JP3435111B2 - Semiconductor wafer heat treatment equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor wafer heat treatment apparatus, and more particularly to a heat treatment apparatus for heat-treating a semiconductor wafer without degrading the lifetime of minority carriers.

[0002]

2. Description of the Related Art In the process of manufacturing a semiconductor device, a semiconductor wafer may be subjected to heat treatment. Such heat treatment is performed, for example, to form a silicon oxide film on the surface of the semiconductor wafer.

FIG. 16 is a perspective view of a conventional reaction tube for heat-treating a semiconductor wafer. The conventional reaction tube can house the wafer boat 8 therein. A plurality of semiconductor wafers 12 are horizontally held on the wafer boat 8 in multiple stages. The reaction tube is provided with a reaction gas introduction tube 7 for introducing the reaction gas into the internal space and a reaction gas exhaust port 5 for exhausting the reaction gas from the internal space.

The reaction gas introducing pipe 7 can supply the reaction gas from the upper portion of the wafer boat 8 to the inside of the reaction pipe. A shower head 14 is provided above the reaction tube to evenly distribute the reaction gas into the internal space. The reaction gas that has passed through the shower head 14 passes around the silicon wafer 12 and is exhausted from the reaction gas discharge port 5 provided in the lower portion of the reaction tube.

The reaction tube is also equipped with thermocouples 16, 17 and 18 for monitoring the temperature inside. The thermocouple 16 is provided so that the temperature near the upper end of the reaction tube can be detected. The thermocouple 17 is provided so that the temperature near the center of the reaction tube can be detected. Further, the thermocouple 18 is provided so that the temperature near the lower end of the reaction tube can be detected.

The conventional reaction tube is heated to a predetermined temperature during heat treatment. For example, during the heat treatment for forming a silicon oxide film on the semiconductor wafer 12, the reaction tube is heated to a predetermined oxide film generation temperature. When the reaction gas is introduced into the reaction tube in this state, the semiconductor wafer 12 can be appropriately heat-treated.

As an apparatus for heat-treating a semiconductor wafer, for example, as disclosed in Japanese Patent Laid-Open No. 6-216056, there is known an apparatus capable of introducing a cooling gas around the above-mentioned reaction tube. According to such an apparatus, after the semiconductor wafer is subjected to the heat treatment, the reaction tube and the semiconductor wafer housed therein can be cooled rapidly. Therefore, according to such a heat treatment apparatus, the heat treatment of the semiconductor wafer can be efficiently performed.

[0008]

FIG. 17 shows the result of measuring the minority carrier lifetime of a semiconductor wafer heat-treated by the above method (method of cooling a reaction tube with a cooling gas). More specifically, FIG. 17A shows the average value, minimum value, maximum value, deviation, and median value of the lifetime. Further, FIG. 17B shows a histogram showing the distribution of lifetime. Further, FIG. 17C shows a diagram in which the cumulative distribution of lifetime is expressed in percentage.

When the heat treatment by the above-mentioned method is performed, the lifetime of the minority carriers contained in the semiconductor wafer becomes about 127.8 μsec on average as shown in FIG. This value is significantly shorter than the lifetime before the heat treatment, and is also a shorter time than the usual required value for a semiconductor wafer (for example, 350 μsec). As described above, the heat treatment on the semiconductor wafer may shorten the lifetime of the minority carriers contained in the semiconductor wafer.

In order for the semiconductor device to function properly, it is necessary that the minority carriers have a sufficient lifetime. Therefore, in order to stably secure the function of the semiconductor device, it is necessary to heat treat the semiconductor wafer by a method that does not shorten the lifetime of minority carriers.

The present invention has been made to solve the above problems, and it is an object of the present invention to provide a semiconductor wafer heat treatment apparatus capable of performing heat treatment on a semiconductor wafer without shortening the lifetime of minority carriers. To aim.

[0012]

The invention according to claim 1 is
In order to achieve the above object, a semiconductor wafer heat treatment apparatus for guiding a reaction gas into a reaction tube to perform heat treatment on a semiconductor wafer , wherein a plurality of semiconductor wafers are provided at predetermined intervals in the longitudinal direction.
A reaction tube that holds c and is held inside the reaction tube
It is provided to blow the cooling gas to the semiconductor wafer.
And a gas ejection portion extending in the longitudinal direction of the reaction tube.
The cooling gas introduction pipe and the cooling gas introduced inside the reaction pipe.
Position facing the cooling gas introduction pipe for exhausting gas
And a gas discharge part provided in the reaction tube and extending in the longitudinal direction of the reaction tube.
And a cooling gas discharge pipe,
Gradually increases from the side closer to the cooling gas supply source to the side farther away.
Multiple cooling gas ejection holes
The gas discharge unit may include a plurality of cooling gas discharge holes .

The invention according to claim 2 is the semiconductor wafer heat treatment apparatus according to claim 1, wherein the plurality of cooling gas discharge holes are gradually extended from a side closer to a cooling gas exhaust port to a side farther from the exhaust port. It is characterized in that it is provided to be large.

Further, the invention according to claim 3 is the semiconductor wafer heat treatment apparatus according to claim 1 or 2 , wherein:
The degassing gas ejection holes are formed on the plurality of wafers held in the reaction tube.
It is provided at the position corresponding to each of the
The gas discharge holes are provided for the plurality of wafers held in the reaction tube.
It is characterized in that it is provided at the position corresponding to each
To do .

