Method of etching substrate

A method of forming patterns of a semiconductor device includes forming a photoresist pattern, which contains a first carbon compound, on a substrate, reforming a top surface of the photoresist pattern to form an upper mask layer which contains a second carbon compound, different from the first carbon compound, on the photoresist pattern, and etching a portion of the substrate using the upper mask layer and the photoresist pattern as an etch mask.

PRIORITY STATEMENT

This U.S. non-provisional patent application claims priority under 35 U.S.C. § 119 to Korean Patent Application Nos. 10-2017-0131509 and 10-2018-0010176, filed on Oct. 11, 2017 and Jan. 26, 2018, respectively, in the Korean Intellectual Property Office, the entire contents of which are hereby incorporated by reference.

BACKGROUND

The inventive concept relates to a method of fabricating a semiconductor device, and in particular, to a photolithographic method of forming patterns of a semiconductor device.

In general, a semiconductor device is fabricated by a plurality of unit processes. The unit processes include a deposition process, a mask forming process, and an etching process. The deposition process and the etching process may be performed using plasma. The plasma is used to process a substrate at a high temperature. Generally, the plasma is generated by a radio frequency (RF) power. The mask forming process may include a process of forming a layer of photoresist on the substrate, an exposure process that exposes select portions of the layer of photoresist corresponding to patterns to be formed, and a developing process that removes select (exposed or unexposed) portions of the layer of photoresist, thereby forming a photoresist mask. The etching process is then carried out through the mask to transfer the pattern of the mask to the underlying layer(s) which may include that formed by the deposition process.

SUMMARY

According to the inventive concept, a pattern forming method of forming patterns in a substrate may include forming a photoresist pattern on the substrate, the photoresist pattern containing a first carbon compound, a reforming process of form an upper mask layer on a top surface of the photoresist pattern, the upper mask layer containing a second carbon compound different in kind from the first carbon compound, and etching a portion of the substrate using the upper mask layer and the photoresist pattern as an etch mask.

According to the inventive concept, there is also provided a pattern forming method including forming a hard mask layer comprising silicon oxynitride on a substrate, forming a photoresist pattern of material photo-sensitive to extreme ultraviolet (EUV) light on the hard mask layer, a reforming process of forming an upper mask layer a top surface of the photoresist pattern, and etching the hard mask layer and a portion of the substrate using the photoresist pattern and the upper mask layer as an etch mask. The reforming process includes supplying a nitrogen gas and a methane gas into a region over the substrate at a flow rate ratio of 10:1, applying an upper power to the region over the substrate to induce plasma and to deposit radicals in the plasma onto the upper mask layer, and applying a lower power to a region below the substrate to re-induce the plasma and to remove a portion of the upper mask layer using ions in the plasma.

Also, according to the inventive concept, a pattern forming method includes forming a photoresist pattern on a substrate, supplying a nitrogen gas and a methane gas into a region over the photoresist pattern at a first flow rate ratio, applying an upper power to the nitrogen gas and the methane gas to induce plasma and to deposit radicals in the plasma on the photoresist pattern, cutting off the upper power, supplying the nitrogen gas and the methane gas at a second flow rate ratio, in which a fraction of the nitrogen gas is higher than that in the first flow rate ratio, and applying a lower power to the nitrogen gas and the methane gas to re-induce the plasma and to remove a portion of the deposited radicals using ions in the plasma.

DETAILED DESCRIPTION

FIG. 1illustrates a method of forming patterns of a semiconductor device according to the inventive concept.

Referring toFIG. 1, the pattern forming method according to the inventive concept may include forming a hard mask layer on a substrate (S10), forming a photoresist pattern (S20), reforming a top surface of the photoresist pattern (S30), etching the substrate (S40), removing an upper mask layer and the photoresist pattern (S50), and removing the hard mask layer (S60).

FIGS. 2 to 7are sectional views of a substrate illustrating the method ofFIG. 1.

