CN101266915A - A method for measuring the intermediate variable of the liquid film under the wafer in the process of CMP - Google Patents

Abstract

A method for measuring intermediate variable of a liquid film under a wafer during CMP process comprises: (1) adding fluorescent material in the polishing slurry, and transferring the fluorescent slurry to the space between the polishing pad of the polisher and the wafer, in order to form a liquid film; (2) starting a laser to irradiate the liquid film so that the liquid film generates fluorescence after the irradiation; (3) the fluorescence generated by the liquid film is transferred to the camera via a filter for fluorescence information collection; (4) carrying out image process on fluorescence image collected by the camera, and calculating to obtain the fluorescence intensity, obtaining thickness of the liquid film according to corresponding relation between the intensity and thickness of the fluorescence, and obtaining the temperature of liquid film according to corresponding curve between the intensity and temperature of the fluorescence, also obtaining the pH value of the liquid film according to corresponding curve of intensity and pH value of the fluorescence. The invention can effectively measure the intermediate variable (such as thickness, temperature, pH value) of a liquid film under a wafer during CMP process.

Description

A method for measuring the intermediate variable of the liquid film under the wafer in the process of CMP

technical field

The invention relates to the field of laser measurement, in particular to a method for measuring intermediate variables (polishing liquid film thickness, liquid film temperature and liquid film pH) under a wafer in a CMP process.

Background technique

With the development of VLSI multilayer interconnection technology, it is necessary to implement multilayer wiring structures on silicon wafers, and each layer requires high global flatness to meet etching requirements. In 1990, IBM took the lead in proposing the chemical mechanical polishing (CMP, Chemical Mechanical Planarization) global planarization technology, which was successfully applied in 64Mb DRAM production in 1991. After that, CMP technology developed rapidly. At present, the research and development work of CMP technology has developed to the whole world, and presents a fierce competition momentum.

Although CMP is considered to be the most effective method to obtain a smooth and non-damaged surface, and has been widely used in integrated circuit manufacturing and other fields, a large number of experiments are still needed before determining the CMP processing technology for a specific processing object. Constantly adjust the process parameters until a satisfactory processing effect is obtained. The reason is that people have not fully grasped the processing mechanism of CMP. The key to revealing the processing mechanism of CMP lies in whether there is a deep understanding of its processing process. However, due to the unique processing method of CMP: the close contact between the wafer and the polishing pad, the tiny size of the polishing liquid film and abrasive particles in the processing area, and the interaction of physical and chemical parameters, it is difficult to observe the CMP process.

In the actual CMP process, the input parameters (pressure, rotational speed, polishing pad structure, etc.) are independent of each other, while the intermediate variables are interactive, for example: the thickness of the liquid film is different, the contact state between the test piece and the polishing pad ( Direct contact, non-contact or quasi-contact) are different, the flow and mixing of the polishing liquid (the percentage of newly added polishing liquid) is also different, resulting in a different temperature field, and the temperature has a great influence on the chemical reaction, so the pH of the polishing liquid The distribution is also different. Therefore, the change of the intermediate variable will directly affect the contact state between the wafer and the polishing pad and the mechanism of material removal. In addition, from the perspective of the nature of variables, the input parameters of a specific process are state variables (time-independent), and the output parameters (removal rate, surface uniformity, etc.) are process variables (changing with time), directly establishing the relationship between the two The relationship will definitely fall into the category of physiognomy for the classification and statistics of a large number of experiments. Although it has a strong guiding significance for the processing technology, it is unable to reveal the CMP processing mechanism. The intermediate variable is a process variable. If the relationship between the intermediate variable and the input parameter, the output parameter and the intermediate variable can be determined, and the input and output parameters are connected through the intermediate variable, it is expected to analyze the mechanism of CMP.

Laser technology is a new technology developed in the 1960s. Since its advent, it has developed rapidly. It is not only widely used in industrial production, national defense, medical and health, but also in forestry production. Using laser to measure thickness has short detection time, sensitive response, high measurement speed, wide measurement range, and no radiation hazard to the environment. When the fluorescent substance is irradiated by ultraviolet light or visible light with a shorter wavelength, it will emit visible fluorescence of various colors and different intensities, and when the light source stops irradiating, the fluorescence will disappear. Utilizing this characteristic of fluorescent substances, one or several fluorescent substances are irradiated with laser light of a certain wavelength, and the method of predicting parameters according to the emission fluorescence spectrum or fluorescence image analysis is LIF technology. LIF technology has become a very powerful experimental method in molecular reaction dynamics. In addition to being widely used in the fields of material structure, state, valence, micro-region, section, non-destructive testing and remote sensing, it can also be used for temperature, Measurement of physical quantities such as stress, lubricating oil film thickness, and OH group concentration. The principle is that when these parameters change, the fluorescence peak shifts or the fluorescence intensity changes, and the changes of these parameters can be deduced by using this change.

