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

Abstract

A method and apparatus for depositing an epitaxial layer on a substrate wafer made of a semiconductor material. The method includes: arranging a substrate wafer and a pedestal in a deposition apparatus such that the substrate wafer rests on the pedestal and the pedestal is held by an arm of a support shaft; monitoring for misalignment of the pedestal with respect to its position relative to a preheating ring surrounding the pedestal; monitoring for misalignment of the support shaft with respect to its position relative to the preheating ring position; if at least one of the misalignments occurs, eliminating the corresponding misalignment; and depositing the epitaxial layer on the substrate wafer.

Description

FIELD OF THE INVENTION

[0001] The subject of the present invention is a method for depositing an epitaxial layer on a substrate wafer made of semiconductor material, and a device for implementing the method. BACKGROUND OF THE INVENTION

[0002] Semiconductor wafers with epitaxial layers are the product of such methods and are necessary for particularly demanding applications in the electronics industry. Therefore, the requirements for the thickness uniformity of the epitaxial layer and the uniformity of the dopant distribution in the epitaxial layer are particularly challenging. Therefore, there is a strong motivation to create production conditions that allow the production of semiconductor wafers with epitaxial layers that meet strict requirements in high volumes.

[0003] Depositing an epitaxial layer on a semiconductor wafer substrate is typically carried out using CVD (Chemical Vapor Deposition) in a deposition device that can receive the substrate wafer. During the deposition of the epitaxial layer, the substrate wafer is located on a pedestal that is supported by a support arm of a support shaft and rotated by the support shaft, and the deposition gas is directed onto the front surface, the free upper surface of the substrate wafer. The deposition device typically also has a preheating ring that is arranged around the pedestal and separated by a gap. The upper dome and the lower dome define a reaction chamber in which the epitaxial layer is deposited on the substrate wafer. Radiant heat from a lamp group is irradiated through the dome to provide the necessary deposition temperature. Deposition devices with these characteristics are commercially available. In addition, as described in US2018 0 282 900 A1, it is possible to load the substrate wafer into the deposition device and place it on the pedestal, or to load the pedestal with the substrate wafer placed thereon into the deposition device.

[0004] It has long been known that misalignment of the position of the substrate wafer relative to the pedestal has an adverse effect on the yield. Generally, the substrate wafer should be centered on the pedestal so that the substrate wafer forms a concentric circle with the circumferential line of the pedestal.

[0005] JP2017-69 414 A describes how to monitor the position of the substrate wafer on the pedestal with the aid of a camera system and, if necessary, horizontally move the pedestal support shaft to center the substrate wafer on the pedestal.

[0006] US2009 0 314 205 A1 relates to details of an observation system that can monitor the position of the preheating ring and other functions.

[0007] US2016 0 125 589 A1 describes a method that can be used to detect misalignment.

[0008] The inventors of the present invention have found that due to the presence of particles, due to the non-uniform thickness of the epitaxial layer, and due to the non-uniform dopant distribution in the epitaxial layer, yield losses may occur, which cannot be attributed to misalignment of the substrate wafer with respect to its position relative to the pedestal. Summary of the Invention

[0009] It is an object of the present invention to point out the causes of such yield losses and to show how to remedy them.

[0010] The object of the present invention is achieved by a method for depositing an epitaxial layer on a substrate wafer of semiconductor material, the method comprising arranging the substrate wafer and a pedestal in a deposition apparatus such that the substrate wafer rests on the pedestal and the pedestal is held by an arm of a support shaft; monitoring for misalignment of the pedestal with respect to its position relative to a preheating ring surrounding the pedestal; monitoring for misalignment of the support shaft with respect to its position relative to the preheating ring position; if at least one of the misalignments occurs, eliminating the corresponding misalignment; and depositing an epitaxial layer on the substrate wafer.

