Thin film deposition method and thin film deposition apparatus

Abstract

To improve an accuracy of a pattern to be formed on a substrate.SOLUTION: A deposition method includes Step a), Step b), Step c), Step d), and Step e). In Step a), a substrate having an underlayer film and a resist provided on the underlayer film and formed with a predetermined pattern is carried into a chamber. In Step b), gas of a first monomer is supplied into the chamber. In Step c), a purge gas is supplied into the chamber. In Step d), gas of a second monomer is supplied into the chamber to form a polymer film on a front surface of the substrate by a polymer reaction of the first and the second monomers. In Step e), the purge gas is supplied into the chamber. Further, a vapour pressure ratio in the monomer lower in saturation vapor pressure of the first monomer and the second monomer is 0.05 or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] Various aspects and embodiments of the present disclosure relate to a film forming method and a film forming apparatus. [Background Art]

[0002] Patent Document 1 below discloses "a method for manufacturing a semiconductor device including: a film forming step of modifying the surface layer of a resist patterned on an object to be processed, thereby forming a film that has elasticity and is incompatible with the resist so as to cover the surface of the resist; and a heating step of heating the object to be processed on which the film has been formed". [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 2014-209270 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] The present disclosure provides a film forming method and a film forming apparatus capable of improving the accuracy of a pattern formed on a substrate. [Means for Solving the Problem]

[0005] A film formation method in one aspect of this disclosure includes steps a), b), c), d), and e). In step a), a substrate having a base film and a resist provided on the base film and having a predetermined pattern formed on it is introduced into a chamber. In step b), a gas of a first monomer is supplied into the chamber. In step c), a purge gas is supplied into the chamber. In step d), a gas of a second monomer is supplied into the chamber, causing a polymer film to be formed on the surface of the substrate by a polymerization reaction between the first monomer and the second monomer. In step e), a purge gas is supplied into the chamber. Furthermore, the vapor pressure ratio of the first monomer and the second monomer with the lower saturated vapor pressure is 0.05 or less. [Effects of the Invention]

[0006] According to various aspects and embodiments of this disclosure, the accuracy of patterns formed on a substrate can be improved. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram showing an example of a processing device. [Figure 2] Figure 2 is a flowchart showing an example of the substrate processing procedure. [Figure 3A] Figure 3A is a schematic diagram illustrating an example of the process of forming a polymer film on an uneven pattern. [Figure 3B] Figure 3B is a schematic diagram illustrating an example of the process of forming a polymer film on an uneven pattern. [Figure 4A] Figure 4A is a schematic diagram illustrating an example of the process of polymer film formation on a hole. [Figure 4B] Figure 4B is a schematic diagram illustrating an example of the process of polymer film formation on a hole. [Figure 5A] Figure 5A is a schematic diagram illustrating an example of the process of polymer film formation into two interconnected holes. [Figure 5B] Figure 5B is a schematic diagram illustrating an example of the process of polymer film formation into two interconnected holes. [Figure 6] Figure 6 shows an example of the relationship between the number of repeated film deposition processes and the change in the thickness of the polymer film. [Figure 7A] Figure 7A shows an example of the shape of the hole opening before the polymer film is formed. [Figure 7B] Figure 7B shows an example of the shape of the hole opening after the polymer film has been formed. [Figure 8A] Figure 8A shows an example of the cross-sectional shape of a hole before the polymer film is formed. [Figure 8B] Figure 8B shows an example of the cross-sectional shape of a hole after a polymer film has been formed. [Figure 9A] Figure 9A shows an example of the shape of the hole opening before the polymer film is formed. [Figure 9B] Figure 9B shows an example of the shape of the hole opening after the polymer film has been formed. [Figure 10A] Figure 10A shows an example of the shape of the hole opening before the polymer film is formed. [Figure 10B] Figure 10B shows an example of the shape of the hole opening after the polymer film has been formed. [Figure 11A] Figure 11A shows an example of the line shape of the resist before the polymer film is formed. [Figure 11B] Figure 11B shows an example of the line shape of the resist after the polymer film has been formed. [Figure 12A] Figure 12A shows an example of the shape of the hole openings in a resist where no polymer film has been formed. [Figure 12B] Figure 12B shows an example of the shape of the hole openings in the underlying film after etching is performed through a resist that does not have a polymer film formed on it. [Figure 13A] Figure 13A shows an example of the shape of the hole openings in a resist on which a polymer film has been formed. [Figure 13B]FIG. 13B is a diagram illustrating an example of the shape of an opening of a hole in an underlying film after etching has been performed through a resist on which a polymer film has been formed. Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments of a film forming method and a film forming apparatus will be described in detail with reference to the drawings. The disclosed film forming method and film forming apparatus are not limited to the following embodiments.

[0009] Incidentally, with the miniaturization of processes, control of the line width (CD: Critical Dimension) of a pattern formed on a substrate has become increasingly important. In order to accurately form a pattern having a desired CD on a substrate, further improvement in the accuracy of CD in a pattern formed on a resist is required.

[0010] Therefore, the present disclosure provides a technique capable of improving the accuracy of a pattern formed on a substrate.

[0011] [Configuration of Processing Apparatus 1] FIG. 1 is a schematic diagram illustrating an example of a processing apparatus 1. In the present embodiment, the processing apparatus 1 is, for example, a capacitively coupled plasma processing apparatus. The processing apparatus 1 is an example of a film forming apparatus. The processing apparatus 1 includes a chamber 10, a gas supply unit 20, a power source 30, and an exhaust system 40. The processing apparatus 1 also includes a substrate support unit 11 and a gas introduction unit. The gas introduction unit is configured to introduce at least one type of gas into the chamber 10. The gas introduction unit includes a shower head 13. The substrate support unit 11 is disposed inside the chamber 10. The shower head 13 is disposed above the substrate support unit 11. In one embodiment, the shower head 13 constitutes at least a part of the ceiling of the chamber 10. The chamber 10 has a processing space 10s defined by the shower head 13, a side wall 10a of the chamber 10, and the substrate support unit 11.

[0012] Chamber 10 has at least one gas supply port for supplying at least one type of gas to the processing space 10s, and at least one gas outlet for discharging gas from the plasma processing space. Chamber 10 is made of a conductor such as aluminum and is grounded. The shower head 13 and the substrate support part 11 are electrically insulated from the housing of chamber 10. An opening 10b is formed in the side wall 10a of chamber 10 for loading the substrate W into the chamber 10 and unloading the substrate W from the chamber 10. The opening 10b is opened and closed by a gate valve G.

