JPS6216538B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a preprocessing process in semiconductor device manufacturing, that is, a substrate processing process before semiconductor device manufacturing.

In general, when manufacturing semiconductor devices (including integrated circuits such as IC LSI), there are so-called process-induced defects and harmful impurities (defects) that have a large effect on the characteristic defects of the devices.

These defects and impurities not only reduce the lifetime of the carrier, but also have a serious adverse effect on device characteristics due to spike diffusion and the like in the impurity diffusion process. In order to prevent the occurrence of these defects in the device operating region and to remove harmful impurities, a method of intentionally generating crystal defects inside a silicon wafer and using them as sinks for gettering, so-called intrinsic gettering. A gettering method such as an interinsic gettering method (hereinafter referred to as IG method) is incorporated into the manufacturing process.

In this IG method, defects are generated inside the silicon wafer, and defects are generated near the wafer surface related to device operation.
Defect-free Denuded Zone
Create an area called DZ (hereinafter referred to as DZ). That is,
This cleans the DZ related to device operation by gettering harmful impurities mixed in the DZ into internal defects.

As a wafer with IG effect, the DZ width is as narrow as possible to enable effective gettering, and the density of defects generated is as large as possible.
It is preferably 10 ⁵ cm ⁻² or more. In addition, the above D.
Z. Width varies depending on the element to be formed. For example, the distance from the substrate surface related to device operation is about 5 μm for a bipolar transistor and about 3 μm for a MOS transistor.
For each DZ width, set the optimum value as narrow as possible.

An overview of the currently known IG method will be explained below with reference to the drawings.

As shown in FIG. 1a, a silicon wafer is first heat-treated at 1100° C. for about 20 hours in an N ₂ atmosphere.

Silicon wafers manufactured by the normal CZ method (Czochralski method) have a surface area of 0.5 to 2.0×10 ¹⁸ cm inside.
Oxygen is contained at a density of ^-3 (ASTM standard, hereinafter the same applies), and although the mechanism itself is still not publicly known, this oxygen concentration is an important factor in the formation of crystal defects. It is known.

Here, by performing heat treatment at 1000° C. or higher, oxygen near the surface is out-diffused to the outside as schematically shown by arrows. At the same time, inside the wafer, the wafer formation state (as-
The defective nuclei that existed in the grown state) disappear or dissolve into solid solution. In addition, in the usual IG method, a protective film such as SiO ₂ is coated in advance to prevent the wafer surface from becoming rough due to long-term high-temperature treatment.

Next, as shown in FIG. 1b, heat treatment is performed at a temperature of 700 to 800° C. for about 40 hours in the same N ₂ atmosphere. This is a process of forming high-density defect nuclei by so-called low-temperature annealing.

In the process a, oxygen near the wafer surface is out-diffused to the outside, but the oxygen concentration inside the wafer is still high. By applying heat treatment at 700 to 800°C, the oxygen is concentrated to form defect nuclei.

That is, in this process, a high density of defect nuclei is increased to some extent inside the wafer. However, in the vicinity of the wafer surface, the oxygen concentration is sufficiently lowered by the high-temperature annealing in step a above, and the defect nuclei are eliminated or dissolved into solid solution, so that a high density of defect nuclei is not formed.

Then, as shown in Figure 1c, in an _N2 atmosphere.
A DZ is formed by heat treatment at about 1050℃ for about 20 hours.

By performing heat treatment at a relatively high temperature again, the high density defect nuclei formed in the process b above are removed by IG.
It grows on crystal defects that can be sources. Under high-temperature heat treatment, if the defect nucleus has already grown larger than the critical size, it is possible to grow it into a defect, but if not, the defect nucleus disappears as shown in process a. Or it becomes a solid solution.

Furthermore, even if defect nuclei are formed near the wafer surface in the process b, almost all of the defect nuclei disappear or become solid solution in the process c, so a clean DZ can be obtained. .

