Method for predicting optimal focal depth in photoetching process
By using the optimal focal depth of the reference wafer and the difference in the thickness of the lithographic material layer, the optimal focal depth of the target wafer is solved, and the problem of repeated collection of FEM data for different wafers under the same lithography process is improved, and the lithography efficiency is saved and resources are saved.
Patent Information
- Application Number
- CN202510061528.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-14
- Publication Date
- 2025-04-01
AI Technical Summary
During semiconductor manufacturing, different wafers under the same lithography process need to re-collect FEM data to confirm the optimal depth of focus, resulting in wasted time, manpower and resources.
By providing a reference wafer and a target wafer, the optimal focal depth of the target wafer is calculated using the difference in the optimal focal depth of the reference wafer and the thickness of the lithographic material layer, avoiding the need for repeated collection of FEM data.
The evaluation speed of the lithography process window has been greatly improved, the lithography efficiency has been improved, and human and material resources have been saved.
Smart Images
Figure CN119739010A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of semiconductor lithography technology, and in particular to a method for predicting an optimal focal depth in a lithography process. Background Art
[0002] In the semiconductor manufacturing process, the establishment of the best conditions for the photolithography process is crucial to the stability of the process. Photolithography usually confirms the best depth of focus (DOF) by doing energy-focus (exposure energy-focal length) deviation. This method is more suitable for new processes on new platforms. However, for the same photolithography process, when performing photolithography on different wafers, it is usually necessary to re-collect FEM (Focus on energy matrix) data. Since the amount of FEM data is very large, it takes a lot of time, manpower and machine resources, and the work is cumbersome. In particular, if only the thickness of the photolithography material layer stacked on the wafer surface is changed, FEM data needs to be re-collected to confirm the best exposure conditions (best depth of focus), which is even more time-consuming and labor-intensive. Summary of the invention
[0003] The present application provides a method for predicting the optimal focal depth in a lithography process, which can solve the problem that when the same lithography process is performed on different wafers, each wafer needs to be re-confirmed with FEM for the optimal focal depth, which is time-consuming and labor-intensive.
[0004] The present application embodiment provides a method for predicting an optimal focal depth in a photolithography process, comprising: Providing a photoresist material layer with a qualified light transmittance; Providing a reference wafer, on which the photolithography material layer having a first thickness is further formed; According to the photolithography material layer of the first thickness, collecting the best focal depth of the reference wafer under specific photolithography conditions during the photolithography process as a reference focal depth; Providing a target wafer to be subjected to a photolithography process, wherein a photolithography material layer having a second thickness is formed on the target wafer; An optimal focal depth for performing a photolithography process on the target wafer under specific photolithography conditions is obtained according to the reference focal depth, the first thickness, and the second thickness.
[0005] Optionally, in the method for predicting the optimal focal depth in the lithography process, the step of obtaining the optimal focal depth for performing the lithography process on the target wafer under specific lithography conditions according to the reference focal depth, the first thickness, and the second thickness includes: Acquire a reference zero point of the photolithography material layer of the first thickness according to the first thickness; acquiring a target zero point of the photolithography material layer of the second thickness according to the second thickness; According to the reference focal depth, the reference zero point and the target zero point, an optimal focal depth for performing a photolithography process on the target wafer under specific photolithography conditions is obtained.
[0006] Optionally, in the method for predicting the optimal depth of focus in the photolithography process, in the process of obtaining the reference zero point of the photolithography material layer of the first thickness according to the first thickness, the calculation formula for the reference zero point of the photolithography material layer of the first thickness is: Z1=L1 / 2; wherein Z1 is the reference zero point of the photolithography material layer of the first thickness; L1 is the thickness value of the photolithography material layer of the first thickness.
[0007] Optionally, in the method for predicting the optimal depth of focus in the photolithography process, in the process of obtaining the target zero point of the photolithography material layer of the second thickness according to the second thickness, the calculation formula for the target zero point of the photolithography material layer of the second thickness is: Z2=L2 / 2; wherein Z2 is the target zero point of the photolithography material layer of the second thickness; L2 is the thickness value of the photolithography material layer of the second thickness.