The invention according to claim 4 is the semiconductor wafer heat treatment apparatus according to any one of claims 1 to 3 , wherein the reaction gas is introduced into the reaction tube from one end thereof.
Reaction gas introduction pipe to be introduced and gas of the reaction gas introduction pipe
Shower interposed between the ejection hole and the internal space of the reaction tube
-The head and the shroud formed on the entire surface of the shower head.
A shower head hole, the shower head hole
Gradually increase from the center of the reaction tube to the periphery.
It is characterized in that it is formed as .

According to the invention of claim 5, the reaction is carried out in a reaction tube.
Semiconductor wafer that guides gas and heat-treats it
Heat treatment equipment, which is a semi-heat treatment device
Introduce cooling gas to spray cooling gas on conductor wafer
To exhaust the cooling gas introduced inside the tube and reaction tube
The cooling gas provided at a position facing the cooling gas introduction pipe.
From the exhaust gas exhaust pipe and one end of the reaction pipe,
The reaction gas introducing pipe for introducing the reaction gas, and the reaction gas
Between the gas ejection hole of the introduction tube and the inner space of the reaction tube,
The existing shower head and the entire surface of the shower head
And a shower head hole formed in the shower head.
The saddle hole gradually moves from the center of the reaction tube to the peripheral edge.
Characterized by being formed so as to become larger
It The invention according to claim 6 is the same as that of claims 1 to 5.
The semiconductor wafer heat treatment apparatus according to claim 1,
As a cooling gas, low in oxygen, ozone, and water vapor
Both are characterized by using a gas containing one.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. It should be noted that elements common to each drawing are denoted by the same reference numerals, and redundant description will be omitted.

Embodiment 1. 1 is a sectional view showing a main part of a semiconductor wafer heat treatment apparatus according to a first embodiment of the present invention. The heat treatment apparatus of this embodiment includes a reaction tube 11. The circumference of the reaction tube 11 is surrounded by the cylindrical heater 1. An air supply port 2 is provided at the bottom of the heater 1. A blower 10 is connected to the upper part of the heater 1 via a cooler 9.

In the space between the heater 1 and the reaction tube 11,
By rotating the blower 10, cooling air can flow through. Therefore, according to the heat treatment apparatus of the present embodiment, the reaction tube 11 can be forcibly cooled by rotating the blower 10. The cooler 9 and the blower 10 may be provided on the air supply port 2 side.

Inside the reaction tube 11, a wafer boat 8 mounted on the cap 4 is inserted. The wafer boat 8 is provided with a reaction tube 11 by a boat elevator (not shown).
It is inserted inside and is pulled out from inside.
When the wafer boat 8 is inserted into the reaction tube 11, the reaction tube 1
The opening of 1 is closed by the cap 4.

FIG. 2 shows an enlarged perspective view of the reaction tube 11. The reaction tube 11 can house the wafer boat 8 therein. A plurality of semiconductor wafers 12 are horizontally held on the wafer boat 8 in multiple stages. The reaction tube 11 is provided with a reaction gas introduction tube 7 for introducing the reaction gas into the inner space thereof and a reaction gas exhaust port 5 for discharging the reaction gas from the inner space thereof.

The reaction gas introducing pipe 7 can supply the reaction gas from the upper portion of the wafer boat 8 to the inside of the reaction pipe. A shower head 14 is provided above the reaction tube to evenly distribute the reaction gas into the internal space. The shower head 14 is provided with a shower head hole on the entire surface thereof. The shower head hole is provided such that the opening diameter thereof gradually increases from the central portion of the shower head 14 toward the peripheral portion thereof so that the reaction gas is uniformly introduced into the reaction tube 11. Shower head 1
The reaction gas that has passed through 4 passes through the periphery of the silicon wafer 12 and is exhausted from the reaction gas discharge port 5 provided in the lower portion of the reaction tube 11.

The reaction tube 11 also includes a cooling gas introduction tube 6 and a cooling gas discharge tube 3. Cooling gas introduction pipe 6
Has a gas ejection portion extending vertically inside the reaction tube 11 along the wafer boat 8. A plurality of cooling gas ejection holes 13 are provided in the gas ejection portion of the cooling gas introduction pipe 6 so as to correspond to the position of the semiconductor wafer 12 held by the wafer boat 8. Cooling gas exhaust pipe 3
Has a gas discharge portion extending in the vertical direction inside the reaction tube 11 along the wafer boat 8. A plurality of cooling gas discharge holes 15 are provided in the gas discharge portion of the cooling gas discharge pipe 6 so as to correspond to the position of the semiconductor wafer 12 held by the wafer boat 8.

The cooling gas ejection holes 13 and the cooling gas discharge holes 15 are gradually formed from the bottom side to the upper side of the reaction tube 11 so that the cooling gas uniformly flows inside the reaction tube 11. It is provided so that the opening diameter is large. The cooling gas supplied from the cooling gas ejection hole 13 directly cools the semiconductor wafer 12, and then is discharged from the cooling gas discharge hole 15. Therefore, according to the heat treatment apparatus of this embodiment, the semiconductor wafer 12 can be directly cooled inside the reaction tube 11.

The reaction tube 11 is equipped with thermocouples 16, 17 and 18 for monitoring the temperature inside. Thermocouple 1
6 is provided so that the temperature near the upper end of the reaction tube can be detected. The thermocouple 17 is provided so that the temperature near the center of the reaction tube can be detected. Also, thermocouple 1
8 is provided so that the temperature near the lower end of the reaction tube can be detected. The results of the measurement by the thermocouples 16, 17, 18 are used for controlling the heater 1 and the like. The reaction tube 1
The number of thermocouples incorporated in one is not limited to three, and a larger number of thermocouples may be attached depending on the control method of the heater 1.

