JP2003504295A - Edge meniscus control for crystal ribbon growth - Google Patents

Abstract

An apparatus for growing a crystal ribbon includes a crucible holding a melt of semiconductor material, a pair of strings passing through a pair of openings provided in the crucible, and a meniscus controller. A pair of strings define the edges of the crystal ribbon grown from the melt. The crystal ribbon and the upper surface of the melt form a meniscus. The meniscus controller controls the properties of the meniscus near the edges of the crystal ribbon. A method of growing a crystal ribbon includes providing a melt of a semiconductor material in a crucible, placing a seed crystal of the semiconductor material in the melt, and passing through a pair of openings provided in the crucible. Solidifying the melt to form a crystal ribbon by pulling a seed crystal from the melt between the pair of strings, and controlling the properties of the meniscus near the edges of the crystal ribbon using a meniscus controller Steps.

Description

Detailed Description of the Invention

Government Assistance The work described herein was supported by Federal Grant No. ZAX-8-17647-07 awarded by the Department of Energy. The government has certain rights in this invention.

FIELD OF THE INVENTION The present invention relates generally to crystal growth, and more particularly to ribbon crystal growth.

BACKGROUND OF THE INVENTION In order to produce low cost solar cells, and thus to exploit large-scale electrical applications of solar electricity, low cost substrate materials for making solar cells have been developed. It is important to have. The preferred method for obtaining crystalline silicon in this case is U.S. Pat. Nos. 4,661,200; 4,627,887; 4,689,10.
9 and 4,594,229 through the growth of silicon ribbons in a continuous process.

Continuous silicon ribbons are formed in this case by introducing two strings of high temperature material through a crucible containing a shallow layer of molten silicon. The strings anchor the edges of the growing ribbon and the molten silicon solidifies just above the molten layer into a solid ribbon. The molten layer that forms between the string and the growing ribbon is defined by the molten silicon meniscus. The height of the meniscus assumed to contact the infinite vertical plane of silicon is about 7 mm along the width of the ribbon. At the edge of the ribbon, the radius of curvature of the edge itself causes the meniscus to have a locally significantly lower height, often shrinking the meniscus to less than 5% of its height in the middle of the ribbon. Since there is a thermal gradient due to the melt at the growth interface, the reduced meniscus height at the ribbon edge causes more heat to be transferred to the growth interface, resulting in ribbons with significantly thinner edges than in the middle. Become. These thin edges can reduce the yield in making solar cells on silicon ribbon substrates. This is because the edge is weak and a crack that propagates throughout the substrate can be generated.

Further, the low meniscus at the edge of the ribbon causes the crystal growth interface to dent downwards. The downwardly depressed growth interface results in the nucleation of many high angle grain boundaries at the edges of the ribbon, which in turn tend to grow a few millimeters towards the middle of the ribbon. These high angle grain boundaries can contain defects that can reduce the efficiency of the solar cell.

Means for controlling the height of the meniscus at the edge of the growing crystal ribbon are therefore very useful in solving these problems. The following invention describes such a technique.

SUMMARY OF THE INVENTION The present invention features systems and methods in which the height of the meniscus at the edge of a crystal ribbon grown in a continuously performed process can be varied and controlled. This can be accomplished with a specially shaped structure that wets the melt and is located near the growth ribbon edge. Control of the meniscus at the edge of the ribbon can then be influenced by the specific design and placement of the structure. Specifically, the meniscus at the edge may be higher, lower, or flush with the meniscus along the width of the growth ribbon.

Moreover, these structures may also have thermal properties, such as thermal conductivity and thermal emissivity, that allow them to lose heat faster than the surrounding melt. By losing heat faster, these structures can make the ribbon thicker. The combined effect of heat loss and modified meniscus height is to control the edge thickness of the growing ribbon regardless of the thickness of the middle portion of the ribbon. The height of the meniscus along the width of the ribbon defines the shape of the crystal growth interface. The effect of changing the height of the edge meniscus with respect to the height of the meniscus in the middle portion of the ribbon is that the shape of the crystal growth interface can be controlled. By making this interface downwardly convex, the growth direction is almost downward and slightly toward the edge. This significantly reduces the effects of small, high-angle grain boundaries, where large crystal grains grown in the middle of the ribbon propagate toward the edge and are nucleated near the edge.