[0008] Optionally, in the method for predicting the optimal focal depth in the lithography process, in the process of obtaining the optimal focal depth for performing the lithography process on the target wafer under the specific lithography conditions based on the reference focal depth, the reference zero point and the target zero point, the calculation formula for the optimal focal depth of the target wafer is: F'=F-(Z2-Z1), wherein F' is the optimal focal depth of the target wafer; F is the optimal focal depth of the reference wafer; Z2 is the target zero point of the lithography material layer of the second thickness; and Z1 is the reference zero point of the lithography material layer of the first thickness.
[0009] Optionally, in the method for predicting the optimal focal depth in the photolithography process, the photolithography material layer includes, from bottom to top, a stacked spin-on carbon layer, a low-temperature oxidation layer, an anti-reflection layer and a photoresist layer.
[0010] Optionally, in the method for predicting the optimal depth of focus in the photolithography process, in the process of obtaining the reference zero point of the photolithography material layer of the first thickness according to the first thickness, the calculation formula for the reference zero point of the photolithography material layer of the first thickness is: Z1=(d1+d2+d3+d4) / 2; wherein Z1 is the reference zero point of the photolithography material layer of the first thickness; d1 is the reference thickness of the spin-coated carbon layer; d2 is the reference thickness of the low-temperature oxide layer; d3 is the reference thickness of the anti-reflective layer; and d4 is the reference thickness of the photoresist layer.
[0011] Optionally, in the method for predicting the optimal depth of focus in the photolithography process, in the process of obtaining the target zero point of the photolithography material layer of the second thickness according to the second thickness, the calculation formula for the target zero point of the photolithography material layer of the second thickness is: Z2=(D1+D2+D3+D4) / 2; wherein Z2 is the target zero point of the photolithography material layer of the second thickness; D1 is the target thickness of the spin-coated carbon layer; D2 is the target thickness of the low-temperature oxide layer; D3 is the target thickness of the anti-reflective layer; and D4 is the target thickness of the photoresist layer.
[0012] Optionally, in the method for predicting the optimal depth of focus in the photolithography process, in the process of providing a photolithography material layer with qualified light transmittance, if the K value of the negative refractive index of the photolithography material layer under visible light is less than 0.05, it is confirmed that the light transmittance of the photolithography material layer is qualified.
[0013] Optionally, in the method for predicting the optimal depth of focus in the photolithography process, in the process of providing a photolithography material layer with qualified light transmittance, if the K values of the negative refractive index of the spin-coated carbon layer, the low-temperature oxidation layer, the anti-reflective layer and the photoresist layer under visible light are all less than 0.05, then the light transmittance of the photolithography material layer is confirmed to be qualified.
[0014] The technical solution of this application has at least the following advantages: In the present application, based on a photolithography material layer with a qualified degree of light transmittance, the best focal depth of a reference wafer under a certain photolithography process is obtained as a reference focal depth, and based on the reference focal depth and the first thickness of the photolithography material layer formed on the reference wafer and the second thickness of the photolithography material layer formed on the target wafer, the best focal depths of different target wafers under the same photolithography process are predicted. In the present application, only one FEM is required in the photolithography process of the reference wafer, and FEM data is collected once. Subsequently, different target wafers under the same photolithography process can predict and obtain the best focal depth based on the reference focal depth and the first thickness and the second thickness, thereby improving the evaluation speed of the photolithography process window of different target wafers under the same photolithography process, improving the photolithography efficiency, and greatly saving manpower and material resources. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.
[0016] Figure 1 The flowchart of the method for predicting the optimal focal depth in the photolithography process according to an embodiment of the present invention. DETAILED DESCRIPTION
[0017] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in this application. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.
[0018] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.
[0019] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.
[0020] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.
[0021] The present invention provides a method for predicting the optimal focal depth in a photolithography process. Figure 1 , Figure 1 : is a flow chart of a method for predicting an optimal focal depth in a photolithography process according to an embodiment of the present invention. The method for predicting an optimal focal depth in a photolithography process includes: First, step S1 is performed: providing a photoresist material layer with a qualified light transmittance.
[0022] Preferably, in the process of providing a photoresist material layer with qualified light transmittance, if the K value of the negative refractive index of the photoresist material layer under visible light is less than 0.05, it is confirmed that the light transmittance of the photoresist material layer is qualified.
