JP3261660B2 - Monitoring method of etching in dry etching - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method suitable for monitoring the progress of dry etching and detecting the end point of the etching.

[0002]

2. Description of the Related Art Conventionally, as an optical end point detection monitor in a dry etching apparatus, an etching end point for a light shielding film b formed on a substrate a to be etched in a dry etching apparatus as shown in FIG. There is known a method of monitoring the reflectance (or transmittance) of the monitoring area c shown in FIG.
149595).

The dry etching apparatus will be described in more detail. A high-frequency electrode h connected to a high-frequency power source g and a counter electrode i opposed thereto are provided in a vacuum chamber f provided with an exhaust port d and a gas inlet port e. A product substrate a to be etched is placed on the high-frequency electrode h, and a laser beam k from an external light source j is applied to the product substrate a via a beam splitter u in order to measure the reflectance of the monitoring area c. Irradiation is performed, and the reflected light is detected by a recorder r or a meter s via a monochromator m, a photodetector n, an amplifier o, an analog / digital converter p, and a control / calculation unit q. The laser beam k is incident on the substrate a through the vacuum chamber f and the optical window l provided in the counter electrode i, and when detecting transmitted light, the optical window l is also provided in the high-frequency electrode h. Is provided with another set of a beam splitter u, a monochromator m, a photodetector n, an amplifier o, and an analog / digital converter p.

[0004] The product substrate a has a resist pattern formed on a light-shielding film b of a photomask blank, and the end point of the etching process of the light-shielding film b is detected as follows. Light ray k emitted from light source j
Is first split by a beam splitter u, passes through an optical window l, enters a monitoring area c on a product substrate a, and the reflected light from there goes back to the beam splitter u to be monochromated by a monochromator m. It enters photodetector n. The detection signal is amplified by an amplifier o, subjected to signal processing by an analog / digital converter p, enters a control / arithmetic unit q, and sequentially outputs an output signal corresponding to the reflectance of the light shielding film b on the product substrate a. And output to the meter s.
When the light shielding film b on the product substrate a is completely etched, FIG.
When the output signal A does not change as shown in (1), the end point of the etching process is detected.

The etching process of the product substrate a is performed in the following procedure. First, the gas in the vacuum chamber f is exhausted from the exhaust port d by a vacuum pump, and an etching gas is introduced from the gas inlet port e to maintain the gas flow rate and the pressure in the vacuum chamber f at a constant operating pressure. When the power supply g is operated to apply a high frequency of 13.5 MHz to the high-frequency electrode h, plasma is formed in a space between the high-frequency electrode h and the counter electrode i, and the excited reaction gas is incident on the surface of the product substrate a to react. Product board a
The etching of the upper light shielding film b proceeds. During this time, when the end point of the etching is detected by monitoring the reflectance of the product substrate a by the end point detection system, the high frequency power supply h is turned off, the supply of gas is stopped, and the gas in the vacuum chamber f is discharged. a
Nitrogen gas or air is introduced into the inside of the furnace to set the atmospheric pressure, the etched product substrate a is taken out, and the next product substrate a is set.

[0006]

In recent years, ultraviolet exposure methods,
Various methods of forming fine patterns by exposure using a phase shift mask with photolithography techniques such as deep ultraviolet exposure have been tried, but among them, semiconductors such as LSI The following method for etching the substrate of the shifter portion has been proposed as a promising method for improving the quality and performance of the semiconductor device (Japanese Patent Laid-Open No. 2-211450, Kenji Nakagawa et al.).
MICRODEVICES May, p.53-58). As shown in FIGS. 4 and 5, this proposed method uses a phase shift mask in which a shifter portion t is provided on a transparent product substrate a and has a concave portion having a depth d = λ / {2 (n−1)}. Then, FIG.
It is formed by the step (b). In this phase shift mask forming method, the depth d of the shifter portion t is set to λ / ｛2 (n−
1) In order to accurately etch to 0.397 μm (λ is i-line 436 nm, n = 1.46 quartz), for example, first, after etching about 90%, confirm the depth, and then etch the rest. ing. In order to apply the conventional method of measuring the reflectance or transmittance of the light-shielding film to detect the end point of etching to the etching of the shifter portion t of this phase shift mask, light for monitoring is incident on the shifter portion t. Even if an attempt is made to detect a change in reflectance or transmittance due to etching, the amount of light with respect to the reflectance shows only a constant value from the start to the end of etching as shown in FIG. 7, and the end point of etching cannot be detected. This method of reflectance and transmittance was not applied to the detection of the etching end point. This is because the glass substrate is thick, the monitor wavelength spectrum of light normally used reflectance relative field [Delta] [lambda] ₁ (or transmittance) poor wavelength resolution for, because the practice, can not be measured interference effects. JP-A-61-1
Even if the laser diode having a wavelength of 800 nm used in the example of JP-A-49955 is used, the spectrum width is still too wide to work. Therefore, if a gas laser such as a He-Ne laser having high monochromaticity is used as a light source for monitoring, it is expected that the interference effect can be measured even when the substrate is thick, but the accuracy for the etching depth Δd ₁ is δ
Δd ₁ / Δd ₁ ≒ ± ΔJ / J (where J is 4nΔd ₂ /
integer close to lambda _1, lambda ₁ is monitored wavelength ΔJ = 1/3 (if etching end point does not coincide with the extreme value), ΔJ = 1/12
(When the etching end point coincides with the extreme value)), and as shown in Table 1, the monitor wavelength is 633 nm (He-
Ne laser), photo exposure wavelength λ ₂ = 365 nm
(Hgi line), δΔd ₁ / Δd ₁ = 13%, and at the photo exposure wavelength λ ₂ = 248 nm (KrF excimer laser), δΔd ₁ / Δd ₁ = ± 20%, and the necessary shifter depth is required. Accuracy does not fall within ± (3-6)%. This is because there are not many types of practical laser light sources with high wavelength accuracy, and it is difficult to find a laser light source with a measurement wavelength whose reflectance or transmittance just corresponds to the end point of etching. This is because accurate etching accuracy cannot be obtained. In addition, the substrate being etched has a thickness of 64-200 μm at a temperature rise of, for example, 18 ° C. to 55 ° C.
Is also thermally expanded, and the shifter etching depth Δd ₁ corresponding to the exposure wavelength of 248 nm (Kr-F laser) or the exposure wavelength of 365 nm (Hg i line) is about the same as 84.5 nm or 125 nm. Can not.

