JPH0265225A - Coating process of photoresist - Google Patents

Abstract

PURPOSE:To enable the finished film thickness to be anticipated instantaneously by a method wherein the surface of a wafer is irradiated with beams so that the specified minimum point of reflected beams may be detected by monitoring the reflected beams to decide the total baking time by the time for reaching the minimum point. CONSTITUTION:A resist is dripped on a wafer being turned at high revolution to spread the resist evenly and then the surface of the wafer is irradiated with beams to monitor the reflected beams so that the specified minimum point of the reflected beams may be detected to measure the time (CPT) for reaching this minimum point. The reflected beams led by an optical fiber 6 are detected by a phototransistor 7 through a filter 8. The detection signals from the phototransistor 7 are converted into digital signals through an A/D converter 10 to be inputted to a computer 9 for thorny analysis. Respective baking times, spinner revolutions and spinner revolution times or the combination thereof as to the film thickness can be controlled by the CPT detected.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for coating a photoresist in a photolithography process included in the process of manufacturing semiconductor integrated circuits, and more specifically, to a method for coating a photoresist in a photolithography process included in the process of manufacturing semiconductor integrated circuits. This invention relates to a monitoring method and a method of controlling photoresist film thickness using the monitoring results.

(Prior Art) The process of manufacturing semiconductor integrated circuits includes a photolithography process.

In the photolithography process, a photoresist is applied onto the base,
The resist is exposed to light through a mask or through a reticle in the case of reduction projection exposure, and is then developed to form a circuit pattern in the resist.

For resist coating, photoresist is dropped onto the wafer using either static dispensing or dynamic dispensing, and after spreading the resist solution over the entire surface of the wafer, the wafer is rotated at high speed for a certain period of time. A resist coating film is formed by uniformly spreading the resist over the entire surface of the wafer and then evaporating the solvent on a pot plate at a constant temperature for a certain period of time.

After the hot plate hazing is completed, the resist coating thickness is determined.

In the exposure process, light with a single wavelength such as 436 nm or 365 nm is generally used, so in the resist film applied to the base, the incident light and the light reflected from the base interfere with each other, causing standing waves. arise.

Due to the influence of this standing wave, when the resist on the base is developed with a constant development time, the period of the resist film (λ is the exposure wavelength and n is the resist refractive index) increases and decreases.

The film thickness of the photoresist 1 is shown as T = ω4η” (1) (
Here, T is the resist film thickness, ω is the wafer rotation speed, η is the resist viscosity, and K, α, and β are constants).

Therefore, in order to keep the resist film thickness constant, the rotational speed ω
In order to keep the resist viscosity constant and the resist viscosity η constant, it is common to keep the temperature and humidity in the coating chamber constant to suppress variations in resist film thickness.

(Problem to be solved by the invention) However, controlling the humidity inside the coating chamber is technically difficult;
and requires expensive equipment. Furthermore, this method has the problem that it is not possible to control changes in film thickness due to time factors during transfer from the coating chamber to the hot plate.

(Means for Solving the Problems) Conventional techniques cannot solve the problems of controlling the temperature and humidity in the coating chamber over a long period of time, and the temperature and humidity in the baking chamber.
Instead of humidity control, the evaporation rate of the resist solvent during baking is measured, and the end point detected by an automatic end point detection method is used to control the spinner rotation speed, rotation time, or baking time. The finished film thickness of the resist film can be controlled at a constant level,
Furthermore, the present invention was completed by discovering that the resist film thickness can be monitored.

That is, in the process of applying a resist solution to a wafer, the present invention drips the resist onto the wafer, rotates the wafer at high speed to spread the resist uniformly, and then evaporates the solvent on a hot plate. By emitting light and monitoring the reflected light, a specific minimum point of the reflected light is detected, and the time to the minimum point (hereinafter referred to as control point time rcPTj) is determined.
The present invention provides a method for monitoring a photoresist film thickness, which is characterized in that the film thickness is determined from a straight line of a linear function of the logarithm of the determined time and the logarithm of the photoresist film thickness, and furthermore, A photoresist film thickness control method characterized by determining the total baking time based on the time to a specific minimum point, and determining the high-speed spin time or rotational speed of the next wafer based on the time to the minimum point. The present invention provides a method for controlling photoresist film thickness, characterized by determining the thickness of a photoresist film.

In the present invention, when the solvent of the photoresist coated on the wafer is evaporated, the apparatus shown in FIG. 1 may be used, for example, as a method of irradiating light from above the wafer and monitoring the reflected light.

In FIG. 1, 1 is a hot plate, and 11 is a plate timer that controls the hot plate time. The hot plate 1 is equipped with a suction mechanism, and the base 3 is attached by suction. 4
is a light source having a long wavelength of an optical system for measuring the film thickness of the resist 1 on the underlayer 3, such as a tungsten lamp or a mercury lamp. Reference numeral 5 denotes a filter for passing light of a wavelength that does not expose the resist 1 to light from the light source 4. For example, a filter that blocks light of a short wavelength of 460 nm or less is used. A bundle of optical fibers 6 guides the light that has passed through the filter 5 onto the base 3, and irradiates the light so that the diameter of the light on the base 3 is, for example, about 10 mm.

