JPH04279030A - Surface temperature measuring method of polished semiconductor wafer - Google Patents

Abstract

PURPOSE:To enable the temperature on the polished surface of a wafer to be measured highly accurately through the polished surface in order to control the polishing speed properly when the semiconductor wafer is polished. CONSTITUTION:After the oxygen thermal doner erasure treatment is performed to a wafer for allowing an entire specific resistance to be virtually equal, this wafer is polished for a specified amount of time and the specific resistance on the wafer polished surface is measured. By fitting this specific resistance to a temperature-specific resistance curve(calibration curve) which is prepared previously, the temperature on the abrasion surface is determined. Thus, by obtaining a temperature based on an actually measured specific resistance of the wafer abrasion surface, the temperature of the abrasion surface can highly accurately be measured.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for measuring the temperature of a polished surface of a semiconductor wafer, and in particular, a method for measuring the temperature of a polished surface of a semiconductor wafer. The present invention relates to a method for measuring the temperature of a polished surface of a semiconductor wafer that can be measured with high accuracy.

0002

2. Description of the Related Art Semiconductor devices such as VLSIs are formed by subjecting a semiconductor wafer cut from a semiconductor single crystal such as silicon to predetermined processes. In this case, the element forming surface (front surface) of the semiconductor wafer is subjected to mirror polishing treatment in advance.

[0003] A specific method for the above surface polishing treatment is as follows:
For example, as shown in the half-sectional view of FIG.
A wafer W is bonded to the lower surface with the polishing surface facing downward using wax, and the polishing plate 14 is brought into contact with the polishing pad 12 mounted on the surface plate 10 with pressure. A method is known in which the lower surface (front surface) of the wafer W is polished to form a mirror surface by rotating the polishing plate 14 and the surface plate 10 in a direction along the wafer surface while supplying a polishing liquid. It is being

When polishing the surface of, for example, a silicon wafer by the method described above, so-called mechanochemical polishing is performed, and the polishing rate Vmcp by this mechanochemical polishing is expressed by the following equation (1). (“Precision processing technology for crystalline materials for electronics”, published by Science Forum, 1985, p.
319).

[0005]Vmcp=Vm+Vc

......(1) Here, Vm: Polishing rate due to mechanical action, Vc: Polishing rate due to chemical action.

In particular, high-quality silicon wafers used in VLSI manufacturing require a polished surface with very little crystal distortion, so polishing is mainly performed by chemical action, that is, the condition of Vc >> Vm. Mirror polishing is performed.

By the way, the polishing rate V due to the above chemical action
It is known that c is mainly affected by temperature, distortion of the crystal lattice, and changes in surface energy due to the generation of fresh surfaces. Now, if the activation energy of the chemical reaction is E0, the thermal energy is E1', and the processing strain energy is E2', then the polishing rate due to chemical action is Vc.
can be expressed by the following equation (2) (Toshiro Karaki et al., Precision Machinery, 46, 1980, p. 331).

Vc =V0 exp {-(E0 -E')/R
T} ......(2) Here, E'=E1'+E2' V0: proportionality constant, R: gas constant, T: temperature.

According to the above equation (2), it can be seen that the polishing rate Vc due to chemical action is greatly influenced by temperature.

[0010] Therefore, in order to polish a high quality silicon wafer for VLSI and form a mirror surface with high flatness,
It is extremely important to control the polishing rate Vmcp with high precision, and for this purpose it is necessary to measure the temperature of the polishing surface of the wafer with high precision.

Conventionally, as shown in FIG. 9, a groove 18 having a width of about 5 mm and a length of about 150 mm is formed in the wafer contact surface of the polishing plate 14, and a thermistor or the like is used to measure the temperature of the polished surface of a wafer. temperature sensor 20
There is a known method in which the temperature sensor 20 is brought into contact with the side (back side) opposite to the polished surface of the wafer W, and the temperature is measured with the temperature sensor 20 (Takao Nakamura et al., Journal of Precision Engineering, 56,
1990, P. 1046).

