TWI626426B - Method of measuring thickness of epitaxial layer - Google Patents

Abstract

A method for measuring the thickness of an epitaxial film, which comprises the following steps. Providing a first substrate, the first substrate has a growth region; and the first substrate is placed in the cavity for performing a first epitaxial process to selectively grow the first epitaxial film on the growth region; The sheet resistance value and thickness of the epitaxial film; repeating the above steps at least once to establish a relationship between the sheet resistance value and the thickness of the first epitaxial film; placing the second substrate in the cavity for the second epitaxial process, Selecting a second epitaxial film selectively on the second substrate; and measuring a sheet resistance value of the second epitaxial film, and according to the sheet resistance value of the second epitaxial film and the sheet of the first epitaxial film The relationship between the resistance value and the thickness calculates the thickness of the second epitaxial film.

Description

Epitaxial film thickness measurement method

Embodiments of the present invention are directed to a method of measuring the thickness of an epitaxial film.

Epitaxial films have been widely used in the fabrication of semiconductor devices today. In the semiconductor element, the thickness of the epitaxial film has a certain influence on the performance of the semiconductor element, so how to measure the thickness of the epitaxial film quickly and accurately becomes very important. In the existing film thickness measurement technology, Transmission Electron Microscope (TEM) is most commonly used, because transmission electron microscopy requires a longer time for film thickness measurement (several days) And transmission electron microscopy is a destructive measurement. Therefore, there is still room for improvement in the thickness measurement of epitaxial films by transmission electron microscopy.

Embodiments of the present invention provide a method for measuring the thickness of an epitaxial film, which includes the following steps. Providing a first substrate, the first substrate has a growth region; and the first substrate is placed in the cavity for performing a first epitaxial process to selectively grow the first epitaxial film on the growth region; The sheet resistance value and thickness of the epitaxial film; repeating the above steps at least once to establish a relationship between the sheet resistance value and the thickness of the first epitaxial film; placing the second substrate in the cavity for the second epitaxial process, Selecting a second epitaxial film selectively on the second substrate; and measuring a sheet resistance value of the second epitaxial film, and according to the sheet resistance value of the second epitaxial film and the sheet of the first epitaxial film The relationship between the resistance value and the thickness calculates the thickness of the second epitaxial film.

Another embodiment of the present invention provides a method for measuring the thickness of an epitaxial film, which includes the following steps. Forming a mask layer on the first substrate; patterning the mask layer and the first substrate to form an opening in the mask layer and forming a recess in the first substrate; placing the first substrate in the cavity Performing a first epitaxial process to selectively grow a first epitaxial film on the cavity; measuring a sheet resistance value of the first epitaxial film, and measuring the first epitaxial film by electron microscopy Thickness; repeating the foregoing steps at least once to establish a relationship between the sheet resistance value and the thickness of the first epitaxial film; placing the second substrate in the cavity for performing a second epitaxial process to form on the second substrate a second epitaxial film; and measuring a sheet resistance value of the second epitaxial film, and calculating a second epitaxial layer according to a sheet resistance value of the second epitaxial film and a relationship between a sheet resistance value of the first epitaxial film and a thickness The thickness of the film.

The following disclosure provides many different embodiments or examples for implementing different features of the subject matter provided. Specific components of the components and configurations are described below to simplify the present invention. Of course, such components and configurations are merely examples and are not intended to be limiting. For example, in the following description, the formation of the first feature over or over the second feature can include embodiments in which the first feature and the second feature are formed in direct contact, and can also include additional features that can be associated with the first feature Embodiments are formed between the second features such that the first feature and the second feature may not be in direct contact. In addition, the present invention may repeat the graphical element symbols and/or letters in various examples. This repetition is for the purpose of simplicity and clarity, and is not a limitation of the various embodiments and/or configurations discussed.

