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DE-102024003712-A1 - Method for growing a single crystal from silicon

DE102024003712A1DE 102024003712 A1DE102024003712 A1DE 102024003712A1DE-102024003712-A1

Abstract

A method for growing a single crystal from silicon according to the Czochralski method, comprising growing a seed crystal to form a thin neck, characterized in that, during the growing of a portion of the thin neck, the growing speed is periodically varied for not fewer than 5 periods and not more than 30 periods such that the diameter of the thin neck in each period initially increases linearly from an initial value, is then held constant, and subsequently decreases linearly again to the initial value (see Fig. 1); in each period, the axial length of the section of the thin neck in which the diameter decreases linearly (L2) is at least three times the axial length of the section of the thin neck in which the diameter increases linearly (L1); and the crucible and seed crystal rotate in the same direction during the drawing of the part of the thin neck in which the drawing speed is periodically changed, and the rotational speeds of the crucible and the rotational speeds of the seed crystal are independent of each other and are not less than 0.5 and not more than 15 revolutions per minute.

Inventors

  • Alicia Dorner
  • Dieter Knerer
  • Michael Skrobanek
  • Ludwig Stockmeier

Assignees

  • SILTRONIC AG

Dates

Publication Date
20260513
Application Date
20241113

Claims (15)

  1. A method for growing a single crystal from silicon according to the Czochralski method, comprising the following steps in this order: (i) providing a crucible containing a silicon melt and a seed crystal of single-crystal silicon above the silicon melt; (ii) lowering the seed crystal until contact is established between the seed crystal and the surface of the silicon melt; (iii) growing the seed crystal to a thin neck with a maximum diameter not exceeding 20 mm by lifting the seed crystal while rotating it; (iv) expanding the diameter of the thin neck to a target diameter; (v) growing a cylindrical section of the single crystal to the target diameter; (vi) reducing the target diameter to an end cone; and (vii) separating the single crystal from the melt; characterized in that in step (iii) during the drawing of a portion of the thin neck, the drawing speed is periodically varied for not fewer than 5 periods and not more than 30 periods such that the diameter of the thin neck in each period initially increases linearly from an initial value, is then held constant, and subsequently decreases linearly again to the initial value; in each period, the axial length of the section of the thin neck in which the diameter decreases linearly (L2) is at least three times the axial length of the section of the thin neck in which the diameter increases linearly (L1); and the crucible and the seed crystal rotate in the same direction during the drawing of the portion of the thin neck in which the drawing speed is periodically varied, and the rotational speeds of the crucible and the rotational speeds of the seed crystal are independent of each other and are not less than 0.5 and not more than 15 revolutions per minute.
  2. Method for growing a single crystal from silicon according to the Claim 1 , wherein the axial length of one period of the thin neck is not less than 10 mm and not more than 50 mm.
  3. Method for growing a single crystal from silicon according to the Claim 1 or 2 , wherein the length of the part of the thin neck in which the drawing speed is periodically varied is not less than 100 mm and not more than 450 mm.
  4. Method for growing a single crystal from silicon according to one of the Claims 1 until 3 , wherein the difference between the maximum diameter (D2) and the minimum diameter of the thin neck (D1) in one period is not less than 0.5 mm and not more than 3.0 mm.
  5. Method for growing a single crystal from silicon according to one of the Claims 1 until 4 , where the minimum diameter of the thin neck (D1) in one period is not less than 3.0 mm.
  6. Method for growing a single crystal from silicon according to one of the Claims 1 until 5 , where the maximum diameter of the thin neck (D2) in one period does not exceed 15 mm.
  7. Method for growing a single crystal from silicon according to one of the Claims 1 until 6 , wherein the minimum diameter of the thin neck (D1) in one period is not less than 3.5 mm and not more than 5.5 mm.
  8. Method for growing a single crystal from silicon according to one of the Claims 1 until 7 , wherein the maximum diameter of the thin neck (D2) in one period is not less than 5.5 mm and not more than 10 mm.
  9. Method for growing a single crystal from silicon according to one of the Claims 1 until 8 , wherein the direction of the draw does not deviate by more than 5° from the orientation (110).
  10. Method for growing a single crystal from silicon according to one of the Claims 1 until 9 , wherein in step (iii) during the drawing of the part of the thin neck in which the drawing speed is periodically changed, the rotational speed of the crucible is initially kept constant and then continuously reduced.
  11. Method for growing a single crystal from silicon according to one of the Claims 1 until 10 , wherein in step (iii) during the drawing of the part of the thin neck in which the drawing speed is periodically changed, the rotational speed of the crucible is initially kept constant at a value of not less than 5 and not more than 15 revolutions per minute and is subsequently continuously reduced.
  12. Method for growing a single crystal from silicon according to one of the Claims 1 until 11 , wherein in step (iii) during the drawing of the part of the thin neck in which the drawing speed is periodically changed, the seed crystal is first rotated at a constant first rotation speed, then at a reduced constant second rotation speed and finally rotated again at the constant initial rotational speed.
  13. Method for growing a single crystal from silicon according to the Claim 12 , wherein the first rotational speed is not less than 8 revolutions per minute and the second rotational speed is not more than 4 revolutions per minute.
  14. A method for producing wafers from single-crystal silicon, comprising the following steps: drawing a single crystal from silicon according to the method of one of the Claims 1 until 13 ; Grinding of the single crystal; sawing of the ground single crystal into slices; grinding and/or lapping of the slices; chemical etching and/or cleaning of the slices; and polishing of the slices.
  15. Method for producing wafers from single-crystal silicon according to the Claim 14 , wherein the process additionally includes the following step: deposition of an epitaxial layer of semiconductor material onto the disks of single-crystal silicon.

