Method for depositing an epitaxial layer on a substrate wafer of semiconductor material in a deposition apparatus - Patents.com

Abstract

1. A method for depositing an epitaxial layer on a substrate wafer of a semiconductor material in a deposition apparatus, comprising: placing a substrate wafer on a susceptor of a deposition apparatus surrounded by a gap, separated from a preheat ring and held by a support shaft; Determining an eccentricity between an axis passing vertically through a center of the preheat ring and an axis passing vertically through a center of the susceptor; passing a deposition gas over the substrate wafer along a flow direction from a gas inlet to a gas outlet; passing a purge gas along an underside of the preheat ring and an underside of the susceptor; rotating a support shaft about an axis of rotation at a frequency; The method includes displacing a support shaft at a frequency of rotation of the support shaft from a start position disposed along an axis passing perpendicularly through a center of the preheat ring to an end position and back to the start position, the displacement path from the start position to the end position being dependent on the eccentricity.

Description

[Technical field]

[0001] The present invention relates to a method for depositing an epitaxial layer on a substrate wafer of a semiconductor material in a deposition apparatus. [Background technology]

[0002] Conventional technology / challenges The deposition of epitaxial layers on substrate wafers of semiconductor materials is usually accomplished by CVD (Chemical Vapor Deposition) in a deposition apparatus capable of accommodating the substrate wafer. During deposition of the epitaxial layer, the substrate wafer is placed on a susceptor held and rotated by a support shaft, and a deposition gas passes over the free upper surface of the substrate wafer, in other words its front surface, while a purge gas passes along the underside of a preheat ring and the underside of the susceptor. The preheat ring is placed around the susceptor and separated by a gap. The upper and lower domes define a reaction chamber in which the epitaxial layer is deposited on the substrate wafer. Radiant heat from the lamp array is irradiated through one or both domes to provide the required deposition temperature.

[0003] A deposition apparatus having these characteristics is described, for example, in US Patent Application Publication No. 20160010239A1.

[0004] Semiconductor wafers with epitaxial layers (epitaxial wafers) are required for particularly demanding applications in the electronics industry. For example, the requirements regarding the uniformity of the thickness of the deposited epitaxial layers are therefore particularly challenging.

[0005] German Patent No. 112018001223T5 discloses how epitaxial layer thickness differences can be mitigated by a preheat ring, the shape of whose inner circumference deviates from circular, when the cause of the thickness difference is the almost unavoidable non-centered position of the susceptor during deposition of the epitaxial layer. The non-centered position is manifested by an eccentricity between an axis passing vertically through the center of the preheat ring and an axis passing vertically through the center of the substrate wafer.

[0006] JP 2016213242 A2 addresses the same problem by adapting the conditions under which the epitaxial layers are grown, the adaptation being performed as a function of the decentering determined by the camera system. Summary of the Invention [Problem to be solved by the invention]

[0007] The drawback of these solutions is that the geometry of the preheat ring represents a static system that does not allow an immediate response to changing eccentricities. Adaptation of the growth conditions is problematic since it requires intervention in the flow dynamics of a complex system that is particularly sensitive with regard to the distribution of dopants.

[0008] It is therefore desirable to provide a solution that is easy to implement and does not have such drawbacks. [Means for solving the problem]

[0009] The object of the present invention is to provide a deposition apparatus having a susceptor, the susceptor being surrounded by a gap, separated from a preheat ring, and held by a support shaft, the susceptor comprising: Determining an eccentricity between an axis passing vertically through a center of the preheat ring and an axis passing vertically through a center of the susceptor; passing a deposition gas over the substrate wafer along a flow direction from a gas inlet to a gas outlet; passing a purge gas along an underside of the preheat ring and an underside of the susceptor; rotating a support shaft about an axis of rotation at a frequency; This is achieved by a method for depositing an epitaxial layer on a substrate wafer of semiconductor material in a deposition apparatus, comprising displacing a support shaft at a frequency of rotation of the support shaft from a start position, the axis of rotation of the support shaft being disposed along an axis passing perpendicularly through a center of a preheat ring, to an end position, and back to the start position, the displacement path from the start position to the end position being dependent on the eccentricity.

[0010] The method may also be carried out at elevated temperatures in the deposition chamber, for example at the deposition temperature, since there is no need to open the deposition chamber.

[0011] The eccentricity is preferably determined by a camera system which ascertains, at at least one position, the change in width of the gap between the inner edge of the preheat ring and the outer edge of the susceptor and calculates the eccentricity on the basis thereof. For a given rotation speed of the susceptor, it is possible, for example, to measure the rotation angle at which the maximum width of the gap from the start of one revolution is observed, with the start of one revolution defining the home signal of the deposition apparatus.

