JPH0494533A - Detection of film thickness to be etched, film thickness detector, and etcher - Google Patents

Abstract

PURPOSE:To enable high-precision detection of the thickness of a remainder of a film to be etched by irradiating a film to be etched with laser light to detect variation in light intensity caused by interference of light beams reflected from the bottom and top faces of the film. CONSTITUTION:The periodical variation in light intensity is calculated by detection of variation in light intensity caused by interference of laser beams reflected from the bottom and top faces of a film to be etched W. Next, reference time t2 is made of a point of time when any of the maximum and minimum values of light intensity and the maximum and minimum values of variations with time of light intensity are reached. The thickness d1 of the film to be etched W at this reference time t2 is operated, and further etching amount alphat after the reference time t2 is determined. This process enables high-precision detection of the thickness D of a residual of a film to be etched W which is being etched.

Description

[Detailed Description of the Invention] [Summary] Regarding a film thickness detection method, a film thickness detection device, and an etching device for a film to be etched, the purpose is to accurately detect the film thickness of a film being etched. After irradiating the film to be etched with a laser beam, detecting the change in light intensity due to the interference of the light reflected from the lower and upper surfaces of the film, and calculating the periodic change in the light intensity, the periodic change in the light intensity is calculated. The etching rate before the reference time is calculated by setting the time when the light intensity reaches either the maximum value or the minimum value in the change, or the maximum value or the minimum value of the amount of change over time of the light intensity as a reference time. , calculate the film thickness of the film to be etched at the reference time from the wavelength of the laser beam and the refractive index of the film to be etched, and then integrate the time measured from the reference time and the etching rate to determine the etching rate at the reference time. The method includes detecting the thickness of the film to be etched after the reference time by determining the amount of etching from the reference time and subtracting the etching amount from the film thickness at the reference time.

[Industrial application field]

The present invention relates to a method for detecting the thickness of a film to be etched, a thickness detecting device, and an etching device.

[Conventional technology]

In the process of manufacturing semiconductor devices, when a film grown on a semiconductor substrate is etched using an etching device, a method has been proposed to check the etching state by detecting the wavelength of the emission spectrum of the gas generated by etching. Since the wavelength depends on the composition of the film to be etched, this method is only used to detect the end point of etching by a change in wavelength.

Therefore, in Japanese Patent Application No. 1-129513, the present applicant proposed a method of irradiating a film to be etched with laser light and detecting the amount of etching by utilizing the interference of the reflected light.

In this method, a light-transmissive film to be etched, such as a SiO□ film, is irradiated with laser light in a vertical direction.

The device is configured to detect the amount of etching removal by examining changes in intensity due to interference of light reflected from the bottom and top surfaces of the etching film.

[Problem to be solved by the invention]

By the way, when growing a film to be etched, film forming conditions are set so as to obtain the desired film thickness, but slight differences in the conditions may cause errors in the film thickness.

For this reason, when trying to detect the film thickness during etching, there is a problem in that it is not possible to accurately measure the film thickness by simply checking the amount of etching.

The present invention has been made in view of these problems, and provides a method for detecting the thickness of a film to be etched, a film thickness detecting device, and an etching device that can accurately detect and manage the thickness of a film being etched. The purpose is to provide