In the heat treatment apparatus of this embodiment, the semiconductor wafer 12 can be heated to a predetermined temperature by heating the heater 1. Further, by supplying a reaction gas into the reaction tube 11 in this state, the semiconductor wafer 12 can be subjected to a predetermined heat treatment. Specifically, for example,
Heat treatment for forming a silicon oxide film on the surface of the semiconductor wafer 12 by heating the inside of the reaction tube 11 to about 900 ° C. by the heater 1 and supplying water vapor or oxygen as a reaction gas into the reaction tube 11. It can be performed.

Further, in the heat treatment apparatus of the present embodiment, as described above, the cooling gas is circulated between the heater 1 and the reaction tube 11 to efficiently cool the reaction tube 11, and The semiconductor wafer 12 can be directly cooled by circulating the cooling gas inside. Therefore, according to the apparatus of this embodiment, the semiconductor wafer 12 heated in the heat treatment process can be quickly cooled after the heat treatment is completed.

It is important to cool the semiconductor wafer 12 immediately after the heat treatment in order to prevent the minority carriers contained in the semiconductor wafer 12 from having a short lifetime. In this respect, the heat treatment apparatus of the present embodiment has an excellent effect that the desired heat treatment can be efficiently performed while suppressing the reduction of the minority carrier lifetime.

Grounds for the effects of the present invention. Hereinafter, based on the results of various experiments conducted to find out factors that affect the minority carrier lifetime included in the semiconductor wafer 12, the cooling rate of the semiconductor wafer 12 has a great influence on the minority carrier lifetime. Will be explained.

Table 1 shows a list of heat treatment conditions used for preparing the samples in the above-mentioned experiment. The heat treatment according to the conditions shown in Table 1 is performed on a semiconductor wafer having a silicon oxide film with a film thickness of about 50 nm on the surface of a silicon single crystal. Hereinafter, the semiconductor wafer that has not been subjected to the above heat treatment will be referred to as a “preprocessed wafer”, and the semiconductor wafer that has been subjected to the above heat treatment will be referred to as a “processed wafer”.

[0031]

[Table 1]

In Table 1, "Push Temp." Indicates the temperature inside the tube when the semiconductor wafer 12 is inserted into the reaction tube 11. “Anneal Temp.” And “Anneal Time” indicate the temperature inside the tube when the semiconductor wafer 12 is held inside the reaction tube 11, and the holding time thereof. Also, "Pullout Tim
“E” indicates the temperature inside the tube when the semiconductor wafer 12 is pulled out from the reaction tube 11. It should be noted that An in conditions B-01 to B-03
neal Temp., the temperature inside the pipe is 7 at a speed of -2.5 ° C / min.
This means that the temperature was lowered from 00 ° C. to each display temperature.

Experiment 1. The cause of the deterioration of the minority carrier lifetime is considered to be the influence of the thermal donor. Therefore, an experiment was conducted to confirm the relationship between the minority carrier lifetime and the thermal donor.

FIG. 3 shows the unprocessed wafer and the conditions B-01 and B-.
The results of measuring the sheet resistance of the processed wafer that has been heat-treated with 02 or B-03 are shown. As for the sheet resistance, the silicon oxide film formed on the surface of each sample is
After removing by wet treatment using HF, it was measured at a density of 49 points / wafer using VR-120 manufactured by Kokusai Electric Co., Ltd.

As shown in FIG. 3, the temperature of the heat treatment is 700
When the temperature is lowered from ℃ to 600 ° C (condition B-03) and when the temperature is lowered to 500 ° C (condition B-0)
2) shows a sheet resistance (about 290 Ω / □) which is almost the same as that when no heat treatment is applied. On the other hand, when the temperature of the heat treatment is lowered from 700 ° C to 400 ° C (condition B-0
1) has a higher sheet resistance than other cases (about 4
30Ω / □). The sheet resistance of the semiconductor wafer 12 rises due to the formation of the thermal donor and the formation of the state in which the carrier is captured by the thermal donor. Therefore, the above results show that the thermal donor is 450 ° C.
It is thought to have occurred because it occurred in the nearby temperature range.

FIG. 4 shows an unprocessed wafer and a processed wafer prepared by heat-treating the wafer under the condition B-03 (condition that the heat treatment temperature is 700 ° C. → 600 ° C.).
The result of measuring the minority carrier lifetime is shown. More specifically, FIGS. 4 (A) to 4 (C) show the measurement results (average lifetime value, minimum value, maximum value, deviation, and median value) of unprocessed wafers and lifetime distribution. , And the cumulative distribution of lifetime are shown. Also, FIG.
4D to FIG. 4F show measurement results, lifetime distributions, and lifetime cumulative distributions of processed wafers. As shown in FIG. 4, in the processed wafer that has been subjected to the heat treatment under the condition B-03, although the lifetime deteriorates, the maximum value of the lifetime is still maintained at the same level as that before the heat treatment.

The lifetime of a minority carrier is Semilab
Using a WT-85XA manufactured by Co., Ltd., measurement was performed in a raster 2 mm range (2 mm □ range). The lifetime measuring device and measuring range are common to all the following samples. According to the above-mentioned measuring machine, in addition to the various results shown in FIG. 4, a planar distribution of lifetime within the measuring range can be obtained.