[0012] The susceptor is arranged with a bearing surface on a holding surface of an arm of the support shaft, the eccentricity being in particular the result of manufacturing tolerances exerted firstly by the holding surface on the arm of the support shaft and secondly by the bearing surface on the susceptor.

[0013] Depending on the magnitude of the eccentricity, the gap between the inner edge of the preheat ring and the outer edge of the susceptor is wider at one point on the periphery of the susceptor than at the other. Due to the wider gap, more purge gas enters the reaction chamber above the substrate wafer, where it dilutes the deposition gas more strongly. This effect causes a more uneven distribution of the layer thickness of the epitaxial layer deposited on the substrate wafer.

[0014] According to the invention, the support shaft of the susceptor is displaced at the frequency of the rotation of the support shaft from a start position, located along an axis passing vertically through the center of the preheat ring, to an end position and back to the start position, the displacement path from the start position to the end position depending on the eccentricity between the axis passing vertically through the center of the preheat ring and the axis passing vertically through the center of the susceptor.

[0015] The support shaft may be displaced using a drive arrangement, for example as described in US Patent Application Publication No. 20160010239A1. The support shaft is preferably piezoelectrically displaced by at least one actuator.

[0016] The susceptor is preferably heated at 30 rpm -1 ~60rmin -1 The rotor rotates at a speed of 1000 rpm, and the support shaft is displaced in response to a periodic time of 1 to 2 s.

[0017] The substrate wafer is made of a semiconductor material, preferably monocrystalline silicon, as well as an epitaxial layer deposited on the front side of the substrate wafer. The diameter of the substrate wafer is preferably at least 200 mm, more preferably at least 300 mm.

[0018] The deposition gas comprises a compound that contains a semiconductor material, such as, for example, a silane or a chlorosilane, for example, trichlorosilane, and the purge gas preferably comprises hydrogen.

[0019] According to a first configuration of the invention, the displacement path from the start position to the end position is represented by a vector whose magnitude is the magnitude of the eccentricity and whose direction is opposite to the direction of the eccentricity. The magnitude and direction of the displacement of the support shaft is thus guided by the eccentricity between the axis passing vertically through the center of the preheat ring and the axis passing vertically through the center of the susceptor. Depending on the frequency of the rotational movement of the support shaft, the support shaft is displaced from the start position to the end position and back to the start position. In the start position, the support shaft of the susceptor is disposed along an axis passing vertically through the center of the preheat ring. This axis is usually also the axis passing vertically through the center of the deposition device.

[0020] The displacement of the support shaft and the susceptor it holds reduces the imbalance of the rotational motion of the susceptor due to eccentricity. On an average time basis, the substrate wafer resting on the susceptor is more centered with respect to the preheat ring, and therefore the width of the gap between the preheat ring and the susceptor is more uniform on an average time basis. This affects the thickness of the epitaxial layer deposited on the substrate wafer, and its distribution becomes more uniform.

[0021] In accordance with a second aspect of the present invention, the wedge characteristic of the substrate wafer is determined and factored into the displacement of the susceptor support shaft.

[0022] A substrate wafer is wedge-shaped if its cross-section undergoes a linear increase or decrease in thickness when viewed along its diameter. The wedge characteristic may be quantified, for example, by the ratio between the maximum cross-sectional thickness and the minimum cross-sectional thickness.

[0023] The inventors have found that if the susceptor support shaft is displaced back and forth during deposition from a start position to an end position at a frequency at which the susceptor support shaft rotates along the deposition gas flow direction, the wedge-shaped characteristic decreases with the deposition of the epitaxial layer. At the start position, the susceptor support shaft is positioned along an axis that passes vertically through the center of the preheat ring. The magnitude of the displacement path from the start position to the end position is guided by the degree of the wedge-shaped characteristic of the substrate wafer. The correlation of the magnitude of the displacement path required in the presence of a particular wedge-shaped characteristic of the substrate wafer in order to eliminate the wedge-shaped characteristic mainly due to the deposition of the epitaxial layer must be experimentally determined in advance. The magnitude and direction of this displacement path may therefore be indicated by a further vector that depends on the wedge-shaped characteristic of the substrate wafer.

[0024] A second configuration of the present invention takes into account the wedge-shaped nature of the substrate wafer and the eccentricity between an axis passing vertically through the center of the preheat ring and an axis passing vertically through the center of the susceptor.

