JP2606923B2 - Dry etching method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is suitable, for example, for manufacturing a semiconductor device using a so-called polycide film having a two-layer structure in which a refractory metal silicide film and a polysilicon film are stacked. The present invention relates to a dry etching method to be performed and an apparatus therefor.

[Conventional technology]

Conventionally, a polysilicon film has been widely used as a gate electrode material of a MOS transistor, but recently, as shown in FIG. 7, a two-layer structure in which a high melting point silicide film 4 and a polysilicon film 3 are laminated. The so-called refractory metal polycide film (hereinafter referred to as “polycide film”) has been used. This is because the sheet resistance of the polycide film is about one order of magnitude smaller than that of the conventional polysilicon film, thereby increasing the circuit operation speed and achieving high-speed access of the device. This takes into account the stability of the interface with the film. In FIG. 7, 1 is a silicon substrate, 2
Is a gate oxide film.

The polycide film exhibits properties very similar to the polysilicon film, and can be etched by dry etching using a Freon-based gas. In the dry etching of the polycide film, generally, the end point of the etching is detected using an etching monitor using a fluorine-based emission spectrum.

[Problems to be solved by the invention]

However, since the polycide film has a two-layer structure of the lower polysilicon film 3 in contact with the gate oxide film 2 and the like and the refractory metal silicide 4 laminated on the polysilicon film 3, the polycide film is dry-etched. When the patterning is performed by the method described above, the side portion of the polysilicon film 3 becomes tapered as shown in FIG.
As shown in FIG. 8 (2), a problem such as the so-called undercut state of the polysilicon film 3 as the lower film often occurs with respect to the refractory metal silicide film 4 as the upper film. Becomes As described above, when the polysilicon film 3 in contact with the gate oxide film 2 is not properly etched, a desired voltage cannot be applied to the gate of a MOS transistor or the like, or a desired voltage cannot be applied to the gate. Problems such as an inability to obtain an operation speed occur.

A cause of the poor etching of the polycide film is a variation in impurity concentration in the polysilicon film 3 which is a lower layer film of the polycide film. That is, phosphorus is usually diffused in the polysilicon film 3 to reduce its sheet resistance. However, the etching rate and the side etching amount of the polysilicon film 3 change depending on the phosphorus concentration. is there. The etching rate is the amount of decrease in the polysilicon film per unit time, and the side etching amount is the lateral etching rate per unit time, that is, the ratio of the polysilicon film 3 to the high melting point silicide film 4 in FIG. It means the amount of undercut.

FIG. 9 shows the dependency of the etching rate of the polysilicon film on the phosphorus concentration by a curve l1, and the dependency of the side etching amount on the phosphorus concentration by a curve l2. This ninth
From the figure, it is understood that the etching rate changes almost in proportion to the phosphorus concentration in the polysilicon film, and the amount of side etching sharply changes in a substantially quadratic curve with the increase in the phosphorus concentration in the polysilicon film. It can be seen that it increases.
As described above, since the amount of side etching greatly changes due to the change in the phosphorus concentration in the polysilicon film, it is difficult to stably etch the polycide film to have the ideal cross-sectional shape shown in FIG. It's not easy.

An object of the present invention is to solve the above-mentioned technical problems and to provide a dry etching method and a device capable of contributing to improvement of element characteristics of a semiconductor device or the like.

[Means for solving the problem]

The dry etching method of the present invention detects an emission spectrum intensity of an impurity in a film to be etched, calculates an impurity concentration in the film to be etched based on the emission spectrum intensity, and performs etching conditions corresponding to the impurity concentration. Is set.

Further, the dry etching apparatus according to the present invention includes a detecting means for detecting the emission spectrum intensity of the impurity in the film to be etched, a calculating means for calculating the impurity concentration in the film to be etched based on the output of the detecting means, Control means for setting the etching conditions in response to the output of the means.

[Action]

According to the configuration of the present invention, the impurity concentration in the film to be etched is calculated from the emission spectrum intensity of the impurity in the film to be etched, and the etching conditions corresponding to the impurity concentration are set. Etching can be favorably performed by setting optimum etching conditions for the film to be etched.

〔Example〕

FIG. 1 is a conceptual diagram showing a basic configuration of a dry etching apparatus according to one embodiment of the present invention. In this embodiment, a so-called high-melting-point metal polycide film (hereinafter referred to as a "polycide film") having a two-layer structure in which a high-melting-point metal silicide film and a polysilicon film to be etched are laminated, for example, by the structure shown in FIG. Dry etching) is performed. The dry etching apparatus of this embodiment is:
A processing chamber 11 in which a semiconductor substrate or the like on which the polycide film is formed is placed; and a detection unit 12 that detects the emission spectrum intensity of phosphorus added as an impurity in the polysilicon film using, for example, a polarizing filter; Calculating means 13 for calculating the phosphorus concentration in said polysilicon film based on said emission spectrum intensity given from means 12
And a control means 14 for setting optimum etching conditions (over-etching time in this embodiment) in accordance with the output of the calculating means 13.

