54] METHOD FOR HEAT TREATING
`SEMICONDUCTOR MATERIAL USING
`HIGH INTENSITY CW LAMPS
`
`[76]
`
`Inventor: Arnon Gat, 1875 Newell Rd., Palo
`Alto, Calif. 94303
`
`[21] Appl. No.: 126,458
`
`[22] Filed:
`
`Mar. 3, 1980
`
`Int. 01.3 .................. .. H01L 21/26; H01L 21/265
`[51]
`[52] US. Cl. ...........
`...................... .. 148/15; 148/187;
`357/91; 427/531; 427/55
`[58] Field of Search ................. .. 148/15, 187; 357/91;
`1
`427/451, 53.1, 55
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`'
`4,115,163
`9/1978 Gorina .............................. .. 148/175
`
`4,151,008 4/ 1979 Kirkpatrick . . . . .
`. . . .. 148/ l .5
`4,169,740 10/1979 Kalbitzer et a1.
`.................. .. 148/ 1 .5
`
`OTHER PUBLICATIONS
`
`Cohen et 211., Appl. Phys. Letts., 33 (Oct. 1978), 751.
`Celler et al., J. Appl. Phys., 50 (1979), 7264.
`
`Bomke et al., Appl. Phys. Letts., 33 (1978), 955.
`E G & G Data Sheet, F1008 C—4, DC Krypton Arc
`Discharge Tube.
`Van Gutfeld, IBM Tech. Discl. Bulletin, 19 (1977),
`3955.
`
`Gat et al., Appl. Phys. Letts. 33 (1978), 389.
`
`Primary Examinere—Upendra Roy
`Attorney, Agent, or Firm—Flehr, Hohbach, Test,
`Albritton & Herbert
`
`ABSTRACT
`[57]
`Apparatus for annealing semiconductor wafers includes
`a support for receiving the wafers and resistive heaters
`for heating the wafers by thermal conduction through
`the support or by convection. A high intensity are lamp
`scans the heated wafers thereby raising the temperature
`sufficiently for heat treating. The process is simple,
`rapid, efficient, and does not create damaging thermal
`stresses in the wafers. The high temperature and short
`time treatment enables material properties unobtainable
`with conventional thermal processes.
`
`6 Claims, 3 Drawing Figures
`
`
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`- * — — AS IMPLANTED
`o e o e LAMP ANNEALED
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`ARSENICCONCENTRATIONATOMxcm3
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`DEPTH (3]
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`Page 1 of 5
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`Samsung Exhibit 1012
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`Page 1 of 5
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`Samsung Exhibit 1012
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`

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`Sheet 1 of2
`Patent May 25, 1982
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`Page 2 of 5
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`Page 2 of 5
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`

`

`U.S. Patent May 25, 1982
`
`Sheet 2 of 2
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`4,331,485
`
`low
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`---*-ASIMPLANTED
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`0 o o o LAMP ANNEALED
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`Page 3 0f 5
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`Page 3 of 5
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`1
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`4,331,485
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`2
`recrystallize. All the apparatus has to be in vacuum to
`inhibit the oxidation of the hot filament. Because of the
`vacuum no preheating of the material is proposed and
`therefore the large gradient between the molten surface
`‘of- the substrate may include strain and stress in the
`material.
`
`Accordingly, an object of the present invention is an
`improved method of heat treating semiconductor mate-
`rial.
`
`Another object of the invention is apparatus for
`quickly annealing doped and undoped semiconductor
`material.
`Still another object of the invention is apparatus
`which is relatively simple and inexpensive and which
`requires little space in a semiconductor manufacturing
`facility.
`Briefly, in accordance with the invention a support is
`provided for holding a semiconductor wafer for heat
`treatment. The support includes heater means for heat-
`ing the wafer to an elevated temperature below the
`temperature for heat treatment and below a tempera-
`ture which causes migration of dopant atoms in the
`semiconductor lattice structure. A high intensity inco-
`herent CW light source is positionable with respect to
`the support for irradiation of a semiconductor body
`held on the support. Means can be provided for varying
`the spacing between the light source and the support,
`and means is provided for effecting relative motion
`between the light source and the support whereby the
`surface of the wafer can be scanned by the light source.