FIG. 5 shows an unprocessed wafer and a processed wafer prepared by heat-treating the wafer under the condition B-02 (condition for setting the heat treatment temperature to 700 ° C. → 500 ° C.).
The result of measuring the minority carrier lifetime is shown. The contents of FIGS. 5A to 5F are respectively shown in FIG.
4 to FIG. 4F correspond to the contents. As shown in FIG. 5, before and after the heat treatment under the condition B-02, the lifetime of the minority carrier is rapidly deteriorated from about 1200 μsec to about 30 μsec.

FIG. 6 shows an unprocessed wafer and a processed wafer prepared by heat-treating the wafer under the condition B-01 (condition that heat treatment temperature is 700 ° C. → 400 ° C.).
The result of measuring the minority carrier lifetime is shown. The contents of FIGS. 6A to 6F are respectively shown in FIG.
4 to FIG. 4F correspond to the contents. As shown in FIG. 6, before and after the heat treatment under the condition B-01, the lifetime of the minority carrier is rapidly deteriorated from about 1200 μsec to about 40 μsec.

FIG. 7 shows a diagram in which the results relating to the average lifetime are extracted from the results shown in FIGS. 4 to 6 and the results are compared. As shown in FIG. 7, the lifetime of the minority carrier has a lower limit of the heat treatment temperature of 500 ° C.
Alternatively, when the temperature is 400 ° C., the lower limit is remarkably deteriorated as compared with the case where the lower limit is 600 ° C. In addition, the lifetime is when the lower limit of the heat treatment temperature is 500 ° C,
When the lower limit is 400 ° C., the deterioration is almost the same.

As described above, the semiconductor wafer 12 has 45
It is considered that thermal donors are generated in the temperature range of about 0 ° C (see Fig. 3). On the other hand, the lifetime of the minority carrier is significantly deteriorated even when the lower limit of the heat treatment is 500 ° C. Therefore, it can be considered that the cause that significantly deteriorates the minority carriers before and after the heat treatment is not the thermal donor.

Experiment 2. Next, the contents and results of the experiment conducted to understand the relationship between the heat treatment temperature and the minority carrier lifetime will be described. FIG. 8 shows the measurement result of the lifetime of the unprocessed wafer as a sample and the unprocessed wafer at a single temperature (A-01 to A-03, A-05, A-07 to A-09). FIG. 5 is a diagram showing a comparison of the measurement result of the lifetime of the processed wafer prepared by heat treatment under the condition (1). In this experiment, the heat treatment of each material was performed in an N ₂ atmosphere.

As shown in FIG. 8, the temperature of the heat treatment is 700
When the temperature is ℃, the lifetime of minority carriers is not deteriorated. As the temperature of heat treatment decreases to 650 ° C and 600 ° C, the deterioration of lifetime becomes more remarkable,
It becomes most prominent when the temperature is 550 ° C. And the temperature of heat treatment is further 500 ° C, 450 ° C, 400 ° C.
And the degree of deterioration becomes smaller again.

FIG. 9 shows the measurement results of the lifetime of the unprocessed wafer as a sample and the unprocessed wafers A-04 to A-06.
2 is a diagram showing a comparison with the measurement result of the lifetime of the processed wafer produced by performing the heat treatment at a temperature of 550 ° C. that causes the lifetime to be most deteriorated. Conditions A-04 to A-06 have different heat treatment times. Therefore, the measurement results shown in FIG. 9 show the dependence of the lifetime on the heat treatment time.

As shown in FIG. 9, the lifetime of minority carriers is significantly deteriorated as the heat treatment time increases. However, when the heat treatment temperature is fixed at a single temperature (550 ° C.), even if the heat treatment time is extended, the treatment condition B
-01 to B-03 are used, the lifetime is deteriorated, that is, the lifetime is 20 to 40 μse.
It does not deteriorate to concentrate in the range of c. Also,
When the heat treatment temperature is a single temperature, the deterioration of the lifetime progresses from the peripheral portion of the semiconductor wafer 12 as the sample.

Experiment 3. Next, an experiment conducted to confirm whether the deteriorated lifetime is recovered by the heat treatment will be described. 10A to 10C,
The result of having measured the minority carrier lifetime for the unprocessed wafer is shown. In addition, FIGS.
(F) shows the result of measuring the lifetime after heat treating the untreated wafer under the condition B-01. Furthermore, FIG.
(G) to FIG. 10 (I) show the results of measuring the lifetime after the heat treatment of the processed wafer treated under the condition B-01 again under the condition A-09.

In this experiment, as shown in FIG. 10, the heat treatment under the condition B-01, that is, the heat treatment temperature is 700
The lifetime (average value) of the minority carriers deteriorated from 606 μsec to 26,29 μsec by performing the heat treatment under the condition of decreasing the temperature from ℃ to 400 ℃. Hereinafter, the lifetime after such deterioration is referred to as “post-deterioration lifetime”.

In this experiment, the processed wafer having the deteriorated lifetime was subjected to the heat treatment under the condition A-09,
That is, when heat treatment was performed at a single temperature of 700 ° C., the lifetime (average value) of minority carriers was restored to 673.4 μsec, which was the same level as the initial value. It was also confirmed that after the heat treatment under the condition A-09, the planar distribution of the lifetime returned to the same distribution as the initial state (the state of the unprocessed wafer).

As described above, the lifetime of the minority carriers can be restored to the initial value by performing proper heat treatment again even if the life time of the minority carrier is once deteriorated by the heat treatment. Hereinafter, the heat treatment performed for the purpose of recovering the lifetime after deterioration is referred to as “recovery heat treatment”, and the lifetime measured on the processed wafer subjected to the recovery heat treatment is referred to as “post-recovery lifetime”.