[0011] The object of the present invention is further achieved by an apparatus for depositing an epitaxial layer on a substrate wafer made of semiconductor material, comprising: a pedestal; a preheating ring; a support shaft with a pedestal support arm; a camera system for monitoring the width of a portion of the gap between the pedestal and the preheating ring and the distance from the camera system to the pedestal; an image processing device for determining the presence of misalignment of the pedestal with respect to its position relative to the preheating ring position and / or the presence of misalignment of the support shaft with respect to its position relative to the preheating ring position; a drive unit for moving and tilting the pedestal support shaft; and a control device for generating a signal in the case of misalignment, wherein the signal causes the drive unit to move in a manner to correct the existing misalignment.

[0012] The inventors have found that the mentioned yield losses can be attributed to misalignment of the position with respect to the pedestal and / or the position with respect to its support shaft relative to the preheating ring position. A gap is usually provided between the preheating ring and the pedestal, and this gap has the same width along the inner circumference of the preheating ring. The preheating ring and the pedestal are concentrically arranged with each other, and the pedestal is horizontally arranged. The support shaft is aligned along a vertical axis passing through the center of the preheating ring.

[0013] Thus, if the pedestal is eccentrically positioned with respect to the preheating ring on the support arm of the support shaft, or if the pedestal is tilted out of the horizontal plane on the support arm of the support shaft, there is misalignment of the pedestal. If the support shaft is vertical but not aligned along the vertical axis passing through the center of the preheating ring, or if the support shaft deviates from the vertical axis passing through the center of the preheating ring, there is misalignment of the position of the support shaft with respect to the preheating ring.

[0014] If the susceptor touches the preheating ring, particles are generated, which act as impurities and render the resulting semiconductor wafer with an epitaxial layer unusable for its intended purpose. If the width of the gap between the preheating ring and the susceptor varies along the inner circumference of the preheating ring due to one of the aforementioned misalignments, a loss of production can also occur. Then, there is a risk that the process gas is diluted to different extents at different points of this gap by the purge gas directed along the lower side of the susceptor, with the result that the thickness of the epitaxial layer and the distribution of the dopant in the epitaxial layer can vary along the circumferential direction of the substrate wafer.

[0015] The aforementioned misalignments can already be present in the cold state of the deposition apparatus, or can occur only during the process of heating the deposition apparatus to the operating temperature, and may disappear again during the cooling to the cold state, for example when cooling to room temperature.

[0016] Therefore, it is advisable to monitor the presence of at least one misalignment and, if necessary, correct this misalignment. For this purpose, in principle, the deposition apparatus can be cooled to the ambient temperature and the corresponding misalignment can be eliminated.

[0017] If possible, it is preferably carried out by moving the support shaft with the deposition apparatus switched off. In other cases, the deposition apparatus is opened and the cause of the misalignment is corrected. For example, if the susceptor is misaligned because it is horizontally positioned on the support arm of the support shaft but is eccentric with respect to the preheating ring, or because the susceptor is concentrically positioned with respect to the preheating ring on the support arm of the support shaft but is tilted out of the horizontal position, the deposition apparatus is opened, the susceptor is lifted and placed as intended on the support arm of the support shaft.

[0018] In cases where the misalignment can be corrected by moving the support shaft, the deposition apparatus remains closed and there is no need to cool the deposition apparatus to the ambient temperature. If the reaction chamber of the deposition apparatus is already in a hot state, which is the case at least at a temperature of 450 °C or higher, when a misalignment of the support shaft occurs, it is preferably corrected without cooling the deposition apparatus below the specified temperature of 450 °C, particularly preferably without reducing the temperature reached in the deposition apparatus. The misalignment of the support shaft can be corrected by moving the support shaft if the cause of the misalignment is that the support shaft is vertical but not aligned along the vertical axis passing through the center of the preheating ring, or because the support shaft is tilted from the vertical axis passing through the center of the preheating ring.