0012

[Problems to be Solved by the Invention] However, when five wafers were actually polished using the polishing plate 14 provided with the grooves 18, as shown in Table 1 below, the wafers were TT is an index expressing flatness
V (Total Thickness Variation
n) was 6.6 μm worse than the case without grooves.

[0013]

[Table 1]

Furthermore, in order to examine the measurement accuracy when measuring the surface temperature from the back surface of the wafer W as described above, FIG.
As shown in FIG. 9, a hot plate 22 is placed at the position of the surface plate 10 in FIG. 9, and the temperature of the hot plate 22 is changed to heat the polished surface of the wafer W. As a result of actual measurements, the results shown in Table 2 below were obtained.

[0015]

[Table 2]

From Table 2 above, there is a large error between the hot plate temperature, that is, the temperature of the polished surface of the wafer W, and the temperature measured by the temperature sensor 20, and the error increases as the temperature increases. Hot plate temperature is 100
It can be seen that the error is 66.2% when the temperature is ℃.

As described above, in the case of the method of polishing the wafer W by forming the groove 18 on the wafer contact surface of the polishing plate 14 and bringing the temperature sensor 20 into contact with the back surface of the wafer W at the position of the groove 18, In this case, the flatness of the polishing surface is impaired due to the structure of the polishing plate 14, and the temperature of the polishing surface cannot be accurately measured, so the polishing speed cannot be accurately controlled by the temperature of the polishing surface. There was a problem.

The present invention has been made to solve the above-mentioned conventional problems, and provides a method for measuring the temperature of a polished surface of a semiconductor wafer, in which the temperature of the polished surface of a wafer can be measured with high precision through the polished surface. The challenge is to provide the following.

[0019]

[Means for Solving the Problems] The present invention provides the following methods for measuring the temperature of a polished surface during mirror polishing of a semiconductor wafer.
After subjecting the semiconductor wafer to oxygen thermal donor elimination heat treatment, polishing the semiconductor wafer, measuring the resistivity of the polished surface of the semiconductor wafer after polishing, and determining the temperature of the polished surface based on the resistivity value. Thus, the above-mentioned problem has been achieved.

[0020]

[Operation] As mentioned above, in order to form a highly flat polished surface on a wafer, it is necessary to avoid forming grooves, holes, or other concave parts on the wafer contact surface of the polishing plate, and to control the temperature of the wafer polished surface with high precision. It is extremely important to measure. The technology that makes this possible will be described in detail below. Note that the present invention is not limited to the specific examples shown below.

The present inventor focused on the oxygen originally contained in Czochralski-grown silicon single crystals, and as a result of various studies, the following findings were obtained.

[0022] A silicon wafer cut from the Czochralski grown silicon single crystal usually has a crystal grain size of 27 to 33
Oxygen is inherently contained as an impurity at a concentration of ppma (ASTM F121-79). This oxygen impurity is initially located between the lattices of silicon atoms and is electrically inactive, but it is known that when heat-treated at around 450°C, it becomes a donor and becomes electrically active (J.Ap.
pl, Phys, 62 1987, P. 1287
).

FIG. 11 is a graph showing the relationship between the heat treatment temperature for generating an oxygen thermal donor and the measured donor generation amount, and FIG. 12 is a graph showing the relationship between the heat treatment time and the measured donor generation amount. This is the graph shown. From FIGS. 11 and 12, it can be seen that the oxygen thermal donor concentration is sensitive to the wafer temperature and also largely depends on the heat treatment time. It can also be seen that the generated oxygen thermal donor reduces the resistivity of the wafer, but the wafer has an inherent resistivity determined by the temperature and time of the heat treatment and the initial oxygen concentration.

