CN108598018B - Method for evaluating characteristics of an interconnect structure - Google Patents
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Abstract
The invention provides a method for evaluating the characteristics of an interconnection structure. The method comprises the following steps: measuring ellipsometric optical parameters of a laminated body comprising a barrier layer and a low dielectric constant material layer in the interconnection structure; fitting the measured ellipsometry optical parameter result of the laminated body by adopting a double-layer model so as to calculate the characteristic value of the low dielectric constant material layer in the laminated body; comparing the original characteristic value of the low-dielectric-constant material with the characteristic value of the low-dielectric-constant material layer in the laminated body obtained through calculation; evaluating the amount of the impurity in the laminated body based on the comparison result. The method of the invention is simple, fast and lossless. Furthermore, the method of the present invention may provide information not only about metal penetration but also about low-k damage and moisture adsorption compared to the prior art.
Description
Technical Field
The invention relates to the technical field of semiconductor manufacturing, in particular to a simple, quick and nondestructive method for evaluating the characteristics of an interconnection structure.
Background
The substitution of copper (Cu) for aluminum (Al) in advanced interconnect structures is intended to reduce interconnect resistance and improve electromigration performance. Aluminum is a self-passivating material with a very stable native oxide layer that prevents the aluminum surface from being contaminated or prevents the aluminum from diffusing into the surrounding dielectric. In contrast, the native copper oxide layer is easily stripped into flake-like fragments, causing further corrosion of the copper and diffusion of the copper into the surrounding medium. Thus, Cu has a high diffusion coefficient in silicon, which can create deep trap states and/or short circuits upon deposition. Therefore, in order to prevent Cu from diffusing into the surrounding low-k (dielectric constant) and active silicon, a barrier layer must be provided therebetween. At the same time, it is important to reduce the thickness of the barrier layers to reduce their effect on the overall RC (R is the resistivity of the metal conductor and C is the capacitance) delay (resistance-capacitance effect) of the interconnect structure. However, reducing the thickness of the barrier layer is incompatible with increasing the pore size of the low-k dielectric, since large pore sizes obviously require thicker barrier layers to cover the pores. In addition, the large pore size also allows for more significant penetration and deposition of barrier layer precursors within the low-k pores and damage caused by active species and Vacuum Ultraviolet (VUV) photons generated in the plasma used for barrier layer deposition. For example, Physical Vapor Deposition (PVD) of metal barrier layers uses argon or nitrogen ions to sputter a metal target. Therefore, the optimization of existing processes is very important and new solutions must be found when developing new barrier layers.
One important issue is the modification of the low-k material during barrier layer deposition. N used during metal barrier layer deposition2And Ar plasma emits VUV light, which destroys Si-CH in the organosilicate film3A key. As a result, the film becomes hydrophilic to adsorb moisture, which greatly increases the k value and degrades the electrical properties and reliability of the low-k material. Another problem is associated with metal infiltration into the pores. It is not clear at present how these problems can be distinguished in a simple and reliable manner.
Typically, the skilled person performs TEM (transmission electron microscopy) examinations on cross-sections of fully integrated structures (after barrier and copper deposition, Chemical Mechanical Polishing (CMP), etc.). For example, it is clearly seen on the Transmission Electron Microscope (TEM) cross section shown in FIG. 1 that there is haze at the bottom, i.e., metal penetration is evident (M.R. Baklanov. incorporated Paper: Innovative technical Solutions for Low-k Integration Beyond 10nm. AVS 62 and International Symposium & inhibition in 2017, USA). Although the presence or absence of metal penetration can be visually indicated using TEM cross-sections, all of these integrated processes and TEM detection are very expensive and destructive, providing only information about metal penetration and no information about low k damage and moisture adsorption.
In addition, simpler evaluation methods are based on the evaluation of XPS (X-ray photoelectron spectroscopy) or TOF SIMS (time of flight secondary ion mass spectroscopy) depth profiling. For example, as shown in FIG. 2, the XPS depth profile clearly shows W penetration into low-k films with limited but insignificant Co penetration (Peng Xe, Xu Wang, Guang Yan, Xin-ping Qu.study of Co-W alloy as single layer diffusion barrier for Copper/low-k-synthesis. advanced metrology Conference in 2017, USA). In this case, it is also possible to see the metal profile and draw conclusions as to how much metal has penetrated the pores. However, this analysis also only provides information about metal penetration and no information about low-k damage and moisture adsorption. Meanwhile, moisture absorption is a key factor determining the electrical reliability of the integrated structure.
