JP2013229351A - Dry etching method - Google Patents

Abstract

Provided is a dry etching method capable of vertical processing while suppressing side etching even in high aspect ratio silicon etching.
In a dry etching method in which a groove having a groove width of 30 nm or less and an aspect of 4.5 or more is formed in an object to be processed using plasma, an etching gas to which a deposition gas that easily reaches the bottom of the groove is added is used. By performing dry etching, the groove is formed while protecting the side wall of the groove by the deposit 405 generated from the bottom of the groove by sputtering.
[Selection] Figure 4

Description

  The present invention relates to a dry etching method using plasma.

  In recent years, in plasma etching for silicon-based materials, it is difficult to control the shape with high precision due to the fine line width and the increased aspect ratio.

Regarding such a problem, Patent Document 1 discloses that resistance to ion bombardment and radical attack is obtained by using chlorine gas (hereinafter referred to as Cl ₂ ) as an etching gas and using COx gas and NOx gas for protecting the sidewall. It has been shown to form a sidewall protective film having high properties. Further, in Patent Document 2, it is possible to realize a reduction in density difference in etching shape by adding carbon dioxide gas (hereinafter referred to as CO ₂ ) to a mixed gas of Cl ₂ and hydrogen bromide (hereinafter referred to as HBr). It is shown.

JP-A-8-115900 JP 2008-192759 A

  With respect to the technique described in the above patent document, the present inventors have studied from the viewpoint of forming a fine pattern having a high aspect ratio. As a result, the above technique is effective, but, for example, a fine line width of 30 nm or less and a high aspect ratio shape of an aspect ratio of 4.5 or more are insufficient from the viewpoint of precise shape control. I understood. In conventional ion-assisted etching, side etching or deposition occurs due to the balance between the deposition material and the etchant from the plasma incident on the sidewall of the groove. The amount of deposition in the vertical direction of the side wall is not uniform because it is distributed depending on the adsorption coefficient of the deposited material, and therefore vertical machining becomes difficult. There was no problem in the generation with relatively large processing dimensions of the element, but it is difficult to apply the above technique as it is in the generation that requires finer processing, and an etching method with higher perpendicularity will be required. .

  In view of the above problems, an object of the present invention is to provide a dry etching method capable of performing vertical processing while suppressing side etching even in high aspect ratio silicon etching.

  In order to solve the above problems, the present invention employs the following means.

  In a dry etching method for forming a groove having a groove width of 30 nm or less and an aspect of 4.5 or more in an object to be processed using plasma, an etching gas added with a deposition gas that easily reaches the bottom of the groove is used. The dry etching method is characterized in that the groove is formed while protecting the side wall of the groove with deposits generated by sputtering at the bottom of the substrate.

  In addition, using a process for preparing a target object having a silicon film and an etching gas to which a deposition gas that can easily reach the bottom of the groove is added, a high-frequency power that is intermittently time-modulated with a peak high-frequency power of 200 W or more. An etching step for forming a groove in the silicon film while supplying the object to be processed.

  Further, in a dry etching method for forming a FinFET gate electrode using plasma, a mixed gas containing chlorine gas, hydrogen bromide gas, and carbon dioxide gas is used, a peak high frequency power is 200 W or more, an off time is an on time or more. A first step of etching the polysilicon film while supplying intermittent time-modulated high-frequency power to the object, and a mixed gas containing hydrogen bromide gas, carbon dioxide gas, argon gas, and methane gas A second etching method is used to etch the polysilicon film after the first step while supplying intermittently time-modulated high-frequency power having a peak high-frequency power of 200 W or more and an off time of the on-time or more to the object to be processed. A dry etching method characterized by comprising the steps of:

  According to the present invention, it is possible to provide a dry etching method capable of performing vertical processing while suppressing side etching even in high aspect ratio silicon etching.

It is a schematic sectional drawing which shows an example of the vacuum processing apparatus used in order to implement the dry etching method concerning the 1st Example of this invention. It is a cross-sectional schematic diagram of polysilicon groove processing, (a) shows a situation where side etching occurs, and (b) shows a situation where vertical etching is satisfactorily performed. It is a figure explaining the conventional ion assist etching. It is a figure explaining the side wall protection by the physical sputter | spatter of the groove bottom in the etching method which concerns on 1st Example of this invention, (a) is the initial stage of etching, (b) shows the state just before the end of etching. It is a graph which shows the relationship between the peak electric power of a bias voltage, and the amount of side etching. It is a schematic perspective view of FIN-FET which is a target object used with the etching method of the 2nd example.