By the way, in a silicon wafer cut from a Czochralski-grown silicon single crystal, even in an untreated state, some of the oxygen contained therein has already been converted into oxygen, depending on the thermal history during crystal growth. It is converted into a thermal donor, and the rate of conversion differs depending on the position of the crystal. Therefore, in this state, it is inconvenient to determine the temperature of the wafer based on the resistivity measurement value using the method described later.

Therefore, in the present invention, for example, "Silicon Crystals and Doping" by Takao Abe et al., 1986, published by Maruzen, P. The resistivity of the wafer is measured after the wafer has been previously subjected to an oxygen thermal donor quenching heat treatment as described in No. 24 to render oxygen electrically inert. Further, as the above-mentioned wafer, a non-doped wafer having a high resistivity and containing no dopant that is normally added during crystal growth is used.

FIG. 13 shows a non-doped silicon wafer that has undergone sufficient oxygen thermal donor erasure as described above.
It is a graph showing the relationship between the heating temperature and the actually measured resistivity when heating was performed with a hot plate while changing the heat treatment time. At this time, the heating temperature ranges from room temperature (25°C) to 200°C, which is the polishing temperature that is thought to occur in actual mirror polishing.
Temperatures up to ℃ were used. Further, the heating time was 20 minutes to 200 minutes, which is considered to be used in actual mirror polishing. Note that the above-mentioned resistivity measurement was performed on a 25° C. wafer after the wafer was heated to a predetermined temperature for a predetermined period of time.

From the results shown in FIG. 13 above, the heat treatment time (20
It can be seen that unique resistivity curves A, B, and C are obtained, which are different for each period (100 minutes, 200 minutes), but decrease with increasing temperature. By utilizing this relationship between resistivity and heat treatment temperature, it has become possible to determine the temperature of the wafer inversely from the polishing time and resistivity.

The present invention has been made based on the above findings, and by measuring the resistivity of the polished surface (surface) of a wafer, based on the resistivity, for example, the graph (resistivity-temperature) shown in FIG. This makes it possible to determine the temperature of the polished surface with high accuracy from the curve).

FIG. 14 shows a specific method for measuring the temperature of the polished surface of a wafer. As shown in Table 2 above, since it is impossible to measure the temperature of the polished surface from the opposite side, it is necessary to directly measure the temperature in the vicinity of the polished surface. Therefore, using a spreading resistance measuring device having a probe 24 as shown in FIG.
is brought into contact with the wafer W to measure the specific resistance near the polished surface of the wafer W.

Now, when a voltage V is applied between the probe 24 in contact with the polished surface of the wafer W and the back surface of the wafer,
If the current flowing between the probe 24 and the back surface of the wafer is I, the specific resistance ρ is given by the following equation (3) (Kenichi Goto et al., "Exercise on Electromagnetism" 1970, published by Kyoritsu Shuppan, P1
71).

ρ=[πa/{K(ρ)−1+C}]・(V/I
) ......(3) Here,
a: radius of contact between the probe and the wafer, K(ρ), C: correction coefficient.

Further, as shown in FIG. 14, the probe 2 is attached to the wafer W.
When measuring resistivity by contacting the probe 24, the measurement area is the shaded area in the same figure, and the depth of this area is the depth of the probe 24.
is approximately the radius of the diameter in contact with the wafer W. For example, if a device with a probe tip of 4 μm is used, it is possible to measure the resistivity in a region up to a depth of about 2 μm from the polished surface of the wafer W, that is, in the very vicinity of the polished surface. Furthermore, by bringing the probe 24 into contact with any arbitrary point on the wafer W and measuring the resistivity, it becomes possible to measure the polished surface temperature at any arbitrary position on the wafer.

As detailed above, according to the present invention, by polishing the wafer W and actually measuring the resistivity of the polished surface, it is possible to determine the temperature of the polished surface with high accuracy from the resistivity value. becomes. As a result, it becomes possible to appropriately control the polishing rate Vc due to the chemical action of the above equation (2), which is largely dependent on temperature, as well as the polishing speed Vmcp of the above equation (1).