[0013] The substrate support portion 11 includes a main body portion 111 and a ring assembly 112. The main body portion 111 has a central region 111a for supporting the substrate W and an annular region 111b for supporting the ring assembly 112. A wafer is an example of the substrate W. The annular region 111b of the main body portion 111 surrounds the central region 111a of the main body portion 111 in a plan view. The substrate W is placed on the central region 111a of the main body portion 111, and the ring assembly 112 is placed on the annular region 111b of the main body portion 111 so as to surround the substrate W on the central region 111a of the main body portion 111. Therefore, the central region 111a is also called the substrate support surface for supporting the substrate W, and the annular region 111b is also called the ring support surface for supporting the ring assembly 112.

[0014] In one embodiment, the main body 111 includes a base 1110 and an electrostatic chuck 1111. The base 1110 includes a conductive member. The conductive member of the base 1110 can function as a lower electrode. The electrostatic chuck 1111 is placed on the base 1110. The electrostatic chuck 1111 includes a ceramic member 1111a and an electrostatic electrode 1111b placed within the ceramic member 1111a. The ceramic member 1111a has a central region 111a. In one embodiment, the ceramic member 1111a also has an annular region 111b. Other members surrounding the electrostatic chuck 1111, such as an annular electrostatic chuck (not shown) or an annular insulating member (not shown), may also have an annular region 111b. In this case, the ring assembly 112 may be placed on the annular electrostatic chuck or the annular insulating member, or on both the electrostatic chuck 1111 and the annular insulating member. Furthermore, at least one RF / DC electrode, coupled to the RF (Radio Frequency) power supply 31 and / or DC (Direct Current) power supply 32 described later, may be placed within the ceramic member 1111a. In this case, at least one RF / DC electrode functions as a lower electrode. When a bias RF signal and / or DC signal, described later, is supplied to at least one RF / DC electrode, the RF / DC electrode is also called a bias electrode. Note that the conductive member of the base 1110 and at least one RF / DC electrode may function as multiple lower electrodes. Also, the electrostatic electrode 1111b may function as a lower electrode. Therefore, the substrate support portion 11 includes at least one lower electrode.

[0015] The ring assembly 112 includes one or more annular members. In one embodiment, the one or more annular members include one or more edge rings and at least one covering ring. The edge rings are formed of a conductive or insulating material, and the covering rings are formed of an insulating material.

[0016] The substrate support section 11 may also include a temperature control module configured to adjust at least one of the electrostatic chuck 1111, the ring assembly 112, and the substrate W to a target temperature. The temperature control module may include a heater, a heat transfer medium, a flow path 1110a, or a combination thereof. A heat transfer fluid such as brine or gas flows through the flow path 1110a. In one embodiment, the flow path 1110a is formed within the base 1110, and one or more heaters are arranged within the ceramic member 1111a of the electrostatic chuck 1111. The substrate support section 11 may also include a heat transfer medium supply section configured to supply a heat transfer medium such as a heat transfer gas to the gap between the back surface of the substrate W and the central region 111a.

[0017] A through-hole (not shown) is formed in the electrostatic chuck 1111 below the central region 111a, and a lift pin (not shown) is inserted into the through-hole. The lift pin moves up and down by a lifting mechanism (not shown). By moving the lift pin up and down, the substrate W placed on the central region 111a can be raised and lowered. For example, after the gate valve G is opened, the substrate W is transported into the chamber 10 through the opening 10b by a transport robot (not shown) and placed on the lift pin whose tip protrudes from the upper surface of the electrostatic chuck 1111. Then, as the lift pin descends, the substrate W is placed on the electrostatic chuck 1111, the gate valve G is closed, and processing of the substrate W is performed in the chamber 10. After processing, the substrate W is lifted off the upper surface of the electrostatic chuck 1111 as the lift pin rises. Then, after the gate valve G is opened, the substrate W is transported out of the chamber 10 through the opening 10b by a transport robot (not shown).

[0018] The shower head 13 is configured to introduce at least one type of gas from the gas supply unit 20 into the processing space 10s. The shower head 13 has at least one gas supply port 13a, at least one gas diffusion chamber 13b, and a plurality of gas inlet ports 13c. The gas supplied to the gas supply port 13a passes through the gas diffusion chamber 13b and is introduced into the processing space 10s through the plurality of gas inlet ports 13c. The shower head 13 also includes at least one upper electrode (not shown). In addition to the shower head 13, the gas introduction unit may also include one or more side gas injectors (SGI) attached to one or more openings (not shown) formed in the side wall 10a.

[0019] The gas supply unit 20 may include at least one gas source 21 and at least one flow controller 22. In one embodiment, the gas supply unit 20 is configured to supply at least one type of gas to the shower head 13 from a corresponding gas source 21 via a corresponding flow controller 22. Each flow controller 22 may include, for example, a mass flow controller or a pressure-controlled flow controller. Furthermore, the gas supply unit 20 may include one or more flow modulation devices that modulate or pulse the flow rate of at least one type of gas.

[0020] The power supply 30 includes an RF power supply 31 coupled to the chamber 10 via at least one impedance matching circuit. The RF power supply 31 is configured to supply at least one RF signal (RF power) to at least one lower electrode and / or at least one upper electrode. This causes plasma to be formed from at least one type of gas supplied to the processing space 10s. Thus, the RF power supply 31 can function as at least part of a plasma generation unit configured to generate plasma from one or more types of gas in the chamber 10. In addition, by supplying a bias RF signal to at least one lower electrode, a bias potential is generated on the substrate W, and ionic components in the formed plasma can be drawn into the substrate W.

[0021] In one embodiment, the RF power supply 31 includes a first RF generation unit 31a and a second RF generation unit 31b. The first RF generation unit 31a is coupled to at least one lower electrode and / or at least one upper electrode via at least one impedance matching circuit and is configured to generate a source RF signal (source RF power) for plasma generation. In one embodiment, the source RF signal has a frequency in the range of 10 MHz to 150 MHz. In one embodiment, the first RF generation unit 31a may be configured to generate a plurality of source RF signals having different frequencies. One or more generated source RF signals are supplied to at least one lower electrode and / or at least one upper electrode.

