JP2003315424A - Apparatus and method for evaluation of electrical characteristic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrical-characteristic evaluation apparatus by which an electrical characteristic of a specimen surface layer is evaluated at low costs and with high spatial resolution and which is handled easily. <P>SOLUTION: An electro-optical crystal 5 is installed at a tip (a part adjacent to a measuring part) of a waveguide 3 used to guide microwaves to the measuring part of a specimen 6, and the electro-optical crystal 5 is irradiated with pulsed light synchronized with a cycle of the microwaves. After reflected light and transmitted light of the pulsed light have been passed through a polarizing plate 10, the intensity of the light is detected, and the strength of an electric field near the measuring part generated by the microwaves is detected. On the basis of the strength of the electric field and on the basis of the strength of a reference electric field measured in advance regarding the specimen as a reference, the electrical characteristic of the measuring part is evaluated. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric characteristic evaluation apparatus and method for evaluating the electric characteristics determined by the structure and material of the surface layer of an object such as a semiconductor wafer with a high spatial resolution and in a non-contact manner.

[0002]

2. Description of the Related Art Conventionally, Japanese Patent Laid-Open No. 2001-343205 (publication 1) discloses a high-frequency current as a noncontact evaluation of the electrical characteristics of the surface layer of an object such as a semiconductor wafer having a conductive film printed thereon. There is disclosed a method and apparatus for exciting an eddy current in a subject by energizing the coil and measuring the eddy current loss in the coil to evaluate the electrical characteristics of the surface layer of the subject. This is an electrical parameter determined by the eddy current loss and the structure and material of the surface layer of the test object, for example, the thickness and defects of the conductive film printed on the surface layer of the test object, the material of the wafer and the material purity of the conductive film. Since the characteristics (resistivity, etc.) have a certain correlation, the electrical characteristics of the surface layer of the subject are evaluated by comparing the reference value of the eddy current loss previously measured for the reference subject and the measured value. Is. As a result, it is possible to evaluate the electrical characteristics such as the film thickness of the conductive film on the surface layer of the subject without contact. On the other hand, Japanese Patent Laid-Open No. 2001-305039 (publication 2) discloses a scanning microwave microscope using microwaves. This is an electromagnetic wave (microwave)
When the opening at the one end of the coaxial resonator excited by is brought close to the surface layer of the object, the electromagnetic wave locally leaked from the opening of the coaxial resonator changes due to the electrical characteristics of the object. As the impedance (electrical coupling state) of the opening changes, the resonance frequency and the Q value of the coaxial resonator change. Therefore, the change of the resonance frequency and the Q value is imaged as a contrast. This publication 2
According to this technique, it is possible to measure the electric impedance along the unevenness of the surface layer of the subject with higher spatial resolution.

[0003]

However, according to the technique of the publication 1, since the coil is formed of a thin wire conductor, the size of the coil is about several mm as shown in the publication 1, There is a problem that the electrical characteristics of the surface layer of the subject cannot be evaluated with higher spatial resolution. Further, in the technique of the above-mentioned publication 2, since the change of the electromagnetic wave locally leaked from the opening of the coaxial resonator is extremely small, in order to detect this with high sensitivity,
A resonance system having an extremely high Q value (a member with high processing accuracy and low loss) is required. For this reason, the technique of the above-mentioned publication 2 has a problem that the manufacturing cost of the resonance system is high and that rigorous calibration is required on a regular basis. Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to evaluate the electrical characteristics of the surface layer of a subject at low cost with high spatial resolution and to easily handle the electrical characteristics. An apparatus and a method thereof are provided.

