Method of measuring overlay error

Abstract

The application provides a method for measuring overlay deviation. After forming an epitaxial layer, first relative displacement data of first-in-layer alignment marks on the epitaxial layer and pre-layer alignment marks on a substrate are obtained through one optical diffraction-based overlay error measurement. After coating a photoresist layer, second relative displacement data of second-in-layer alignment marks on the photoresist layer and the first-in-layer alignment marks on the epitaxial layer are obtained through one image recognition-based overlay error measurement. Finally, real overlay deviation between the second-in-layer and the pre-layer after deposition of the epitaxial layer is obtained according to the first relative displacement data and the second relative displacement data. The method solves the problem of large error in the measurement result of overlay deviation between the in-layer and the pre-layer caused by lateral displacement of lithography alignment due to pattern drift, and improves the accuracy of the measurement result of overlay deviation.

Description

Technical Field

[0001] This application relates to the field of semiconductor lithography technology, specifically to a method for measuring overlay deviation. Background Technology

[0002] Epitaxy is a process in which a single-crystal layer is deposited on a single-crystal substrate; this newly deposited single-crystal layer is called the epitaxial layer. Epitaxy provides device designers with great flexibility in optimizing device performance, such as controlling the doping thickness, concentration, and outline of the epitaxial layer, factors independent of the silicon substrate. This control is achieved through doping during the epitaxial growth process. Epitaxial layers can also reduce latch-up effects in CMOS devices.

[0003] refer to Figure 1 , Figure 1 This is a schematic diagram of a semiconductor structure after the formation of an epitaxial layer in the prior art. However, in the epitaxial process, due to the anisotropy of the growth rate of the crystallographic plane, this crystallographic plane is constrained by the bottom and edges of the low-lying region (the low-lying region is, for example, the alignment mark pattern). Therefore, relative to the low-lying region in the previous layer (substrate 1), the two parallel step edges of the low-lying region of the epitaxial layer 2 will move to the left or right by a certain distance d. The lateral displacement (X-direction displacement) of the pattern between substrate 1 and epitaxial layer 2 is called pattern drift.

[0004] Because pattern drift causes lateral offset / displacement in photolithography alignment, conventional IBO (image-based overlay) measurements cannot reflect the true overlay deviation between the current layer and the previous layer. In other words, the overlay deviation error obtained by conventional IBO measurements is large, and the measurement results of the overlay deviation are not accurate enough. Summary of the Invention

[0005] This application provides a method for measuring overlay deviation, which can solve the problem that pattern drift caused by epitaxial layer pattern drift during photolithography alignment, and that conventional IBO measurement cannot reflect the true overlay deviation between the current layer and the previous layer.

[0006] This application provides a method for measuring overlay deviation, including:

[0007] A substrate is provided, wherein the substrate is defined as a front layer, and a front layer alignment mark is formed therein;

[0008] An epitaxial layer is formed on the substrate by an epitaxial process, wherein the epitaxial layer is defined as a first layer and an alignment mark for the first layer is formed therein;

[0009] The overlay error of the semiconductor structure after the formation of the epitaxial layer is measured based on optical diffraction to obtain the first relative displacement data of the first alignment mark of the current layer and the alignment mark of the previous layer.

[0010] A photoresist layer is coated on the surface of the epitaxial layer, wherein the photoresist layer is defined as a second layer and an alignment mark for the second layer is formed in the photoresist layer;

[0011] The semiconductor structure after the photoresist layer is coated is subjected to overlay error measurement based on image recognition to obtain the second relative displacement data of the second in-layer alignment mark and the first in-layer alignment mark;

[0012] Based on the first relative displacement data and the second relative displacement data, the overlay deviation between the second current layer and the previous layer is obtained.

[0013] Optionally, in the method for measuring overlay deviation, the step of obtaining the overlay deviation between the second current layer and the previous layer based on the first relative displacement data and the second relative displacement data includes:

[0014] The difference between the second relative displacement data and the first relative displacement data is obtained, and the difference between the second relative displacement data and the first relative displacement data is used as the overlay deviation between the second current layer and the previous layer.