[0022] The second RF generation unit 31b is coupled to at least one lower electrode via at least one impedance matching circuit and is configured to generate a bias RF signal (bias RF power). The frequency of the bias RF signal may be the same as or different from the frequency of the source RF signal. In one embodiment, the bias RF signal has a frequency lower than the frequency of the source RF signal. In one embodiment, the bias RF signal has a frequency in the range of 100 kHz to 60 MHz. In one embodiment, the second RF generation unit 31b may be configured to generate a plurality of bias RF signals having different frequencies. One or more generated bias RF signals are supplied to at least one lower electrode. In various embodiments, at least one of the source RF signal and the bias RF signal may be pulsed.

[0023] The power supply 30 may also include a DC power supply 32 coupled to the chamber 10. The DC power supply 32 includes a first DC generation unit 32a and a second DC generation unit 32b. In one embodiment, the first DC generation unit 32a is connected to at least one lower electrode and configured to generate a first DC signal. The generated first bias DC signal is applied to at least one lower electrode. In one embodiment, the second DC generation unit 32b is connected to at least one upper electrode and configured to generate a second DC signal. The generated second DC signal is applied to at least one upper electrode.

[0024] In various embodiments, at least one of the first and second DC signals may be pulsed. In this case, a sequence of voltage pulses is applied to at least one lower electrode and / or at least one upper electrode. The voltage pulses may have a rectangular, trapezoidal, triangular, or combination thereof pulse waveform. In one embodiment, a waveform generation unit for generating a sequence of voltage pulses from a DC signal is connected between the first DC generation unit 32a and at least one lower electrode. Thus, the first DC generation unit 32a and the waveform generation unit constitute a voltage pulse generation unit. When the second DC generation unit 32b and the waveform generation unit constitute a voltage pulse generation unit, the voltage pulse generation unit is connected to at least one upper electrode. The voltage pulses may have positive or negative polarity. The sequence of voltage pulses may also include one or more positive voltage pulses and one or more negative voltage pulses within one cycle. The first and second DC generation units 32a and 32b may be provided in addition to the RF power supply 31, and the first DC generation unit 32a may be provided in place of the second RF generation unit 31b.

[0025] The exhaust system 40 may be connected to, for example, a gas outlet 10e located at the bottom of the chamber 10. The exhaust system 40 may include a pressure regulating valve and a vacuum pump. The pressure regulating valve regulates the pressure in the processing space 10s. The vacuum pump may include a turbomolecular pump, a dry pump, or a combination thereof.

[0026] The control unit 2 processes computer-executable instructions that cause each processing unit 1 to perform the various processes described herein. The control unit 2 may be configured to control each element of the processing unit 1 to perform the various processes described herein. In one embodiment, part or all of the control unit 2 may be included in the processing unit 1. The control unit 2 may include a processing unit 2a1, a storage unit 2a2, and a communication interface 2a3. The control unit 2 is implemented, for example, by a computer 2a. The processing unit 2a1 may be configured to perform various control operations by reading a program from the storage unit 2a2 and executing the read program. This program may be stored in the storage unit 2a2 in advance, or it may be obtained via a medium when needed. The obtained program is stored in the storage unit 2a2 and read from the storage unit 2a2 and executed by the processing unit 2a1. The medium may be various storage media readable by the computer 2a, or it may be a communication line connected to the communication interface 2a3. The processing unit 2a1 may be a CPU (Central Processing Unit). The memory unit 2a2 may include RAM (Random Access Memory), ROM (Read Only Memory), HDD (Hard Disk Drive), SSD (Solid State Drive), or a combination thereof. The communication interface 2a3 communicates with the processing unit 1 via a communication line such as a LAN (Local Area Network).

[0027] [Processing procedure for substrate W] Figure 2 is a flowchart showing an example of the processing procedure for substrate W. Each process illustrated in Figure 2 is realized by the control unit 2 controlling each part of the processing apparatus 1. The processing procedure illustrated in Figure 2 is an example of a film deposition method.

[0028] First, the substrate W is loaded into the chamber 10 (step S10). Step S10 is an example of step a). In this embodiment, the substrate W has a base film and a resist provided on the base film, on which a predetermined pattern is formed. In step S10, the control unit 2 controls the drive mechanism of a lift pin (not shown) so that the tip of the lift pin protrudes from the upper surface of the electrostatic chuck 1111. The control unit 2 then controls the gate valve G to open the gate valve G. The substrate W is loaded into the chamber 10 through the opening 10b by a transport robot (not shown) and placed on the lift pin. The control unit 2 then controls the drive mechanism of the lift pin so that the lift pin descends. As a result, the lift pin descends and the substrate W is placed on the electrostatic chuck 1111. The control unit 2 then controls the gate valve G to close the gate valve G.

[0029] Next, plasma is generated in the chamber 10 (step S11). Step S11 is an example of step f). In step S11, oxygen gas is supplied into the chamber 10 from the gas supply unit 20 via the shower head 13, and the oxygen gas is converted into plasma by RF power supplied into the chamber 10 from the power supply 30. The oxygen radicals contained in the plasma then modify the surface of the substrate W (for example, the surface of the resist) into a hydrophilic surface. This makes it easier for monomer molecules to adsorb onto the surface of the substrate W.

[0030] Furthermore, the gas used to generate the plasma is not limited to oxygen gas, as long as it is an oxygen-containing gas. Examples of oxygen-containing gases include H2O, NO, N2O, CO2, and H2O2. Another method for modifying a surface to be hydrophilic is to perform plasma treatment using a hydrogen-containing gas, argon gas, etc., followed by exposure to the atmosphere.

[0031] Next, a gas of the first monomer is supplied into the chamber 10 (step S12). Step S12 is an example of step b). In this embodiment, the first monomer is, for example, an isocyanate. In step S12, a gas of the first monomer is supplied from the gas supply unit 20 into the chamber 10 via the shower head 13. Molecules of the first monomer contained in the gas supplied into the chamber 10 are adsorbed onto the surface of the substrate W. Step S12 is performed for, for example, 4 seconds.

[0032] Next, a purge gas is supplied into the chamber 10 (step S13). Step S13 is an example of step c). In this embodiment, the purge gas is an inert gas such as nitrogen gas or a noble gas. In step S13, the purge gas is supplied from the gas supply unit 20 into the chamber 10 via the shower head 13. The purge gas supplied into the chamber 10 purges the molecules of the first monomer that have been excessively adsorbed on the surface of the substrate W. Step S13 is performed for, for example, 4 seconds.