Disclosure of Invention
In view of the above problems in the prior art, it is an object of the present invention to provide a simple, fast and lossless method for evaluating the characteristics of an interconnect structure.
To achieve the above object, the present invention provides a method for evaluating characteristics of an interconnect structure. The method comprises the following steps: measuring ellipsometric optical parameters of a laminated body comprising a barrier layer and a low dielectric constant material layer in the interconnection structure; fitting the measured ellipsometric optical parameter result by using a double-layer model to calculate a characteristic value of the low dielectric constant material layer in the laminated body; comparing the original characteristic value of the low-dielectric-constant material with the characteristic value of the low-dielectric-constant material layer in the laminated body obtained through calculation; evaluating the amount of the impurity in the laminated body based on the comparison result.
Preferably, after evaluating the amount of the impurity in the laminated body based on the comparison result, the method may further include the steps of: annealing the laminate; measuring ellipsometric optical parameters of the laminate after annealing; fitting the measured ellipsometry optical parameter result of the annealed laminated body by adopting a double-layer model so as to calculate the characteristic value of the low dielectric constant material layer in the annealed laminated body; comparing the characteristic values of the low dielectric constant material layers in the laminated body before and after annealing; the composition of the impurities in the laminate was evaluated based on the comparison result.
Preferably, the step of evaluating the composition of the impurities in the laminated body based on the comparison result may include: if the characteristic value of the low dielectric constant material in the laminated body after annealing is equal to or lower than the characteristic value of the low dielectric constant material layer in the laminated body before annealing, the impurity in the laminated body is adsorbed water; if the characteristic value of the low dielectric constant material in the laminated body after annealing is higher than the characteristic value of the low dielectric constant material layer in the laminated body before annealing, the component of the impurity in the laminated body is metal.
Preferably, the characteristic value may be a refractive index.
Preferably, the annealing temperature in the annealing treatment may be 250 to 400 ℃. In particular, the annealing temperature may be 400 ℃.
Preferably, the annealing time in the annealing treatment may be 30 seconds to 1 hour. In particular, the annealing time may be 1 hour.
Preferably, the measurement of the ellipsometric optical parameter is performed using an ellipsometer.
In the evaluation method provided by the invention, the optical characteristic information of the interconnection structure can be accurately obtained only by adopting an optical test means, and the method has no damage to a sample and consumes less time for measurement. That is, the evaluation method provided by the invention is simple, rapid and lossless. Furthermore, compared to TEM cross-sections and XPS depth profiles, with the evaluation method provided by the present invention, not only information about metal penetration but also information about low-k damage and moisture adsorption can be provided. Furthermore, it can be estimated from the information obtained from the present invention which part of the low-k damage is related to metal penetration and which part is related to plasma damage and moisture adsorption.
It will be appreciated by those skilled in the art that the objects and advantages that can be achieved with the present invention are not limited to the specific details set forth above, and that these and other objects that can be achieved with the present invention will be more clearly understood from the detailed description that follows.
Also, it is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.
Drawings
Further objects, features and advantages of the present invention will become apparent from the following description of embodiments of the invention, with reference to the accompanying drawings, in which:
FIG. 1 is a transmission electron microscope cross-sectional view of an integrated structure in the prior art.
FIG. 2 is an XPS depth profile of an integrated structure of the prior art.
Fig. 3 is a schematic diagram of a metal interconnect structure in the prior art.
Fig. 4 is a flowchart of a method for evaluating characteristics of an interconnect structure according to a first embodiment of the present invention.
Fig. 5 is a flowchart of a method for evaluating characteristics of an interconnect structure according to a second embodiment of the present invention.
FIG. 6 is a schematic of the two-layer model used in this measurement.
Fig. 7 is an example of experimental data for refractive index obtained after an ellipsometry experiment performed on a sample before and after annealing.
