JP4849875B2 - Plasma etching method - Google Patents

Description

  The present invention relates to a plasma etching method, and more particularly, to a plasma etching method in which an etching target film formed on a target object is etched with plasma in a manufacturing process of a semiconductor device.

For example, in the manufacture of a semiconductor device having a multilayer wiring structure, when etching an interlayer insulating film for the purpose of forming a recess such as a hole for wiring connection, a silicon nitride film or carbonized carbon is used as a base stopper film immediately above the lower layer wiring. A silicon film is formed. Such a stopper film is removed by etching at the final stage of the recess formation in order to make electrical connection between the wirings.
Regarding etching of silicon nitride film, silicon carbide, etc., for example, a fluorocarbon gas containing carbon and fluorine in its molecule (CF-based gas) for the purpose of obtaining an etching selectivity of an organic SiO ₂ film with respect to the underlying SiN film. And plasma etching using a hydrofluorocarbon gas (CHF-based gas) containing carbon, hydrogen and fluorine in the molecule has been proposed (see, for example, Patent Document 1).

In addition, in order to anisotropically etch a silicon nitride layer from a multilayer structure, a plasma etching method using fluorocarbon gas and CH ₂ F ₂ or CH ₃ F as a hydrogen source (for example, Patent Document 2), nitriding Plasma etching using fluorocarbon gas and CHF ₃ , CH ₂ F ₂ , CH ₃ F, etc. as a hydrogen source to maintain high selectivity to the mask layer when forming high aspect ratio trenches in the silicon layer A processing method (for example, Patent Document 3) has been proposed.

By the way, it is considered that the design rule of a large scale integrated circuit (LSI) will reach 65 nm and further 45 nm from the present 90 nm, and there is a tendency for further miniaturization of wiring. With the miniaturization of wiring, it is necessary to take measures against signal delay caused by the electric capacity generated in the insulating layer between the wirings. To suppress this, a low dielectric constant material (Low-k material) is used. Development of the used interlayer insulation film is underway. As an interlayer insulating film using such a low-k material, attention is paid to a porous low-k film having a lower dielectric constant and a low resistance than a conventional low-k film. However, the porous low-k film has a low dielectric constant, but has a problem of low strength and low etching resistance because it has pores in the film.
JP 2003-234337 A JP-A-11-102896 JP 2000-340552 A

When plasma etching is performed on the underlying silicon nitride film or silicon carbide film as described above, it is necessary to ensure etching selectivity with respect to the uppermost etching mask film.
In addition, when the polymer formed by the reaction between the component of the processing gas and the component in the film adheres to the surface of the object to be processed during etching, the etching rate is lowered, so that the formation and adhesion of the polymer must be suppressed. It is.
Furthermore, if side etching occurs in which the underlying silicon nitride film or silicon carbide film, which is a film to be etched, is etched in the lateral direction, device characteristics are impaired, and therefore it is necessary to prevent side etching.

Further, when a porous Low-k film is used as an interlayer insulating film above the underlying silicon nitride film or silicon carbide film, the porous Low-k film is oxidized and plasma damage is likely to occur. As a result, there has been a problem that when hydrofluoric acid treatment is performed in a later step, the oxidized portion is removed and damage becomes obvious. Furthermore, there has been a problem in that the surface of the porous Low-k film is indefinitely formed by exposure to plasma, resulting in surface roughness.
As described above, when the porous Low-k film as the interlayer insulating film deteriorates, the reliability of the semiconductor device is lowered. Therefore, it is necessary to perform the plasma etching under a condition that the porous Low-k film is not damaged. is there.

  As described above, when the plasma etching process is performed on the target object having the porous Low-k film formed above the target film, the target object having no porous Low-k film is subjected to the plasma etching process. Compared with the case where it does, selection of plasma etching conditions is remarkably difficult, and the conditions which can satisfy all the said subjects have not been found until now.