In addition, for ease of description, spatially relatives such as "under", "below", "lower", "above", "upper", and the like may be used herein. Terminology to describe the relationship of one element or feature to another element or feature as illustrated in the figures. In addition to the orientation depicted in the figures, spatially relative terms are intended to encompass different orientations of the device in use or operation. The device may be otherwise oriented (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein may be interpreted accordingly.

1 is a flow chart of a method for measuring thickness of an epitaxial film according to an embodiment of the present invention, and FIG. 2 is a flow chart of a method for measuring thickness of an epitaxial film according to another embodiment of the present invention, and FIGS. 3 to 8 are A schematic flow chart of a method for measuring the thickness of an epitaxial film according to an embodiment of the invention.

Referring to FIG. 1 , the method for measuring the thickness of the epitaxial film of the embodiment includes at least steps S110, S120, S130, S140, S150, and S160. As shown in step S110 of FIG. 1, first, a first substrate 400 is provided, which has at least one growth region GR. In some embodiments, the first substrate 400 is, for example, a sampling wafer on which no electronic components (such as transistors, resistors, capacitors, etc.) are formed, and the sample wafer can be used to build The relationship between the sheet resistance value and the thickness of the epitaxial film, and the growth region GR on the first substrate 400 (ie, the sampling wafer) can be formed by the step S210 and the step 220 shown in FIG.

The formation of the growth region GR will be exemplified below with reference to FIGS. 2 to 5. As shown in FIG. 2 to FIG. 5, a mask layer 410 is formed on the first substrate 400 (step S210 in FIG. 2), and the mask layer 410 is entirely covered on the surface of the first substrate 400. . In some embodiments, the first substrate 400 is, for example, a germanium substrate having an n-type doping and/or a p-type doping, and the mask layer 410 formed on the first substrate 400 is, for example, a tantalum nitride layer. Or other layers of dielectric material. Next, the mask layer 410 on the first substrate 400 and the first substrate 400 are patterned to form an opening 412 in the mask layer 410 and form a recess 402 in the first substrate 410 (as in FIG. 2). Step S220 is shown).

In some embodiments, the patterning process of the first substrate 400 and the mask layer 410 may include the following steps: First, the photoresist layer PR may be formed on the mask layer 410 by spin coating (FIG. 3). Then, the photoresist layer PR is exposed/developed to transfer a specific pattern on the photo-mask to the photoresist layer PR, thereby forming a pattern with a specific pattern on the mask layer 410. The photoresist layer PR' (as shown in FIG. 4); afterwards, the patterned photoresist layer PR' is used as a mask, for example, by etching process to remove the portion not covered by the patterned photoresist layer PR' The mask layer 410 and a portion of the first substrate 400 (as shown in FIG. 5). In some embodiments, the opening 412 is formed after the mask layer 410 is partially removed, and the recess 402 is formed below the opening 412 after the first substrate 410 is partially removed, and the depth of the recess 402 is, for example, Between 10 nm and 200 nm. Here, the bottom surface of the pocket 402 can be regarded as the growth region GR of the first substrate 400. After the fabrication of the recess 402 and the opening 412 is completed, the patterned photoresist layer PR' is removed.

As shown in step S120 of FIG. 1, step S230 of FIG. 2, and FIG. 6, next, the first substrate 410 having the growth region GR (ie, the recess 402) is placed in the cavity for the first epitaxial process ( For example, a chemical vapor deposition process) selectively grows the first epitaxial film 420 on the growth region GR (ie, the bottom surface of the cavity 402). As shown in FIG. 6, the thickness of the first epitaxial film 420 is, for example, higher than the depth of the cavity 402. In other words, the volume of the first epitaxial film 420 is greater than the volume of the cavity 402 and the opening 412, for example. In some embodiments, the first epitaxial film 420 grown in the cavity 402 fills the cavity 402 and the opening 412, and the first epitaxial film 420 protrudes from the upper surface of the mask layer 410.