[0023] Then, step S2 is performed: providing a reference wafer, on which the photolithography material layer with a first thickness is formed.
[0024] Next, step S3 is performed: according to the photolithography material layer of the first thickness, the best focal depth of the reference wafer under specific photolithography conditions is collected during the photolithography process as a reference focal depth F.
[0025] In this embodiment, the specific photolithography conditions at least include: the wavelength of the exposure light source is: 248nm; the exposure energy is: 30mj, the pull-off range is: ±5mj; the focal depth is: 0μm, and the pull-off range is: ±0.3μm.
[0026] Preferably, in the reference wafer lithography process, a FEM is performed and FEM data is collected to evaluate the optimal lithography conditions, including collecting the optimal focal depth of the reference wafer under specific lithography conditions as the reference focal depth F.
[0027] Further, step S4 is performed: providing a target wafer to be subjected to a photolithography process, wherein a photolithography material layer having a second thickness is formed on the target wafer.
[0028] Finally, step S5 is performed: according to the reference focal depth, the first thickness and the second thickness, an optimal focal depth for performing a photolithography process on the target wafer under the same specific photolithography conditions as step S3 is obtained.
[0029] Preferably, step S5 of obtaining an optimal focal depth for performing a photolithography process on the target wafer under specific photolithography conditions according to the reference focal depth, the first thickness and the second thickness comprises: Step S5.1: acquiring a reference zero point of the photolithography material layer of the first thickness according to the first thickness; Among them, in the process of obtaining the reference zero point of the photolithography material layer of the first thickness according to the first thickness, the calculation formula of the reference zero point of the photolithography material layer of the first thickness is: Z1=L1 / 2; wherein Z1 is the reference zero point of the photolithography material layer of the first thickness; L1 is the thickness value of the photolithography material layer of the first thickness.
[0030] Step S5.2: acquiring a target zero point of the photolithography material layer of the second thickness according to the second thickness; Among them, in the process of obtaining the target zero point of the photolithography material layer of the second thickness according to the second thickness, the calculation formula of the target zero point of the photolithography material layer of the second thickness is: Z2=L2 / 2; wherein Z2 is the target zero point of the photolithography material layer of the second thickness; L2 is the thickness value of the photolithography material layer of the second thickness.
[0031] Step S5.3: According to the reference focal depth, the reference zero point and the target zero point, an optimal focal depth for performing a photolithography process on the target wafer under specific photolithography conditions is obtained.
[0032] Among them, in the process of obtaining the optimal focal depth of the target wafer for performing a lithography process on the target wafer under the specific lithography conditions according to the reference focal depth, the reference zero point and the target zero point, the calculation formula for the optimal focal depth of the target wafer is: F'=F-(Z2-Z1), wherein F' is the optimal focal depth of the target wafer; F is the optimal focal depth of the reference wafer; Z2 is the target zero point of the lithography material layer of the second thickness; and Z1 is the reference zero point of the lithography material layer of the first thickness.
[0033] Furthermore, the photolithography material layer includes, from bottom to top, a stacked spin-on carbon layer (SOC), a low temperature oxide layer (LTO), an anti-reflection layer (BARC) and a photoresist layer.
[0034] Among them, the spin-coated carbon layer, the anti-reflective layer and the photoresist layer are used as photolithography materials and are formed on the reference wafer and the target wafer by spin coating; the low-temperature oxide layer acts as a hard mask and is formed on the reference wafer and the target wafer by low-temperature CVD (chemical vapor deposition).
[0035] It is worth noting that when the photolithography material layer includes: a stacked spin-coated carbon layer, a low-temperature oxidation layer, an anti-reflection layer and a photoresist layer, in the process of providing a photolithography material layer with qualified light transmittance, if the K values of the negative refractive index of the spin-coated carbon layer, the low-temperature oxidation layer, the anti-reflection layer and the photoresist layer under visible light are all less than 0.05, then the light transmittance of the photolithography material layer is confirmed to be qualified.
