Method and apparatus for depositing an epitaxial layer on a substrate wafer of a semiconductor material

Abstract

The present invention relates to a method and an apparatus for depositing an epitaxial layer on a substrate wafer made of a semiconductor material, the substrate wafer having a wedge-shaped cross section with a thinner edge and a thicker edge. The method includes: arranging the substrate wafer and a pedestal in a deposition apparatus such that the substrate wafer is concentrically rested on the pedestal and the pedestal is held by a support shaft; rotating the support shaft for a certain period of time; passing deposition gas above the substrate wafer in a direction from a gas inlet to a gas outlet; passing purge gas along the lower side of a preheating ring and the lower side of the pedestal at a certain flow rate; moving the support shaft along a displacement path in a direction from an initial position to a final position and back to the initial position for the certain period of time, wherein at the initial position, the thinner edge is at a minimum distance from the gas inlet, and at the final position, the thinner edge is at a maximum distance from the gas inlet.

Description

Technical Field

[0001] The present invention relates to a method for depositing an epitaxial layer on a substrate wafer of a semiconductor material, the substrate wafer having a wedge-shaped cross-section with a thinner edge and a thicker edge. The present invention also relates to an apparatus suitable for implementing the method. Background Art

[0002] Depositing an epitaxial layer on a substrate wafer of a semiconductor material is generally carried out by means of CVD (Chemical Vapor Deposition) in a deposition apparatus capable of accommodating the substrate wafer. During the deposition of the epitaxial layer, the substrate wafer is placed on a pedestal held by a support shaft and rotated, and the deposition gas passes above the free upper surface on the front side of the semiconductor wafer. The deposition apparatus generally also has a preheating ring, which is arranged around the pedestal and separated by a gap. The upper dome and the lower dome define a reaction space in which the epitaxial layer is deposited on the substrate wafer. The radiant heat of the lamp group is introduced through one or both domes to provide the required deposition temperature. A deposition apparatus having these features is described, for example, in US 2016 0 010 239A1.

[0003] Semiconductor wafers with epitaxial layers (epitaxial wafers) are necessary for particularly demanding applications in the electronics industry. Accordingly, for example, the requirements related to the thickness uniformity of such semiconductor wafers are particularly challenging.

[0004] Even after depositing the epitaxial layer, especially when the epitaxial layer has a uniform thickness, irregularities in the thickness of the substrate wafer are usually retained. However, there are also some proposals aimed at improving the thickness uniformity by depositing the epitaxial layer.

[0005] DE 11 2018 001 223 T5 discloses influencing the thickness of the epitaxial layer and the width of the gap between the preheating ring and the pedestal by means of a purge gas passing along the lower side of the preheating ring and the lower side of the pedestal in the deposition apparatus.

[0006] In US 2009 0 269 861A1, it is proposed to select process conditions during the deposition of the epitaxial layer according to the flatness of the substrate wafer. Similar proposals are made in WO 2018 117 402A2 and JP 2002 43 230A.

[0007] A common feature of these proposals is that they utilize the effects generated by the rotation of the substrate wafer during the deposition of the epitaxial layer: the change in process conditions results in a rotationally symmetric change in the thickness distribution of the epitaxial layer. Therefore, these proposals are only applicable to substrate wafers in which the thickness irregularities are rotationally symmetrically distributed.

[0008] However, there are also substrate wafers with a thickness distribution that is not rotationally symmetric. When the thickness decreases from a region at the periphery to the region opposite the 180° of the periphery, the substrate wafer has a wedge-shaped cross-section. The cross-section of such a substrate wafer from the thinner region to the thicker region is wedge-shaped with a thinner edge and a thicker edge. The deposition of an epitaxial layer with a rotationally symmetric thickness distribution cannot eliminate this wedge-shaped structure. Summary of the Invention

[0009] The object of the present invention is to improve the thickness uniformity of a semiconductor wafer having an epitaxial layer when the substrate wafer has a wedge-shaped cross-section.

[0010] The object is achieved by a method for depositing an epitaxial layer on a substrate wafer of a semiconductor material, the substrate wafer having a wedge-shaped cross-section with a thinner edge and a thicker edge, the method comprising:

[0011] Arranging the substrate wafer and a pedestal in a deposition apparatus such that the substrate wafer is concentrically placed on the pedestal and the pedestal is held by a support shaft;

[0012] Rotating the support shaft for a certain period of time;

[0013] Passing deposition gas above the substrate wafer in a direction from a gas inlet to a gas outlet;

[0014] Passing purge gas along the lower side of a preheating ring and the lower side of the pedestal at a certain flow rate;

[0015] Moving the support shaft along a displacement path in a direction from an initial position to a final position and back to the initial position for the certain period of time, wherein at the initial position, the thinner edge is at a minimum distance from the gas inlet, and at the final position, the thinner edge is at a maximum distance from the gas inlet.

