JP4969545B2 - Semiconductor manufacturing equipment - Google Patents

Description

  The present invention relates to an apparatus for manufacturing a semiconductor element by etching a semiconductor wafer, and to an apparatus provided with means for measuring the etched depth.

  In the process of forming a semiconductor element, dry etching is performed in order to remove a layer of various materials such as a dielectric material and an insulating material layer formed on the surface of a semiconductor wafer and to form a pattern in these layers. Widely used. In performing this dry etching, it is important to adjust the etching so that the desired etching depth and layer thickness are obtained during the processing of the above-mentioned layers. Therefore, the etching end point and the film thickness are accurately set. To be detected.

  By the way, it is known that the intensity of light emission from light of a specific wavelength included in plasma light changes as the etching of a specific film progresses during the process of dry etching a semiconductor wafer using plasma. ing. Therefore, as one of techniques for detecting the etching state such as the etching end point and film thickness of the semiconductor wafer, a change in emission intensity of a specific wavelength from the plasma is detected during the dry etching process, and based on the detection result. A technique for detecting the etching end point and film thickness of a specific film is known. In order to improve the accuracy of this detection, it is necessary to reduce false detection caused by fluctuations in the detection waveform due to noise.

  In recent years, with the miniaturization and high integration of semiconductors, the aperture ratio (area to be etched of a semiconductor wafer) has decreased, and the emission intensity of a specific wavelength taken into the photodetector from the optical sensor has become weak. As a result, the level of the sampling signal from the photodetector is reduced, and it is difficult for the end point determination unit to reliably detect the etching end point based on the sampling signal from the photodetector.

  In addition, when detecting the end point of etching and stopping the process, it is actually important that the remaining thickness of the dielectric layer is equal to a predetermined value. Conventional processes monitor the entire process using time thickness control techniques based on the assumption that the etch rate of each layer is constant. The value of the etching rate is obtained, for example, by processing a sample wafer in advance. In this method, the etching process is stopped simultaneously with the elapse of time corresponding to a predetermined etching film thickness by the time monitoring method.

However, it is known that an actual film, such as a SiO ₂ layer formed by the LPCVD technique, has a low thickness reproducibility. Thickness tolerance due to process variations during LPCVD corresponds to about 10% of the initial thickness of the SiO ₂ layer. Therefore, the time monitoring method cannot accurately measure the actual final thickness of the SiO ₂ layer remaining on the silicon substrate. The actual thickness of the remaining layer is then finally measured by standard spectroscopic interferometry techniques and if it is found to be over-etched, the wafer will be rejected and discarded.

  As techniques for detecting the end point of etching of such a semiconductor wafer by measuring the wafer surface, Japanese Patent Application Laid-Open No. 5-179467 (Patent Document 1), Japanese Patent Application Laid-Open No. 8-274082 (Patent Document 2), and Those using interferometers disclosed in Japanese Patent Application Laid-Open No. 2000-97648 (Patent Document 3), Japanese Patent Application Laid-Open No. 2000-106356 (Patent Document 4), and the like are known.

  In JP-A-5-179467 (Patent Document 1), interference light (plasma light) is detected using three types of color filters of red, green, and blue, and etching end point detection is performed. In JP-A-8-274082 (USP5658418) (Patent Document 2), an interference waveform extreme value (maximum and minimum of waveform: zero of differential waveform) is obtained by using temporal change of the interference waveform of two wavelengths and its differential waveform. Count the passing point). The etching rate is calculated by measuring the time until the count reaches a predetermined value, the remaining etching time until the predetermined film thickness is reached based on the calculated etching rate, and the etching process is stopped based on this. ing.

  In Japanese Patent Laid-Open No. 2000-97648 (Patent Document 3), a waveform (wavelength) of a difference between a light intensity pattern of interference light before processing (with wavelength as a parameter) and a light intensity pattern of interference light after processing or during processing. And the step (film thickness) is measured by comparing the difference waveform with the difference waveform stored in the database. Japanese Patent Application Laid-Open No. 2000-106356 (Patent Document 4) relates to a spin coater and obtains a film thickness by measuring temporal changes of interference light over multiple wavelengths.