In one aspect, the invention features an apparatus for growing a crystal ribbon. The device includes a crucible, a pair of strings, and a meniscus controller. The crucible holds a melt of semiconductor material. The crucible has a pair of openings through which a pair of strings pass. This pair of strings defines the edges of the crystal ribbon grown from the melt. The crystal ribbon and the upper surface of the melt form a meniscus. A meniscus controller controls the characteristics of the meniscus near the edges of the crystal ribbon.

In some embodiments, the meniscus controller is a structural member located in the crucible adjacent to at least one of the strings. For example, the structural member may include at least one pin or a generally cylindrical tube. In another embodiment,
The structural member may be oriented substantially perpendicular to the plane of the melt. In another example, the pair of strings includes a first string and a second string,
The structural member includes a first structural member and a second structural member disposed adjacent to the first string.
A second structural member disposed adjacent to the string of. In yet another embodiment, the structural member and the top surface of the melt form a meniscus that affects the shape and height of the meniscus near the edges of the crystal ribbon. In another embodiment, the meniscus controller includes a crucible wall.

In some embodiments, the meniscus controller provides a substantially flat growth interface. Alternatively, the meniscus controller provides a substantially convex growth interface. In another embodiment, the meniscus controller controls the thickness of the crystal ribbon. For example, a meniscus controller can provide a crystal ribbon with a uniform thickness. In yet another embodiment, the meniscus controller is
Increase the height of the meniscus near the edge of the crystal ribbon.

In another aspect, the invention features an apparatus for growing a crystal ribbon. The apparatus includes a crucible for holding a melt of semiconductor material, a pair of strings passing through a pair of openings in the crucible, and a structural member disposed in the crucible adjacent at least one of the strings. Including and A pair of strings defines the edges of the crystal ribbon grown from the melt. The crystal ribbon and the upper surface of the melt form a meniscus. Structural members located in the crucible near at least one of the strings raise the meniscus height near the edges of the crystal ribbon.

In yet another aspect, the invention features a method of growing a crystal ribbon. A melt of semiconductor material is provided in a crucible. A seed crystal of semiconductor material is placed in the melt. The melt is solidified by pulling the seed crystal from the melt between the pair of strings passing through the pair of openings in the crucible to form a crystal ribbon. The crystal ribbon and the upper surface of the melt form a meniscus.
A meniscus controller controls the characteristics of the meniscus near the edges of the crystal ribbon.

In some embodiments, the meniscus properties are controlled with a structural member disposed in the melt adjacent at least one of the pair of strings. For example, the structural member can be at least one pin or a generally cylindrical tube. In another embodiment, the meniscus properties are controlled using the crucible wall.

In some embodiments, the height of the meniscus at the edge of the ribbon can be controlled. For example, the meniscus height at the ribbon edge can be controlled independently of the meniscus height at the middle portion of the ribbon. By varying the height of the meniscus at the edge of the ribbon relative to the height of the meniscus at the middle portion of the ribbon, the growth interface can be concave, flat, or convex. In another embodiment, the thickness at the edge of the ribbon can be controlled. For example, the thickness at the edges of the ribbon can be less than, the same as, or greater than the thickness at the middle portion of the ribbon.

In yet another embodiment, the invention features a method of growing a crystal ribbon. A melt of semiconductor material is provided in a crucible. Structural members are provided in the crucible adjacent to at least one of the pair of strings passing through the pair of openings in the crucible. A seed crystal is pulled from the melt between a pair of strings. The melt solidifies to form a crystal ribbon. The crystal ribbon and the upper surface of the melt form a meniscus. The height of the meniscus near the edge of the crystal ribbon is increased.

The above, and other objects, features, and advantages of the invention, as well as the invention itself,
A better understanding will be obtained by reading the following detailed description of the preferred embodiments with reference to the accompanying drawings.

Detailed Description As shown in FIGS. 1 a-1 c, a ribbon crystal growth system 10 includes a crucible 12, a melt 14 disposed in the crucible 12, and a pair of strings 13 passing through the crucible 12. The crucible 12 has a pair of openings (not shown) through which the pair of strings 13 pass. The melt 14 solidifies as the ribbon is pulled out of the melt 14, forming a crystalline ribbon 15. The pair of strings 13 is the crystal ribbon 1.
Stabilize the edge of 5. The meniscus 18 forms the surface of the melt 14 and the ribbon 15
And the growth interface 20 thereof. The upper surface of the meniscus 18 as viewed from the front is substantially concave. Growth occurs from the free surface of the melt, minimizing contact with the crucible material and separating impurities. The free surface of the melt refers to the upper surface of the melt. As the ribbon material solidifies, atoms of the trace material are free to return to the melt, causing the impurities to separate, resulting in a crystal ribbon that is purer than the melt. This effect makes it possible to utilize lower purity and therefore lower cost starting materials or to produce higher quality crystalline ribbons.