Referring toFIGS. 1 and 2, a hard mask layer14may be formed on the substrate W (S10). For example, the substrate W may include or be a silicon wafer. In certain examples, the substrate W further includes at least one thin film on the silicon wafer layer, i.e., the substrate may be a semiconductor substrate including a base and one or more layers formed on the base. The hard mask layer14may include a silicon oxynitride (SiON) layer, which is formed by a plasma-enhanced chemical vapor deposition (PECVD) method.

Referring toFIGS. 1 and 3, a photoresist pattern16may be formed on the hard mask layer14(S20). The photoresist pattern16may be formed by, for example, an extreme ultraviolet (EUV) photolithography method as opposed to an ArF or KrF photolithography method. First, a layer of photoresist that is photo-sensitive to EUV light is formed on the hard mask layer14. Then select portions of the layer of photoresist are irradiated by EUV light generated by an EUV light source. Then the exposed layer of photoresist is developed.

Because the depth to which the EUV light can penetrates a photoresist layer is less than the depth to which ArF or KrF light can penetrate, the photoresist pattern16is formed thinner than an ArF-sensitive photoresist layer (which has a thickness of about 45 nm or more). For example, the photoresist pattern16may be formed of an EUV-sensitive photoresist material a thickness of about 17 nm. The photoresist pattern16may be formed of a polyacetal resin. The photoresist pattern16may be formed of or include first carbon compounds. In some examples, the photoresist pattern16includes a hydrocarbon compound (CxHyRz), where R is a halogen, x and y are positive real numbers, and z is zero or a positive real number.

Referring toFIGS. 1 and 4, an upper mask layer18may be formed on a top surface of the photoresist pattern16by a reforming process which may be referred to as a process of reforming the top surface of the photoresist pattern (S30).

FIG. 8is a flow chart exemplarily illustrating the reforming step S30ofFIG. 1, which affects an upper portion of the photoresist pattern16.

Referring toFIG. 8, the reforming process (S30) may include disposing a substrate W in a chamber (S32), providing a nitrogen (N2) gas and a methane (CH4) gas in the chamber (S34), supplying an upper power to the chamber (S36), cutting off the upper power (in S38), and supplying a lower power to the chamber (S39).

FIG. 9illustrates an example of a plasma treatment system100, which may be used to form the upper mask layer18in the stage of the method shown inFIG. 4.

Referring toFIG. 9, the plasma treatment system100may be an inductively coupled plasma (ICP) system. Alternatively, the plasma treatment system100may be a capacitively coupled plasma (CCP) or micro power plasma etching system. The plasma treatment system100may include a chamber110, a gas supply unit120, an electrostatic chuck130, a lower electrode140, an antenna150, and a power supply unit160. The chamber110may be configured to provide an isolated space for the substrate W. The gas supply unit120may be adapted to supply a nitrogen gas122and a methane gas124into (an upper region of) the chamber110. The electrostatic chuck130may be operative to fix the substrate W in place (in a lower region of the chamber110) during processing. The lower electrode140may be provided below and/or in the electrostatic chuck130. The antenna150may be provided on the chamber110. The power supply unit160may be configured to supply a lower power142and an upper power152to the lower electrode140and the antenna150, respectively.

Referring toFIGS. 8 and 9, the substrate W may be provided on the electrostatic chuck130in the chamber110using, for example, a robot arm (S32). Although not shown, the chamber110may include a lower housing and an upper housing. If the lower and upper housings are spaced apart from each other, the substrate W may be loaded on the electrostatic chuck130in the lower housing.

Next, the gas supply unit120may be configured to supply the nitrogen gas122and the methane gas124into the chamber110(S34). If the lower and upper housings are coupled to each other and the chamber110is pumped out (evacuated), the nitrogen gas122and the methane gas124may be induced into the chamber110. The nitrogen gas122may consist of a first reaction gas and/or a dilution gas. The methane gas124may be a second reaction gas or an etching gas. For example, in the case in which the nitrogen gas122is supplied at a flow rate of about 10 SCCM to about 200 SCCM, the methane gas124may be supplied at a flow rate of about 1 SCCM to about 20 SCCM. In some examples, the nitrogen gas122and the methane gas124are provided at respective flow rates having a ratio of 10:1. For example, in the case in which the nitrogen gas122is supplied at a flow rate of about 100 SCCM, the methane gas124may be provided at a flow rate of about 10 SCCM.