  When detecting the end point of etching and stopping the process, it is actually important that the remaining thickness of the film layer is as close as possible to or equal to a predetermined value. In the prior art, the thickness of the film is monitored by adjusting the time based on the premise that the etching rate of each layer is constant. The reference etching rate value is obtained, for example, by processing a sample wafer in advance. In this technique, the etching process is stopped when a time corresponding to a predetermined film thickness elapses.

JP-A-5-179467 JP-A-8-274082 JP 2000-97648 A JP 2000-106356 A

  However, when manufacturing a large number of semiconductor wafers having different types of film structures, a multi-wavelength differential interference pattern database is created for each wafer to be processed and processed. For this reason, if a test etching process is performed using a wafer having the same film configuration as the actual wafer, the cost of the wafer itself is high, and this test process is performed. It is necessary to prepare an extra wafer as much as the wafer, and there is a problem that the cost for this test is high in a small amount of production, and consequently the production cost of the element is increased.

  Further, in the above conventional technology, when detecting the film thickness of the wafer used, and setting the operating conditions of the semiconductor manufacturing apparatus when processing the product wafer using the thickness detection result, A sample wafer was required for thickness measurement. For example, an arbitrary wafer was selected from one lot and used for measurement. For this reason, time and wafers for measurement are required, and the throughput of semiconductor manufacturing is reduced.

  An object of the present invention is to provide a semiconductor manufacturing apparatus with improved processing throughput.

An object of the present invention is to provide a semiconductor wafer having a multi-layer film including a first film as a lower film formed on a surface of a container and a second film formed above the film. A semiconductor manufacturing apparatus that performs an etching process using plasma generated in a container, the intensity of which is a parameter having a wavelength of interference light obtained from the wafer surface during a predetermined period during which the second film is etched. Based on the detector that detects the change in the differential value, and the differential data obtained from the output of the detector, and the zero cross wavelength that greatly increases before and after the differential data at an arbitrary time between the predetermined times. And a function of detecting the thickness of the lower film.

In addition, a semiconductor wafer having a multi-layered film including an oxide film as a lower film formed on the surface of the container and a film formed above the oxide film is generated in the container. A semiconductor manufacturing apparatus that performs an etching process using plasma, and a change in a differential value of intensity using a wavelength of interference light obtained from the wafer surface as a parameter during a predetermined period in which the film formed above is etched. And the differential film obtained from the output of the detector and the lower film based on the wavelength of the zero cross that greatly increases before and after the differential data at an arbitrary time during the predetermined period This is achieved by providing a function of detecting the thickness of

Further, the zero crossing wavelength is detected in the differential data at a plurality of times with a change in the predetermined time, and at a time earlier than a longer wavelength among the plurality of crossing wavelengths at the plurality of times. This is accomplished by detecting a short wavelength that crosses zero and detecting the thickness of the underlying film based on this wavelength .

  A differential interference pattern for interference light having a plurality of wavelengths up to a predetermined film thickness obtained in the etching process is created, and the multi-wavelength differential interference pattern is accumulated for each wafer etching process. The data values of the interference pattern may be averaged to obtain highly reliable multi-wavelength differential interference data. By using this data, it is possible to select and determine the etching conditions such as the film thickness with higher accuracy by selecting the interference waveforms of two different wavelengths that have a correlation that reaches the peak and the valley at the predetermined film thickness. can do.

  Embodiments of the present invention will be described below with reference to the drawings.

  In the following embodiments, those having the same functions as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed description thereof is omitted. In the following embodiments, a semiconductor manufacturing apparatus according to the present invention and a method for measuring etching conditions such as an etching amount (etching depth or film thickness) in an etching process of a wafer as a material to be processed will be described.

  The first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a diagram schematically showing the configuration of a first embodiment of a semiconductor manufacturing apparatus according to the present invention using a longitudinal section and a block. FIG. 2 is a schematic diagram showing a configuration on a wafer to be processed and an outline of light interference in the first embodiment. FIG. 3 is a graph showing an example of data obtained using light interference in the first embodiment.