Description

Technical field The present invention relates to a method for growing a single crystal from silicon according to the Czochralski method and a method for producing wafers from single-crystal silicon. State of the art Single-crystal disks made of semiconductor material (also called wafers) are the basis of modern electronics. They are manufactured in a variety of process steps, including pulling a single-crystal rod from a melt, grinding and sawing the crystal into disks, and surface finishing of the disks. Single-crystal semiconductor wafers, particularly silicon wafers, are typically manufactured by first drawing a monocrystalline rod using the Czochralski (CZ) process. The resulting rods are then cut into crystal fragments using suitable saws such as wire saws, internal hole saws, or band saws. These fragments are then usually processed into semiconductor wafers using a wire saw. After further mechanical, chemo-mechanical, and/or chemical steps, a layer can optionally be deposited onto the wafer using chemical vapor deposition (CVD). The CZ process typically involves lowering a seed crystal, usually referred to as a seedling, into a silicon melt at a temperature above 1410°C until contact is established. Crystal growth occurs by slowly and rotating the seed crystal back up as the melt solidifies at the forming interface. This process first creates a thin neck, then an initial cone of the single crystal with increasing diameter, followed by a cylindrical section with the desired diameter, and finally a final cone with decreasing diameter, before the single crystal is separated from the melt and removed. When the seed crystal is brought into contact with the hot molten silicon, stresses arise within the seed crystal, leading to the formation of dislocations. These dislocations can propagate along the entire length of the crystal rod, but in most cases, they can be removed by forming a thin neck from the single crystal. To form a thin neck, also known as a dash neck, the rotating seed crystal is pulled upwards to reduce the diameter of the essentially cylindrical thin neck to typically 3 to 8 mm. Starting from this dislocation-free thin neck, the diameter of the single crystal rod is increased again, and a dislocation-free single crystal with the desired diameter can be grown. This process is also known as the dash method or dash-neck method. Step displacements can generally be avoided using the dash-neck method. This is not as true for screw displacements. The following describes... EP 1 498 517 A1 that, in a seed with a crystal orientation <110>, dislocations in the center of the seed cannot be easily removed using the dash-neck method. When a seed with a <110> crystal orientation is immersed in the melt, sliding dislocations can form in the center, which can propagate axially, i.e., along the drawing direction of the single-crystal rod, over the entire length of the rod, even when the dash-neck method is applied. EP 1 498 517 A1 This describes a method for growing a single-crystal rod in which the formation of dislocations in the seed is prevented. Therefore, no dislocations need to be removed, and the method thus eliminates the need for the dash-neck technique. JP2007070131 , EP1897976B1 , US7641734B2 and DE112012006260 A high boron doping of the melt and seed is used to reduce the mobility of the dislocations, but this limits the electrical resistance in the single crystal to a certain range. In US 7,226,506 B2 , EP 1 498 516 A1 and US 5,769,941 B2 Tilted seed crystals are used to grow single-crystal rods from silicon with an orientation <110>. The tilt causes the growing single-crystal rod's direction of growth, and thus its axis, to be non-perpendicular to the crystal faces with a <110> orientation. Increasing the tilt increases the probability of dislocation emergence. However, to produce wafers with a <110> orientation, the tilt of the single-crystal rod must be corrected by grinding, resulting in increased material loss as the tilt increases. US 4,002,523 describes a method for drawing a single crystal rod with a crystal orientation <110> in which a thin neck with alternating thin and thick regions is drawn, thereby creating dislocations parallel to the growth The dislocations run in the direction (drawing direction) of the single crystal, gradually moving away from the crystal's axis and towards the periphery. This increases the probability that the dislocations terminate at a surface and thus disappear from the crystal. However, this elaborate and complex process requires a reduction of the thin neck to 2.5 mm, which reduces the thin neck's stability and makes extracting large crystal rods more difficult. US 5,911,823 and US 6,652,824 The diameter of the thin neck is even reduced to less than 2 mm, which further reduces the stability of the thin neck. In JP 2007-84358 A , JP 2011-57460 A and JP 2023-65064 A A thin neck is drawn with alternating thin and thick areas. JP 2007-84358 A describes a thi