[0016] It has been observed that the purge gas sometimes enters through the gap between the preheating ring and the pedestal and dilutes the deposition gas, thereby having the effect of reducing the rate of material deposition. This effect increases with the width of the gap, and this is utilized according to the present invention.

[0017] The width of the gap increases periodically as the distance of the thinner edge from the gas inlet increases, and the certain time period is synchronized with the duration of the rotation of the susceptor, specifically such that the thinner edge of the substrate wafer is at the minimum distance from the gas inlet at the start of the time period. At this time, the dilution effect is minimal and the deposition rate of the material is relatively high. After the susceptor rotates half a turn (half a circle), when the thicker edge is at the minimum distance from the gas inlet, the gap at this position is relatively large, the dilution effect is relatively obvious, and the deposition rate of the material is relatively low. Due to the procedure according to the invention, the epitaxial layer deposited on the substrate wafer has a thickness distribution such that this thickness distribution also has a wedge-shaped cross-section. However, the latter is complementary to the cross-section of the substrate wafer, such that the wedge shape of the semiconductor wafer with the epitaxial deposition layer is at least not as pronounced as that of the substrate wafer. The method according to the invention is also applicable to converting a substrate wafer with a wedge shape into a semiconductor wafer having an epitaxial layer and a shape corresponding to that of a wafer with a substantially planar parallel front and back side.

[0018] When the edges of the cross-section have different thicknesses, the substrate wafer has a wedge-shaped cross-section in the sense of the present invention. It is preferred but not essential that the thickness continuously increases from the thinner edge to the thicker edge.

[0019] The substrate wafer is placed on a susceptor. The susceptor has a circular outer perimeter in a plan view and preferably has a pocket (recess) and a support surface on which the substrate wafer rests in the edge region of its back side. The substrate wafer is positioned concentrically with the outer perimeter of the susceptor and preferably rests on its support surface in such a way that there is a distance between the back side of the substrate wafer and the bottom defining the pocket. A hole can be formed in the bottom of the pocket to facilitate the transport of dopants from the back side of the substrate wafer to the reaction space below the susceptor. Instead of the hole, the bottom can be made of a material containing fibers and ensure the transport of dopants due to the porosity of the material.

[0020] In order to vary the width of the gap between the preheating ring and the susceptor in a desired manner during the deposition of the epitaxial layer, the support shaft moves periodically from an initial position to a final position and back to the initial position, wherein the susceptor is held by means of the support shaft. The movement of the support shaft is carried out by means of at least one actuator, for example via one or more piezoelectric adjustment elements. The displacement path between the initial position and the final position extends in the direction between the gas inlet and the gas outlet. When observed over the duration of one full rotation (one circle) of the susceptor, the thinner edge of the cross-section of the substrate is at a minimum distance from the gas inlet in the initial position and at a maximum distance from the gas inlet in the final position.

[0021] The length of the displacement path from the initial position to the final position is preferably not less than 30% and not greater than 130% of the gap width that exists when the outer perimeter of the susceptor and the inner perimeter of the preheating ring are concentrically arranged. The length of this displacement path is preferably proportional to the difference in thickness between the thicker edge and the thinner edge of the cross-section.

[0022] The susceptor rotates at a speed preferably of 30 rpm to 60 rpm. With this rotational speed, the time period for the displacement movement of the susceptor is 1 s (second) to 2 s.

[0023] Preferably, the shape of the substrate wafer is measured before depositing the epitaxial layer, and the deposition process parameters (such as the speed of the displacement movement and the flow rate of the purge gas) are adapted to the shape.

[0024] The speed of the displacement movement can be substantially constant or vary according to a curve (profile) of the thickness variation along the perimeter of the substrate wafer.

[0025] The flow rate of the purge gas is preferably not less than 5 slm and not greater than 30 slm, wherein the flow rate of the purge gas jointly determines the radial extent of the effect associated with the dilution of the deposition gas. It can be constant or vary according to a curve of the thickness variation along the perimeter of the substrate wafer.

[0026] The substrate wafer is made of a semiconductor material (preferably single-crystalline silicon), and the same applies to the epitaxial layer deposited on the front side of the substrate wafer. The diameter of the substrate wafer is preferably at least 200 mm, particularly preferably at least 300 mm.

[0027] The deposition gas contains a compound containing a semiconductor material, such as silane or chlorosilane (such as trichlorosilane), and the purge gas preferably contains hydrogen.