FIG. 10illustrates the lower power142and the upper power152over time in the plasma processing system ofFIG. 9when carrying out the reforming step (S30).

Referring toFIGS. 8 to 10, the power supply unit160may be configured to supply the upper power152and the lower power142in a sequential and/or independent manner, when the upper portion of the photoresist pattern16is reformed.

Firstly, the upper power152may be supplied to the antenna150(S36). The upper power152may be used to induce (i.e., start) a plasma112in the chamber10. In addition, the upper power152may be used to produce radicals111and ions113, which constitute the plasma112, from the nitrogen gas122and the methane gas124. The radicals111may be deposited on the photoresist pattern16. As a result of the deposition of the radicals111, the upper mask layer18may be formed on the photoresist pattern16. For example, the radicals111may include carbon-nitrogen radicals (e.g., CN or C3N) or nitrogen-hydrogen radicals (e.g., NH). The ions113may include hydrocarbon ions (CH+) or hydrogen ions (H+). The ions113may be recombined in the plasma112in several seconds, thereby forming the methane gas124or the hydrogen gas, and then may be exhausted to the outside of the chamber110. The upper power152may have a frequency of about 13.56 MHz. The upper power152may be about 300 W. The upper power152may be a source power.

Next, the power supply unit160may cut or turn off the upper power152(S38). The upper power152from the power supply unit160may be supplied to the antenna150for about 60-90 seconds.

The lower power142from the power supply unit160may be provided to the lower electrode140(S39). As soon as the supply of the upper power152to the antenna150is terminated, the lower power142may be provided to the lower electrode140. The lower power142may be used to re-induce the plasma112and to concentrate the ions113in the plasma112onto the top surface of the substrate W. The ions113may be used to remove the radicals111on the photoresist pattern16or a portion of the upper mask layer18. The lower power142may have the same frequency as that of the upper power152. At least a portion of each of the lower and upper powers142and152may be provided in the form of a continuous wave. The lower power142may have a frequency of about 13.56 MHz, for example. By contrast, the lower power142may have a frequency ranging from about 10 MHz to about 1 MHz. The lower power142may have a voltage whose polarity is opposite to that of the voltage of the upper power152. For example, in the case in which the upper power152has a positive voltage, the lower power142may have a negative voltage. The lower power142may be higher than the upper power152. The lower power142may be about 500 W. The lower power142may be a bias power.

FIGS. 11A to 11Care XPS graphs of first to third carbon compounds50,60, and62in the photoresist pattern16or the upper mask layer18.FIGS. 12A to 12Care XPS graphs of first and second nitrogen compounds70and80in the photoresist pattern16and the upper mask layer18.

FIG. 11Ashows results of an example of the method according to the inventive concept before the reforming process (S30) is performed. At this time, the photoresist pattern16contains first carbon compounds50. The first carbon compounds50include a first carbon bonding structure52, a second carbon bonding structure54, and a carbon-oxygen (C—O) compound56. The first carbon bonding structure52has a binding energy ranging from about 282.5 eV to about 283 eV. The first carbon bonding structure52has C—C sp2 bonds. The second carbon bonding structure54has a binding energy ranging from about 284 eV to about 284.5 eV. The second carbon bonding structure54has C—C sp3 bonds. The carbon-oxygen compound56has a binding energy ranging from about 286 eV to about 286.5 eV. The amount of each of the first and second carbon bonding structures52and54is more than the amount of the carbon-oxygen compound56in the first carbon compound50because the graph shows that the intensity of each of the first and second carbon bonding structures52and54is higher than the intensity of the carbon-oxygen compound56.

At this time, too, as shown byFIG. 12A, the photoresist pattern16does not contain a nitrogen compound. In this example, the photoresist pattern16does not contain a carbon-nitrogen compound.