[0007]

[Table 1]

SUMMARY OF THE INVENTION An object of the present invention is to provide an etching monitoring method capable of accurately etching a substrate to be dry-etched to an arbitrary depth.

[0009]

According to the present invention, a monitor plate is provided on or near a product substrate to be etched in a vacuum chamber of a dry etching apparatus, and a monitor illuminated on the monitor plate is provided. In a method of monitoring the etching amount of a thin film formed on the product substrate by measuring the reflectance or transmittance of light,
Using at least one layer of a thin film of substantially the same material as the substrate material of the product substrate on the monitor plate substrate,
Etching depth [Delta] d ₁ and the etching speed ratio by the etching rate distribution _{C = d 2 / d 1 (} d 1 is the etch rate representative value of the product substrate of the product substrate, d ₂ is the substrate of the substrate material and the material of the product substrate Etching rate when installed at the position of the monitor plate) and the etching rate ratio D = d ₄ / due to the difference in material between the substrate material of the product substrate and a thin film of substantially the same material.
From d ₃ (d ₃ is the etching rate of the product substrate, d ₄ is the etching rate of a thin film of the same material as the substrate material of the product substrate), the etching amount Δd ₂ of the thin film on the monitor plate substrate is Δd ₂
= CDΔd ₁ , and the wavelength λ _{1 of the} monitor light is λ
₁ = 4n ₁ Δd ₂ / J ( n ₁ is the thin film on the monitor plate substrate
Refractive index, J is selected by a positive integer), pre-etching
Before grayed process the thickness d ₅ of the thin film on the substrate for a monitor plate
d ₅ = j ₀ λ ₁ / 4n ₁ (j ₀ is a positive integer equal to or greater than J)
By setting the J-th extreme value as the end point of the etching based on the change in reflectance or transmittance due to the decrease in the thickness of the thin film, the end point of the etching can be reliably detected.

[0010]

[0011]

A monitor light is introduced into a vacuum chamber of a dry etching apparatus through an optical window, and the monitor light is set on a high-frequency electrode or near a product substrate to be etched or formed on the product substrate. Then, the light enters the monitor plate, and its reflectance or transmittance is measured. The etching depth Δd ₁ of the product substrate and the etching rate ratio C = d ₂ / d ₁ based on the etching rate distribution on the high-frequency electrode (where d ₁ is the typical etching rate of the product substrate, and d ₂ is the value of the monitor plate. And the etching rate ratio D = d ₄ / d ₃ due to the difference between the thin film of the product substrate being etched and the thin film of substantially the same material as the substrate of the product substrate formed on the monitor plate. Thus, the etching amount Δd ₂ of the thin film on the monitor plate is determined by Δd ₂ = CDΔd ₁ , and the monitor wavelength λ ₁ is selected by the following equation (4). That is, C = d ₂ / d ₁ (1) D = d ₄ / d ₃ (2) Δd ₂ = CDΔd ₁ (3) λ ₁ = 4n ₁ Δd ₂ / J (J is a positive integer) (4) Then, the monitor wavelength λ ₁ is kept constant, and the J-th extreme value of the reflectance or transmittance of the monitor plate, which is measured as the etching proceeds, is detected, and this is set as the etching end point. Here, n ₁ is the refractive index of the thin film of the monitor plate.

Instead of keeping the monitor wavelength λ ₁ constant and monitoring the temporal change in reflectance or transmittance, the monitor wavelength λ ₁ is constantly changed with the passage of time during the etching process.
Is measured, and the spectral reflectance or spectral transmittance of the monitor plate is measured, and the thin film on the monitor plate is calculated by performing an arithmetic processing in real time based on the extreme wavelength and the number of the reflectance or transmittance. The end point of the etching process can be detected based on the film thickness.

Instead of directly measuring the reflectance or transmittance of a product substrate to be etched, a monitor plate having a thin film of substantially the same material as that of the product substrate, which is significantly thinner than the thickness of the product substrate, is formed. Since the reflectance or transmittance is measured, the thickness of the thin film can be accurately measured even by an optical monitor using a white light source and a monochromator. The end point of the etching of the product substrate can be detected with high accuracy from the proportional relationship with the decrease in the plate thickness.

The optical action of the monitor plate is as follows. The substrate material of the product substrate is transparent glass, and its refractive index is n. The substrate of the monitor plate is a transparent glass or a crystal having a refractive index of n ₂ . In this case, the spectral reflectance R ₁ (λ) of the glass substrate of the product substrate and the spectral transmittance T ₁ (λ) are related by the following equation. λ is the wavelength. R ₁ (λ) = 1−T ₁ (λ) (5) For simplification of description, only one of the reflectance and the spectral reflectance will be described for convenience. First, a conventional example will be considered for comparative explanation. Light is incident on the glass substrate of the product substrate, the refraction angle is i, and the Fresnel coefficient is r, r _1.
Then, "wave optics" (Hiroshi Kubota: pp.62-
65, and pp.199-214, (1984) issued by Iwanami Shoten), the transmittance is given by the following equation. _{T 1 (λ) = (1} -r 2) 2 / (1-2r 2 cosδ 1 + r 1 4) ... (6) Here, [delta] ₁ is given by the phase. δ ₁ = 4πndcosi / λ (7) Hereinafter, for simplicity, it is assumed that the monitor light is perpendicularly incident on the product substrate or the monitor plate. With i = 0 (7)
The formula is as follows: δ ₁ = 4πnd / λ (8) r ² = {(1-n) / (1 + n)} ² (9) T ₁ (λ) is a periodic function of δ ₁ and the phase is δ ₁₁ = πj .. (10) has an extreme value, or the transmittance spectral curve obtained by sweeping the wavelength while keeping the plate thickness constant has an extreme value at the following wavelengths. λj = 4nd / j (11) The interval Δλj between peaks of the spectral curve is given by the following equation.

