JP4537818B2 - Plasma processing method - Google Patents

Description

  The present invention relates to a plasma processing method, and more particularly to a plasma processing method suitable for performing surface treatment of a semiconductor element or the like using plasma.

When performing an etching process using a plasma processing apparatus, the process gas is ionized and activated to speed up the process, and a high frequency bias power is supplied to the material to be processed so that ions are incident vertically. High-precision etching process such as isotropic shape is realized. A conventional plasma processing method for an oxide film (SiO ₂ ) uses an etching gas Ar, O ₂ , CxFy (for example, C ₄ F ₈ , C ₅ F ₈ , C ₄ F _6, etc.) and CO as described. Etching is performed (for example, see Non-Patent Document 1).

However, in the damascene process for forming plugs connecting between wirings and between the wirings, a low dielectric constant film such as a SiOCH film has been used as an interlayer insulating film from the viewpoint of reducing power consumption. These are known to deteriorate in K value by irradiation with O ₂ plasma or the like (for example, see Non-Patent Document 2).

For this reason, a method of removing C component by adding N ₂ gas in place of O ₂ gas is used, but N radical has a lower C component removal efficiency than O radical, and therefore a process with less deposition. Is required.

Further, with the miniaturization of devices, the exposure of the resist mask is also shifted to the short wavelength side, so that the resist thickness is reduced, and it has been required to ensure a high mask selectivity when performing the etching process. In particular, it is known that plasma resistance at the time of etching is significantly reduced in an ArF resist. Therefore, it is urgent to reduce resist damage in the etching process.
H. Hayashi: 1996 DPS p135 K. Maex et. al. : J.M. Appl. Phys, Vol93 (2003) p8793

  An object of the present invention is to provide a processing condition capable of realizing high-selectivity and high-precision etching without causing ArF resist damage in a low dielectric constant film (Low-k film, for example, SiOCH) corresponding to an ArF resist mask. There is to do.

In order to solve the above-described problems, the present invention is a plasma that etches a SiOCH film using an ArF resist mask using an apparatus that generates plasma and applies a high-frequency voltage to a sample to etch a material to be processed. In the treatment method, the material to be treated is etched without using a rare gas (for example, Ar). Further, the plasma processing method is performed at a low pressure of 0.4 to 0.7 Pa . The plasma processing method is performed without using a gas such as N ₂ or O ₂ .

The present invention uses a mixed gas of CF ₄ and CHF ₃ not containing a rare gas (for example, Ar) as an etching gas in the above plasma processing method, or a mixed gas of CHF ₃ and N ₂ , or CF _This is performed using a mixed gas of ₄ and N ₂ .

  Furthermore, the present invention generates plasma using a magnetic field in the plasma processing method.

  In the plasma processing method of the present invention, the amount of deposit deposited on the wafer is reduced by performing an etching process at a low pressure, and the composition is controlled to reduce ArF resist damage. Processing is possible.

Etching of the ArF resist mask SiOCH film does not include a rare gas (for example, Ar) and is performed at a low pressure (for example, 0.4 to 0.7 Pa ), thereby enabling etching processing that is highly vertical and has low ArF resist damage. is there.

FIG. 1 is a conceptual diagram showing a cross-sectional structure of a material to be etched (sample) subjected to typical via etching.
Samples include various films such as an etching stop film (for example, SiC) 104 and a material to be processed (for example, SiOCH: Black Diamond from AMAT, Aurora from ASM, and Coral from Novellus on a silicon substrate (Si) 105. ) 103 and an antireflection film (BARC) 102 are laminated, and an ArF photoresist film 101 is formed on the surface thereof.

  In the via etching, first, the BARC film 102 is etched using the ArF photoresist mask 101 as a mask, and then the material film 103 is etched, and the etching is preferably selectively stopped on the etching stop film 104.

Conventionally, when a contact hole is formed in a thin film of SiO ₂ , etching is selectively performed on a photoresist (PR) that is a mask. Therefore, Ar, O ₂ , CxFy (for example, C ₄ F ₈ , C) ₅ F ₈ , C ₃ F ₆ , C ₄ F _6, etc.) and CO, etc., are used for etching. However, in the via processing, a process with a relatively small amount of deposit is required from the viewpoint of a relatively small aspect ratio and damage of k value deterioration of the Low-k (SiOCH) film 103.

Therefore, in the present invention, a gas system in which N ₂ is added to a mixed gas of CF ₄ and CHF ₃ as an etching gas for the low-k (SiOCH) film 103 is used. Furthermore, as a method of further reducing the deposition amount, two kinds of comparisons were performed: a method of diluting an etchant gas with a rare gas (for example, Ar) and a method of reducing the pressure.

The results will be described with reference to FIG. 2, which is a characteristic diagram showing the relationship between the etchant partial pressure and the etching characteristics depending on whether or not Ar is diluted. That is, the deposition rate decreases as the partial pressure of the mixed gas of CF ₄ and CHF ₃ is decreased regardless of whether Ar dilution is present (◯ mark) or not (□ mark). However, the etching rate of the SiOCH film decreases sharply in the case of Ar dilution (● mark) and decreases in pressure (■ mark) as the partial pressure of the mixed gas of CF ₄ and CHF ₃ is reduced. Will increase.

In order to clarify the cause of this difference, the results of the emission spectroscopic measurement are shown in FIG. FIG. 3 is a characteristic diagram showing the relationship between the etchant partial pressure and the plasma composition with and without Ar dilution. Also, the gas residence time is plotted on the right axis. In the case of Ar dilution (marked with ●), if the mixed gas partial pressure of CF ₄ and CHF ₃ is decreased, the CF ₂ / C ₂ ratio is rapidly decreased, so that the C component of the plasma composition is excessive. I can guess. In addition, the gas residence time is almost the same regardless of whether Ar dilution is present (○ mark) or not (□ mark). Therefore, when Ar dilution is performed, the electron temperature rises to an excessively dissociated state, and etch stop, etc. It is thought that it is easy to occur. Therefore, it is desirable not to add a rare gas such as Ar gas (■ mark) in etching the SiOCH film.