Next, the temperature used in the heat treatment for recovery and
An experiment was conducted to understand the relationship with the post-recovery lifetime. FIG. 11 is a diagram showing the initial values of lifetimes, the lifetimes after deterioration, and the lifetimes after recovery for a plurality of semiconductor wafers in comparison. In FIG. 11, the heat treatment temperature shown on the horizontal axis is the temperature used in the recovery heat treatment. That is, the post-recovery lifetime shown in FIG.
-05, A-07 to A-09, and the value after recovery by heat treatment for recovery (N ₂ atmosphere).

As shown in FIG. 11, when the temperature used in the heat treatment for recovery is 400 ° C. or 450 ° C., there is almost no difference between the lifetime after deterioration and the lifetime after recovery. The temperature used in the heat treatment for recovery is 500
When the temperature exceeds ℃, the effect of recovery gradually starts to occur, and under the condition that the temperature exceeds 600 ° C., the post-recovery lifetime is recovered to a level equivalent to the initial value of the lifetime. In the above experiment, it was also confirmed that the recovery of the lifetime proceeded from the vicinity of the central portion of the semiconductor wafer 12.

Experiment 4. The minority carriers of semiconductor wafer 12 occur in the silicon portion of the wafer. The minority carrier lifetime is the lifetime of carriers generated inside the silicon part (hereinafter referred to as “internal carrier”) and the carrier generated on the surface of the silicon part (hereinafter referred to as “surface carrier”). Lifetime and is determined by. Below, an explanation will be given of an experiment conducted to understand the contribution of the internal carriers and the contribution of the surface carriers to the deterioration of the lifetime due to the heat treatment.

FIG. 12 shows a plurality of semiconductor wafers.
Initial value of lifetime, lifetime after heat treatment,
The figure which compared and represented the lifetime in the oxide film removal state is shown. In FIG. 12, the temperature shown on the horizontal axis is the condition of heat treatment (no heat treatment, or A-01 to A-03, A-05,
Any of A-07 to A-09, B-01, and B-02). In addition, the "lifetime when the oxide film is removed" is
The silicon oxide film that covers the surface of the processed wafer is
It is the lifetime measured immediately after removal by HF treatment.

When the surface of the processed wafer is covered with the silicon oxide film, many silicon dangling bonds are present on the surface of the silicon portion (interface with the silicon oxide film). These silicon dangling bonds trap and eliminate surface carriers. Therefore, the lifetime of the surface carrier is greatly affected by the state of the boundary surface between the silicon portion and the silicon oxide film.

In other words, when the surface of the processed wafer is covered with the silicon oxide film, the lifetime of the surface carrier greatly changes depending on the state of the boundary surface between the silicon portion and the silicon oxide film. So in this case,
The lifetime of the surface carrier has a contribution to the average lifetime.

Immediately after the silicon oxide film covering the surface of the processed wafer is removed by the BHF processing, the surface of the exposed silicon portion is covered with BHF. In this case, since dangling bonds existing on the surface of the silicon part are terminated by hydrogen, even if the surface state of the silicon part is different between samples, the lifetime of the surface carrier is almost the same in all samples. It is believed that Therefore, under such circumstances, it is considered that the contribution of the lifetime of the surface carrier to the average lifetime is extremely small. That is, it is considered that the lifetime of the internal carrier has a large contribution to the lifetime in the state where the oxide film is removed.

As shown in FIG. 12, the lifetime after the heat treatment (before the removal of the oxide film), that is, the lifetime that is contributed by both the lifetime of the surface carrier and the lifetime of the internal carrier depends on the heat treatment conditions. Differences occur depending on the differences. On the other hand, the lifetime in the oxide film removed state in which only the lifetime of the internal carrier has a large contribution is approximately the same value (150 μsec to 250 μsec) for all wafers including the unprocessed wafer. Therefore, it is considered that the difference in the lifetime caused by the heat treatment is caused by the difference in the lifetime of the surface carrier, that is, the difference in the state of the boundary portion between the silicon portion and the silicon oxide film.

Experiment 5. Next, an experiment conducted to understand the relationship between the influence of the gas desorbed from the semiconductor wafer 12 during the heat treatment and the lifetime of the minority carrier will be described. FIG. 14 shows TDS (Thermal Desorp) performed on a semiconductor wafer having a 100 nm oxide film as a sample.
shows the results of ionization spectroscopy. TDS samples are
It was prepared by oxidizing the surface of the silicon wafer by a so-called pyro oxidation (Pyro oxidation) method, that is, by oxidizing the surface of the silicon wafer with water vapor generated by reacting hydrogen and oxygen. At this time, the oxidation temperature was 900 ° C.

For TDS, EMD-WA1000 manufactured by Denshi Kagaku Co., Ltd. was used, and the sample was heated from room temperature to 1000 °
The temperature was raised to 0 ° C. In addition, in this experiment,
H ₂ , NH, O, HO, H ₂ O, and N ₂ were used as TDS measurement elements, and the desorption spectrum intensities corresponding to these measurement elements were measured in the process of raising the temperature of the sample.

The desorption spectrum shown in FIG.
Around ° C., a small spectral peak of H _2, and the prominent spectral peaks of H ₂ O is observed. If the deterioration of lifetime is due to the desorption of hydrogen, there should be a large difference in lifetime before and after those peaks, and the existence of hydrogen is required for recovery of lifetime. Should be.

