JPS6160576B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of measuring semiconductor properties using microwaves.

Recent semiconductor devices are becoming increasingly sophisticated, as exemplified by LSIs, and the characteristics of the semiconductor materials used in them are also required to be strictly controlled. Therefore, it is necessary to accurately understand the raw material of the mirror-polished semiconductor substrate for device processing, and various characteristics during each process during device processing or at the final stage. What is important in such measurements is (a) measuring and evaluating local lifetime fluctuations of large-diameter silicon and other semiconductor wafers, and (b) measuring and evaluating large quantities of wafer products without contaminating or damaging them. It is to measure.

However, no prior art technology that can meet such demands has yet been found. In other words, in this type of measurement method, a sample is sealed inside a waveguide or inserted through a slit, and the signal is detected by utilizing absorption by the injected carrier when microwaves pass through the sample. The method of detecting this is to make the tip of the waveguide thin (approximately 1 mm on each side) and sharpen it (however, in order to guide the microwave to the tip, it is necessary to remove the H-plane of the waveguide) and apply a sample to the tip. In addition, a horn antenna that is one to two orders of magnitude larger than the cross-sectional area of the waveguide is used to radiate microwaves, transmit them through the sample, and then There are other known methods of collecting and detecting radio waves using a horn antenna, but these methods cannot sufficiently meet the needs (a) and (b) above. for example,
In the method described above, the size and handling of the sample are restricted by the dimensions of the waveguide, so it is not possible to meet the needs of both (a) and (b) above.
Although it is possible to meet the need in (b), it is not possible to meet the need in (b) because it is a contact measurement, and furthermore, because it is a non-contact measurement, it cannot meet the need in (b) above. However, since the microwave beam is greatly expanded by the horn antenna, it is impossible to meet the need (a), and there are problems such as the S/N ratio is extremely deteriorated.

The present invention has been made in consideration of the above points, and
By adopting a completely new method of reflection type non-contact measurement outside the waveguide, the above (a) and
The purpose of the present invention is to provide a method for measuring semiconductor characteristics that can meet both of the needs of (b).

To achieve this objective, the present invention uses a waveguide whose side walls are closed to the open end of the tip,
Microwaves are incident from the open end of the waveguide onto the surface of a semiconductor facing the open end at a predetermined distance, and the modulated microwave reflected from the surface of the semiconductor is absorbed from the open end and measured. By this, the characteristics of the semiconductor described above are measured.

Embodiments of the present invention having such characteristics will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram of an apparatus used in one embodiment of the invention to measure the resistivity or carrier concentration of a semiconductor sample, such as silicon. In this figure, the microwave generated by Gunn oscillator 1 passes through impedance matching device 2 and E-H tuner 3 to magic T.
4 and is transmitted in three directions through three waveguides. The microwave transmitted to the non-reflection terminal 5 disappears, but the microwave transmitted by the waveguide 9 is held and conveyed by the support and conveyance mechanism 11 so as to face the open end in parallel at a predetermined distance d. It enters the surface of the sample 10 where the microwave is being held, undergoes a considerable change in amplitude and phase due to interaction with the free carrier in the crystal, and then returns to the magic T4 via the waveguide 9 again as a reflected microwave. It passes through the E-H tuner 6, is detected by the detector 7, and is displayed on the detection current indicator 8 as a quantity representing the characteristic to be measured.

Next, the waveguide 9 and the sample 10, which are the features of the present invention, will be described.
Explain the arrangement relationship. As shown in FIG. 2, the sample 10 and the tip of the opening of the waveguide 9 are placed apart from each other by a distance d within a range where reflected microwaves can be detected without contacting each other. As the waveguide 9, one whose side wall is closed to the opening at the tip is used.
In the figure, a shows a case in which the waveguide 9 is open without being constricted, and is suitable for determining average characteristics within a large measurement area, whereas b shows a case in which the waveguide 9 is constricted into a tapered shape and is open to obtain the average characteristics within a large measurement area. Used when determining local characteristic values when the end is an open end. In local measurement, for example, both walls parallel to the H-plane of the waveguide are tapered, and the distance between the two walls at the tip is preferably 0.1 to 0.5 mm when the microwave frequency used is 10 GHz.

It is clear that by using the above-mentioned apparatus, continuous measurement can be performed in a non-contact manner without processing the sample to be measured, but examples with various characteristics will be shown below.

Figure 3 shows the result of actually measuring the relationship between the resistivity of a semiconductor silicon (N type) wafer with a certain thickness (0.5 mm) and the microwave detection current using the equipment shown in Figure 1 as is. This is an example. The microwave was 10 GHz, the sample was supported by a Teflon roller, and the distance d between the waveguide tip and the sample surface was 1.0 mm.
In this case, the magnitude of the obtained detection current will change if the sample thickness or the above-mentioned distance d changes for a sample with a constant resistivity, so it is necessary to adjust these to a constant value or make corrections. be. In addition, if there is a conductive substance near the sample part where the incident microwave has a sufficiently large value, the measurement signal will change, so it is recommended to place the sample on a copper plate, hold it with an insulator, hold it at a distance, etc. It is necessary to keep the conditions constant and find the relationship between resistivity (or carrier concentration) and measurement signal for each condition.