  First, the overall configuration of a semiconductor wafer etching apparatus provided with the film thickness measuring apparatus of the present invention will be described with reference to FIG.

  The etching apparatus 1 includes a vacuum vessel 2, and an etching gas introduced therein is decomposed by microwave power or the like into plasma 3, and the plasma 3 causes a material to be processed such as a semiconductor wafer on the sample stage 5. 4 is etched. Multi-wavelength radiated light from a measurement light source (for example, a halogen light source) of the film thickness measuring device 10 is guided into the vacuum vessel 2 by the optical fiber 8 and applied to the material 4 to be processed at a vertical incident angle. The material to be processed 4 includes a polysilicon layer, and the radiated light is reflected and refracted at the upper surface of the polysilicon layer, and the radiated light is reflected and refracted at the boundary surface formed between the polysilicon layer and the base layer. As a result, interference light is formed. The interference light is guided to the spectroscope 11 of the film thickness measuring device 10 through the optical fiber 8 and performs film thickness measurement and end point determination processing based on the state.

  The film thickness measuring device 10 includes a spectroscope 11, a first digital filter circuit 12, a differentiator 13, a second digital filter circuit 14, a differential data storage device 15 that is a differential waveform database, a differential waveform comparator 16, and a processing state determiner. 26, a result display 17 and the like. FIG. 1 shows a functional configuration of the film thickness measuring apparatus 10. The actual configuration of the film thickness measuring apparatus 10 includes a CPU, a film thickness measurement processing program, an interference light differential waveform pattern database, and the like. The storage device includes a ROM holding various data, a RAM for holding measurement data and an external storage device, a data input / output device, and a communication control device.

  In the semiconductor manufacturing apparatus of this example, when plasma processing a material to be processed such as a semiconductor wafer, the optical interference waveform is calculated in advance using the optical property value of the material to be processed, and then the predetermined film thickness is measured. A wavelength group in which the differential value of the interference light crosses zero (or takes an extreme value) is selected in advance, and the zero cross changes from positive to negative (or takes a maximum value) and the wavelength group λ1 and zero cross changes from negative to positive. The data of the wavelength group λ2 (or the minimum value) is stored / recorded in a storage or recording means provided in the semiconductor manufacturing apparatus main body or configured to be communicable. In the actual processing of the material 4 to be processed, the intensities of the interference light beams of the wavelength groups λ1 and λ2 are measured, and the differential value of each wavelength group of the measured interference light intensity is zero cross (extreme value and And the zero crossing time is compared with a predetermined value to determine the film thickness of the material to be processed.

  The emission intensity of one wavelength included in the wavelength group λ1 captured by the photodetector 11 is converted into a voltage signal as a current detection signal corresponding to the emission intensity. Signals of a plurality of specific wavelengths output as sampling signals by the spectroscope 11 are stored in a storage device such as a RAM as time series data yij. The time series data yij is then smoothed by the first digital filter circuit 12 and stored in a storage device such as a RAM as smoothed time series data Yij. Based on the smoothed time series data Yij, the differentiator 13 calculates the time series data dij of the differential coefficient value (primary differential value or secondary differential value) and stores it in a storage device such as a RAM. The time series data dij of the differential coefficient value is smoothed by the second digital filter circuit 14 and stored in a storage device such as a RAM as smoothed differential coefficient time series data Dij. Then, an actual pattern of the differential value of each wavelength of the interference light intensity is obtained from the smoothed differential coefficient time series data Dij.

  On the other hand, the emission intensity of one wavelength included in the wavelength group λ2 captured by the photodetector 21 becomes a current detection signal corresponding to the emission intensity, and is converted into a voltage signal. Signals of a plurality of specific wavelengths output as sampling signals by the spectroscope 11 are stored in a storage device such as a RAM as time series data yij. Next, the time series data y′ij is smoothed by the first digital filter circuit 22 and stored in a storage device such as a RAM as smoothed time series data Y′ij. Based on the smoothed time series data Y′ij, the differentiator 23 calculates the time series data d′ ij of the differential coefficient value (primary differential value or secondary differential value) and stores it in a storage device such as a RAM. The The time series data dij of the differential coefficient value is smoothed by the second digital filter circuit 24 and stored in a storage device such as a RAM as smoothed differential coefficient time series data D′ ij. Then, a real pattern of the differential value of each wavelength of the interference light intensity is obtained from the smoothed differential coefficient time series data D′ ij.