As shown by the results of Experiment 2 (see FIG. 8),
The lifetime of a minority carrier has a heat treatment temperature of 40
When the temperature is from 0 ° C to 450 ° C, no deterioration occurs. Further, as shown by the result of Experiment 4 (see FIG. 11), the deteriorated lifetime is restored to almost the initial value only by performing the heat treatment (treatment temperature 600 ° C.) in the N ₂ atmosphere.
Therefore, it is considered that the deterioration of the lifetime is not due to the desorption of hydrogen from the boundary surface between the silicon portion and the silicon oxide film.

Hypothesis for explaining the cause of lifetime deterioration. The lifetime τ of the minority carrier is calculated by using the lifetime of the internal carrier (hereinafter referred to as “bulk lifetime τb”) and the lifetime of the surface carrier (hereinafter referred to as “surface lifetime τs”) as follows. It can be expressed as an expression. 1 / τ = 1 / τb + 1 / τs

From the results of Experiment 1 (see FIGS. 3 and 7), it has been confirmed that the thermal donor does not affect the deterioration of the lifetime τ. In addition, the result of Experiment 4 (Fig. 1
2), it is considered that the bulk lifetime τb (corresponding to the lifetime in the oxide film removed state) does not deteriorate even if the lifetime τ deteriorates with the execution of the heat treatment. Therefore, the deterioration of the lifetime τ is caused by the boundary surface between the silicon portion and the silicon oxide film (hereinafter,
It is considered to be due to the time until the carriers disappear at the “Si / SiO ₂ interface” due to recombination, that is, the change in the surface lifetime τs.

Surface lifetime τ at Si / SiO ₂ interface
As a factor that influences s, the bonding state of silicon and hydrogen at the interface and the bonding state of silicon and oxygen at the interface are considered. From the result of Experiment 5 (see FIG. 13), it is confirmed that the deterioration of the lifetime τ is not due to the influence of hydrogen. Therefore,
It is considered that the cause of the deterioration of the lifetime τ is that the bonding state between silicon and oxygen changes at the Si / SiO ₂ interface as the heat treatment is performed.

Considering that the deterioration of the lifetime τ is due to the change of the bonding state of silicon and oxygen at the Si / SiO ₂ interface, the dependence of the lifetime τ on the heat treatment temperature (Experiment 2: FIG. 8 and FIG. 9). ) Is qualitatively explained using the following model.

FIG. 14 is a state transition diagram showing the concept of the model used in the following description. As shown in FIG. 14, Si / S
The density of states of the state in which silicon and oxygen are bonded at the iO ₂ interface (hereinafter, referred to as “state A”) is n _A , and the state where they are separated (hereinafter, referred to as “state B”) Let the density be n _B. Further, the probability of transition from state A to state B and the probability of transition from state B to state A are P1 (T) and P2 (T) as functions of temperature T, respectively. In this case, the interface trap density Itr that occurs in state B
Is considered to be given by In the following equation, T1 and T2 are the starting temperature and the ending temperature of the heat treatment.

[0067]

[Equation 1]

A silicon oxide film is formed on the surface of the semiconductor wafer 12.
Immediately after the film formation, Si / SiO₂Silicon and oxygen at the interface
A good bonded state of is formed. In this case,
Degree n _AIs the density of states n_BSince it is higher than
And the interface trap density Itr is
It increases with the execution of reason. Therefore, according to the above model
If this is the case, the life time of minority carriers
It is possible to explain the phenomenon that the τ deteriorates.

In the above model, the temperature dependence of the lifetime τ for heat treatment at a single temperature is the transition probability P1.
This results in the temperature dependence of (T). The above model is consistent with the result of Experiment 2 (see FIG. 8) if the transition probability P1 (T) has a distribution having a maximum value near 550 ° C.
Further, when the heat treatment temperature is gradually lowered, the contribution at each temperature is added to the interface trap density Itr, and its value is
The heat treatment temperature is higher than that when the heat treatment temperature is single. Therefore, according to the above model, it is possible to explain the phenomenon that the lifetime significantly deteriorates under the condition B-01 or the condition B-02.

After the semiconductor wafer 12 is subjected to the heat treatment for gradually lowering the treatment temperature (heat treatment under the condition B-01, etc.), silicon and oxygen are separated at the Si / SiO ₂ interface, and the silicon portion It is considered that the silicon dangling bond formed on the surface acts as a recombination center with the surface carrier. In this state, the density of states n _B is higher than the density of states n _A , so the integrand in Eq. 1 becomes negative and the interface trap density Itr decreases with the execution of heat treatment. Therefore, according to the above model, it is possible to explain the phenomenon in which the lifetime τ deteriorated by the proper heat treatment is recovered to a value equivalent to the initial value.
As described above, according to the model shown in FIG. 14, various phenomena (experimental results) related to deterioration of lifetime can be properly explained.

The difference between silicon and oxygen due to the heat treatment is
It is considered that the higher the temperature reduction rate of the heat treatment temperature, the less likely it is to occur. Therefore, it is considered that the lifetime of minority carriers is less likely to deteriorate as the temperature is lowered at a higher rate of temperature reduction after the heat treatment. Further, in the oxygen atmosphere, the transition probability P2 (T) from the state B to the state A is higher than the transition probability P1 (T) from the state A to the state B. Therefore, it is considered that the separation of silicon and oxygen is less likely to occur in the atmosphere in which oxygen is present, and the deterioration of lifetime is less likely to occur.