In some embodiments, the first epitaxial film 420 is, for example, a boron-doped germanium epitaxial layer, and the boron dopant and the germanium content in the boron-doped germanium epitaxial layer are in a gradient distribution, wherein the boron doping The boron dopant concentration in the germanium epitaxial layer is, for example, between 1E20 and 2.8E21, and the germanium content in the boron-doped germanium epitaxial layer is, for example, between 20% and 58%. For example, the reaction gas (for example, methane (SiH ₄ ), dimethyl hydride (GeH ₄ ) and diborane (B ₂ H ₆ )) and a carrier gas (for example, hydrogen) can be introduced into the cavity. The first epitaxial process described above forms a boron-doped germanium epitaxial layer on the growth region GR. In other embodiments, the first epitaxial film 420 is, for example, a phosphorus-doped germanium epitaxial layer, and the phosphorus dopant and the germanium content in the phosphorus-doped germanium epitaxial layer are in a gradient distribution, wherein the phosphorus doping The phosphorus dopant concentration in the germanium epitaxial layer is, for example, between 0.5% and 10%, and the germanium content in the phosphorus-doped germanium epitaxial layer is, for example, between 20% and 58%. For example, the foregoing can be carried out by introducing a reaction gas such as methane (SiH ₄ ), dimethyl hydride (GeH ₄ ) and phosphine (PH ₃ ), and a carrier gas (for example, hydrogen) into the cavity. The first epitaxial process is to form a phosphorus-doped germanium epitaxial layer on the growth region GR. However, the present embodiment does not limit that the dopant in the first epitaxial film 420 must be boron or phosphorus. Those skilled in the art can change the dopant in the first epitaxial film 420 according to the design requirements of the actual device.

Taking the boron-doped germanium epitaxial layer and the phosphorus-doped germanium epitaxial layer as an example, since boron and phosphorus doping concentrations and germanium content are all heavy doping grades, boron is used. The sheet resistance of the doped germanium epitaxial layer or the phosphorus-doped germanium epitaxial layer is only related to the thickness of the epitaxial layer, and is not related to the doping concentration of the dopant (boron, phosphorus) and germanium. The content is related. In other words, when the doping concentration of boron and phosphorus and the content of germanium are all heavily doped, the boron-doped germanium epitaxial layer or the phosphorus-doped sheet resistance value no longer follows the dopant (boron, phosphorus). The doping concentration and the change in the germanium content vary, and the boron-doped germanium epitaxial layer or the phosphorus-doped sheet resistance value changes as the thickness changes.

As shown in step S130 of FIG. 1 and step S240 of FIG. 2, after the growth of the first epitaxial film 420 is completed, the sheet resistance of the first epitaxial film 420 positioned on the first substrate 400 is then measured. And the thickness, and a set of correspondence between the sheet resistance value and the thickness is recorded. In some embodiments, the sheet resistance of the first epitaxial film 420 is measured, for example, by a four-point probe method, and the thickness of the first epitaxial film 420 is measured, for example, by electron microscopy.

In some embodiments, the sheet resistance value of the first epitaxial film 420 (eg, a boron-doped germanium epitaxial layer or a phosphorus-doped germanium epitaxial layer) formed on the first substrate 400 may be Between 100 ohms/square and 800 ohms/square, and the thickness of the first epitaxial film 420 (for example, a boron-doped germanium epitaxial layer or a phosphorus-doped germanium epitaxial layer) may be between 30 nanometers. Rice to 70 nm.

