JP2011071223A - Dry etching method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dry etching method suppressing increase of specific permittivity of a porous insulating film having low permittivity. <P>SOLUTION: When etching a porous and low-permittivity insulating film I having specific permittivity &le;2.2 by inductively-coupled plasma, a fluorocarbon-based gas represented by general formula C<SB>a</SB>F<SB>b</SB>X<SB>c</SB>or C<SB>4</SB>F<SB>8</SB>is used as an etching gas, and the pressure of the etching gas is kept at 0.5-5.0 Pa. In addition, high-frequency power of 13.56 MHz is applied to a high-frequency antenna 30 in the range of 100-600 W to induce plasma using the etching gas. The high-frequency power of 13.56 MHz is applied to a substrate S including the insulating film I in the range of 50-300 W while exposing the substrate S to the plasma, whereby the insulating film I is etched in a condition where an etching reaction by an ion component in the plasma becomes dominant. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an insulating film having a low dielectric constant formed by a CVD method using a vacuum process or a coating method using a spin coater, for example, a porous silica film and an organosilicon compound vapor-phase polymerized thereon. The present invention relates to a method for dry-etching an insulating film including a hydrophobic compound.

  In recent years, miniaturization and densification of elements and wirings constituting a semiconductor device have been increasing as equipment equipped with the semiconductor device has been reduced. As the miniaturization of such elements and wiring advances, so-called wiring delay, which is a delay of signals conducted in the wiring, increases, and as a result, the responsiveness of the semiconductor device is significantly reduced. .

  The wiring delay is proportional to the product of the wiring resistance and the capacitance between the wirings. Therefore, as means for reducing the wiring delay, the wiring resistance is reduced and the capacitance between the wirings is reduced. It is possible to take Among these, in order to reduce the resistance of the wiring, copper having a resistivity lower than that of aluminum, which has been widely used conventionally, is being used as a wiring forming material.

  On the other hand, the capacitance between the wires is proportional to the material filled between the wires, that is, the relative dielectric constant of the insulating film forming material and the area of the wire, and inversely proportional to the distance between the wires. . Here, as described above, since the wirings and the like included in the semiconductor device are being miniaturized, it is inevitable to reduce the distance between the wirings. That is, in order to reduce the capacitance between the wirings, the insulating film must be formed of a material having a lower relative dielectric constant.

  Therefore, for example, as described in Patent Document 1, an insulating material obtained by vapor-phase polymerization of a hydrophobic compound such as cyclic siloxane on a porous silica film is used as a material for forming an insulating film filled between the wirings. It is being considered. According to such a porous insulating material, air having a low dielectric constant can be included in the pores of the porous insulating material, so that the dielectric constant of an insulating film made of the same insulating material is reduced by the amount of such air. Will do. In addition, since hydrophobic functional groups such as methyl groups and ethyl groups are introduced into the inner surface of the pores contained in the porous silica, water having a high relative dielectric constant is difficult to be adsorbed into the pores of the porous silica, Along with this, an increase in relative dielectric constant is suppressed.

JP 2006-265350 A

By the way, a reactive dry etching process using a fluorocarbon (CF) gas is performed when forming a groove or a through hole for forming the wiring, electrode, etc. in the insulating film made of such a low dielectric constant material. It is common to do. When a reactive dry etching process is performed using this CF-based gas, CF ions (C _x F _y ⁺ ), CF radicals functioning as an etchant for the porous silica are contained in the gas phase in which the reaction is performed. (C _x F _y ^* ) and F radicals (F ^* ) are generated. However, among these etchants, highly reactive CF radicals, F radicals, etc. not only etch the porous silica film, but also the hydrophobic functional groups on the film surface after the etching and the introduction destination thereof. It breaks even the bond. When the hydrophobic functional group introduced into the porous silica membrane is cleaved from the porous silica membrane in this way, the hydrophobicity of the porous silica membrane is lowered and is present around the porous silica membrane. It becomes easy for water to enter into the porous silica membrane. That is, when the porous silica film is dry-etched in this way, its relative dielectric constant increases, and as a result, the capacitance between wirings facing each other through the porous silica film increases. Therefore, when the low dielectric constant insulating material is used for the insulating film between the wirings, there is a possibility that a sufficient wiring delay reduction effect cannot be obtained.

