JP2006083433A - Plasma etching system and plasma etching method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a plasma etching system capable of suitably controlling plasma etching time for a metal thin film. <P>SOLUTION: The plasma etching system is provided with: a sensor 22 provided between a discharge electrode and a high frequency power source and measuring the higher harmonic component of the reactance in plasma; and a means 24 of calculating the end point time of etching corresponding to the average value of the high frequency component utilizing a prescribed linear function. The prescribed linear function is selected from a plurality of linear functions in accordance with the opening ratio of the pattern in a thin film to be plasma-etched. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technical field of dry etching for manufacturing a semiconductor device, and more particularly to a plasma etching apparatus and a plasma etching method.

  For miniaturization of a semiconductor device, it is necessary to miniaturize and increase the accuracy of a photomask, which is an original layout pattern. A photomask usually has a light shielding film (metal thin film) made of chromium or the like formed on a transparent substrate such as quartz, and forms a mask pattern to be transferred to a semiconductor device. The pattern formed on the photomask is formed, for example, by providing a resist on the metal thin film by electron beam drawing, removing a part of the resist, and removing the exposed metal thin film by plasma etching. This etching is continued for a total time of the etching time progressing along the surface direction thereafter, in addition to the etching time proceeding mainly in the film thickness direction of the metal thin film (direction perpendicular to the plasma discharge electrode). . For convenience of explanation, the former time is called an etching end time, and the time including the former and the latter is called an overetching end time. Since the overetching end time is determined based on the etching end point time, it is necessary to accurately control or grasp the etching end point time in order to appropriately control the plasma etching time.

  A first method for detecting a conventional etching end point time is an optical emission spectrometry (OES). This analyzes light contained in the plasma emission spectrum caused by the film to be processed or the etching gas, and attempts to detect the etching end point time based on the change in emission intensity. According to this method, the end point time can be detected during the etching without affecting the plasma state and without using a specific monitor pattern. The monitor pattern is a layout pattern for measurement specially provided on the substrate for detecting the etching end point.

  The second method for detecting the etching end point time utilizes the difference in reflectivity of the thin film with respect to laser light having a specific wavelength. The substrate is irradiated with laser light, and the reflected light intensity is measured. When the etching progresses and reaches the interface of the film, the reflectance changes, and the etching end point time is obtained by detecting the change. According to this method, a measurement result (end point time) that does not depend on process conditions such as processing pressure and the type of etching gas can be obtained.

The third method for detecting the etching end time is to detect the etching end time by measuring the plasma current, voltage, phase difference, etc. using an RF sensor and detecting the change in the plasma state. is there. According to this method, as in the first method, the etching end point time can be detected without providing a special monitor pattern (see, for example, Patent Document 1).
JP-A-10-125660

  However, since the plasma emission spectrum in the first method depends complicatedly on the pattern aperture ratio and process conditions (processing pressure, etching gas type, flow rate, flow rate ratio, and other conditions), the emission spectrum analysis and plasma Control is not easy and is not convenient for mass production. Here, the “pattern aperture ratio” is an amount determined by the ratio or area ratio of the etched portion of the entire surface to be processed. For example, when etching a metal thin film, if 80% of the total surface area of the metal thin film is covered with a resist and 20% is exposed, the pattern aperture ratio is 20%. In general, when the pattern aperture ratio is large (when the aperture is wide), the etch rate tends to be slow, and when it is small (when the aperture is small), the etch rate tends to be fast. Therefore, the etching rate is delayed depending on the pattern aperture ratio, and there is a possibility that the etching accuracy may vary. Further, when the pattern aperture ratio changes variously, since the emission spectrum also changes variously, there is a concern that highly accurate end point time detection becomes increasingly difficult.

  Further, in order to detect the etching end point time by the second method, it is necessary to obtain a sufficiently large change in reflected light intensity, for example, a large opening of several hundred μm or more is required. Therefore, this method is not convenient for detecting the end point of etching of a portion having only a small pattern aperture ratio such as a via or a contact hole. On the other hand, since the laser beam is irradiated to a relatively small area in a spot shape, there is a concern that the detection accuracy of the etching end point time varies depending on the location when the pattern aperture ratio varies depending on the location.

  Further, even in the third method, the change in the spectral intensity in the vicinity of the etching end point time becomes small when the pattern aperture ratio is small, so there is a concern that the detection accuracy of the etching end point time may be lowered.