As shown in step S140 of FIG. 1 and step S250 of FIG. 2, after obtaining a set of correspondence between the sheet resistance value and the thickness, repeating the above steps (step S110 to step S130 or step S210 to step S240) one or more times. To further obtain the correspondence between the sheet resistance value and the thickness of more groups. The plurality of sets of resistance values of the sheet resistance and the thickness may be used to establish a relationship between the sheet resistance value and the thickness of the first epitaxial film 420, and the relationship between the sheet resistance value and the thickness may be a lookup table (LUT), an equation, or the like. Presented. Since the relationship between the sheet resistance value and the thickness of the first epitaxial film 420 may vary depending on the conditions of the epitaxial process, the present embodiment does not represent the sheet resistance of the first epitaxial film 420 by a specific look-up table or equation. The thickness is related. The relationship between the sheet resistance value and the thickness of the first epitaxial film 420 can be roughly described as follows: when the measured sheet resistance value of the first epitaxial film 420 is higher, the thickness of the first epitaxial film 420 is smaller; On the contrary, when the measured sheet resistance value of the first epitaxial film 420 is lower, the thickness of the first epitaxial film 420 is larger.

During the repetition of the above steps S110 to S130 or the above steps S210 to S240, conditions such as the flow rate of the carrier gas flowing into the chamber, the flow rate of each reaction gas, and/or the temperature may be appropriately changed to the first substrate 400. The first epitaxial film 420 having different thicknesses and sheet resistance values is grown on the growth region GR, and a plurality of sets of correspondences between different sheet resistance values and thicknesses are recorded.

During the repetition of the above steps S110 to S130 or the above-described steps S210 to S240, in addition to the plurality of sets of correspondences between the sheet resistance value and the thickness, various conditions (the carrier gas flow rate into the chamber) can be further recorded. The influence of the flow rate, temperature, and the like of each reaction gas on the thickness of the first epitaxial film 420. Taking the epitaxial process of a boron-doped germanium epitaxial layer as an example, increasing the gas flow rate of the germane gas (GeH ₄ ) will increase the thickness of the boron-doped germanium epitaxial layer and reduce the methotane (GeH). The gas flow rate of ₄ ) will reduce the thickness of the boron-doped germanium epitaxial layer; increasing the gas flow rate of diborane (B ₂ H ₆ ) will increase the thickness of the boron-doped germanium epitaxial layer and decrease The gas flow rate of diborane (B ₂ H ₆ ) will reduce the thickness of the boron-doped germanium epitaxial layer; increasing the gas flow rate of hydrogen will reduce the thickness of the boron-doped germanium epitaxial layer and reduce hydrogen. The gas flow rate will increase the thickness of the boron-doped germanium epitaxial layer; increasing the process temperature will reduce the thickness of the boron-doped germanium epitaxial layer, while lowering the process temperature will cause boron-doped germanium epitaxial The thickness of the layer is increased.

As shown in step S150 of FIG. 1 and step S260, FIG. 7 and FIG. 8 of FIG. 2, the second substrate 500 is placed in the cavity for performing a second epitaxial process to selectively serve on the second substrate 500. A second epitaxial film 530 is grown. In some embodiments, as shown in FIG. 7 and FIG. 8, the second substrate 500 is, for example, a mass production wafer on which an insulator 510 has been formed (for example, shallow). a trench isolation structure) and a fin field effect transistor 520, wherein the fin field effect transistor may be an n-type and/or a p-type fin field effect transistor, and the fin field effect transistor includes a spacer 510 located between the insulator 510 and protruding from the insulator 510 The upper surface of the semiconductor fin 522 and the gate stack structure 524, and the semiconductor fin 522 and insulator 510 are partially covered by the gate stack structure 524. As shown in FIG. 7, in some embodiments, portions of semiconductor fin 522 that are not covered by gate stack structure 524 can be removed to form fin recesses R between insulators 510, while second The epitaxial film 530 is selectively grown on the semiconductor fin 522 of the FinFET 520, and the second epitaxial film 530 is filled in the fin pocket R and protrudes from the surface of the insulator 510. In other embodiments, portions of semiconductor fin 522 that are not covered by gate stack structure 524 may be retained (ie, fin recesses R are not formed), while second epitaxial film 530 may selectively grow to fin field effect The semiconductor fin 522 of the transistor 520 is on.