`Means is provided to control the light intensity by vary-
`ing the current through the lamp.
`Preferably, the high intensity light source comprises a
`CW arc discharge tube of sufficient length to scan the
`entire width of a semiconductor body. The support
`preferably includes a vacuum chuck for holding a semi-
`conductor wafer, and resistive heater means are embed-
`ded in the support for heating of the wafer by thermal
`conduction through the support.
`In another embodiment of the invention, the substrate
`is placed'on isolated pins but close to the heater surface.
`The semiconductor material
`is heated to the heater
`temperature. When the lamp is scanning, the wafer is far
`enough from the heater so that its temperature can rise
`quickly and independently of the chuck temperature
`throughout because of heat conduction. This reduces
`thermal gradients and facilitates the increase in temper-
`ature for a given light intensity.
`In annealing a semiconductor wafer and the like, the
`high intensity light source is scanned across the surface
`of the wafer at a speed determined by the spacing be—
`tween the light source and wafer and by the particular
`temperature desired for annealing the semiconductor
`material and the preheated temperature of the wafer.
`Thus, a semiconductor wafer can be annealed in a mat-
`ter of seconds thereby increasing the throughput of
`annealed semiconductor material and without introduc—
`
`ing residual stresses in the annealed wafer and without
`causing dopant migration. Moreover, polycrystalline
`silicon is readily recrystallized with increased crystal
`Size.
`
`The invention and objects and features thereof will be
`more readily apparent from the following, detailed de-
`scription and appended claims when taken with the
`drawing, in which:
`i
`'
`FIG. 1 is a perspective view of one embodiment of
`apparatus in accordance with the invention.
`
`METHOD FOR HEAT TREATING
`SEMICONDUCTOR MATERIAL USING HIGH
`INTENSITY CW LAMPS
`
`‘
`
`This invention relates generally to semiconductor
`technology, and more particularly the invention relates
`to heat treating of semiconductor wafers.
`'
`Electronic devices are formed in a single crystal semi-
`conductor wafers by the selective introduction of dop-
`ant atoms into the lattice structure of the semiconductor
`material. Group III elements of the periodic table, such
`as boron and gallium, when diffused or implanted into
`the semiconductor lattice structure render the semicon-
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`ductor material P type since these elements are accept-
`ers of electrons in the atomic valence bands of the ele-
`ments. Group V elements of the period table, such as
`phosphorous and arsenic, when introduced into the
`semiconductor lattice structure render the semiconduc-
`tor material N type since the elements are donors of 20
`electrons from the valence bands of the atoms.
`. The dopant atoms can be introduced into the semi-
`conductor material by diffusion from a dopant atmo-
`sphere in a diffusion furnace or by ion implantation in
`which charged dopant ions are driven into the semicon-
`ductor material by a particle accelerator. Particularly in
`ion implanted semiconductor material
`lattice defects
`result and require thermal annealing to properly orient
`the dopant atoms in the lattice structure.
`‘
`Additionally, polycrystalline silicon is heat treated by
`a furnace or by laser scanning and the like to increase
`crystal grain size and also to activate dopants in the
`polysilicon.
`.
`Heretofore, thermal annealing of semiconductOr ma
`terial has been effected in a furnace with temperature
`cycled to 700° C.—1100° C. to effect activation of the
`implanted ions in the semiconductor lattice or to in-
`crease grain size in polycrystalline material. This proce-
`dure is time consuming and results in a diffusion or
`migration of the dopant atoms with decreasing perfor—
`mance of the semiconductor product.
`More recently, laser annealing has been introduced.