Furthermore, since the temperature of the wafer polishing surface can be directly measured through the polishing surface, there is no need to form the groove 18 in the polishing plate 14 as shown in FIG. This makes it possible to flatten the wafer contact surface.

As described above, according to the present invention, a wafer can be polished using a polishing plate with a flat contact surface.
Furthermore, since the polishing rate Vmcp can be appropriately controlled, it is possible to form a mirror surface with high flatness on the wafer.

[0036]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

After the silicon wafer is subjected to oxygen thermal donor erasing treatment, the silicon wafer is heated on a hot plate, and the temperature of the hot plate at that time, the resistivity measurement value, and the resistivity measurement value are used to determine the present invention. The relationship with temperature determined by this method was investigated. The silicon wafer used had a diameter of 150 mm and an initial oxygen concentration of 27.8 p.
pma, initial specific resistance was 250 Ωcm, and heat treatment time was 100 minutes.

FIG. 1 shows a method of determining the wafer temperature from the resistivity actually measured under the above conditions using the curve B in FIG. 13. The wafer temperatures determined by this method are listed in Table 3 below, along with the hot plate temperature and resistivity measurements.

[0039]

[Table 3]

Table 3 above shows that according to the method of the present invention, the surface temperature of the wafer can be measured with extremely high accuracy. In addition, the second section showing the measurement results by the conventional method
When compared with the table, it is clear that the method of the present invention is superior.

Next, the results of actually polishing a silicon wafer using the polishing apparatus shown in FIG. 2 and measuring the temperature distribution within the mirror surface of the polished wafer using the method of the present invention will be described.

The polishing apparatus used for polishing the silicon wafer is substantially the same as that shown in FIG. 9, except that the wafer contact surface of the polishing plate 14 is flat. In addition, the polishing of the silicon wafer described above is performed in the fourth manner below.
It was carried out under the conditions shown in the table.

[0043]

[Table 4]

First, a non-doped silicon wafer W having a diameter of 150 mm was subjected to an oxygen thermal donor erasing process. FIG. 3 shows the measured values of the resistivity on the surface of the wafer W after this treatment. The specific resistance was measured at approximately equal intervals along the arrows on the wafer W shown in the figure. From FIG. 3, after the oxygen thermal donor is erased, the specific resistance is uniform over the entire wafer W.

The above-mentioned silicon wafer, which had undergone oxygen thermal donor elimination, was polished for 100 minutes using the above-mentioned polishing apparatus, and then the specific resistance of the polished surface at the same position as in the case of FIG. 3 was measured. FIG. 4 shows the results of this measurement. FIG. 5 shows the temperature at each measurement position determined by the method shown in FIG. 1 based on the measured values of resistivity shown in FIG. 4. Note that since the polishing time can be considered to be substantially the same as the heat treatment time, curve B in FIG. 11 was used as in the case of FIG. 1.

As described above, according to the method of the present invention, it is also possible to measure the temperature with high accuracy over the entire range of the polished surface of the wafer. Therefore, accurate temperature distribution during polishing of the wafer surface can be obtained.

Next, mirror polishing was actually performed and an attempt was made to improve the flatness of the wafer using the highly accurate polishing surface temperature measurement method of the present invention. At this time, a wafer having a diameter of 150 mm was used, and a polishing machine capable of independently applying pressure to the center and periphery of the top ring as shown in FIG. 6 was used.

First, mirror polishing was performed without applying pressure to the periphery, and the temperature of the polished surface was measured in the diametrical direction of the wafer using the method of the present invention, and the results shown in FIG. 7 were obtained. Here, the temperature at the center of the wafer is TC (°C), the temperature at a point 10 mm inside the wafer edge is TE (°C), and the difference between them is ΔT (°C) = TC - TE...(
4) is an index representing the uniformity of polishing temperature within the wafer surface. The polishing temperature uniformity is the best when ΔT is 0 (° C.).

