CN1380541A

CN1380541A - Method for measuring temp. and monitoring etching rate by using optical method

Info

Publication number: CN1380541A
Application number: CN 01110453
Authority: CN
Inventors: 李世琛
Original assignee: Winbond Electronics Corp
Current assignee: Winbond Electronics Corp
Priority date: 2001-04-10
Filing date: 2001-04-10
Publication date: 2002-11-20
Anticipated expiration: 2021-04-10
Also published as: CN1153056C

Abstract

The present invention provides a method for measuring temp. and monitoring etching rate by using optical method and etching equipment using said method. Said invention method is applicable to a plasma etching equipment. Said method is characterized by that fistly, an etching process is made, then the intensity distribution of specific wavelength light proudced by saijd discharge can monitored, finally, according to the intensity distribution and an operational rule an optical method is used to obtain a temp. and said temp. is referred to the etching rate.

Description

Method for optically measuring temperature and monitoring etch rate

The present invention relates to a method for monitoring an etching rate and an etching apparatus using the same, and more particularly, to an in-situ (in situ) etching rate monitoring method and an etching apparatus using the same.

In semiconductor processing, the etch rate of an etch process must be precisely controlled to achieve the desired end of the process.

Known methods for calculating the etching rate can be roughly classified into two main types, the first method using control wafers (control wafers) to directly perform an etching process, and then measuring a value of a variation in the thickness of a thin film on the control wafer divided by a process time to obtain the etching rate. However, such a method requires an additional preparation of the control wafer on the one hand and a special period of time for etching the control wafer on the other hand, and therefore, the cost of calculating the entire etching rate is very large. Moreover, the accuracy of the etching rate depends on the accuracy of a thickness measuring machine (thickness measuring tool), and as long as the thickness measuring machine has a problem or is stopped, the etching rate cannot be accurately obtained. Another approach is more advanced and is known as in situ thickness monitoring. Mainly, a laser is irradiated on a semiconductor chip which is undergoing an etching process, then an interferometer (interferometer) is used to monitor an interference wave pattern (interference wave pattern) caused by a thin film on the semiconductor chip, and the thickness of the thin film is judged according to the interference wave pattern, and the change of the thickness along with time is the etching rate. The greatest benefit of this approach is cost savings, and the need for control wafer preparation and process time management can be eliminated. However, the interference effect is very easily affected by the variation of the film characteristics (such as refractive index and reflection coefficient) and the measurement position at the measurement point, and it is a problem whether the film characteristics can be controlled within a certain range every time. All this suggests that the reliability of the etch rate obtained is highly uncertain because the measured film thickness is very unstable during the etching process.

An object of the present invention is to provide a method and an apparatus for monitoring an in-situ (in situ) etching rate, which can simultaneously control the etching rate of an etching process when the etching process is performed.

Another object of the present invention is to provide an etching rate monitoring method that is not affected by the characteristics of the thin film, and can obtain an accurate etching rate monitoring method.

The invention provides an etching rate monitoring method, which is suitable for a plasma etching device. The method of the present invention first performs a plasma etching process, and then monitors the intensity distribution of light of a specific wavelength generated by the plasma discharge while the etching process is performed. Finally, according to the intensity distribution of the light with specific wavelength and an operation rule, an optical temperature is obtained by an optical method and the etching rate of the plasma etching process is compared.

The invention also provides an etching device which has the function of in-situ monitoring the etching rate (with in situ monitoring of the etching rate). The etching apparatus of the present invention comprises a vacuum chamber, a multi-channel spectrometer (optical multi-channel analyzer) and a computer. The vacuum chamber is used for carrying out a plasma etching process. The multi-channel spectrometer is used for monitoring the intensity of light with specific wavelength generated by plasma discharge in the vacuum chamber during the plasma etching process. The computer optically calculates a temperature according to the intensity distribution of the light with specific wavelength and an operation rule, and compares the temperature with the etching rate of the plasma etching process.

The light of the specific wavelength may be generated by transitions between energy states of a specific gas molecule in the device. The gas molecules may be selected from one of the gas molecules participating in the plasma etching process reaction or one of the gas molecules not participating in the plasma etching process reaction. Therefore, the specific gas molecule may be one of carbon monoxide (CO), carbon dioxide (CO2), CF2, SiF, C2, and HF. Meanwhile, the transition between energy states can select the transition between electronic energy states, vibration energy states or rotation energy states.

A first advantage of the invention is the cost saving. The present invention is an in-situ (in situ) method of monitoring etch rate, so that wafer cost and measurement time cost need not be controlled.