Δλj = λj−1−λj + 1 (12) or Δλj = 8nd / (j ² −1) (13) The extreme value order j is given by the following equation. j = 4nd / λj ... (14 ) the lambda ₁ and the monitor wavelength, when to be measured near the j-th _{extremum, λj ≒ λ 1 ... (15} ) (13) (14) Δλj from the equation ≒ lambda ₁ ² / {2nd (1-1 / j ² )} (16)

The mountain spectral curve, conditions that can be measured as a mountain is given by the following equation spectral width of the monitor light as [Delta] [lambda] _1. Δλ ₁ ≦ Δλj (17) The thickness of the product substrate usually used for the photomask is d ₆
= 1.5 to 6.35 mm, n = 1.46 for a quartz substrate, and monitor wavelength λ ₁ = 718 nm, j ≒ 12200 to 51650 (18) Δλj ≒ 0.1 to 0.03 nm (19) Combining a white light source and a monochromator In a commercially available optical monitor, Δλ ₁ = 2 to 10 nm (20) is general. Therefore, the conditional expression (17) is not satisfied, and
Therefore, by directly monitoring the product substrate, it is impossible to detect the interference effect of the reflectance and the transmittance due to multiple reflection in the plate. Instead of measuring the reflectance or transmittance of the product board, the wavelength or film of the reflectance or transmittance of the monitor board due to the interference of multiple reflections of a thin film of the same material as the board material of the product board formed on the monitor board Considering the case of monitoring the thickness dependence, it is as follows. In this case, for the sake of simplicity, it is assumed that light is incident on the substrate vertically.

According to the "wave optics", when only one layer of a thin film having substantially the same material as the substrate material of the product substrate is formed on the substrate of the monitor plate, the reflectance R ₂ of the monitor plate is expressed by the following equation. Given. ^{_{R 2 = 1- [4n 1 2}} n 2 / {n 1 2 (1 + n 2) 2 - (n 2 2 -n 1) 2 (n 1 2 -1) sin 2 (δ 2/2)] ... (21 ) δ ₂ = 4πn ₁ d ₅ / λ ₁ (22) where n ₁ is the refractive index of a thin film of substantially the same material as the substrate material of the product substrate, n ₂ is the refractive index of the substrate of the monitor plate, and d ₅ is the thin film. the film thickness lambda ₁ the monitor wavelength (21) is an expression that ignores reflections at the back surface of the substrate of the monitor plate, the reflectance R ₃ also in consideration of back reflection is given by the following equation. R ₃ = R ₂ + (1-R ₂ ) ² R ₄ / (1-R ₂ R ₄ ) (23) where R ₄ = (1-n ₂ ) ² / (1 + n ₂ ) ² (24) dependence on the phase [delta] ₂ or wavelength lambda ₁ or the thickness d ₅ of the reflectance, so essentially the same in the R ₃ and R _2, the value R ₂ will be described ignoring back reflection in the following for simplicity. From the equation (21), the reflectance R ₂ is a periodic function of the phase δ ₂ , and the maximum value R ₂ max or δ ₂ = πj (25) or 4n ₁ d ₅ / λ ₁ = j (26) Take the minimum value R ₂ min. _{R 21 = (1-n 2} ) 2 / (1 + n 2) 2 (j = when an even _{number) ... (27) R 22 =} (n 1 2 -n 2) 2 / (n 1 2 + n 2) 2 (j = When it is odd) (28) And R ₂ min = R ₂₂ , R ₂ max = R ₂₁ (when n ₁ <n ₂ ) (29) R ₂ max = R ₂₂ , R ₂ min = R ₂₁ (When n ₁ > n ₂ ) (30)

When the wavelength λ ₁ is swept and the spectral reflectance is measured while keeping the thickness d ₅ of the thin film of the monitor plate constant,
Λ j = 4n ₁ d ₅ / j (31), and the peak-to-peak interval Δλ j is given by the following equation. Δλj = λj-1-λj + 1 ... (32) or _{Δλj = 8n 1 d 5 / (} j 2 -1) ... (33) Here j is an order of interference is given by the following equation. j ≒ 4n ₁ d ₅ / λ ₁ (34) Here, λ ₁ ≒ λ j (35) was considered. The thickness d ₅ of the thin film of the monitor plate and _{d 5 = 0.4~10μm ... (36)} , the monitor wavelength λ ₁ = 718nm, When _{n 1 = 1.46 j ≒ 3~80 ...} (37) Δλj ≒ 500~18nm … (38) In a commercially available optical monitor combining a white light source and a monochromator, Δλ ₁ = 2 to 10 nm is general from (20), and the conditional expression (17) Δ in which the peak of the spectral curve can be measured as a peak
λ ₁ ≦ Δλ j satisfies 2 to 10 nm <18 to 500 nm (39), which is sufficiently satisfied, and the extreme wavelength of the spectral curve can be accurately measured.

When the reflectance of the monitor plate is measured during the etching process while keeping the monitor wavelength λ ₁ constant, the thickness of the monitor plate becomes d ₅ = jλ ₁ / (4n ₁ ) (40) according to the equation (26). ), The reflectivity shows an extreme value, and the recorder trace with respect to the etching time of the amount of reflected light shows clear peaks and valleys alternately, so that the end point of etching with high accuracy can be detected. Monitoring wavelength lambda ₁ is (3) with respect to the etching depth [Delta] d ₁ of the product substrate (4) so are selected to satisfy the formula, advance _{d 5 = j 0 λ 1 /} (4n 1 to monitor plate (J ₀ : an integer) A thin film is formed to the value of (41), or the film thickness of this thin film is formed in advance in this form, and the reflectance or transmittance shows an extreme value with respect to the monitor wavelength λ ₁ . If the etching is performed as described above, the J-th extreme value counted from j ₀ is set as the end point of the etching, so that the decrease in the thickness of the thin film on the monitor plate is Δd ₂ = Jλ ₁ / (4n ₁ ). 42) The amount of decrease in the thickness of the product substrate can be accurately etched to the target etching depth Δd ₁ by the formula (3) or Δd ₁ = Δd ₂ / (CD) (43).