[0028] The periodic movement of the support shaft according to the invention does not need to be carried out continuously during the deposition of the epitaxial layer. It can also be carried out only temporarily (intermittently). Thus, according to another embodiment of the invention, the epitaxial layer is deposited without periodically moving the support shaft until a specific layer thickness is reached, and then the deposition of the epitaxial layer is continued while moving the support shaft according to the invention. This procedure can also be modified in such a way that the epitaxial layer is initially deposited while periodically moving the support shaft, and subsequently the deposition of the epitaxial layer is continued without moving the support shaft. It is particularly advantageous to implement one of these embodiments when the wedge shape of the substrate wafer is relatively less pronounced.

[0029] The object is also achieved by a device for depositing an epitaxial layer on a substrate wafer of semiconductor material, the device comprising:

[0030] a pedestal,

[0031] a preheating ring,

[0032] a support shaft,

[0033] at least one actuator for moving the support shaft, and

[0034] a control device configured to periodically move the support shaft by means of the actuator in a direction from a gas inlet to a gas outlet.

[0035] According to a preferred embodiment, the device further comprises at least one actuator for tilting the support shaft. After tilting the support shaft, the axis of rotation of the support shaft is no longer vertical but inclined towards the preheating ring.

[0036] The invention will be described in more detail below with reference to the accompanying drawings. Description of the Drawings

[0037] Figure 1 A device suitable for implementing the method according to the invention is shown in cross-section.

[0038] Figure 2 Further details of the device are shown.

[0039] Figure 3 The starting state and the end state of the movement of the support shaft during a 180° rotation of the pedestal are shown.

[0040] Figure 4 For comparison, the cross-section of a wedge-shaped substrate wafer and the cross-section of a substrate wafer coated according to the invention are shown.

[0041] List of Reference Numerals Used

[0042] 1 Substrate wafer

[0043] 2 Base

[0044] 3 Preheating ring

[0045] 4 Support surface

[0046] 5 Gap

[0047] 6 Image part

[0048] 7 Camera system

[0049] 8 Image processing

[0050] 9 Support shaft

[0051] 10 Support arm

[0052] 11 Lifting shaft

[0053] 12 Base

[0054] 13 Actuator

[0055] 14 Actuator

[0056] 15a,b Gas inlet

[0057] 16a,b Gas outlet

[0058] 17 Upper dome

[0059] 18 Lower dome

[0060] 19 Lamp group

[0061] 20 Deposition equipment

[0062] 21 Control device

[0063] 22 Axis of rotation

[0064] 23 Rear side

[0065] 24 Bottom

[0066] 25 Bellows

[0067] 26 Thinner edge

[0068] 27 Thicker edge

[0069] 28 Epitaxial layer Detailed implementation mode

[0070] Detailed description of exemplary embodiments according to the present invention

[0071] Figure 1The device for depositing an epitaxial layer on a substrate wafer of semiconductor material (i.e., a substrate wafer made of semiconductor material) is shown in cross-section. This device is suitable for implementing the method according to the invention. The reaction space of the deposition device 20 is bounded at the top by an upper dome 17 and at the bottom by a lower dome 18. A support shaft 9 extends into the middle of the reaction space, from the upper part of which a support arm 10 branches off. The support arm 10 supports a pedestal 2, on which the substrate wafer 1 is placed during the deposition of the epitaxial layer. In the illustrated embodiment, during the loading of the deposition device 20, it is provided that the substrate wafer 1 is placed on a lift shaft 11 and is placed on the pedestal 2 by lowering the lift shaft 11. A preheating ring 3 is provided between the side wall of the deposition device and the pedestal 2. The deposition gas passes from a gas inlet 15a to a gas outlet 16a above the front side of the substrate wafer facing the upper dome 17, wherein the gas inlet 15a and the gas outlet 16a are provided at the side wall of the deposition device. In addition, corresponding gas inlets 15b and gas outlets 16b for a flushing gas are provided, and the flushing gas passes through the reaction space below the preheating ring 3 and the pedestal 2. The arrows indicate the direction of the gas flow. Depending on the width of the gap 5 between the preheating ring and the pedestal, a part of the flushing gas enters the deposition gas stream and dilutes the deposition gas. The reaction space is heated from the outside by a lamp set 19, which introduces radiant energy through the upper dome 17 and the lower dome 18. The lower dome 18 of the deposition device 20 is connected to a base 12 by a bellows 25 in order to allow the movement of the support shaft 9 and to seal the interior space provided thereby against the inflow of the ambient atmosphere.

[0072] A specific feature of the device is a control device 21, which is configured to periodically move the support shaft 9 in a direction from the gas inlets 15a, 15b to the gas outlets 16a, 16b by means of at least one actuator 13. The illustrated embodiment has two actuators 13 and 14, which move the support shaft 9 with the same type of actuation. In addition, when the actuations are different, tilting of the support shaft 9 is also possible. During the tilting, the axis of rotation 22 of the support shaft 9 is inclined with respect to the vertical direction towards the preheating ring 3. An additional tilting of the support shaft 9 may be useful, for example, in order to bring the substrate wafer 1 into a horizontal position in the case where the substrate wafer 1 is not placed horizontally on the pedestal 2 as expected.