  The present invention has been made in view of the above problems, and an object thereof is to provide a plasma etching apparatus and a plasma etching method capable of appropriately controlling the plasma etching time of a metal thin film.

The plasma etching apparatus according to the present invention comprises:
A sensor that is provided between the discharge electrode and the high-frequency power source and measures a harmonic component of the reactance of the plasma;
Means for calculating an etching end point time corresponding to the average value of the high-frequency components using a predetermined linear function.

  According to the present invention, the plasma etching time for a metal thin film or the like can be appropriately controlled.

  According to one aspect of the present invention, one linear function is selected from a plurality of linear functions in accordance with the pattern aperture ratio of a thin film to be plasma etched. During plasma etching, the harmonic component of the reactance of the plasma is measured, and the time average value of the measured values is calculated. The etching end point time corresponding to the time average value is determined using the one linear function.

  An appropriate linear function is selected according to the pattern aperture ratio, and the etching end point time is determined based on the linear function. Therefore, even if the pattern aperture ratio is low, an appropriate etching end time can be obtained. Since the etching end point time is accurately determined, the entire etching time including over-etching is also accurately determined, and consequently, the etching can be highly accurate. Since the harmonic component of the reactance is sensitive to changes in the plasma state, it is convenient for detecting the end point time of etching. In addition, since an appropriate etching end point time is determined according to the pattern opening ratio, variations in etching accuracy due to the slow etching rate due to the wide and narrow pattern openings are reduced, and this property is advantageous for mass production.

  According to an aspect of the present invention, the linear functions include those having a positive gradient and those having a negative gradient. Thereby, a linear function can be set according to the size of the pattern aperture ratio. As an example, a negative gradient function is used when the pattern aperture ratio is large, and a positive gradient function is used when the pattern aperture ratio is small.

  Hereinafter, although the Example which plasma-etches the metal thin film formed into a photomask is described, this invention is not limited to such a use, It is applicable to the arbitrary uses which plasma-etch a thin film.

  FIG. 1 is a schematic configuration diagram of a plasma etching apparatus according to an embodiment of the present invention. Although this apparatus is an ICP type etching apparatus, the present invention is applicable to other plasma etching apparatuses. The apparatus includes a processing chamber or chamber 10, a pair of discharge electrodes 12, 14, a first power supply unit 16, a second power supply unit 18, a coil 20, a sensor 22, and a data processing unit 24. Have

  A pair of discharge electrodes 12 and 14 are provided in the processing chamber 10, and plasma is generated between the discharge electrodes. A first power supply unit 16 is connected to the first discharge electrode or lower electrode 12. The first electrode unit 16 forms a first high-frequency power source unit, and is composed of, for example, an AC power source of 13.56 MHz. A second power supply unit 18 is connected to the second discharge electrode or upper electrode 14. The second power supply unit 18 forms a second high-frequency power supply unit, and is composed of, for example, a 2 MHz AC power supply. The second discharge electrode 14 is provided with a coil 20, which is used to induce plasma between the electrode plates. The apparatus according to this embodiment includes a sensor 22 between the lower electrode 12 and the high frequency power supply unit 16, and an output of the sensor 22 is given to the data processing unit 24. In the present embodiment, the first and second power supply units 16 and 18 are provided independently, but the present invention can also be used for plasma devices having other power supply circuit configurations.

  On the other hand, an object to be etched is provided in the processing chamber 10, and the object in this embodiment includes a metal thin film (for example, made of chromium, aluminum, tungsten, etc.) 32 that is appropriately patterned on the substrate 30. Have.

  The sensor 22 measures the voltage V and current I of the plasma in the processing chamber 10 and the phase difference θ between them, and supplies it to the data processing unit 24. Such a sensor may be constituted by, for example, a coil that outputs a measured value as a secondary current or a secondary voltage. The data processing unit 24 calculates the plasma reactance X [Ω] according to the following equation based on the measurement value from the sensor 22.

X = (V / I) × sin θ
Here, V is an effective value of the plasma voltage, I is an effective value of the plasma current, and θ represents a phase difference between the voltage and the current. Furthermore, it should be noted that the reactance X calculated by the data processing unit 24 is not for the fundamental frequency f ₁ of the high-frequency power supply 16 but is a reactance for a harmonic component. Although the fifth harmonic component f ₅ in the present embodiment is used, in general, it can utilize second and higher harmonics.