[0025] Correspondingly, during deposition of an epitaxial layer, the support shaft of the susceptor is displaced from a start position to an end position and back to the start position at the frequency of rotation of the support shaft as prescribed by a resultant vector. At the start position, the support shaft of the susceptor is aligned along an axis that passes perpendicularly through the center of the preheat ring. The resultant vector corresponds to a vector sum of a further vector that describes a displacement path that depends on the wedge-shaped characteristics of the substrate wafer and a vector that describes a displacement path that depends on the eccentricity between the axis that passes perpendicularly through the center of the preheat ring and the axis that passes perpendicularly through the center of the susceptor.

[0026] The invention is further presented below with reference to the drawings, in which it is assumed that the substrate wafer is centered on the susceptor and that the eccentricity is due to a non-centered position of the susceptor on the transport arm of the susceptor's support shaft. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 shows an apparatus, shown in cross-section, suitable for carrying out the method of the invention. [Diagram 2] FIG. 2 shows further details of the device. [Diagram 3] FIG. 1 is a plan view showing the relative positions of the susceptor and preheat ring, and the displacement of the support shaft when there is eccentricity between an axis passing vertically through the center of the preheat ring and an axis passing vertically through the center of the susceptor, according to the first configuration of the present invention. [Figure 4] FIG. 13 is a plan view showing the relative positions of the susceptor and preheat ring, and the displacement of the support shaft, when there is eccentricity between an axis passing vertically through the center of the preheat ring and an axis passing vertically through the center of the susceptor, according to the second configuration of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Detailed Description of the Invention FIG. 1 shows in cross section an apparatus for depositing epitaxial layers on substrate wafers of semiconductor material, suitable for carrying out the method of the invention. The reaction chamber of this deposition apparatus 20 is surrounded on the top by an upper dome 17 and on the bottom by a lower dome 18. In the center of the reaction chamber is arranged a support shaft 9, from which a transport arm 10 branches off at the top. The transport arm 10 supports a susceptor 2 on which a substrate wafer 1 is placed during deposition of an epitaxial layer. In the illustrated embodiment, in the process of loading the deposition apparatus 20, the substrate wafer 1 is placed on the lift shaft 11 and is placed on the susceptor 2 by lowering the lift shaft 11. Between the side wall of the deposition apparatus and the susceptor 2 a preheat ring 3 is arranged. The deposition gas passes in front of the substrate wafer 1, which points to the upper dome 17, from a gas inlet 13 to a gas outlet 14, which inlet and outlet are arranged on one side wall of the deposition apparatus. Furthermore, corresponding further gas inlets 15 and further gas outlets 16 for purge gas are also provided, which pass through the reaction chamber below the preheat ring 3 and below the susceptor 2. The arrows indicate the flow direction of the gas stream. Depending on the width of the gap 5 between the preheat ring 3 and the susceptor 2, a part of the purge gas enters the flow of deposition gas and dilutes it. The reaction chamber is heated from the outside by a lamp array 19 which irradiates radiant energy through the upper dome 17 and the lower dome 18. The lower dome 18 of the deposition device 20 is joined to the base 12 by a bellows 25 to allow the movement of the support shaft 9 and to seal the interior created by the bellows against the incoming ambient atmosphere.

[0029] The apparatus comprises a control device 21 configured for periodic displacement of the support shaft 9. For displacement of the support shaft 9 in the horizontal direction there are actuators 27 (for displacement in x direction) and 28 (for displacement in y direction). Optionally there may also be further actuators 29 and 30 provided for tilting the support shaft 9 out of the viewing plane of FIG.

[0030] The apparatus further comprises a camera system 7 with image processing 8 (FIG. 2) for determining the eccentricity between an axis 22 passing vertically through the center of the preheat ring 3 and an axis 26 passing vertically through the center of the susceptor 2. The camera system 7 comprises a camera for observing an image detail 6 during the rotation of the susceptor 2 by the support shaft 9. The image detail 6 captures a radially extending area, which preferably includes a part of the outer periphery of the substrate wafer 1, a part of the outer periphery of the susceptor 2 and a part of the inner periphery of the preheat ring 3 and thus also a part of the gap 5 between the susceptor 2 and the preheat ring 3. The substrate wafer 1 is in a pocket of the susceptor 2 on the placement area 4, so that the backside 23 of the substrate wafer 1 is at a distance from the base 24 of the susceptor 2. The information contained in the image detail 6 is evaluated by image processing 8.

[0031] The substrate wafer 1 shown in Figure 2 has a wedge-shaped cross-section, the thickness of which increases linearly from the thinner edge to the thicker edge.