(Means for Solving the Problems) The above problems are achieved by irradiating the film being etched with a laser beam, detecting the change in light intensity due to the interference of the light reflected from the lower and upper surfaces of the film, and detecting the changes in the light intensity. After calculating the periodic change in intensity, the point in time when the periodic change in light intensity reaches either the maximum value or minimum value of the light intensity, or the maximum value or minimum value of the amount of change over time in the light intensity is the reference point. At times, the etching speed before the reference time is calculated, and the thickness of the film to be etched at the reference time is calculated from the wavelength of the laser beam and the refractive index of the film to be etched, and then the etching speed is calculated from the wavelength of the laser beam and the refractive index of the film to be etched. The etching amount from the reference time is determined by integrating the time measured from the time and the etching rate, and the etching amount is subtracted from the film thickness at the reference time to determine the etching amount of the film to be etched after the reference time. A method for detecting the film thickness of a film to be etched, characterized by detecting the film thickness, or as illustrated in FIG. means for detecting a change in light intensity due to interference of light reflected from a lower surface and an upper surface and calculating a periodic change in the light intensity; and a maximum value and a minimum value of the light intensity in the periodic change in the light intensity. LMIN, maximum value Δ of the amount of change in the light intensity over time;
means for detecting any two of lAX, minimum value Δ, and lIH; means for calculating the etching rate α between the two time points Ll and L2; and the later of the two time points 1. The film thickness d of the film W to be etched at
1 from the wavelength λ of the laser beam and the refractive index n of the film W to be etched;
! After calculating the etching amount crt from the later time point t2 by integrating the time t measured from the later time point t2 and the etching rate α, the film thickness d1 at the later time point is determined.
A method for detecting the thickness of a film to be etched, characterized in that the method comprises means for detecting the remaining film thickness of the film to be etched W after the late time point t2 by subtracting the etching amount crt from Alternatively, as illustrated in Fig. 1.2, a laser beam is irradiated onto a film W to be etched during etching, and changes in light intensity due to interference of light reflected from the bottom and top surfaces of the film W are detected. means for calculating a periodic change in the light intensity; a maximum value of the light intensity in the periodic change in the light intensity; AX;
Minimum value L, N, maximum value Δ of the amount of change over time in the light intensity
, AX, any two time points t of the minimum value ΔMIN,
, t, and means for detecting said two time points j+, LxO
means for calculating an etching rate α between the etching points, and calculating a film thickness d of the film W to be etched at time t2, which is the later of the two points, from the wavelength λ of the laser beam and the refractive index n of the film to be etched 1w. and means for determining the two time points L.
L, L! After calculating the etching amount αL from the late time point L2 by integrating the time t measured from the later time point t2 and the etching rate α, the etching amount αL is subtracted from the film thickness d1 at the later time point L2. By doing so, the means for detecting the remaining film thickness of the film to be etched W at the late time point L2, and the means for detecting the remaining film thickness of the film to be etched W at the time point when the remaining film thickness coincides with the target film thickness D0. This is achieved by an etching apparatus characterized by having means for stopping the etching process.

[Function] According to the present invention, after detecting changes in light intensity due to interference of laser beams reflected from the lower and upper surfaces of Iw to be etched and calculating periodic changes in light intensity, the maximum value of the light intensity is calculated. 14All, the minimum value L□0, the maximum value Δ□0, or the minimum value Δ111% of the amount of change in light intensity over time is reached as the reference time t! Then, calculate the etching speed before this reference time L2, calculate the film thickness d1 of the film to be etched W at the reference time t-, and then integrate the elapsed time L from the reference time t2 and the etching speed α. The etching amount αL after the reference time L2 is calculated, and the film thickness of the film to be etched W after the reference time t2 is detected by subtracting this etching amount "t" from the film thickness d1 at the reference time L2. .

In this case, as shown in FIG. 2, the etched lI! W
When the laser beam is completely etched, the intensity due to the interference of the reflected laser beam reaches its maximum, so the maximum value of the light intensity L
MAX, the minimum value L68, the maximum value ΔMAX and the minimum value ΔDIN of the amount of change over time in the light intensity can be easily calculated, so if the etching amount αt is investigated based on this, the etching amount αt can be calculated. The thickness of the remaining amount of etching film W can be detected with high accuracy.

Therefore, even if an error occurs in the thickness of the film W to be etched when it is grown, the thickness of the film during etching can be controlled with high precision.

〔Example〕

Therefore, the details of the present invention will be explained below based on the drawings.

(a) Description of the first embodiment of the present invention Fig. 1 is a block diagram of an apparatus showing the first embodiment of the present invention, in which reference numeral 1 denotes an etching device for etching a film such as a SiO□ film. This etching apparatus 1 has a herger 4 having a gas inlet 2 and an exhaust port 3, a support electrode 5 provided at the bottom of the herger, and a counter electrode 6 provided at the top thereof. It is configured to etch a film W to be etched on a semiconductor substrate A placed on a support electrode 5.

Reference numeral 7 denotes an optical fiber for irradiation that is exposed and attached from the center of the counter electrode 6, one end surface of which is connected to the semiconductor laser 8, and the other end surface of which is placed toward the film W to be etched on the support electrode 5. The light with the wavelength λ emitted from the irradiation optical fiber 7 is reflected from the upper and lower surfaces of the film to be etched W, and enters the light receiving element 10 through the light receiving optical fiber 9 adjacent to the irradiation optical fiber 7. It is configured.

Reference numeral 11 denotes a film thickness detector that detects the film thickness of the film to be etched W based on the output signal of the light receiving element 10. circuit 13, reference time calculation circuit 14, etching speed calculation circuit 15, reference time film thickness calculation circuit 16, time measurement circuit 17
, remaining film thickness calculation circuit 18 and etching stop command circuit 1
It has 9.