As shown in step S160 of FIG. 1 and step S270 of FIG. 2, the sheet resistance value of the second epitaxial film is measured, and the sheet resistance value of the second epitaxial film and the sheet resistance value and thickness of the first epitaxial film are measured. The correlation is calculated by the thickness of the second epitaxial film. In some embodiments, measuring the sheet resistance value of the second epitaxial film 530 is measured, for example, by a four-point probe method. The recess 402 shown in FIG. 5 provides a loading effect, a topography, and an epitaxial process in the same cavity as the fin cavity R illustrated in FIG. Therefore, the thickness of the second epitaxial film 530 grown on the second substrate 500 can be calculated according to the relationship between the sheet resistance value of the first epitaxial film 420 and the thickness, without using electron microscopy.

In some embodiments, the second epitaxial film 530 is, for example, a boron-doped germanium epitaxial layer, and the boron dopant and the germanium content in the boron-doped germanium epitaxial layer are in a gradient distribution, wherein the boron is doped The boron dopant concentration in the germanium epitaxial layer is, for example, between 1E20 and 2.8E21, and the germanium content in the boron-doped germanium epitaxial layer is, for example, between 20% and 58%. For example, the reaction gas (for example, methane (SiH ₄ ), dimethyl hydride (GeH ₄ ) and diborane (B ₂ H ₆ )) and a carrier gas (for example, hydrogen) can be introduced into the cavity. The first epitaxial process described above forms a boron doped germanium epitaxial layer on the semiconductor fin 522. In other embodiments, the second epitaxial film 530 is, for example, a phosphorus-doped germanium epitaxial layer, and the phosphorus dopant and the germanium content in the phosphorus-doped germanium epitaxial layer are in a gradient distribution, wherein the phosphorus doping The phosphorus dopant concentration in the germanium epitaxial layer is, for example, between 0.5% and 10%, and the germanium content in the phosphorus-doped germanium epitaxial layer is, for example, between 20% and 58%. For example, the foregoing can be carried out by introducing a reaction gas such as methane (SiH ₄ ), dimethyl hydride (GeH ₄ ) and phosphine (PH ₃ ), and a carrier gas (for example, hydrogen) into the cavity. A first epitaxial process is performed to form a phosphor-doped germanium epitaxial layer on the semiconductor fin 522. However, the present embodiment does not limit that the dopant in the second epitaxial film 530 must be boron or phosphorus. Those skilled in the art can change the dopant in the second epitaxial film 530 according to the design requirements of the actual device.

The above-described epitaxial film thickness measurement method can be applied to chamber matching and process monitoring, and the thickness of the epitaxial film (ie, the second epitaxial film 530) can be quickly and accurately confirmed. Efficiently achieve cavity matching and process monitoring purposes.

The foregoing has outlined the features of several embodiments, such that those of ordinary skill in the art can understand the invention. It will be appreciated by those of ordinary skill in the art that the present invention can be readily utilized as a basis for designing or modifying other processes and structures for the same purposes and/or advantages of the embodiments disclosed herein. It should be understood by those of ordinary skill in the art that the present invention is not limited to the spirit and scope of the invention, and various changes and substitutions may be made herein without departing from the spirit and scope of the invention. And changes.

S110~S160, S210~S270‧‧‧ steps
400‧‧‧First substrate
402‧‧‧ recess
410‧‧‧ Cover layer
412‧‧‧ openings
420‧‧‧First epitaxial film
500‧‧‧Second substrate
510‧‧‧Insulator
520‧‧‧Fin field effect transistor
522‧‧‧Semiconductor fins
524‧‧ ‧ gate stack structure
530‧‧‧Second epitaxial film
GR‧‧‧ Growing Area
PR‧‧‧ photoresist layer
PR'‧‧‧ patterned photoresist layer
R‧‧‧Fin pocket

1 is a flow chart of a method for measuring the thickness of an epitaxial film according to an embodiment of the invention. 2 is a flow chart of a method for measuring the thickness of an epitaxial film according to another embodiment of the present invention. 3 to FIG. 8 are schematic flow charts of a method for measuring the thickness of an epitaxial film according to an embodiment of the invention.