[0033] Next, a gas of the second monomer is supplied into the chamber 10 (step S14). Step S14 is an example of step d). In this embodiment, the second monomer is, for example, an amine. In step S14, a gas of the second monomer is supplied from the gas supply unit 20 into the chamber 10 via the shower head 13. The molecules of the second monomer contained in the gas supplied into the chamber 10 undergo a polymerization reaction with the molecules of the first monomer adsorbed on the surface of the substrate W. Then, the polymerization reaction between the molecules of the first monomer and the molecules of the second monomer forms a polymer film having urea bonds on the surface of the substrate W. Step S14 is carried out for, for example, 4 seconds.

[0034] Next, purge gas is supplied into the chamber 10 (step S15). Step S15 is an example of step e). In step S15, purge gas is supplied into the chamber 10 from the gas supply unit 20 via the shower head 13. The purge gas supplied into the chamber 10 purges the molecules of the second monomer that have been excessively adsorbed on the surface of the substrate W. Step S15 is performed for, for example, 4 seconds.

[0035] Next, the control unit 2 determines whether the processes in steps S12 to S15 have been repeated a predetermined number of times (step S16). Hereinafter, the processes in steps S12 to S15 will be referred to as the film formation process. If the film formation process has not been repeated a predetermined number of times (step S16: No), the control unit 2 executes the process shown in step S12 again. The predetermined number of times is the number of times the film formation process is repeated until a polymer film of a desired thickness is formed on the surface of the substrate W. In this embodiment, the desired thickness of the polymer film is, for example, 1 nm to 2.5 nm. Note that the predetermined number of times may be 1.

[0036] Furthermore, the resist applied to the substrate W may deteriorate at temperatures above 130°C. Also, a temperature above room temperature is required for the polymerization reaction between the first monomer and the second monomer. Therefore, it is preferable to maintain the temperature of the substrate W during the film formation process within a range of, for example, 20°C to 120°C.

[0037] If the film deposition process is repeated a predetermined number of times (Step S16: Yes), etching of the underlayer film is performed (Step S17). In Step S17, etching gas is supplied from the gas supply unit 20 to the chamber 10 via the shower head 13. In this embodiment, the underlayer film is, for example, a silicon oxide film, and the etching gas is, for example, a fluorine-containing gas. RF power for plasma generation is supplied from the power supply 30 to the chamber 10, and the etching gas is converted into plasma within the chamber 10. RF power and DC signals for biasing are also supplied from the power supply 30 to the chamber 10 as needed. The underlayer film is then etched along the pattern formed on the resist by active species and ions contained in the plasma.

[0038] Next, the substrate W is discharged from the chamber 10 (step S18). In step S18, the control unit 2 controls the lift pin drive mechanism so that the tip of the lift pin protrudes from the upper surface of the electrostatic chuck 1111. This lifts the processed substrate W from the electrostatic chuck 1111. Then, the control unit 2 controls the gate valve G to open the gate valve G. The processed substrate W is discharged from the chamber 10 through the opening 10b by a transport robot (not shown). Then, the control unit 2 controls the gate valve G to close the gate valve G and controls the lift pin drive mechanism so that the lift pin descends.

[0039] Next, the control unit 2 determines whether or not to terminate the processing of the substrate W (step S19). If the processing of the substrate W is not terminated (step S19: No), the control unit 2 executes the process shown in step S10 again. On the other hand, if the processing of the substrate W is terminated (step S19: Yes), the control unit 2 terminates the processing procedure for the substrate W shown in this flowchart. Although the above processing procedure for the substrate W describes an example in which steps S11 to S17 are performed in a single processing device, the disclosed technology is not limited to this. As another example, steps S11, steps S12 to S16, and step S17 may be performed in separate devices.

[0040] [Method of polymer film formation] Figures 3A and 3B are schematic diagrams illustrating an example of the process of forming a polymer film on an uneven pattern. On the surface of the resist 50, there are protrusions 50a and recesses 50b due to the surface roughness of the resist 50, as shown in Figures 3A and 3B. Although Figures 3A and 3B illustrate the protrusions 50a and recesses 50b on the upper surface of the resist 50, similar protrusions 50a and recesses 50b also exist on the sides of the resist 50.

[0041] When the gas of the first monomer is supplied in step S12 of Figure 2, molecules of the first monomer are adsorbed along the surface of the resist 50. That is, as shown in Figure 3A, for example, molecules 55 of the first monomer are adsorbed to the convex portions 50a and concave portions 50b on the surface of the resist 50 with a similar thickness.

[0042] Then, when the purge gas is supplied in step S13 of Figure 2, the molecules 55 of the first monomer that have been excessively adsorbed on the surface of the resist 50 are purged. At this time, as shown in Figure 3B, for example, more molecules 55 of the first monomer adsorbed on the protrusions 50a are purged than the molecules 55 of the first monomer adsorbed on the recesses 50b.

[0043] Then, when the gas of the second monomer is supplied in step S14 of Figure 2, the molecules of the second monomer are adsorbed along the surface of the resist 50 on which the molecules of the first monomer are adsorbed. Then, a polymerization reaction between the molecules of the first monomer and the molecules of the second monomer forms a polymer film having urea bonds on the surface of the resist 50.

[0044] In this case, as shown in Figure 3B, for example, the number of molecules 55 of the first monomer adsorbed on the protrusions 50a is less than the number of molecules 55 of the first monomer adsorbed on the recesses 50b. On the other hand, the number of molecules 55 of the first monomer adsorbed on the recesses 50b is greater than the number of molecules 55 of the first monomer adsorbed on the protrusions 50a. Therefore, the thickness of the polymer film formed by the polymerization reaction with the molecules of the second monomer is greater on the recesses 50b than on the protrusions 50a. As a result, the height difference between the protrusions 50a and the recesses 50b after the polymer film is formed is smaller than the height difference between the protrusions 50a and the recesses 50b before the polymer film is formed. Consequently, the surface roughness of the resist 50 after the polymer film is formed is reduced compared to the surface roughness of the resist 50 before the polymer film was formed. This makes it possible to reduce the difference between the pattern formed on the resist 50 and the desired pattern. Furthermore, by etching the underlying film beneath the resist 50 through the resist 50 after the polymer film has been formed, the accuracy of the pattern formed on the underlying film can be improved.