[0004]

In order to achieve the above object, the present invention is an electrical characteristic evaluation apparatus for measuring the electrical characteristics of a measurement site on the surface layer of an object, which is provided near the measurement site. An electro-optical element, an electromagnetic wave output means for outputting a predetermined electromagnetic wave, a waveguide means for guiding the electromagnetic wave in the vicinity of the measurement site, a light irradiation means for irradiating the electro-optical element with light, and the electro-optical element. It is provided with light detection means for detecting reflected light and / or transmitted light of the emitted light, and characteristic evaluation means for evaluating the electrical characteristics of the measurement site based on the detection result of the light detection means. It is an electrical characteristic evaluation device characterized by the above. Here, as the light detecting means, for example, a polarization degree detecting means for detecting the polarization degree of the reflected light and / or the transmitted light, irradiation light to the electro-optical element by an interferometer, etc., and the reflected light and / or Alternatively, a means for detecting the phase difference from the transmitted light may be considered. As a result, the electric field strength of the electric field generated in the vicinity of the measurement site by electromagnetic waves changes according to the electrical characteristics of the measurement site (film thickness and material of the surface conductive film), and the so-called electro-optical effect causes the proximity of the measurement site. Since the characteristics of the reflected light or the transmitted light in the electro-optical element, for example, the characteristics such as the degree of polarization and the phase change according to the change of the electric field strength, the measurement of the measurement site by detecting the reflected light or the transmitted light. It is possible to evaluate the electrical characteristics. Furthermore, since the detection end that detects the electrical characteristics of the measurement site is an electro-optical element (electro-optic crystal), by making it fine, the electrical characteristics of the surface layer of the subject with extremely high spatial resolution and high sensitivity can be obtained. Can be evaluated.

Further, the waveguide means is a means for irradiating the electromagnetic wave to the vicinity of the measurement site from the tip end thereof which is close to the measurement site (for example, a waveguide or a microstrip line), and It is conceivable that an optical element is provided at the tip of the waveguide means.

Further, it is conceivable that the light irradiating means irradiates pulsed light synchronized with the cycle of the electromagnetic wave. As a result, the light detected by the light detecting means becomes light reflected and / or transmitted through the electro-optical element at the timing when the electromagnetic wave has a constant output, so that the cycle of the electromagnetic wave is short (that is, , The frequency is high), even if the detection speed (response speed) of the photodetector cannot sufficiently follow this, the influence of the electric field strength generated in the vicinity of the measurement site changing at the same period as the electromagnetic wave. Therefore, the correct electric field strength can be measured by eliminating.

Further, it is provided with a position changing means for changing a distance between the electro-optical element and the measurement site, and the characteristic evaluation means is based on a change in a detection result of the light detecting means according to a change in the distance. It is also conceivable that the electrical characteristics of the measurement site are evaluated. For example, the characteristic evaluation means has the same cycle as the distance change cycle in the detection result of the photodetector when the distance between the electro-optical element and the measurement site is periodically changed by the position changing means. For example, the electrical characteristics of the measurement site are evaluated based on the component of. Thereby, even if the absolute distance between the electro-optical element and the measurement site is not positioned with high accuracy, for example, the time-series data of the detection result (index indicating the electric field intensity) of the photodetection means for the subject. By performing waveform fitting and the like on the basis of the time-series data of the reference object that has been measured in advance, it becomes possible to evaluate the electrical characteristics of the object to be measured. Similarly, an electromagnetic wave frequency changing means for changing the frequency of the electromagnetic wave is provided, and the characteristic evaluation means electrically changes the electrical characteristics of the measurement site based on the change in the detection result of the photodetection means according to the frequency change of the electromagnetic wave. It may be one for evaluating characteristics. Further, as the polarization degree detecting means, a means for detecting the light intensity after the reflected light and / or the transmitted light of the light applied to the electro-optical element is passed through the polarizing plate can be considered.

The evaluation method by the electric characteristic evaluation device may be regarded as an electric characteristic evaluation method. That is, it is an electrical characteristic evaluation method for measuring the electrical characteristics of a predetermined measurement site on the surface layer of an object, in which electromagnetic waves are guided near the measurement site by using a predetermined waveguide means and close to the measurement site. It is characterized in that the provided electro-optical element is irradiated with light, reflected light and / or transmitted light of the irradiated light is detected, and the electrical characteristics of the measurement site are evaluated based on the detection result. It is an electrical characteristic evaluation method. Further, it is conceivable that the light applied to the electro-optical element is pulsed light synchronized with the cycle of the electromagnetic wave. Further, the distance between the electro-optical element and the measurement site is changed, and the electrical characteristic of the measurement site is evaluated based on the change in the detection result of the reflected light and / or the transmitted light according to the change in the distance. Or the reflected light and / or the frequency of the electromagnetic wave, and the reflected light and / or
Alternatively, the electrical characteristics of the measurement site may be evaluated based on changes in the detection result of transmitted light.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments and examples of the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention. It should be noted that the following embodiments and examples are merely examples embodying the present invention and are not of the nature to limit the technical scope of the present invention. Here, FIG. 1 is a diagram showing a configuration of an electrical characteristic evaluation apparatus X according to an embodiment of the present invention, and FIG. 2 shows a low frequency microwave used in the electrical characteristic evaluation apparatus according to an example of the present invention. 3A and 3B are a plan view and a side view of a microstrip line guided to the surface of a sample to be measured.