A second advantage of the present invention is that the monitored etch rate can be made more accurate. Because the wavelength distribution of the light emitted by each gas molecule is different, the intensity of the specific wavelengths of light can be monitored to obtain the corresponding excited state density distribution of the gas molecule, and then the temperature (energy distribution) of the gas molecule is deduced, so as to obtain a corresponding etching rate. Therefore, the monitoring of the etching rate can become more accurate.

In order to make the aforementioned and other objects, features and advantages of the present invention more comprehensible, preferred embodiments accompanied with figures are described in detail below:

brief description of the drawings:

FIG. 1 is a schematic illustration of a monitoring method of the present invention;

FIG. 2 is a schematic view of an etching apparatus of the present invention;

FIG. 3 is a schematic illustration of transitions between energy states of a gas molecule;

FIG. 4 is a graph showing the relationship between the light intensity distribution and the vibration temperature;

FIG. 5 is a graph of oxygen gas flow rate versus vibration temperature, etch rate;

FIG. 6 is a graph of CHF3 gas flow rate versus vibration temperature and etch rate;

FIG. 7a is a graph of the emitted light profile for a particular gas; and

FIG. 7b is an enlarged view of a portion of d->s in FIG. 7 a.

Description of the figure numbers:

20 etching device 22 vacuum chamber

24 multi-channel spectrometer 26 computer

Electron energy state 32 at electron energy state 30

Example (b):

please refer to fig. 1, which is a schematic diagram of the monitoring method according to the present invention. The invention provides an etching rate monitoring method, which is suitable for a plasma etching device. The method of the present invention begins with a plasma etch process 10. The intensity distribution 12 of the particular wavelength of light generated by the plasma discharge is then monitored as the plasma etch process progresses. Finally, according to the intensity distribution of the light with specific wavelength and an operation rule, a temperature is obtained by an optical method and the etching rate 14 of the plasma etching process is obtained.

By using the monitoring method of the present invention, the present invention also provides an etching apparatus having in-situ (in situ) etching rate monitoring function. As shown in FIG. 2, the etching apparatus 20 of the present invention includes a vacuum chamber 22, an optical multi-channel spectrometer (OMA) 24 and a computer 26. The vacuum chamber 22 is used to perform a plasma etching process. The multi-channel spectrometer 24 is used to monitor the intensity of light of a particular wavelength generated by the plasma discharge in the vacuum chamber 22 during the plasma etching process. The computer 26 optically determines a temperature according to the intensity distribution of a plurality of predetermined wavelengths of light and the algorithm, and compares the temperature with the etching rate of the plasma etching process.

The subject of the invention is to establish a correlation between the distribution of excited states of gas molecules and the etching rate. The method of the present invention monitors the excited state distribution (excitation distribution) of the gas molecules during the etching process. And deducing the optical temperature according to the distribution of the excited state of the gas molecules, and then contrasting the etching rate. Thus, an accurate etching rate can be obtained.

Referring to fig. 3, fig. 3 is a schematic diagram of transitions between states of a gas molecule. The energy levels of the gas molecules can be separated into electronic, vibrational, and rotational energy states. As shown in fig. 3, the two curves in fig. 3 represent the energy-to-atomic distance relationship between the upper electronic state (upper electronic state)30 and the lower electronic state (bottom electronic state)32, respectively. The upper electronic energy state 30 and the lower electronic energy 32 can be further subdivided into a plurality of vibrational energy states 34, e.g. FIG. 3_a1To E_a5And E_b1To E_b4Shown in parallel lines. The generation of photons (photons) is one of the methods of energy conversion when gas molecules transition between different energy states. As shown in fig. 3, from E_b1Transition of vibrational energy to E_a1When the vibration energy state is existed, an energy of h upsilon is radiated₁₁(＝E_a1-E_b1) I.e. emits photons of frequency v₁₁Light wave of (2). While different transitions produce light of different frequencies, e.g. h upsilon in figure 3₁₁To h υ₄₁As shown.

As known from quantum mechanics, the energy state distribution of each gas molecule is different. Therefore, the light intensity and wavelength distribution generated by the transition of the gas molecules between different energy states also vary with the gas molecules, such as the wavelengths of light generated by CO and HF during the etching process. Thus, the intensity levels of certain wavelengths of light may be monitored to determine the presence or absence of gas molecules. At the same time, this also means that different molecular gases can be monitored.