As shown in FIGS. 1b and 1c, the meniscus 18 has a height h and a radius of curvature R.
1 and R2. R1 represents the radius of curvature in the vertical plane, and R2 represents the radius of curvature in the horizontal plane.

Using the generalized Laplace equation, the meniscus shape and height can be determined for a given material and geometry based on the following equations:

[0021]

[Equation 1] In the above equation, Δp is the pressure difference between the melt surface and the meniscus height h, γ is the melt surface tension, ρ is the density of the melt material, and g is Gravity acceleration and h is the height of the meniscus. R ₁ and R ₂ are the meniscus curve radii in the vertical and horizontal planes. R ₁ and R ₂ change with vertical height along the meniscus. By integrating this equation from the melt free surface to the meniscus contact point, or the upper limit of the meniscus on the ribbon 15, the height and shape of the meniscus can be determined.

The meniscus 18 near the center of the ribbon 15 is not substantially bent in the horizontal plane, so 1 / R ₂ is omitted from the above equation, and the equation is solved to determine the height of the meniscus. Can be obtained. For example, the meniscus height can be about 7 mm for molten silicon that wets the silicon ribbon. Where ρ is about 2
． ³ gm / cm ³ , γ is about 720 dynes / cm, and g is about 980 cm / s ² . For the meniscus 18 near the edge of the ribbon, 1 / R ₂ is an important factor and the resulting meniscus height is lower. As mentioned above, R ₁ and R ₂ vary with vertical height along the meniscus. At the top of the meniscus, R ₂ can be about half the thickness of the ribbon. For example, about 0.3 mm used to grow silicon ribbons used in solar cell applications.
In the case of a silicon ribbon 15 having a thickness of, the height of the meniscus near the edge of the ribbon 15 is about 0.3 mm. The height of the meniscus near the edge is much smaller than the height near the center. FIG. 1 a shows the difference between the height of the meniscus near the center of the ribbon 15 and the height of the meniscus near the edge of the ribbon 15.

In the ribbon growth process, heat is transferred from the melt 14 to the growth interface 20 and from the growth interface 20 to the ribbon 15. The ribbon 15 then radiates heat to the surrounding environment. Further, the heat of fusion is radiated at the growth interface 20 as the molten silicon solidifies. The balance of these heat flows determines the ribbon thickness. By reducing the height of the meniscus at the edge of the ribbon, the growth interface 20 approaches the melt 14, so more heat is transferred from the melt 14 to the growth interface 20. In addition, the lower meniscus at the edge places the growth interface in a hotter thermal environment. This hotter thermal environment is closer to the molten surface. For the above reasons, less heat is radiated. The balance of these heat flows is
Provides a thinner edge.

Referring to FIG. 2, the ribbon crystal growth system 30 of the present invention comprises a crucible 32, a melt 34, a pair of strings 36 passing through a pair of holes in the crucible 32, and a meniscus controller 38. . Crystal ribbon 40 is grown from melt 34 substantially as described above with reference to FIGS. However, the meniscus controller 38 does not include the meniscus 42 formed between the melt 34 and the ribbon 40.
To fix. In one embodiment, the meniscus controller 38 includes a crucible 32.
A pair of structural members located within and adjacent to a pair of strings 36. When the molten material wets the surface of the structural members 38, a meniscus 44 is formed around each structural member 38. A liquid is said to "wet" a solid when the contact angle between the solid and the liquid measured through the liquid is between 0 ° and 90 °. As the molten material wets the surface of structural member 38, the melt rises above structural member 38. Therefore, the material of the structural member 38 is selected based on the wettability of the molten material with the structural member 38. For example, when growing a silicon ribbon, the material of the structural member can be graphite. Alternatively, the material of the structural member and / or the crucible is carbon, oxygen, silicon,
It may include nitrogen, or compounds containing any of these elements. A meniscus 44 formed around the structural member 38 overlays the meniscus 42 and modifies the height of the meniscus 44 near the ribbon edge without substantially affecting the meniscus 42 near the center of the ribbon 40. . The height of the meniscus near the edge of the ribbon 40 is increased. As a result, the growth interface 43 is substantially straight or substantially convex. The specific design (eg, shape and size) of these structures, and the placement of the structures can therefore be used to control and vary the meniscus. For example, the height of the meniscus near the edge of the ribbon can be made higher, lower, or as high as the meniscus along the entire width of the ribbon.

