Semiconductor crystal growth via variable melt rotation

Claim 2

An improvement in an apparatus for growing a semiconductor crystal by the Czochralski method, said apparatus comprising a crucible for containing a molten material from which the semiconductor crystal is grown, a heater for melting said material and maintaining said material in a molten state, and a seed holder for holding a monocrystalline seed and means operable to dip said seed into said molten material and to withdraw said seed from said molten material to thereby grow a crystal of increasing length therefrom, said improvement comprising; rotation means designed for rotating only said molten material at a rotation rate apart from said crucible rotation rate; and means for controlling said rotation means to increase the rotation rate of said molten material as a function of the increasing length of said crystal grown from said molten material.

Claim 3

The improvement as defined in claim 1, further comprising; means for rotating said seed.

Claim 4

The improvement as defined in claim 1, further comprising; means for rotating said crucible.

Claim 5

The improvement as defined in claim 1, further comprising: means for rotating said seed in the opposite direction that said molten material is rotating; and means for rotating said crucible in the same direction that said molten material is rotating.

Claim 6

The improvement as defined in claim 1 wherein said molten material is highly conductive; and wherein said rotating means comprises means for generating a rotating transverse magnetic field in said molten conductive material in said crucible to thereby rotate said material.

Claim 7

The improvement as defined in claim 5, wherein said magnetic field generating means comprises means for generating an n+ phase alternating current at a frequency which varies as a function of the length of said crystal grown from said molten material, where n is at least three; and an n phase magnetic structure surrounding said crucible and connected to receive current from said n phase current generating means for generating said transverse magnetic field in said molten material

Claim 8

The improvement as defined in claim 6, wherein said n phase alternating current generating means comprises means for generating an n phase signal which varies over the frequency range 30-200 Hz.

Claim 9

The improvement as defined in claim 3, further comprising: means for rotating said seed.

Claim 10

The improvement as defined in claim 2, further comprising: means for rotating said crucible.

Claim 11

The improvement as defined in claim 3, further comprising: means for rotating said seed in the opposite direction that said molten material is rotating; and means for rotating said crucible in the same direction that said molten material is rotating

Claim 12

The improvement as defined in claim 6, wherein said n phase magnetic structure includes structure for heating said molten material by radiation/conduction; and wherein said n phase alternating current generating means comprises: a direct current source for generating direct current; means for controlling the power of said direct current generated by said direct current source in accordance with the temperature of said molten material; and means for generating said n phase alternating current from said power-controlled direct current.

Claim 13

The improvement as defined in claim 6, wherein said molten material comprises silicon, and wherein said n phase alternating current generating means comprises means for generating said n phase alternating current with a frequency which varies in accordance with the following equation: Frequency (Hz)=40+(4)×(L-7.5), where L is the length of said crystal in cm.

Claim 14

The improvement as defined in claim 6, further comprising: means for rotating said seed; and means for rotating said crucible.

Claim 15

The improvement as defined in claim 13, wherein said n phase alternating current generating means comprises means for generating an n phase signal which varies over the frequency range 30-200 Hz.

Claim 16

The improvement as defined in claim 14, wherein said n phase alternating current generating means includes means for providing constant electrical power to said n phase magnetic structure.

Claim 17

The improvement as defined in claim 14, wherein said molten material comprises silicon, and wherein said n phase alternating current generating means comprises means for generating said n phase alternating current with a frequency which varies in accordance with the following equation: Frequency (Hz)=40+(4)×(L-7.5), where L is the length of said crystal in cm.

Claim 18

The improvement as defined in claim 6, wherein said n phase alternating current generating means includes means for providing constant electrical power to said n phase magnetic structure.

Claim 19

The improvement as defined in claim 17, wherein said constant power providing means comprises: a source of multi-phase alternating current; and a power controller for rectifying said multi-phase alternating current and controlling the power thereof in accordance with the temperature of said molten material.

Claim 20

An improvement in an apparatus for growing a semiconductor crystal by the Czochralski method, said apparatus comprising a crucible for containing a molten conductive material from which the semiconductor crystal is grown, a heater for melting said material and maintaining said material in a molten state, and a seed holder for holding a monocrystalline seed and means operable to dip said seed into said molten material and to withdraw said seed from said molten material to thereby grow a crystal of increasing length therefrom, said improvement comprising: means for rotating said seed; means for rotatiang said crucible; means for generating an n phase alternating current at a frequency which increases as a function of the length of said crystal grown from said molten material, where n is at least three; an n phase heating sturcture surrounding said crucible and connected to receive said n phase alternating current for inductively heating said molten material and for generating a transverse magnetic field in said molten material to cause it to rotate apart from said crucible rotation rate and at a rate approximately proportional to said frequency; and means for maintaining the temperature of said molten material approximately constant.