  Further, the differential data storage devices 15 and 25 store the interference light intensity data of each wavelength due to the change of the film thickness, or the values and times of the waveforms of these differential data. In particular, the maximum value and the minimum value that become peaks and troughs of the differential data waveform and their times Tm and T′n are stored. Each time Tm, T′n is compared with a predetermined value in which the magnitude of the time between the times is preset or stored / recorded in the differential waveform comparator 16. If the amount of time between Tm and T′n is smaller than this predetermined value, it is determined that the remaining film thickness has reached or nearly reached the predetermined film thickness, and the remaining film of the material to be processed The thickness is determined. The result is displayed on the result display 17.

  When etching a film formed on a semiconductor wafer, the inventors have a plurality of differential waveform data in which one of the differential waveform data has a maximum value and the other has a minimum value in the vicinity of the time before and after the time when the specific film thickness is reached. It has been discovered that the time between the time when the wavelength group can be selected and the waveform of the wavelength belonging to these groups becomes maximum or minimum becomes smaller as the film thickness becomes smaller. Thus, for a specific film thickness, the interval between the time when one takes the maximum value and the time when the other takes the minimum value is determined. The knowledge that it was possible to determine whether the film thickness was reached was obtained.

  The differential data storage device 15 stores changes in differential waveform data of interference light from the semiconductor wafer 4 to be processed, and the differential waveform data takes extreme values (maximum values and minimum values). The time is stored. That is, data on the time of peaks and valleys of the interference light intensity due to the change in film thickness is stored. Further, from the differential data storage device 15, for example, the differential data value of the interference light data at a predetermined time during the processing is stored in the result display 17 for a predetermined range of wavelengths when the etching processing is performed. The result is displayed on the display 17. In addition, data about times when the differential values of the interference light having a plurality of wavelengths become maximum and minimum can be displayed on the display unit 17.

  In the differential waveform comparator 16, the actual pattern and the differential waveform pattern data value Pj are compared to determine the film thickness of the material to be processed. The result is displayed on the result display 17.

  In addition, although the case where only one photodetector 11 is shown in the embodiment, a plurality of photodetectors 11 may be provided when it is desired to measure and control the surface of the material to be processed widely.

FIG. 2 shows an example of a vertical cross-sectional shape of a material 4 to be processed such as a semiconductor wafer used for gate etching. In FIG. 2, a member to be processed (polysilicon) 40 that is a film to be processed is formed on an oxide film 42 that is a base material on a semiconductor wafer (substrate) 4, and this member to be processed A mask material 41 is laminated on 40. For example, when the gate film is etched, the base material of the member to be processed 40 is an SiO ₂ insulating film, and a polysilicon gate layer is formed on the polycrystalline base material corresponding to the space between the source and drain. . In addition, an element isolation groove 49 is formed of an oxide film in order to ensure the independent operation of the gate electrode portion 48 of each element. In the present embodiment, a gate electrode portion 48 is formed on the side where an element isolation trench (Shallow Trench Isolation, STI) 42 is formed below the mask 71.

  The light emitted from the spectroscope 11 or the plasma 3 over a plurality of wavelength ranges is applied to the material to be processed 4 including the laminated structure of the material to be processed 40 and the oxide film 42 as the base material at an incident angle substantially perpendicular. The radiated light guided to the gate electrode portion 48 where the base material 42 is thin is reflected at the boundary surface formed between the processed member 40 and the base material 42 and the radiated light reflected from the upper surface of the material 40 to be etched. The interference light 95A is formed by the emitted light. Similarly, the radiated light guided to the element isolation part 49 with the thick base material 42 is a boundary formed between the radiated light reflected by the upper surface of the processing target member 40 and the processing target member 40 and the base material 42. Interference light 95B is formed by the radiated light reflected by the surface. These interference lights are related to 95B> 95A because the interference intensity decreases as the base oxide film thickness decreases.

