JPH11329793A - Dry etching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable suppression of etching mount of photoresist to minimum without side etching in spite of a high aspect ratio pattern in metal film dry etching. SOLUTION: This dry etching method is provided with an etching device controllable separately of plasma generating and ion detecting, by which bias power or frequency of high frequency power supply 8 for ion detecting is increased as time lapses linearly or in curved line to etching time (t), so that a wafer is dry etched without changing the number of etching ions against the etching depth thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method for a metal film, and more particularly to a dry etching method capable of minimizing the amount of reduction of a resist film without side etching even in a pattern having a high aspect ratio. About.

[0002]

2. Description of the Related Art As integrated circuits become finer, Al
When a remote plasma type etching apparatus as shown in FIG. 14 is used for etching a Cu thick film, side etching occurs at a deep etching depth. FIG. 14 shows a remote plasma type etching apparatus. The remote plasma method refers to a method in which plasma generation and ion attraction can be controlled independently. In this etching apparatus, the wafer 10 to be etched is placed at the bottom in the plasma generation and etching chamber 6.
Electrode and support base 10 for holding the
An etching gas inlet 12 for introducing an etching gas into the processing chamber 6 and an exhaust port 13 for exhausting the inside of the processing chamber 6 are provided on a side surface of the processing chamber 6. The electrode / support base 10 is connected to a high-frequency power supply 8 for ion attraction via a blocking capacitor 9 provided outside the processing chamber 6. The processing chamber 6 itself is connected to a high frequency power source 7 for plasma generation. The etching apparatus configured as described above is, for example, an electron cyclotron resonance discharge (EC
R; Electron Cyclotron Re
sound, inductively coupled radio frequency plasma (ICP;
Inductively Coupled Plasm
a), helicon, dual frequency reactive ion etching (RI
E: Reactive Ion Etching; hereinafter, reactive ion etching is abbreviated as RIE. ) And 2
Two or more power supplies, such as a power supply RIE or other high-frequency power supply 7 for generating plasma and a high-frequency power supply 8 for changing the plasma sheath potential and controlling the strength of ion attraction onto the semiconductor substrate, are independent or nearly independent. Among them, those corresponding to almost all etching apparatuses other than the parallel plate type RIE apparatus.

FIG. 15 is a sectional view for explaining an etching progress surface in a conventional dry etching method using this etching apparatus. As the wiring pitch becomes smaller due to the miniaturization of the integrated circuit, it becomes difficult for ions or radicals to enter the narrow space, and as a result, the deposition 5 for protecting the side wall tends to be insufficient. If the bias is increased to prevent side etching, the remaining film of the resist 4 decreases, and the over-etching margin decreases.

In a conventional etching method, FIG.
As shown in (a), the applied power of the high-frequency power supply 8 for ion attraction is fixed to prevent over-etching,
Alternatively, as shown in FIG. 16B, the etching is performed by a method of switching the bias power of the high frequency power supply 8 for ion pulling in stepwise. For example, the bias power is increased stepwise at a constant frequency. Also, a method of increasing the frequency stepwise while keeping the amplitude of the high frequency constant has been disclosed (Japanese Patent Application Laid-Open No. 5-275194). Also disclosed is a method of controlling the lamp voltage of an ultraviolet light source as a function of time by using an electron cyclotron resonance discharge dry etching apparatus, thereby changing an etching rate to make a sidewall of an etched portion gentle. (JP-A-6-29265).

[0005]

However, when etching is performed by the above-described conventional method, it is difficult to determine at what stage the bias power is switched.

FIG. 17 shows a conventional etching method.
FIG. 7 is a graph showing a change in the number of reached etching ions depending on an etching depth d. FIG. 18 is a graph showing the dependency of the deposition depth d on the side wall of the etching depth d in the conventional etching method. As shown in FIG. 17, the number N _{ions of} ions reaching the etching progress surface or the number N _rad of the etching and polymerizable radicals decreases as the height d of the resist pattern increases. In FIG. 15, the thickness a of the deposition 5 serving to protect the side wall is determined by the amount N of the polymerizable radical reaching the etched surface.
_{When the} high-frequency bias power is kept constant as shown in FIG. 16A, the protection of the side wall becomes difficult as the etching proceeds as shown in FIG.
Side etching is likely to occur. Simply increasing the number of polymerizable radicals by changing the density of the gas or plasma does not improve the formation of the sidewall deposition 5 having a non-uniform thickness as shown in FIG.