Claim 21

An improvement in an apparatus for growing a semiconductor crystal by the Czochralski method, said apparatus comprising a crucible for containing a molten conductive material from which the semiconductor crystal is grown, a heater for melting said material and maintaining said material in a molten state, and a seed holder for holding a monocrystalline seed and means operable to dip said seed into said molten material and to withdraw said seed from said molten material to thereby grow a crystal of increasing length therefrom, said improvement comprising: means for rotating said seed; means for rotatiang said crucible; means for generating an n phase alternating current at a frequency which increases as a function of the length of said crystal grown from said molten material, where n is at least three; an n phase heating sturcture surrounding said crucible and connected to receive said n phase alternating current for inductively heating said molten material and for generating a transverse magnetic field in said molten material to cause it to rotate apart from said crucible rotation rate and at a rate approximately proportional to said frequency; and means for maintaining the temperature of said molten material approximately constant.

Claim 22

The improvement as defined in claim 19, wherein said n phase current generating means comprises means for generating said n phase current with a frequency that varies over the frequency range 30-200 Hz.

Claim 23

The improvement as defined in claim 20, wherein said seed rotating means comprises means for rotating said seed in the opposite direction that said molten material is rotating; and wherein said crucible rotating means comprises means for rotating said crucible in the same direction that said molten material is rotating.

Claim 24

The improvement as defined in claim 21, wherein said temperature maintaining means comprises means for controlling the power of said n phase current generated by said n phase current generating means to maintain the temperature of said molten material approximately constant.

Claim 25

The improvement as defined in claim 22, wherein said n phase alternating current generating means and said temperature control means comprise: a source of multi-phase alternating current; a power controller for rectifying said multi-phase alternating current into direct current and controlling the power thereof in accordance with the temperature of said molten material; and means for generating said n phase alternating current from said power-controlled direct current.

Claim 26

The improvement as defined in claim 23, wherein said molten material comprises silicon, and wherein said n phase alternating current generating means includes means for generating said n phase alternating current with a frequency which varies in accordance with the following equation: Frequency (Hz)=40+(4)×(L-7.5), where L is the length of said crystal in cm.

Claim 27

The improvement as defined in claim 19, wherein said molten material comprises silicon, and wherein said n phase alternating current generating means includes means for generating said n phase alternating current with a frequency which varies in accordance with the following equation: Frequency (Hz)=40+(4)×(L-7.5), where L is the length of said crystal in cm.

Claim 28

An improvement in a method of growing semiconductor crystals by the Czochralski technique wherein a semiconductor seed crystal is dipped into a crucible holding a molten conductive material suitable for semiconductor crystal growth and slowly withdrawn to grow a semiconductor crystal with a length which increases the further the seed crystal is withdrawn, said improvement comprising the steps of: applying a rotating transverse magnetic field to said molten material during the gorwing of said crystal to cause it to rotate apart from said crucible rotation rate; and increasing the rotational velocity of said magnetic field during said crystal growing as a function of the increasing length of said crystal grown from said molten material to thereby vary the rotation rate of said molten material.

Claim 29

An improvement in a method of growing semiconductor crystals by the Czochralski technique wherein a semiconductor seed crystal is dipped into a crucible holding a molten conductive material suitable for semiconductor crystal growth and slowly withdrawn to grow a semiconductor crystal with a length which increases the further the seed crystal is withdrawn, said improvement comprising the steps of: applying a rotating transverse magnetic field to said molten material during the gorwing of said crystal to cause it to rotate apart from said crucible rotation rate; and increasing the rotational velocity of said magnetic field during said crystal growing as a function of the increasing length of said crystal grown from said molten material to thereby vary the rotation rate of said molten material.

Claim 30

The method as defined in claim 26, further comprising the step of rotating said seed crystal.

Claim 31

The method as defined in claim 26, further comprising the step of rotating said crucible.

Claim 32

The method as defined in claim 26, further comprising the steps of: rotating said seed crystal in the opposite direction that said molten material is rotating; and rotating said crucible in the same direction that said molten material is rotating.

Claim 33

The method as defined in claim 26, further comprising the step of maintaining the temperature in said molten material approximately constant.

Claim 34

The method as defined in claim 30, wherein said magnetic field applying step comprises the steps of: generating an n phase alternating current at a frequency which varies as a function of the length of said crystal grown from said molten material, where n is at least three; applying said n phase current to an n phase magnetic structure surrounding said crucible for generating said transverse magnetic field in said molten material.

Claim 35

The method as defined in claim 31, wherein said n phase current generating step comprises the step of generating said n phase current with a frequency that varies over the frequency range 30-200 Hz.

Claim 36

The method as defined in claim 31, further comprising the step of rotating said crucible.

Claim 37

The method as defined in claim 31, further comprising the step of: rotating said seed crystal; and rotating said crucible.