[0019] The arrangement of the susceptor and the support shaft with respect to their positions relative to the preheating ring is observed by means of a camera system that captures an image excerpt which preferably extends radially over at least one region that encloses a part of the circumference of the substrate wafer and a part of the inner circumference of the preheating ring. The image excerpt also includes a part of the gap between the susceptor and the preheating ring. The image excerpt recorded by the camera system has an azimuthal width that is preferably not less than 12°. The image processing device identifies the positions of the respective parts based on the characteristic contrast differences and preferably the distance of the camera system to the upper surface of the susceptor or the change in that distance. In appropriate cases, for example, an illumination system including one or more LED lights can be provided to illuminate the reaction chamber when the deposition device is in the cold state. During the rotation of the support shaft, the image excerpts are recorded and evaluated at fixed intervals. Based on the time variation of the positions relative to each other and based on the time fluctuations of the distances, the image processing device determines whether there is a misalignment of the susceptor and / or the support shaft as described above. Based on the determined result, the control device generates a control signal to move the drive unit to move and tilt the support shaft with the aim of eliminating the existing misalignment by moving the support shaft.

[0020] For example, the image processing device can use the algorithm described in US2016 0 125 589 A1 or preferably perform image processing using the Sobel operator for edge detection.

[0021] The camera system includes at least one camera, or preferably at least two cameras, which record two image excerpts that have an azimuthal distance of 90° from each other. Advantageously, for comparison purposes, data obtained from the evaluation are stored by means of the image processing device when the deposition device is in the cold state and there is no such misalignment as described above. Particularly advantageously, when the support shaft and the susceptor are arranged as expected, the corresponding image excerpts are evaluated with respect to the width of the gap between the susceptor and the preheating ring, and the width of the gap is stored.

[0022] The lower dome and the drive unit of the deposition device are preferably connected via a bellows so that, if necessary, it is possible to initiate the displacement and / or tilting movement of the support shaft relative to the stationary lower dome without ambient air reaching the support shaft.

[0023] To suppress vibrations, the upper end of the support arm is preferably connected to the outer side of a so-called "base ring" to keep the upper dome and the lower dome separate, and the lower end of the support arm is mounted on the drive device to move and tilt the support shaft.

[0024] The drive device for the support shaft for moving and tilting the base includes at least the necessary number of actuators so as to be able to move the support shaft in the x-direction and in the y-direction and tilt the support shaft about a rotational axis parallel to the x-direction and about a rotational axis parallel to the y-direction. Thus, for example, four actuators are provided, each actuator causing one movement. The actuators are preferably piezoelectric actuator elements.

[0025] If misalignment occurs while the deposition device is in the heated state, the above misalignment is corrected by moving the support shaft, preferably also when the deposition device is heated and turned off.

[0026] If the support shaft is actually vertically aligned as expected but not along the vertical axis passing through the center of the preheating ring, and if the base is positioned on the support arm as expected, a gap width in the image excerpt of the camera system will be observed to be different from the expected stored width when the base rotates around the support shaft, or, if the camera system includes two cameras arranged at an azimuthal distance of 90°, the observed gap widths will be different. In this case, there is a misalignment of the support shaft with respect to its position relative to the preheating ring. It is corrected by horizontally moving the support shaft to a position along the vertical axis passing through the center of the preheating ring.

[0027] If the support shaft is aligned as expected along the vertical axis passing through the center of the preheating ring and the base is indeed concentrically positioned relative to the position of the preheating ring but tilted out of the horizontal plane on the support arm, during the rotation of the base around the support shaft, it will be observed that the distance from the camera system to the base varies sinusoidally during the observation. This misalignment of the base is corrected by restoring the base to the expected position.

[0028] If the base is actually positioned on the support arm as expected but the support shaft deviates from the expected alignment along the vertical axis passing through the center of the preheating ring, there is also a misalignment of the support shaft with respect to its position relative to the preheating ring. In this case, it is found that the observed gap width between the base and the preheating ring is different from the gap width observed and stored when the support shaft and the base are positioned as expected. This misalignment of the support shaft is corrected by tilting the support shaft to the expected position along the vertical axis passing through the center of the preheating ring so that the observed gap width corresponds to the stored gap width.

[0029] For example, it can sometimes be the case that there is no misalignment in the cold state of the deposition device, i.e., the support shaft is aligned as expected along the vertical axis passing through the center of the preheating ring, and the base is horizontally and concentrically positioned on the support arm relative to the position of the preheating ring, and the misalignment of the support shaft only occurs during the heating of the deposition device due to the support shaft tilting out of the expected position.