FIGS. 11B and 12Bshow results at the time of S30inFIG. 8when the radicals111are deposited using the upper power152. At this time, the photoresist pattern16and the upper mask layer18include the second carbon compound60and the first nitrogen compound70.

Referring toFIG. 11B, the second carbon compound60is different from the first carbon compound50represented by the graph ofFIG. 11A. In this example, the second carbon compound60contains the first and second carbon bonding structures52and54and a first carbon-nitrogen (C—N) compound58. The first carbon-nitrogen compound58has a binding energy similar to that of the carbon-oxygen compound56. The first carbon-nitrogen compound58has a binding energy of about 286 eV. The binding energy intensity or amount of the first carbon-nitrogen compound58in the second carbon compounds60may be higher or greater than those of the first and second carbon bonding structures52and54. The first carbon-nitrogen compound58contains the carbon-oxygen compound56(refer toFIG. 11A). However, the carbon-oxygen compound56in the upper mask layer18is removed by the plasma112. For example, the carbon-oxygen compound56is converted into a gaseous material by the plasma112, and such a gaseous material may be exhausted to the outside of the chamber.

FIG. 12Bshows the upper mask layer18as containing the first nitrogen compound70. In this example, the first nitrogen compound70includes a second carbon-nitrogen compound72and a nitrogen hydrogen (N—H) compound74. The second carbon-nitrogen compound72has a binding energy of about 397.5 eV. The second carbon-nitrogen compound72may contain cyanoethynyl radicals (e.g., C3N) or polyaniline. The nitrogen-hydrogen compound74has a binding energy of about 399 eV. The nitrogen-hydrogen compound74comprises ammonia (NH3). A binding energy intensity or amount of the nitrogen-hydrogen compound74in the first nitrogen compound70is higher or greater than that of the second nitrogen compound80.

FIGS. 11C and 12Cshow results of this example when the lower power142is supplied to remove the upper mask layer18and a portion of the photoresist pattern16using the ions113. At this time, the upper mask layer18and the photoresist pattern16contain the third carbon compound62and the second nitrogen compound80.

Referring toFIG. 11C, the third carbon compound62is different from the first and second carbon compounds50and60(refer back toFIGS. 11A and 11B). The third carbon compound62contains the first and second carbon bonding structures52and54and the first carbon-nitrogen compound58. In this example, the amount of the first carbon-nitrogen compound58in the third carbon compound62is less than that of the first carbon-nitrogen compound58in the second carbon compound60. In addition, the amount of the first carbon-nitrogen compound58in the third carbon compound62is less than that of the carbon-oxygen compound56in the first carbon compound50. The first carbon-nitrogen compound58may constituent of the mask layer18. Thus, the difference in amounts of the first carbon-nitrogen compounds58in the second and third carbon compounds60and62indicates that the upper mask layer18mainly consists of the first carbon-nitrogen compound58.

As shown inFIG. 12C, the second nitrogen compound80is different from the first nitrogen compound70(refer back toFIG. 12B). The amount of the second carbon-nitrogen compound72is greater than the amount of the nitrogen-hydrogen compound74in the second nitrogen compound80because the intensity of the second carbon nitrogen compound72is higher than the intensity of the nitrogen-hydrogen compound74. In the upper mask layer18, most of the nitrogen-hydrogen compound74may exist in the form of a gaseous material (e.g., ammonia (NH3)), and thus, may be easily removed by the plasma112. The second carbon-nitrogen compound72remains in the upper mask layer18. Thus, when the substrate W is etched, the first and second carbon-nitrogen compounds58and72may compose the upper mask layer18, but the nitrogen-hydrogen compound74is not present in the upper mask layer18.

FIG. 13is a graph showing peak intensities of binding energies of the first and second carbon-nitrogen compounds58and72according to a flow rate of the nitrogen gas122in the plasma processing system ofFIG. 9.