[0036] Preferably, step S5 of obtaining an optimal focal depth for performing a photolithography process on the target wafer under specific photolithography conditions according to the reference focal depth, the first thickness and the second thickness comprises: Step S5.1: acquiring a reference zero point of the photolithography material layer of the first thickness according to the first thickness; Among them, in the process of obtaining the reference zero point of the photoresist material layer of the first thickness according to the first thickness, the calculation formula of the reference zero point of the photoresist material layer of the first thickness is: Z1=(d1+d2+d3+d4) / 2; wherein Z1 is the reference zero point of the photoresist material layer of the first thickness; d1 is the reference thickness of the spin-coated carbon layer; d2 is the reference thickness of the low-temperature oxidation layer; d3 is the reference thickness of the anti-reflective layer; and d4 is the reference thickness of the photoresist layer.
[0037] Step S5.2: acquiring a target zero point of the photolithography material layer of the second thickness according to the second thickness; Among them, in the process of obtaining the target zero point of the photoresist material layer of the second thickness according to the second thickness, the calculation formula of the target zero point of the photoresist material layer of the second thickness is: Z2=(D1+D2+D3+D4) / 2; wherein Z2 is the target zero point of the photoresist material layer of the second thickness; D1 is the target thickness of the spin-coated carbon layer; D2 is the target thickness of the low-temperature oxide layer; D3 is the target thickness of the anti-reflective layer; and D4 is the target thickness of the photoresist layer.
[0038] Step S5.3: According to the reference focal depth, the reference zero point and the target zero point, an optimal focal depth for performing a photolithography process on the target wafer under specific photolithography conditions is obtained.
[0039] Among them, in the process of obtaining the optimal focal depth of the target wafer for performing a lithography process on the target wafer under the specific lithography conditions according to the reference focal depth, the reference zero point and the target zero point, the calculation formula for the optimal focal depth of the target wafer is: F'=F-(Z2-Z1), wherein F' is the optimal focal depth of the target wafer; F is the optimal focal depth of the reference wafer; Z2 is the target zero point of the lithography material layer of the second thickness; and Z1 is the reference zero point of the lithography material layer of the first thickness.
[0040] It is worth noting that when the photolithography material layer includes: a stacked spin-coated carbon layer, a low-temperature oxidation layer, an anti-reflective layer and a photoresist layer, the thickness of the spin-coated carbon layer, the thickness of the low-temperature oxidation layer, the thickness of the anti-reflective layer and the thickness of the photoresist layer formed on the target wafer can all be adjusted, or only the thickness of any one layer, any two layers or any three layers can be adjusted.
[0041] The inventors have found that the difference between the best focal depth in the lithography process predicted by the prediction method provided in the present application and the best focal depth obtained by the traditional method of performing FEM and collecting FEM data is controlled within ±0.005μm. It can be seen that the method for predicting the best focal depth in the lithography process provided in the present application is completely effective and feasible.
[0042] The present application obtains the best focal depth of a reference wafer under a certain lithography process as a reference focal depth based on a photolithography material layer with a qualified light transmittance, and predicts the best focal depth of different target wafers under the same lithography process according to the reference focal depth and the first thickness of the photolithography material layer formed on the reference wafer and the second thickness of the photolithography material layer formed on the target wafer. The present application only needs to perform FEM once in the lithography process of the reference wafer and collect FEM data once. Different target wafers under the same subsequent lithography process can predict and obtain the best focal depth based on the reference focal depth and the first thickness and the second thickness, thereby improving the evaluation speed of the lithography process window of different target wafers under the same subsequent lithography process, improving the lithography efficiency, and greatly saving manpower and material resources.
[0043] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection created by this application.
Claims
1. A method for predicting the optimal depth of focus in a photolithography process, characterized in that: include: Providing a photoresist material layer with a qualified light transmittance; Providing a reference wafer, on which the photolithography material layer having a first thickness is further formed; According to the photolithography material layer of the first thickness, collecting the best focal depth of the reference wafer under specific photolithography conditions during the photolithography process as a reference focal depth; Providing a target wafer to be subjected to a photolithography process, wherein a photolithography material layer having a second thickness is formed on the target wafer; An optimal focal depth for performing a photolithography process on the target wafer under specific photolithography conditions is obtained according to the reference focal depth, the first thickness, and the second thickness.