The electrical characteristic evaluation apparatus X according to the embodiment of the present invention will be described below with reference to FIG. Here, a case will be described in which the electrical characteristics of a surface layer of a semiconductor wafer 6 (hereinafter, referred to as a wafer) having a conductive film printed on the surface layer is evaluated as an object. As shown in FIG. 1A, the electric characteristic evaluation apparatus X includes a microwave oscillator 1 that outputs a predetermined microwave (that is, an electromagnetic wave),
A branching circuit 1a for branching the output microwaves into two, a matching unit 2 for matching the branched microwaves, a waveguide 3 for guiding the matched microwaves to a measurement site on the surface layer of the wafer 6, A pulse laser 7 that outputs a predetermined pulsed light,
A microwave detector 16 for detecting the other branched microwave, and a component for outputting a synchronization signal synchronized with the oscillation cycle of the microwave by dividing the detection signal by the microwave detector 16. Circular circuit 11, displacement sensor 12 for detecting the distance between waveguide 3 and wafer 6 (hereinafter referred to as proximity distance), and tip of waveguide 3 by vertically driving waveguide 3. It is provided with a vertical drive unit 13 for adjusting the distance between the unit and the measurement site of the wafer 6, and a signal processing / control circuit 17 for performing various kinds of signal processing and controlling the vertical drive unit 13.

The inside diameter of the waveguide 3 is 10 mm × 23 mm
And the tip of the waveguide 3 close to the wafer 6
Is about 0.1 mm in width and length as shown in Fig. 1 (b).
A slit 4 (opening) of about 0.5 mm is provided
It The microwave leaks from the slit 4 and the wafer 6
The measurement site on the surface is locally irradiated (guided). Well
In addition, the slit 4 has tantalum of about 0.1 mm square.
Lithium acid (LiTaO ₃) And KTP (KTiOPO_Four)
Electro-optic crystal 5 having the electro-optic effect such as
Equivalent to the science element) is provided. Thus, the dielectric constant
Of high electro-optic crystal (eg, relative permittivity> 40) 5
Is close to the measurement site,
The electric field generated by the microwave is the electro-optic crystal
Focus on 5 neighborhoods. The vicinity of this electro-optic crystal 5 (that is, the front
The electric field strength of the electric field generated in the vicinity of the
Varies depending on the electrical characteristics of the fixed part and the proximity distance
This is well known. Therefore, when measuring the electric field strength
Thus, it is possible to evaluate the electrical characteristics of the surface layer of the wafer 6.
is there.