[0030] The present invention can be applied whether the substrate wafer is loaded into the deposition equipment alone or together with the susceptor. Preferably, the method according to the present invention is applied in a closed deposition equipment and at an operating temperature of at least 450 °C.

[0031] The susceptor has a circular outer periphery in a plan view and preferably has a recess and a placement surface, on which the substrate wafer rests in the edge region of its back side. The substrate wafer is preferably placed on the placement surface in such a way that there is a distance between the back side of the substrate wafer and the base forming the boundary of the recess. A hole can be incorporated at the bottom of the recess to facilitate the transport of dopants from the back side of the substrate wafer into the reaction chamber below the susceptor. Instead of the hole, the base can be made of a fibrous material, and due to the porosity of the material, the transport of dopants can be ensured.

[0032] The substrate wafer preferably consists of single-crystalline silicon, and so does 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.

[0033] The present invention preferably further includes features known to those skilled in the art in order to determine and correct the misalignment of the substrate wafer with respect to its position relative to the susceptor.

[0034] The present invention will be described below with reference to the drawings of exemplary embodiments. Description of the Drawings

[0035] Figure 1 An exemplary embodiment of a deposition equipment having features according to the present invention is shown.

[0036] Figure 2 An observation of the gap between the susceptor and the preheating ring is shown.

[0037] List of Reference Numerals

[0038] 1 Substrate Wafer

[0039] 2 Susceptor

[0040] 3 Preheating Ring

[0041] 4 Placement Surface

[0042] 5 Gap

[0043] 6 Image Excerpt

[0044] 7 Camera System

[0045] 8 Image Processing Equipment

[0046] 9 Support Shaft

[0047] 10 Support Arm

[0048] 11 Lift shaft

[0049] 12 Drive unit

[0050] 13 Actuator (x - direction)

[0051] 14 Actuator (y - direction)

[0052] 15 Actuator (tilt angle φ)

[0053] 16 Actuator (tilt angle θ)

[0054] 17 Upper dome

[0055] 18 Lower dome

[0056] 19 Lamp group

[0057] 20 Deposition device

[0058] 21 Control device

[0059] 22 Vertical axis

[0060] 23 Back side

[0061] 24 Substrate

[0062] 25 Bellows Detailed implementation mode

[0063] Figure 1 The reaction chamber of the deposition device 20 shown is bounded from above by the upper dome 17 and from below by the lower dome 18. The support shaft 9 extends into the center of the reaction chamber and has support arms 10 that fork from the upper end of the shaft. The support arms 10 support the pedestal 2, on which the substrate wafer 1 is placed during the deposition of the epitaxial layer. In the illustrated embodiment, the substrate wafer 1 is placed on the lift shaft 11 during the loading of the deposition device 20 and is placed on the pedestal by lowering the lift shaft 11. The deposition gas is directed from the inlet to the outlet through the front side of the substrate glass facing the upper dome 17, both the inlet and the outlet being located on the side wall of the deposition device. The preheating ring 3 is provided between the side wall of the deposition device and the pedestal 2. Additionally, corresponding inlets and outlets can be provided for the purge gas, which is directed below the pedestal and through the reaction chamber, parallel to its downward - facing side. The arrows indicate the direction of the gas flow. The reaction chamber is heated from the outside by the lamp group 19, which irradiates radiant energy through the upper dome 17 and the lower dome 18.

[0064] In the expected arrangement of the position of the base 2 with respect to its position relative to the preheating ring 3 (around the base 2), a gap 5 is provided between the preheating ring 3 and the base 2, and the width of this gap 5 is constant along the outer circumference of the base and the inner circumference of the preheating ring. The axis passing through the center of the base 2 and the vertical axis 22 passing through the center of the preheating ring 3 coincide. In the expected arrangement of the position of the support shaft 9 with respect to its position relative to the preheating ring 3, the gap 5 along the outer circumference of the base 2 and the inner circumference of the preheating ring has a constant width, and when the support shaft rotates, the axis of rotation of the rotation coincides with the vertical axis 22.