As the time elapses during the etching process, the monitor wavelength λ ₁ is swept from time to time to measure the spectral reflectance or spectral transmittance of the monitor plate, and the extreme wavelengths λj, λj + of the reflectance or transmittance are measured. based on the number 2m of 2m and extremum wavelength using expression (47), it is possible to calculate the thickness d ₅ of the thin film by performing arithmetic processing in real time. 1 / λ j = j / (4n ₁ d ₅ ) (44) 1 / λ j +2 m = (j + 2 m) / (4n ₁ d ₅ ) (45) is solved with j and d ₅ as unknowns (46) ( 47) is obtained. j = (2mλj + 2m) / (λj−λj + 2m) (46) d ₅ = (mλjλj + 2m) / 2n ₁ (λj−λj + 2m) (47) The substrate of the monitor plate has a refractive index n _21. = N ₂ , an intermediate layer having a refractive index n ₁₁ and a film thickness d ₅₁ = J ₁ λ ₁ / (4n ₁₁ ) (J ₁ is a positive integer) is formed thereon, and the refractive index n ₁₂ =
In a monitor plate on which a thin film having n ₁ and a film thickness d ₅₂ = d ₅ is formed, the reflectance R ₂ of the monitor plate is given by the following equation according to the “wave optics”. R ₂ = 1 + (r ₀ ² −1) (r ₁ ² −1) (r ₂ ² −1) / D ₂ (48) where D ₂ = 1 + (r ₀ r ₁ ) ² + (r ₁ r _{2 ^{) 2 + (r 2 r 0}} ) +2 [r 1 r 2 (1 + r 0 2) cosδ 2 + r 0 r 1 (1 + r 2) 2 cosδ 1 + r 2 r 0 {cos (δ 1 + δ 2) + r 1 2 cos ( δ ₁ −δ ₂ )｝] (49) Considering normal incidence, i ₁ = i ₂ = 0 (50) Therefore, δ ₁ = 2π (2n ₁₁ d ₅₁ cosii ₁ ) / λ ₁ = 4πn ₁₁ d ₅₁ / λ ₁ ... (51) δ ₂ = 2π (2n ₁₂ d ₅₂ cos ₂ ) / λ ₁ = 4πn ₁₂ d ₅₂ / λ ₁ ... (52) d ₅₁ = J ₁ λ ₁ / (4n ₁₁ ) (J ₁ = 1) , 2,...) (53) From (50) (53), δ ₁ = πJ ₁ (54) n ₂₁ = n ₂ , n ₁₂ = n ₁ , n ₁₃ = 1 (55) 48) and (49) are as follows. _{R 22 = 1- (1-r} 0 2) (1-r 1 2) (1-r 2 2) / D 2 ... (56) However _{D 2 = D 2 (1)} + D 2 (2) cosδ 2 ... (57)

[0021]

(Equation 1)

[0022]

(Equation 2)

Δ ₂ = 4πn ₁ d ₅ / λ ₁ (60) r ₀ = (n ₂₁ −n ₁₁ ) / (n ₂₁ + n ₁₁ ) = (n ₂ −n ₁₁ ) / (n ₂ + n ₁₁ ) (61) r ₁ = (n ₁₁ −n ₁₂ ) / (n ₁₁ + n ₁₂ ) = (n ₁₁ −n ₁ ) / (n ₁₁ + n ₁ ) (62) r ₂ = (n ₁₂ −n ₁₃ ) / (N ₁₂ + n ₁₃ ) = (n ₁ −1) / (n ₁ +1) (63) The reflectance given by the equation (56) has the phase δ ₂ similarly to the reflectance given by the equation (21). of a periodic function, (60) since the same form as given phase [delta] ₂ is the phase given by (22) by the formula, the single layer thereto even when a thin film is formed of a multilayer on the monitor plate The description of the same operation as in the case of forming a thin film can be applied. When the thin film of the monitor plate is substantially the same material as the substrate of the monitor plate, when it is considered that n ₁₂ = n ₁ ≒ n ₂ for simplicity, the equation (62) gives r ₁ = (n ₁₁ −n ₂ ). / (N ₁₁ + n ₂ ) = − r ₀ (64), and the equations (56) to (59) are as follows. When J ₁ = even number R ₂₂ = 1− (1−r ₀ ² ) ² (1−r ₂ ² ) / ｛1 + r ₀ ² (2 + r ₀ ² + 4r ₂ ² ) −4r ₀ r ₂ (1 + r ₀ ² ) cos δ ₂ ... (65) J ₁ = time of odd ^{_{R 22 = r 2 2 = (}} n 2 -1) 2 / (n 2 +1) 2 ... (66) i.e., when n ₁ = n _2, J ₁ is an even number , Even if δ ₂ changes, the reflectance is constant and the film thickness cannot be monitored. _{n 1 = n 2 + Δn |} Δn | even = 0.06, the ratio of the value of a measure of reflectance change D ₂ (2) is _{D 2 (2) (J 1} = even number) / D _{2 (2)} (J ₁ = odd number) ≒ 0.03 (67) where J ₁ = odd number has a larger change in reflectance and is easier to monitor. Generally, when J ₁ = odd, R ₂₂ = R ₂₂ max (δ = 0, 2π, 4π,...) (68) R ₂₂ = R ₂₂ min (δ = π, 3π, 5π,...) (68) J _{When 1} = even R ₂₂ = R ₂₂ min (δ = 0, 2π, 4π,...) (69) R ₂₂ = R ₂₂ max (δ = π, 3π, 5π,...) (69) When a monitor thin film of almost the same material as the product substrate is formed on the top layer and a metal thin film is formed immediately below the monitor, the reflectance is `` American Insti
tute of Physics Handbook "(DEGray, 3rd edition)
1982, McGraw-Hill Book Company, pp.6-118-6-123)
Is represented by the following equation. ^{_{R 22 = {r 1 2 +}} r 2 2 -2r 1 r 2 cos (δ 2 -δ 0)} / 1 + r 1 2 r 2 2 -2r 1 r 2 cos (δ 2 -δ 0) ... (70) where r ₁ = (n ₁ −1) / (n ₁ +1) (71) r ₂ = {(n ₁₂ −n ₁ ) ² + k ₂ ² } / {(n ₁₂ + n ₁ ) ² + k ₂ ² } ( _{72) δ 2 = 4πn 1 d} 51 / λ 1 ... (73) δ 0 = tan - 1 {2n 1 k 2 / (n 1 2 -n 2 2 -k 2 2)} ... (74) reflectivity extremum Occurs at δ ₂ −δ ₀ = πj (j = 0, 1, 2,...) (75), and the extreme value is given by the following equation. _{Rmin = (r 1 -r 2)} 2 / (1-r 1 r 2) 2 (j = 0,2,4, ...) ... (76) Rmax = (r 1 + r 2) 2 / (1 + r 1 r 2 ) ² (j = 1, 3, 5,...) (77) When the wavelength λ _{1 is} constant and the film thickness d ₅ of the thin film of the monitor plate decreases, the film thickness becomes d ₅ = (j + δ ₀ / π) λ. ₁ / (4n ₁ )... (78) indicates an extreme value, so that the thickness of the monitor thin film of the monitor plate becomes an extreme value of j = j _{0 in} the same manner as when a single-layer thin film is formed on the monitor plate. Start the etching of the product substrate from the corresponding place, J of the reflectance of the monitor thin film of the monitor plate
If the end point is detected and the end point is detected, the decrease in the thickness of the monitoring thin film is also given by equation (42), and the etching depth of the product substrate is given by equation (43). Etching can be performed with high accuracy.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A dry etching apparatus used for carrying out the method of the present invention will be described with reference to FIG. 8. In FIG. 8, reference numeral 1 denotes a vacuum chamber having an exhaust port 2 and a gas inlet 3 connected to a vacuum pump. As shown in FIG.
High-frequency electrode 5 and counter electrode 6 facing the high-frequency electrode 5
And a product substrate 7 to be etched is placed on the high-frequency electrode 5. Reference numeral 8 denotes an insulating material for supporting the high-frequency electrode 5, reference numeral 9 denotes a coupling capacitor, and the counter electrode 5 is grounded.