In this electrical characteristic evaluation apparatus X, the electric field strength is not measured electrically by a coil or the like, but is measured by utilizing the electro-optical effect of the electro-optical crystal 5. For the apparatus and method for measuring the electric field strength using an electro-optic crystal, see, for example, JP-A-5-240884 and
It is disclosed in Japanese Patent Laid-Open No. 5-267407. In the electrical characteristic evaluation apparatus X, the laser light from the pulse laser 7 is transmitted through the wave plate 14a and the beam splitter 1.
5, guided by the mirror 18 or the like so as to irradiate the electro-optical crystal 5 through the light guide hole 8 provided in the waveguide 3, and further, the laser light is reflected by the electro-optical crystal 5. The light and the light transmitted through the electro-optic crystal 5 and reflected by the wafer 6 again pass through the light guide hole 8 and the mirror 18, the beam splitter 15, the wave plate 14b, and the polarizing plate 10. The light is received by the photodetector 9. The light received by the photodetector 10 is photoelectrically converted, and the intensity signal of the light is input to the signal processing / control circuit 17. Here, the light reflected and transmitted by the electro-optic crystal 5 has a polarization plane different from that of the original laser light due to the electro-optic effect. The degree of polarization (angle of polarization plane) changes depending on the electric field strength near the electro-optic crystal 5. Therefore, the intensity of light after passing through the polarizing plate 10 is
It corresponds to the degree of polarization. That is, the intensity of light after passing through the polarizing plate 10 represents the electric field intensity in the vicinity of the electro-optical crystal 5 (that is, in the vicinity of the measurement site). In addition, the electro-optic crystal 5 is made to have a thickness of 0.
The reason why the size is as small as about 1 mm square is that the change in the electric field strength caused by variations in the thickness of the conductive thin film is very small, and therefore this minute change is detected with high sensitivity. In this way, the detection end (the electro-optic crystal 5) for detecting the electric field strength of the measurement site can be made fine, so that the electrical characteristics of the surface layer of the subject can be evaluated with a very high spatial resolution. Of course, the electro-optic crystal 5
The size and shape of the object may be determined according to the change range of the electrical characteristics to be evaluated and the shape of the surface layer of the subject.

However, since the electric field strength fluctuates in the same cycle as the microwave oscillation cycle, for example, when the frequency of the microwave is 10 GHz, the electric field strength changes in a cycle of 0.1 ns. It will be. On the other hand, the response of the ordinary photodetector 9 (photoelectric converter) is 1
Since it is about ns, the electric field strength cannot be correctly measured while continuously irradiating the laser light (value becomes 0, etc.). Therefore, by inputting the synchronizing signal (signal synchronized with the cycle of the microwave) generated by the frequency dividing circuit 11 to the pulse laser 7, pulsed light (for example, pulse) synchronized with the cycle of the microwave is input. Width 1p
s or less) is applied to the electro-optic crystal 5. As a result, the light detected by the photodetector 9 becomes the light reflected and transmitted by the electro-optic crystal 5 at the timing when the microwave has a constant output, so that the electric field strength is the microwave. The correct electric field strength can be measured without the influence of the change in the same period.

The following is an example of a method for evaluating the electrical characteristics of the measurement site based on the electric field intensity (the electric field intensity measured by the intensity of the light detected by the photodetector 9 instead of the electric field intensity). One example thereof is a method of performing evaluation based on the electric field strength measured by fixing the distance (close distance) between the tip portion of the waveguide 3 and the measurement site. In this method, first, in the state where the proximity distance is fixed to a predetermined distance (for example, 100 μm or less) by the vertical drive device 13 in advance, a wafer 6 (for example, the wafer 6) having a reference electric characteristic is provided. Thickness of surface conductive film (known)
A plurality of wafers with different numbers, etc., hereinafter referred to as reference wafer 6)
The electric field strength is measured in advance, and based on the measured value, an evaluation table or an evaluation formula representing the relationship between the electric field strength and the electrical characteristic to be evaluated (or its evaluation value) is obtained to perform the signal processing. / Stored in the control circuit 17.
Then, with the proximity distance fixed to the same distance as the predetermined distance, the electric field strength of the wafer 6 to be inspected is measured, and the measured value is applied to the evaluation table or the like to detect the object. The electrical characteristics of the wafer 6 to be the following are quantitatively evaluated.

Another example is a method of evaluating based on the electric field strength measured by periodically changing the proximity distance. In this method, the vertical drive device 13 measures the time series data (waveform data) of the electric field intensity of the reference wafer 6 while changing the proximity distance periodically at a predetermined cycle. This is stored in the signal processing / control circuit 17. Then, while the proximity distance is periodically changed at the same cycle as the above, the time-series data of the electric field intensity is measured for the wafer 6 to be inspected, and the time-series data and the time for the reference wafer are measured. The electrical characteristics of the wafer 6 to be inspected are evaluated by performing waveform fitting based on the series data. For example, the electric field strength E is E = c · EXP
(−βd) (c and β are constants that depend on the electrical characteristics of the subject, d is the proximity distance), and the absolute value of the proximity distance d is unknown, Wafer 6
Further, waveform fitting is performed on the time-series data of each of the reference wafers, and the electrical characteristics of the subject are evaluated by comparing c and β representing the electrical characteristics of the subject with c and β of the reference wafer. it can. Similarly, the microwave oscillator 1 changes the output frequency of the microwave, and the electric field strength is changed based on the change of the electric field strength (time series data) according to the change of the microwave frequency at that time. It can also be applied when evaluating characteristics.