  Therefore, the present invention is a case where the silicon nitride film or the silicon carbide film is subjected to plasma etching treatment in an object to be processed using a porous Low-k film as an interlayer insulating film above the underlying silicon nitride film or silicon carbide film. An object of the present invention is to provide a plasma etching method capable of ensuring etching selectivity to a hard mask film, suppressing polymer adhesion and side etching, and suppressing damage to a porous Low-k film and surface roughness. .

In order to solve the above problems, a first aspect of the present invention is a plasma etching method in which an object to be processed is etched with plasma of a processing gas in a processing chamber of a plasma processing apparatus,
The object to be processed has a film to be etched and a porous Low-k film formed above the film to be etched.
The etched film is a silicon nitride film or a silicon carbide film,
The processing gas is composed of carbon and fluorine, and is composed of a fluorocarbon compound having 2 or less carbon atoms and CO ₂ , or is composed of carbon and fluorine and having 2 or less carbon atoms, and CO 2 _2, Ri Do from the _{N 2,}
A plasma etching method is provided, wherein the etching target film is etched using a hard mask film made of a silicon oxide film formed above the porous Low-k film as a mask .

In the first aspect, the fluorocarbon compound is more preferably CF ₄ .
Further, it said fluorocarbon compound, the ratio of the CO ₂ is fluorocarbon _compounds: CO 2 = _{3: 1~10:} is preferably 1.
The porous Low-k film is preferably an inorganic Low-k film having a dielectric constant of 2.0 to 2.7.

The plasma etching method of the first aspect, the etching selection ratio of the film to be etched for the previous SL hard mask film is preferably greater than 2.
Preferably, an adhesion film is provided between the film to be etched and the porous Low-k film, and between the porous Low-k film and the hard mask film.

A second aspect of the present invention is a control program that operates on a computer and controls a plasma processing apparatus, and the plasma processing apparatus is configured to perform the plasma etching method of the first aspect at the time of execution. There is provided a control program characterized by controlling the above.

A third aspect of the present invention is a computer-readable storage medium that operates on a computer and stores a control program for controlling a plasma processing apparatus ,
Wherein the control program, when executed, characterized by the Turkey controls the plasma processing apparatus as a plasma etching method of the first aspect is performed, a computer-readable storage medium.

According to the plasma processing method of the present invention, an object to be processed having a film to be etched made of a silicon nitride film or a silicon carbide film and a porous Low-k film formed in an upper layer than the film to be etched is obtained by using silicon nitride. when plasma etching the hard mask layer made of a film as a mask, as the process gas, the composed of carbon and fluorine, and carbon atoms 2 following fluorocarbon compounds, or consists of CO ₂ Prefecture, or carbon and fluorine By using a composition composed of a fluorocarbon compound having 2 or less carbon atoms, CO ₂ and N ₂ , high etching selectivity to the hard mask film can be secured, and polymer adhesion and side etching are suppressed, In addition, while suppressing damage to the porous Low-k film and roughening of the surface of the porous Low-k film, It can be carried out quenching.
Therefore, for example, the plasma processing method of the present invention can be suitably used as an etching process in the manufacturing process of a semiconductor device having a multilayer wiring structure including a porous Low-k film as an interlayer insulating film.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 schematically shows a plasma processing apparatus suitably used in an etching process according to an embodiment of the present invention. The plasma processing apparatus 1 can be used as a capacitively coupled parallel plate plasma etching apparatus in which electrode plates are opposed in parallel in the vertical direction and a high frequency power source is connected to both of them.

  The plasma processing apparatus 1 has a chamber 2 formed into a cylindrical shape made of aluminum, for example, whose surface is anodized (anodized), and the chamber 2 is grounded. In the chamber 2, a semiconductor wafer (hereinafter simply referred to as “wafer”) W made of, for example, silicon and having a predetermined film formed thereon is horizontally placed and functions as a lower electrode. The susceptor 5 is provided in a state of being supported by the susceptor support 4. A high pass filter (HPF) 6 is connected to the susceptor 5.

  A temperature control medium chamber 7 is provided inside the susceptor support 4, and the temperature control medium is introduced into the temperature control medium chamber 7 through the introduction pipe 8 and circulated so that the susceptor 5 can be controlled to a desired temperature. It is like that.