[0045] Figures 4A and 4B are schematic diagrams illustrating an example of the process of forming a polymer film in a hole. Holes 51 are formed in the resist 50, for example, as shown in Figures 4A and 4B. However, the shape of the holes 51 may be an oval shape rather than a perfect circle due to surface roughness of the resist 50.

[0046] When the gas of the first monomer is supplied in step S12 of Figure 2, molecules of the first monomer are adsorbed along the surface of the resist 50. That is, for example, as shown in Figure 4A, molecules 55 of the first monomer are adsorbed along the inner wall of the hole 51.

[0047] Then, when a purge gas is supplied in step S13 of Figure 2, the molecules 55 of the first monomer that are excessively adsorbed on the inner wall of the hole 51 are purged. In this case, for example, as shown in Figure 4B, in an oval-shaped hole 51, more molecules 55 of the first monomer adsorbed on the inner wall portion 51a with less curvature are purged than molecules 55 of the first monomer adsorbed on the inner wall portion 51b with greater curvature.

[0048] Then, when the gas of the second monomer is supplied in step S14 of Figure 2, the molecules of the second monomer are adsorbed along the inner wall of the hole 51 where the molecules of the first monomer are adsorbed. Then, a polymerization reaction between the molecules of the first monomer and the molecules of the second monomer forms a polymer film having urea bonds on the surface of the resist 50.

[0049] In this case, as shown in Figure 4B, for example, the number of molecules 55 of the first monomer adsorbed on the inner wall portion 51a with low curvature is less than the number of molecules 55 of the first monomer adsorbed on the inner wall portion 51b with high curvature. On the other hand, the number of molecules 55 of the first monomer adsorbed on the inner wall portion 51b with high curvature is greater than the number of molecules 55 of the first monomer adsorbed on the inner wall portion 51a with low curvature. Therefore, the thickness of the polymer film formed by the polymerization reaction with the molecules of the second monomer is thicker in the inner wall portion 51b with high curvature than in the inner wall portion 51a with low curvature. As a result, the shape of the hole 51 after the polymer film is formed is closer to a perfect circle than the shape of the hole 51 before the polymer film is formed. This makes it possible to bring the shape of the hole 51 closer to the desired shape. Furthermore, by etching the underlying film of the resist 50 through the hole 51 after the polymer film has been formed, the accuracy of the shape of the holes formed in the underlying film can be improved.

[0050] Figures 5A and 5B are schematic diagrams illustrating an example of the process of forming a polymer film into two interconnected holes. Holes 52 are formed adjacent to each other in the resist 50, for example, as shown in Figures 5A and 5B. However, due to surface roughness of the resist 50, the two adjacent holes 52 may have shapes other than perfect circles, and a so-called kissing defect may occur where they communicate at the connecting portion 52a between the two adjacent holes 52.

[0051] When the gas of the first monomer is supplied in step S12 of Figure 2, molecules of the first monomer are adsorbed along the surface of the resist 50. That is, molecules 55 of the first monomer are adsorbed along the inner walls of the two holes 52 and the inner wall of the connecting portion 52a, for example, as shown in Figure 5A.

[0052] Then, when a purge gas is supplied in step S13 of Figure 2, the molecules 55 of the first monomer that are excessively adsorbed on the inner walls of the holes 52 and the connecting portion 52a are purged. In this case, as shown in Figure 5B, for example, more molecules of the first monomer adsorbed on the inner wall of the holes 52 are purged than the molecules of the first monomer adsorbed on the inner wall of the connecting portion 52a.

[0053] Then, when the gas of the second monomer is supplied in step S14 of Figure 2, the molecules of the second monomer are adsorbed along the inner walls of the holes 52 and the connecting portion 52a where the molecules of the first monomer are adsorbed. Then, a polymerization reaction between the molecules of the first monomer and the molecules of the second monomer forms a polymer film having urea bonds on the surface of the resist 50.

[0054] In this case, as shown in Figure 5B, for example, the number of molecules 55 of the first monomer adsorbed on the inner wall of hole 52 is less than the number of molecules 55 of the first monomer adsorbed on the inner wall of the connecting portion 52a. On the other hand, the number of molecules 55 of the first monomer adsorbed on the inner wall of the connecting portion 52a is greater than the number of molecules 55 of the first monomer adsorbed on the inner wall of hole 52. Therefore, the polymer film formed by the polymerization reaction with the molecules of the second monomer is thicker on the inner wall of the connecting portion 52a than on the inner wall of hole 52. As a result, the connecting portion 52a is blocked by the polymer film. This makes it possible to make two adjacent holes 52 into independent holes 52 that are not connected. Furthermore, by etching the underlying film of the resist 50 through the holes 52 after the polymer film has been formed, the accuracy of the shape of the holes formed in the underlying film can be improved.

[0055] [Relationship between film thickness and vapor pressure ratio] Figure 6 shows an example of the relationship between the number of film formation cycles and the change in polymer film thickness. In Figure 6, experiments were conducted for different vapor pressure ratios for the monomer with the lower saturated vapor pressure among the first and second monomers. In this embodiment, the first monomer is an isocyanate and the second monomer is an amine, and the isocyanate has a lower saturated vapor pressure than the amine. Therefore, Figure 6 shows the vapor pressure ratio for the isocyanate.

[0056] vapor pressure ratio P r When the partial pressure of the monomer gas is P1 and the saturated vapor pressure of the monomer gas is P0, it can be expressed by the following equation (1). P r =P1 / P0···(1)

[0057] For example, as shown in Figure 6, the higher the vapor pressure ratio, the greater the rate of increase in the polymer film thickness relative to the number of film deposition treatments, and the lower the vapor pressure ratio, the smaller the rate of increase in the polymer film thickness relative to the number of film deposition treatments.

[0058] When forming patterns of several tens of nanometers or less, if the polymer film formed on the resist is too thick, the pattern may be filled with the polymer film. Conversely, if the polymer film formed on the resist is too thin, the accuracy of the resist pattern will not be sufficiently improved, and the accuracy of the pattern formed on the substrate using the resist may also be insufficient. Therefore, it is preferable that the thickness of the polymer film formed on the resist be within the range of 1 nm to 2.5 nm.