Experiment 6. Next, based on the above hypothesis, an experiment conducted to determine a heat treatment condition suitable for suppressing the deterioration of lifetime will be described. In this experiment, the first to third samples were prepared, and the minority carrier lifetime was measured for them.

The first sample was prepared by the following procedure. First, the semiconductor wafer 12 is oxidized in the reaction tube 11 at a temperature of 900 ° C. Next, the atmosphere inside the reaction tube 11 is set to N 2, and the cooling gas is introduced only between the reaction tube 11 and the heater 1 to cool the semiconductor wafer 12. Cooling rate is 15 on average
C./min. And cooling is performed until the internal temperature of the reaction tube 11 reaches 400.degree. When the lifetime of the first sample prepared by the above procedure was measured, it was 25 μsec.

The second sample was prepared by the following procedure. First, the semiconductor wafer 12 is oxidized in the reaction tube 11 at a temperature of 900 ° C. Next, with the inside of the reaction tube 11 kept in an oxygen atmosphere, a cooling gas is introduced only between the reaction tube 11 and the heater 1 to cool the semiconductor wafer 12. The average cooling rate is 15 ° C./min, and cooling is performed until the internal temperature of the reaction tube 11 reaches 400 ° C. When the lifetime of the second sample prepared by the above procedure was measured, it was 128.8 μse.
It was c.

The third sample was prepared by the following procedure. Destination
First, the semiconductor wafer 12 is heated in the reaction tube 11 at a temperature of 900 ° C.
It oxidizes in degrees. Next, the inside of the reaction tube 11 is made an oxygen atmosphere.
The cooling gas is introduced between the reaction tube 11 and the heater 1 as it is.
And N in the reaction tube 11 ₂Introduced the cooling gas of
To cool the semiconductor wafer 12. Cooling rate is 15 on average
℃ / min, the internal temperature of the reaction tube 11 becomes 400 ℃
Cool down. For the third sample created by the above procedure,
And measured the lifetime, it was 818.9 μsec.
there were. Various measurements for Sample 3 are shown in FIG.
You

In the above experiment, the cooling rate is controlled on the basis of the monitor values by the thermocouples 16-18.
Since the monitored values of the thermocouples 16 to 18 are not the temperature of the semiconductor wafer 12 itself, the rate of temperature decrease of the semiconductor wafer 12 in the process of creating the sample 3 is higher than that of the semiconductor wafer 12 in the process of creating the sample 2. Is considered to be. From this result, it is understood that the lower limit value of the temperature lowering rate that does not deteriorate the lifetime is around 15 ° C./min. Furthermore, in order to prevent the deterioration of lifetime, the reaction tube 1
It can be seen that it is important to direct the cooling gas into the interior of 1.

The heat treatment apparatus of this embodiment is as described above.
After heat-treating the semiconductor wafer 12, the semiconductor wafer 12 is directly cooled by circulating a cooling gas between the heater 1 and the reaction tube 11 and inside the reaction tube 11. More specifically, when the semiconductor wafer 12 is subjected to the oxidation treatment, the semiconductor wafer 1 is processed according to the procedure for forming the sample 3 described above.
2 is cooled. Therefore, according to the heat treatment apparatus of this embodiment, the semiconductor wafer 12 can be appropriately heat-treated without deteriorating the lifetime of the minority carrier.

By the way, in the above embodiment, the reaction tube 1
Although the cooling gas that leads to 1 is limited to N ₂ gas, the cooling gas is not limited to this, and oxygen, water vapor,
Alternatively, ozone or the like can be used as the cooling gas. When these gases are used as cooling gas, it becomes possible to further prevent the dissociation between silicon and oxygen, further prolonging the lifetime of the minority carrier, and in some cases securing a lifetime of about 1 msec. It will be possible.

[0079]

Since the present invention is constructed as described above, it has the following effects. Claim 1
According to the above-described invention, the cooling gas can be introduced into the reaction tube to directly cool the semiconductor wafer that has been subjected to the heat treatment. Therefore, according to the present invention, it is possible to sufficiently reduce the degree of deterioration that occurs in the lifetime of minority carriers during the temperature decrease process of the semiconductor wafer. Also,
According to Ming, the size of the cooling gas outlets, their location
Flow inside the reaction tube by changing according to
The flow rate of the cooling gas can be made uniform. Therefore, the book
According to the invention, a plurality of semiconductor wafers housed in a reaction tube
Can be cooled uniformly. Also, claim 2
According to the invention of the
Flow inside the reaction tube by changing it depending on the location.
The flow rate of the cooling gas to be generated can be made uniform. Obey
According to the present invention, a plurality of semiconductors accommodated in the reaction tube are provided.
The wafer can be cooled more uniformly.

According to the invention described in claim 3, in the reaction tube
Blows the cooling gas introduced to the wafer directly to the semiconductor wafer.
You can stick to it. Therefore, according to the present invention, the semiconductor
Effectively cools the body wafer to prevent lifetime deterioration.
It can be suppressed to a minute.

According to the invention of claim 4 or 5,
The size of the shower head from the center of the reaction tube to the periphery.
The reaction that flows inside the reaction tube
The gas flow rate can be made uniform. Therefore, the present invention
According to the method, a plurality of semiconductor wafers stored in the reaction tube
Then, uniform heat treatment can be performed.

[0082]

According to the invention of claim 6, a semiconductor wafer
Continue the cooling process while supplying abundant oxygen to the surface of the c
be able to. Abundance of oxygen on the surface of semiconductor wafer
Then, it is effective to dissociate the bond between silicon and oxygen.
Can be prevented. Therefore, according to the present invention,
Effectively prevent minority carrier lifetime degradation
can do.