Contents of the invention

In order to overcome the inadequacy of the existing technology that cannot measure the intermediate variables under the wafer in the CMP process, the present invention provides a method based on LIF technology that can effectively measure the intermediate variables (such as thickness, temperature, and pH value) under the wafer in the CMP process. A method for the measurement of under-wafer intermediate variables during the CMP process.

The technical solution adopted by the present invention to solve its technical problems is:

A method for measuring intermediate variables of a liquid film under a wafer in a CMP process, the method for measuring comprises the following steps:

(1) Fluorescent substances are added to the polishing liquid, and the polishing liquid is transported between the polishing pad and the wafer of the polishing machine to form a liquid film;

(2), turn on the laser to irradiate the liquid film, and the liquid film will generate fluorescence after being excited;

(3) The fluorescence emitted by the liquid film is transmitted to the camera through the filter to collect the fluorescence information;

(4) Process the fluorescence image collected by the camera to calculate the fluorescence intensity, obtain the thickness of the liquid film according to the corresponding relationship between the fluorescence intensity and thickness; obtain the temperature of the liquid film according to the corresponding curve between the fluorescence intensity and temperature; obtain the temperature of the liquid film according to the fluorescence intensity The curve versus pH yields the pH of the liquid film.

As a preferred solution: add two different fluorescent substances in the above (1); in the above (3), the fluorescence emitted by the liquid film is divided into two beams of light of the same intensity by a spectroscope, and then separately Send to two camera; In described (4), after calculating two kinds of fluorescence intensities, obtain the thickness of liquid film according to the corresponding curve of fluorescence intensity and thickness; The ratio of two kinds of fluorescence intensities is regarded as relative fluorescence intensity, and The temperature of the liquid film is obtained according to the corresponding curve of relative fluorescence intensity and temperature; the pH value of the liquid film is obtained according to the corresponding curve of relative fluorescence intensity and pH value.

Further, in the above (4), a synchronizer is used to eliminate the shooting time difference of the two cameras, and the collected fluorescence images of the two cameras are output for image processing.

The laser is an Ar ion laser.

The wafer is optical glass.

The camera is a CCD camera.

The technical idea of the present invention is: the thickness of the liquid film between the polishing pad and the wafer is very small to micron level under working conditions, so it is difficult to measure the liquid film under the wafer by contact.

An Ar ion laser is used to irradiate the liquid film of the polishing liquid to be tested in the transparent microchannel, and the polishing liquid is marked with two kinds of fluorescent substances with different excitation wavelengths. After the fluorescent substance is excited, the molecule undergoes electron transition from a lower energy level to a higher energy level. Due to the instability of the molecule, the molecule returns to the ground state through the radiation transition and generates fluorescence at the same time. Two kinds of fluorescent substances produce fluorescence of two wavelengths after being excited, and the emitted fluorescence is divided into two beams of light of the same intensity by a spectroscope, and then passed through their respective filters to obtain fluorescence of a certain wavelength, and finally transmitted to two CCDs The camera collects the fluorescence information, which is input to the computer through the image acquisition card to obtain two fluorescence images with different fluorescence wavelengths. Using the image processing technology, the mixing condition, thickness, temperature and pH value of the polishing fluid in the CMP process are calculated.

The selected laser must have good directivity and stable power output. The more stable the output power, the smaller the monitoring noise, and the higher the signal-to-noise must be. The measured fluorescence intensity is generally weak. In this detection system, the signal loss of each link is fully considered to minimize the error. According to the principle of optical imaging, the focal length, magnification, aberration and spherical aberration are considered. The purpose of using the filter is to eliminate the scattered light and laser light source caused by various particles in the liquid film to be measured, and pass the required fluorescence, but the filter reduces the intensity of the fluorescent light entering the CCD camera, so the selection of the filter is not only necessary Considering the center wavelength, also consider the half-wave bandwidth and peak refractive index. In the measurement process, two CCD cameras are required to take two images at the same time, and each image has a different light frequency color. In order to achieve synchronization, a synchronizer needs to be added to the computer to ensure that the two images describe the same Moments of liquid film information.