  The reflected light is guided to the spectroscope 11 and generates a signal whose intensity changes depending on the thickness of the layer of the material 40 to be etched. The interference light detected through the spectroscope 11 is more dominant in the interference light 95B from the portion where the processing film is thick than the interference light 95A. The etching state such as the etching groove depth is higher on the element isolation groove 42 (for example, film thickness 46).

  The result display 17 may be a display using liquid crystal or CRT, a notification means for notifying that a predetermined film thickness or end point has been reached by light, sound, or a combination thereof. In this embodiment, a result display unit 17 including a display for displaying measurement data as a graph and means for informing with light and sound is provided.

  Furthermore, in the apparatus according to the present embodiment, the measurement data displayed on the result display 17 is used to display specific information desired by the user who has viewed the displayed data, or to detect or calculate specific information. It has a function that allows the user to specify necessary information. For example, a specific point or an arbitrary point on the time-wavelength coordinates displayed on the result display 17 or a designation function such as a pointer for designating the data, a data value at the designated point, or these A function that calculates or detects a specific amount, for example, a time or wavelength between specific times, an etching speed or a film thickness indicating the state of etching, and recognizes these amounts at predetermined positions. It has a function to display easily.

  The means for calculating the above quantity may be an arithmetic unit provided in the apparatus, or another arithmetic unit that is arranged at a distance from the apparatus and that can exchange measured or detected data via the communication means. May be used.

  FIG. 1 shows the functional configuration of the etching amount measuring apparatus. The actual configuration of the measuring instrument 152 excluding the result display 17 and the spectroscope is the CPU, the etching depth, and the film. Consists of a ROM that stores various data such as a thickness measurement processing program and a differential waveform pattern database of interference light, a storage device including a measurement data storage RAM and an external storage device, a data input / output device, and a communication control device be able to. The same applies to the other embodiments described below.

  FIG. 3 is a graph showing changes over time for a plurality of wavelengths of data obtained by differentiating the interference light data detected by the semiconductor manufacturing apparatus of this example. As shown in this figure, it can be seen that the wavelength at which the data becomes the minimum value can be selected at the time before and after the time when one of the values becomes the extreme value (maximum value) by combining several wavelengths. The inventors have found that the time difference between the times when the maximum and minimum values are reached at each of the two wavelengths decreases as the processing proceeds (as the film thickness decreases), and there is a correlation between this time difference and the film thickness. There is a relationship, and the knowledge that the remaining film thickness (etching (groove depth)) and the end point can be determined by determining the time difference is obtained, and the present invention is recalled based on this knowledge.

  FIG. 4 shows a flow of operation of the semiconductor manufacturing apparatus shown in FIG. 1, and particularly shows a flow of operation for adjusting an etching process by detecting an etching state of a member to be processed.

  In this embodiment, the semiconductor manufacturing apparatus acquires the conditions for the etching process for the polysilicon film that is the member to be processed 40 in Step 800. In this step, data on a database of processing conditions stored and recorded in advance in a storage device, a recording device, or the like may be received, and the user may use a keyboard, mouse, etc. provided in the result display unit 17. What is input by the input device may be received, and data indicating the configuration of the film previously recorded on the cassette containing the semiconductor wafer 4 or the semiconductor wafer 4 itself is acquired, and arithmetic means not shown Or the like.

  Next, in step 801, etching is performed using the data stored in the differential data storage device or by comparing each wavelength stored in / recorded on another storage / recording device with differential data of each intensity. Wavelength groups λ1 and λ2 for determining the state are detected, and the direction at the zero crossing at these wavelengths is detected. Furthermore, a reference time difference ΔT is set for the time difference between the opposite extreme times.

  In steps 802, 803, and 804, the waveform data of the interference light obtained by processing the actual semiconductor wafer 4 is detected, and the interference waveforms of the wavelength groups λ1 and λ2 for determination set in step 801 are differentiated. Then, times T1 and T2 at which the differential data becomes extreme values in the respective wavelength groups are calculated.