[0073] Therefore, it is also advantageous to provide a camera system 7 with image processing 8 in order to check the position of the substrate wafer 1. Figure 2The camera system 7 shown includes a camera for observing an image section 6 during rotation of the base 2 about the support axis 9. The image section 6 captures a radially extending region which preferably includes a part of the outer periphery of the substrate wafer 1, a part of the outer periphery of the base 2, and a part of the inner periphery of the preheating ring 3, and thus also includes a part of the gap 5 between the base 2 and the preheating ring 3. The substrate wafer 1 is placed in a pocket of the base 2 on the support surface 4 such that the rear side (back side) 23 of the substrate wafer 1 is at a distance from the bottom 24 of the base 2. The information contained in the image section 6 is evaluated by means of image processing 8, which particularly relates to the width of the gap 5 and the distance of the camera system 7 from the base 2. By means of the control device 21, it is checked whether there is an improper arrangement of the base 2, and if appropriate, a signal is generated which causes the support axis 9 to tilt to such an extent that the substrate wafer is moved from the improper arrangement to the desired horizontal position.

[0074] According to the invention, the support axis moves periodically along a displacement path from an initial position to a final position and back to the initial position. The start state (upper figure) and the end state (lower figure) of such movement up to the final position of the support axis 9 are shown in Figure 3 . The substrate wafer 1 is centered on the support surface of the base 2. It has a wedge-shaped cross-section which has a thinner edge 26 and a thicker edge 27. During rotation of the base 1, the thinner edge is at a minimum distance from the gas inlets 15a,b in the initial position of the support axis 9 and at a maximum distance from the gas inlets 15a,b in the final position of the support axis 9. Due to the movement of the support axis 9, the gap 5 between the preheating ring 3 and the base 2 is smaller on the side where the gas inlets 15a,b are located in the initial position of the support axis 9, and the dilution effect brought about by the flushing gas entering the space above the base along the arrows shown as bifurcated arrows is smaller. When the thicker edge of the substrate wafer enters the vicinity of the gas inlets 15a,b during rotation of the base 2, the gap 5 is larger and the dilution effect is also larger. This means that overall more material is deposited in the region of the thinner edge 26 of the substrate wafer 1 than in the region of the thicker edge 27.

[0075] Figure 4 Shows the manner (situation) in which the cross-section of a substrate wafer with a deposited epitaxial layer (lower figure) changes compared to the cross-section of the substrate wafer (upper figure). The epitaxial layer 28 also has a wedge-shaped cross-section, but it is complementary to the cross-section of the substrate wafer 1 such that in an ideal case the coated substrate wafer has plane-parallel side surfaces.

Claims

1. A method for depositing an epitaxial layer on a substrate wafer of semiconductor material, the substrate wafer having a wedge-shaped cross-section with a thinner edge and a thicker edge, the method comprising: Arranging the substrate wafer and a pedestal in a deposition apparatus such that the substrate wafer is concentrically rested on the pedestal and the pedestal is held by a support shaft; Rotating the support shaft for a certain period of time; Passing deposition gas above the substrate wafer in a direction from a gas inlet to a gas outlet; Passing purge gas at a certain flow rate along the lower side of a preheating ring and the lower side of the pedestal; Moving the support shaft along a displacement path in a direction from an initial position to a final position and back to the initial position for the certain period of time, wherein at the initial position, the thinner edge is at a minimum distance from the gas inlet, and at the final position, the thinner edge is at a maximum distance from the gas inlet.

2. The method according to claim 1, characterized in that, The length of the displacement path from the initial position to the final position is proportional to the difference in thickness between the thicker edge and the thinner edge of the cross-section.

3. The method according to claim 1 or 2, characterized in that, Measuring the shape of the substrate wafer before depositing the epitaxial layer and changing the moving speed of the support shaft according to the shape.

4. The method according to any one of claims 1 to 2, characterized in that Measuring the shape of the substrate wafer before depositing the epitaxial layer and changing the flow rate of the purge gas according to the shape.

5. The method according to any one of claims 1 to 2, characterized in that, The support shaft is tilted towards the preheating ring.

6. An apparatus for depositing an epitaxial layer on a substrate wafer of semiconductor material, comprising: A pedestal, A preheating ring, A support shaft, At least one actuator for moving the support shaft, A control device configured to periodically move the support shaft along a direction from a gas inlet to a gas outlet by means of the actuator during deposition of an epitaxial layer on a substrate wafer of semiconductor material, and At least one other actuator for tilting the support shaft towards the preheating ring.

7. The device according to claim 6, characterized in that The apparatus has a camera system for observing the outer edge of the substrate wafer and the gap between the pedestal and the preheating ring.

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