The beneficial effects of the present invention are mainly manifested in: 1. On-line measurement of the intermediate variable of the liquid film under the wafer in the CMP process; 2. Two kinds of fluorescent substances are used as measurement tools, and the beam splitter divides the fluorescence into two beams, and two kinds of different optical filters Fluorescence with a specified wavelength is obtained, and the relative fluorescence intensity is used as reference information for measuring temperature and pH value in image processing, which eliminates the influence of environmental errors; 3. The synchronizer ensures that the two fluorescence images describe the liquid film information at the same time.

Description of drawings

FIG. 1 is a schematic diagram of a measurement device for intermediate variables under the wafer in the CMP process of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

With reference to Fig. 1, a kind of measuring method of liquid thin film intermediate variable under wafer in a kind of CMP process, described measuring method comprises the following steps:

(1), add fluorescent substance in polishing fluid 5, and polishing fluid 5 is transported between the polishing pad of polishing machine 6 and wafer 7, forms liquid thin film;

(2), turn on the laser 1 to irradiate the liquid film, and the liquid film generates fluorescence after being excited;

(3), the fluorescence emitted by the liquid film is transmitted to the camera 10 through the optical filter 9 to collect the fluorescence information;

(4), carry out image processing on the fluorescent image collected by the camera, in the computer 12, calculate the fluorescent intensity, obtain the thickness of the liquid film according to the corresponding relationship between the fluorescent intensity and the thickness; obtain the thickness of the liquid film according to the corresponding curve of the fluorescent intensity and temperature Temperature: According to the corresponding curve of fluorescence intensity and pH value, the pH value of the liquid film is obtained.

Add two different fluorescent substances in the above (1); in the above (3), the fluorescence emitted by the liquid film is divided into two beams of light with the same intensity by the beam splitter 7, and then sent to the two cameras respectively; In the above (4), after calculating the two kinds of fluorescence intensities, the thickness of the liquid film is obtained according to the corresponding curve of the fluorescence intensity and thickness; the ratio of the two kinds of fluorescence intensities is regarded as the relative fluorescence intensity, and according to the relative fluorescence intensity and temperature According to the corresponding curve of the liquid film, the temperature of the liquid film is obtained; according to the corresponding curve of the relative fluorescence intensity and the pH value, the pH value of the liquid film is obtained.

In the above (4), the collected fluorescence images of the two cameras are input into the synchronizer 11 used to eliminate the shooting time difference of the two cameras, and the synchronizer 11 performs image processing after the output.

Said laser 1 is an Ar ion laser. The wafer 7 is optical glass. The camera 10 is a CCD camera.

In this embodiment, as shown in Fig. 1, the double laser-induced fluorescence telemetry device of liquid thin film in the CMP process includes an Ar ion laser, an optical fiber 2, a diverging lens 3, a three-way valve 4, and a laser containing two fluorescent substances rhodamine B and fluorescein. Polishing fluid input device 5, optical glass 6, beam splitter 7, optical filter 8, CCD camera, synchronizer 11, computer 12. In the detection process, because the transparency of the silicon wafer is not good, which affects the transmission of fluorescence and is not conducive to detection, the transparent optical glass with physical and chemical properties similar to the silicon wafer is used instead of the silicon wafer. The Ar ion laser irradiates the liquid film to be tested under the optical glass, and two fluorescent substances with different excitation wavelengths are dissolved in the liquid. The two fluorescent substances generate fluorescence of two wavelengths after being excited. The emitted fluorescence is divided into two beams of light of the same intensity by the spectroscope, and then passed through their respective filters to obtain fluorescence of a certain wavelength, and finally transmitted to two CCD cameras for fluorescence information collection, and input to the computer through the image acquisition card Finally, two fluorescence images with different fluorescence wavelengths were obtained. In the measurement process, two CCD cameras are required to take two images at the same time, and each image has a different light frequency color. In order to achieve synchronization, a synchronizer needs to be added to the computer to ensure that the two images describe the same Moments of liquid film information. Finally, image processing technology is used to calculate the mixing condition, thickness, temperature and pH value of the polishing fluid during the CMP process.