[Brief description of drawings]

FIG. 1 is a diagram showing a main part of a semiconductor wafer heat treatment apparatus according to a first embodiment of the present invention.

FIG. 2 is a perspective view of a reaction tube included in the semiconductor wafer heat treatment apparatus according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a comparison of sheet resistance values of a plurality of semiconductor wafers under different processing conditions.

FIG. 4 shows the results of measuring the minority carrier lifetime before and after heat treatment under condition B-03.

FIG. 5 shows the results of measuring the minority carrier lifetime before and after heat treatment under condition B-02.

FIG. 6 shows the results of measuring the minority carrier lifetime before and after heat treatment under condition B-01.

FIG. 7 is a diagram comparing lifetimes of minority carriers for a plurality of semiconductor wafers having different processing conditions.

FIG. 8 is a diagram showing a comparison of minority carrier lifetimes measured before and after a single temperature heat treatment.

FIG. 9 is a diagram showing the processing time dependence of lifetime for heat treatment at a single temperature.

FIG. 10 is a diagram comparing and representing an initial value of lifetime, a lifetime after deterioration, and a lifetime after recovery.

FIG. 11 is a diagram showing the processing temperature dependence regarding the recovery of the lifetime.

FIG. 12 is a diagram showing a comparison between an initial value of lifetime, a lifetime after heat treatment, and a lifetime in a state where the silicon oxide film is removed.

FIG. 13 is a result of TDS performed on a semiconductor wafer provided with a silicon oxide film.

FIG. 14 is a conceptual diagram of a model assumed to explain the cause of deterioration of lifetime.

FIG. 15 is a measurement result regarding a lifetime of a semiconductor wafer processed by the heat treatment apparatus according to the first embodiment of the present invention.

FIG. 16 is a perspective view of a reaction tube provided in a conventional heat treatment apparatus.

FIG. 17 is a measurement result regarding a lifetime of a semiconductor wafer processed by a conventional heat treatment apparatus.

[Explanation of symbols]

1 heater 2 Air supply port 3 Cooling gas exhaust pipe 5 Reaction gas exhaust port 6 Cooling gas introduction pipe 7 Reaction gas introduction pipe 8 wafer boats 11 reaction tubes 13 Cooling gas ejection holes 14 shower head 15 Cooling gas exhaust hole 16-18 thermocouple

Claims (6)

(57) [Claims] 1. A semiconductor wafer heat treatment apparatus for introducing a reaction gas into a reaction tube to heat-treat a semiconductor wafer, the reaction tube holding a plurality of semiconductor wafers at predetermined intervals in a longitudinal direction, and the reaction tube. A cooling gas introducing pipe provided for blowing a cooling gas to the semiconductor wafer held inside the cooling pipe, the cooling gas introducing pipe having a gas ejection portion extending in the longitudinal direction of the reaction pipe, and the cooling gas introduced into the reaction pipe. A cooling gas exhaust pipe provided at a position facing the cooling gas introduction pipe for exhausting gas, the cooling gas exhaust pipe having a gas exhaust portion extending in a longitudinal direction of the reaction pipe; and the gas ejection portion having a supply source of the cooling gas. A semiconductor wafer having a plurality of cooling gas ejection holes provided so as to gradually increase from a side closer to the side toward a far side, and the gas discharge part includes a plurality of cooling gas discharge holes. Processing apparatus. 2. The semiconductor wafer according to claim 1, wherein the plurality of cooling gas discharge holes are provided such that the cooling gas discharge holes gradually increase from a side closer to the cooling gas exhaust port to a side farther from the exhaust port. Heat treatment equipment. 3. The cooling gas ejection hole is provided at a position corresponding to each of the plurality of wafers held by the reaction tube, and the cooling gas discharge hole is provided by the plurality of wafers held by the reaction tube. The semiconductor wafer heat treatment apparatus according to claim 1 or 2, which is provided at a position corresponding to each of the wafers. 4. A reaction gas introducing pipe for introducing the reaction gas into the reaction pipe from one end thereof, and a shower interposed between a gas ejection hole of the reaction gas introducing pipe and an internal space of the reaction pipe. A shower head hole and a shower head hole formed on the entire surface of the shower head, wherein the shower head hole is formed so as to gradually increase from a central portion of the reaction tube toward a peripheral portion thereof. The semiconductor wafer heat treatment apparatus according to any one of claims 1 to 3. 5. A semiconductor wafer heat treatment apparatus for conducting a heat treatment on a semiconductor wafer by introducing a reaction gas into a reaction tube, the cooling gas introduction for blowing the cooling gas to the semiconductor wafer held inside the reaction tube. A pipe, a cooling gas discharge pipe provided at a position facing the cooling gas introducing pipe for exhausting the cooling gas introduced into the reaction pipe, and the reaction gas inside the reaction pipe from one end of the reaction pipe. A reaction gas introducing pipe for introducing a gas, a shower head interposed between a gas ejection hole of the reaction gas introducing pipe and an internal space of the reaction pipe, and a shower head hole formed on the entire surface of the shower head. The semiconductor wafer heat treatment apparatus, wherein the shower head hole is formed so as to gradually increase from a central portion of the reaction tube toward a peripheral portion thereof. 6. The semiconductor wafer heat treatment apparatus according to claim 1, wherein a gas containing at least one of oxygen, ozone, and water vapor is used as the cooling gas.