  The upper center portion of the susceptor 5 is formed into a convex disk shape, and an electrostatic chuck 11 having substantially the same shape as the wafer W is provided thereon. The electrostatic chuck 11 has a configuration in which an electrode 12 is interposed between insulating materials. When a DC voltage of, for example, 1.5 kV is applied from a DC power source 13 connected to the electrode 12, the electrostatic chuck 11 has a Coulomb force. The wafer W is electrostatically adsorbed.

  The insulating plate 3, the susceptor support 4, the susceptor 5, and the electrostatic chuck 11 are heated to a predetermined pressure (back pressure) with a heat transfer medium, for example, He gas, on the back surface of the wafer W that is a target object. A gas passage 14 is formed for supply, and heat transfer is performed between the susceptor 5 and the wafer W via the heat transfer medium so that the wafer W is maintained at a predetermined temperature. .

  An annular focus ring 15 is disposed at the upper peripheral edge of the susceptor 5 so as to surround the wafer W placed on the electrostatic chuck 11. The focus ring 15 is made of, for example, silicon and acts to improve etching uniformity.

  An upper electrode 21 is provided above the susceptor 5 so as to face the susceptor 5 in parallel. The upper electrode 21 is supported on the upper portion of the chamber 2 via an insulating material 22, constitutes a surface facing the susceptor 5, and has a large number of discharge holes 23, for example, an electrode plate 24 made of quartz, A conductive material that supports the electrode 24, for example, an electrode support 25 made of aluminum having an anodized aluminum surface is used. The interval between the susceptor 5 and the upper electrode 21 can be adjusted.

A gas introduction port 26 is provided at the center of the electrode support 25 in the upper electrode 21, and a gas supply pipe 27 is connected to the gas introduction port 26. Further, a valve is connected to the gas supply pipe 27. 28 and a mass flow controller 29 are connected to a processing gas supply source 30, and an etching gas for plasma etching is supplied from the processing gas supply source 30. As the etching gas, it is preferable to use a combination of a gas of a fluorocarbon compound such as CF ₄ and C ₂ F ₆ and CO ₂ , for example. Here, the fluorocarbon compound gas is a gas that exerts an etching action by a radical reaction, and CO ₂ is a gas that controls the radical to act optimally on the film to be etched. Further, in addition to the fluorocarbon compound gas and CO ₂ , for example, N ₂ , He, or the like can be mixed. In FIG. 1, only one processing gas supply source 30 is representatively illustrated, but a plurality of processing gas supply sources 30 are provided, for example, a fluorocarbon compound gas such as CF ₄ , CO ₂ or the like. The flow rate is controlled independently of each other so as to be supplied into the chamber 2.

  An exhaust pipe 31 is connected to the bottom of the chamber 2, and an exhaust device 35 is connected to the exhaust pipe 31. The exhaust device 35 includes a vacuum pump such as a turbo molecular pump, and is configured so that the inside of the chamber 2 can be evacuated to a predetermined reduced pressure atmosphere, for example, a predetermined pressure of 1 Pa or less. Further, a gate valve 32 is provided on the side wall of the chamber 2 so that the wafer W is transferred to and from an adjacent load lock chamber (not shown) with the gate valve 32 opened. It has become.

  A first high frequency power supply 40 is connected to the upper electrode 21, and a matching unit 41 is provided on the feeder line. Further, a low pass filter (LPF) 42 is connected to the upper electrode 21. The first high-frequency power source 40 has a frequency in the range of 50 to 150 MHz. By applying such high-frequency high-frequency power, a high-density plasma in a preferable dissociated state in the chamber 2. Can be formed, and plasma treatment under low pressure conditions becomes possible. Furthermore, the frequency of the first high frequency power supply 40 is preferably 50 to 80 MHz, and typically, a condition of 60 MHz or its vicinity is adopted as shown in FIG.

  A second high frequency power supply 50 is connected to the susceptor 5 as the lower electrode, and a matching unit 51 is provided on the power supply line. The second high frequency power supply 50 has a frequency in the range of several hundred kHz to several tens of MHz, and damages the wafer W by applying a high frequency power having a frequency in such a range. And an appropriate ionic effect can be provided. As the frequency of the second high frequency power supply 50, for example, a condition such as 13.56 MHz or 800 KHz is adopted as shown in FIG.