It is not possible to increase the thickness of the resist only by increasing the thickness of AlCu. Rather, as semiconductor devices become more miniaturized, they are becoming thinner. In the case of lithography, the photoresist film thickness is 10 for I-line.
000Å is optimal, and 7000Å-80 for KrF line
00 ° is the optimum film thickness, and the resist becomes thinner in the KrF region. Photoresist etching rate /
The selectivity of the Al etching rate also has an upper limit, and if it is simply increased too much, the side wall protective film becomes insufficient and side etching occurs.

The present invention has been made in view of such a problem, and does not perform side etching even in a pattern having a high aspect ratio by dry etching of a metal film, and minimizes the etching amount of a photoresist. It is an object of the present invention to provide a dry etching method capable of performing the method.

[0009]

A method for dry etching a metal film according to the present invention is a method for dry etching a wafer by an etching apparatus capable of independently controlling plasma generation and ion attraction. It is characterized in that the wafer is etched while the ion energy is continuously increased by keeping the frequency of the power supply constant and increasing the voltage over time.

In this dry etching method, the voltage of the high frequency power supply for ion attraction is controlled as a function of time using a linear function obtained from a voltage at the start of etching, a voltage at the end of etching, and a total etching time. And can be increased linearly with time. Further, the voltage of the high-frequency power supply is controlled as a function of time by using a downwardly convex increasing function obtained from a change with time of the number of arrivals of the etching ions on the etching surface, so that the voltage rises in a curve with time. It can also be done.

A dry etching method for a metal film according to the present invention is a method for dry etching a wafer by an etching apparatus capable of independently controlling plasma generation and ion attraction, wherein the voltage of a high-frequency power supply for ion attraction for inducing ions is kept constant. In addition, the wafer is etched while the ion energy is continuously increased by increasing the frequency over time.

In this dry etching method, the frequency of the high frequency power supply is set to the frequency at the start of etching,
Using a linear function obtained from the frequency at the end of the etching and the total etching time, it can be controlled as a function of time and can be increased linearly with time. Further, the frequency of the high-frequency power supply is controlled as a function of time using a downwardly convex increasing function obtained from a change with time of the number of etching ions reaching the etching surface, and is increased in a curve with time. You can also.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a dry etching method according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing a sample to be etched according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing how an etching progress surface changes in the embodiment of the present invention.
The etching apparatus used in the etching method of this embodiment is the same as that shown in FIG. FIG.
FIG. 4 is a graph illustrating the relationship between general ion energy and the etching rate of AlCu, and FIG.
FIG. 5 is a graph showing changes in the number of etching ions reached according to the etching depth d in the conventional etching method, and FIG. 6 is a graph showing general ion energy and photoresist. FIG. 7 is a graph illustrating the relationship between the etching rates of the photoresist, FIG. 7 is a graph illustrating the amount of etching of the photoresist from the start of etching in the etching method of this embodiment to the lapse of time t, and FIG. FIG. 9 is a graph showing the amount of etching of the photoresist from the start to after a lapse of time t. In FIG. 8, the dashed line indicates the etching amount of the photoresist in the present embodiment, and the hatched portion indicates the total etching amount.

As shown in FIG. 1, in the etching sample, an insulating film 2 is formed on a semiconductor substrate 1, and a metal film 3 is formed on the insulating film 2 by a PVD method or a CVD method. The type of the insulating film 2 and the thickness of the insulating film are arbitrary, and an electric circuit may be formed on the substrate.
Further, a conductive film such as polysilicon may be present between the insulating film 2 and the metal film 3. On the metal film 3, a photoresist 4 is patterned. Although a hard mask such as an oxide film or a SiON film may be used as the photoresist 4 in some cases, it is assumed that the photoresist at the time of forming the hard mask is left.