The light intensity/time characteristic calculation circuit 12 described above is shown in FIG.
), the amount of change over time in the light intensity due to the interference of the laser beams reflected from the upper and lower surfaces of the film W to be etched, respectively, is detected based on the output signal of the light receiving element 10. The sine wave characteristics shown in Figure (b) are obtained using techniques such as Fourier transform, and the maximum value of the light intensity is determined. , , *It is configured to detect the small value LMIN, the maximum value Δ, 8, and the minimum value ΔHIM of the slope of the sine wave. In this case, the intensity of the reflected light reaches its maximum because the phases of the interference lights match when the film thickness of the etching target 1w becomes zero.

Further, the passing setting circuit 13 detects when the light intensity reaches the maximum #1LHAX based on the output of the light receiving element 10, and when etching progresses, the light intensity reaches the maximum value at first and 1. IAX
The reference time setting circuit 4 is configured to determine the point in time when 1. is reached as the passing time L1. Etching progresses from then on, and the signal from the light receiving element 10 reaches the minimum light intensity value L.
The configuration is such that the time point when +si++ coincides with the reference time t2 is determined.

In this case, when passing 1. The time from the time to the reference time L2 is 1/2 period (T/2) of the sine wave.

The etching speed calculation circuit 15 calculates the etching speed of the film W to be etched, and calculates the film thickness d0 etched from the passing time t1 to the reference time t2, and also calculates the etching thickness d0 from the passing time t1 to the reference time t2. The time from t to reaching the reference time t2 (t
z −t+> and calculate the etching rate α (α=do
/ (tz−t+)). In this case, the wavelength of the laser beam is λ, and the etching target WI
If the refractive index of W is n, then 1. -1. The film thickness d0 to be etched in between is determined from the equation d++=λ/4n. Also, when passing 1. The film thickness at is d − m
It can be calculated from the formula λ/2n, where m is an integer, and is determined by taking into account the intended film thickness and the error range when forming the film to be etched, for example, the wavelength of the laser beam. When the film thickness is 670 nm and the refractive index is 1.45, when the film to be etched W is stacked to a thickness of about 300 nm, m becomes "l".
And, when the thickness is about 500 nm, m is "
2".

The reference time film thickness calculation circuit 16 calculates the reference time 1. This is to calculate the remaining film thickness d of the film to be etched W at the reference time L.
2 is the minimum value, and in the case of 4IN, the interference light is in the most destructive state, so the amount can be found by the formula d, = (m1/2)λ/2n, and the difference from the maximum value L MAX is λ/
4 n.

The remaining film thickness calculating circuit 18 calculates the film thickness of the film W to be etched, which is being etched.
The etching amount αt after the reference time t2 is obtained by multiplying the elapsed time t from the reference time L2 outputted from 7 and the immediately preceding etching speed α, and the etching amount αt is subtracted from the film thickness d1 at the reference time t2. It is configured such that the value obtained is the remaining film thickness.

The etching stop command circuit 19 is connected to the etching control circuit 2.
0, and outputs a stop signal when the film thickness calculated by the remaining film thickness calculating circuit 18 matches the film thickness D0 that is to be left in the end. It is configured as follows.

In the figure, reference numeral 21 indicates a gas supply device that supplies etching gas to the gas supply port 2, 22 indicates an exhaust pump connected to the exhaust port 3, and Rf indicates a high frequency power source connected to the support electrode 5. There is.

Next, a method of detecting the remaining film thickness using the above-described embodiment apparatus will be described.

First, after attaching the semiconductor substrate A on which the film to be etched W is laminated to the support electrode 5, the pressure inside the bell jar 4 is reduced, an etching gas is supplied therein, and a high frequency voltage is applied to the support electrode 5. Etching of the etching film W is started (FIG. 3(a)).

Then, the film to be etched W is passed through the irradiation optical fiber 6.
When the film is irradiated with a laser beam (FIG. 3(b)), the light is reflected from the lower and upper surfaces of the film, and the interfering light enters the light receiving element 9 through the light receiving optical fiber and is converted into an electrical signal.

In this state, as etching progresses, the phase of the reflected light from the upper surface of the film to be etched changes, and the light intensity changes over time due to interference with the reflected light from the lower surface. Then, the light intensity/time characteristic calculating circuit 12 examines the amount of change and calculates the relationship between the light intensity and time by Fourier transform or the like, and obtains the sine wave characteristic as shown in FIG. 2(b). Figure 3 (C)
). In this case, when the film thickness becomes zero, the reflected light that interferes with each other becomes stronger, so the light intensity reaches the maximum value L MAX
becomes.