Next, mirror polishing was performed by applying a predetermined pressure to the peripheral portion, and according to the present invention, the temperature of the polished surface was measured in the diametrical direction of the wafer, and ΔT was determined from the results. The peripheral pressure was increased little by little each time, and ΔT was measured at each pressure. The results are shown in FIG. From FIG. 8, it can be seen that ΔT becomes 0 (°C) when the peripheral pressure is 1.8 kg/cm2. In other words, the peripheral pressure is 1.8 kg/cm
2, the wafer polishing temperature uniformity is the best,
As shown in equation (2) above, the polishing rate uniformity is also the best. In fact, when we measured the flatness of five mirror-polished wafers under these conditions and compared them with those with a peripheral pressure of 0 kg/cm2, we found that the flatness was as shown in Table 5, and the TTV was 2.
．． We were able to improve this by 8 μm.

[0050]

[Table 5]

Although the present invention has been specifically explained above, it goes without saying that the present invention is not limited to what has been described in the above embodiments.

For example, the specific resistance of the polished surface of a wafer is not limited to being measured using the spreading resistance measuring device.
Similarly, any means can be used as long as it can measure the specific resistance of the polished surface.

[0053]

As described above, according to the present invention, it is possible to directly measure the temperature of the polished surface (surface) of a semiconductor wafer with high precision. Therefore, it is possible to appropriately control the polishing rate of the wafer, which depends on the temperature of the polishing surface, so that it is possible to form a mirror surface with extremely high flatness on the wafer. In addition, since the temperature is not measured from the back side of the wafer, it becomes possible to hold the back side of the wafer with a flat surface and perform polishing, which also makes it possible to improve the flatness of the mirror surface of the wafer. .

[Brief explanation of the drawing]

FIG. 1 is a graph for explaining a temperature measurement method according to an embodiment of the present invention.

FIG. 2 is a half-sectional view schematically showing a polishing apparatus applied to this embodiment.

FIG. 3 is a graph showing specific resistance measurements of a silicon wafer before polishing.

FIG. 4 is a graph showing measured resistivity values of silicon wafers after polishing.

FIG. 5 is a graph showing the polishing surface temperature determined from the resistivity values shown in FIG. 4;

FIG. 6 shows a polishing apparatus applied to adjust the polishing rate of silicon wafers.

FIG. 7 is a graph showing the results of polishing the peripheral area with no load using the polishing apparatus described above.

FIG. 8 is a graph showing the relationship between peripheral pressure and temperature difference on the polished surface of a silicon wafer.

FIG. 9 is a half-sectional view schematically showing a conventional polishing apparatus.

FIG. 10 is a schematic explanatory diagram showing a state in which a silicon wafer is heated with a hot plate.

FIG. 11 is a graph showing the relationship between heat treatment temperature of a silicon wafer and oxygen thermal donor concentration.

FIG. 12 is a graph showing the relationship between silicon wafer heat treatment time and oxygen thermal donor concentration.

FIG. 13 is a graph showing the relationship between heat treatment temperature and specific resistance in a silicon wafer after oxygen thermal donor erasure.

FIG. 14 is a schematic explanatory diagram showing an example of a method of measuring the resistivity of a polished surface of a wafer.

[Explanation of symbols]

10...Surface plate, 12...polishing pad, 14...polishing plate, 16...polishing liquid supply pipe, 18...Groove, 20...Temperature sensor, 22...hot plate, 24... Probe, W...Wafer.

Claims (1)

[Claims] 1. In measuring the temperature of the polished surface during mirror polishing of a semiconductor wafer, the semiconductor wafer is polished after being subjected to an oxygen thermal donor erasing heat treatment, and the temperature of the semiconductor wafer is measured after polishing. A method for measuring the temperature of a polished surface of a semiconductor wafer, comprising measuring the resistivity of the polished surface and determining the temperature of the polished surface based on the resistivity value.