In one embodiment, the vertical pin 52 provided in the melt 54 functions as a meniscus controller as shown in FIG. 3a. In this embodiment, two vertical graphite pins 52a and 52b are provided for growth of the silicon ribbon.
It is installed in a blind hole at the bottom of the crucible 59 near each string 51. A first pin 52a is provided on one side of the ribbon 56 and a second pin 52b
Is provided on the other side of the ribbon 56. The meniscus has pins 52a and 52b.
Formed around each. The meniscus formed around each of the pins 52a and 52b overlaps the meniscus 58 formed between the growth interface 60 and the melt 54, thus increasing the height of the meniscus 58 near the edge of the ribbon 56. .

In another embodiment, a vertical wall 7 provided in the melt 74, as shown in FIG. 3b.
2 modifies the meniscus 76 near the edge of the ribbon 78. Each vertical wall 72
Located near the edge of ribbon 78 and substantially perpendicular to the plane of ribbon 78. A meniscus 79 formed around each vertical wall 72 overlies the meniscus 76 and changes the height of the meniscus 76 near the edge of the ribbon 78. These walls 72
It may be machined into crucible 71 or may be a separate part that is pinned into a blind hole in the bottom of crucible 71.

In yet another embodiment, as shown in FIG. 3c, a ribbon crystal growth system 80.
Comprises a crucible 82 having an inner wall 84 that modifies the meniscus 86. Inner wall 84
Ribbons such that the meniscus 89 formed around each inner wall 84 interacts with the meniscus 86 formed between the melt 90 and the ribbon 88 to modify the meniscus 86 near the edges of the ribbon 88. Located substantially near the edge of 88. When the molten material wets the surface of the inner wall 84, a meniscus 89 is formed around each inner wall 84.

Referring to FIG. 4, the ribbon crystal growth system 100 comprises a hollow semi-cylinder 102 that is placed in the melt 106 near the edge of the ribbon 104. The inner surface of cylinder 102 faces the ribbon edge and the outer surface of cylinder 102 faces away from ribbon 104. The inner surface of cylinder 102 substantially surrounds the edge of ribbon 104. The melt 106 is
Wet the inner surface of the cylinder 102 and raise the meniscus height near the edge of the ribbon 104. In this embodiment, as shown in FIG. 4, a pair of strings 108 pass through the hollow interior of cylinder 102. The advantage of the hollow semi-cylinder 102 is that the meniscus 103
Can rise very high along the inner surface of the cylinder 102. The half cylinder 102 can be prepared by cutting a full cylinder in half. Alternatively, the full cylinder can be machined to provide an opening along the side of the cylinder, allowing the meniscus to connect this inner surface of the cylinder with the growing crystal ribbon.

In addition to raising the meniscus height near the edge of the ribbon, the meniscus controller may facilitate cooling of the melt as it solidifies, thus providing a thicker ribbon near the edge. It Since the structural member typically extends above the melt and can be made of a material having an emissivity greater than that of the material of the melt, for example, a structural member used as a meniscus controller will dissipate heat and near the ribbon edge. The molten silicon can be cooled directly. Therefore, ribbon thickness can be controlled by material selection and size of the meniscus controller. For example, a meniscus controller formed of graphite can be used to grow crystalline silicon ribbons.

5a and 5b show the difference between the cross section of a silicon ribbon grown in the presence of a meniscus controller and the cross section of a silicon ribbon grown in the absence of a meniscus controller. FIG. 5 a shows a cross section of ribbon 120 with no meniscus modification at edge 122. The edge 122 hits a region near the string 124. As a result, the vicinity of the edge 122 becomes constricted and the edge becomes brittle, which may lead to damage. FIG. 5b shows a significant improvement in ribbon 130 thickness near edge 132 when the meniscus is modified according to the present invention. The constriction near the edge 132 is substantially removed so that the ribbon 130 does not break.