2. The method for predicting the optimal depth of focus in a photolithography process according to claim 1, characterized in that: The step of obtaining an optimal focal depth for performing a photolithography process on the target wafer under specific photolithography conditions according to the reference focal depth, the first thickness, and the second thickness comprises: Acquire a reference zero point of the photolithography material layer of the first thickness according to the first thickness; acquiring a target zero point of the photolithography material layer of the second thickness according to the second thickness; According to the reference focal depth, the reference zero point and the target zero point, an optimal focal depth for performing a photolithography process on the target wafer under specific photolithography conditions is obtained.
3. The method for predicting the optimal focal depth in a photolithography process according to claim 2, characterized in that: In the process of obtaining the reference zero point of the photolithography material layer of the first thickness according to the first thickness, the calculation formula of the reference zero point of the photolithography material layer of the first thickness is: Z1=L1 / 2; wherein Z1 is the reference zero point of the photolithography material layer of the first thickness; L1 is the thickness value of the photolithography material layer of the first thickness.
4. The method for predicting the optimal focal depth in a photolithography process according to claim 3, characterized in that: In the process of obtaining the target zero point of the photolithography material layer of the second thickness according to the second thickness, the calculation formula of the target zero point of the photolithography material layer of the second thickness is: Z2=L2 / 2; wherein Z2 is the target zero point of the photolithography material layer of the second thickness; L2 is the thickness value of the photolithography material layer of the second thickness.
5. The method for predicting the optimal focal depth in a photolithography process according to claim 4, characterized in that: In the process of obtaining the optimal focal depth for performing a lithography process on the target wafer under the specific lithography conditions according to the reference focal depth, the reference zero point and the target zero point, the calculation formula for the optimal focal depth of the target wafer is: F'=F-(Z2-Z1), wherein F' is the optimal focal depth of the target wafer; F is the optimal focal depth of the reference wafer; Z2 is the target zero point of the lithography material layer of the second thickness; and Z1 is the reference zero point of the lithography material layer of the first thickness.
6. The method for predicting the optimal focal depth in a photolithography process according to claim 4, characterized in that: The photolithography material layer includes, from bottom to top, a stacked spin-on carbon layer, a low-temperature oxidation layer, an anti-reflection layer and a photoresist layer.
7. The method for predicting the optimal focal depth in a photolithography process according to claim 6, characterized in that: In the process of obtaining the reference zero point of the photoresist material layer of the first thickness according to the first thickness, the calculation formula of the reference zero point of the photoresist material layer of the first thickness is: Z1=(d1+d2+d3+d4) / 2; wherein Z1 is the reference zero point of the photoresist material layer of the first thickness; d1 is the reference thickness of the spin-coated carbon layer; d2 is the reference thickness of the low-temperature oxide layer; d3 is the reference thickness of the anti-reflective layer; and d4 is the reference thickness of the photoresist layer.
8. The method for predicting the optimal focal depth in a photolithography process according to claim 6, characterized in that: In the process of obtaining the target zero point of the photoresist material layer of the second thickness according to the second thickness, the calculation formula of the target zero point of the photoresist material layer of the second thickness is: Z2=(D1+D2+D3+D4) / 2; wherein Z2 is the target zero point of the photoresist material layer of the second thickness; D1 is the target thickness of the spin-coated carbon layer; D2 is the target thickness of the low-temperature oxide layer; D3 is the target thickness of the anti-reflective layer; and D4 is the target thickness of the photoresist layer.
9. The method for predicting the optimal depth of focus in a photolithography process according to claim 1, characterized in that: In the process of providing a photoresist material layer with qualified light transmittance, if the K value of the negative refractive index of the photoresist material layer under visible light is less than 0.05, it is confirmed that the light transmittance of the photoresist material layer is qualified.
10. The method for predicting the optimal focal depth in a photolithography process according to claim 6, characterized in that: In the process of providing a photoresist material layer with qualified light transmittance, if the K values of the negative refractive indexes of the spin-on carbon layer, the low-temperature oxidation layer, the anti-reflection layer and the photoresist layer under visible light are all less than 0.05, it is confirmed that the light transmittance of the photoresist material layer is qualified.