JPS6263430A - Method for detecting end point - Google Patents

Abstract

PURPOSE:To eliminate a waste of development work time by specifying the spot diameter of a laser beam applied, thereby enabling the end point of the development work in the process for fabricating semiconductor devices to be detected accurately. CONSTITUTION:The laser beam having exited from a laser transmitter portion 7 is applied through a projection fiber cord 3 to the surface of a photoresist film 1c with a spot of a 0.5mm-10mm diameter. If applied with a spot with a 0.5mm-10mm diameter, for instance, the spot ranges over a wide area, and even if the applied site deviates in either upward, downward, left or right direction, the proportion of the portion from which the photoresist is removed to the whole portion of be applied does not vary, and thus the level of change in the amount of the received light is constant. Moreover, the amount of the reflected light is sufficient for the analysis of change of the light strength for detecting the end point with a diameter of this range. With this, the accurate development end point can be detected with a spot of a 0.5mm-10mm diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting the formation end point of a circuit pattern in four semiconductor device manufacturing steps.

[Prior art]

Photolithography technology is used to create semiconductor devices such as integrated circuits.

This involves forming a layer of the material to be etched on the substrate, then coating the surface layer with photoresist, exposing the circuit pattern, and developing this to expose exposed areas (or unexposed areas) of the photoresist layer. portion) to form a circuit pattern. Next, this is immersed in a corrosive liquid to etch away the areas where the surface photoresist has been removed, exposing the layer of the underlying material.Finally, the photoresist on the surface layer is removed to form a predetermined area. It forms a circuit pattern.

Therefore, it is important for work management to detect the progress of development or corrosion when forming a circuit pattern using a corrosive substance, that is, whether or not development or corrosion has been completed to the underlying surface.

However, in the past, there was no way to directly detect the end point of photoresist development, and development was performed for a time determined from experience.
It was just corroding.

For this reason, it is possible to make the wrong decision to discontinue these operations even though development and corrosion have not yet been completed, or conversely, to continue working even though development and corrosion have already been completed, thereby reducing time efficiency. There were drawbacks such as poor performance. Therefore, an application for an end point detection method applicable to development end point detection has been filed by the applicant of the present invention (Japanese Patent Application No. 84053/1983). This end point detection method is summarized as follows.

When laser light, which is coherent light, is projected onto the film to be removed,
The light reflected from the front surface and the light reflected from the back surface interfere, but as the thickness of the surface layer changes due to progress of development and corrosion, the degree of interference between the two emitted lights, that is, the light intensity of the reflected light, changes over time. change. When the film is completely removed due to the progression of development 2 corrosion, the intensity of the reflected light remains constant because the coherent light is reflected only from the surface of the underlying layer. Therefore, it is possible to detect the end point of development and corrosion by detecting the light intensity of the reflected light over time and analyzing the light intensity data over time. FIG. 3 shows the change over time in the reflected light intensity, and the end point is when the amount of change remains unchanged for a certain period of time.

[Problem that the invention seeks to solve]

FIG. 4 is a schematic diagram showing the circuit pattern of a semiconductor device. In the figure, the parts surrounded by solid lines are the parts where the photoresist remains (therefore, the etching target layer remains), and the parts not surrounded are the parts surrounded by solid lines. It represents the portion where the photoresist is removed (therefore, the layer to be etched is removed).

Now, to explain the case of developing a photoresist, if the spot diameter of the laser irradiation light is small, the results shown in Fig. 4 a, b,
The spot will be as shown in c.

If the laser beam is irradiated onto the portion where the photoresist is to be removed as shown in 3, the photoresist film thickness will change over time, so the end point of development can be detected based on the above-mentioned theory.

However, it is practically impossible to always set the irradiation area at the same position on the pattern, so the spot may straddle the area where the photoresist remains and the area where the photoresist is removed, as shown in b, or the area where the photoresist is removed. This may result in a spot where only the remaining photoresist is irradiated. In case b, the ratio of the portion of the photoresist removed to the entire irradiated area differs depending on the irradiated area, so the level of change in the amount of received light fluctuates greatly, and since there is less interference light than in case a, the signal width of the change in received light varies. becomes small and the accurate end point cannot be detected. In the case of C, all the spots belong to the area where the photoresist remains and the photoresist film thickness does not change over time, so the above theory cannot be applied at all and it is impossible to detect the end point.

