JP5042162B2 - Semiconductor processing method - Google Patents

Description

  The present invention relates to a semiconductor processing method, and more particularly to a semiconductor processing method for processing a semiconductor having a structure in which a metal film is deposited on a high dielectric constant insulating film.

  In recent years, in order to increase the speed of transistors, a high-k film called a high-k dielectric such as HfO or ZrO has a structure in which a metal such as TiN or TaN is deposited for the purpose of controlling the work function. Semiconductor devices having a gate electrode have been manufactured. When processing a semiconductor device having this structure, a metal for the purpose of controlling the work function, such as TiN or TaN, is deposited on a high-k film (usually an oxide film of Hf or Zr) constituting the gate. Further, a structure in which polycrystalline Si (poly-Si) is deposited on these metals is etched using a resist or the like as a mask.

As a method of etching TiN or TaN, TiN or TaN is etched using BCl3 / N2 gas (mixed gas), TaN is etched using SiCl4 / NF3 gas, TiN or TaN is etched using BCl3 gas. A method of etching using TaN and a method of etching TaN using BCl 3 / Ar / O 2 gas are known. Patent Document 1 describes a method of etching TaN or TiN using Cl2 / HBr / O2 gas. Patent Document 2 describes a method of etching TaN using SF6 gas.
Journal of Vacuum Science and Technology, A 23 (4), Jul / Aug 2005 P964-970 American Vacuum Society Journal of Vacuum Science and Technology, B 15 (6), Nov / Dec 1997 P2259-2263 American Vacuum Society

  As described above, a method for etching TiN or TaN is disclosed. However, a structure in which a metal film for controlling the work function such as a TiN film or a TaN film is deposited on the high-k film constituting the gate, and further, polycrystalline Si is deposited on these metals. When etching using a resist or the like as a mask, the required processing size (line width) is miniaturized and is currently 45 nm or less.

  Further, in the case of manufacturing a semiconductor element called CMOS, two gate electrodes constituting a CMOS transistor are formed of different metal materials, respectively, and the two different metal materials and the polycrystals deposited thereon. Each Si must be etched vertically.

  Here, when polycrystal Si is deposited on the base metal material, the state of the deposited polycrystal Si (for example, orientation) varies depending on the type of the base metal material. That is, the state of the deposited crystal is affected by the underlying metal material. For this reason, the etching rate of the deposited polycrystalline Si differs for each of the underlying metal materials, and it is difficult to uniformly process the polycrystalline Si formed on each of the underlying metal materials.

  The present invention has been made in view of such problems, and a semiconductor processing method capable of vertically and finely processing a semiconductor having a structure in which a metal film and polycrystalline Si are deposited on a high dielectric constant insulating film. Is to provide.

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

An insulating film containing Hf or Zr formed on a semiconductor substrate, first and second metal films formed in parallel on the insulating film and having different work functions, and on the first and second metal films And etching the polycrystalline silicon film and the first and second metal films in a plasma atmosphere using a resist formed on the polycrystalline silicon film. In the semiconductor processing method, the first metal film is a metal film containing Ti, the second metal film is a metal film containing Ta, and the etching of the polycrystalline silicon film on the second metal film is completed. Thereafter, a gas containing HBr and oxygen is used as the processing gas.

  Since the present invention has the above configuration, a semiconductor having a structure in which a metal film and polycrystalline Si are deposited on a high dielectric constant insulating film can be vertically and finely processed.

  Hereinafter, the best embodiment will be described with reference to the accompanying drawings. FIG. 1 is a view for explaining a semiconductor processing method according to the embodiment, and FIG. 1A is a cross-sectional view of a semiconductor element to be processed. As shown in FIG. 1A, the semiconductor element is disposed on the Si substrate 101, the HfSiON film 102 as a high dielectric constant insulating film formed on the Si substrate 101, and the HfSiON film 102 as the high dielectric constant insulating film. A first metal film 103 as a work function control metal for a p-type channel FET and a second metal film 104 for an n-type channel FET.

  Here, a metal such as Ti or Mo having a relatively high work function or a compound thereof is used for the first metal film, and Ta or a compound having a relatively low work function is used for the second metal film. .

  On the first and second metal films, a polycrystalline Si film 105 as an electrode material, a SiN film 106 as a cap, an antireflection film 107, and a resist 108 patterned by lithography are sequentially deposited.

  The thicknesses of the HfSiON film 102 are 2 nm, the TiN film 103 is 10 nm, the polycrystalline Si film 105 is 50 nm, the SiN film 106 is 50 nm, the antireflection film 107 is 80 nm, and the resist 108 is 200 nm.