  In step 805, as described above, the time difference between T1 and T2 calculated in step 804 using the differential waveform comparator 16 is compared with the reference time difference ΔT set in step 801. If it is determined that the time difference ΔT is smaller, it is determined that the desired film thickness has not been reached, and the process returns to step 803 to continue the processing of the target member 40. On the other hand, if it is determined that ΔT is larger, it is determined that the desired film thickness has been reached or less.

  In this embodiment, the etching is stopped here, and the sampling of the interference light of the wavelength groups λ1 and λ2 via the spectroscope 11 is also stopped.

  According to the inventors, according to the theoretical interference analysis of the member to be processed (polysilicon film) 40 in consideration of the influence of the base film (oxide film) 42, the polysilicon 40 is etched and the film thickness changes. It was found that the interference waveform that appears sometimes depends on the thickness of the underlying film (oxide film).

  FIGS. 5 and 6 show the case where the etching process is performed in the apparatus shown in FIG. 1, and when the differential value of the measured detection results of the light having the wavelengths of 400 nm and 380 nm crosses from negative to positive zero, The influence of the thickness of the underlying oxide film on the interference light of these wavelengths obtained from the film (depending on the underlying oxide film) and the differential value of the detection result of light of the above wavelength at the film thickness change from positive to negative It is a graph which shows the base oxide film dependence at the time of zero crossing.

  FIG. 5A shows the polysilicon film thickness with respect to the base oxide film thickness of light having a wavelength of 400 nm in which the zero crossing changes from negative to positive (has reached a minimum value) when the polysilicon film thickness is approximately 60 nm. As shown in this figure, the polysilicon film thickness changes with a periodicity of the base oxide film thickness of about 130 nm. This is because the interference of the polysilicon film is connected and the interference of the underlying oxide film continues.

  That is, it has a periodicity of sin (4πnd / λ). Here, n is the refractive index of the underlying oxide film, d is the thickness of the underlying oxide film, and λ is the wavelength. FIG. 5B shows a wavelength group in which the zero crossing of the interference light changes from positive to negative when the zero crossing of the light having a wavelength of 400 nm changes from negative to positive. . As shown in the figure, the wavelength group exists from about 430 to 500 nm. Therefore, by measuring a wavelength of 400 nm light and a wavelength group of about 430 to 500 nm, a rough thickness can be obtained for the base oxide film.

  For example, when the extreme values of the wavelength of 400 nm and the wavelength of 440 nm coincide with each other, the base oxide film is found to be about several nm to 130 nm, about 170 nm to 260 nm, or about 330 nm to 380 nm.

  When the zero crossing of the wavelength 400 nm matches the wavelength 440 nm and 480 nm, the base oxide film is determined to be about 140 nm to 170 nm and about 300 nm to 330 nm. Furthermore, when considering the product specifications of the wafer, the base oxide film thickness is more limited. A wavelength group in which the measured wavelength 380 nm shown in FIG. 6A crosses from positive to negative zero crossing from negative to positive using the base oxide film thickness (about 300 nm to 330 nm) thus obtained. λ2 is narrowed from about 410 nm to 420 nm (about 410 nm to 450 nm) (see FIG. 6B), and the polysilicon film thickness judgment is about 48 nm to 56 nm, and the accuracy is about 52 nm to 55 nm. Improvement can be achieved.

  Note that a plurality of spectroscopes may be provided when it is desired to measure and control the surface of the material to be processed widely.

  Further, as in the above embodiment, the interference light is measured using the spectroscope 11 using light from the plasma 3 generated in the vacuum chamber 103 without using a light source that supplies light into the vacuum chamber 103. You may measure with the instrument. In this case, the reflection of the plasma light from the surface of the semiconductor wafer 4 is supplied to the photodetector 11 which is a spectroscope. Further, in order to measure changes in plasma light, a measurement port and an optical transmission means are arranged on the side wall of the vacuum chamber 103 so as to be able to receive the inner light, and a signal detected thereby is used as reference light. This reference light must not be light that passes through the optical path directly incident from the wafer surface, but light that can detect changes in the plasma light. In this embodiment, the light received by the plasma light on the side wall is required. It is gained with a vessel.