The optical fiber bundle 6 also serves to guide reflected light from the substrate 3. The reflected light guided by the optical fiber 6 passes through the filter 8 and is received by Fol-1 to Lansy Stuff. The filter 8 is a pass filter to the narrowband pan 1 that transmits only light in a specific wavelength range, and is used so that the wavelength that provides the highest S/N ratio can be selected depending on the type of the substrate 3 and the like. The detection signal of transistor 10 to photo 1 is A
The signal is converted into a digital signal via the /D converter 10, and is input into the computer 9, where a light color analysis is performed.

Furthermore, the following four types of algorithms can be cited as methods for detecting a specific minimum point of reflected light.

■ Basic end-fringe algorithm A flowchart of the end-fringe algorithm is shown in FIG.

As parameters, the algorithm action start time α from the computer's measurement start point and the allowable period extension rate β (>1.0) are input.

After starting development and exceeding α, the algorithm is applied. If the next minimum point appears up to the time interval Xβ between the two last minimum points known at time t, further calculations are performed. If the next minimum point does not appear within the time interval Xβ between the two last minimum points known at time t, the last minimum point is detected as CPT.

(2) Algorithm End Time Specified End-Fringe Algorithm (Figure 3) Figure 6 shows the flowchart 1 to 1 of this algorithm.

As a parameter, input the algorithm end time γ. After the start of development, the last minimum point found at time γ is defined as CRT.

■ - End-fringe algorithm compatible with valley fringes (
(Figure 4) This algorithm is applied to a development waveform in which one or more large valleys appear.

The input parameters are the algorithm start time α, and the maximum waiting time Tw or ratio multiple when waiting for the next minimum point to appear after one minimum point is found.

The last minimum point C detected during α elapsed @TW is detected as CRT.

■ Esteima Chirad curvature detection algorithm (Figure 5) This algorithm searches left and right from Es time to find the nearest minimum point or maximum point, and then searches left and right from that point for data within Tb time. The curvature of the fringe is calculated, and the point with the largest curvature is detected as the CRT.

CPT was measured using the above device and algorithm, and the relationship between CRT and finished film thickness was determined.

FIG. 6 shows the relationship between CRT and resist film thickness when the baking temperature and time during baking are kept constant.

As shown in Figure 6, CPT and resist film thickness T can be approximated by a straight line in a double logarithmic plot, and the relationship between them can be expressed by the exponential function T = K・CPT 1 (2) can. (In the above equation, n is a constant) A filter that generates CRT at a specific position and the S/N of the reflected light from the wafer is selected, and a specific minimum point of the interference wave is detected. The minimum point can also be generated by mathematically inverting the resulting interference wave.

Under various conditions, determine ■g and n in formula (2), and calculate C
By determining the relational expression between PT and resist film thickness, the film thickness can be determined by CRT measurement.

The film thickness is controlled by controlling the baking time (TBT) and spinner rotation speed (FSS) using the CPT detected by the above method.
), spinner rotation time (T S T ), each or a combination thereof.

This will be explained with reference to FIG.

FIG. 7 shows the relationship between the intensity of reflected light at a certain wavelength and the thickness of the resist film during baking.

As is clear from FIG. 7, the time to the control point can be easily determined by measuring the interference light of the reflected light.

However, if baking is stopped at the control point, the desired film thickness cannot be obtained. In the past, several wafers were actually coated, the wafer rotation speed at which the desired resist film thickness was obtained was determined, and subsequent operations were performed based on this rotation speed.

However, in general, the temperature, humidity or solvent concentration in the coating chamber,
The temperature, humidity, etc. of the baking chamber change for each wafer, and the optimal wafer rotation time, rotation speed, and baking time also change.

The time it takes to reach the control point is the time when λ is the monitor wavelength and n is the refractive index of the resist, whereas TBT and TST are the time it takes to determine the desired resist film thickness or the time it takes to determine the desired resist film thickness. , FSS can be said to be the wafer rotation speed.

The present inventors believe that this CPT and TBT, TST or FSS
It was found that in reality, the line becomes almost an approximate straight line.

This ratio is defined as the α value.

i.e. It is.

Furthermore, it has been found that this α value is not the only absolute value, but varies depending on the desired resist film thickness, wafer rotation speed, filter wavelength, substrate, and type of underlayer. (8th
However, once this value is obtained through calibration, it can be obtained as TPT-α1·CRT TST-α2·CRT FSS-α3·CRT, and film thickness control with good reproducibility can be performed.

Here, we will describe in detail a method of fixing the wafer rotation speed and wafer rotation time, controlling only the baking time, and controlling the resist film thickness. The resist film thickness decreases as time passes from the start of baking.

At this time, light is irradiated onto the base 1 from above the resist 2,
When the reflected light is detected, the intensity of the detection signal has a waveform of peaks and valleys as shown in FIG.