The inventors have studied a dry etching method capable of suppressing side etching even in high aspect ratio silicon etching, and as a result, added a deposition gas such as CO _{2 that} easily reaches the bottom of the groove to the etching gas. It has been found that sputter etching is effective. The present invention was born based on the above findings.

One embodiment is shown below. As a deposition gas that can easily reach the bottom of the groove in a mixed gas containing HBr, Cl ₂ , and oxygen (hereinafter referred to as O ₂ ) in a process of etching single crystal silicon or polycrystalline silicon on a substrate using a general hard mask. The plasma is obtained by adding CO ₂ , and the plasma obtained thereby is used to switch the presence / absence of output at a constant frequency and Duty. By using a time-modulated high-frequency power source, ions having a high ion energy can be used. The plasma etching is performed while protecting the side wall with the sputtered material from the bottom. As a result, the vertical shape can be processed with good controllability.

  Hereinafter, an example explains.

  A first embodiment will be described with reference to FIGS. FIG. 1 is a schematic cross-sectional view showing an example of an etching apparatus for carrying out the dry etching method according to the present embodiment, which is a microwave plasma etching apparatus using a microwave and a magnetic field as plasma generating means. This apparatus is provided with a chamber 101 capable of evacuating the inside, a sample stage 103 on which a wafer 102 to be processed is placed, a microwave transmitting window 104 such as quartz provided on the upper surface of the chamber 101, and an upper part thereof. It comprises a waveguide 105, a magnetron 106, a solenoid coil 107 provided around the chamber 101, an electrostatic adsorption power source 108 connected to the sample stage 103, and a high frequency power source 109.

  The wafer 102 is carried into the chamber 101 from the wafer carry-in port 110 and then electrostatically adsorbed to the sample stage 103 by the electrostatic adsorption power source 108. Next, process gas is introduced into the chamber 101. The inside of the chamber 101 is evacuated by a vacuum pump (not shown) and adjusted to a predetermined pressure (for example, 0.1 Pa to 50 Pa). Next, a microwave having a frequency of 2.45 GHz is oscillated from the magnetron 106 and propagated into the chamber 101 through the waveguide 105. The processing gas is excited by the action of the microwave and the magnetic field generated by the solenoid coil 107, and plasma 111 is formed in the space above the wafer 102. On the other hand, the sample stage 103 is supplied with continuous high frequency power or time-modulated intermittent high frequency power by a high frequency power source 109. The high-frequency power supply 109 is in a mode for supplying continuous high-frequency power (hereinafter referred to as CW mode) when the duty ratio, which is the ratio of the on-time to the modulation pulse period, is set to 100%. If the value is set to other than 100%, a mode (hereinafter referred to as TM mode) in which time-modulated intermittent high-frequency power is supplied is set.

Ions in the plasma 111 are accelerated and incident vertically on the wafer 102. The wafer 102 is anisotropically etched by the action of radicals and ions from the plasma 111. The etching apparatus used in this example is an apparatus for processing a wafer having a diameter of 300 mm. The inner diameter of the chamber 101 is 44.2 cm, and the distance between the wafer 102 and the microwave transmission window 104 is 24.3 cm (in the space where plasma is generated). A device with a volume of 37267 cm ³ ) was used.

  An example of a semiconductor substrate on which the etching method in this embodiment is performed, hereinafter referred to as a wafer, will be described. On the wafer, a polysilicon film 202 having a thickness of 200 nm and a silicon nitride (hereinafter referred to as SiN) film 210 having a thickness of 30 nm are laminated in this order from above on the silicon oxide film 203 (for example, FIG. 2), using the silicon nitride (SiN) film 201 as a hard mask, a pattern composed of a 30 nm wide space and a 30 nm wide line can be formed in the polysilicon (poly Si) layer 202 between the SiN films 201. Has a groove-like opening. However, the thickness of the laminated film is not limited to this value, but the aspect ratio is 4.5 or more. The aspect ratio is a value obtained by dividing the sum of the initial film thickness of the hard mask 201 and the initial film thickness of the polysilicon film 202 by the groove pattern dimension. In FIG. 2, reference numeral 204 indicates ions, and reference numeral 205 indicates deposits. FIG. 2A is a schematic diagram showing a situation where side etching is occurring, and FIG. 2B is a schematic diagram showing a situation where vertical etching is satisfactorily performed.

  Table 1 shows the optimum etching conditions for the wafer.