As shown in Figures 6a-6c, the meniscus controller used in the present invention also controls the shape of the growth interface. The growth interface 140 of the ribbon 142 grown without the meniscus controller is substantially concave and faces downward (ie frowns), as shown in Figure 6a. The crystal ribbon 142 is
Since the crystal grows in a direction substantially perpendicular to the growth interface 140, a large number of crystal grains that nucleate at the edge and then propagate toward the middle of the ribbon 142 are generated at the frowning interface 140. As a result, a significant amount of grain boundaries 144 may be formed. By modifying the meniscus near the edge of the ribbon as described herein, the growth interface can be made substantially flat as shown in Figure 6b, or substantially convex as shown in Figure 6c. With a pattern, you can turn upwards (ie, laughing).

Referring to FIG. 6c, when the interface 150 is substantially convex, the grains are
Nucleation occurs near the middle of the ribbon 152 and propagates toward the edge 154. Therefore, it is generally very large grains or coherent twins.
Grains of wins) grow downward and toward the edge of the ribbon 152. The cohesive twin grains have crystal structures that are mirror images of each other. These grains are
It then predominates in the ribbon 152 and suppresses many high angle grains nucleating at the edges, resulting in a ribbon with significantly larger grains and reduced high angle grain boundaries as shown in Figure 6c.

This invention is a co-owned and pending “filed on May 3, 1999.
Melt Depth Control for Semiconductor
It may be used with a ribbon growth system with melt depth control as described in the US patent application entitled "Materials Grown from a Melt". This application is incorporated herein by reference.

With reference to FIGS. 7 and 8, a continuous ribbon growth system 210 includes a crucible 212 containing a reservoir of molten silicon (“melt”) 214 and a pair of strings 216 extending through the crucible 212. . The meniscus controller 211 is positioned near each string 216. The thin polycrystalline sheet 218 melts 21 as the colder liquid silicon crystallizes on top of the meniscus 219.
It is slowly pulled up from 4. A string 216 running through a hole (not shown) in the bottom of crucible 212 is incorporated into and defines the edge boundary of crystal sheet 218. The string 216 secures the edges as the sheet 218 grows. The meniscus controller 211 corrects the meniscus. The surface tension of the silicon prevents the string 216 from leaking through the holes in the crucible 212. In continuous ribbon growth system 210, melt 214 and crucible 212 are contained within a housing (not shown) filled with an inert gas to prevent oxidation of molten silicon. As the sheet 218 grows by rollers (not shown), the sheet 218 continues to move vertically. The crucible 212 remains heated to maintain the melting of the melted silicon in the melt 214.

The depth of the melt 214 is measured and this information is provided to the feeder 226.
This regulates the rate at which silicon is introduced into the melt 214 and maintains a constant melt depth during crystal growth. The feeder 226 adds silicon pellets to the melt 214 as the crystal sheet 218 grows from the melt 214, compensating for silicon lost from the melt 214. The depth of the melt 214 is measured by transmitting an input signal to the crucible 212 and the melt 214 and measuring an output signal generated in response to the input signal. The output signal indicates the depth of the melt.

In one embodiment, the current I _IN passes through a pair of electrodes A and B to the crucible 212.
And the melt 214 are applied in combination, and the combined potential is measured. The resultant potential V _OUT is measured by the differential amplifier 222 via a pair of electrodes C and D to provide a bulk resistance signal. The resulting potential is the feedback circuit section 224.
Is supplied to the circuit portion 224, and the circuit portion 224 generates a control signal for controlling the feeding speed of the feeder 226. The feedback circuitry 224 is set to maintain the resulting voltage at a constant level, which corresponds to the desired melt height. In one embodiment, the pair of electrodes C and D is located between the pair of electrodes A and B.

The relationship between the melt depth and the output signal measured in response to the input signal is described below. This method of measuring depth takes advantage of the unique properties of semiconductors and widely used crucible materials such as graphite. For example, at room temperature, silicon is usually a semiconductor. However, at the melting point, silicon, like other semiconductors,
It becomes an electric conductor and has a conductivity almost the same as that of metal. Graphite is also
It is an electric conductor. However, the conductivity of molten silicon is higher than that of graphite and, therefore, dominates when measured simultaneously.