  Such a problem is not limited to the low dielectric constant film using the porous silica film as described above as a base material. In general, an insulating organic / inorganic hybrid material or a porous film of an organic material is used as the low dielectric constant film. The pores of the porous film have pores at the end of the material constituting the film. It is configured to form the inner surface of the. When this porous film is dry-etched with the fluorocarbon gas, CF radicals or F radicals deviated from the fluorocarbon-based gas cause the hydrophobic functional group such as a hydrocarbon group and the introduction destination thereof to bond. Easy to be cut. As described above, when the hydrocarbon group is separated from the porous membrane, the hydrophobic property of the porous membrane is lowered, and a hydrophilic functional group is introduced into the atom bonded to the cut hydrocarbon group. In addition to this, water molecules are adsorbed in the pores of the porous film, and the relative dielectric constant of the insulating film is greatly increased.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a dry etching method capable of suppressing an increase in relative dielectric constant of a porous insulating film having a low dielectric constant.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
The invention described in claim 1 is a dry etching method for etching a porous low dielectric constant insulating film having a relative dielectric constant of 2.2 or less by inductively coupled plasma, wherein the general formula C _a F _b X _c (X is One of H, Cl, and Br, a fluorocarbon gas represented by a = 1 to 5, b = 2a + 2-c, and c = 0,1), or C ₄ F ₈ is used as an etching gas. While maintaining the pressure of the etching gas at 0.5 Pa to 5.0 Pa, a high frequency power of 13.56 MHz is applied to the high frequency antenna in the range of 100 W to 600 W to induce plasma using the etching gas, By exposing a substrate having a low dielectric constant insulating film to the plasma and applying high frequency power of 13.56 MHz to the substrate in a range of 50 W to 300 W, the plasma As its gist to the etching the low dielectric constant insulating film under a condition that the etching reaction becomes dominant due to ionic components.

In the method of claim 1, when dry etching treatment is performed on the low dielectric constant insulating film, a fluorocarbon-based gas represented by the general formula C _a F _b X _c or C ₄ F ₈ is used as an etching gas. The etching gas pressure is 0.5 Pa to 5.0 Pa, the power applied to the substrate, so-called bias power is 50 W to 300 W, and the high frequency power that induces plasma of the etching gas, so-called antenna power is 100 W. Etching is performed under the condition of ˜600 W, that is, under the condition that the etching reaction by the ion component in the plasma is dominant. By setting the etching gas pressure and the antenna power, it is possible to suppress the generation amount of the CF radicals more than the generation amount of CF ions. In addition, by setting the bias power, CF ions can be preferentially drawn into the insulating film side to be etched, and the etching of the insulating film proceeds with the CF ions. In other words, even if the generation amount of CF ions is suppressed in order to suppress the generation amount of the CF radical, the bias power is set to strongly attract the CF ions to the insulating film side by setting the bias power. In addition, the etching of the insulating film can be advanced. Therefore, if the same amount of the low dielectric constant insulating film is etched, the functional group for forming the vacancies, for example, the insulating film, is compared with the aspect in which the etching reaction by the CF radical in the plasma is dominant. It is possible to suppress defects such as a terminal group and a hydrophobic functional group in the constituent material. As a result, it is possible to perform the dry etching process while suppressing an increase in the relative dielectric constant of the insulating film.

  According to a second aspect of the present invention, in the dry etching method according to the first aspect, the low dielectric constant insulating film is a porous silica film having a hydrophobic hydrocarbon group.

  As in the above method, a porous silica film having a hydrophobic hydrocarbon group can be used as the porous insulating film having a low dielectric constant. In such an insulating film, during etching using a fluorocarbon-based gas, the bond between the silicon atom and the hydrocarbon group is easily broken by CF radicals or F radicals separated from the fluorocarbon-based gas. As described above, when the hydrocarbon group is separated from the porous silica film, the hydrophobicity of the porous silica film decreases, and the hydrophilic functional group is bonded to the silicon atom bonded to the cut hydrocarbon group. Not only is introduced, but also water molecules are adsorbed in the pores of the porous silica film, and the relative dielectric constant of the insulating film is greatly increased. Therefore, in the dry etching method, the use of the porous silica film in which the silicon and the hydrocarbon group are combined as the target insulating film suppresses an increase in the relative dielectric constant of the insulating film. The effect to do becomes more remarkable.