  FIG. 1A shows an initial state of processing, and a resist 108 patterned by lithography is in the uppermost layer.

  When this structure is dry-etched, the structure of FIG. 1B is obtained. That is, the polycrystalline Si film formed on the first metal film (Ti) 103 and the polycrystalline Si film formed on the second metal film (Ta) 104 have the same film thickness. Regardless, it is observed that the progress of etching is different between the polycrystalline Si film on the first metal film (Ti) 103 and the polycrystalline Si film on the second metal film (Ta) 104. This is considered to be due to a difference in structure such as the orientation of the polycrystalline Si deposited thereon due to the difference in the structure of the metal film, resulting in a difference in the etching rate.

  For this reason, as shown in FIG. 1B, the polycrystalline Si on the first metal film 103 remains at the time when the etching of the polycrystalline Si on the second metal film 104 is completed. Further, the polycrystalline Si on the second metal film 104 has a tapered shape.

  Note that a gas containing a large amount of fluorine or Cl 2 that is usually used in etching of polycrystalline Si is used as a processing gas after the time of FIG. 1B (the time when etching of polycrystalline Si on the second metal film 104 is completed). Is used, side etching occurs in the polycrystalline Si on the second metal film 104.

  In order to prevent this, the gas may be changed to one in which side etching is difficult to enter when the etching of the polycrystalline Si on the first metal film 103 is not completed.

  As a specific example, a gas mixture of, for example, SF6 / CHF3 / CF4 / Ar is used up to a time point of FIG. / 115/30 ml / min Supply at a pressure of 0.8 Pa and etch with a wafer bias of 40 W. Further, until the time shown in FIG. 1C, a mixed gas of Cl2 / HBr / O2 / Ar is supplied at a flow rate of 10/80/4/30 ml / min and a pressure of 0.4 Pa, and etching is performed with a wafer bias of 30 W.

  Here, when the flow rate ratio of HBr / Cl2 is set to 1 or more and 10 or less, as shown in FIG. 1C, when the etching of the polycrystalline Si on the first metal film 103 is completed, the second metal film is formed. The polycrystalline Si on 104 can be kept in a vertical shape. If the Cl2 flow rate is too high, the underlying metal film 104 is scraped off. On the other hand, if the amount is too small, the etching rate of polycrystalline Si becomes very slow. In addition, an appropriate ratio of oxygen is 0% or more and 5% or less. Although a small amount of oxygen is added for the purpose of protecting the side walls of the polycrystalline Si, if it is too much, the etching stops.

  Next, etching is performed by switching the processing gas to, for example, HBr 200 ml / min, pressure 5 Pa, wafer bias 20 W, and over the polycrystalline Si on the first metal film (Ti) 103 as shown in FIG. Etch. Thereby, the polycrystalline Si on the first and second metal films can be etched into a vertical shape. Since the gas system having a high flow rate ratio of the HBr gas does not etch the underlying metal, only the side walls of the polycrystalline Si are etched and the taper shape is improved by over-etching with the gas system.

 FIG. 2 is a diagram for explaining a processing apparatus (plasma etching apparatus) for processing a semiconductor element. This apparatus is called an electron spin resonance (ECR) system, and introduces electromagnetic waves emitted from a plasma power source 201 into a vacuum chamber (decompression processing chamber) 204 through an antenna 202 and a window 203 that transmits electromagnetic waves such as quartz. . Etching gas is held in the chamber 204 at a constant pressure, and etching proceeds by making the gas into plasma by the electromagnetic wave and causing reactive ions to enter the wafer 206.

  A bias power source 207 for accelerating incident ions is connected to the sample stage 205 that holds the wafer 206. In this apparatus, a magnetic field is generated in the chamber 204 by the electromagnetic coil 208. When the magnetic field strength is set so that the electron spin frequency in the plasma matches the frequency of the plasma power source 201, the power is efficiently absorbed by the plasma, and a high plasma density can be maintained at a low pressure. By changing the value of the current passed through the electromagnetic coil 208, the magnetic field strength can be set so that ECR occurs. Note that the processing apparatus used for etching is not limited to the ECR system, and for example, an inductively coupled or capacitively coupled plasma processing apparatus can be used.

  Next, a method for processing the first and second metal films and the polycrystalline Si film deposited on the metal film will be described.

  In the processing of the metal film, the materials constituting them must be processed vertically and side etching of the polycrystalline Si film deposited on the metal film must be suppressed as much as possible. For this purpose, it is important to select a gas system that has a maximum etching rate for the metal material. According to experiments, it has been found that the TiN film may be etched using a gas mainly composed of Cl2, and the TaSi, TaSiN or TaC film may be etched using a gas mainly composed of F such as CF4.