The conductivity of the silicon melt is directly proportional to the cross-sectional area of the silicon melt. A change in the melting depth of the molten silicon changes the cross-sectional area of the silicon melt, which in turn changes the conductivity and vice versa. When current flows through both the crucible 212 and the melt 214, the walls of the melt 214 and the crucible 212 are separated by making electrical connections to two points on the crucible 212 (ie, electrodes A and B). Form a parallel resistive path. Therefore, the potential generated in response to the applied current is affected by the depth of the melt 214 in the crucible 212. The voltage measured between two points on crucible 212 (ie, electrodes C and D) provides a signal representative of the combined resistance of melt 214 and graphite 212, and thus the high melt 214 in crucible 212. (Or depth).
The bulk resistivity of a typical graphite material used in the construction of semiconductor processing crucibles is about 1 milliohm centimeter. The bulk resistivity of molten silicon is
On the order of 20 times smaller values. Thus, if the crucible cross-sectional area is significantly less than 20 times the typical melt cross-sectional area (which is the typical case), the molten silicon will be a "short layer" on the graphite resistive layer. Can be considered to be The criterion is then preferably considered to be the resistance of the melt, since the melt determines the overall conductance. FIG. 9 shows a schematic diagram of the continuous ribbon growth system 210 of FIGS. 7 and 8.

The present invention was further filed on Mar. 3, 1999, “Continuous
melt replenishment for crystal glow
US patent application Ser. No. 09,304
, 284 may be incorporated into a crystal growth system having a continuous melt replenisher. This application is incorporated herein by reference.

With reference to FIGS. 10 and 11, the continuous ribbon growth system 350 includes a crucible 343 containing a pool of molten silicon (“melt”) 342 and a pair of strings 344 extending through the crucible 343. The meniscus controller 340 is located near each string. Polycrystalline sheet 341 of silicon melt 3
From 42, it is slowly pulled up and the colder liquid silicon crystallizes on top of the meniscus. The meniscus controller 340 corrects the meniscus near the edge of the ribbon 341. A string 344 through a hole (not shown) in the bottom of the crucible 343 becomes incorporated into the edge boundary of the crystal sheet 341,
The edge boundary of the crystal sheet 341 is defined. String 344 is seat 341
Stabilizes the edges as grows. The surface tension of the silicone prevents leakage through the holes in the crucible 343 through which the string 344 passes. In an actual continuous crystal growth apparatus, the melt 342 and crucible 343 are contained in a housing (not shown) filled with an inert gas to prevent oxidation of the molten silicon. Rollers (not shown) continue to move sheet 341 vertically as it grows. The crucible 343 remains heated in the melt 342 to keep the silicon molten. Further, the crucible 343 remains stationary.

Since a portion of melt 342 is lost by solidifying to form a crystal ribbon, melt 342 needs to be continuously replenished to provide a continuous crystal growth process. . In one embodiment, as shown in FIG.
5 enters hopper 322 through a large opening and exits hopper 312 through a small opening. Granular feedstock 335 may have particles of non-uniform size. The raw material can be, for example, a semiconductor material. In one embodiment, the raw material is silicon,
And a dopant such as boron. The raw material 335 exiting the hopper 312 is
Arranged on translational belt 334 to form a pile of raw material 335. The pile of raw material 335 has an angle of repose. The angle of repose is determined by the shape and size distribution of the particles forming the raw material 335.

Referring to FIG. 11, the raw material 335 arranged on the motion belt 334 is continuously supplied to the crucible 343 containing the melted material of the raw material 335 at a predetermined speed. The raw material is placed in the crucible through the funnel 345 and the tube 347. Tube 3
47 is placed inside one end of the crucible 343. In one embodiment,
The feed rate is constant. The feed rate is based on the angle of repose of the raw material.

The amount of raw material is equal to the product of the mass cross-sectional area of the raw material and the speed of the moving belt. Figure 1
2 shows the mass sectional area. The mass cross section is equal to H ² / tan α + HL. Where α is the angle of repose, H is the height, and L is the size of the hopper opening just above the belt. The feed rate can be controlled by the speed of movement of the belt in combination with the angle of repose. For example, the belt may move at a constant speed and accordingly feed the ingredients into the crucible at a constant speed. Also, the belt is 2 mm / min-10 m
It can move at speeds in the range of m / min. In other embodiments, the feed rate is based on cross-sectional area when the feed is on the belt, or based on belt speed.

As shown in FIGS. 10, 11 and 12, by using the concept of angle of repose with a slowly moving belt, the desired amount of granular silicon is melted continuously and very accurately. It becomes possible to carry it to a crucible. The cross section of the material exiting the narrow orifice is constant due to the characteristic stability of the angle of repose. Due to this constant cross-section, the amount of material carried can be modified by simply changing the speed of the belt carrying the granular material. This allows for a large degree of tolerance in the choice of particle size distribution and particle shape distribution of the silicon feedstock.