A light-shielding film as shown in FIG. 4 is provided on the surface of the product substrate 7, and this light-shielding film is removed by dry etching. At this time, in order to monitor the end point of the etching, On the high-frequency electrode 5 near the product substrate 7 to be processed or on the surface of the product substrate 7
As shown in FIG. 9, a monitor plate 10 is provided,
At 1, the reflectance (or transmittance) of the monitor plate 10 was monitored. This monitoring is performed by the monitor light 13 from the light source 12.
Is performed by an optical system that measures reflected light or transmitted light. In the vacuum chamber 1, the high-frequency power supply 5 and the counter electrode 6, an optical window 14 for transmitting the monitor light 13 is provided at one or several places so that their axes are aligned.

The configuration of the optical system itself is the same as that of the conventional optical system shown in FIG. 1. A monitor light 13 from a light source 12 is applied to a monitor plate 10 via a beam splitter 15, and the reflected light is transmitted to a monochromator 16 by a monochromator 16. Detector 17, amplifier 1
8, analog / digital converter 19, control / arithmetic unit 20
Through the recorder 21 or the meter 22. The control / arithmetic unit 20 includes a beam splitter 23, a monochromator 24, and a photodetector 2 for detecting transmitted light from the monitor plate 10.
5, an optical system including an amplifier 26 and an analog / digital converter 27 is provided as necessary. These optical systems are provided for a specific monitoring area 11. 28 is a display unit.

The operation of this apparatus is different from that of FIG. 1 in that the monitoring of the etching of the product substrate 7 is performed by the monitor plate 10, and the reflected light (or transmitted light) of the monitor plate 10 during the etching of the product substrate 7 is different. Goes back to the beam splitter 15 and is made monochromatic by the monochromator 16, and an output signal corresponding to the reflectance is detected by the recorder 21 or the meter 22 via the photodetector 17 or the like. The end point of the etching can be known from the periodic change of the output signal.

An example of implementing the method of the present invention using the apparatus shown in FIG. 8 will be described in detail below. In the following examples,
As shown in FIG. 10, the monitor plate 10 is formed by forming a thin film 10b (hereinafter, also referred to as a monitor thin film) having substantially the same material as that of the substrate of the product substrate 7 on the substrate 10a of the monitor plate 10. As shown in FIG.
And the monitor thin film 10b having an intermediate layer 10c between the monitor substrate 10a and the monitor thin film 10b, and as shown in FIG. The formed one was used. FIG.
The substrate 10a of the monitor plate 10 is preferably a transparent glass or a crystal.
0a is a transparent glass or crystal, the intermediate layer 10c is a transparent thin film having a different refractive index from the monitoring thin film 10b,
The film thickness d ₇ is formed as follows: d ₇ = J ₁ λ ₅ / 4n ₃ d ₇ (79). In the configuration of FIG. 12, the intermediate layer 10c is a light shielding film such as a metal thin film. Is preferred.

First Embodiment A monitor plate 10 having the structure shown in FIG. 10 was used in the apparatus shown in FIG. The substrate 10a of the monitor plate 10 has a refractive index n ₂
= 1.61, high refractive index glass with a thickness of 2 mm and 30 mm square (SK-1
On a surface of the substrate 10a, a vacuum deposited film of SiO ₂ having substantially the same material as the product substrate 7 and a refractive index of n = 1.48 was formed to a thickness of 1476 nm while monitoring the film thickness with an optical monitor.