  FIG. 3 shows the etching rate of TiN and TaSiN when a mixed gas of Cl2 and N2 is used, and FIG. 4 shows the etching rate of TiN and TaSiN when a mixed gas of CF4 and N2 is used.

  As shown in FIG. 3, it can be seen that to increase the etching rate of TiN, the proportion of Cl2 in the etching gas should be increased, and to increase the etching rate of TaSiN, the proportion of CF4 should be increased.

  Incidentally, as shown in FIG. 3, TiN has the highest etching rate when an etching gas containing 100% Cl 2 gas is used. However, it is understood that the etching does not proceed unless a modified film such as an oxide film formed on the TiN surface is removed using a gas containing fluorine such as CF4 before the etching is started using the Cl2 gas. It was.

  That is, in order to minimize the etching time and suppress side etching on the polycrystalline Si film, etching with respect to TaSiN is first performed using CF4 gas, thereby removing the modified layer formed on the TiN film. It is desirable to keep it. If the metamorphic layer is removed in this way, the subsequent etching with respect to the TiN film using Cl2 gas proceeds without any trouble.

  For example, after the over-etching of polycrystalline Si shown in FIG. 1D, the second metal film (TaSiN) 104 is formed by supplying CF 4 gas at a flow rate of 100 ml / min, a pressure of 0.2 Pa, and a wafer bias of 10 W for 15 s. Etching is performed, and then the first metal film (TiN) 103 is etched by supplying Cl 2 gas at a flow rate of 100 ml / min, a pressure of 0.4 Pa, and a wafer bias of 20 W for 5 s. As a result, the polycrystalline Si film was not side-etched, and the TiN film and the TaSiN film could be etched vertically.

  Even when TaSi or TaC was used as the second metal film 104 instead of TaSiN, it could be processed vertically using the same gas. If the ratios of Cl2 and CF4 in the etching gas were both 60% or more, vertical processing was possible.

  When the respective gas ratios are reduced, the etching rate of TiN and TaSiN is reduced and the etching time is increased. During this time, the side etching of polycrystalline Si by radicals proceeds and the shape deteriorates. Also, vertical machining can be performed by using NF3 or SF6 instead of CF4. The pressure when etching TiN and TaSiN is preferably 1 Pa or less and 0.05 Pa or more. When the pressure is low, the ion / radical ratio in the plasma increases, so that the vertical shape is maintained. If the pressure is too low, the plasma becomes unstable.

  If the order of the etching is reversed from the above, a modified layer removal process using a gas containing fluorine is required to etch the first metal film (TiN) 103. During this process period, polycrystalline Si is removed. An extra side etch for the film will proceed.

  FIG. 5 is a diagram for explaining an example of simultaneously etching the first and second metal films. In order to suppress side etching on the polycrystalline Si film and to etch the first and second metal films in a short time, a gas capable of etching the first and second metal films at substantially the same rate is used. Use it.

  According to experiments, in order to etch the first metal film (TiN) and the second metal film (TaSiN) at approximately the same rate, a mixed gas of CF4 gas and Cl2 gas is used, and the mixing ratio is set to an appropriate value. It turns out that it only has to be controlled.

  FIG. 5 is a diagram showing etching rates of the first metal film (TiN) 103 and the second metal film (TaSiN) 104 when a gas in which CF4 gas and Cl2 gas are mixed is used. As shown in the figure, when the ratio of CF4 is increased, the etching rate of the first metal film (TiN) is decreased, and the etching rate of the second metal film (TaSiN) is increased. When etching was performed while changing the gas mixture ratio, the etching rates of the first metal film (TiN) and the second metal film (TaSiN) were almost the same when the CF4 ratio was 35% to 50%. I understand that. Further, both the first metal film (TiN) and the second metal film (TaSiN) could be processed vertically. Even when a rare gas or nitrogen is mixed with the mixed gas of CF4 and Cl2, the mixing ratio of CF4 and Cl2 is changed from 35% to 50%, so that the first metal film (TiN) and the second metal film are mixed. (TaSiN) can be etched at approximately the same rate. Also, the first metal film (TiN) and the second metal film (TaSiN) could be processed vertically.

  In the etching described above, it is desirable that the amplitude of the bias voltage applied to the wafer is 350 V or less in order to keep the selection ratio with the underlying HfSiON film high. If the voltage is too high, the etching rate of the HfSiON film increases, and the selection ratio decreases. On the other hand, if it is too low, the metal etching rate decreases and the shape deteriorates.