FIG. 4 also shows the minority carrier life (lifetime) τ of a silicon ribbon crystal (P type) according to the present invention.
FIG. 3 is a block diagram when applied to the measurement of Fourth
In the figure, the microwave radiated from the Gunn oscillator 1 into the waveguide is adjusted by the impedance matching device 2, E-H tuner 3, magic T4, and non-reflection termination 5, and is transmitted from the open end of the waveguide 9 to the holding table. Combined transport mechanism 11
The radiation is emitted toward the surface of the semiconductor sample 10 supported and conveyed by the semiconductor sample 10, and is reflected inside the sample with changes in phase and amplitude corresponding to the carrier concentration at each moment.
Returning again to the open end of the waveguide 9, the process is the same as the example shown in FIG. A light pulse, which is the output of a light pulse generator 12 using either a laser light source or the like, is irradiated onto the surface of the sample where the microwaves are incident and within the diffusion distance of the carrier to determine the equilibrium concentration at the measurement temperature. The microwave detects the generation of more excess carriers, and the process in which the excess minority carriers recombine with the majority carriers and gradually decrease, so that the carrier concentration gradually attenuates to an equilibrium concentration. 7 as an output signal and display it as an attenuation curve on a synchroscope 13 to determine the life time τ of the sample.
The difference is in how they are obtained.

Next, the arrangement of the waveguide 9 and the sample 10 and the method of irradiating light pulses, which are features of the present invention, will be explained. That is, the opening tip of the waveguide 9 and the surface of the sample 10 are placed apart from each other by a distance d without contacting each other, and the light pulse can be easily irradiated near the microwave incident position even from outside the waveguide. Since it is possible to apply a light pulse to the surface of the sample on the waveguide side where microwaves are incident, it is the most sensitive method because it detects changes on the surface where the largest amount of excess carriers are generated by incident photons. Can be measured. Of course,
If the thickness of the sample is sufficiently thin and the absorption of light from the back side of the sample occurs to a depth that the reflected microwaves reach, it is also possible to irradiate the light pulse from the back side of the sample. Therefore, it is valid.

Figure 5 shows the life time τ of silicon single crystal wafers (P and N type) measured in relation to the distance d between the opening tip of the waveguide 9 and the back surface of the sample using the above measuring device. The results are shown below. As is clear from this figure, changing the distance d does not affect the measurement results.

As is clear from the above explanation, the present invention, which employs a completely new method of reflection type non-contact measurement outside the waveguide, meets the needs of local measurement of minute parts and non-contact non-contamination as described above. The excellent effect of being able to fully respond to the following can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention for measuring carrier concentration or resistivity, and FIG.
A layout diagram showing the arrangement of the waveguide and the semiconductor sample to be measured when the open end of the waveguide has standard dimensions corresponding to the microwave frequency used in the embodiment shown in FIG. Figure 3 shows the resistivity of N-type silicon obtained using the method in Figure 1 and the detector. An explanatory diagram showing the relationship with the output current; FIG. 4 is a block diagram showing an example of measuring the minority carrier life according to the present invention;
FIG. 5 is a data diagram showing the relationship between the life time of silicon, the open end, and the distance between the sample surfaces measured using the method shown in FIG. 1... Gunn oscillator, 2... Impedance matching device, 3... E-H tuner, 4... Magic T,
5...Reflection-free termination, 6...E-H tuner, 7...
...Detector, 8...Detection current indicator, 9...Waveguide with an open end, 10...Sample to be measured, 11...
Sample holding table, 12... Optical pulse generator, 13...
Synchronoscope, R...Light pulse irradiation and minority carrier diffusion distance range.

Claims (1)

[Claims] 1. Using a waveguide whose side wall is closed to the opening at the tip, microwaves are applied from the open end of the waveguide to the surface of a semiconductor facing the open end at a predetermined distance. A method for measuring semiconductor characteristics, characterized in that the characteristics of the semiconductor are measured by absorbing modulated microwaves incident on the semiconductor surface and reflected from the surface of the semiconductor through the aperture end. 2. The semiconductor characteristic measuring method according to claim 1, wherein the waveguide has a shape that becomes thinner toward the open end. 3 Using a waveguide whose side wall is closed up to the opening at the tip, microwaves are incident from the open end of the waveguide to the surface of the semiconductor facing the open end at a predetermined distance, and the microwave Excess minority carriers are injected by a predetermined means into a region of minority carrier diffusion caused by wave incidence, and when the open end of the waveguide receives the modulated microwave reflected from the surface of the semiconductor, the excess minority carriers become majority carriers. A method of measuring the minority carrier life of a semiconductor by measuring the process of decrease in combination with 4. A method for measuring minority carrier lifetime of a semiconductor according to claim 3, wherein the predetermined means is irradiating a light pulse.