Fig. 8 is an example of experimental data of refractive index obtained after an ellipsometry experiment is performed on another sample before and after annealing.
Detailed Description
Hereinafter, specific embodiments of the present invention will be described in detail. Examples of these embodiments are illustrated in the accompanying drawings. The embodiments of the present invention shown in the drawings and described according to the drawings are merely exemplary, and the technical spirit of the present invention and the main operation thereof are not limited to these embodiments.
It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and/or processing steps closely related to the scheme according to the present invention are shown in the drawings, and other details not so relevant to the present invention are omitted.
It is also emphasized that the term "comprises/comprising" when used herein, is taken to specify the presence of stated features, steps or components, but does not preclude the presence or addition of one or more other features, steps or components.
Furthermore, it is also emphasized that the description herein of one element on another does not imply that there are no other elements between the two elements.
Before the technical solution of the present invention is described in detail, terms mentioned in the present invention are first appropriately explained.
The "interconnect structure" or "metal interconnect structure" referred to herein includes a metal line for electrical connection, which has a diffusion barrier layer formed on a surface thereof, as shown in fig. 3. More specifically, metal lines are embedded in the inter-level dielectric layer. A diffusion barrier layer is formed on the bottom surface of the inter-level dielectric layer to prevent interdiffusion between the metal lines and the underlying low-k material layer. Such a diffusion barrier layer may reduce the effective dielectric constant of the metal interconnect structure and preferably also improve the thermal conductivity.
As used herein, a "low dielectric constant material" or "low-k material" refers to a material having a dielectric constant that is lower than that of silicon dioxide (SiO)2) Such as organic polymers, amorphous fluorinated carbon, nanofoam, polymer silicon-based insulators containing organic polymers, carbon doped silicon oxides, and fluorine doped silicon oxides, and the like.
Reference herein to a "barrier layer" refers to any material used in the art to seal metal (e.g., Cu) lines in an interconnect structure to minimize diffusion of the metal into the dielectric material. For example, the materials of the barrier layer include tantalum, titanium, ruthenium, hafnium, tungsten and other refractory metals, as well as nitrides and silicides thereof.
As used herein, an "ellipsometric optical parameter" refers to a characteristic that can be characterized by analyzing changes in the polarization state of light reflected from a sample, including phase shift (Delta ) and amplitude ratio (Psi ), among others.
As used herein, "characteristic values" include film thickness, reflectivity, refractive index, absorption coefficient, extinction coefficient, and the like.
In order that the technical solutions of the present invention will be more clearly understood, the present invention will be described in detail below with reference to the accompanying drawings in conjunction with specific embodiments.
Fig. 4 shows a flow chart of a method for evaluating characteristics of an interconnect structure according to a first embodiment of the invention. An interconnect structure as used herein includes a barrier layer/low-k material stack. As shown in fig. 4, first, in step S301, an ellipsometry optical parameter of the barrier layer/low-k material stack sample is measured by using an ellipsometer, such as phase shift (Delta, Δ) and amplitude ratio (Psi, ψ) of the barrier layer/low-k material stack sample. Next, in step S302, the measured ellipsometric optical parameter results are fitted by using a two-layer model (as shown in fig. 6),to calculate the characteristic value of the low-k material layer in the k material/barrier layer stack. In the present invention, the optical characteristics of the barrier layer are fixed to be constant, and only the characteristic value of the low-k material is extracted as a variable parameter. For example, the measured values are compared with a theoretical model using a two-layer model as shown in fig. 6, and the characteristics of the reflection system are obtained from the best fit. When measuring barrier/low-k material stack samples on top of Si (or other known material), n is used1And k1Denotes the refractive index and extinction coefficient, n, of the barrier layer2And k2Representing the refractive index and extinction coefficient of the substrate, n3And k3Are the substrate refractive index and the extinction coefficient. n is0，k0Which represents the refractive index and extinction coefficient of air, which are the same values as the environment, lambda is the wavelength,
is the angle of incidence and d is the low-k film thickness. When the thickness and refractive index of the barrier layer are fixed and k is known1，k 20, only 1 unknown parameter n2Which is fitted to the simulation results from the measurements of delta and psi to calculate the refractive index of the low-k material layer in the k material/barrier layer stack. Then, in step S303, the raw characteristic values of the low-k material layer are compared with the calculated characteristic values of the low-k material layer in the barrier layer/low-k material stack. Here, the original characteristic value of the low-k material layer may be measured in advance. Finally, in step S304, based on the comparison in step S303, the amount of breakthrough impurities in the barrier/low-k material stack may be estimated. Specifically, if the difference between the original characteristic value of the low-k material layer and the calculated characteristic value of the low-k material layer in the calculated barrier layer/low-k material stack is large, it indicates that a significant amount of impurities are present in the barrier layer/low-k material stack.
