Method for depositing an epitaxial layer on a substrate wafer

Abstract

The present invention relates to a method for depositing an epitaxial layer on a substrate wafer from a gas phase, comprising: measuring the edge geometry of the substrate wafer, wherein the edge geometry assigns a thickness characteristic value to the edge of the substrate wafer based on the edge position; placing the substrate wafer in a pocket-shaped portion of a base of an apparatus for depositing the epitaxial layer, wherein the pocket-shaped portion is surrounded by a boundary having a circular circumference; heating the substrate wafer; and passing a process gas over the substrate wafer; characterized in that the substrate wafer is placed in the pocket-shaped portion so that the distance from the substrate wafer to the boundary of the pocket-shaped portion at the edge position with the thickness characteristic value of the thicker edge is smaller than the distance from the substrate wafer to the boundary of the pocket-shaped portion at the edge position with the thickness characteristic value of the thinner edge.

Description

Technical Field

[0001] The invention relates to a method for depositing an epitaxial layer on a substrate wafer. Background Art

[0002] For high-demand applications in the electronics industry, epitaxially coated semiconductor wafers are required, in particular substrate wafers made of single-crystalline silicon which are epitaxially coated with a silicon layer.

[0003] The common method for depositing this layer is chemical vapor deposition. The material for this layer is provided by a process gas, which passes over the side of the substrate wafer to be coated at a temperature at which the precursor compound contained in the process gas and containing the material is chemically cracked. During the deposition of this layer, the substrate wafer is located in the pocket (recess) of the base and is surrounded by the annular boundary of the base. This process is usually carried out in a device designed as a single wafer reactor. For example, this single wafer reactor is described in EP0 870 852 A1.

[0004] In order to grow the epitaxial layer on the substrate wafer as uniformly as possible, it is particularly important that the substrate wafer is located centrally in the pocket relative to the boundary.

[0005] In US 2010 0216261 A1 it is proposed to monitor the correct position of a substrate wafer on a receptacle by means of a camera system.

[0006] WO 17 135 604 A1 proposes measuring characteristic thickness values ​​in the edge region after deposition of the epitaxial layer and modifying certain process parameters for the subsequent deposition process based on the measurement results.

[0007] WO 14 103 657 A1 and JP 2015 201 599 A disclose methods in which the eccentricity is calculated based on the distribution of thickness characteristic values ​​in the edge region of a semiconductor wafer having an epitaxially deposited layer so as to correct the position of a subsequent substrate wafer on a susceptor as a function of (depending on) the eccentricity.

[0008] US2009 252 942A1 and JP2002 043 230A propose measuring the flatness of a substrate wafer before depositing an epitaxial layer and modifying certain process parameters during the deposition process so that the coating of the substrate wafer reduces edge roll-off.

[0009] However, such a procedure does not prevent the occurrence of thickness differences in the edge region of the epitaxially coated substrate wafer if the substrate wafer itself already has thickness differences in the edge region. Summary of the invention

[0010] The object of the present invention is to provide a solution to the problem, which allows the thickness of the epitaxial layer to be adjusted differently at different locations on the circumference of the substrate wafer.

[0011] The object of the present invention is achieved by a method for depositing an epitaxial layer on a substrate wafer from a gas phase, the method comprising:

[0012] measuring an edge geometry of the substrate wafer, wherein the edge geometry assigns a thickness characteristic value to an edge of the substrate wafer as a function of edge position;

[0013] placing the substrate wafer in a pocket of a base of an apparatus for depositing the epitaxial layer, the pocket being surrounded by a border having a circular circumference;

[0014] heating the substrate wafer; and

[0015] passing a process gas over the substrate wafer;

[0016] It is characterized in that

[0017] The substrate wafer is placed in the pocket so that the distance from the substrate wafer to the boundary of the pocket at an edge position having a thickness characteristic value of a thicker edge is smaller than the distance from the substrate wafer to the boundary of the pocket at an edge position having a thickness characteristic value of a thinner edge.