[0015] Optionally, in the method for measuring overlay deviation, the step of measuring the overlay error of the semiconductor structure after the formation of the epitaxial layer based on optical diffraction, and obtaining the first relative displacement data of the first alignment mark of the current layer and the alignment mark of the previous layer, includes:

[0016] The overlay error of the semiconductor structure after the formation of the epitaxial layer is measured based on optical diffraction to obtain the light intensity of the positive first-order light and the light intensity of the negative first-order light.

[0017] Based on the light intensity of the positive first-order light and the light intensity of the negative first-order light, obtain the light intensity difference between the positive first-order light and the negative first-order light.

[0018] Based on the linear relationship between the light intensity difference and the first relative displacement data, the first relative displacement data of the first current layer alignment mark and the previous layer alignment mark are obtained.

[0019] Optionally, in the method for measuring overlay deviation, in the same measurement of overlay error based on optical diffraction, the same light source is used to penetrate the epitaxial layer and the substrate to perform optical diffraction; in different measurements of overlay error based on optical diffraction, light sources of different wavelengths are used to penetrate the epitaxial layer and the substrate to perform optical diffraction.

[0020] Optionally, in the method for measuring overlay deviation, the thickness of the epitaxial layer is 0–10 μm.

[0021] Optionally, in the method for measuring overlay deviation, the previous layer alignment mark is formed by photolithography and etching processes; the first current layer alignment mark is formed by epitaxial deposition using the previous layer alignment mark as a substrate; and the second current layer alignment mark is formed by exposure and development processes.

[0022] Optionally, in the method for measuring overlay deviation, the first current layer alignment mark formed epitaxially in the epitaxial layer undergoes pattern drift in the X or Y direction relative to the previous layer alignment mark.

[0023] Optionally, in the method for measuring overlay deviation, the placement area of ​​the front layer alignment mark is the device side within the dicing or exposure area.

[0024] The technical solution of this application has at least the following advantages:

[0025] This application, after forming an epitaxial layer on a substrate, obtains the first relative displacement data of the first alignment mark on the epitaxial layer and the alignment mark of the previous layer on the substrate through a diffraction-based overlay measurement (DBO). After coating a photoresist layer on the epitaxial layer, it obtains the second relative displacement data of the second alignment mark on the photoresist layer and the first alignment mark on the epitaxial layer through an image-based overlay measurement (IBO). Finally, based on the first and second relative displacement data, the true overlay deviation between the second layer and the previous layer after epitaxial layer deposition is obtained. This solves the problem of large errors in the measurement results of the overlay deviation between the layer and the previous layer caused by lateral displacement of photolithography alignment due to pattern drift, and improves the accuracy of the overlay deviation measurement results. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the semiconductor structure after the epitaxial layer is formed in the prior art;

[0028] Figure 2 This is a flowchart of the method for measuring overlay deviation according to an embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of the substrate structure according to an embodiment of the present invention;

[0030] Figure 4 This is a schematic diagram of the semiconductor structure after the epitaxial layer is formed according to an embodiment of the present invention;

[0031] Figure 5 This is a schematic diagram of the semiconductor structure after the formation of the photoresist layer according to an embodiment of the present invention;

[0032] The reference numerals in the attached figures are explained as follows:

[0033] 1-Substrate, 2-Epipolar layer;

[0034] 10 - Substrate, 20 - Epitaxial layer, 30 - Photoresist layer. Detailed Implementation

[0035] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0036] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0037] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0038] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0039] This application provides a method for measuring overlay deviation, referring to... Figure 2 , Figure 2 This is a flowchart of a method for measuring overprinting deviation according to an embodiment of the present invention. The method for measuring overprinting deviation includes:

[0040] Step S1: Refer to Figure 3 , Figure 3 This is a schematic diagram of the structure of a substrate according to an embodiment of the present invention. A substrate 10 is provided, wherein the substrate 10 is defined as the front layer, and a front layer alignment mark is formed in the substrate 10.

[0041] In this embodiment, the placement area of ​​the front layer alignment mark is the device side within the cutting channel or exposure area.

[0042] Step S2: Reference Figure 4 , Figure 4 This is a schematic diagram of the semiconductor structure after the formation of the epitaxial layer according to an embodiment of the present invention. An epitaxial layer 20 is formed on the substrate 10 by an epitaxial process. The epitaxial layer 20 is defined as the first epitaxial layer, and a first epitaxial layer alignment mark is formed in the epitaxial layer 20.