FIG. 2 is a characteristic diagram showing the dependence of the emission spectrum intensity of fluorine and the emission spectrum intensity of phosphorus on the phosphorus concentration in the polysilicon film when the polysilicon film is subjected to dry etching using a chlorofluorocarbon gas. In FIG. 2, a curve IF indicates the dependency of the emission spectrum intensity of fluorine on the phosphorus concentration, and a curve IP indicates the dependency of the emission spectrum of phosphorus on the phosphorus concentration.

As shown by the curve 1F, the emission spectrum intensity of fluorine decreases with an increase in the phosphorus concentration. However, this is because the etching rate increases with the increase in the phosphorus concentration as shown by a curve 11 in FIG. This is due to an increase in the consumption of fluorine radicals, and has no direct relationship with the phosphorus concentration in the polysilicon film. On the other hand, as shown in the curve IP, the emission spectrum intensity of phosphorus is directly affected by the phosphorus concentration in the polysilicon film. Therefore, if the etching condition of the polysilicon film is controlled based on the intensity of the emission spectrum of phosphorus, optimization of the etching condition can be realized with high accuracy.

FIG. 3 and FIG. 4 are cross-sectional views showing the state of dry etching of the polycide film by the structure shown in FIG. In FIGS. 3 and 4, parts corresponding to the respective parts shown in FIG. 7 described above are denoted by the same reference numerals. Reference numeral 5 denotes a photoresist patterned on the polycide film. Using the photoresist 5 as a mask, the polycide film is patterned by dry etching.

3 and 4, the state of processing of the polycide film is illustrated in chronological order from (1). In the case of FIG. 4, the phosphorus concentration in the polysilicon film 3 is higher than the phosphorus concentration in the polysilicon film 3 of FIG. 3, and FIGS. 4 (1) to (5) show FIGS. The elapsed time from the start of etching substantially corresponds to (1) to (5). That is, when the etching of the polycide film using the polysilicon film 3 having a relatively low phosphorus concentration and the etching of the polycide film using the polysilicon film 3 having a relatively high phosphorus concentration are simultaneously started, the phosphorus of the polysilicon film 3 is not changed. At the time when the concentration is low, the state shown in FIG. 3 (3) is reached, and the phosphorus concentration is high, the state shown in FIG. 4 (3).

FIG. 5 is a diagram showing a temporal change in the emission spectrum intensity of phosphorus during dry etching. FIG. 5 (1) corresponds to the case of FIG. 3 (when the phosphorus concentration is relatively low).
FIG. 2 corresponds to the case of FIG. 4 (when the phosphorus concentration is relatively high). FIG. 6 shows the time change of the emission spectrum intensity of fluorine. FIG. 6 (1) corresponds to the case of FIG. 3, and FIG. 6 (2) corresponds to the case of FIG. Yes, it is.

First, the case of FIG. 3, that is, the case where the phosphorus concentration of the polysilicon film 3 is relatively low will be described. At time t1 in FIGS. 5 (1) and 6 (1), dry etching is started, and etching of the refractory metal silicide film 4 is started. Accordingly, the emission spectrum intensity of phosphorus increases during the period from time t1, and the emission spectrum intensity of fluorine decreases due to consumption of fluorine radicals. Then, the respective emission spectrum intensities are as shown in FIG.
In the period until time t2 when the state shown in the figure is reached, the value becomes a certain value.

During the period from time t2, the etching of the polysilicon film 3 is started, and the emission spectrum intensity of phosphorus increases due to the phosphorus contained in the polysilicon film 3 to be etched. The emission spectrum intensity of fluorine decreases according to the etching rate of the polysilicon film 3. From time t2, through the state shown in FIG.
In the period until time t3 when the polysilicon film 3 shown in FIG. 3 (4) is removed by etching, each emission spectrum intensity has a certain value.

In the period from time t3, over-etching is performed, whereby the tapered portion on the side of the polysilicon film 3 is removed, and the state shown in FIG. 3 (5) is obtained.

In the case shown in FIG. 4, that is, when the phosphorus concentration of the polysilicon film 3 is relatively high, the respective emission spectra of phosphorus and fluorine show similar changes. That is, the etching of the refractory metal silicide film 4 starts at time T1 in FIGS. 5 (2) and 6 (2), and the state shown in FIG. 4 (2) is obtained at time T2. Then, from time T2, the etching of the polysilicon film 3 is started, and at time T3, the state shown in FIG. Further, by performing over-etching for an appropriate period during the period from time T3, the state shown in FIG. 4 (4) is obtained. If the over-etching time is set to the same length as that of FIG. 3, the polysilicon film 3 is undercut as shown in FIG. 4 (5). This is because the amount of side etching depends on the phosphorus concentration in the polysilicon film 3 as described above.

The period between times t1 and t2 in FIGS. 5 (1) and 6 (1) corresponds to the period between times T1 and T2 in FIGS. 5 (2) and 6 (2). Since the refractory metal silicide film 4 is etched, there is no difference between the emission spectrum intensities of phosphorus and fluorine.