[0065] If the base 2 is horizontally positioned on the support arm 10 but is eccentric with respect to the preheating ring, or if the base 2 is not horizontally positioned on the support arm 10, that is, is located in a plane not aligned perpendicular to the vertical axis 22, there is misalignment of the position of the base 2 with respect to its position relative to the preheating ring 3 (around the base 2). Then, in the first case, a change in the width of the gap 5 observed between the base 2 and the preheating ring 3 occurs, and in the second case, the distance from the base 2 to the camera system 7 changes ( Figure 2 ), and when the base 2 is rotated by means of the support shaft 9, the width of the gap 5 can be observed.

[0066] If, because the support shaft 9 is vertically oriented but not along the vertical axis 22 passing through the center of the preheating ring 3, a change in the width of the gap 5 between the base 2 and the preheating ring 3 is observed, there is misalignment of the position of the support shaft 9 with respect to its position relative to the preheating ring 3 (around the support shaft 9). If, because the support shaft 9 is tilted out of the expected position, that is, if when the base 2 rotates, the axis of rotation of the support shaft 9 and the vertical axis 22 are not parallel and pass through the center of the preheating ring 3, and a change in the width of the gap 5 compared to the stored width of the gap 5 is observed, there is also misalignment of the position of the support shaft 9 with respect to its position relative to the preheating ring 3 (around the support shaft 9).

[0067] Figure 2 The camera system 7 shown in the figure includes a camera for observing the image excerpt 6 during the rotation of the base 2 by means of the support shaft 9. The image excerpt 6 captures a radially extending region that preferably surrounds a part of the outer circumference of the substrate wafer 1, a part of the outer circumference of the base 2, a part of the inner circumference of the preheating ring 3, and also a part of the gap 5 between the base 2 and the preheating ring 3. The substrate wafer 1 is located in the recess of the base 2 on the placement surface 4 such that the rear side 23 of the substrate wafer 1 is at a distance from the base 24 of the base 2. The information contained in the image excerpt 6 is evaluated by means of an image processing device 8, especially with respect to the width of the gap 5 and the distance from the camera system 7 to the base 2. The control device 21 is used to check whether there is misalignment of the base 2 and / or the support shaft 9, and if necessary, if there is misalignment of the support shaft 9, a signal is generated, and this signal causes the drive device 12 (Figure 1 ) Move to correct the misalignment of the support axis that exists. If there is misalignment of the base, place the deposition device at ambient temperature and turn it on if necessary, and correct the misalignment.

[0068] The drive device 12 has the special property of being able to move or tilt the support axis 9, and of course both occur simultaneously. A possible embodiment of the drive device 12 is shown in Figure 1 . The movement of the support axis 9 is triggered by an actuator such as a piezoelectric actuator. To displace the support axis 9 in the horizontal plane, an actuator 13 (for displacement in the x direction) and an actuator 14 (for displacement in the y direction) are provided, and an actuator 16 is provided to tilt the support axis 9 at an inclination angle φ around a rotation axis parallel to the x direction in the Figure 1 observation plane, and an actuator 15 is provided to tilt the support axis 9 at an inclination angle θ around a rotation axis parallel to the y direction in the Figure 1 observation plane.

[0069] The lower dome 18 of the deposition device 20 is connected to the drive device 12 by means of a bellows 25 so that the support axis 9 can move and seal the resulting internal space against the inflow of ambient atmosphere.

Claims

1. A method for depositing an epitaxial layer on a substrate wafer (1) of a semiconductor material, characterized in that, The method includes: Arranging a substrate wafer (1) and a susceptor (2) in a deposition apparatus (20) such that the substrate wafer (1) rests on the susceptor (2) and the susceptor (2) is held by an arm of a support shaft (9); Monitoring whether there is misalignment of the susceptor (2) with respect to its position relative to a preheating ring (3) surrounding the susceptor (2); Monitoring whether there is misalignment of the support shaft (9) with respect to its position relative to the preheating ring (3); If at least one of the misalignments occurs, controlling a device (21) to move a drive unit (12) to move and tilt the support shaft (9) to eliminate the corresponding misalignment at a temperature not less than 450 °C; and Depositing an epitaxial layer on the substrate wafer (1).

2. The method according to claim 1, characterized in that, Correcting at least one of the misalignments with the deposition apparatus (20) turned off.

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