The schematic block diagram which shows schematic structure of the plasma etching apparatus with which the dry etching process using one Embodiment of the dry etching method which concerns on this invention is implemented. The graph which shows the area | region prescribed | regulated by the range of the bias power used in the dry etching method of this Embodiment, and the range of antenna power.

Hereinafter, an embodiment embodying a dry etching method according to the present invention will be described with reference to FIGS.
FIG. 1 shows a schematic configuration of a plasma etching apparatus in which dry etching processing using the dry etching method of the present embodiment, particularly plasma etching processing is performed. As shown in FIG. 1, a quartz plate 12 that seals a plasma generation region 11 a that is an internal space of the vacuum chamber 11 is attached to the upper opening of the vacuum chamber 11 included in the plasma etching apparatus 10. The plasma generation region 11a surrounded by the vacuum chamber 11 and the quartz plate 12 is depressurized to a predetermined pressure by an exhaust unit such as a vacuum pump (not shown).

  A substrate stage 13 for supporting the substrate S, which is an object to be etched in the plasma etching apparatus 10, is disposed in the plasma generation region 11a. The substrate stage 13 is electrically connected via a bias matching circuit 20 to a bias high frequency power source 21 that is a bias power source. The high frequency power of 13.56 MHz output from the bias high frequency power source 21 is first impedance matched by the bias matching circuit 20 so that the reflected wave from the load side becomes small. Next, high-frequency power is applied through the substrate stage 13 to the substrate S placed on the upper surface of the substrate stage 13 in a state in which impedance matching is taken in this way. If plasma is generated in the plasma generation region 11a, a negative bias potential with respect to the plasma generation region 11a is applied to the substrate S by applying such high frequency power from the bias high frequency power supply 21. The Rukoto.

  A ring-shaped protection member 14 that surrounds the outer periphery of the substrate S is disposed on the substrate mounting surface that is the upper surface of the substrate stage 13. The protective member 14 is made of, for example, glassy carbon having high resistance to chlorine-based or iodine-based plasma, and has a function of protecting the outer peripheral portion of the substrate stage 13 from the plasma generated in the plasma generation region 11a. is doing. Further, the substrate stage 13 is provided with a temperature control mechanism (not shown) that adjusts the temperature of the substrate S placed thereon to a predetermined temperature. When an etching process is performed in the plasma etching apparatus 10, a temperature corresponding to the processing condition is applied to the substrate S by the temperature control mechanism.

  The substrate S to be etched in the plasma generation region 11a is a low dielectric constant insulating material on the surface of a substrate made of a known semiconductor material such as silicon or a substrate made of a non-semiconductor material such as glass or quartz. The film I is formed. Moreover, a low dielectric constant insulating material as a material for forming the insulating film I, a so-called low-k material, is a hydrocarbon group such as a methyl group or an ethyl group on the inner surface of a hole contained in the porous silica film, a fluoroalkyl. It has a structure in which a hydrophobic functional group such as a group is introduced. Examples of such a hydrophobic compound into which a hydrophobic hydrocarbon group is introduced include an organosilicon compound having a methyl group (TMCTS). This organosilicon compound and the porous silica film are formed by causing a dehydration polymerization reaction between a hydroxyl group remaining on the inner surface of the pores contained in the porous silica film and a hydrogen group of the organosilicon compound. Binding, which introduces hydrophobic functional groups to the inner surface of the pores. According to the insulating film I having such a structure, air having a very low relative dielectric constant k is taken into the pores of the porous silica film, and water having a high relative dielectric constant k enters the insulating film I. In combination with the suppression, the dielectric constant k as the insulating film I is kept low. Specifically, the dielectric constant k of the insulating film I is k ≦ 2.2, for example, k = 1.97.

  In the present embodiment, the insulating film I having a particularly low dielectric constant on the substrate S is etched by the plasma etching process, and a concave portion or a through hole having a predetermined shape is formed in the insulating film I.

  On the other hand, a high frequency antenna 30 having a double winding loop is disposed above the quartz plate 12, and the high frequency antenna 30 is electrically connected to a discharge high frequency power source 32 via a discharge matching circuit 31. It is connected. The 13.56 MHz high-frequency power output from the discharge high-frequency power source 32 is first of all a discharge matching circuit so that the reflected wave from the load side is reduced, like the high-frequency power output from the bias high-frequency power source 21. Impedance matching is achieved by 31. Next, high-frequency power is applied from the discharge matching circuit 31 to the high-frequency antenna 30 in a state in which impedance matching is thus achieved. The high-frequency power applied to the high-frequency antenna 30 in this way generates an induction electric field in the plasma generation region 11a for generating plasma using the etching gas supplied to the plasma generation region 11a, that is, so-called inductively coupled plasma.