The etching gas is C when the film type is Al.
CH _x F _y , N if necessary for the mixed gas of l ₂ and BCl _3
2 or a gas to which diluent gas Ar or the like is added, and when the film type is W, SF ₆ and O ₂ , N ₂ and Ar as additional gases are used.
Use a mixed gas of These halogen gases are turned into plasma by a voltage applied from a high frequency power supply for plasma generation, and anisotropic etching of the metal film is performed. In this embodiment, a case where a thin film of an Al alloy is used will be described.

It is assumed that the minimum incident energy of etching ions required for volatilization of Cu in AlCu is V ₀ . The value of V ₀ varies depending on etching conditions such as temperature, pressure, plasma density and exhaust port ratio of the device, film forming conditions such as a film forming temperature and a Cu content, and a device, but at a practical level, it is approximately 10 eV to 50 eV. It is.

Next, let V ₁ be the incident energy of the etching ions at which the deposition on the side wall is sufficiently obtained by the aspect ratio at the end of the etching of AlCu. The aspect ratio is the ratio of d to s shown in FIG.
/ S, where s is constant but d changes. d
Is the AlCu etching depth d1 and the remaining resist film amount d2
Is added.

The etching ion incident energy is not the thermal energy when the ions are turned into plasma, but the electrostatic energy accelerated by the absolute potential Vdc of the plasma sheath generated by the power supply 7 for drawing in. When it reaches 10, it is converted into kinetic energy, the speed of which is proportional to the speed of normal incidence on the wafer 10. Further, as shown in FIG. 4, there is a characteristic that the etching rate of Al has a region that hardly depends on the ion energy. That is, the reaction of the following reaction formula 1 does not require ion assist.

[0019]

## STR1 ## On the other hand, the etching rate of an organic film such as a photoresist depends on the ion incident energy as shown in FIG. 7, and the reaction requires a certain degree of ion assist.

[0020] The number N _rad radical The more the number N _ion ion etching incident as shown in Equation 1 below, the number of times receiving a collision incident ion energy V The larger ions, increases the speed after the collision, increased I do.

[0021]

## EQU1 ## Deposition amount (sidewall deposition thickness a)
∝Radical amount N _rad = f (N _ion , V) Since the distance D between the sheath and the wafer 10 is sufficiently larger than d, the energy V of the arriving ions does not depend on d, and the thickness a of the deposition side wall film a only depends on the number n _{io n} of arrival ions gradually decreases n _ion decreases. f
(N _ion , V) is an increasing function of N _ion and V. In the present embodiment, by continuously increasing the power P applied to the power supply 7, this V is continuously increased as d increases. This increases the N _ion entering the narrow _space and increases the N _rad, making the deposition thickness a independent of d.

The increasing rate R of the bias power P is derived by the following method. That is, the bias power P and the time t have a linear function relationship as shown in the following Expression 2.

[0023]

## EQU2 ## P = Rt + P₀  As shown in FIG. 4, the etching rate of Al
Since there is a region that hardly depends on energy,
Ching end time t_endMade the bias power P constant
Is almost the same in both cases.
The rate of increase R of aspower P can be derived by the following experiment.
You. That is, while the bias power P is kept constant,
And etching is performed using the conventional etching end point detection method._endTo
Measure. The value of P depends on the device, but V₀give
Bias power P₀All you have to do is to have it. Soshi
And V₁Bias power P that gives₁Ask for. P₁And t
_endSince there is a relationship of the following formula 3, the following formula 4
Is obtained, and P obtained in the experiment is obtained.₁And P₀Assign
Then the bias power increase rate R can be calculated
You.