The measured value of the etching rate of the product substrate 7 and the etching rate ratio of the substrate made of the same material as that of the product substrate 7 at the position where the monitor plate 10 is installed is C = d ₂ / d ₁ = 0.9.
3. The etching rate of the SiO ₂ thin film of substantially the same material as the substrate of the product substrate 7 on the monitor plate 10 and the etching rate of the substrate of the product substrate are substantially the same, and D = d ₄ / d ₃ = 1. Was.

Based on the values of C and D, the monitor wavelength and the like were set as shown in Table 2. The product substrate 7 is a thin film as shown in FIG. 5 (g) on a synthetic quartz substrate having a thickness of 6.35 mm and a square of 152 mm, and has a phase shift pattern as shown in FIG. 4 and an etching depth Δd ₁ = 397 nm. In order to perform the etching process, the reflectivity of the monitor plate 10 is monitored during the etching process of the product substrate 7, and the reflectance is 5 minutes from the start of the etching.
The etching was stopped at the end point of the second extreme value. Subsequent to the first etching process, a second etching process was performed using the same monitor plate 10.
FIG. 13 shows an example of a recorder chart of the amount of reflected light versus time on the monitor plate 10. A transmission measurement was performed simultaneously with the reflection measurement, and a trace similar to that of FIG. 13 was obtained.

The gas used for etching is CF ₄ , the flow rate is 100 sccm, the pressure is 0.1 Torr, the supply frequency to the high frequency electrode 5 and the power density are 13.56 MHz and 0.25 Watt / cm ² , respectively. The distance between the electrodes is 60 mm. The etching time is 21 minutes, and the average etching rate d ₁ on the product substrate 7 is 1
The etching rate d ₂ of the thin film on the monitor plate 10 in the monitoring area 11 was 8.7 nm / min and 17.4 nm / min. The accuracy of the etching depth of the shifter portion of the product substrate 7 is as follows: δ (Δd ₁ ) / Δd ₁ = ± 3% for a predetermined depth Δd ₁ = 397 nm.
Was in the range.

Second Embodiment Using the same product substrate 7 as in the first embodiment and the monitor plate 10 used twice in the first embodiment, etching was performed under the same arrangement and the same etching conditions. During the etching process so that the monitor light 13 hits the center of the monitor plate 10, the monitor wavelength is swept every 6 seconds, and the spectral reflectance (relative value) in the wavelength range of 300 to 700 nm is measured. 20 to read the extreme wavelength of the reflectance and the number of the extreme wavelength in real time by 20 and perform an arithmetic processing to output the thickness of the thin film of the monitor plate 10 to the display unit 28 and the recorder 21;
An end point signal was output at a set predetermined thickness.

The reflectance curve measured at each sampling time is as shown in FIG. 14. After elapse of 10 minutes, each interval Δλj between peaks is close to λj = 547 nm and Δλj = 188 n
m. The used spectrometer has a measurement range of 220 to 800 nm,
The detection element is a photodiode array, and has a measurement wavelength spectrum width Δλ ₁ = 2 nm and a wavelength accuracy δλ = ± 0.5 nm. The measurement time was about 4 seconds until the display of the analysis result.

The actual etching depth is δ (Δd ₁ ) /
Δd ₁ = ± 5%. Subsequent to the first etching process, a second etching process was similarly performed. The calculation of the thickness d ₅ of the thin film of the monitor plate, (4
6) Equation (47) was used.

Third Embodiment Under substantially the same product substrate 7 and etching conditions as in the first embodiment,
The etching process and the etching amount of the monitor plate 10 having the structure shown in FIG. 11 were monitored. The monitor plate 10 was provided on a part of the product substrate 7 as shown in FIG. The photo exposure wavelength λ ₂ of the product substrate 7 is 248 nm, and the target shifter portion etching depth Δd ₁ is 270 nm. As the substrate 10a of the monitor plate 10, the substrate itself of the product substrate 7 was used, and a 10 mm square region of a part of the product substrate 7 was used as the monitor plate 10. The ZnS vapor deposited film as the intermediate layer 10c has an optical thickness n ₃ d ₇ of λ ₁ for a monitor wavelength λ ₁ = 532 nm.
/ 4 wavelength thickness, that is, d ₇ = 58 nm. The uppermost thin film 10b for monitoring is made of substantially the same material as the substrate material of the product substrate 7.
An SiO ₂ deposited film having an optical thickness of n ₁ d ₅ = 18.
It formed in the lambda _1/4 i.e. d ₅ = 540 nm. Table 2 shows the refractive index and other details of these thin films.

In the etching process of the product substrate 7 as in the first embodiment, the monitor plate 10 provided on the product substrate 7
The change over time in the reflectivity of the sample was monitored and 3
The etching was stopped at the end point of the second extreme value. Subsequent to the first product substrate etching, second to sixth etching processes were performed using the same monitor plate 10. The recorder chart of the amount of reflected light versus time on the monitor plate 10 is the same as that of FIG. 13, and the difference between the peak and the valley of the amount of reflected light is almost eight times that of the first embodiment. The accuracy of the etching depth of the shifter portion of the product substrate 7 is the predetermined depth Δd ₁
= 270 nm, it was in the range of δ (Δd ₁ ) / Δd ₁ = ± 4%. Fourth Embodiment A monitor plate 10 having the same configuration as that of the first embodiment and having the structure shown in FIG. 12 is mounted on the high-frequency electrode 5 near the product substrate 7 as shown in FIG. 9 to monitor the etching process. Was. Photo exposure wavelength λ ₂ = 365n for product substrate 7
m, the desired shifter etching depth is Δd ₁ = 397 n
m. The monitor wavelength λ ₁ = 546 nm. The monitor plate 10 has an optical thickness of an SiO ₂ vapor deposited film of substantially the same material as the substrate of the product substrate 7 as a monitor thin film 10 b on the monitor plate 10.
₁ d ₅ = _{λ 1/4} HachoAtsu, i.e. d ₅ = is formed to a thickness of 92 nm, to immediately below, as an intermediate layer 10c for shielding
A two-layer film in which a Cr vapor-deposited film is formed to a thickness of d ₇ ≒ 102 nm is superposed three times, and a total of six layers are formed on a substrate 10a of a monitor plate 10 having a thickness of 2 mm and a 30 mm square made of a blue plate. Things. Table 2 shows the optical constants and other details of the intermediate layer 10c.