  Each component of the plasma processing apparatus 1 is connected to and controlled by a process controller 60 having a CPU. The process controller 60 includes a user interface 61 including a keyboard for a command input by a process manager to manage the plasma processing apparatus 1, a display for visualizing and displaying the operating status of the plasma processing apparatus 1, and the like. It is connected.

  Further, the process controller 60 stores a recipe in which a control program (software) for realizing various processes executed by the plasma processing apparatus 1 under the control of the process controller 60 and processing condition data are recorded. A storage unit 62 is connected.

  Then, if necessary, in response to an instruction from the user interface 61, an arbitrary recipe is called from the storage unit 62 and is executed by the process controller 60, so that the plasma processing apparatus 1 performs the process under the control of the process controller 60. Desired processing is performed. In addition, recipes such as the control program and processing condition data may be stored in a computer-readable storage medium such as a CD-ROM, a hard disk, a flexible disk, a flash memory, or other recipes. It is also possible to transmit the data from the device at any time via, for example, a dedicated line and use it online.

  Next, a process of performing plasma etching on a stacked body having a film to be etched by the plasma processing apparatus 1 configured as described above will be described with reference to FIGS. 2 to 4 are schematic views showing an enlarged main part of a longitudinal section of the wafer W in order to explain the outline of the etching process according to the embodiment of the present invention. On the silicon substrate (not shown) constituting the wafer W, as shown in FIG. 2, for example, a lower wiring insulating film 101 is formed, and a stopper film 102 which is a film to be etched is formed thereon, Further, a first adhering film 103, a porous low-k film 104, a second adhering film 105, and a hard mask film 106 are formed on the upper layer in this order from the bottom to form a laminate 200.

The stopper film 102 is, for example, a Si ₃ N ₄ film or a SiC film formed by a method such as plasma CVD or spin-on-glass, and a recess 210 such as a wiring groove or a hole is etched. It functions as an etch stopper when forming.

  The porous Low-k film 104 is an interlayer insulating film formed by, for example, a CVD (Chemical Vapor Deposition) method, and the material thereof is not limited, but a low dielectric constant (k value) of 2.0 to 2.7. A dielectric constant material is preferably used, and an inorganic low dielectric constant material is preferably used. As a low dielectric constant material constituting the porous Low-k film 104, for example, Black Diamond 2X, Black Diamond 3 (both trade names: manufactured by Applied Materials), LKD (trade name: manufactured by JSR), Aurora ULK, Aurora ELK (all trade names; manufactured by ASM), Porous Coral (trade names; manufactured by Novellas), NCS (trade names; manufactured by Catalyst Kasei Kogyo Co., Ltd.), and the like can be used.

For the hard mask film 106 which is an etching mask, for example, a silicon oxide film (SiO ₂ film) formed from TEOS (tetraethoxysilane) or the like is used.

  The first adhesion film 103 and the second adhesion film 105 are both formed so as to sandwich the porous Low-k film 104 from above and below for the purpose of improving the adhesion of the porous Low-k film 104. For example, a dense low-k film, a carbon-containing silicon oxide film, or the like can be used.

  In the stacked body 200, a recess 210 is formed at a depth from the uppermost hard mask film 106 to the exposure of the stopper film 102 by etching based on a resist pattern formed by photolithography.

As shown in FIG. 3, the stacked body 200 having the recesses 210 is etched by using plasma processing apparatus 1 (see FIG. 1), for example, with plasma formed using CF ₄ and CO ₂ . The plasma etching conditions will be described in detail later.

As an etching gas used for removing the stopper film 102, a processing gas containing a fluorocarbon compound gas (CF gas) such as CF ₄ and C ₂ F ₆ composed of carbon and fluorine, and CO ₂ is used. In this case, if a fluorocarbon compound having a large number of carbon atoms is used, a large amount of a polymer as a reaction product is formed and adheres to the recess 210, the etching rate is lowered, and etching with respect to the hard mask film 106 is performed. Selectivity also decreases. Therefore, the carbon number of the fluorocarbon compound is preferably 2 or less.