[0059] Referring to Figure 6, when the vapor pressure ratio is 0.07 or higher, the thickness of the polymer film increases with the number of repeated film formation treatments, and may reach 2.5 nm or more. On the other hand, when the vapor pressure ratio is 0.05, although the thickness of the polymer film increases with the number of repeated film formation treatments, the increase in film thickness is gradual, with the film thickness remaining at around 2.0 nm. From the trend shown in Figure 6, it is considered that when the vapor pressure ratio is lower than 0.05, the thickness of the polymer film will be in the range of 1 nm to 2 nm. If the change in the thickness of the polymer film can be kept within the range of 1 nm to 2.5 nm, the polymer film can be easily formed within a preferred thickness range. Therefore, in order to form a polymer film with a preferred thickness range in this embodiment, it is preferable that the vapor pressure ratio is 0.05 or lower.

[0060] [Experimental Results] Figure 7A shows an example of the shape of the openings of holes 60 before the polymer film is formed. In Figure 7A, multiple holes 60 are formed in the resist 61. In Figure 7A, the average CD of the openings of the holes 60 was 16.6 nm, and the LCDU (Local Critical Dimension Uniformity) was 4.5 nm.

[0061] On the other hand, when a polymer film with a thickness of 2 nm was formed on the resist 61 shown in Figure 7A, the state of the holes 60 was as shown in Figure 7B, for example. Figure 7B shows an example of the shape of the opening of the holes 60 after the polymer film has been formed. In Figure 7B, the average CD of the opening of the holes 60 was 12.9 nm, and the LCDU was 3.3 nm. Comparing Figure 7A and Figure 7B, the LCDU of the opening of the holes 60 has improved by approximately 22%.

[0062] Figure 8A shows an example of the cross-sectional shape of the holes 60 before the polymer film is formed. In Figure 8A, multiple holes 60 are formed in the resist 61 laminated on the underlayer film 62. In Figure 8A, the average height of the resist 61 was 39.0 nm, and the average CD of the hole 60 openings was 16.9 nm.

[0063] On the other hand, when a polymer film with a thickness of 2 nm was formed on the resist 61 shown in Figure 8A, the state of the holes 60 was as shown in Figure 8B, for example. Figure 8B is a diagram showing an example of the cross-sectional shape of the holes 60 after the polymer film has been formed. In Figure 8B, the average height of the resist 61 was 39.2 nm, and the average CD of the openings of the holes 60 was 16.0 nm. A polymer film was also formed inside the holes 60, suggesting that the LCDDU was improved not only at the openings of the holes 60 but also inside the holes 60. Note that in Figures 8A and 8B, the width of the holes 60 at the positions indicated by the dashed lines was measured as CD.

[0064] Figure 9A shows an example of the shape of the hole openings before the polymer film is formed. In Figure 9A, multiple holes 60 are formed in the resist 61, and the spacing between adjacent holes 60 is wider than in Figure 7A. In Figure 9A, the average CD of the hole openings in the x-direction was 33.0 nm, and the average CD in the y-direction was 32.2 nm. The LCDU was 3.5 nm.

[0065] On the other hand, when a polymer film with a thickness of 2.5 nm was formed on the resist 61 shown in Figure 9A, the state of the holes 60 was as shown in Figure 9B, for example. Figure 9B is a diagram showing an example of the shape of the hole openings after the polymer film has been formed. In Figure 9B, the average CD value in the x-direction of the hole openings 60 was 25.4 nm, and the average CD value in the y-direction was 26.3 nm. The LCDU was 1.5 nm. Comparing Figure 9A and Figure 9B, the LCDU of the hole openings 60 has been improved by approximately 57%.

[0066] Figure 10A shows an example of the shape of the hole openings before the polymer film is formed. In Figure 10A, multiple holes 60 are formed in the resist 61, and some adjacent holes 60 (e.g., holes 60a and 60b) are in communication with each other.

[0067] On the other hand, when a polymer film with a thickness of 2.5 nm was formed on the resist 61 shown in Figure 10A, the state of the holes 60 became as shown in Figure 10B, for example. Figure 10B is a diagram showing an example of the shape of the hole openings after the polymer film has been formed. Some of the holes 60 that were in communication in Figure 10A (for example, holes 60a and holes 60b) are not in communication in Figure 10B, and each forms an independent hole 60. Comparing Figure 10A and Figure 10B, the kissing defects have been improved in multiple holes 60.

[0068] Figure 11A shows an example of the line shape of the resist 61 before the polymer film is formed. In Figure 11A, multiple line-shaped patterns are formed on the resist 61. In Figure 11A, the average CD of the lines of the resist 61 was 17.1 nm, and the LER (Line Edge Roughness) was 2.14 nm.

[0069] On the other hand, when a polymer film with a thickness of 2.5 nm was formed on the resist 61 shown in Figure 11A, the state of the resist 61 became as shown in Figure 11B, for example. Figure 11B shows an example of the line shape of the resist 61 after the polymer film has been formed. In Figure 11B, the average CD of the lines of the resist 61 was 20.5 nm, and the LER was 1.68 nm. Comparing Figure 11A and Figure 11B, the LER has improved by approximately 21%.

[0070] Figure 12A shows an example of the shape of the openings of holes 60 in a resist 61 where no polymer film has been formed. In Figure 12A, multiple holes 60 are formed in the resist 61, and the openings of each hole 60 are oval-shaped. In Figure 12A, the average difference between the CD in the x-direction and the CD in the y-direction of the openings of the holes 60 was 4.2 nm.

[0071] Figure 12B shows an example of the shape of the hole openings in the underlying film after etching is performed through a resist 61 that does not have a polymer film formed on it. When the underlying film 62 is etched through the resist 61 shown in Figure 12A, holes 60' are formed in the underlying film 62, for example, as shown in Figure 12B. Since the shape of the holes 60 shown in Figure 12A is transferred to the underlying film 62, oval-shaped holes 60' are formed in the underlying film 62. In Figure 12B, the average difference between the CD in the x direction and the CD in the y direction of the opening of the hole 60' was 3.1 nm.