[0038]

[Table 2]

During the etching process of the product substrate 7, the change over time in the reflectance of the monitor plate 10 placed on the high-frequency electrode 5 is monitored, and the reflectance of the fourth extreme value from the start of etching and the reflectance of the Cr intermediate layer 10c is monitored. The etching was terminated with the point where the amount of reflected light became constant corresponding to the end point as the end point. The etching conditions for the quartz substrate of the product substrate 7 are almost the same as those in the first embodiment. Prior to the second etching process, the Cr film as the intermediate layer 10c was removed by etching to expose the monitoring thin film 10b. The gas used for etching the Cr film was CH ₂ Cl ₂ (dichloromethane)
And a mixture of oxygen O ₂ at flow rates of 25 sccm and 75 sccm, respectively.
It is. The pressure is 0.3 Torr. The supply frequency and the power density to the high frequency electrode 5 are 13.56 MHz and 0.25 Watt / cm ² , respectively. The distance between the electrodes is 100 mm, the etching time is about 5 minutes, and the etching rate of the Cr film is 260 nm / min. C
r Using the monitor plate 10 from which the film is removed by etching to expose the SiO ₂ deposited film, the product substrate 7 to be etched
Was placed in the vacuum chamber 1 to perform a second product etching process. The monitoring of the etching process and the etching depth is exactly the same as the first time. Following the second product etching, the Cr film was removed by etching, and
A second product etching process was performed. The accuracy of the etching depth of the shifter portion of the product substrate 7 is the predetermined depth Δd ₁
= 397 nm, it was within the range of δ (Δd ₁ ) / Δd ₁ = ± 3%. The recorder trace in which the output proportional to the amount of reflected light was recorded with respect to time was the same as in FIG. 13, and the difference between the peaks and valleys in the amount of reflected light was about 10 times that of the first embodiment. In the above embodiment, instead of directly irradiating the product substrate 7 with monochromatic light and measuring the interference effect on the product substrate 7 itself, the interference effect of the thin film 10b of the monitor plate 10 is measured. The peak-to-peak interval Δλj of the curve (referred to as a spectral curve) indicating the wavelength dependence of the spectral reflectance or the spectral transmittance increases as is clear from equation (16),
Becomes sufficiently larger than the spectral width Δλ ₁ of the monitor light,
Conditions Δλ1 interference effect can be measured <Δλj ... (17) comes to satisfy the equation, when measuring the temporal change in reflectivity by the monitoring wavelength lambda ₁ constant crests as shown in Figure 13 in an etching process Is obtained, and a film thickness d corresponding to the reflectance or the transmittance extreme value is obtained.
₅ is given in the same form as in equation (40) for the first, third and fourth embodiments, and the thickness reduction Δd ₂ is given in the same form as in (42). The thickness decrease Δd ₁ of the product substrate 7 is calculated from the thickness decrease Δd ₂ of the monitor thin film 10b and the equation (3). The extreme values of the reflected light quantity of the recorder trace indicating the temporal change of the reflected light quantity are (2) in the first, third, and fourth embodiments, respectively.
7) to (29), calculated from the values of (65) and (68), (76) and (77), the extreme values of the reflectance are as shown in Table 3, and the measurement results of the examples. Matches. In the second embodiment, the film thickness was calculated from the peak and valley wavelengths of the transmittance spectral curve using Equation (47).

[0040]

[Table 3]

In contrast to the required shifter etching depth accuracy, for example, δΔd ₁ / Δd ₁ <0.05 (80), the expected accuracy in the conventional example is δΔd ₁ / Δd ₁か ら from equations (11) and (12). _{(4d 8 δλ / Δd 1 λj} ) is _{(1 + 2nd 8 / mλj)} ... (81), in the second embodiment _{δΔd 1 / Δd 1 ≒ (4d} 5 δλ / Δd 1 λj) (1 + 2nd 5 / mλj) ... ( 82). Here, δλ is the measurement wavelength accuracy. Conventionally, since the thickness of the product substrate itself is monitored, when the wavelength is swept and the thickness is determined from the extreme value wavelength, δΔd ₁ / Δd ₁に 対 し て12000… (83), which does not satisfy the expression (80). In the second embodiment, δΔd ₁ / Δd ₁ ≒ 0.02 (84), which sufficiently satisfies the required accuracy of Expression (80). (83)
And in calculating the (84) _{equation, Δd 1 = 397nm, λj ≒} 500nm, n = 1.46 ... (85) in common, d ₈ = 6.35 mm for the prior art example (8 1), [delta] [lambda] = 0.1 nm, m = 40 ... with (86), in the second embodiment was used (8 2) d ₅ = 738 nm for expression, δλ = 0.5nm, m = 3 ... (87).

Next, the effect of the thermal expansion on the measurement of the etching depth is examined. The thermal expansion coefficient (linear expansion coefficient) of the product substrate 7 is α ₁ , and the monitor is made of the same material as that of the product substrate. Assuming that the thermal expansion coefficient of the thin film 10b is α ₂ , and the temperature rises during the etching of the product substrate 7 and the monitoring thin film 10b are ΔT ₁ and ΔT ₂ , respectively, the thickness change Δdth due to thermal expansion.
₁ and the film thickness change Δdth ₂ are given by the following equations. ? Dth with respect to the conventional example _{1 = α 1 d 8 ΔT 1} ... (88) Example respect _{Δdth 2 = α 2 d 5 ΔT} 2 ... (89) as a numerical example _{α 1 ≒ α 2 ≒ 5.5 ×} 19 - 7 / ℃ .. (90) ΔT ₁ ≒ ΔT ₂ ≒ 10-100 ° C. (90) Δd ₁ = 397 nm (90) d ₈ = 6.35 mm (90) d ₅ = 738 nm (90) Δdth ₁ ≒ 35~350nm, or Δdth ₁ / Δd ₈ = 0.09~
0.9 In the embodiment, Δdth ₂ ≒ 0.004 to 0.4 nm, or Δdth ₂ / Δd ₈ = 1
× 10 ^{- 5} ~1 × 10 ^- becomes ^4, in the conventional example and the error of the etching depth increases place which is not practical due to thermal expansion, free from practically the influence of thermal expansion in the embodiment.