Further, a gas supply unit 40 for supplying an etching gas used in the plasma etching process is connected to the plasma generation region 11a of the vacuum chamber 11. The gas supply unit 40 adjusts an etching gas serving as an etchant of the insulating film I having a low dielectric constant, for example, a CF-based gas such as carbon tetrafluoride (CF ₄ ), and is connected to the plasma generation region 11a to which the gas is supplied. To supply. That is, in the plasma etching apparatus 10 according to the present embodiment, the etching gas supplied to the plasma generation region 11a is turned into plasma by the high frequency power applied to the high frequency antenna 30, and the ionized species and the dissociated species generated thereby. Reactive ion etching (RIE) is performed to etch the substrate S to be etched, more precisely, the insulating film I formed on the surface thereof.

The CF gas as the etching gas is not limited to carbon tetrafluoride, but is CHF.
₃ , other gases represented by the general formula C _a F _b X _c , such as CClF ₃ , CBrF ₃ , C ₂ F ₆ , C ₃ F _8, etc., can also be used. Here, X is any of hydrogen (H), chlorine (Cl), and bromine (Br). In addition, as a, any one of 1 to 5 is the number of carbon atoms, b is “2a + 2-c” as the number of fluorine atoms, and c is the number of atoms included in 0 or 1 in X Is assigned as In addition to the gas represented by these general formulas C _a F _b X _c , C ₄ F ₈ that is a fluorocarbon-based cyclic molecule can also be used as the etching gas.

  The plasma etching apparatus 10 is provided with a control unit 50 for controlling the plasma etching process performed in the plasma generation region 11a to a desired condition. The control unit 50 is connected to the substrate stage 13, the bias matching circuit 20, the bias high-frequency power source 21, the discharge matching circuit 31, and the discharge high-frequency power source 32. Various control signals are output from the control unit 50 to each unit.

  For example, when the plasma etching apparatus 10 performs the plasma etching process, the control unit 50 refers to the conditions of the plasma etching process stored in the storage area inside the control unit 50. And the control signal for providing the temperature according to this condition to the said board | substrate S is output to the temperature control mechanism of the substrate stage 13, and the temperature control mechanism is performed based on this.

  Further, when the plasma etching process is performed, the control unit 50 outputs a control signal for applying high-frequency power corresponding to the conditions to the substrate S to the bias high-frequency power source 21 to cope with this. The high frequency power to be output is output to the high frequency power supply 21 for bias.

  Then, based on the conditions of the plasma etching process, the control unit 50 outputs a control signal for applying a high frequency power of 13.56 MHz to the high frequency antenna 30, for example, to the discharge high frequency power supply 32, and the process is performed. In this case, the discharge high-frequency power source 32 outputs such high-frequency power.

Further, the control unit 50 supplies a control signal for supplying a CF-based gas as an etching gas, for example, carbon tetrafluoride (CF ₄ ) gas, at a flow rate corresponding to the conditions of the plasma etching process. When the plasma etching process is performed, the gas supply unit 40 is supplied with such a flow rate gas.

When the plasma etching treatment is performed in the plasma etching apparatus 10, first, carbon tetrafluoride gas having a flow rate corresponding to the conditions of the plasma etching treatment is supplied to the plasma generation region 11 a. Next, a high frequency electric power for discharge according to the above conditions is applied to the high frequency antenna 30, whereby a high frequency magnetic field according to the high frequency power is formed in the plasma generation region 11 a, and an induction electric field generated by the high frequency magnetic field is generated. Converts the carbon tetrafluoride gas supplied to the plasma generation region 11a into plasma. Thereafter, when high frequency power from the bias high frequency power supply 21 is applied to the substrate S, a bias voltage corresponding to the high frequency power is applied to the substrate S, and active species in the plasma formed in the plasma generation region 11a, More precisely, the carbon trifluoride ions (CF ₃ ⁺ ) and the carbon difluoride ions (CF ₂ ²⁺ ) generated by the ionization of carbon tetrafluoride, or the separation of the nitrogen tetrafluoride gas. The generated CF radicals such as fluorine radicals (F ^* , hereinafter referred to as F radicals) and carbon trifluoride radicals (CF ₃ ^* ) collide with the insulating film I having a low dielectric constant formed on the surface of the substrate S. Thus, a predetermined region on the surface of the insulating film I is etched along the direction perpendicular to the surface of the insulating film, that is, the thickness direction of the substrate S, by CF ions and CF radicals that hit the substrate S, so-called etchants.