[0032] FIG. 3 shows in plan view the relative positions of the inner edges of the susceptor 2 and the preheat ring 3 in the case of an eccentricity between the axis 22 passing vertically through the center of the preheat ring 3 and the axis 26 passing vertically through the center of the susceptor 2. The axis of rotation of the support shaft 9 is located at a starting position along the axis 22 passing vertically through the center of the preheat ring 3. The magnitude and direction of the eccentricity are indicated by the vector E. When the substrate wafer 1 is centered on the susceptor 2, the axis 26 passing vertically through the center of the susceptor and the axis passing vertically through the center of the substrate wafer have the same position. According to a first configuration of the invention, the support shaft 9 rotates with a frequency during the deposition of the epitaxial layer on the substrate wafer 1 and is displaced during each rotation from a starting position to an end position and back to the starting position. The magnitude and direction of the displacement are indicated by the vector Vr1, the magnitude of which is that of the vector E and the direction of which is opposite to the direction of the vector E. In the starting position, the axis of rotation of the support shaft 9 is oriented along an axis 22 passing perpendicularly through the centre of the preheat ring 3, and in the ending position it is displaced to the extremity of the vector Vr1.

[0033] The second configuration of the invention also takes into account the wedge-shaped nature of the substrate wafer when the support shaft of the susceptor is displaced. FIG. 4 is a view similar to FIG. 3, showing the second configuration. According to the second configuration of the invention, the support shaft 9 of the susceptor 2 rotates with a certain frequency during the deposition of the epitaxial layer on the substrate wafer 1, displacing during each rotation from a start position to an end position and back to the start position. The magnitude and direction of the displacement path from the start position to the end position is represented by a resultant vector Vr2. This vector corresponds to the sum of the vectors Vr1 and K, the vector K having a direction from the deposition gas inlet 13 to the gas outlet 14, in other words the flow direction of the deposition gas, and has a magnitude that depends on the wedge-shaped nature of the substrate wafer 1. In the start position, the rotation axis of the support shaft 9 is oriented along an axis 22 that passes vertically through the center of the preheat ring 3, and in the end position it is displaced to the tip of the resultant vector Vr2.

[0034] The lengths of the vectors shown in Figures 3 and 4 are exaggerated for illustrative purposes. In reality, each displacement path is typically 100-1000 μm. [Explanation of symbols]

[0035] List of references used 1. Substrate wafer 2 Susceptor 3 Preheat Ring 4. Sedimentation surface 5. Gap 6 Image details 7 Camera System 8. Image Processing 9 Support shaft 10. Transport Arm 11 Lifting shaft 12 base 13 Gas inlet 14 Gas outlet 15 Further gas inlets 16 Further gas outlets 17 Upper Dome 18 Lower Dome 19 Lamp Array 20. Accumulation Equipment 21 Control Device 22 Axis passing vertically through the center of the preheat ring 23 Rear side 24 Bottom 25 Bellows 26 Axis passing vertically through the center of the susceptor 27 Actuator 28 Actuator 29 Actuator 30 Actuator

Claims

1. 1. A method for depositing an epitaxial layer on a substrate wafer of a semiconductor material in a deposition apparatus, comprising: placing the substrate wafer on a susceptor of the deposition apparatus surrounded by a gap, separated from a preheat ring, and held by a support shaft; determining an eccentricity between an axis passing vertically through a center of the preheat ring and an axis passing vertically through a center of the susceptor; passing a deposition gas over the substrate wafer along a flow direction from a gas inlet to a gas outlet; passing a purge gas along an underside of a preheat ring and an underside of the susceptor; rotating the support shaft about an axis of rotation at a frequency; displacing the support shaft at the frequency of rotation of the support shaft from a start position disposed along an axis whose rotation axis passes perpendicularly through a center of the preheat ring to an end position and back to the start position, the displacement path from the start position to the end position being dependent on the eccentricity.

2. The method of claim 1 , wherein the displacement path from the start position to the end position is described by a vector whose magnitude is the magnitude of the eccentricity and whose direction is opposite to the direction of the eccentricity.

3. 3. The method of claim 2, wherein the displacement path from the start position to the end position is described by a resultant vector that is a sum vector of the vector and a further vector as an augend, the magnitude of the further vector being dependent on a wedge-shaped characteristic of the substrate wafer and a direction of the further vector having the flow direction of the deposition gas.

4. The method according to any of claims 1 to 3, wherein the support shaft is displaced by at least one actuator.

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