[0024]

## EQU3 ## P ₁ = Rt _end + P ₀

[0025]

R = (P ₁ −P ₀ ) / t _end By using the conditions obtained in this way, the bias power is continuously increased as shown in FIG. It is possible to make the protective deposition thickness a uniform and perform etching without side etching. Since the resist is located not in the narrow pattern but in the uppermost layer, the reduction in the number of etching ions as shown in FIG. 5 does not need to be considered, and the etching rate of the photoresist shown in FIG. FIG. 7 is a graph showing the change over time of the etching amount of FIG. The hatched portion indicates the total etching amount in this embodiment. FIG. 8 is a graph showing the change over time of the etching amount of the photoresist by the conventional method for comparison with the present embodiment. The etching amount of the photoresist is smaller than that of the present embodiment by the conventional method. More. Therefore, in this embodiment, it can be said that the margin of the resist remaining film is larger than that of the conventional method, and a thick AlCu film can be etched by a fine pattern.

FIG. 9 is a graph showing the relationship between the etching time t and the frequency ω of the high frequency power supply 7 according to the second embodiment of the present invention.

In the second embodiment, the metal film is etched by continuously increasing the ion energy by changing the frequency while the bias power V of the high frequency power supply 7 is kept constant. Ion attraction is controlled by the difference in mobility between ions and electrons.
(100 MHz to several hundred MHz), so that it flows to the chamber wall or electrode, but heavy ions
Above, it becomes impossible to follow, and a potential difference occurs between the plasma and the surface of the wafer 10. Therefore, positive ions are drawn toward the electrically negative surface of the wafer 10.
According to this principle, the ion energy is large at 1 to 2 MHz where the ions can easily follow, and the ion energy decreases as the frequency is increased. Therefore, if the frequency is continuously changed with respect to the etching time t as shown in FIG. In addition, dry etching can be performed by continuously increasing the ion energy, the margin of the resist remaining film is larger than in the conventional method, and a thick AlCu film can be etched by a fine pattern.

FIG. 10 is a graph showing the relationship between the etching time t of the high frequency power supply 7 and the bias power P according to the third embodiment of the present invention. FIG. 11 is a graph showing a change in the etching amount of the oxide film with respect to the etching time t according to the third embodiment of the present invention. FIG. 12 is a graph showing a change in an etching rate depending on an etching time t according to the third embodiment of the present invention. FIG. 13 is a diagram showing the relationship between the etching depth d and the thickness a of the deposition attached to the side wall in the etching method of the present invention.

In the third embodiment, the bias power P is changed with respect to the etching time t as shown in the graph of FIG. 10 so that the arrival number N _ion of the etching ions on the etching surface does not change with the etching depth. It is to be raised continuously in a curved shape.

The relationship between the etching time t and the bias power P shown in FIG. 10 is obtained as follows. First, a sample in which the metal film 1 is replaced with a thermal oxide film is prepared in order to obtain the relationship between the number of ions reaching the etching surface and the etching depth d. Bias V under the same conditions as Al etching
Then, the sample is etched, and the time change of the etching amount is measured to obtain FIG. The etching rate is obtained from FIG. 11, and FIG. 12 showing the time change of the etching rate is obtained. Since the amount of etching is proportional to the number of etching ions reaching the etching surface, the following equation 5 is used to obtain FIG. 5 showing the relationship between the number of ions reaching the etching surface and the etching depth d from FIG.

[0031]

D = (etching rate) × (etching time t) Since the bias powers V ₀ and V ₁ are the same as those of the conventional etching method, the bias power is inversely proportional to the arrival number of ions in FIG. The process of the time change of the bias power from ₀ to V ₁ is derived as a downward convex increasing function shown in FIG.

By performing dry etching by increasing the bias power with respect to the etching time t as shown in FIG. 10, N _ion becomes constant irrespective of the etching depth as shown in FIG. Is more uniform, a shape without side etching is obtained, and the remaining film amount of the resist is further increased.

[0033]

As described in detail above, according to the present invention,
By continuously increasing the bias power or frequency of the high-frequency power supply with respect to the etching time t, the number of etching ions becomes constant regardless of the etching depth, the deposition thickness for sidewall protection is made uniform, and the side etching is performed. It is possible to perform a dry etching, and to manufacture a semiconductor device having a large remaining amount of photoresist.