  Further, in order to perform vertical processing with a high ion / radical ratio in the plasma, the pressure is desirably 1 Pa or less and 0.05 Pa or more.

  As described above, according to the present embodiment, the first metal film having a relatively slow etching rate of the polycrystalline Si film deposited thereon and the second metal film having a relatively fast etching speed are arranged side by side. When the polycrystalline Si formed on the first and second metal films is etched, the etching of the polycrystalline Si on the metal film (first metal film) whose etching rate is slower is terminated. In addition, an etching time or an over-etching time is set.

  Further, in order to prevent side etching of polycrystalline Si on the metal film (second metal film) whose etching rate is higher, at least after the etching on the second metal film is finished, HBr and O2 are used as etching gases. A gas containing is used.

  When the first metal film and the second metal film are mixed on the wafer, the end point of the etching of the polycrystalline Si formed on the first and second metal films is a change in the light emission waveform, For example, it can be known by observing a change in the light emission waveform that changes in two stages or a state during the etching with an electron microscope or the like.

  Here, when light emission is used, the end of etching is determined as follows. FIG. 6 shows the change over time of the emission intensity from the reaction product of Si from the plasma. Assuming that the maximum of the emission intensity is 100%, the emission intensity decreases and the period between 90% and 0% is determined as the etching end period, and the etching step may be switched during this period.

  Further, as described above, in the etching process of the first and second metal films following the etching of the polycrystalline Si, it is necessary that the polycrystalline Si is not side-etched during the etching of the metal film. . For this purpose, it is necessary to set the etching rate in the vertical direction of the metal film sufficiently higher than the side etching rate of polycrystalline Si.

  In the present embodiment, when the first metal film contains Ti as a main component and the second metal film contains Ta as a main component, the first metal film is made of a gas containing Cl2 as a main component. Etching is performed, and the second metal film is etched with a gas containing F such as CF4, NF3, SF6, and the second metal film is further etched before the first metal film. That is, the metal film containing Ti (first metal film) often has a metamorphic layer such as an oxide film on the surface thereof, and if this layer is not removed, the first metal film is mainly composed of Cl2. This is because the etching does not proceed. Thus, by etching the second metal film with a gas containing F in advance, the oxide film formed on the first metal film is removed, so that the first gas by the next gas mainly composed of Cl 2 is used. Etching of the metal film can be carried out satisfactorily.

It is a figure explaining the semiconductor processing method concerning an embodiment. It is a figure explaining the processing apparatus which processes a semiconductor element. It is a figure which shows the etching rate of TiN. It is a figure which shows the etching rate of TaSiN. It is a figure which shows the etching rate of TiN and TaSiN. It is a figure which shows the time change of the emitted light intensity from a plasma.

Explanation of symbols

101 Si substrate 102 HfSiON
103 First metal film 104 Second metal film 105 Polycrystalline Si film 106 SiN
DESCRIPTION OF SYMBOLS 107 Antireflection film 108 Resist 201 Plasma power supply 202 Antenna 203 Window 204 Vacuum chamber 205 Sample stand 206 Wafer 207 Bias power supply 208 Electromagnetic coil

Claims (4)

An insulating film containing Hf or Zr formed on a semiconductor substrate, first and second metal films formed in parallel on the insulating film and having different work functions, and on the first and second metal films And etching the polycrystalline silicon film and the first and second metal films in a plasma atmosphere using a resist formed on the polycrystalline silicon film. In the semiconductor processing method to
The first metal film is a metal film containing Ti, the second metal film is a metal film containing Ta, and after the etching of the polycrystalline silicon film on the second metal film, the processing gas is used. As a semiconductor processing method, a gas containing HBr and oxygen is used. The semiconductor processing method according to claim 1,
After the etching of the polycrystalline silicon on the first and second metal films is completed, the second metal film is etched using a gas containing CF4, NF3, or SF6, and then the first metal film contains Cl2. semiconductor processing wherein that you etched using gas. The semiconductor processing method according to claim 1 ,
After the etching of the polycrystalline silicon on the first and second metal films, the second metal film is etched using a gas containing 60% or more of CF4, NF3 or SF6, and then the first metal film is formed. Etching using a gas containing 60% or more of Cl 2 . The semiconductor processing method according to claim 1 ,
After the etching of polycrystalline silicon on the first and second metal films, the first metal film and the second metal film are mixed containing 35% to 50% of CF4 with respect to the sum of CF4 and Cl2. A semiconductor processing method, wherein etching is performed using a gas .

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