Thereafter, the passing setting circuit 13 detects the point in time when the intensity of the light reflected from the upper and lower surfaces of the thinned film W to be etched reaches the maximum value L WAX based on the output data of the light receiving element 10. , when passing this time 1. (Fig. 3(e)).

Next, the reference time setting circuit 14 detects the point in time when the intensity of the light reflected from the film W to be etched, which has further progressed in etching, reaches the minimum value Hl,l (FIG. 3(f)), and sets this time as the reference time. Set as t2.

After this, the etching speed calculation circuit 15 calculates 1. Let d be the time from to the reference time L2 and the film thickness d0 etched during that time. -λ/4n, and the etching rate α(α-do/(tz L+
)) is calculated (30th (8)).

Next, the film thickness calculation circuit 1 calculates the film thickness d1 of the film to be etched W at the reference time L2 when the light intensity reaches the minimum value LHIN.
6, while the reference time t is determined by the clock circuit 17.
Measure the elapsed time from 2 (Figure 3 (h), (i)
).

After this, the remaining film thickness calculating circuit 18 calculates the reference time t2.
The subsequent etching amount αt is subtracted from the film thickness d, and this value is taken as the remaining film thickness of the film to be etched W (see Fig. 3).
D).

Then, when the remaining film thickness matches the target film thickness D0, the etching stop command circuit 19 starts the etching control circuit 2.
In order to output an etching stop signal to 0, the etching control circuit 20 sends a signal to the gas supply device 21 and the high frequency power source Rf to stop the supply of gas and electric power (FIG. 3(k),
(jlri). This completes the etching.

Here, the above embodiment will be explained by giving a specific example.

For example, when forming a SiO
□When etching is performed while irradiating the film perpendicularly, the intensity of the reflected light changes due to interference as the film thickness decreases.

The degree of change in this reflected light over time was measured and the results were shown in Figure 2 (b).
), the maximum value LTIAX and the minimum value L□8 of the light intensity of the reflected light are determined, and the time when the actual measured value of the light intensity becomes L□8 is defined as the time of passage tl. Then, the time when the etching progresses further and the measured value of the light intensity reaches LNIN is defined as a reference time t2.

Here, the etching amount d0 from passing time t to reference time t2 is d, = λ/4 n = 115 nm, and if the etching time is 2 minutes, before the actual measured value of light intensity reaches L918. The etching rate α is α''-57,
The speed is 5 nm/min.

On the other hand, the film thickness d1 at the reference time t2 is d+ = (ml/
2) Determined by λ/2n, the initial film thickness is approximately 250
1, so if the integer m is 1, it becomes d-115 nm.

After this, when 15.78 seconds have passed from the reference time t2, the etching amount αt becomes 15, so the remaining film thickness is 15.78 seconds.
The thickness is 100n, which corresponds to the target film thickness. Etching may be stopped at this point.

In addition, in this example, the light intensity is the maximum value L MA
Although the time point at which the light intensity reaches X is defined as the passing time t, the time point at which the amount of change over time in the light intensity reaches its maximum value, that is, the time when the slope of the sine wave reaches the maximum value ΔWAX, can also be defined as the passing time.

When the slope becomes the maximum value ΔMAX or the minimum value LMIN, the light intensity becomes (LHAX-L□)/2, so the etching amount from the passing time t to the reference time t2 is λ/8 n
Therefore, the calculation is easy.

(b) Description of other embodiments of the present invention According to the embodiments described above, since the etching rate before the minimum value LMIN is checked and the film thickness is detected from the state of minimum 4aLMIH, the minimum value LHIN is reached. If the previous film thickness cannot be measured, in this case, use the following method.

That is, as shown in FIG. 2(c), the maximum value MAX is set as the reference time t2, and the minimum value L□8 or the minimum value ΔHIM of the slope before the maximum value LWAX is set as the passing time t. When passing 1. Etching speed α between t2 and reference time t2
Find out the maximum value. , to find the film thickness of l,
It becomes possible to measure the film thickness after the point when it reaches the maximum (!LxAx).

Note that the above reference time 1. took the maximum or minimum value of the light intensity, but the slope is the maximum value Δl'lAX, the minimum value (+[L
The time point when □8 can be set as the reference time t2, and the maximum value LMAX and minimum value LIIIN of the light intensity before that can be set as the passing time L+.