  FIG. 2 shows an experimental result when the metal thin film is subjected to plasma etching with the apparatus shown in FIG. Graph A in the figure is a graph showing the relationship between the etching time and the fifth harmonic component (the spectral intensity) of reactance X. A graph B in the figure is a graph corresponding to the differential curve of the graph A. In the experiment, a substrate was used in which a resist having a thickness of 400 nm was provided on a chromium thin film 32 having a thickness of about 73 nm. The first power supply unit 16 was supplied with 65 W RF power, and the second power supply unit 18 was supplied with 750 W RF power. The pressure in the processing chamber 10 was maintained at 8 mTorr. As the plasma etching gas, chlorine, oxygen and helium were used in a ratio of 48:15:22.

  As shown in graph A, as the etching progresses, the spectral intensity of the reactance decreases, and an inflection point is formed when the etching end point time is reached. The inflection point of graph A gives the peak α of graph B of the differential curve. Therefore, it can be seen from these graphs that the etching end time is about 145 seconds.

FIG. 3 shows the relationship between the etching end point time y calculated as described in FIG. 2 and the average value x of the fifth harmonic component of the reactance X. Graph P shows a state where a layout pattern having a pattern aperture ratio of 27% is etched. Graph Q shows a state where a layout pattern having a pattern aperture ratio of 1% is etched. As shown in the figure, it can be seen that the relationship between the average value x of the fifth-order reactance and the etching end time y when etching a substrate having a large pattern aperture ratio can be approximated by a linear function having a negative slope. More specifically, the graph P is represented by the following formula:
y = -25.0 × x + 257.0 (P)
It can also be seen that the relationship between the average value x of the fifth-order reactance and the etching end time y when etching a substrate having a small pattern aperture ratio can be approximated by a linear function having a positive slope. More specifically, the graph Q is represented by the following formula:
y = + 15.9 × x + 321.3 (Q)
According to research results by the inventors of the present invention, it has been found that the sign of the slope of the linear function is reversed at a pattern aperture ratio of about 6%. Specific numerical values such as the linear function gradient and intercept values, and the critical value of the pattern aperture ratio regarding the sign inversion of the gradient are expected to vary to some extent depending on the material of the etching target and the process conditions. . However, the fact that the high-order harmonic component x of the reactance and the etching end time y can be approximated by a linear function, the sign of the gradient changes at a certain pattern aperture ratio, and the like will be applicable in any case. Therefore, an experiment as shown in FIG. 3 is performed in advance, and a plurality of approximate linear functions of the reactance average value x and the etching end point time y are prepared in accordance with various pattern aperture ratios. If selected, the etching end point time can be appropriately estimated for any pattern aperture ratio. In this embodiment, the linear function is one of the two formulas (P) and (Q), but more linear functions can be obtained by examining the relationship between the average value and the end point time for more pattern aperture ratios. May be prepared.

  Further, according to the research results by the inventors of the present invention, it has been found that the average value of the fifth-order reactance changes with time as the number of processed wafers increases, as shown in FIG. Therefore, in consideration of such a change in the average value over time, the linear function as shown in the formulas (P) and (Q) may be calibrated, and the linear function used is processed into the wafer processing. You may change according to the number of sheets.

  FIG. 5 is a flowchart illustrating a plasma etching method according to an embodiment of the present invention. The flow begins at step 502 and proceeds to step 504.

  In step 504, parameters such as the pattern opening ratio of the substrate on which plasma etching is performed, the averaging time T for obtaining the average value of the reactance X, and the amount of overetching are set. In this embodiment, T = 40 seconds, but other values may be adopted.

  In step 506, it is determined whether the pattern aperture ratio is larger or smaller than a predetermined value. In this embodiment, the pattern aperture ratio is compared with a value of 6%, and if it is larger than 6%, the flow proceeds to step 508, and if smaller, the process proceeds to step 509.

  In step 508, for example, a linear function having a negative slope as expressed by the above equation (P) is selected.

  In step 509, for example, a linear function having a positive slope expressed by the above equation (Q) is selected.

  In step 510, plasma etching is started.

  In step 512, it is determined whether the etching has been performed for a predetermined averaging time T (40 seconds in this embodiment) or more. If the etching is still within the averaging time, the flow proceeds to step 514, and so on. If not, go to step 516.

  In step 514, the reactance X (= V / I × sin θ) is calculated based on the measured values of the plasma voltage V and current I obtained by the sensor 22 as shown in FIG. Calculated. This reactance X corresponds to an instantaneous value and is sampled over a period of T = 40 seconds.