An insulating film I formed on the surface of the substrate S, for example, an insulating film I in which a hydrophobic functional group is introduced into a porous silica film as described above, and reactive ions using carbon tetrafluoride as an etching gas. When etching is performed by etching, the following reaction is induced. That is, the carbon tetrafluoride gas supplied into the plasma generation region 11a is converted into plasma by an induction electric field generated by a high-frequency magnetic field formed by application of high-frequency power applied to the high-frequency antenna 30, so-called antenna power. The The plasma thus generated contains CF ions (CF ₃ ^{+ and the} like) that are positive ions generated by ionization of carbon tetrafluoride and fluorine ions (F ⁻ ) that are anions. In addition, the plasma contains CF radicals (CF ₃ ^*, etc.), which are radicals generated by the dissociation of carbon tetrafluoride, and fluorine radicals (F ^* , hereinafter referred to as F radicals).

  When high frequency power, so-called bias power, is applied from the bias high frequency power source 21 to the substrate S in a state where these four kinds of particles and carbon tetrafluoride molecules exist in the plasma as described above, a negative potential is applied. An ion species having a positive charge, that is, CF ions, is attracted toward the substrate S biased in the negative direction, and the insulating film I formed on the surface of the substrate S is etched. Since the CF ions are highly reactive with the insulating film I, particularly with silicon constituting the porous silica film, most of the CF ions drawn into the substrate S react with the silicon.

  At this time, as described above, particles such as other ions and radicals are contained in the plasma, and these particles are moved according to the flow of the particles in the plasma generation region 11a regardless of the biased substrate potential. It will fly toward the substrate S. Among these particles, CF radicals and F radicals in particular are highly reactive and react with the insulating film I existing in the formation region of the through-holes and recesses as an etchant. The insulating film I is shaved by reacting with silicon in the film. However, because these CF radicals and F radicals are highly reactive, they are insulated at least in the vicinity of the formation region of the through-holes and recesses, for example, in the side walls of the through-holes and recesses and at the portions that become the bottom surfaces of the recesses. The bonding site between the hydrocarbon group of the organosilicon compound bonded to the film I and silicon may be cut. When the hydrocarbon group is cleaved in this way, the hydrophobicity at the site decreases, and the silicon atom that has lost one bonding group has a new bond such as a supply bond or a coordinate bond with another molecule at that site. Easy to form bonds. Here, oxygen and water derived from outside air exist in the plasma etching apparatus 10 where the reactive ion etching process is performed and in the space where the plasma etching apparatus 10 is installed. Among these, water has a large polarity in the molecule, and is easily bonded to silicon in which the bonding group in the insulating film I is cut. This water molecule has a relative dielectric constant k of, for example, k = 80.4 at 20 ° C., which is higher than the relative dielectric constant k of the insulating film I, which is about 40 times that. Therefore, when the water molecules are bonded to the insulating film I, the relative dielectric constant k is increased.

  Therefore, in this embodiment, by increasing the ratio of CF ions to all particles that collide with the substrate S as an etchant during the reactive ion etching process, silicon and hydrocarbon groups in the insulating film I due to CF radicals and F radicals are increased. The breakage of the bond is suppressed. That is, the insulating film I is etched under the condition that the etching reaction due to the ion component in the plasma is dominant.

Specifically, when a reactive plasma etching process, which is one of the dry etching processes, is performed on the insulating film I having a low dielectric constant, a CF-based etching gas is used to apply the etching gas pressure P to the substrate S. The high frequency power (bias power Pbis) to be generated and the high frequency power (antenna power Pant) for inducing plasma of the etching gas are set within the following ranges, respectively.
・ 0.5 (Pa) ≦ P ≦ 5.0 (Pa)
・ 50 (W) ≦ Pbis ≦ 300 (W)
・ 100 (W) ≦ Pant ≦ 600 (W)
The value of the bias power Pbis is 0.12 (W / cm ² ) ≦ Pbis ≦ 0.72 (W / cm ² ) when normalized as power per unit area applied to the substrate. The thickness of the insulating film I etched per unit time, the so-called etching rate, is 0.1 μm / sec to 1 μm / sec.