From physics textbooks, it is known that the light intensity of different wavelengths should be proportional to the density of the transition gas molecule, and the formula can be expressed as follows:

I_λαФNqλ^-3- - - - - - - - (1) wherein I_λDenotes the light intensity at wavelength λ, λ denotes the wavelength of the light, Φ denotes the sensitivity of the monitor, N denotes the concentration of the gas molecules, q denotes the Frank-Condon factor and is proportional to the probability of the transition. The concentration distribution of gas molecules in an excited state may represent the kinetic energy, i.e. the optical temperature, of a gas molecule. The spectral intensity distribution under different vibrational energy state transitions is defined to correspond to a vibrational temperature T of the gas molecule_vib. Concentration distribution and vibration temperature T of gas molecules_vibThe following formula can be obtained from a general textbook

N(υ)αexp[-E(υ)/(k_bT_vib)]Wherein N (upsilon ') represents the number concentration of gas molecules under the vibration state upsilon', E (upsilon ') represents the vibration energy state of the vibration state upsilon', and k represents the vibration energy state of the vibration state upsilon_bDenotes the Boltzman constant, T_vibIndicating the vibration temperature.

The method of the present invention for determining the etching rate first must select the light generated by the transition between energy states of a certain gas molecule, such as d of CO gas molecule, as the judgment standard³П (v') to a³П (υ ") state transitions (distribution of light wavelengths about 430nm to 830 nm.) it is assumed that 0 to 9 vibrational energy states are chosen from υ', the lowest vibrational energy state (ground state) is chosen for υ"³П (v') to s³П (upsilon') having 10 different wavelengths, monitoring the light intensity of 10 wavelengths, and obtaining the distribution of CO gas molecule concentration in excited state by formula (1), wherein the light intensity of one wavelength corresponds to d³П (upsilon ') and then selecting d by using the value of formula (2) E (upsilon')³П(υ') of 10 energy states are known, and the vibration temperature T_vibIt can be obtained by curve approximation (curve fitting), sampling (sampling) or some simple operation rules. As shown in FIG. 4, there are two different light intensity distributions in FIG. 4, each representing a vibration temperature T of a gas molecule_vib1And T_vib2Wherein T is_vib2Greater than T_vib1. From the data values accumulated in the experiment, a set of vibration temperature T can be established_vibA correlation equation with etch rate, or a correlation look-up table. Then, each time the same etching process is performed, the proper vibration temperature T can be obtained by monitoring the intensity distribution of the 10-wavelength light of the CO gas molecules to obtain a light intensity distribution diagram_vibFinally, the etching rate is compared. All the calculation processes can be processed by a simple program on a computer, and the corresponding etching rate can be obtained immediately when the etching process is carried out.Therefore, the etching rate monitoring method of the present invention is an in-situ (in situ) etching rate monitoring method.

Referring to FIG. 5, FIG. 5 is a graph showing the relationship between the oxygen gas flow rate and the vibration temperature and etching rate. Since the increase of the oxygen gas leads to the increase of the fluorine gas to accelerate the etching rate, the etching rate is accelerated

. The experimental data in fig. 5 thus show that the etching rate becomes faster with the increase of oxygen gas while the vibration temperature T derived from the optical wavelength intensity profile_vibAnd also increases with increasing oxygen gas. Referring to FIG. 6, FIG. 6 shows CHF3 gas flow and vibration temperature T_vibAnd Etching Rate (ER). Since an increase in the CHF3 gas increases the chance of polymer (polymer) formation to block the progress of etching, the etching rate decreases as the CHF3 gas flow rate increases. And, at the same time, the vibration temperature T derived from the optical wavelength intensity profile_vibAnd also decreases with increasing CHF3 gas. As can be seen from both FIGS. 5 and 6, the vibration temperature T_vibApproximately in a positive relationship with the etching rate, so that the vibration temperature T_vibWill be a good one of the etch ratesThe coefficients are monitored.

The selection of the specific gas molecule in the present invention may be one of the gas molecules participating in the reaction of the plasma etching process, or may be one of the gas molecules not participating in the reaction of the etching process. For example, in a silicon oxide etching process, the gas molecules in the vacuum chamber include carbon monoxide (CO), carbon dioxide (CO2), CF2, SiF, C2, HF, etc., and the light emitted from these gas molecules can be used as the monitoring target of the present invention. The intensity of the emitted light must be sufficient to allow monitoring by the multichannel spectrometer, taking into account the stability of the gas molecules and the amount of concentration. Of course, it is also possible to select two or more kinds of gas molecules emitting light as the monitoring targets, and to make the estimated etching rate more accurate by double checking (double check) of the vibration temperatures of the two kinds of gas molecules.