In this way, when determining the passing time t1 and the reference time t2, which one of the maximum value, the minimum value, the maximum value of the amount of change over time, and the minimum value of the light intensity in the periodic change of the light intensity is determined. It is sufficient to select two points in time, define the earlier point as the passing time, and set the subsequent point in time as the reference time L2.

〔Effect of the invention〕

As described above, according to the present invention, after detecting changes in light intensity due to interference of laser beams reflected from the lower and upper surfaces of the film to be etched and calculating periodic changes in light intensity, the maximum value of the light intensity is , the minimum value, the maximum value, or the minimum value of the amount of change over time in the light intensity is set as the reference time, and the etching rate before this reference time is calculated, and the lI of the film to be etched at the reference time is calculated. After calculating JN, the amount of etching after the reference time is calculated by integrating the elapsed time from the reference time and the etching speed, and the amount of etching after the reference time is calculated by subtracting this etching amount from the film thickness at the reference time. Since the film thickness of the etched film is detected, the maximum value, minimum value of light intensity, maximum value of the amount of change in light intensity over time,
By checking the etching amount based on the time point when the minimum value is reached, the thickness of the remaining amount of the film to be etched can be detected with high accuracy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an apparatus according to an embodiment of the present invention, and FIG. 2 is a sectional view showing a film to be etched by the apparatus according to an embodiment of the present invention, and the intensity of light reflected from the film to be etched. FIG. 3, a characteristic diagram showing an example of the relationship between time and time, is a flowchart showing a method according to an embodiment of the present invention. (Explanation of symbols) 1... Etching device, 2... Gas supply port, 3... Exhaust port, 4... Herger 5... Support electrode, 6... Counter electrode, 7... Optical fiber for irradiation, 8... Laser, 9... Fiber for light reception, 10... Light receiving element, 11... Film thickness detector, 12... Light intensity/time characteristic calculation circuit, 13... - Passing time setting circuit, 14... Reference time setting circuit, 15... Etching speed calculation circuit, 16... Reference time film thickness calculation circuit, 17... Timing circuit, 18... Remaining film thickness Arithmetic circuit, 19... Etching stop command circuit, 20... Etching controller.

Claims (3)

[Claims] (1) After irradiating the film to be etched during etching with laser light, detecting changes in light intensity due to interference of light reflected from the lower and upper surfaces of the film, and calculating periodic changes in the light intensity, the maximum value of the light intensity in the periodic change of the light intensity;
The etching rate before the reference time is calculated by setting the time when the light intensity reaches either the minimum value, the maximum value, or the minimum value of the amount of change over time of the light intensity as a reference time, and the wavelength of the laser light and the etching rate are calculated. Calculating the film thickness of the film to be etched at the reference time from the refractive index of the etching film, and then calculating the etching amount from the reference time by integrating the time measured from the reference time and the etching rate; A method for detecting the thickness of a film to be etched, characterized in that the thickness of the film to be etched after the reference time is detected by subtracting the etching amount from the film thickness at the reference time. (2) means for irradiating the film to be etched during etching with laser light, detecting changes in light intensity due to interference of light reflected from the lower and upper surfaces of the film, and calculating periodic changes in the light intensity; the maximum value of the light intensity in the periodic change of the light intensity;
means for detecting any two of the minimum value, the maximum value, and the minimum value of the amount of change over time of the light intensity; means for calculating the etching rate between the two time points; means for calculating the film thickness of the film to be etched at the later of the two time points from the wavelength of the laser beam and the refractive index of the film to be etched; and a time measured from the later of the two time points and the etching rate; means for detecting the residual film thickness of the film to be etched after the late time point by integrating the values to obtain the etching amount from the late time point, and then subtracting the etching amount from the film thickness at the late time point. A film thickness detection device for a film to be etched, characterized by comprising: (3) means for irradiating the film to be etched during etching with laser light, detecting changes in light intensity due to interference of light reflected from the lower and upper surfaces of the film, and calculating periodic changes in the light intensity; the maximum value of the light intensity in the periodic change of the light intensity;
means for detecting any two of the minimum value, the maximum value, and the minimum value of the amount of change over time of the light intensity; means for calculating the etching rate between the two time points; means for calculating the film thickness of the film to be etched at the later of the two time points from the wavelength of the laser beam and the refractive index of the film to be etched; and a time measured from the later of the two time points and the etching rate; After calculating the amount of etching from the late point in time, the remaining thickness of the film to be etched after the late point in time is detected by subtracting the etching amount from the film thickness at the late point in time. An etching apparatus comprising: means; and means for stopping the etching process of the film to be etched when the remaining film thickness matches a target film thickness.