`Laser annealing allows nearly instantaneous heating and
`cooling of the semiconductor material with reduced
`dopant ion migration within the semiconductor lattice
`structure. However, because of the small‘beam of the
`laser, considerable time is necessary for the total scan-
`ning of the semiconductor wafer. Moreover,
`laser
`equipment is expensive and very inefficient in power
`usage- Further,
`laser annealing equipment as well as
`annealing furnaces require considerable space in the
`clean room atmosphere of a semiconductbr production
`area.‘
`1-
`_
`v
`' Thermally assisted flash annealing using high inten-
`‘sity xenon flash lamps has been proposed. However, the
`short pulses of incoherent light induce a very short
`temperature rise in the material. To observe any anneal-
`ing effect, the sample must be heated considerably (ap—
`proximately 600" C.). Also since the energy discharged
`into the lamp is limited, only very small‘areas (e.g.
`1
`cm X 1 cm) Can be annealed. The resultant material was
`reported to contain‘defects in a concentration thatindi-
`cates incomplete annealing. Hotfilament ribbons‘have
`been proposed. This scheme is intended to be used for
`the productions. of siliconwhich .is deposited on a sub-
`strate for solar cell usage.:ln this application it is in-
`tended to melt the amorphous silicon with a hot tung-
`sten filament and let this molten silicon cool down and
`
`Page 4 of 5
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`Page 4 of 5
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`

`4,331,485
`
`:3
`FIG. 2 is a perspective View .of another embodiment
`of, apparatus in accordance with the invention.
`FIG. 3 is a plot of dopant concentration of three
`wafers as implanted after conventional thermal anneal-
`ing and after processing in accordance with the present
`invention.
`‘
`'
`"
`'
`'
`In the drawing, a semiconductor wafer to be annealed
`is placed on a support pedestal 8 within housing 10 and
`positioned by means of a chuck 12 through a vacuum
`line 14. The support 8 is a heat conductive material such
`as brass with a graphite top plate'in which a plurality of
`resistive heaters 16 are provided with the resistive heat-
`ers interconnected with an electrical power source
`through lines 18. In one embodiment the resistive heat-
`ers are CalRods and a sufficient number of heaters are
`provided whereby the support 8 and a wafer maintained
`on vacuum chuck 12 can be heated to 500° C. The
`support 8 is vertically moveable by means of lead
`screws 20 which are driven by suitable motor driven
`gear train shown generally at 22. Alternatively, support
`8 can be made stationary.
`I
`Mounted within housing 10 above pedestal 8 is ther-
`mal radiation apparatus 30 including a radiant heater 32.
`A concave surface 34 reflects radiant energy down-
`wardly onto the semiconductor body. In a preferred
`embodiment the radiant heater comprises a CW arc
`discharge tube such as the dc crypton arc discharge
`tube FK-l l 1C-3 available from EG & G. The tube 32 is
`of sufficient length to irradiate the entire surface of a
`semiconductor wafer on a vacuum chuck 12 in a single
`scan.
`
`The radiant heater apparatus 30 is moveably mounted
`on a pair of horizontal rails 36 and is driven by means of
`motor 38 and lead screw 40. Thus, the radiant heater 30
`can be moved from one side of the housing assembly 10
`to the other side to thereby scan a wafer on pedestal~8.
`Alternatively, the radiant heater 30 can be fixed and the
`support 8 moved along rails.
`In annealing a semiconductor wafer in accordance
`with the present
`invention, the current through the
`radiant heater 32 is selected along with the linear speed
`of heater assembly 30 whereby the surface of the semi-
`conductor wafer is heated to sufficient temperature for
`annealing. Normally,
`the annealing temperature for
`silicon semiconductor material will be in the range of
`1200°—1400° C. In some applications higher tempera-
`tures and melting can be achieved. Importantly, by
`preheating the semiconductor wafer 12 to a tempera—
`ture of about 500° C. by means of the resistive heaters
`16, excessive thermal stresses in the semiconductor
`wafer are avoided since the temperature rise provided
`by the radiant heater 30 need be only 700°—900° C.