  Next, a second embodiment of the present invention will be described with reference to FIGS.

  7 and 8 are diagrams showing interference waveforms detected by the semiconductor manufacturing apparatus according to the second embodiment of the present invention.

  In FIG. 7, the left graph shows the change in the intensity of the interference light with the vertical axis indicating the wavelength and the horizontal axis indicating the film thickness (processing time). The right graph is a dotted line on the left graph. It is a graph which shows the change of the intensity | strength of the wavelength range over the wavelength of 700 nm or more from the wavelength of less than 300 nm of specific time shown by.

  As shown in this figure, the interference light shows a sudden change before and after a specific wavelength, and it can be seen that the differential data of the intensity greatly fluctuates. FIG. 8 is a film showing the change in the intensity of interference light with the wavelength on the vertical axis and the film thickness (processing time) on the horizontal axis, as in FIG. When the thickness of the oxide film 42 which is a film formed below a certain polysilicon is 290 nm, (b) is the case where the underlying oxide film is 330 nm. As can be seen from these figures, the inventors change the value of the wavelength at which the intensity of the differential data of the interference light greatly changes depending on the thickness of the underlying oxide film 42, and this wavelength and the underlying oxide film 42. The thickness of the lower oxide film can be detected using the interference light data obtained during the etching process of the target film above it. Obtained. Examples of the present invention are conceived based on this finding.

FIG. 9 is a flowchart showing a flow of operation of the semiconductor manufacturing apparatus of the embodiment that has obtained the interference waveform according to FIGS. In this embodiment, during polysilicon gate etching, when the interference light intensity of a wavelength in the region of about 300 nm to 700 nm is detected and its differential data is obtained, the thickness of the polysilicon film 40 to be processed decreases. Unlike the property where the wavelength that crosses zero (extremely) shifts to the short wavelength side sequentially, the property that the short side wavelength crosses zero before the long wavelength side wavelength depends on the underlying oxide film thickness. Is used to calculate the base oxide film thickness from the inverted wavelength.

  Thus, the thickness of the lower film (underlying oxide film), which has been determined by selecting and measuring a wafer as an arbitrary sample until now, is used with the data of the interference light when the upper film is processed. Therefore, it is possible to suppress an increase in throughput and manufacturing cost that have been reduced due to sample measurement.

  Furthermore, it is possible to improve the accuracy of the predetermined film thickness determination of polysilicon, which is a member to be processed, using the calculated thickness of the underlying oxide film.

  In FIG. 9, the etching condition (etching discharge condition, etching residual film thickness condition) for the member to be processed (polysilicon) is input (step 900), and the data stored in the data storage device from the etching residual film thickness condition is input. To the determination two wavelength groups λ1 and λ2, the direction of each zero cross (maximum or minimum (inclination of the derivative)), and the determination time width ΔT (step 901).

  Next, the etching and sampling of the semiconductor wafer 4 are started (step 902), the differential coefficient time series data Di, j is calculated from the multi-wavelength output signals yi, j from the spectrometer (step 903), and the differential coefficient time series is calculated. A wavelength λi at which the zero crossing times Ti and Tm of the data Di, j and Dm, j are inverted is calculated (904). Here, i is the long wavelength side, and m is the short wavelength side measurement wavelength.

  In the wavelength region where there is no influence of the underlying oxide film, the relationship between time Ti and Tm is Ti <Tm, but in the wavelength region where the influence of the underlying oxide film is present, time Ti and Tm are such that Ti> Tm. A base oxide film is calculated from the base oxide film thickness and the strain wavelength value having this wavelength λi as a database in advance (step 905). Using the calculated base oxide film thickness, the two-wavelength groups for determination λ1, λ2, the direction of the zero cross, the determination time ΔT, etc. are reset from the differential zero cross table (step 906).