The present invention, which provides control of meniscus by changing shape and / or height, control of ribbon thickness, greater yield, reduced defects, and other advantages described herein. Can be similarly incorporated into other crystal growth systems and methods.

Equivalents While the present invention has been illustrated and described with particular reference to certain preferred embodiments, those skilled in the art will appreciate that various changes in shape and detail are It is understood that the invention can be made without departing from the spirit and scope of the invention as defined by the following claims.

[Brief description of drawings]

Figure 1a   FIG. 1a is a perspective view of a crystal ribbon growth system.

Figure 1b   1b is a side view of the crystal ribbon growth system of FIG. 1a.

[Fig. 1c]   1c is a plan view of the crystal ribbon growth system of FIG. 1a.

[Fig. 2]   FIG. 2 is a perspective view of one embodiment of the crystal ribbon growth system of the present invention.

FIG. 3a   FIG. 3a is a perspective view of one embodiment of the crystal ribbon growth system of the present invention.

FIG. 3b   FIG. 3b is a perspective view of one embodiment of the crystal ribbon growth system of the present invention.

[Fig. 3c]   FIG. 3c is a perspective view of one embodiment of the crystal ribbon growth system of the present invention.

[Figure 4]   FIG. 4 is a perspective view of one embodiment of the crystal ribbon growth system of the present invention.

FIG. 5a is a cross-sectional view of a ribbon crystal grown using the crystal ribbon growth system of FIG. 1a.

FIG. 5b is a cross-sectional view of a ribbon crystal grown using the crystal ribbon growth system of the present invention.

6a is a front view of a ribbon crystal grown using the crystal ribbon growth system of FIG. 1a.

FIG. 6b is a front view of a ribbon crystal grown using one embodiment of the crystal ribbon growth system of the present invention.

FIG. 6c is a front view of a ribbon crystal grown using one embodiment of the crystal ribbon growth system of the present invention.

[Figure 7]   FIG. 7 is a schematic diagram of one embodiment of a continuous crystal growth system.

FIG. 8 is a cross-sectional view of the crystal growth system of FIG. 7, taken along line 8′-8 ″ and showing only the crucible and melt.

[Figure 9]   FIG. 9 is a circuit diagram showing the resistance of the crystal growth system of FIGS. 7 and 8.

[Figure 10]   FIG. 10 is a diagram showing a part of a continuous crystal growth system.

FIG. 11   FIG. 11 is a diagram illustrating one embodiment of a continuous ribbon crystal growth system.

[Fig. 12]   FIG. 12 is a diagram showing the calculation of the mass cross-sectional area of a pile of granular material on a horizontal plane.

─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Gabary, Eric Bruce             United States New Hampshire             03055, Milford, Fern Wood             Drive 2 (72) Inventor Azarowsky, Scene M.             United States New Hampshire             03060, Nashua, West Glen             Wood drive 107 (72) Inventor Share, Brian             United States Massachusetts             02062, Norwood, Roosevelt             Avenue 192 F term (reference) 4G077 AA02 BA04 CF03 EG01 EG25                       EH06 PA16                 5F051 AA03 BA14 CB06

Claims (34)