[Brief description of the drawings]

FIG. 1 is a sectional view of a sample to be etched according to a first example of the present invention.

FIG. 2 is a schematic view showing an etching progress surface according to the first example of the present invention.

FIG. 3 is a graph illustrating a general relationship between ion energy and an etching rate of AlCu.

FIG. 4 is a graph showing a relationship between an etching time and a change in bias power according to the first embodiment of the present invention.

FIG. 5 is a graph showing a change in the number of reached etching ions depending on an etching depth d in a conventional etching method.

FIG. 6 is a graph illustrating a general relationship between ion energy and a photoresist etching rate.

FIG. 7 is a graph showing the amount of etching from the start of etching to the lapse of time t in the etching method of the present invention.

FIG. 8 is a graph showing the amount of etching from the start of etching to the lapse of time t in the conventional etching method.

FIG. 9 shows an etching time t according to a second embodiment of the present invention.
FIG. 4 is a graph showing the relationship between the frequency and the frequency ω of the high frequency power supply 7.

FIG. 10 is a graph showing a relationship between an etching time t and a bias power P of a high-frequency power supply 7 according to a third embodiment of the present invention.

FIG. 11 is a graph showing a change in an etching amount of an oxide film according to an etching time t according to a third example of the present invention.

FIG. 12 is a graph showing a relationship between an etching time t and an etching rate of an oxide film according to a third example of the present invention.

FIG. 13 is a diagram showing a relationship between an etching depth d and a thickness a of deposition deposited on a side wall in the etching method of the present invention.

FIG. 14 is a schematic diagram of a remote plasma type etching apparatus.

FIG. 15 is a cross-sectional view showing a relationship between an etching depth d and a deposition thickness a attached to a side wall in a conventional etching method.

FIG. 16 is a graph showing the relationship between etching time and bias power in a conventional etching method.

FIG. 17 is a graph showing the relationship between the etching depth d and the number of reached etching ions in a conventional etching method.

FIG. 18 is a graph showing a relationship between an etching depth d and a thickness a of deposition deposited on a side wall in a conventional etching method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1; Semiconductor base 2; Insulating film 3; Metal film 4; Resist 5; Deposition 6; Processing chamber 7; High-frequency power supply for plasma generation 8; Table 12; Etching gas inlet 13;

Claims (6)

[Claims] 1. A method for dry-etching a wafer using an etching apparatus capable of independently controlling plasma generation and ion attraction, wherein the frequency of a high-frequency power supply for ion attraction for inducing ions is made constant, and the voltage is increased with time. And etching the wafer while continuously increasing the ion energy. 2. The voltage of the high-frequency power supply for ion attraction is calculated using a linear function obtained from a voltage at the start of etching, a voltage at the end of etching, and a total etching time,
2. The dry etching method according to claim 1, wherein the method is controlled as a function of time, and is increased linearly with time. 3. The voltage of the high-frequency power supply for ion attraction is controlled as a function of time by using a downwardly convex increasing function obtained from a change over time of the number of etching ions reaching the etching surface. 2. The dry etching method according to claim 1, wherein the temperature is raised in a curve. 4. A method for dry-etching a wafer by an etching apparatus capable of independently controlling plasma generation and ion attraction, wherein a voltage of a high-frequency power supply for ion attraction for inducing ions is kept constant and its frequency is increased with time. And etching the wafer while continuously increasing the ion energy. 5. The frequency of the high-frequency power supply for ion attraction is controlled as a function of time by using a linear function obtained from a frequency at the start of etching, a frequency at the end of etching, and a total etching time. 5. The dry etching method according to claim 4, wherein the temperature is increased linearly. 6. The frequency of the high-frequency power supply for ion attraction is controlled as a function of time by using a downwardly convex increasing function obtained from a time-dependent change in the number of etching ions reaching the etching surface. 5. The dry etching method according to claim 4, wherein the temperature is raised in a curve.