In addition to monitoring light generated by transitions between different vibrational energy states in the previous example, as shown in FIG. 4, the present invention can also monitor light generated by transitions between different electronic energy states or between different electronic energy states, see FIGS. 7a and 7b, FIG. 7a is a graph of emitted light from a specific gas, FIG. 7b is a partial enlargement of d->s in FIG. 7a, FIG. 7b, assuming that electronic energy states are divided from low to high as s, p, d, and e, vibrational energy states are divided into 0, 1, 2, and 3, and rotational energy states are divided into α, β, and γ. as shown in FIG. 7a, emitted light can be significantly classified into groups of e->s, d->s, and p->s generated by transitions between different electronic energy states, as shown in FIG. 7b, each group can be classified into sub 0, 1->0, 2->0, and 3->0 subgroups generated by transitions between different vibrational energy states (as well as the result of the light intensity distribution of each group being capable of generating different light intensity distributions of being monitored by sub-0, and 3-sub-groups (as shown in FIG. 7 b), and as a spectrometer 34) generated by transitions of course, and as different light intensity distributions of light intensity, and temperature, as a spectrometer 34, and temperature, as a result of the emission of the_elec) And the distribution of light intensity (rotation temperature T) produced by transitions between different rotation energy states_rota) May be used as an indicator of etch rate.

The invention uses the distribution of the light intensity with different wavelengths to judge the excitation state of the gas molecules in the vacuum chamber, and uses an optical method to calculate a temperature and contrast the etching rate in the etching process. Because the wavelength of the emitted light of each gas molecule is different, the method of the invention can obtain the result which is not easily interfered by other irrelevant gases, and the etching rate can be accurately obtained when the etching process is carried out.

Compared with the known etching rate monitoring method, the method of the invention takes the excited state of the gas molecules in the vacuum chamber as a pointer to obtain the etching rate. Therefore, the preparation of the control wafer and the waste of monitoring time are not needed, and meanwhile, the method is not influenced by the characteristics of the thin film on the semiconductor chip and can obtain accurate etching rate when the etching process is carried out.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow, and the description and drawings are to be interpreted accordingly.

Claims

1. A method for optically measuring temperature and monitoring etch rate for a plasma etching apparatus, the method comprising:

performing a plasma etching process;

monitoring an intensity distribution of light of a specific wavelength generated by a plasma discharge while the plasma etch process is in progress; and

according to the intensity distribution of the light with the specific wavelength and an operation rule, a temperature is obtained by an optical method and the etching rate of the plasma etching process is compared.

2. The method of claim 1 wherein the specific wavelength light is generated by transitions between specific gas molecular states in the plasma device.

3. The method of claim 2, wherein the specific gas molecule is one of gas molecules participating in a reaction of the plasma etching process.

4. The method of claim 2, wherein the specific gas molecule is one of carbon monoxide (CO), carbon dioxide (CO2), CF2, SiF, C2, and HF.

5. The method of claim 1, wherein the light of the specific wavelength is generated by transitions between different electronic energy states (electronic energy states) of a specific gas molecule in the plasma device.

6. The method of claim 1 wherein the light of the specific wavelength is generated by transitions between different rotational energy states (rotational energies) of a specific gas molecule in the plasma device.

7. The method of claim 1, wherein the light of the specific wavelength is generated by transitions between different vibrational energy states (vibrational energies) of a specific gas molecule in the plasma device.

8. An etching apparatushaving in-situ (in situ) monitoring of etch rate, comprising:

a vacuum chamber for performing a plasma etching process;

a multi-channel spectrometer for monitoring the intensity of light of a specific wavelength generated by plasma discharge in the vacuum chamber during the plasma etching process; and

a computer, according to the intensity distribution of the light with specific wavelength and an operation rule, optically obtaining a temperature and comparing the etching rate of the plasma etching process.

9. The apparatus of claim 8 wherein the light of the specific wavelength is generated by transitions between energy states of a specific gas molecule in the plasma apparatus.

10. The apparatus of claim 9 wherein the specific gas is one of the gas molecules that participates in the plasma etch process.

11. The apparatus of claim 9, wherein the specific gas molecule is one of carbon monoxide (CO), carbon dioxide (CO2), CF2, SiF, C2, and HF.

12. The apparatus of claim 8 wherein the light of a particular wavelength is generated by transitions between different electronic energy states (electronic states) of a particular gas molecule in the plasma device.

13. The apparatus of claim 8 wherein the light of a specific wavelength is generated by transitions between different rotational energy states (rotational states) of a specific gas molecule in the plasma device.

14. The apparatus of wherein the light ofthe specified wavelength is generated by transitions between different vibrational energy states (vibrational states) of a specified gas molecule in the plasma device.