[0043] Preferably, the thickness of the epitaxial layer 20 is 0–10 μm.

[0044] In this embodiment, the thickness of the epitaxial layer 20 is 4.5 μm.

[0045] Step S3: Perform an overlay error measurement based on optical diffraction on the semiconductor structure after the formation of the epitaxial layer 20 to obtain the first relative displacement data of the first alignment mark of the current layer and the alignment mark of the previous layer.

[0046] Preferably, the step of measuring the overlay error of the semiconductor structure after the formation of the epitaxial layer based on optical diffraction to obtain the first relative displacement data of the first alignment mark of the current layer and the alignment mark of the previous layer (step S3) may specifically include:

[0047] Step S3.1: Perform an overlay error measurement based on optical diffraction on the semiconductor structure after the formation of the epitaxial layer 20 to obtain the light intensity of the positive first-order light and the light intensity of the negative first-order light;

[0048] Step S3.2: Obtain the intensity difference between the positive first-order light and the negative first-order light based on their intensity.

[0049] Step S3.3: Based on the linear relationship between the light intensity difference and the first relative displacement data, obtain the first relative displacement data between the first current layer alignment mark and the previous layer alignment mark.

[0050] Preferably, in the same optical diffraction-based overlay error measurement, the same light source is used to penetrate the epitaxial layer and the substrate to perform optical diffraction; in different optical diffraction-based overlay error measurements, light sources of different wavelengths are used to penetrate the epitaxial layer and the substrate to perform optical diffraction.

[0051] In this embodiment, during the same optical diffraction-based overlay error measurement, ultraviolet light can be used to penetrate the epitaxial layer and the substrate to perform optical diffraction, thereby completing the optical diffraction-based overlay error measurement of the first current layer and the previous layer.

[0052] In this embodiment, the epitaxial layer and the substrate are two stacked gratings. It is worth noting that when the grating of one layer overlaps the grating of the previous layer, the intensity distribution of the first-order light after diffraction by the two gratings will have an approximately linear relationship with the displacement dislocation of the two gratings. The linear relationship (linear function) between the positive and negative first-order intensity difference of the same light source and the relative displacement data between the current and previous layers can be obtained through the DBO measurement module in a measuring instrument with DBO measurement capabilities. Measuring instruments with DBO measurement capabilities include ASML's YieldStar series and KTE's Archer LCM series, with the Archer LCM series combining both IBO and DBO measurement systems. Further, information on overlay error measurement platforms and the DBO measurement principle of the measurement platform can be found in Mao Xiaoming's (author) master's thesis, "A Novel Overlay Error Measurement System for Advanced Node Processes."

[0053] Step S4: Reference Figure 5 , Figure 5 This is a schematic diagram of a semiconductor structure after the formation of a photoresist layer according to an embodiment of the present invention. A photoresist layer 30 is coated on the surface of the epitaxial layer, wherein the photoresist layer 30 is defined as a second layer, and a second layer alignment mark is formed in the photoresist layer 30.

[0054] Preferably, the front layer alignment mark is formed by photolithography and etching processes; the first current layer alignment mark is formed by epitaxial deposition using the front layer alignment mark as a substrate; and the second current layer alignment mark is formed by exposure and development processes.

[0055] It is worth noting that, relative to the previous layer alignment mark, the first current layer alignment mark formed by epitaxy in the epitaxial layer 20 undergoes pattern drift in the X or Y direction.

[0056] In this embodiment, the first alignment mark formed by epitaxy in the epitaxial layer 20 undergoes pattern drift in the X direction (lateral direction).

[0057] Step S5: Perform overlay error measurement on the semiconductor structure after coating the photoresist layer 30 based on image recognition, and obtain the second relative displacement data of the second current layer alignment mark and the first current layer alignment mark.

[0058] Step S6: Based on the first relative displacement data and the second relative displacement data, obtain the overlay deviation between the second current layer and the previous layer.

[0059] Specifically, the step of obtaining the overlay deviation between the second current layer and the previous layer based on the first relative displacement data and the second relative displacement data (step S6) includes: obtaining the difference between the second relative displacement data and the first relative displacement data, and using the difference between the second relative displacement data and the first relative displacement data as the overlay deviation between the second current layer and the previous layer.