  The etching gas pressure P and the antenna power Pant are regions in which the amount of F radicals and CF radicals contained in the plasma is lower than that of the CF ions based on the emission analysis of the plasma generated by them. Is selected. In addition, the bias power Pbis is a region in which CF ions are preferentially drawn into the insulating film I to be etched, and the bonds in the insulating film I having a low dielectric constant are drawn into the CF ions. It is selected as an area that is difficult to be cut by the energy of.

  That is, the range of the antenna power refers to the amount of ionized species or dissociated species contained in the plasma while the plasma is stably generated, and the substrate S It can be said that the number of CF ions drawn into the substrate S by the negative voltage applied to the substrate S is superior to the number of radical species particles toward the side. On the other hand, the range of the bias power means that even if the number of CF ion particles is suppressed by suppressing the number of radical species contained in the plasma in this way, CF ions are efficiently drawn. It can be said that this is a condition that can achieve the above-described etching rate.

  Then, by setting the pressure P, the antenna power Pant, and the bias power Pbis in such a region, while the bond responsible for the low dielectric constant is held inside the insulating film I, the etching with respect to the insulating film I becomes CF ions. It will be dominated by. That is, the insulating film I can be dry etched while suppressing an increase in the relative dielectric constant of the insulating film I having a low dielectric constant. In addition, by setting the bias power Pbis in this way, the generation amount of CF ions is reduced in addition to the generation amount of radical species due to a decrease in the pressure P of the CF gas as the etching gas and the antenna power Pant. However, the CF ions can be strongly attracted to the insulating film I, and the etching of the insulating film I can be advanced.

  Moreover, in this embodiment, the porous insulating film I having a low dielectric constant is made of a porous silica film, and an organosilicon compound having a hydrocarbon group is vapor-phase polymerized on the inner surface of the pores contained therein. I'm trying to use something. In such an insulating film I, during etching using carbon tetrafluoride gas, the bond between the silicon atom of the organosilicon compound and the hydrocarbon group is easily broken by F radicals or CF radicals separated from the CF gas. Thus, when hydrocarbon groups are separated from the inner surface of the pores contained in the porous silica membrane, the hydrophobicity of the porous silica membrane is reduced, and hydrophilic groups and water in place of the hydrocarbon groups are removed from the pores. Not only is it introduced into the inner surface, but also water molecules are adsorbed in the pores contained in the porous silica film, so that the dielectric constant of the insulating film I is greatly increased. Therefore, in the dry etching method, the dielectric constant of the insulating film I is increased by using the porous silica film obtained by vapor-phase polymerization of the organosilicon compound as the insulating film I to be etched. The effect which suppresses doing becomes more remarkable.

Incidentally, the reactive ion etching process is performed under conditions other than the antenna power, bias power, and pressure ranges, that is,
(I) Antenna power Pant <100 (W)
(Ii) Antenna power Pant> 600 (W)
(Iii) Bias power Pbis <50 (W)
(Iv) Bias power Pbis> 300 (W)
(V) Pressure P <0.5 (Pa)
(Vi) Pressure P> 5.0 (Pa)
When the etching process is performed in the six regions,
For example, under the condition (i), since the antenna power is small and plasma is not stably induced, the etching process does not proceed. In the condition (ii), both the ratio of ionized molecules and the ratio of dissociated molecules in the etching gas molecules increase, and even if the bias power is set within the above range, particles generated by ionization and dissociation The number of particles that collide with each other and toward the substrate S side, in particular, the number of particles that CF radicals and F radicals travel toward the substrate S side increases, and the cutting of the hydrocarbon groups of the insulating film by such CF radicals and F radicals is remarkable. Become. As a result, the dielectric constant after etching exceeds 2.25.

  Under the condition (iii), even when the antenna power condition is the optimum condition as described above, the bias power is small, so the number of CF ions drawn into the substrate S side is small, and the etching rate of the insulating film I is near zero. Thus, the etching process itself does not proceed. In addition, when the condition (iv) is set, even if the antenna power condition is the above optimum condition, the energy of the drawn CF ions becomes large and not as high as the CF radical or F radical. Cutting of hydrocarbon groups in the insulating film I by CF ions cannot be ignored. As a result, the dielectric constant after etching exceeds 2.25.