[0072] Figure 13A shows an example of the shape of the openings of holes 60 in a resist 61 on which a polymer film has been formed. In Figure 13A, a polymer film with a thickness of 2 nm has been formed on the resist 61. As a result, the openings of each hole 60 are closer to a perfect circle than the holes 60 shown in Figure 12A. In Figure 13A, the average difference between the CD in the x-direction and the CD in the y-direction of the openings of the holes 60 was 1.6 nm. Comparing Figure 12A and Figure 13A, the average difference between the CD in the x-direction and the CD in the y-direction of the openings of the holes 60 has improved by approximately 62%.

[0073] Figure 13B shows an example of the shape of the hole openings in the underlying film after etching is performed through the resist 61 on which the polymer film is formed. When the underlying film 62 is etched through the resist 61 shown in Figure 13A, holes 60' are formed in the underlying film 62, for example, as shown in Figure 13B. Since the shape of the holes 60 shown in Figure 13A is transferred to the underlying film 62, holes 60' with openings that are closer to perfect circles than the holes 60' shown in Figure 12B are formed in the underlying film 62. In Figure 13B, the average difference between the CD in the x-direction and the CD in the y-direction of the hole 60' opening was 1.2 nm. Comparing Figure 12B and Figure 13B, the average difference between the CD in the x-direction and the CD in the y-direction of the hole 60 opening has improved by approximately 61%.

[0074] The embodiments have been described above. As described above, the film formation method in this embodiment includes steps a), b), c), d), and e). In step a), a substrate (substrate W) having a base film (base film 62) and a resist (resist 50, resist 61) provided on the base film and having a predetermined pattern formed on it is brought into a chamber (chamber 10). In step b), a gas of the first monomer is supplied into the chamber. In step c), a purge gas is supplied into the chamber. In step d), a gas of the second monomer is supplied into the chamber, and a polymer film is formed on the surface of the substrate by a polymerization reaction between the first monomer and the second monomer. In step e), a purge gas is supplied into the chamber. Furthermore, the vapor pressure ratio of the first monomer and the monomer with the lower saturated vapor pressure among the second monomers is 0.05 or less. This makes it possible to improve the accuracy of the pattern formed on the substrate.

[0075] Furthermore, in the embodiments described above, steps b), c), d), and e) may be repeated multiple times in this order. By controlling the number of repetitions, a polymer film of a desired thickness can be easily formed on the surface of the substrate.

[0076] Furthermore, the film formation method in the above-described embodiment may further include step f). Step f) is performed before step b), and involves supplying oxygen gas into the chamber and plasma-generating the oxygen gas in the chamber. This allows for the efficient formation of a polymer film on the resist.

[0077] Furthermore, in the embodiments described above, in steps b), c), d), and e), the substrate is maintained at a temperature within the range of 20°C to 120°C. This allows for the formation of a polymer film by the polymerization reaction of the first monomer and the second monomer while avoiding deterioration of the resist.

[0078] Furthermore, in the embodiments described above, the first monomer is an isocyanate, the second monomer is an amine, and the polymer film formed on the substrate contains urea bonds. This makes it possible to easily form a polymer film that can improve the accuracy of the pattern formed on the substrate.

[0079] Furthermore, the film deposition apparatus (processing apparatus 1) in the above-described embodiment comprises a chamber (chamber 10) having a gas supply port (gas supply port 13a) and a gas outlet (gas outlet 10e), a substrate support section (substrate support section 11) provided in the chamber and supporting a substrate (substrate W) having a base film (base film 62) and a resist (resist 50, resist 61) provided on the base film and having a predetermined pattern formed thereon, a lifting mechanism for raising and lowering lift pins that support the substrate, a gas supply section (gas supply section 20) for supplying gas into the chamber, and a control section (control section 2). The control section executes steps a), b), c), d), and e). In step a), the control section controls the lifting mechanism to place the substrate brought into the chamber onto the substrate support section via the lift pins. In step b), the control section controls the gas supply section to supply gas of the first monomer into the chamber. In step c), the control unit supplies purge gas into the chamber by controlling the gas supply unit. In step d), the control unit supplies gas of the second monomer into the chamber by controlling the gas supply unit, thereby forming a polymer film on the surface of the substrate by a polymerization reaction between the first monomer and the second monomer. In step e), the control unit supplies purge gas into the chamber by controlling the gas supply unit. Furthermore, the vapor pressure ratio of the first monomer and the monomer with the lower saturated vapor pressure among the second monomers is 0.05 or less. This improves the accuracy of the pattern formed on the substrate.

[0080] [others] Furthermore, the technology disclosed in this application is not limited to the embodiments described above, and numerous modifications are possible within the scope of its essence.

[0081] For example, in the above-described embodiment, an isocyanate was used as the first monomer and an amine as the second monomer to form a polymer film having a urea bond (-NH-CO-NH-) on the surface of the substrate W, but the disclosed technology is not limited thereto. For example, a carboxylic acid anhydride may be used as the first monomer and an amine as the second monomer to form a polymer film having an imide bond (-CO-N(-)-CO-) on the surface of the substrate W. Alternatively, an epoxide may be used as the first monomer and an amine as the second monomer to form a polymer film having a 2-aminoethanol bond (-NH-CH2-CH(OH)-) on the surface of the substrate W. Alternatively, an isocyanate may be used as the first monomer and an alcohol as the second monomer to form a polymer film having a urethane bond (-NH-CO-O-) on the surface of the substrate W. Alternatively, an acyl halide may be used as the first monomer and an amine as the second monomer to form a polymer film having an amide bond (-NH-CO-) on the surface of the substrate W.

[0082] Furthermore, in the above-described embodiment, a processing apparatus 1 that uses capacitively coupled plasma (CCP) as an example of a plasma source was explained, but the plasma source is not limited to capacitively coupled plasma. Examples of plasma sources other than capacitively coupled plasma include inductively coupled plasma (ICP), microwave-excited surface wave plasma (SWP), electron cycloton resonance plasma (ECP), and helicon wave-excited plasma (HWP).

[0083] Furthermore, the embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. Indeed, the embodiments described above can be embodied in a variety of forms. Moreover, the embodiments described above may be omitted, replaced, or modified in various ways without departing from the scope and spirit of the appended claims.

[0084] Furthermore, the following additional information is disclosed regarding the above embodiments.