[0016]

[Embodiment] In the electrical characteristic evaluation apparatus X, the waveguide 3 is used as the waveguide means for guiding the microwave to the measurement portion of the wafer 6, but the invention is not limited to this. A strip line may be used. FIG. 2 is a diagram showing a plane and a side surface of the microwave strip line 20 used as the waveguide unit. As shown in FIG. 2, the microwave strip line 20 is sandwiched between a transmission line 21, which is a conductor on one side, a ground plate 23, which is a conductor on the other side, and between them. A dielectric (insulator) 22 is provided, and the electro-optic crystal 5 is provided at the tip (the portion of the wafer 6 close to the measurement site). The microwave generated by the microwave oscillator 1 is output to the transmission line 21.
As a result, the microwave is guided to the measurement site through the transmission path 21. In addition, a light guide hole 24 for passing a laser beam with which the electro-optic crystal 5 is irradiated is provided at the tip of the microwave strip line 20. In the plan view of FIG. 4, for the sake of convenience, the electro-optic crystal 5 is illustrated as being transparent (a hole penetrating the electro-optic crystal 5 is not provided at the tip portion).

Microwave (electromagnetic wave) guided to the measurement site
When using a frequency of several GHz or more,
In the transmission line having a dielectric such as the microwave strip line 20, the dielectric loss becomes large and the microwave cannot be transmitted efficiently, so that the hollow waveguide 3 needs to be used. However, lower frequencies (eg,
When a microwave of several hundred MHz or less) is used, the microwave strip line 20 is used as the waveguide means.
It is possible to use a coaxial cable or the like. In this case, the change period of the measured electric field intensity becomes long (for example, about 10 ns), and the photodetector 9 is in a responseable range. Therefore, if the microwave of low frequency and the microwave strip line 20 or the like is used as the waveguide means thereof, the pulsed light in which the light (laser light) with which the electro-optic crystal 5 is irradiated is synchronized with the cycle of the microwave is used. Therefore, it is possible to measure the electric field intensity using continuous light. Such embodiments are also within the scope of the present invention.

Further, the above-mentioned electrical characteristic evaluation device X is
Although the degree of polarization of the reflected light and / or the transmitted light radiated to the electro-optic crystal 5 is detected, the reflected light and / or the reflected light may be detected by the electro-optic effect of the electro-optic crystal 5.
Alternatively, since the phase of the transmitted light also changes, the electro-optic crystal 5
It is also possible to detect the phase difference between the light irradiating the light and the reflected light and / or the transmitted light. This is, for example, to split the laser light from the pulse laser 7, irradiate the electro-optic crystal 5 with one of them, and use its reflected light and / or transmitted light as measurement light, and the other as reference light to form an interference fringe image. The phase difference may be obtained by subjecting the image data of the interference fringe image to a predetermined unwrap process using an interferometer to be formed. Phase difference data obtained in this way, that is,
The method of evaluating the electrical characteristics of the measurement site of the object based on the phase difference data of the object to be measured which is a reference measured in advance and the phase difference data of the object to be characterized is It is similar to the case based on the evaluation.

[0019]

As described above, according to the present invention,
Since the detection end for detecting the electric field intensity at the measurement site is an electro-optic crystal, by making it fine, the electrical characteristics of the surface layer of the subject can be evaluated with extremely high spatial resolution and high sensitivity. Moreover, the electro-optic crystal, the microwave and laser light output device, and the like do not require special labor and care for maintenance and handling, and are low in cost as compared with the case where a resonance system having a high Q value is used. And is easy to handle.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an electrical characteristic evaluation apparatus X according to an embodiment of the present invention.

2A and 2B are a plan view and a side view of a microstrip line for guiding a low-frequency microwave to the surface of a sample to be measured, which is used in the electrical characteristic evaluation apparatus according to the embodiment of the present invention.