Claim 38

The method as defined in claim 31, wherein said molten material is silicon, and wherein said n phase current generating step comprises the step of generating said n phase alternating current at a frequency which varies in accordance with the following equation: Frequency=40+(4)×(L-7.5), where L is the length of said crystal in cm.

Claim 39

The method as defined in claim 31, further comprising the steps of: rotating said seed crystal in the opposite direction that said molten material is rotating; and rotating said crucible in the same direction that said molten material is rotating.

Claim 40

The method as defined in claim 36, wherein said n phase current generating step comprises the step of generating said n phase current to vary over the frequency range 30-200 Hz.

Claim 41

The method as defined in claim 36, wherein said molten material is silicon, and wherein said n phase current generating step comprises the step of generating said n phase alternating current at a frequency which varies in accordance with the following equation: Frequency=40+(4)×(L-7.5), where L is the length of said crystal in cm.

Claim 42

The method as defined in claim 31, wherein said n phase current applying step comprises the step of heating said crucible by induction by means of the n phase current applied to said n phase magnetic structure; and wherein said n phase current generating step comprises the steps of: generating a direct current; controlling the power of said direct current in accordance with the temperature of said molten material to maintain said temperature constant; and generating said n phase alternating current from said power-controlled direct current.

Claim 43

The method as defined in claim 39, wherein said direct current generating step and said power controlling step comprise the steps of: obtaining a multi-phase alternatIng current; and rectifying said multi-phase alternating current and controlling the power thereof in accordance with the temperature in said molten material.

Claim 44

An improvement in a method for growing semiconductor crystals by the Czochralski method wherein a semiconductor seed crystal is dipped in a crucible holding a conductive molten material suitable for semiconductor crystal growth and slowly withdrawn to grow a semiconductor crystal with a length which increases the further the seed crystal is withdrawn, said improvement comprising the steps of: rotating said seed crystals; rotating said crucibel; generating an n phase alternating current at a frequency which increases as a function of the length of said crystal grown from said molten material, where n is at least three; applying said n phase current to an n phase magnetic heating sturcture surrounding said crucible for heating said molten material and for generating a transverse magnetic field in said molten material to cause it to rotate apart from said crucible rotation rate; while maintaining the temperature of said molten material approximately constant.

Claim 45

An improvement in a method for growing semiconductor crystals by the Czochralski method wherein a semiconductor seed crystal is dipped in a crucible holding a conductive molten material suitable for semiconductor crystal growth and slowly withdrawn to grow a semiconductor crystal with a length which increases the further the seed crystal is withdrawn, said improvement comprising the steps of: rotating said seed crystals; rotating said crucibel; generating an n phase alternating current at a frequency which increases as a function of the length of said crystal grown from said molten material, where n is at least three; applying said n phase current to an n phase magnetic heating sturcture surrounding said crucible for heating said molten material and for generating a transverse magnetic field in said molten material to cause it to rotate apart from said crucible rotation rate; while maintaining the temperature of said molten material approximately constant.

Claim 46

The method as defined in claim 41, wherein said n phase current generating step comprises the step of generating said n phase current with a frequency that varies over the frequency range 30-200 Hz.

Claim 47

The method as defined in claim 42, wherein said seed crystal rotating step comprises the step of rotating said seed crystal in the opposite direction that said molten material is rotating; and wherein said crucible rotating step comprises the step of rotating said crucible in the same direction that said molten material is rotating.

Claim 48

The method as defined in claim 43, wherein said temperature maintaining step comprises the step of controlling the power of said n phase current to maintain the temperature of said molten material approximately constant.

Claim 49

The method as defined in claim 44, wherein said power controlling step comprises the steps of: generating a direct current; simultaneously controlling the power of said direct current generated in said direct current generating step in accordance with the temperature of said molten material to maintain said temperature constant; and generating said n phase alternating current from said power-controlled direct current.

Claim 50

The method as defined in claim 44, wherein said molten material is silicon, and wherein said n phase current generating step comprises the step of generating said n phase alternating current at a frequency which varies in accordance with the following equation: Frequency (Hz)=40+(4)×(L-7.5), where L is the length of said crystal in cm.

Claim 51

The method as defined in claim 41, wherein said temperature maintaining step comprises the steps of: generating a direct current; simultaneously controlling the power of said direct current generated in said direct current generating step in accordance with the temperature of said molten material to maintain said temperature constant; and generating said n phase alternating current from said power-controlled direct current.

Claim 52

The method as defined in claim 47, wherein said molten material is silicon, and wherein said n phase current generating step comprises the step of generating said n phase alternating current at a frequency which varies in accordance with the following equation: Frequency (Hz)=40+(4)×(L-7.5), where L is the length of said crystal in cm.