Step 1 is a breakthrough step for removing the surface oxide film formed on the polysilicon layer, which is a film to be etched, and Step 2 is a main step for forming a shape while removing the polysilicon film. This is a main etching step, and step 3 is an over-etching step for removing the polysilicon film remaining after step 2 and making the bottoming shape vertical. Hereinafter, description will be made regarding Step 2. In this embodiment, as shown in Table 1, Cl ₂ , HBr, and CO ₂ are used as a mixed gas. The pressure of the mixed gas is 0.5 Pa. When this mixed gas is turned into plasma with a microwave input power of 750 W and this plasma is supplied to the wafer with a bias power of 300 W, a duty of 40%, and a frequency of 1000 Hz, the polysilicon layer is etched using SiN as a mask. Table 1 is an optimum embodiment for embodying the present embodiment, but is effective under etching conditions other than Table 1.

Table 2 is a performance characteristic table regarding the first embodiment, and is a table for explaining advantages of using the CO ₂ gas and the TM mode according to the first embodiment. In order to show the superiority of the CO ₂ process, a process using O ₂ which is a commonly used deposition gas is also shown. As a parameter indicating the etching performance, side etching and good / bad mask damage are shown.

From Table 2, it can be confirmed that when the CO ₂ gas and the TM mode are combined, the process margin is dramatically increased. This phenomenon can be explained as follows.

FIG. 3 is a cross-sectional view of a sample when the poly Si film 302 deposited on the oxide film 303 is etched using a SiN mask (SiN film) 301, and describes a conventionally known ion-assisted etching mechanism. . In ion-assisted etching, ions 304 are accelerated by a wafer bias and vertically incident on the surface of halogen atoms 305 such as Cl attached to the poly Si film 302. When the ion energy is relatively low, a reaction product 308 such as SiCl ₄ having a high vapor pressure and a low adsorption coefficient is generated. The reaction product is released into the plasma, repeatedly collides with other molecules or electrons in the plasma, re-dissociates, and has a high adsorption probability and re-enters the groove. The reaction product entering the groove of the Poly Si film 302 collides with the side wall of the groove and is adsorbed on the side wall depending on the adsorption probability to generate a deposit 306. The thickness of the deposit 306 is not uniformly formed depending on the groove shape (aspect ratio) and the adsorption probability. On the other hand, the radical 305 is incident on the side wall, and a side etch 307 occurs in a portion where the deposit 306 on the side wall is thin. In the generation of semiconductor devices with relatively large dimensions and small groove aspect ratios, side etch was relatively small and not a problem. However, as miniaturization progresses and groove dimensions become smaller, side etch becomes relatively large and higher vertical. Sex is necessary. Side etching in the comparison table shown in Table 2 occurs by this mechanism.

  In order to solve this problem, it is necessary to realize etching that deposits uniformly adhere to the side wall regardless of the aspect ratio. As a technique for realizing such etching, it is only necessary to perform etching mainly by physical sputtering by increasing ion energy, instead of etching mainly by ion-assisted etching as in the prior art. In physical sputtering, etching proceeds by cutting off the atomic bonds of the etching substance by high-energy ions and blowing them into a vacuum. For this reason, a reaction product produced by physical sputtering produces a substance having a low vapor pressure and a high adhesion coefficient, such as SiCl. FIG. 4 shows the concept of etching mainly using physical sputtering, in which the polysilicon film 402 on the oxide film 403 is etched using the silicon nitride film 401 as a mask. 4A shows the initial state of etching, and FIG. 4B shows the state just before the end of etching. When the energy of the ions 404 is increased, a reaction product 405 having a high adsorption probability is generated. This reaction product 405 is almost adsorbed on the side wall which collided first. Since the dependency of the angle at which the reaction product is released does not depend on the aspect ratio, the side wall protective film is formed on the side wall with a substantially uniform thickness, so that vertical etching is possible even when the aspect ratio increases.

In order to realize etching mainly using physical sputtering as described above, ion energy is increased, and at the same time, the side wall protection is effective when the adsorption probability is small and reaches the bottom of the groove to some extent and is sputtered and adsorbed to the side wall. It is necessary to select a material that forms a film. This combination needs to be selected experimentally, but in the Cl ₂ / HBr mixed gas system shown in Table 1, CO ₂ is a suitable mixed gas. In oxygen, the amount of oxygen radicals generated in plasma is large. Oxygen radicals have a high probability of adsorption and oxidize polysilicon to form a strong side wall protective film. Therefore, the influence of oxygen radicals incident from the groove entrance is more than the side wall protection by physical sputtering material from the groove bottom. Because it wins and aspect dependence comes out, side etching occurs. The high adsorption rate of oxygen radicals is obvious from the fact that O radicals do not exist in nature and reactions such as oxidation easily occur. With respect to CO ₂ , the adsorption rate increases if it is completely radicalized, but it is considered that the adsorption rate is smaller than that of oxygen radicals because it is easy to form a state such as CO.