`In the embodiment of FIG. 2, a semiconductor wafer
`50 is supported on ‘a plurality of thermally insulating
`,ceramic posts 52 above theyacuum chuck 54. By re-
`versing the air flow in the chuck, uniform heating of the
`wafer is facilitated by convection heating. In some cases
`convection heating is sufficient and reverse air flow is
`not necessary. Thus, as the lamp is scanned across the
`wafer surface, temperature can increase thrOughout the
`thickness of the wafer and temperature gradients in the
`wafer are minimized.
`'
`FIG. 3 is a plot of dopant concentrations in three
`identicalwafers two of which were annealed by con-
`ventional thermal processing and by the scanning pro-
`cess in accordance with the present
`invention. The
`dopant profile 60 for the conventionally processed
`wafer shows considerable dopant migration during an-
`nealing as compared to the dopantzprofile 62 for the
`scanned .wafer. This profile '62 is identical :to the as
`implanted profile 61 meaning that annealing with the
`
`Page 5 of 5
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`4
`present invention does not alter the dopant concentra-
`tion profile. Priorjto’ annealing all' wafers had sheet
`resistivity of 3100 0th per square. After Conventional
`annealing, one wafer had sheet resistivity of 150 ohms
`per square, while the scanned wafer had sheet resistivity
`of 168 ohms per square. The difference stems from the
`fact that the thermal annealing profile is more diffused
`and has slightly higher average mobility. In both cases
`all the dopants are active and contribute to the electrical
`conductivity of the crystal.
`The annealing or heat treating of semiconductor wa-
`fers using the apparatus and method in accordance with
`the present invention has proved to be advantageous in
`initial cost of the equipment, limited space required in
`the semiconductor manufaéturing facility, and semicon-
`ductor material
`throughput. Also, steeper and shal—
`lower
`junctions are achieved meaning potentially
`smaller and faster devices. Also since achievable scan-
`ning temperature ranges are higher than furnace tem—
`peratures larger poly grain can be grown with the
`above method. By preheating the semiconductor wafer
`through the support pedestal prior to the radiation beam
`scanning, deleterious thermal stresses within the semi—
`conductor wafer are avoided and the light intensity
`needed to raise the semiconductor temperature is re-
`duced considerably. The resulting annealed wafers are
`high quality. The invention has heat treating applica-
`tions other than annealing and including polycrystalline
`semiconductor regrowth to increase crystal grain size,
`aluminum sintering and grain growth, phosphorous
`glass reflow and the like.
`Thus, while the invention has been described with
`reference to a specific embodiment, the description is
`illustrative of the invention and is not to be construed as
`limiting the invention. Various modifications and appli-
`cations may occur to those skilled in the art without
`departing from the true spirit and scope of the invention
`as defined by the appended claims.
`What is claimed is:
`1. A method of heat treating a semiconductor body at
`a high temperature for a short duration comprising the
`steps of
`preheating said semiconductor body to a first temper-
`ature, and
`-
`radiating a surface of said semiconductor body with a
`high intensity CW lamp thereby rapidly heating
`said radiated surface to a' second temperature
`higher than said first temperature for a short dura-
`tion of time.
`-
`V
`v
`2. The method as defined by claim 1 and further
`including the step of adjusting the spacing between said
`semiconductor body and said lamp and the scan speed
`whereby said semiconductor body is heated to a prese-
`lected temperature by said lamp.
`.
`3. The method as defined by claim 1 and further
`including the step of adjusting the power to said lamp
`whereby said semiconductorbody is heated to a prese—
`lected temperature by said scanned light source.
`4. The method as defined by claim 1 wherein the step
`of preheating said semiconductor body includes mount-
`ing said semiconductor body on a support and heating
`said support.
`.
`5. The method as defined, by claim 1 wherein the step
`of preheating said semiconductor body includes posi-
`tioning said body in spaced relationship with respect to
`a top surface of a support pedestal whereby said body is
`heated by convection.
`6. The method as defined by claim 1 wherein said step
`of radiating a surface includes scanning said surface
`with said lamp.
`'
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`Page 5 of 5
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