Under the condition (v), the amount of gas that can be ionized is too small, so that it is difficult to induce plasma. On the other hand, under the condition (vi), the plasma becomes unstable when the pressure P is greater than 5.0 Pa. End up.
[Example]
Using the plasma etching apparatus, a reactive ion etching process is performed on a substrate in which an insulating film made of a porous silicon film and an organic silicon compound is laminated on a quartz wafer of about 20 × 20 mm with a thickness of 150 nm as follows. Conducted under conditions. At this time, carbon tetrafluoride gas was used as the etching gas.
-Pressure of carbon tetrafluoride gas 0.1 Pa to 10.0 Pa
・ Bias power 0W ~ 350W
・ Antenna power 50W ~ 700W
-Substrate temperature Room temperature FIG. 2 is a graph illustrating the relative dielectric constant of the insulating film I after the etching process using CF ₄ as an etching gas, the bias power dependence of the dielectric constant after etching, and the antenna power. Shows the dependency.

  As shown in FIG. 2, the value of the antenna power Pant is set to 100 (W) ≦ Pant ≦ 600 (W), and the value of the bias power Pbis is set to 50 (W) ≦ Pbis ≦ 300 (W). In the case of setting, the relative dielectric constant k of the insulating film I after the etching treatment was calculated by performing, for example, IV measurement and CV measurement, and 1.95 ≦ k ≦ 2.23. In the present embodiment, since the initial value of the relative dielectric constant k of the insulating film I, that is, the relative dielectric constant before the etching process is k = 1.97 as described above, the antenna power and the bias power are In the range, the relative dielectric constant k is guaranteed to be the initial value when the rate of increase is the lowest, and on the other hand, it is only 0.28 higher than the initial value even when the rate of increase is the highest. Was recognized.

Further, Fourier transform infrared spectroscopy (FT-IR) measurement is performed on the insulating film I before and after the etching process in the range of the pressure, antenna power, and bias power, and Si—C contained in the insulating film I is obtained. The amount of change in the amount of bonds was measured as the amount of change in the amount of hydrocarbon groups. As a result, the amount of change from the amount of hydrocarbon groups in the insulating film I before the etching process, that is, the amount of decrease was 10% or less. From this, the Si—C bonds contained in the insulating film I are generally maintained before and after the etching process, whereby the amount of vacancies contained in the insulating film I, that is, the relative dielectric constant k of the insulating film I is reduced. It was observed that the level was generally maintained before and after.

  For example, when the relative dielectric constant after performing the reactive ion etching treatment on the substrate under the conditions of Examples 1 to 4 below was calculated based on the measurement results of IV measurement and CV measurement, 2.19, 2.18, 2.23, and 2.10. Moreover, when the variation | change_quantity of the hydrocarbon group was computed based on the measurement result of FT-IR measurement, the amount of reduction | decrease was 10% or less. For these reasons, the hydrocarbon groups contained in the insulating film I are generally retained before and after the etching process, whereby the amount of vacancies contained in the insulating film I, that is, the relative dielectric constant k of the insulating film I is reduced. It was observed that the level was generally maintained before and after. In addition, outside the ranges of the pressure, antenna power, and bias power, it was recognized that the relative dielectric constant exceeded 2.25, and the amount of change of the hydrocarbon group also exceeded 10%.

[Example 1]
・ Pressure of carbon tetrafluoride gas 1.0Pa or less ・ Bias power 50W
・ Antenna power 600W
-Substrate temperature Room temperature [Example 2]
・ Pressure of carbon tetrafluoride gas 1.0Pa or less ・ Bias power 150W
・ Antenna power 600W
-Substrate temperature Room temperature [Example 3]
・ Pressure of carbon tetrafluoride gas 1.0Pa or less ・ Bias power 150W
・ Antenna power 300W
-Substrate temperature Room temperature [Example 4]
・ Pressure of carbon tetrafluoride gas 1.0Pa or less ・ Bias power 150W
・ Antenna power 100W
That is, the range of the antenna power refers to the amount of ionized species and dissociated species contained in the plasma while the plasma is stably generated, and the substrate S It can be said that the condition is such that the number of CF ions drawn into the substrate S by the negative voltage applied to the substrate S is superior to the number of radical species particles toward the side. On the other hand, the range of the bias power means that the CF ions can be efficiently drawn even if the number of CF ion particles is suppressed by suppressing the number of radical species contained in the plasma in this way. Therefore, it can be said that the conditions allow the above-described etching rate to be achieved.