The period between times t2 and t3 corresponds to the period between times T2 and T3, during which the polysilicon film 3 is etched. For this reason, the emission spectrum intensity of phosphorus is strongly affected by the phosphorus concentration in the polysilicon film 3. Further, since the etching rate of the polysilicon film 3 increases as the phosphorus concentration increases, when the phosphorus concentration is high, the consumption of fluorine radicals increases, and the emission spectrum intensity of fluorine decreases. . At this time, the emission spectrum intensity of phosphorus has an extremely high value under the influence of both the high etching rate and the high phosphorus concentration. That is, during the period (t2 to t3, T2 to T3) during which the etching of the polysilicon film 3 is performed, a large level difference ΔP (FIG. 5) is generated in the emission spectrum intensity of phosphorus, and the emission spectrum intensity of fluorine is relatively small. A small level difference ΔF (sixth
Figure) occurs. Further, since the etching rate is higher when the phosphorus concentration is higher, the time T2 is higher than the time t2 to t3.
The period of ~ T3 is shorter.

As described above, the emission spectrum intensity of phosphorus greatly changes according to the phosphorus concentration in the polysilicon film 3, and the time required for etching the polysilicon film 3 changes. Therefore, conversely, it is possible to calculate the phosphorus concentration in the polysilicon film 3 from the length of the period in which the polysilicon film 3 is etched and the emission spectrum intensity of phosphorus during this period.

In this embodiment, based on the output from the detecting means 12 for detecting the intensity of the emission spectrum of phosphorus, a period (t2
To t3, T2 to T3) (or etching start time t1, T1)
From the time t3 to the end time t3, T3 of the etching of the polysilicon film 3), and the detecting means 12 in this period.
, The concentration of phosphorus in the polysilicon film 3 is calculated. For example, in the calculating means 13, a certain reference value regarding the emission spectrum intensity of phosphorus is determined, and a difference between this reference value and the output of the detecting means 12 is calculated, for example.
Calculation of the phosphorus concentration is performed.

The calculation result (phosphorus concentration in the polysilicon film 3) by the calculation means 13 is given to the control means 14. This control means 14
An over-etching time corresponding to the phosphorus concentration in the polysilicon film 3 is set to control the etching process. As a result, the etching is completed in the processing chamber 11 in the optimum state shown in FIG. 3 (5) or FIG. 4 (4).

As described above, in this embodiment, when etching the polysilicon film 3, the phosphorus concentration in the film which greatly affects the etching rate and the side etching amount of the polysilicon film 3 is determined by the light emission of phosphorus in the processing chamber 11. Quantitatively determined by detecting the spectral intensity, and set an over-etching time corresponding to the phosphorus concentration,
The processing chamber 11 is so-called feedback controlled. As a result, the etching process of the polysilicon film 3 is performed favorably, and problems such as undercut of the polysilicon film 3 in the polycide film can be prevented. Thereby, in a semiconductor integrated circuit or the like using the polycide film, the circuit operation can be performed well.

In the above-described embodiment, the polysilicon film applied to the polycide film has been described as an example of the film to be etched. However, in the present invention, dry etching is performed on a film whose etching rate or side etching amount changes depending on the impurity concentration. It can be widely applied to cases.

Further, in the above-described embodiment, an example in which the over-etching time is controlled as the etching condition has been described.
Control of other etching conditions may be performed.

〔The invention's effect〕

As described above, according to the present invention, the impurity concentration in the film to be etched is calculated from the emission spectrum intensity of the impurity in the film to be etched, and the etching conditions corresponding to this impurity concentration are set. Can be favorably performed by setting the optimum etching conditions for the film to be etched.

As a result, for example, in a semiconductor integrated circuit or the like, its electrode wiring and the like can be formed favorably.
The desired circuit operation can be reliably achieved, and the characteristics of the element can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a basic configuration of a dry etching apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram showing the emission spectral intensities of phosphorus and fluorine during dry etching of a polysilicon film. FIG. 3 and FIG. 4 are cross-sectional views showing a time series of a dry etching process of a polycide film, and FIG. 5 is a time chart of the emission spectrum intensity of phosphorus at the time of dry etching of a polycide film. FIG. 6 is a diagram showing the temporal change of the emission spectrum intensity of fluorine, FIG. 7 is a cross-sectional view showing the structure of the polycide film, and FIG. 8 is a diagram showing the dry etching of the polycide film successfully performed. FIG. 9 is a cross-sectional view showing a case where no polysilicon film was formed. FIG. It is a characteristic diagram showing. 11 processing chamber, 12 detection means, 13 calculation means, 14
... Control means

Claims (2)

(57) [Claims] An emission spectrum intensity of an impurity in a film to be etched is detected, an impurity concentration in the film to be etched is calculated based on the emission spectrum intensity, and an etching condition is set in accordance with the impurity concentration. A dry etching method characterized in that: A detecting means for detecting an emission spectrum intensity of an impurity in the film to be etched; a calculating means for calculating an impurity concentration in the film to be etched based on an output of the detecting means; A dry etching apparatus comprising: a control unit for setting an etching condition by performing the etching.