  In addition, since the etching selectivity of the stopper film 102 with respect to the hard mask 106 is lowered, it is important that the processing gas does not contain a hydrofluorocarbon compound gas (CHF-based gas) composed of carbon, fluorine, and hydrogen. It is.

Etching is preferably performed under the condition that the etching selectivity expressed by [Etching rate of stopper film 102] / [Etching rate of hard mask film 106] is larger than 2. When the etching selection ratio is 2 or less, the etching of the hard mask film 106 proceeds, so that the film thickness becomes thin, and when the hard mask film 106 functions as a stopper for the planarization process in a later step, for example. Will cause inconvenience.
The etching can be terminated when, for example, the depth of the recess 210 reaches the lower wiring insulating film 101. In this way, as shown in FIG. 4, the stopper film 102 in the recess 210 is removed, and the lower wiring insulating film 101 is exposed.

  As a specific procedure of the plasma etching process in the plasma processing apparatus 1, first, the wafer W in which the concave portion 210 is formed is loaded into the chamber 2 from a load lock chamber (not shown) by opening the gate valve 32 and electrostatically charged. Place on the chuck 11. The wafer W is electrostatically adsorbed on the electrostatic chuck 11 by applying a DC voltage from the DC power source 13.

Next, the gate valve 32 is closed, and the inside of the chamber 2 is evacuated to a predetermined vacuum level by the exhaust device 35. Thereafter, the valve 28 is opened, and, for example, a fluorocarbon compound such as CF ₄ and CO ₂ as the etching gas from the processing gas supply source 30 are adjusted to a predetermined flow rate ratio by the mass flow controller 29 while being processed gas supply pipe. 27, the gas is introduced into the hollow portion of the gas inlet 26 and the upper electrode 21, and is uniformly discharged onto the wafer W through the discharge holes 23 of the electrode plate 24 as indicated by arrows in FIG. Here, the flow rate of the processing gas can be, for example, CF ₄ / CO ₂ = 75/25 to 600/200 mL / min (sccm), preferably about 150/50 to 500/50 mL / min. At this time, the flow rate ratio between CF ₄ and CO ₂ suppresses side etching and surface roughness of the porous Low-k film, ensures a sufficient selection ratio with the hard mask, and further damages the Low-k film. From the viewpoint of reducing polymer adhesion, it is preferable to set CF ₄ : CO ₂ = 3: 1 to 10: 1.

Further, the residence time of the processing gas is preferably set to, for example, about 3 to 0.17 seconds from the viewpoint of obtaining a sufficient selection ratio with respect to the hard mask and reducing damage to the low-k film. 3 seconds is more preferable.
Here, the residence time means the residence time of the etching gas in the portion that contributes to the etching in the chamber 1, and the lower electrode area (in the case of FIG. 1, the sum of the area of the wafer W and the area of the focus ring 15). The effective chamber volume obtained by multiplying the distance between the upper and lower electrodes (that is, the volume of the space in which the processing gas is converted into plasma) is V [m ³ ], the exhaust speed is S [m ³ / sec], and the pressure in the chamber is p [Pa], where the total flow rate of the processing gas is Q (Pa · m ³ / sec), the residence time τ [sec] can be determined based on the following equation.
τ = V / S = pV / Q

  The pressure in the chamber 2 is predetermined from the viewpoint of suppressing side etching and surface roughness of the porous Low-k film, ensuring a sufficient selection ratio with the hard mask, and further reducing damage to the Low-k film. For example, 5 to 20 Pa, preferably about 6 to 13 Pa. The first high-frequency power source 40 has a high frequency of 200 to 2500 W, preferably about 400 to 1500 W, and the second high-frequency power source 50 has a high frequency of 100 to 1000 W, preferably about 100 to 300 W. Electric power is supplied, and the etching gas is turned into plasma to etch the stopper film 102. The back pressure is preferably set to about 2000 Pa / about 5500 Pa at the center / edge of the wafer W. Further, as the process temperature, for example, the temperature of the wafer W (susceptor 5) is preferably set to 0 to 40 ° C. from the viewpoint of securing a selection ratio with respect to the hard mask and suppressing side etching and polymer adhesion.