In the second embodiment, the thickness of the monitor thin film is calculated from the extreme wavelength of the spectral curve. However, the measured spectral curve is compared with a theoretical spectral curve for a previously assumed film thickness. Data processing may be performed so that the film thickness that best fits the measured value. In the third embodiment, the change in the amount of reflected light is measured while keeping the monitor wavelength constant. However, the change in the amount of transmitted light may be measured. Other transparent dielectrics may be used in place of the ZnS interlayer of the monitor plate in this example. Even if the configuration of the monitor plate is as shown in FIGS. 11 and 12, the wavelength may be swept and the film thickness may be calculated from the spectral curve as in the second embodiment. In the fourth embodiment, the reflectance is measured by monochromatic light. However, the spectral width is the widest, or the wavelength may be any cheap light source such as a light emitting diode, or the monochromator may be omitted. Is also good. Further, in this example, each film of the monitoring thin film is formed by forming the optical film thickness n ₁ d ₅ to be 4/4 wavelength thick of the monitor wavelength λ ₁ , but the wavelength thickness is an integral multiple of λ _1. For example, 2 to 10λ ₁
May be used.

[0044]

As described above, according to the present invention, instead of directly measuring the reflectance or transmittance of a product substrate, it is used for a monitor which is made of the same material as that of the product substrate and which is extremely thin compared to the thickness of the substrate. Since the reflectance or transmittance of the monitor plate on which the thin film is formed is measured, even if an inexpensive light source or a monochromator with a relatively wide monitor wavelength spectrum width is used, the peaks of the spectral curve are clearly separated. The end point of the etching can be detected without being affected by the change in the thickness of the product substrate due to the thermal expansion of the product substrate. Therefore, it is possible to produce a phase shift mask with high accuracy.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an etching monitoring device of a conventional dry etching device.

FIG. 2 is a plan view of the product substrate of FIG. 1;

FIG. 3 is a diagram showing a change in the amount of reflected light in a dry etching process.

FIG. 4 is an enlarged sectional view of a phase shift mask.

FIG. 5 is an enlarged plan view of an application pattern of a phase shift mask.

FIG. 6 is an explanatory view of a step of forming a phase shift mask.

FIG. 7 is a diagram showing a change over time of a reflection amount of a product substrate in a conventional dry etching process.

FIG. 8 is an explanatory diagram of an etching monitoring device of a dry etching device used for carrying out the present invention.

FIG. 9 is a plan view of the product substrate of FIG. 8;

FIG. 10 is an enlarged sectional view of a monitor plate used for carrying out the present invention.

FIG. 11 is an enlarged sectional view of another monitor plate used for implementing the present invention.

FIG. 12 is an enlarged cross-sectional view of another monitor plate used for implementing the present invention.

FIG. 13 is a measurement diagram of the amount of reflected light according to an embodiment of the present invention.

FIG. 14 is a diagram illustrating the measurement of the amount of transmitted light in the example of the present invention.

[Explanation of symbols]

Reference Signs List 1 vacuum chamber 5 high-frequency electrode 6 counter electrode 7 product substrate 10 monitor plate 10a
Monitor board substrate 10b Thin film of the same material as the substrate material of the product substrate

Claims (4)

(57) [Claims] 1. A monitor plate is provided on or near a product substrate to be etched in a vacuum chamber of a dry etching apparatus, and the reflectance or transmittance of monitor light applied to the monitor plate is measured to measure the reflectance of the product substrate. In the method of monitoring the etching amount of the formed thin film, a monitor plate obtained by forming at least one thin film having substantially the same material as the substrate material of the product substrate on the monitor plate substrate is used as the monitor plate. And an etching rate ratio C = d ₂ / d ₁ based on the etching depth Δd ₁ and the etching rate distribution of the product substrate (d ₁ is a typical etching rate of the product substrate, and d ₂ is a substrate having the same material as the substrate material of the product substrate). Rate at the position of the monitor board) and an etching rate ratio D = difference between the material of the product substrate and the thin film having substantially the same material.
From d ₄ / d ₃ (d ₃ is the etching rate of the product substrate, d ₄ is the etching rate of the thin film of the same material as the substrate material of the product substrate), the etching amount Δd ₂ of the thin film on the monitor plate substrate is Δd ₂ = CDΔd ₁ , the wavelength λ of the monitor light
₁ is λ ₁ = 4n ₁ Δd ₂ / J ( n ₁ is on the monitor plate substrate
Refractive index of the thin film, J is selected by a positive integer), advance d
Before the etching process, the thickness of the thin film on the monitor plate substrate
The d ₅ to _{d 5 = j 0 λ 1 /} 4n 1 (j 0 is J or more positive integer)
In addition, an etching monitoring method in dry etching, wherein a J-th extreme value is set as an end point of etching based on a change in reflectance or transmittance due to a decrease in the thickness of the thin film. 2. A monitor plate, wherein a part of the product substrate is used as a monitor plate substrate, and a thin film having substantially the same material as the substrate material of the product substrate is formed on the monitor plate substrate. 2. The method for monitoring etching in dry etching according to claim 1, wherein: 3. The monitor plate according to claim 1, wherein a monitor substrate having an optical constant different from that of the product substrate and one thin film of substantially the same material as the substrate material of the product substrate are formed on the monitor substrate. An etching method in the dry etching according to claim 1. As claimed in claim 4 wherein said monitor plate, the thickness of the J _1/4 wavelength of the of the monitor light film having different film the refractive index of the product substrate on a substrate for a monitor board (J ₁ is an odd number) 2. The dry etching method according to claim 1, wherein a thin film having substantially the same material as that of the product substrate is formed thereon.