[Explanation of symbols] 1. Microwave oscillator 2 ... Matching device 3 ... Waveguide 4 ... slit 5 ... Electro-optic crystal 6 ... Semiconductor wafer (subject) 7 ... Pulse laser 8 ... Light guide hole 9 ... Photodetector 10 ... Polarizing plate 11 ... Divider circuit 12 ... Displacement sensor 13 ... Vertical drive device 14a, 14b ... Wave plate 15 ... Beam splitter 16 ... Microwave detector 17 ... Signal processing / control circuit 18 ... Mirror 20 ... Microwave strip line 21 ... Micro transmission line 22 ... Dielectric (insulator) 23 ... Ground plate 24 ... Light guide hole

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Claims (12)

[Claims] 1. An electrical characteristic evaluation device for measuring an electrical characteristic of a measurement site on a surface layer of an object, the electro-optical element being provided in proximity to the measurement site, and an electromagnetic wave output means for outputting a predetermined electromagnetic wave. A wave guide means for guiding the electromagnetic wave to the vicinity of the measurement site, a light irradiating means for irradiating the electro-optical element with light, and a reflected light and / or a transmitted light of the light with which the electro-optical element is irradiated. An electrical characteristic evaluation device comprising: a light detecting means; and a characteristic evaluating means for evaluating an electrical characteristic of the measurement site based on a detection result of the light detecting means. 2. The electrical characteristic evaluation apparatus according to claim 1, wherein the light detection unit is a polarization degree detection unit that detects the polarization degree of the reflected light and / or the transmitted light. 3. The wave guide means irradiates the electromagnetic wave to the vicinity of the measurement site from a tip part thereof close to the measurement site, and the electro-optical element is provided at the tip part of the wave guide means. The electrical characteristic evaluation apparatus according to claim 1, wherein the electrical characteristic evaluation apparatus comprises: 4. The electrical characteristic evaluation apparatus according to claim 1, wherein the light irradiating means irradiates pulsed light synchronized with the cycle of the electromagnetic wave. 5. A position changing means for changing a distance between the electro-optical element and the measurement site is provided, and the characteristic evaluation means is based on a change in a detection result of the light detecting means in response to a change in the distance. The electrical characteristic evaluation device according to claim 1, wherein the electrical characteristic of the measurement site is evaluated. 6. The change cycle of the distance in the detection result of the photodetecting means when the characteristic evaluating means cyclically changes the distance between the electro-optical element and the measurement site by the position changing means. The electrical characteristic evaluation device according to claim 5, wherein the electrical characteristic of the measurement site is evaluated based on a component of the same period as the above. 7. An electromagnetic wave frequency changing means for changing the frequency of the electromagnetic wave is provided, wherein the characteristic evaluating means changes the detection result of the photodetecting means in response to a change in the frequency of the electromagnetic wave. The electrical characteristic evaluation device according to claim 1, which is for evaluating electrical characteristics. 8. The polarization degree detecting means detects the light intensity after the reflected light and / or the transmitted light of the light irradiated on the electro-optical element has passed through a polarizing plate. 7. The electrical characteristic evaluation device according to any one of 7. 9. A method for evaluating electrical characteristics of a predetermined measurement site on a surface layer of an object, the method comprising: guiding an electromagnetic wave in the vicinity of the measurement site by using a predetermined wave guide means to the measurement site. Irradiating light to an electro-optical element provided in close proximity, detecting reflected light and / or transmitted light of the irradiated light, and evaluating the electrical characteristics of the measurement site based on the detection result. Characteristic electrical property evaluation method. 10. The electrical characteristic evaluation method according to claim 9, wherein the light with which the electro-optical element is irradiated is pulsed light synchronized with the period of the electromagnetic wave. 11. The electrical characteristic of the measurement site is changed based on a change in the detection result of the reflected light and / or the transmitted light in response to a change in the distance between the electro-optical element and the measurement site. The electrical characteristic evaluation method according to claim 9, which is for evaluating 12. The electric characteristic of the measurement site is evaluated based on a change in the detection result of the reflected light and / or transmitted light according to a change in the frequency of the electromagnetic wave, by changing the frequency of the electromagnetic wave. The electrical characteristic evaluation method according to claim 9.