[0085] (Note 1) a) A step of transporting a substrate having a base film and a resist provided on the base film and having a predetermined pattern formed on it into a chamber, b) A step of supplying a gas of the first monomer into the chamber, c) A step of supplying purge gas into the chamber, d) A step of supplying a gas of the second monomer into the chamber to form a polymer film on the surface of the substrate by a polymerization reaction between the first monomer and the second monomer, e) A step of supplying purge gas into the chamber Includes, A film formation method wherein the vapor pressure ratio of the first monomer and the second monomer with the lower saturated vapor pressure is 0.05 or less. (Note 2) The film formation method described in Appendix 1, wherein steps b), c), d), and e) are repeated multiple times in this order. (Note 3) f) A method for forming a film according to Appendix 1 or 2, further comprising a step performed before step b) of supplying oxygen gas into the chamber and plasma-forming the oxygen gas in the chamber. (Note 4) The film formation method according to any one of the appendices 1 to 3, wherein in step b), step c), step d), and step e), the substrate is maintained at a temperature within the range of 20°C to 120°C. (Note 5) The first monomer is an isocyanate, The second monomer is an amine, The film formation method according to either Appendix 1 or 4, wherein the polymer film formed on the substrate contains a urea bond. (Note 6) The first monomer is a carboxylic acid anhydride, The second monomer is an amine, The film formation method according to any one of the appendices 1 to 4, wherein the polymer film formed on the substrate includes an imide bond. (Note 7) The first monomer described above is an epoxide, The second monomer is an amine, The film formation method according to any one of the appendices 1 to 4, wherein the polymer film formed on the substrate contains a 2-aminoethanol bond. (Note 8) The first monomer is an isocyanate, The second monomer is an alcohol, The film formation method according to any one of the appendices 1 to 4, wherein the polymer film formed on the substrate includes a urethane bond. (Note 9) The first monomer is an acyl halogenate, The second monomer is an amine, The film formation method according to any one of the appendices 1 to 4, wherein the polymer film formed on the substrate includes an amide bond. (Note 10) A chamber having a gas supply port and a gas discharge port, A substrate support portion provided within the chamber, which supports a substrate having a base film and a resist provided on the base film and having a predetermined pattern formed thereon, A lifting mechanism for raising and lowering the lift pins that support the substrate, A gas supply unit that supplies gas into the chamber, Control unit and Equipped with, The control unit, a) A step of controlling the lifting mechanism to place the substrate that has been brought into the chamber onto the substrate support via the lift pin, b) A step of supplying the first monomer gas into the chamber by controlling the gas supply unit, c) A step of supplying purge gas into the chamber by controlling the gas supply unit, d) A step of forming a polymer film on the surface of the substrate by a polymerization reaction between the first monomer and the second monomer, by controlling the gas supply unit and supplying a gas of the second monomer into the chamber, e) A step of supplying purge gas into the chamber by controlling the gas supply unit. Execute, A film deposition apparatus in which the vapor pressure ratio of the first monomer and the monomer with the lower saturated vapor pressure among the second monomers is 0.05 or less. [Explanation of Symbols]

[0086] G Gate Valve W board 1 Processing Unit 2 Control Unit 2a Computer 10 Chambers 10a side wall 10b opening 10e Gas outlet 10s processing space 11. Substrate support section 111 Main body 112 Ring Assembly 13 Shower head 13a Gas supply port 13b Gas Diffusion Chamber 13c Gas inlet 20 Gas Supply Department 21 Gas Source 22 Flow controller 30 power supply 31 RF power supply 32 DC power supply 40 Exhaust System 50 Resist 50a protrusion 50b recess 51 holes 51a Inner wall part 51b Inner wall part 52 holes 52a Communication part 55 The molecule of the first monomer 60 holes 61 Resist 62 Undercoat

Claims

1. a) A step of transporting a substrate having a base film and a resist provided on the base film and having a predetermined pattern formed on it into a chamber, b) A step of supplying a gas of the first monomer into the chamber, c) A step of supplying purge gas into the chamber, d) A step of supplying a gas of the second monomer into the chamber to form a polymer film on the surface of the substrate by a polymerization reaction between the first monomer and the second monomer, e) A step of supplying purge gas into the chamber Includes, A film-forming method wherein the vapor pressure ratio of the first monomer and the second monomer with the lower saturated vapor pressure is 0.05 or less.

2. The film formation method according to claim 1, wherein steps b), c), d), and e) are repeated multiple times in this order.

3. f) The method for forming a film according to claim 1 or 2, further comprising a step performed before step b) of supplying an oxygen-containing gas into the chamber and plasma-forming the oxygen-containing gas in the chamber.

4. The film-forming method according to claim 1 or 2, wherein in step b), step c), step d), and step e), the substrate is maintained at a temperature within the range of 20°C to 120°C.

5. The first monomer is an isocyanate, The second monomer is an amine, The film formation method according to claim 1 or 2, wherein the polymer film formed on the substrate contains a urea bond.

6. The first monomer is a carboxylic acid anhydride, The second monomer is an amine, The film formation method according to claim 1 or 2, wherein the polymer film formed on the substrate includes an imide bond.

7. The first monomer is an epoxide, The second monomer is an amine, The film formation method according to claim 1 or 2, wherein the polymer film formed on the substrate contains a 2-aminoethanol bond.

8. The first monomer is an isocyanate, The second monomer is an alcohol, The film-forming method according to claim 1 or 2, wherein the polymer film formed on the substrate includes a urethane bond.

9. The first monomer is an acyl halogenate, The second monomer is an amine, The film formation method according to claim 1 or 2, wherein the polymer film formed on the substrate includes an amide bond.

10. A chamber having a gas supply port and a gas discharge port, A substrate support portion provided within the chamber, which supports a substrate having a base film and a resist provided on the base film and having a predetermined pattern formed thereon, A lifting mechanism for raising and lowering the lift pins that support the substrate, A gas supply unit that supplies gas into the chamber, Control unit and Equipped with, The control unit, a) A step of controlling the lifting mechanism to place the substrate that has been brought into the chamber onto the substrate support via the lift pin, b) A step of supplying the first monomer gas into the chamber by controlling the gas supply unit, c) A step of supplying purge gas into the chamber by controlling the gas supply unit, d) A step of forming a polymer film on the surface of the substrate by a polymerization reaction between the first monomer and the second monomer, by supplying a gas of the second monomer into the chamber by controlling the gas supply unit, e) A step of supplying purge gas into the chamber by controlling the gas supply unit. Execute, A film deposition apparatus in which the vapor pressure ratio of the first monomer and the second monomer with the lower saturated vapor pressure is 0.05 or less.

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