On the other hand, if the spot diameter of the laser irradiation light is large, the amount of irradiation light per unit area of the irradiated area will decrease, resulting in a decrease in the amount of reflected light, which poses a practical problem in that changes over time in the intensity of the reflected light cannot be detected. .

[Means for solving problems]

The present invention was made in view of the above circumstances, and its purpose is to irradiate coherent light onto a film at a spot with a diameter of 0.5 to 10 cm and utilize the interference effect of light. The purpose of this invention is to propose a method that can accurately detect the end point of circuit pattern formation of a semiconductor device, such as development or Ws etching.

An end point detection method according to the present invention is an end point detection method for detecting the end of a process of partially corroding a film to form a circuit pattern of a semiconductor device.
．． It is characterized by detecting the remaining coating thickness by irradiating 5 to 10 fin spots and detecting the change in light intensity due to mutual interference between the light reflected from the surface of the coating and the light reflected from the back surface. .

〔Example〕

The present invention will be described below based on drawings showing embodiments thereof.

FIG. 1 is a schematic diagram of the configuration of an apparatus for implementing the end point detection method according to the present invention. In FIG. 1, l indicates a semiconductor device in the manufacturing process, and a layer 1b to be etched is formed on a substrate la.
is deposited, and a photoresist B11e is formed on top of it. The semiconductor device 1 is immersed in a developer (not shown).

The optical fiber probe 2 having its tip above the semiconductor device 1 is provided with a light emitting fiber cord 3 and a light receiving bundle fiber cord 4 therein. The tip end surface of each of the light-receiving bundle fiber cords 4 corresponds to the tip end surface of the optical fiber probe 2. The proximal end of the light projecting fiber cord 3 is connected to a laser transmitter 7 that includes a collimator lens 5 and a laser transmitter 6 therein. The laser beam emitted from the laser transmitter 6 is adjusted to an appropriate diameter by a collimating lens 5, and is irradiated onto the photoresist film IC surface via a light projection fiber cord 3.

The light-receiving bundle fiber cord 4 is connected to a laser receiver 11 that includes a photodetector 8, a light intensity calculator 9, and an end point indicator 10 therein.

Then, the reflected light from the front and back surfaces of the photoresist film 1c mutually interfere with each other, and the combined light enters the photodetector 8, and its intensity is recorded over time by the light intensity calculator 9. The end point of development is detected by arithmetic processing of the record based on , and the end point is displayed on the end point display lO.

Next, we will explain the principle that the thickness of the photoresist film 1c can be detected and the end point of development can be detected by detecting the change in light intensity due to mutual interference of the reflected light from the front and back surfaces of the photoresist film 1c. do.

Two waves ul =3. cos(kx-ωtL'f
:! =a2cos(kx -ωt), and if they are superimposed through different optical paths Z,, a2, then if the composite wave is U, then u=ul+L12 -alcos (k (x+7!, ) -ωt l+
82Co! i (k (x+62) -ωt)-a
Ieos ((kx-ωt)+!!,)+a2
eos ((kx-ωt) +kI12)=(a
(coskll l+a2coskj!2) eos
(kx-ωt)-(alsjnkj21 +32sj
nkl12) sin(kx −ωt), so the composite wave U
The amplitude of is 1u12- (aleosk!!1 +a2cosk1
2) 2+ (a1sfnk!!1 +a2'5fnkj
! 2) 2,=a, 2 +a22 +2ala2cos (k/1-kI12) where a
If y-32=a, then u2=2a2 (1+cosk(mm J2))・=
(i) - The optical path difference (j!2-I!+) is the second
From the figure (schematic diagram showing the state of reflection of laser light on the photoresist film 1e), 112-1! , 1-n (AC+CA') -AN where AC-CA' -d /cos rAN= 2d
tanr ・sinθ (However, the reflection angles on the front and back surfaces of the photoresist film IC are γ and θ, respectively, and the film thickness of the photoresist film IC is d.) From Fresnel's formula, sin (l sinθ sin (π/2−γ ) cos γ means COS γ COS γ nd = −−2nd sin T CO3γ Here, since the laser beam is incident almost perpendicularly to the photoresist film IC surface, γ−〇 becomes 1! 2 1 I−
2nd - (2) (2) to 411
If substituted into, u2 = 2a2 (1Ieos Znkd), that is, thickness d
The intensity of the combined light of the light reflected from the surface of the photoresist film and the light reflected from the back surface of the photoresist film reaches a maximum value every time the value changes by λ/2n. Therefore, the film thickness can be detected by analyzing changes in the intensity of light received by the photodetector 8.