Next, a more specific application example of the present invention will be described with reference to FIGS. In the manufacturing process of a semiconductor device having a multilayer wiring structure, contact plugs for wiring connection, Cu wiring, and the like are generally formed by forming via holes and grooves in an interlayer insulating film and then embedding metal. In particular, the Cu wiring embedding method is known as a damascene process (single damascene process or dual damascene process). For example, when wiring is formed by a single damascene process, as illustrated in FIG. 5, a metal material such as Cu embedded in a lower wiring insulating film 112 via a barrier metal 113 on a silicon substrate (not shown). A lower-layer wiring 114 is provided, and a multilayer interlayer insulating film 120, that is, a stopper film 115 made of SiC, SiN, or the like, a first adhesion film 116, a porous low-k film 117, a second layer is formed on the lower-layer wiring 114. A laminate 201 in which the adhesion film 118 and the hard mask film 119 are sequentially laminated is prepared. 5 and 6, reference numeral 111 denotes a lower insulating film made of SiO ₂ or the like. The first adhesion film 116 and the second adhesion film 118 are both provided for the purpose of improving the adhesion of the porous low-k film 117 and can be omitted.

  A recess 211 is formed in the multilayer interlayer insulating film 120. For the recess 211, a corresponding resist pattern is formed on the interlayer insulating film 120 by photolithography, and then the interlayer insulating film 120 is etched using the resist pattern as a mask until the stopper film 115 is exposed. Is formed.

Next, the stopper film 115 is etched using the hard mask film 119 as a mask to expose the lower layer wiring 114 made of Cu or the like as shown in FIG. At this time, as described above, the plasma processing apparatus 1 is used to perform the plasma etching process using a processing gas containing a fluorocarbon gas and CO ₂ .

  Although the subsequent steps are not shown in the figure, for example, by using a sputtering method, a PVD method (Physical Vapor Deposition), an electroplating method, etc., the barrier metal and Cu are embedded in the recess 211 to remove excess Cu, and CMP (chemical machine A planarization process is performed by a polishing method (Chemical Mechanical Polishing). In the planarization process, the hard mask film 119 functions as a stopper. As described above, metal wiring can be formed in a semiconductor device having a multilayer wiring structure.

Next, test results for confirming the effects of the present invention will be described.
In a line-and-space laminate having a laminate structure similar to that of FIG. 2 and having a plurality of recesses 210 (grooves) formed at predetermined intervals, the stopper film 102 exposed in the recesses 210 is used as a mask. On the other hand, an etching process was performed using a plasma processing apparatus 1 having a configuration similar to that shown in FIG. As the etching gas, various gases shown in Table 1 were used, and the test was performed by appropriately combining them.

In addition, the gas flow rate in each test division of (1)-(14) shown in Table 1 is as follows.
(1) CF ₄ = 150 mL / min (sccm);
(2) CF ₄ / N ₂ = 150/50 mL / min (sccm);
(3) CF ₄ / O ₂ = 150/15 mL / min (sccm);
(4) CF ₄ / CO ₂ = 300/100 mL / min (sccm);
(5) CF ₄ / N ₂ / CO ₂ = 300/50/100 mL / min (sccm);
(6) CF ₄ / CHF ₃ / CO ₂ = 150/50/100 mL / min (sccm);
(7) CF ₄ / CH ₂ F ₂ / CO ₂ = 150/15/100 mL / min (sccm);
(8) C ₄ F ₈ / CO ₂ = 30/50 mL / min (sccm);
(9) CH ₂ F ₂ / CF ₄ / Ar / O ₂ = 15/60/450/30 mL / min (sccm);
(10) CH ₂ F ₂ / CF ₄ / Ar / CO ₂ = 15/60/450/100 mL / min (sccm);
(11) CHF ₃ / CH ₂ F ₂ / Ar = 80/20/800 mL / min (sccm);
(12) NF ₃ / Ar = 8/200 mL / min (sccm);
(13) NF ₃ / He / Ar = 8/100/200 mL / min (sccm);
(14) NF ₃ / Ar / CO = 8/200/50 mL / min (sccm)