In the method provided by the embodiment, the optical characteristic information of the interconnection structure can be accurately obtained only by adopting an optical testing means, and the method has no damage to a sample and consumes less time for measurement. Therefore, the method provided by the embodiment is simple, quick and lossless.
Fig. 5 shows a flow chart of a method for evaluating characteristics of an interconnect structure according to a second embodiment of the invention. As shown in fig. 5, first, in step S401, an ellipsometry optical parameter of the barrier layer/low-k material stack sample is measured by using an ellipsometer, such as phase shift (Delta, Δ) and amplitude ratio (Psi, ψ) of the barrier layer/low-k material stack sample. Next, in step S402, the measured values are fitted to a theoretical model using a two-layer model (as shown in fig. 6), and the properties of the reflective system are obtained from the best fit, and the refractive index of the low-k material layer in the k material/barrier layer stack is calculated. In the present invention, the optical characteristics of the barrier layer are fixed to be constant, and only the low-k refractive index is extracted as a variable parameter. Then, in step S403, the original refractive index of the low-k material layer is compared to the calculated refractive index of the low-k material layer in the barrier layer/low-k material stack. Here, the original refractive index of the low-k material layer may be measured in advance. Thereafter, in step S404, based on the comparison result in step S403, the amount of breakthrough impurities in the barrier layer/low-k material stack may be estimated. Specifically, if the difference between the original refractive index of the low-k material layer and the calculated refractive index of the low-k material layer in the calculated barrier/low-k material stack is large, it indicates that a significant amount of impurities are present in the barrier/low-k material stack. Next, in step S405, the barrier/low-k material stack is annealed to desorb the physically and chemically adsorbed water molecules. In the annealing treatment, the annealing temperature may be 250 ℃ to 400 ℃, preferably 400 ℃, and the annealing time may be 30 seconds to 1 hour, preferably 1 hour.
After the annealing process is completed, in step S406, an ellipsometer is used to measure ellipsometric optical parameters of the annealed barrier layer/low-k material stack, and a double-layer model is used to fit the measured ellipsometric optical parameter results to calculate the refractive index of the low-k material layer in the annealed k material/barrier layer stack. Next, in step S407, the refractive indices of the low-k material layers in the pre-anneal and post-anneal k-material/barrier layer stacks are compared. Finally, in step S408, based on the comparison result in step S407, the composition of the breakthrough impurity in the barrier layer/low-k material stack may be estimated. Specifically, if the refractive index of the low-k material layer in the k-material/barrier layer stack after annealing is equal to or lower than the refractive index of the low-k material layer in the k-material/barrier layer stack before annealing, the component of the impurity in the k-material/barrier layer stack is adsorbed water, i.e., the low-k material layer is contaminated with adsorbed water. Fig. 7 is an example of experimental data corresponding to this case. In particular, fig. 7 shows the refractive indices of the low-k material/barrier layer stack as received, after annealing at 250 ℃ for 30 seconds, after annealing at 300 ℃ for 1 hour, and after annealing at 400 ℃ for 1 hour, and the refractive indices of the low-k material layer as received, after annealing at 250 ℃ for 30 seconds, and after annealing at 400 ℃ for 1 hour. As shown in fig. 7, the refractive index of the annealed low-k material/barrier layer stack was fully restored to the original value, indicating that the low-k material layer contained only adsorbed moisture. On the other hand, if the refractive index of the low-k material layer in the k-material/barrier layer stack after annealing is higher than the refractive index of the low-k material layer in the k-material/barrier layer stack before annealing, the composition of the impurities in the k-material/barrier layer stack is metal, i.e., the low-k material layer is contaminated by the penetrating metal impurities. Fig. 8 is an example of experimental data corresponding to this case. Specifically, fig. 8 shows the refractive indices of the original sample with the barrier layer, the new sample with the barrier layer, and the low-k material layer as received and after annealing at 400 ℃ for 1 hour, respectively. As shown in fig. 8, the refractive index of the annealed low-k material/barrier layer stack is still higher than the original value, indicating that there is an irremovable residue (metal) deposition at 400 ℃.