FIG. 3 shows the laser receiving section 11 obtained by the light intensity calculator 9.
It is a change diagram of the light intensity level of. When development is started, as time passes, the photoresist film 1c is changed so that the film thickness of the photoresist film 1c becomes maximum each time it changes by λ/2n (n: IfU refractive index) as shown in FIG. The light intensity changes depending on the speed at which 1c decreases. In other words, if the developing speed becomes faster, the time between maximum peaks becomes shorter, and conversely, if the developing speed becomes slower, the time between peaks becomes longer. When the photoresist film 1c disappears, that is, when development is completed, no interference occurs, no change in light intensity occurs, and the slope of the change in light intensity becomes 0 (point a in Figure 3), so this point is the development end point. Detected as.

Next, the spot diameter of the irradiation laser, which is the main part of the present invention, will be explained. When irradiating with a spot smaller than y4 sooμm, the proportion of the photoresist removed in the entire irradiated area easily changes depending on the irradiated area (Fig. 4 a, b, c), so the light receiving pattern It is difficult to accurately detect the end point, especially if the spot is contained in a region where the photoresist remains (Figure 4C). On the other hand, when irradiating with a spot diameter larger than 10 mm, the amount of irradiated light per unit area in the irradiated area decreases, and changes over time in the light intensity of reflected light cannot be detected, making it impossible to detect the end point. It is.

On the other hand, if the spot is irradiated with a diameter of 0.5 to 10, the spot will span a wide area as shown in Figure 4 (d), and even if the irradiated area is shifted in any direction, up, down, left, or right. , the ratio of the area where the photoresist is removed to the entire irradiated area does not change, and the level of change in the amount of light received is constant. Further, the amount of reflected light is sufficient for analysis of light intensity changes for detecting the end point with a diameter within this range. Therefore, it is possible to accurately detect the development end point with a spot having a diameter of 0.5 mm to 10 mm.

Therefore, the spot diameter of the irradiated laser beam is set to a diameter of 0.5 to 10 degrees by adjusting the distance between the tip end surface of the light projecting fiber cord 3 and the surface of the fi-1 resist film 1c.

The laser light emitted from the laser transmitter 7 passes through the light emitting fiber cord 3 and is applied to the surface of the photoresist ll*IC with a diameter of 0.
Irradiation is performed at a spot of 5 mm to 10 mm.

The combined light of the reflected light from the front surface of the photoresist film IC and the reflected light from the back side is detected by the photodetector 8 via the light-receiving bundle fiber cord 4, and the light intensity pattern of the combined light is determined by the light intensity. The photoresist film thickness is then measured from the light intensity pattern based on the principle described above, the end point of development is detected, and the end point indicator 10 is recorded.
The development end point is displayed.

〔effect〕

As detailed above, in the method according to the present invention, by setting the spot diameter of the irradiated laser beam to 0.5 mm to 10 mm, the end point of the developing operation in the semiconductor device manufacturing process can be accurately detected, so that the developing operation time can be reduced. There is no waste. Further, the present invention has excellent effects such as preventing the risk of proceeding to the next step with incomplete development.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the configuration of an apparatus for carrying out the method according to the present invention, Fig. 2 is a schematic diagram showing the state of reflection of laser light on the front and back surfaces of the photoresist film, and Fig. 3 is a temporal change in received light intensity. FIG. 4 is a schematic diagram showing a circuit pattern of a semiconductor device. 1c... Photoresist film 2... Optical fiber probe 3... Fiber cord for light emission 4... Bundle fiber cord for light reception 5... Collimator lens 7
...Laser receiving section 11...Laser receiving section patent
Applicant Dainichi Nippon Electric Cable Co., Ltd. Agent Patent Attorney Noboru Kono Smile 2 Times 3 Concave X 4 Country

Claims (1)

[Claims] 1. An end point detection method for detecting the end of a process of partially corroding a film to form a circuit pattern of a semiconductor device, comprising: applying coherent light to a spot with a diameter of 0.5 mm to 10 mm on the film; An end point detection method characterized in that the remaining coating thickness is detected by detecting a change in light intensity due to mutual interference between light reflected from the surface of the coating and light reflected from the back surface.