  As conditions common to the test sections (1) to (14), the pressure in the chamber 2 is set to 6.7 Pa (50 mTorr), and high frequency power of 400 W is supplied to the upper electrode 21 and 100 W to the susceptor 5 as the lower electrode. Each etching gas was turned into plasma and etching was performed. At this time, the back pressure is 2000 Pa (15 Torr) / 5333 Pa (40 Torr) at the center / edge of the wafer W, the process temperature is the chamber 2 side wall = 60 ° C .; the susceptor 5 = 20 ° C., and the etching time is in the test category. Set accordingly.

The etching characteristics are the damage of the porous Low-k film 104, the selectivity with the hard mask film 106 (TEOS-SiO ₂ ), the effect of suppressing polymer deposits, the surface of the porous Low-k film 104 exposed in the recess 210. Roughness and side etching were determined according to the following evaluation criteria.
<Damage of porous Low-k film>
The wafer W after the etching process was processed with hydrofluoric acid (HF), and the change in the groove width (CD: Critical Dimension) was measured. When plasma damage occurs, the surface of the porous Low-k film 104 is oxidized, so that the oxide film is removed by the hydrofluoric acid treatment and the CD changes. In this test, the CD change rate exceeding 7% was judged as damage. The case where the damage occurred was evaluated as x (defect), and the case where the damage did not occur was evaluated as good (good). The CD change rate of 7% corresponds to 6 nm as the CD change amount, that is, the value of [CD value after hydrofluoric acid treatment] − [CD value before hydrofluoric acid treatment].
<Etching selectivity with hard mask film (SiO ₂ )>
From the etching rate of the stopper film 102 (ER ₁₎ and the etching rate of the hard mask layer 106 (ER _2), find the ratio _ER 1 / ER _2, × about 1 or less (bad), no more than about 1 Ultra to about 2 Δ (ordinary), more than 2 to 3 were evaluated as ○ (good), and more than 3, ◎ (best).

<Inhibition effect of polymer (attachment)>
The case where the adhesion of the polymer was remarkable was evaluated as x (defect), and the case where the adhesion was hardly observed was evaluated as ○ (good).
<Rough surface of porous Low-k film>
The surface of the porous Low-k film 104 exposed in the recesses is scraped and markedly roughened by x (defect), and the slightly roughened surface is marked by △ (normal). Those not present were evaluated as good (good).
<Side etching>
The case where side etching occurred in the stopper film 102 in the recess 210 was evaluated as x (defect), and the case where side etching hardly occurred was evaluated as good (good).

From the above evaluation of the etching characteristics (results shown in Table 1), almost no etching selectivity was obtained with CF ₄ single gas in section (1) and CF ₄ / N ₂ in section (2). A large amount of polymer was observed on the side wall of the porous Low-k film 104. In CF ₄ / O ₂ of category (3), no adhesion of polymer occurred, but damage to the porous Low-k film 104 was significant.

In the sections (6) and (7) in which the fluorocarbon gas (CF ₄ ) and CO ₂ are combined with the hydrofluorocarbon gas (CHF ₃ , CH ₂ F ₂ ), the selectivity with respect to the hard mask film 106 tends to decrease. It was.
Even when the fluorocarbon gas and CO ₂ are combined, the selectivity with respect to the hard mask film 106 is significantly reduced in the section (8) using C ₄ F ₈ having a large carbon number of the fluorocarbon compound.
Further, in the sections (9) to (14) in which Ar is included in the processing gas, the etching selectivity with respect to the hard mask film is high, but the porous Low-k film 104 is damaged and the surface is roughened. This is considered to be because the ion sputtering action is strengthened when Ar is contained in the processing gas, and it has been shown that Ar is unsuitable for etching the interlayer insulating film having the porous Low-k film 104.