As described above, according to the dry etching process according to the present embodiment, the following effects can be obtained.
(1) As the insulating film I of the substrate S, an insulating film I in which an organosilicon compound that is a hydrophobic compound having a methyl group is vapor-phase polymerized on a porous silica film is used. The reactive ion etching process was applied. That is, using carbon tetrafluoride gas, the pressure P of the carbon tetrafluoride gas is 0.5 (Pa) ≦ P ≦ 5 (Pa), and the high frequency power applied to the substrate, so-called bias power Pbis 50 (W) ≦ Pbis ≦ 300 (
W) and high frequency power for inducing plasma of carbon tetrafluoride gas, so-called antenna power Pant, is set to 100 (W) ≦ Pant ≦ 600 (W), respectively. Thereby, it becomes possible to reduce radical content in plasma. In addition, by setting the bias power Pbis in the above range, CF ions can be preferentially drawn to the insulating film I side to be etched, so that the etching on the insulating film I proceeds with the CF ions. Become. That is, the insulating film I can be dry etched while suppressing an increase in the relative dielectric constant of the insulating film I having a low dielectric constant. Further, by setting the bias power Pbis in this way, even if the generation amount of CF ions is reduced in addition to the generation amount of radicals due to the decrease in the pressure P of the carbon tetrafluoride gas and the antenna power Pant, the CF power It is possible to strengthen the drawing of ions to the insulating film I side, and it is possible to progress the etching of the insulating film I. Therefore, in the reactive ion etching process using carbon tetrafluoride gas, the bond between the silicon and the hydrocarbon group is broken by radicals such as CF radical and F radical separated from the carbon tetrafluoride gas, As a result, it is possible to suppress the relative dielectric constant k of the insulating film I from greatly increasing.

It should be noted that the above embodiment can be implemented with appropriate modifications as follows.
An organic silicon compound that is a hydrophobic compound on a porous silica film, that is, a gas phase polymerized one obtained by gas phase polymerization of a hydrophobic compound containing silicon and bonded to the silicon and a hydrocarbon group. The insulating film I was used. However, the present invention is not limited to this, and an insulating film I having a structure in which a hydrocarbon group is introduced into silicon included in a porous silica film may be used.

  The insulating film I is not limited to a low dielectric constant film in which a hydrophobic functional group is introduced into the porous silica film as described above. For example, as a base material for a porous insulating film, an inorganic / organic hybrid material other than silica or a porous film made of an organic material is used, and a hydrophobic functional group such as a hydrocarbon group is introduced into the porous film. It may be a low dielectric constant film.

  DESCRIPTION OF SYMBOLS 10 ... Plasma etching apparatus, 11 ... Vacuum chamber, 11a ... Plasma production | generation area, 12 ... Quartz plate, 13 ... Substrate stage, 14 ... Protection member, 20 ... Bias matching circuit, 21 ... Bias high frequency power supply, 30 ... High frequency antenna , 31 ... discharge matching circuit, 32 ... high frequency power supply for discharge, 40 ... gas supply unit, 50 ... control unit, I ... insulating film, S ... substrate.

Claims (2)

In a dry etching method for etching a porous low dielectric constant insulating film having a relative dielectric constant of 2.2 or less by inductively coupled plasma,
Fluorocarbon-based gas represented by the general formula C _a F _b X _c (X is any one of H, Cl and Br, a = 1 to 5, b = 2a + 2-c, and c = 0, 1) Or using C ₄ F ₈ as an etching gas and applying a high frequency power of 13.56 MHz to the high frequency antenna in a range of 100 W to 600 W while maintaining the pressure of the etching gas at 0.5 Pa to 5.0 Pa. By inducing plasma using an etching gas and exposing the substrate having the low dielectric constant insulating film to the plasma, a high frequency power of 13.56 MHz is applied to the substrate in a range of 50 W to 300 W, thereby generating the plasma. Etching the low-dielectric-constant insulating film under conditions where the etching reaction due to the ionic components therein is dominant. The dry etching method according to claim 1,
The dry etching method, wherein the low dielectric constant insulating film is a porous silica film having a hydrophobic hydrocarbon group.

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