In step 516, an average value X _ave of instantaneous values X acquired over a period of T = 40 seconds is calculated. The instantaneous value X and the average value X _ave of the reactance are calculated by the data processing unit 24 in this embodiment, but all or part of the calculation may be performed by the sensor 22.

In step 518, the average value X _ave is substituted for x of the linear function selected in step 508 or 509, whereby the etching end point time y (x = X _ave ) = T _end is calculated.

In step 520, the overetching end time _Ttotal is calculated. If the amount of overetching is defined as, for example, A% of the time required for etching in the film thickness direction ( _Tend ), the overetching end time is
T _total = (1 + A / 100) × T _end
Can be calculated as Alternatively, if the overetch amount is defined as a fixed value B (seconds), the overetch end time is
_Ttotal = _Tend + B
Can be calculated as In addition to these, the overetching end time can be obtained from the etching end time ( _Tend ) using various relational expressions.

  In step 522, it is determined whether etching has been performed for an overetching end time or longer. If it has not yet been done, flow proceeds to step 524 where the etching continues. If the etching has been performed for the overetching end time or longer, the flow proceeds to step 526 and ends.

  Hereinafter, the means taught by the present invention will be listed as an example.

(Appendix 1)
A sensor that is provided between the discharge electrode and the high-frequency power source and measures a harmonic component of the reactance of the plasma;
Means for calculating an etching end point time corresponding to the high-frequency component using a predetermined linear function.

(Appendix 2)
The plasma etching apparatus according to claim 1, wherein the predetermined linear function is selected from a plurality of linear functions prepared in accordance with a pattern aperture ratio of a metal thin film to be etched.

(Appendix 3)
The plasma etching apparatus according to appendix 2, wherein the plurality of linear functions include a function in which a gradient of the linear function is substantially 0 with reference to one pattern aperture ratio.

(Appendix 4)
The plasma etching apparatus according to appendix 1, wherein the harmonic component is a fifth-order harmonic component.

(Appendix 5)
The plasma etching apparatus according to claim 1, wherein the sensor measures a voltage related to the plasma, a current, and a phase difference between the voltage and the current.

(Appendix 6)
The plasma etching apparatus according to claim 5, further comprising means for calculating an average value of the phase difference.

(Appendix 7)
The plasma etching apparatus according to appendix 1, wherein the sensor is a coil.

(Appendix 8)
The plasma etching apparatus according to appendix 1, wherein the plasma etching gas contains chlorine.

(Appendix 9)
Depending on the pattern aperture ratio of the thin film to be plasma-etched, one linear function is selected from a plurality of linear functions. During plasma etching, the harmonic component of the reactance of the plasma is measured, and the time average value of the measured values is calculated. Calculate
An etching end point time corresponding to the time average value is determined using the one linear function. A plasma etching method, wherein:

1 shows a schematic configuration diagram of a plasma etching apparatus according to an embodiment of the present invention. FIG. It is a figure which shows the experimental result of the etching end time and the spectrum intensity of a 5th-order reactance. It is a figure which shows the relationship between the average value of the spectrum intensity of a 5th-order reactance, and etching completion time. It is a figure which shows the time-dependent change of the average value of a 5th-order reactance. 3 is a flowchart illustrating a plasma etching method according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Processing chamber 12 Lower electrode 14 Upper electrode 16 1st high frequency power supply 18 2nd high frequency power supply 20 Coil 22 Sensor 24 Data processing part

Claims (5)

A sensor that is provided between the discharge electrode and the high-frequency power source and measures a harmonic component of the reactance of the plasma;
Means for calculating an etching end point time corresponding to the high-frequency component using a predetermined linear function. The plasma etching apparatus according to claim 1, wherein the predetermined linear function is selected from a plurality of linear functions prepared in accordance with a pattern aperture ratio of a metal thin film to be etched. The plasma etching apparatus according to claim 2, wherein the plurality of linear functions include a function in which a gradient of the linear function is substantially 0 with respect to one pattern aperture ratio. The plasma etching apparatus according to claim 1, wherein the sensor measures a voltage related to the plasma, a current, and a phase difference between the voltage and the current. Depending on the pattern aperture ratio of the thin film to be plasma-etched, one linear function is selected from a plurality of linear functions. During plasma etching, the harmonic component of the reactance of the plasma is measured, and the time average value of the measured values is calculated. Calculate
An etching end point time corresponding to the time average value is determined using the one linear function. A plasma etching method, wherein:

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