  Further, since it is sufficient to increase the energy of ions in order to cause physical sputtering, the TM mode is not necessarily required. However, when the ion energy is increased in the CW mode, the mask damage is large as shown in Table 2, and a combination with the TM mode in which a bias is provided with a pause period is necessary.

  Next, the ion energy necessary for mainly physical sputtering will be described. The ion energy is proportional to the amplitude (Vpp) of the bias voltage. FIG. 5 shows the relationship between Vpp and the side etch amount of polysilicon under the conditions shown in Step 2 of Table 1. As shown in FIG. 5, when the bias power is set so that Vpp is 500 V or more (peak power is 200 W or more), the side etch amount is suppressed to 1 nm or less, which is an allowable range even for generations having a line width of 30 nm or less and an aspect of 4.5 or more. it can.

Table 3 is a result of the combination of O ₂ , CO ₂ gas and other methods, and summarizes items that can improve parameters indicating etching performance in addition to using the TM mode.

From this result, it is confirmed that the combination of TM mode and CO ₂ is remarkably good. For example, the change of the temperature distribution is effective from the viewpoint of the in-plane shape difference, but the margin in side etching or etch stop is small. Adjustment of the flow rates of the etchant Cl ₂ and HBr is difficult because the margin in the in-plane shape difference is small. Even when a high pull-in voltage is used in the CW mode, it is difficult to use because the margin of mask damage and in-plane shape difference is small. The same applies to the pressure.

Therefore, it can be seen from Table 3 that the margin of side etching, etch stop, in-plane shape difference, and mask damage becomes the widest by the combination of TM mode and CO ₂ . This is considered to be mainly due to the effect of synergistically combining the superiority of the TM mode and the superiority of CO ₂ described above.

As described above, in the first embodiment, the TM mode and CO ₂ are provided, and a sufficient sidewall protective film can be uniformly formed even with a small line width and a high aspect ratio shape. The effect that it becomes possible to process is obtained. In this embodiment, CO ₂ has been described as an example. However, CO, NO, NO _{2 and the} like have a relatively small adhesion coefficient, and can also be used in a gas in which a reaction product is deposited on the sidewall to form a protective film.

  A second embodiment of the present invention will be described with reference to FIG. Note that the matters described in the first embodiment but not described in the present embodiment can be applied to the present embodiment as long as there is no special circumstances.

  Here, an embodiment in which the aspect ratio changes during etching will be described. Since the etching apparatus used for this etching is the same as that of the first embodiment, description thereof is omitted. An example of a structure in which the aspect ratio changes during the etching is shown in FIG. 6, and there is a structure generally called a FinFET (Fin Field Effect Transistor). In the FinFET, a channel 602 that connects a source (not shown) and a drain (not shown) is three-dimensionally formed on an oxide film 601 formed on a silicon substrate (not shown). The gate electrode 603 straddles 602. The channel 602 is hereinafter referred to as Fin602, and the height of the Fin602 is about 20 to 40 nm.

  The gate electrode 603 is formed of a polysilicon film 603 having a thickness of 200 nm, and a pattern composed of spaces and lines is formed on the polysilicon layer using the 30 nm thick SiN film 604 laminated thereon as a hard mask. A groove-like pattern is formed in advance in the SiN film 604 so that it can be formed. However, the film thickness of the laminated film is not limited to this value.

  Regarding the formation of the FinFET gate electrode, Table 4 shows optimum etching conditions for a three-dimensional structure wafer.

Compared with Table 1, it turns out that the number of steps and the gas used for mixed gas are increasing. As a newly mixed gas, a mixed gas composed of Ar and CH ₄ is used. Steps 1 and 4 are steps having the same role as steps 1 and 3 in Table 1, and thus the description thereof is omitted. Further, the two steps 2 and 3 correspond to step 2 (main etching step) in Table 1. Step 3 is a step in which the polysilicon is etched and the Fin 602 is exposed. Note that step 2 switches to step 3 when the polysilicon film thickness on Fin 602 changes from 5 nm to 15 nm.