In this embodiment, double-excitation laser-induced fluorescence telemetry technology is used to measure the following online information of the liquid film under the wafer during the CMP process:

1) The flow and mixing characteristics of the polishing liquid: use two fluorescent substances to calibrate the polishing liquid, one of which is regarded as the "old" polishing liquid, and the other is regarded as the "new" polishing liquid, and the "old" polishing liquid is continuously added , "New" polishing fluid is added regularly. The mixed light composed of two kinds of excited fluorescence is divided into two beams equally by the beam splitter, and after each passes through the corresponding filter, the excited fluorescence of the two fluorescent substances is obtained, which are respectively received by the corresponding CCD, that is, "new" and "" in the observation area. Fluorescence image of "old" polishing fluid. The grayscale ratio of the two images is the proportion of "new" slurry. By continuously taking images, the flow and mixing characteristics of the polishing fluid can be dynamically observed.

2) Measurement of thickness change of polishing liquid film: If a certain fluorescent substance solution satisfies the following conditions, the concentration of the solution is small, the temperature is constant, the pH value is constant, the frequency and intensity of the excitation light are constant, and the percentage of light absorbed is not too large , then when the thickness of the solution is constant, the fluorescence intensity it produces is proportional to the concentration of the solution. Conversely, when the concentration of the solution is constant, the intensity of the fluorescence it produces is proportional to the thickness of the solution. It is reported that LIF technology can distinguish the thickness below 15 μm, and the thickness of the polishing liquid film between the specimen and the polishing pad is tens of microns, so the LIF technology has sufficient resolution to measure the thickness of the polishing liquid film.

3) Measurement of the temperature distribution of the polishing liquid film: usually the fluorescence intensity of the solution containing fluorescent substances is greatly affected by the temperature. The higher the temperature, the weaker the fluorescence intensity. The fluorescence image of the polishing liquid film under the workpiece is used to calculate the temperature value of each point of the polishing liquid film, and then the temperature field is depicted.

4) Measurement of the pH distribution of the polishing liquid film: the fluorescence intensity of the solution of some fluorescent substances (such as fluorescent yellow) within a certain pH range increases with the increase of the pH value. Using a method similar to temperature measurement, the pH value of the polishing liquid film can be measured.

Claims (6)

1, a kind of measurement method of liquid thin film intermediate variable under wafer in the CMP process, it is characterized in that: described measurement method comprises the following steps: (1) Fluorescent substances are added to the polishing liquid, and the polishing liquid is transported between the polishing pad and the wafer of the polishing machine to form a liquid film; (2), turn on the laser to irradiate the liquid film, and the liquid film will generate fluorescence after being excited; (3) The fluorescence emitted by the liquid film is transmitted to the camera through the filter to collect the fluorescence information; (4) Process the fluorescence image collected by the camera to calculate the fluorescence intensity, obtain the thickness of the liquid film according to the corresponding relationship between the fluorescence intensity and thickness; obtain the temperature of the liquid film according to the corresponding curve between the fluorescence intensity and temperature; obtain the temperature of the liquid film according to the fluorescence intensity The curve versus pH yields the pH of the liquid film. 2. The measuring method of the intermediate variable of the liquid film under the wafer in a kind of CMP process as claimed in claim 1, is characterized in that: in described (1), add two kinds of different fluorescent substances; In described ( In 3), the fluorescence emitted by the liquid film is divided into two beams of light of the same intensity by a spectroscope, and then transmitted to the two cameras respectively; in the above (4), after calculating the two fluorescence intensities, the two fluorescence intensities The ratio of the relative fluorescence intensity is used as the relative fluorescence intensity, and the temperature of the liquid film is obtained according to the corresponding curve of the relative fluorescence intensity and temperature; the pH value of the liquid film is obtained according to the corresponding curve of the relative fluorescence intensity and the pH value. 3. The method for measuring the intermediate variable of the liquid film under a wafer in a kind of CMP process as claimed in claim 2, characterized in that: in said (4), a synchronizer is used to eliminate the shooting time difference of the two cameras, and the The collected fluorescence images of the two cameras are output and then image processed. 4. The method for measuring the intermediate variable of the liquid film under the wafer during the CMP process according to any one of claims 1-3, wherein the laser is an Ar ion laser. 5. The method for measuring the intermediate variable of the liquid film under the wafer during the CMP process as claimed in claim 4, wherein the wafer is optical glass. 6. The method for measuring the intermediate variable of the liquid film under the wafer during the CMP process as claimed in claim 4, wherein the camera is a CCD camera.

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