On the other hand, in the section (4) using the processing gas containing only CF ₄ and CO ₂ which is a fluorocarbon gas having a small number of carbon atoms, damage to the porous Low-k film 104, etching selectivity to the hard mask film 106, Only good results were obtained for all the test items of the polymer adhesion suppressing effect, the surface roughness of the porous Low-k film 104 exposed in the recess 210, and the side etching. Further, in the section (5) using the fluorocarbon gases CF ₄ and CO ₂ having a small number of carbon atoms and a processing gas including N ₂ , the etching selectivity with respect to the hard mask film 106 and the surface roughness of the porous low-k film Although the evaluation was somewhat unsatisfactory for the item (2), the etching selectivity was improved in comparison with CF ₄ / N ₂ in category (2), and a significant improvement was observed in the polymer adhesion preventing effect. _Therefore, than the gas system of the CF 4 / _{N 2,} towards the gas system of the CF _{4 /} N _{2 /} CO 2 was confirmed that can improve the etching characteristics.

As mentioned above, although embodiment of this invention was described, this invention is not restrict | limited to the said embodiment, A various deformation | transformation is possible.
For example, in the above embodiment, a capacitively coupled parallel plate etching apparatus is used. However, any apparatus can be used as long as it can form plasma with the gas species of the present invention. Can be used.

BRIEF DESCRIPTION OF THE DRAWINGS Drawing which shows the outline | summary of the plasma processing apparatus of this invention. The schematic diagram of the wafer cross-section before plasma etching. The schematic diagram of the wafer cross-sectional structure explaining the state which is performing plasma etching. The schematic diagram of the wafer cross-section after plasma etching. FIG. 6 is a schematic diagram of a wafer cross-sectional structure illustrating a state where plasma etching is performed, which is an application example to a damascene process. It is an application example to a damascene process, and is a schematic diagram of a wafer cross-sectional structure after plasma etching.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Plasma processing apparatus 2; Chamber 60; Process controller 61; User interface 62; Memory | storage part 101; Insulating film 102 for lower wirings; Stopper film 103; First adhesion film 104; Porous Low-k film 105; Adhesion film 106; Hard mask film 200, 201; Laminate 210, 211; Recess

Claims (8)

A plasma etching method for etching an object to be processed with plasma of a processing gas in a processing chamber of a plasma processing apparatus,
The object to be processed has a film to be etched and a porous Low-k film formed above the film to be etched.
The etched film is a silicon nitride film or a silicon carbide film,
The processing gas is composed of carbon and fluorine, and is composed of a fluorocarbon compound having 2 or less carbon atoms and CO ₂ , or is composed of carbon and fluorine and having 2 or less carbon atoms, and CO 2 _2, Ri Do from the _{N 2,}
A plasma etching method, comprising: etching a film to be etched using a hard mask film made of a silicon oxide film formed above the porous Low-k film as a mask . The plasma etching method according to claim 1, wherein the fluorocarbon compound is CF ₄ . And the fluorocarbon compound, the ratio of the CO ₂ is fluorocarbon _compounds: CO 2 = _{3: 1~10:} characterized in that it is a 1, the plasma etching method according to claim 1 or claim 2.   4. The plasma etching method according to claim 1, wherein the porous Low-k film is an inorganic Low-k film having a dielectric constant of 2.0 to 2.7. 5. . The etching selection ratio of the etched film to the hard mask film, being greater than 2, the plasma etching method according to any one of claims 1 to 4. 6. The plasma etching according to claim 5 , further comprising an adhesion film between the film to be etched and the porous Low-k film, and between the porous Low-k film and the hard mask film. Method. A control program that operates on a computer and controls a plasma processing apparatus, wherein the plasma processing method is performed such that the plasma etching method according to any one of claims 1 to 6 is performed at the time of execution. A control program for controlling an apparatus. A computer-readable storage medium that operates on a computer and stores a control program for controlling the plasma processing apparatus,
7. The computer-readable storage, wherein the control program controls the plasma processing apparatus so that the plasma etching method according to any one of claims 1 to 6 is performed at the time of execution. Medium.

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