Claims (10)

A method for measuring an epitaxial film thickness, comprising: providing a first substrate, the first substrate having a growth region; placing the first substrate in a cavity for performing a first epitaxial process, Selectively growing a first epitaxial film on the growth region; measuring a sheet resistance value and a thickness of the first epitaxial film; repeating the above steps at least once to establish a sheet resistance value of the first epitaxial film Correlating a thickness; placing a second substrate in the cavity for performing a second epitaxial process to selectively grow a second epitaxial film on the second substrate; and measuring the second a sheet resistance value of the epitaxial film, and calculating a thickness of the second epitaxial film according to a sheet resistance value of the second epitaxial film and a sheet resistance value of the first epitaxial film and a thickness. A method for measuring an epitaxial film thickness, comprising: forming a mask layer on a first substrate; patterning the mask layer and the first substrate to form an opening in the mask layer Forming a cavity in the first substrate; placing the first substrate in the cavity for performing a first epitaxial process to selectively grow the first epitaxial film on the cavity; measuring the a sheet resistance value of the first epitaxial film, and measuring the thickness of the first epitaxial film by electron microscopy; repeating the foregoing steps at least once to establish a sheet resistance value of the first epitaxial film Correlating a thickness; placing a second substrate in the cavity for performing a second epitaxial process to form a second epitaxial film on the second substrate; and measuring the second epitaxial film a sheet resistance value, and calculating a thickness of the second epitaxial film according to a sheet resistance value of the second epitaxial film and a sheet resistance value of the first epitaxial film and a thickness. The method for measuring the thickness of an epitaxial film according to the first or second aspect of the invention, wherein the sheet resistance of the first epitaxial film and the second epitaxial film is by a four-point probe method Make measurements. The method for measuring the thickness of an epitaxial film according to the first or second aspect of the invention, wherein the reaction gas introduced into the cavity during the first epitaxial process and the carrier gas and the second bar are The reactive gas introduced into the chamber during the crystallizing process and the carrier gas are the same. The method for measuring an epitaxial film thickness according to claim 4, wherein the reaction gas comprises methane, methane and diborane, and the carrier gas comprises hydrogen, and the first is formed. The epitaxial film and the second epitaxial film comprise a boron-doped germanium epitaxial layer, and the boron dopant and the germanium content in the boron-doped germanium epitaxial layer are distributed in a gradient. The method for measuring an epitaxial film thickness according to claim 5, wherein a concentration of boron dopant in the boron-doped germanium epitaxial layer is between 1E20 and 2.8E21, and the boron is doped. The content of germanium in the germanium epitaxial layer is between 20% and 58%, and the sheet resistance of the boron-doped germanium epitaxial layer is between 100 ohms/square and 800 ohms/square. The method for measuring an epitaxial film thickness according to claim 4, wherein the reaction gas comprises methane, methane and phosphine (PH ₃ ), and the carrier gas comprises hydrogen and is formed. The first epitaxial film and the second epitaxial film comprise a phosphorus-doped germanium epitaxial layer, and the phosphorus dopant and germanium content in the phosphorus-doped germanium epitaxial layer are gradiently distributed. . The method for measuring an epitaxial film thickness according to claim 7, wherein the phosphorus doping concentration in the phosphorus-doped germanium epitaxial layer is between 0.5% and 10%, and the phosphorus The germanium content of the doped germanium epitaxial layer is between 20% and 58%, and the sheet resistance of the phosphorus-doped germanium epitaxial layer is between 100 ohms/square and 800 ohms/square. . The method for measuring an epitaxial film thickness according to claim 1 or 2, wherein the first substrate comprises a sampling wafer. The method for measuring an epitaxial film thickness according to claim 1 or 2, wherein the second substrate comprises a wafer on which a fin field effect transistor has been formed, and A second epitaxial film is formed on the semiconductor fin of the fin field effect transistor.