This is because interference occurs between the light reflected from the surface of the resist 2 and the light reflected from the surface of the base 1. As baking progresses, peaks and valleys appear in the waveform. The period of these peaks and valleys is determined by the thickness of the resist film, λ is the wavelength of the light being monitored,
n is the refractive index of the resist 2.

It shows that it has become.

From experiments under various conditions, the inventor has determined that CRT and TBT
We discovered that the relationship can be expressed by the following empirical formula.

TBT=P (CRT) 2+ Q (CRT)
... 3) However, the above equation is just an experimental equation, and the present invention is not affected by the approximation accuracy of the above equation, and it goes without saying that the correlation between the two can be determined using other approximate and experimental equations. may be expressed.

In equation (3), P and Q are constants, and the following method may be used to determine them.

That is, wafer rotation speed and total baking time (TBT)
The resist is coated with different values, the resist I and the film thickness are measured, and from the measured CRT and the total baking time TPT to make the resist film thickness the desired thickness, P is determined by the above equation (3). It is good to determine Q.

A bare Si substrate is used as the base 1, and a positive die 1~0FPR-800 is applied on it to a finished film thickness of 10B50.
When the constants P and Q were determined to be human, P=4.76 Q--9,48.

This method uses a substrate A1 with high reflectivity. Al-3i, Al
-Cu or low reflectance substrate S i , Po1y-8
il, W polycide, W silicide, T tome, 5in2, Si:
It can be applied to substrates having multilayer films such as +N4, BPSG, PSG, or a combination thereof.

Next, the present invention will be explained in more detail with reference to Examples.

However, the examples of the present invention are described for illustrative purposes only, and the scope of the invention is not limited thereby.

(Example) Using 0FPR-800 for positive molding system 1, the baking temperature was 100° C., the wafer rotation time was 20 seconds, and the wafer rotation speed was varied between 3150 and 3200 rpm.

The CRT was monitored during baking and the resulting CRT was used to control the baking time. The baking time varied from 30 seconds to 90 seconds, and the resist film thickness was 1035.
It was controlled within the range of 0 people ± 30 people. (Figure 10) In contrast, in the conventional method, the resist film thickness is 103
There was a change of 20 people ± 180 people. (Figure 11) In this example,
Although the present invention is carried out by controlling the baking time, it can also be applied to a method of controlling the rotation speed and rotation time of the spinner.

(Effects) In baking after applying resist, the present invention irradiates light from above the wafer, detects the intensity of the reflected light, detects the end point, and uses that time to instantly predict the finished film thickness. .

Furthermore, the finished resist film thickness can be stabilized by determining the total baking time (TBT), wafer rotation speed (TSS), and total rotation time (TST) as linear and quadratic functions of the end point time.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing an example of a device for detecting CPT, Figure 2 is a flowchart of the basic end-fringe algorithm, Figure 3 is a flowchart of the end-fringe algorithm with a specified algorithm end time, and Figure 4 is Ichitani. A flowchart of the fringe compatible en1~fringe algorithm, Figure 5 is a flowchart of the Esteima Chirad curvature detection algorithm, Figure 6 is a graph showing the relationship between LOG CRT and LOG resist film thickness when baking time is constant. Figure 7 is a schematic diagram showing the relationship between baking time and reflection intensity, and changes in resist film thickness.
The figure shows CRT and α to obtain a resist film thickness of 10,350.
FIG. 9 is a graph showing the relationship between baking time and reflection intensity. FIG. 10 is a graph showing the relationship between CRT and resist film thickness when using the present invention. FIG. 11 is a graph showing the relationship between baking time and resist film thickness. 3 is a graph showing the relationship between CRT and resist film thickness when the following conditions are met. Patent Applicant: Sumitomo GCNY Co., Ltd. (4 others)

Claims (1)

[Claims] 1. In the step of applying a resist solution to a wafer, the resist is dropped onto the wafer, the wafer is rotated at high speed to spread the resist uniformly, and then the solvent is evaporated on a hot plate, A photoresist characterized in that a specific minimum point of the reflected light is detected by irradiating light from the top of the wafer and monitoring the reflected light, and the total baking time is determined by the time to this minimum point. How to control the film thickness. 2. In the process of applying resist solution to the wafer, the resist is dropped onto the wafer, the wafer is rotated at high speed to spread the resist uniformly, and then when the solvent is evaporated on the hot plate, light is emitted from the top of the wafer. A specific minimum point of the reflected light is detected by irradiating the wafer and monitoring the reflected light, and the time or rotational speed for the next high-speed spin of the wafer is determined based on the time to this minimum point. How to control resist film thickness. 3. In the process of applying resist solution to the wafer, the resist is dropped onto the wafer, the wafer is rotated at high speed to spread the resist uniformly, and when the solvent is evaporated on a hot plate, light is emitted from the top of the wafer. By irradiating and monitoring the reflected light, a specific minimum point of the reflected light is detected, the time to this minimum point is determined, and the linear function of the logarithm of the determined time and the logarithm of the photoresist film thickness is calculated. A method for monitoring photoresist film thickness, characterized by determining the film thickness from a straight line.