The relationship between the pressure without Ar dilution and the N2 flow rate, the etching rate of via etching of the SiOCH film, the hole perpendicularity, and the CD shift of the photoresist is shown using the contour map of FIG. As shown in (a), the etching rate of the SiOCH film is higher as the pressure is lower, and as shown in (b), the hole perpendicularity is higher in the low pressure / high N ₂ flow rate region, and as shown in (c), It can be seen that the hole CD (Critical Dimension) shift of the photoresist is smaller in the low pressure region, and in particular, the low pressure region of 2 Pa or less is effective in terms of shape controllability.

  In this experiment, a UHF-ECR (Ultra High Frequency-Electron Cyclotron Resonance) plasma device for an insulating film was used as an experimental device. However, since this plasma source uses a magnetic field, it has excellent discharge stability in a low pressure region. By using such a plasma source, high-precision etching can be performed at a low pressure.

FIG. 5 shows an SEM (Scanning Electron Microscopy) image of the surface of the ArF resist 101 after etching. The higher the pressure and the higher N ₂ flow rate region, the smaller the resist surface grain size, and the weaker the resistance to ArF resist damage (striation). The lower the pressure and the lower N ₂ flow rate region, the larger the resist surface grain size, and against ArF resist damage. Strong tolerance.

  In order to elucidate this difference, FIG. 6 shows the results of surface composition analysis of the deposited film deposited without applying a bias using an EDX (Energy Dispersive X-ray Spectrometer). FIG. 6 is a characteristic diagram showing the relationship between the discharge conditions and the deposition film composition. The left axis shows the F / C ratio (bar graph), and the right axis shows the deposition (●). The conditions (a) were 6 Pa, (b) 2 Pa, (c) 0.7 Pa, and (d) 0.4 Pa, respectively. As a result, it can be seen that a film with more F component is deposited as the pressure is lower. Therefore, in order to reduce ArF resist damage, it can be said that it is necessary to form a deposition film having a small C component ratio and a high F component ratio.

  Next, FIG. 7 shows the result of analyzing the resist surface composition using XPS (X-ray Photoelectron Spectroscopy) when etching is actually performed by applying a bias. FIG. 7 is a characteristic diagram showing the relationship between the discharge conditions and the resist surface composition. The conditions (a) 6 Pa, (b) 0.4 Pa, and (c) 0.4 Pa + high voltage were set, respectively. It can be seen that the lower the pressure, the lower the C component ratio. In general, when the wafer bias output is increased and the Vpp (peak-to-peak) voltage is increased, the verticality of the processing performance is improved, but it can be seen that the C component ratio is increased by the increase of Vpp.

  Therefore, it can be seen that there is a trade-off relationship between the vertical workability and ArF resist damage, but it is possible to form a deposition film with a high F component ratio by lowering the pressure, so that low ArF resist damage There is an effect that it is possible to perform highly vertical and highly accurate etching.

In the above embodiment, a gas system in which N ₂ is added to a mixed gas of CF ₄ and CHF ₃ is used as an etching gas, but by adjusting the pressure and gas flow rate and the mixed gas ratio of CF ₄ and CHF ₃ It is possible not to add N ₂ , and there is an effect that k value deterioration of the Low-k (SiOCH) film can be suppressed. In addition, the etching shape can be controlled by adjusting the mixed gas ratio of CF ₄ and CHF ₃ .

In the above description, a mixed gas of CF ₄ and CHF ₃ is used as an etching gas, but a mixed gas of CF ₄ and N ₂ or a mixed gas of CHF ₃ and N ₂ can be used.

As for the mixing ratio of CF ₄ and CHF _3, the higher the CHF ₃ ratio, the higher the resist selection ratio is. However, since the tendency to inhibit etching is strong, the higher the bias output or the lower the pressure, the higher the ratio. Accurate etching is possible.

  Furthermore, although the magnetic field etching apparatus has been described in the present embodiment, the same effect can be obtained in other plasma processing apparatuses such as an ashing apparatus and a plasma CVD apparatus that can operate at a low pressure.

Sectional drawing explaining the structure of a to-be-etched processing material (sample). The characteristic view which shows the relationship between the etchant partial pressure by the presence or absence of Ar dilution, and an etching characteristic. The characteristic view which shows the relationship between the etchant partial pressure by the presence or absence of Ar dilution, and a plasma composition. FIG. 7 is a contour map showing the influence of the pressure and N ₂ flow rate on etching characteristics. Surface SEM image after etching of ArF resist. The characteristic view which shows the relationship between discharge conditions and a deposit film composition. The characteristic view which shows the relationship between discharge conditions and a resist surface composition.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Photoresist mask, 102 ... Antireflection film (BARC), 103 ... Material to be processed, 104 ... Etching stop film, 105 ... Silicon base | substrate.

Claims (2)

In an etching process for etching a SiOCH film using an ArF resist mask using an apparatus that etches a material to be processed by generating a plasma and applying a high-frequency voltage to a sample,
Using C F ₄ mixed gas consisting of CHF ₃ or CF _4, CHF ₃ and a mixed gas consisting of _{N 2} as the etching gas,
A plasma processing method comprising performing plasma processing at a low pressure of 0.4 to 0.7 Pa.   2. The plasma processing method according to claim 1, wherein plasma is generated using a magnetic field.

Images