  Differentiation processing is performed on the interference waveforms of the re-set two wavelength groups for determination λ1 and λ2 (step 907), and etching is performed by comparing the zero crossing times T1 and T2 (T1-ΔT ≦ T2 ≦ T1 + ΔT determination step 908). The end and sampling end are set (step 909). If the comparison between the zero crossing times T1 and T2 (T1-ΔT ≦ T2 ≦ T1 + ΔT determination step 908) is NO, the operation is repeated from step 903. However, when the base oxide film can be calculated, the processing from step 903 to step 905 is not necessarily performed.

  In this way, in the prior art, the measurement using the sample wafer has increased the processing throughput and cost, whereas in the present invention, when the upper layer film is processed as a product, Thus, the film thickness of the lower layer can be detected from the obtained data, the throughput of processing as a whole using the apparatus can be improved, and the increase in cost can be reduced.

It is a figure which shows the whole structure of the etching apparatus of the semiconductor wafer provided with the film thickness measuring apparatus which becomes one Example of this invention. It is a figure which shows the longitudinal cross-sectional example of the to-be-processed material 70 used as the object of a gate etching process. It is a figure which shows the example of the time change of the interference light with respect to several wavelengths in the middle of the etching process of the said FIG. It is a flowchart which shows the procedure which calculates | requires the film thickness of to-be-processed material, when performing an etching process with the film thickness measuring apparatus of FIG. It is a figure which shows the foundation | substrate oxide film dependence of the film thickness of the to-be-processed material obtained from the Example of FIG. 1, and the foundation | substrate oxide film dependence of the wavelength which a differential value crosses zero from negative to positive with the film thickness. It is a figure which shows the foundation | substrate oxide film dependence of the film thickness of the to-be-processed material obtained from the Example of FIG. 1, and the foundation | substrate oxide film dependence of the wavelength which a differential value crosses zero from negative to positive with the film thickness. It is a figure which shows the wavelength dependence of the multi-wavelength differential interference pattern which becomes the other Example of this invention, and the differential value in a polysilicon film thickness. It is a figure which shows the wavelength dependence of the multi-wavelength differential interference pattern in case base oxide film thickness differs, and the differential value in a polysilicon film thickness. It is a flowchart which shows operation | movement of the other Example of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Etching apparatus, 2 ... Vacuum container, 3 ... Plasma, 4 ... Material to be processed, 5 ... Sample stand, 8 ... Optical fiber, 10 ... Film thickness measuring apparatus, 11 ... Spectroscope, 12 ... 1st digital filter circuit, 13 ... differentiator, 14 ... second digital filter circuit, 15 ... differential zero cross time accumulator, 16 ... differential zero cross time comparator, 17 ... result display.

Claims (3)

A semiconductor wafer having a multi-layer film including a first film as a lower film formed on the surface of the container and a second film formed above the film is generated in the container. A semiconductor manufacturing apparatus for performing an etching process using the plasma generated
A detector for detecting a change in the differential value of the intensity with the wavelength of the interference light obtained from the wafer surface during the predetermined period during which the second film is etched as a parameter, and an output from the detector. A function of detecting the thickness of the lower film on the basis of the zero-crossing wavelength that greatly increases before and after the differential data at the predetermined time between the predetermined data . Plasma generated in the container is a semiconductor wafer having a multi-layered film including an oxide film as a lower film formed on the surface of the container and a film formed above the oxide film. A semiconductor manufacturing apparatus that uses and etches,
A detector that detects a change in the differential value of the intensity with the wavelength of interference light obtained from the wafer surface as a parameter during a predetermined period during which the film formed above is etched, and obtained from the output of the detector. A function of detecting the thickness of the lower film on the basis of a zero-crossing wavelength that greatly increases and decreases before and after the differential data at an arbitrary time during the predetermined time. apparatus. 3. The semiconductor manufacturing apparatus according to claim 1 , wherein the zero-crossing wavelength is detected in the differential data at a plurality of times according to a change in time during the predetermined period, and the crossing at the plurality of times is performed. A semiconductor manufacturing apparatus that detects a short wavelength that crosses zero at a time earlier than a long wavelength, and detects the thickness of the lower film based on the wavelength .

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