[0018] The invention is based on the finding that the central placement of the substrate wafer in the pocket is based on the assumption that the substrate wafer has a uniform edge geometry. However, in practice, this rarely happens, since machining steps such as grinding and polishing cannot produce a substrate wafer with a completely uniform edge thickness. The method according to the invention enables a uniform edge geometry of the epitaxially coated semiconductor wafer to be given compared to an uncoated substrate wafer, in particular if the substrate wafer has a relatively low edge thickness in one edge section (segment) and a relatively high edge thickness in the opposite edge section. However, homogenization of the edge thickness can also be achieved if, for example, there is only one edge section with a relatively low edge thickness.

[0019] First, the edge geometry of the substrate wafer is measured so that it can be obtained in the form of a thickness characteristic value. Preferably, as an edge exclusion, the outermost edge portion with a radial length of 1 mm or 2 mm is excluded from the measurement. In principle, any measurement value that allows a statement (description) to be given for the relative thickness at two different sections in the edge region of the substrate wafer can be regarded as a thickness parameter. For example, a suitable parameter for the thickness characteristic value is the positive ZDD (Z double derivative), which describes the curvature of the edge roll-off and is defined in SEMI standard M68-0720, or the ESFQR, which quantifies the flatness of the sector (part) in the edge region and is defined in SEMI standard M67-0720. The remainder of the specification uses ESFQR to represent the thickness characteristic.

[0020] The method according to the invention proposes to measure the edge geometry of the substrate wafer before it is coated with the epitaxial layer. For example, a distribution diagram (map) is provided, which assigns an ESFQR value to each sector, thereby indicating the thickness profile (curve) of the substrate wafer along its circumference. Substrate wafers with a wedge-like cross-sectional shape or those substrate wafers that are thinner at one edge than at the other edges are particularly suitable. An edge segment is an edge area extending in the circumferential direction over a distance of up to 50% of the circumference, preferably 7% to 42% of the circumference. A substrate wafer with a wedge-like shape has a thicker edge segment and a thinner edge segment that are opposite to each other, i.e. have the maximum possible distance between each other.

[0021] A correlation function is created for a deposition chamber, i.e., a single wafer reactor, for coating substrate wafers. The function assigns a thickness characteristic value to a displacement vector. The displacement vector indicates the direction and magnitude in which the thicker edge section of the substrate wafer must be offset from the center position in order to be placed in a pocket of a pedestal so that more material is deposited on the relative, thinner edge section when depositing an epitaxial layer than on a thicker edge section. Therefore, after deposition in the thinner edge section of the substrate wafer, the thickness characteristic value is greater than the thickness characteristic value that will be generated after deposition of the epitaxial layer in which the substrate wafer is centered in the pocket of the pedestal by the assigned thickness characteristic value. The displacement vector thus represents the eccentricity of the position of the center point of the substrate wafer placed on the pedestal compared to the position that the center point will have when the substrate wafer is centered in the pocket of the pedestal. The correlation function is experimentally determined before coating the substrate wafer by determining what kind of eccentricity causes what kind of change in the thickness characteristic value.

[0022] The placement of the substrate wafer in the pocket of the pedestal is advantageously carried out by a robot which performs this task as specified by the relevant function. Alternatively or additionally, the robot can be configured as an autonomous learning system which uses the measured geometry data of the substrate wafer and the resulting epitaxially coated semiconductor wafer to determine and implement the necessary eccentricity for the coating of the subsequent substrate wafer. Furthermore, it is preferred that the placement of the substrate wafer on the pedestal and its position in the pocket of the pedestal are monitored by means of a camera system.

[0023] The substrate wafer and the epitaxial layers deposited thereon preferably consist essentially of semiconductor material, for example single-crystalline silicon. The substrate wafer preferably has a diameter of at least 200 mm, particularly preferably at least 300 mm. The epitaxial layers preferably have a thickness of 1 μm to 20 μm.