In addition to the effect of estimating the amount of penetrating impurities in the barrier layer/low-k material stack achieved by the foregoing embodiments, the present embodiments may also estimate the composition of penetrating impurities in the barrier layer/low-k material stack. Thus, compared to TEM cross-sections and XPS depth profiles in the prior art, the method of the present embodiment can provide not only information about metal penetration, but also information about low-k damage and moisture adsorption. Furthermore, it can be estimated from the information obtained in this embodiment which part of the low-k damage is related to metal penetration and which part is related to plasma damage and moisture adsorption.
In summary, in the method provided by the present invention, the optical property information of the interconnect structure can be accurately obtained by only using an optical test method, and the method has no damage to the sample and consumes less time for measurement. That is, the method provided by the invention is simple, fast and lossless. Furthermore, compared to TEM cross-sections and XPS depth profiles, the method provided by the present invention can provide information not only about metal penetration, but also about low-k damage and moisture adsorption. Furthermore, it can be estimated from the information obtained from the present invention which part of the low-k damage is related to metal penetration and which part is related to plasma damage and moisture adsorption.
Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments in the present invention.
It should be noted that the above-mentioned embodiments are only for illustrating the present invention and not for limiting the scope of the present invention, and any equivalent transformation techniques based on the present invention should be within the scope of the present invention.
Claims (8)
1. A method for evaluating characteristics of an interconnect structure, the method comprising the steps of:
measuring ellipsometric optical parameters of a laminated body comprising a barrier layer and a low dielectric constant material layer in the interconnection structure;
fitting the measured ellipsometric optical parameter result by using a double-layer model to calculate a characteristic value of the low dielectric constant material layer in the laminated body;
comparing the original characteristic value of the low-dielectric-constant material with the characteristic value of the low-dielectric-constant material layer in the laminated body obtained through calculation;
evaluating the amount of the impurities in the laminated body based on the comparison result,
after evaluating the amount of the impurities in the laminated body based on the comparison result, the method further comprises the steps of:
annealing the laminate;
measuring ellipsometric optical parameters of the laminate after annealing;
fitting the measured ellipsometry optical parameter result of the annealed laminated body by adopting a double-layer model so as to calculate the characteristic value of the low dielectric constant material layer in the annealed laminated body;
comparing the characteristic values of the low dielectric constant material layers in the laminated body before and after annealing;
the composition of the impurities in the laminate was evaluated based on the comparison result.
2. The method according to claim 1, wherein the step of evaluating the composition of the impurities in the laminated body based on the comparison result comprises:
if the characteristic value of the low dielectric constant material in the laminated body after annealing is equal to or lower than the characteristic value of the low dielectric constant material layer in the laminated body before annealing, the impurity in the laminated body is adsorbed water;
if the characteristic value of the low dielectric constant material in the laminated body after annealing is higher than the characteristic value of the low dielectric constant material layer in the laminated body before annealing, the component of the impurity in the laminated body is metal.
3. The method according to claim 1 or 2, wherein the characteristic value is a refractive index.
4. The method according to claim 1, wherein the annealing temperature in the annealing treatment is 250 to 400 ℃.
5. The method of claim 1, wherein the annealing temperature in the annealing process is 400 ℃.
6. The method according to claim 1, wherein the annealing time in the annealing treatment is 30 seconds to 1 hour.
7. The method of claim 1, wherein the annealing time in the annealing process is 1 hour.
8. The method of claim 1, wherein the measurement of the ellipsometric optical parameter is performed using an ellipsometer.
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