Step 3 is a step in which the polysilicon is etched and Fin is exposed. In step 3, since Fin 602 is exposed, the aspect ratio for performing polysilicon etching changes greatly. When Fin 602 is exposed by etching under the condition of Step 2 until just before Fin 602 is exposed as a method for achieving both a change in aspect ratio that changes the incident solid angle of deposits and etchants and a reduction in damage to Fin. The polysilicon film is etched under the condition of step 3. In Step 3, in order to reduce damage to the Fin 602, Cl ₂ is not used, and the duty ratio of the TM mode is lowered from 40% to 5%. The reason for reducing the duty ratio from 40% to 5% is to reduce the average high frequency power. In order to reduce the average high-frequency power in the CW mode, it is impossible to cause physical sputtering because the peak power must be lowered. However, by using the TM mode, it is possible to keep the peak power high and cause physical sputtering. Can reduce damage to However, side etching is likely to occur due to the reduction of the average high frequency power and the reduction of the etched area of the polysilicon film. Therefore, the chlorine gas is removed from the gas system in Step 2 and an argon gas and a methane gas are added. Etching was suppressed. Further, increasing the hydrogen bromide gas flow rate in step 3 from the hydrogen bromide gas flow rate in step 2 also contributes to reducing damage to Fin 602.

  As described above, even in a complicated structure in which the incident solid angle such as a deposited substance or an etchant changes during etching, the side wall protective film can be uniformly deposited without depending on the aspect according to this embodiment. The vertical shape can be processed with good performance.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Also, a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of a certain embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 101 ... Chamber, 102 ... Wafer, 103 ... Sample stand, 104 ... Microwave transmission window, 105 ... Waveguide, 106 ... Magnetron, 107 ... Solenoid coil, 108 ... Electrostatic adsorption power source, 109 ... High frequency power source, 110 ... Wafer Loading port, 111 ... plasma, 201 ... silicon nitride film, 202 ... polysilicon film, 203 ... oxide film, 204 ... ion, 205 ... deposit, 301 ... silicon nitride film (SiN mask), 302 ... polysilicon film, 303 ... Oxide film, 304 ... Ion, 401 ... Silicon nitride film, 402 ... Polysilicon film, 403 ... Oxide film, 404 ... Ion, 405 ... Reaction product (deposit), 601 ... Oxide film, 602 ... Fin (channel) 603, polysilicon film (gate electrode), 604 silicon nitride film.

Claims (7)

In a dry etching method for forming a groove having a groove width of 30 nm or less and an aspect of 4.5 or more in an object to be processed using plasma,
The groove is formed using an etching gas to which a deposition gas that easily reaches the bottom of the groove is added, and protecting the side wall of the groove by deposits generated by sputtering at the bottom of the groove. Etching method. The dry etching method according to claim 1,
The deposition gas that can easily reach the bottom of the groove is carbon dioxide gas,
The etching gas is a mixed gas containing chlorine gas and hydrogen bromide gas,
The object to be processed has a polysilicon film,
A dry etching method characterized in that the polysilicon film is etched while supplying intermittently time-modulated high-frequency power having a peak high-frequency power of 200 W or more and an off time of not less than an on-time to the object to be processed. Preparing a target object having a silicon film;
Using an etching gas to which a deposition gas that can easily reach the bottom of the groove is added, a groove is formed in the silicon film while supplying an intermittent time-modulated high-frequency power with a peak high-frequency power of 200 W or more to the object to be processed. And an etching process for performing the dry etching method. The dry etching method according to claim 3, wherein
The deposition gas that can easily reach the bottom of the groove is carbon dioxide gas, carbon monoxide gas, nitrogen monoxide, or nitrogen dioxide,
The dry etching method, wherein the etching gas is a mixed gas containing chlorine gas and hydrogen bromide gas. In a dry etching method for forming a gate electrode of a Fin FET using plasma,
Using a mixed gas containing chlorine gas, hydrogen bromide gas, and carbon dioxide gas, intermittent high frequency power having a peak high frequency power of 200 W or more and an off time of an on time or more is supplied to the object to be processed. While the first step of etching the polysilicon film,
Using a mixed gas containing hydrogen bromide gas, carbon dioxide gas, argon gas, and methane gas, intermittent time-modulated high-frequency power having a peak high-frequency power of 200 W or more and an off time of the on-time or more is applied to the object to be processed. And a second step of etching the polysilicon film after the first step while being supplied. The dry etching method according to claim 5, wherein
The dry etching method according to claim 1, wherein the duty ratio of the intermittent time-modulated high-frequency power in the second step is smaller than the duty ratio of the intermittent time-modulated high-frequency power in the first step. In the dry etching method according to claim 5 or 6,
In the dry etching method, the first step is switched to the second step when the polysilicon film on the Fin serving as a channel is changed from 5 nm to 15 nm.

Images