[Claims] 1. An apparatus for growing a crystal ribbon, comprising a crucible for holding a melt of semiconductor material, the crucible having a pair of openings, and passing through the pair of openings. A pair of strings that define the edges of the crystal ribbon grown from the melt, the top surface of the crystal ribbon and the melt forming a meniscus. A string, and a meniscus controller that controls the properties of the meniscus near the edge of the crystal ribbon without substantially affecting the meniscus away from the edge of the crystal ribbon. 2. The apparatus of claim 1, wherein the meniscus controller includes a structural member disposed in the crucible adjacent to at least one of the strings. 3. The device of claim 2, wherein the structural member comprises at least one pin. 4. The apparatus of claim 2, wherein the structural member is oriented substantially perpendicular to the plane of the melt. 5. The apparatus of claim 2, wherein the structural member comprises a generally cylindrical tube. 6. The apparatus of claim 2, wherein the meniscus controller provides a substantially flat growth interface. 7. The apparatus of claim 2, wherein the meniscus controller provides a substantially convex growth interface. 8. The pair of strings includes a first string and a second string, the structural member being a first string disposed adjacent to the first string.
3. The device of claim 2 including a structural member of claim 2 and a second structural member disposed adjacent to the second string. 9. The apparatus of claim 1, wherein the meniscus controller controls the thickness of the crystal ribbon. 10. The apparatus according to claim 9, wherein the meniscus controller provides a crystal ribbon having a uniform thickness. 11. The apparatus of claim 1, wherein the meniscus controller includes a wall of the crucible that is substantially perpendicular to a face of the ribbon. 12. The apparatus according to claim 1, wherein the meniscus controller raises the height of the meniscus near the edge of the crystal ribbon. 13. The device of claim 1, wherein the structural member is wettable by the semiconductor material. 14. The apparatus of claim 1, wherein the meniscus controller reduces nucleation at the edges of the crystal ribbon. 15. The apparatus according to claim 2, wherein the structural member and the upper surface of the melt form a meniscus, which acts on the meniscus of the crystal ribbon. 16. The device of claim 2, wherein the structural member comprises at least one of carbon, oxygen, silicon, and nitrogen. 17. The device of claim 1, wherein the semiconductor material comprises silicon. 18. An apparatus for growing a crystal ribbon, comprising a crucible for holding a melt of semiconductor material, the crucible having a pair of openings, and passing through the pair of openings. A pair of strings that define the edges of the crystal ribbon grown from the melt, the top surface of the crystal ribbon and the melt forming a meniscus. A string and of the string in the crucible that raises the height of the meniscus in the vicinity of the edge of the crystal ribbon without substantially affecting the meniscus away from the edge of the crystal ribbon. A structural member disposed in the vicinity of at least one,
A device that includes. 19. A method of growing a crystal ribbon, comprising: a) providing a melt of semiconductor material in a crucible; and b) disposing a seed crystal of the semiconductor material in the melt. c) solidifying the melt by pulling the seed crystal from the melt between a pair of strings passing through a pair of openings in the crucible to form the crystal ribbon. A top surface of the crystal ribbon and the melt forms a meniscus, and d) using a meniscus controller without substantially affecting the meniscus away from the edge of the crystal ribbon. Controlling the properties of the meniscus in the vicinity of the edge of the crystal ribbon. 20. The step d) includes controlling structural properties of the meniscus with a structural member disposed in the melt adjacent at least one of the pair of strings. The method according to 19. 21. Step d) includes controlling the properties of the meniscus with at least one pin located in the melt adjacent at least one of the pair of strings. The method according to claim 19. 22. The step d) comprises using a structural member disposed within the melt so as to be adjacent to at least one of the strings and substantially perpendicular to the melt. 20. The method of claim 19, comprising controlling the characteristics of the meniscus. 23. Step d) includes controlling the characteristics of the meniscus using a generally cylindrical tube disposed within the crucible adjacent at least one of the pair of strings. The method according to claim 19. 24. The method of claim 19, wherein step d) comprises controlling the shape of the meniscus. 25. The method of claim 24, wherein controlling the shape of the meniscus comprises providing a substantially flat growth interface. 26. The method of claim 24, wherein controlling the shape of the meniscus comprises providing a substantially convex growth interface. 27. The method of claim 19, wherein step d) comprises controlling the characteristics of the meniscus with the walls of the crucible. 28. The method of claim 19, wherein step d) includes controlling the height of the meniscus. 29. The method of claim 28, wherein step d) includes increasing the height of the meniscus near the edge of the crystal ribbon. 30. The method of claim 19, further comprising: d) controlling the thickness of the crystal ribbon. 31. The method of claim 30, wherein step d) includes increasing the height of the meniscus at the edge of the crystal ribbon to provide a crystal ribbon having a uniform thickness. Method. 32. The step d) includes forming a meniscus with the structural member that interacts with the meniscus of the crystal ribbon.
The method described in. 33. The method of claim 19, wherein step a) comprises providing a melt of silicon in a crucible. 34. A method of growing a crystalline ribbon, comprising: a) providing a melt of semiconductor material into a crucible; and b) a pair of strings passing through a pair of openings in the crucible. Providing a structural member in the crucible so as to be adjacent to at least one of the: c) disposing a seed crystal of the semiconductor material in the melt; and d) of the pair of strings. A step of solidifying the melt to form the crystal ribbon by pulling the seed crystal from the melt between, wherein the crystal ribbon and the top surface of the melt form a meniscus; E) increasing the height of the meniscus in the vicinity of the edge of the crystal ribbon without substantially affecting the meniscus away from the edge of the crystal ribbon. Law.