[0060] In this application, after forming an epitaxial layer on a substrate, a first relative displacement data of the first alignment mark on the epitaxial layer and the alignment mark of the previous layer on the substrate is obtained through an overlay error measurement based on optical diffraction. After coating a photoresist layer on the epitaxial layer, a second relative displacement data of the second alignment mark on the photoresist layer and the first alignment mark on the epitaxial layer is obtained through an overlay error measurement based on image recognition. Finally, based on the first and second relative displacement data, the true overlay deviation between the second and previous layers after epitaxial layer deposition is obtained. This solves the problem of large errors in the measurement results of overlay deviation between the current and previous layers caused by lateral displacement of photolithography alignment due to pattern drift. The overlay deviation measurement method provided in this application can effectively offset this part of the error in the measurement results of overlay deviation caused by lateral displacement of photolithography alignment due to pattern drift in the epitaxial process, thereby improving the accuracy of the overlay deviation measurement results.

[0061] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A method for measuring overlay deviation, characterized in that, include: A substrate is provided, wherein the substrate is defined as a front layer, and a front layer alignment mark is formed therein; An epitaxial layer is formed on the substrate by an epitaxial process, wherein the epitaxial layer is defined as a first layer and an alignment mark for the first layer is formed therein; The overlay error of the semiconductor structure after the formation of the epitaxial layer is measured based on optical diffraction to obtain the first relative displacement data of the first alignment mark of the current layer and the alignment mark of the previous layer. A photoresist layer is coated on the surface of the epitaxial layer, wherein the photoresist layer is defined as a second layer and alignment marks for the second layer are formed in the photoresist layer; The semiconductor structure after the photoresist layer is coated is subjected to overlay error measurement based on image recognition to obtain the second relative displacement data of the second in-layer alignment mark and the first in-layer alignment mark; Based on the first relative displacement data and the second relative displacement data, the overlay deviation between the second current layer and the previous layer is obtained; The step of measuring the overlay error of the semiconductor structure after the formation of the epitaxial layer based on optical diffraction to obtain the first relative displacement data of the first alignment mark of the current layer and the alignment mark of the previous layer includes: The overlay error of the semiconductor structure after the formation of the epitaxial layer is measured based on optical diffraction to obtain the light intensity of the positive first-order light and the light intensity of the negative first-order light. Based on the light intensity of the positive first-order light and the light intensity of the negative first-order light, obtain the light intensity difference between the positive first-order light and the negative first-order light. Based on the linear relationship between the light intensity difference and the first relative displacement data, the first relative displacement data of the first current layer alignment mark and the previous layer alignment mark are obtained.

2. The method for measuring overlay deviation according to claim 1, characterized in that, The step of obtaining the overlay deviation between the second current layer and the previous layer based on the first relative displacement data and the second relative displacement data includes: The difference between the second relative displacement data and the first relative displacement data is obtained, and the difference between the second relative displacement data and the first relative displacement data is used as the overlay deviation between the second current layer and the previous layer.

3. The method for measuring overlay deviation according to claim 1, characterized in that, In the same optical diffraction-based overlay error measurement, the same light source was used to perform optical diffraction through the epitaxial layer and the substrate; In different optical diffraction-based overlay error measurements, light sources of different wavelengths are used to penetrate the epitaxial layer and the substrate to perform optical diffraction.

4. The method for measuring overlay deviation according to claim 1, characterized in that, The thickness of the epitaxial layer is 0–10 μm.

5. The method for measuring overlay deviation according to claim 1, characterized in that, The alignment marks on the front layer are formed by photolithography and etching processes; The first layer alignment mark is formed by epitaxial deposition based on the previous layer alignment mark; The second alignment mark is formed through an exposure and development process.

6. The method for measuring overlay deviation according to claim 5, characterized in that, Relative to the previous layer alignment mark, the first current layer alignment mark formed by epitaxy in the epitaxial layer undergoes pattern drift in the X or Y direction.

7. The method for measuring overlay deviation according to claim 1, characterized in that, The placement area of ​​the front layer alignment mark is the device side within the cutting channel or exposure area.

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