Referring toFIG. 13, when the nitrogen gas122is supplied into the chamber110at a flow rate of about 6 SCCM to 20 SCCM, large amounts of the first and second carbon-nitrogen compounds58and72are formed in the upper mask layer18. The methane gas124was supplied into the chamber110at a flow rate of about 10 SCCM. When the nitrogen gas122and the methane gas124are supplied at a flow rate ratio of about 0.6:1, the amount of the second carbon-nitrogen compound72in the upper mask layer18can be maximized. When the nitrogen gas122and the methane gas124are supplied at a flow rate ratio of about 1:2, the amount of the first carbon-nitrogen compound58in the upper mask layer18can be maximized. Thus, if the nitrogen gas122and the methane gas124are supplied at a flow rate ratio ranging from about 0.6:1 to about 1:2 (in S34) and the upper power152is provided (S36), the amounts of the first and second carbon-nitrogen compounds58and72to be formed in the upper mask layer18may be maximized.

Subsequently, when the upper power152is cut off (S38) and the lower power142is applied to the lower electrode140(S39), the nitrogen gas122and the methane gas124may be provided in a ratio of about 10:1 into the chamber110.

Referring back toFIGS. 1 and 5, the hard mask layer14and the substrate W may be etched using the upper mask layer18and the photoresist pattern16as an etch mask (S40). The step S40of etching the substrate W may be performed in the same manner as the step S39in which the lower power142is provided. In other words, the nitrogen gas122and the methane gas124may be provided at a flow rate ratio of about 10:1 into the chamber110, and the lower power142may be about 500 W. An etch rate of the substrate W may range from about 20 nm/min to about 70 nm/min. In the case in which the amount of the methane gas124supplied into the chamber110is greater than that of the nitrogen gas122, it may be difficult to adjust or control the etch rate of the substrate W. The hard mask layer14and the substrate W exposed by the photoresist pattern16may be etched to a depth ranging from about 50 nm to about 500 nm. The substrate W may have device patterns20and trenches22between the device patterns20. The device patterns20may constitute an active region or a wiring region. The trenches22may be used to provide an insulating region between the device patterns20.

FIG. 14Ais an image showing the photoresist pattern16(e.g., ofFIG. 5) having a remaining thickness T1.FIG. 14Bis an image showing a conventional photoresist pattern119having a remaining thickness T2.FIG. 15is a graph showing a difference between the remaining thickness T1of the photoresist pattern16and the remaining thickness T2of the conventional photoresist pattern119. Here, each of the photoresist pattern16and the conventional photoresist pattern119had a thickness of about 17 nm before an etching process, and the substrate W was etched at an etch rate of about 56 nm/min.

Referring toFIGS. 14A, 14B, and 15, after an etching process, the remaining thickness T1of the photoresist pattern16was larger than the remaining thickness T2of the conventional photoresist pattern119.

Referring toFIGS. 14A and 15, according to examples of the inventive concept, the photoresist pattern16had the remaining thickness T1ranging from about 14 nm to about 17 nm. For example, the photoresist pattern16had the remaining thickness T1of 14.89 nm, 15.38 nm, 15.88 nm, or 16.87 nm.

Referring toFIGS. 14B and 15, the conventional photoresist pattern119had the remaining thickness T2ranging from about 6 nm to about 15 nm. For example, when both of the upper power152and the lower power142were provided, the conventional photoresist pattern119(formed without the reforming of the upper portion thereof) had a remaining thickness T2of 6.45 nm, 8.93 nm, 12.90 nm, or 14.89 nm.

Referring back toFIGS. 1 and 6, the upper mask layer18and the photoresist pattern16may be removed (S50). The upper mask layer18and the photoresist pattern16may be removed by an ashing process or using an organic solvent.

Referring toFIGS. 1 and 7, the hard mask layer14may be removed (S60). The hard mask layer14may be removed by a wet etching process. The device patterns20may be exposed to the outside.

According to an aspect of the inventive concept, a pattern forming method may include a step of reforming the top of a photoresist pattern. This makes it possible to maintain a desired thickness of the photoresist pattern in preparation for the etching of a substrate.

Although examples of the inventive concepts have been particularly shown and described, it will be understood by one of ordinary skill in the art that variations in form and detail may be made thereto without departing from the spirit and scope of the inventive concept as set forth in the attached claims.