[0024] The present invention will be described in further detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The effect of the present invention is qualitatively shown.

[0026] Figure 2 A substrate wafer is shown placed in a pocket of a susceptor in accordance with the present invention.

[0027] Figure 3 A correlation function assigning the expected variation of the thickness characteristic value to the eccentricity E is shown.

[0028] Figure 4 The deviation of the thickness of the substrate wafer from the target thickness along its diameter is shown.

[0029] Figure 5 shows the diameter of the substrate wafer after epitaxial coating according to Figure 4 The thickness of the substrate wafer after epitaxial coating deviates from the target thickness.

[0030] Figure 6 shows the diameter along the epitaxial layer according to Figure 5 The thickness of the epitaxial layer of the coated substrate wafer deviates from the target thickness.

[0031] Figure 7 A graph showing the deviation of a characteristic thickness value from a target value along the circumference of a substrate wafer before and after deposition of an epitaxial layer.

[0032] List of reference symbols used

[0033] 1 substrate wafer

[0034] 2 Epitaxial layer

[0035] 3 Base

[0036] 4. Pouch

[0037] 5 Thicker edge section

[0038] 6 Thinner edge section

[0039] 7 Outer boundary of the pocket

[0040] 8 Distribution Map

[0041] Eeccentricity

[0042] ESFQR ESFQR value

[0043] ΔESFQR The difference between the ESFQR value and the target value

[0044] Δt is the difference between thickness t and target thickness

[0045] dDiameter

[0046] WP Edge Location DETAILED DESCRIPTION

[0047] Figure 1 A cross-sectional view (vertical section) of a substrate wafer 1 is shown which is deposited in a pocket 4 of a susceptor 3 and has a relatively thick edge section (thicker edge section 5) and a relatively thin edge section (thinner edge section 6) opposite thereto. The substrate wafer 1 is not positioned centrally in the pocket 4 but rather eccentrically so that the thicker edge section 5 is at a shorter distance from the outer boundary 7 of the pocket than the thinner edge section 6. As a result of this configuration, the growth rate of the material during epitaxial layer deposition is lower where the distance is smaller than where the distance is larger.

[0048] Figure 1 The lower part shows the situation after the deposition of the epitaxial layer 2. The substrate wafer 1 has become a substrate wafer with a deposited epitaxial layer, wherein the epitaxial layer 2 is thinner in the region of the edge segment at a shorter distance from the border of the pocket 4 than in the region of the edge segment at a greater distance from the border of the pocket 4. Considering the thickness of the substrate wafer with the deposited epitaxial layer 2 and comparing it with the thickness of the substrate wafer 1, it is found that the thickness of the epitaxially coated substrate wafer in its edge region is more uniform compared to the thickness of the substrate wafer 1. The thickness difference in the edge region is more obvious in the case of the substrate wafer 1 than in the case of the epitaxially coated substrate wafer.

[0049] Figure 2A plan view of a substrate wafer placed in a pocket of a base according to the invention is shown. The substrate wafer 1 is not centrally positioned in the pocket of the base. The center of the substrate wafer is offset from the center of the pocket according to the eccentricity E, so that the thicker edge segment 5 is at a shorter distance from the outer boundary 7 of the pocket than the thinner edge segment 6. The direction and magnitude of the eccentricity E depend on the measurement of the edge geometry of the substrate wafer, for example, by measuring the flatness in the form of ESFQR values ​​in a 5° wide edge segment (segment). The results of the measurement are qualitatively indicated by the depicted distribution diagram 8 and clearly (identify) the thicker edge segment 5 highlighted with a "+" sign and the thinner edge segment 6 highlighted with a "-" sign.

[0050] The selected eccentricity E is based on a correlation function determined by preliminary tests of the deposition device to be used. These tests check what changes in the thickness characteristic values ​​are expected when the substrate wafer is placed in the pocket of the pedestal with a certain eccentricity E. In the selected example, according to Figure 3 The correlation function of indicates the difference ΔESFQR between the ESFQR value obtained in the thinner edge section after deposition and the target value when the substrate wafer is not placed in the pocket of the pedestal at a central position but has a corresponding eccentricity E. Therefore, according to Figure 3 The correlation function of φ teaches that if the substrate wafer is not placed centrally in the pocket of the pedestal before deposition, but has an eccentricity of 100 μm, then after deposition of the epitaxial layer the ESFQR value in the sector of the thinner edge section will increase by about 2 nm.

[0051] Figure 4 , Figure 5 and Figure 6 They show the epitaxial layer before deposition ( Figure 4 ) and after ( Figure 5 ) Deviation between the thickness of the single crystal silicon substrate wafer and the target thickness and the thickness of the epitaxial layer and the target thickness ( Figure 6 ) curve. Figure 4 , the substrate wafer has a significantly different edge thickness, with a thinner edge section in the region of 0 mm and a thicker edge section in the region of 300 mm. After the epitaxial layer is deposited according to the invention, the edge thickness differences in these edge sections are almost compensated ( Figure 5 ).according to Figure 6 The curve of the thickness deviation of the epitaxial layer shows that due to the application of the present invention, the epitaxial layer is thicker at the edge position corresponding to the thinner edge section of the substrate wafer and thinner at the edge position corresponding to the thicker edge section of the substrate wafer. The eccentric position of the substrate wafer leads to different amounts of material being deposited at the considered edge sections.

[0052] The solution according to the invention improves the edge geometry, even when considered over the entire circumference. Figure 7 The edge geometry of the substrate wafer before (curve A) and after (curve B) deposition of the epitaxial layer is shown in the form of smooth curves, in this case in the form of ESFQR values ​​as a function of the edge position WP. The curves are based on 72 measurement points, each describing the ESFQR value of a sector with a width of 5° and a radial length of 35 mm (thus allowing an edge exclusion of 1 mm).

[0053] The above description of the exemplary embodiments should be understood to be exemplary. The resulting disclosure, on the one hand, enables those skilled in the art to understand the present invention and its associated advantages, and on the other hand, covers obvious changes and modifications to the described structures and methods within the purview of those skilled in the art. Therefore, all such changes and modifications and their equivalents should be covered by the scope of protection of the claims.

Claims

1. A method for depositing an epitaxial layer on a substrate wafer from a gas phase, comprising: Measuring the edge geometry of the substrate wafer, wherein the edge geometry assigns a thickness characteristic value to the edge of the substrate wafer as a function of the edge position, the substrate wafer having a relatively low edge thickness in one edge segment and a relatively high edge thickness in an opposite edge segment, the substrate wafer having a thicker edge segment and a thinner edge segment relative to each other, the edge segment being an edge region extending along a circumferential direction over a distance up to 50% of the circumference; placing the substrate wafer in a pocket portion of a base of an apparatus for depositing the epitaxial layer, the pocket portion being surrounded by a boundary having a circular circumference; heating the substrate wafer; and passing a process gas over the substrate wafer; characterized in that the substrate wafer is placed in the pocket portion so that the distance from the substrate wafer to the boundary of the pocket portion at the edge position of the thicker edge segment having a larger thickness characteristic value is smaller than the distance from the substrate wafer to the boundary of the pocket portion at the edge position of the thinner edge segment having a smaller thickness characteristic value.

2. The method according to claim 1, characterized in that: There is only one thinner edge section.

3. The method according to claim 1 or claim 2, characterized in that: ESFQR or ZDD is measured as the thickness characteristic value.

4. The method according to any one of claims 1 to 2, characterized in that The substrate wafer is positioned with the aid of a robot.

5. The method according to any one of claims 1 to 2, characterized in that The position of the substrate wafer in the pocket is monitored by means of a camera system.

6. The method according to any one of claims 1 to 2, characterized in that A silicon epitaxial layer is deposited on a single crystal silicon wafer.

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