The IG method, which repeats the above high-temperature treatment and low-temperature treatment, has already been described in JP-A-55-38098, 54-157576 and
53-15764, and is about to be applied as a pretreatment process in the actual manufacture of semiconductor devices.

However, as mentioned above, each heat treatment requires a long time of 20 to 40 hours, so although its effectiveness has been fully confirmed as a result of academic research, it is difficult to apply it to actual processes.

In other words, the silicon wafer surface is subject to high-temperature heat treatment over a long period of time, which causes considerable roughness on the surface of the silicon wafer, even if a sufficiently thick protective film such as SiO ₂ is formed. I can't afford it.

Here, at least one surface treatment such as polishing is required, which increases the number of steps and makes it difficult to accurately control the DZ width.

In addition, heat treatment that actually lasts for more than 60 hours significantly reduces productivity and may also cause warping or distortion of the wafer.

The inventor of the present invention has already proposed a method for growing crystal defects by increasing temperature, which solves the problems caused by the conventional heat treatment methods.

Heat treatment by increasing temperature can significantly shorten the growth time of defects and also form thin DZs with good control for efficient IG.

In the growth of crystal defects due to the temperature increase, there is a close correlation between the temperature increase rate and the width of the DZ.
The correlation is shown in FIG. 3 for a silicon substrate with an oxygen concentration of 1.8×10 ¹⁸ cm ⁻³ . The horizontal axis shows the temperature increase rate (°C/min), and the vertical axis shows the DZ width (μm).

Here, the minimum temperature value is 750℃ and the maximum temperature value is 1100℃
This is the result of heat treatment for 30 minutes at the highest temperature value. , the DZ width tends to increase as the heating rate increases. When heating from a low temperature of 500℃ to 900℃ to a high temperature of 950℃ to 1300℃, the temperature increase rate is 5℃/
If the annealing temperature is lower than min., densification of defect nuclei mainly proceeds rather than out-diffusion of oxygen and disappearance or solid solution of defect nuclei, similar to the aforementioned low-temperature annealing. Further, at a heating rate of 5° C./min to 14° C./min, the desired effect can be obtained, although it is not as effective on defect nuclei and defect formation as when it is 5° C./min or less. Therefore, a temperature increase rate of 14° C./min or less is effective for defect formation.

As mentioned above, in order to perform gettering efficiently, it is desirable that the width of the DZ be as narrow as possible, but especially for substrates with an oxygen concentration of 1.5×10 ¹⁸ cm ^-3 or higher, the heating rate should be 5°C/min or less. However, it is difficult to apply this method to actual manufacturing processes because crystal defects appear near the surface of the substrate, which is involved in device operation.

The present invention provides a method for growing crystal defects that can efficiently produce the IG effect, and in particular,
The purpose is to form a thin DZ in a well-controlled manner in a short time on a substrate with an oxygen concentration of 10 ¹⁸ cm ^-3 or higher.

Further, the object of the present invention can be achieved by performing heat treatment at 950° C. or higher for 10 minutes or more, and then repeating the heat treatment one or more times at a temperature increase rate of 14° C./min or lower. In order to obtain a particularly thin DZ, the heating rate should be 5°C/min at least in the first time.
The following is desirable. In addition, for substrates with an oxygen concentration of 1.5×10 ¹⁸ cm ^-3 or less, 5°C/min
If heat treatment is performed at the following temperature increase rate, DZ will be formed,
A sufficient gettering effect can be obtained. However, in many types of substrates, a single defect may be formed even within the DZ, causing device deterioration.

The present invention provides a method for growing crystal defects that can efficiently produce IG effects.
The purpose is to form a thin DZ in a well-controlled manner in a short time on a substrate with an oxygen concentration of ×10 ¹⁸ cm ^-3 .

Further, the object of the present invention is to perform heat treatment at 950°C to 1300°C for 10 minutes to 10 hours, and then heat treatment at 500°C to 900°C.
Heat treatment for 0 to 15 hours at a low temperature of 500°C to 900°C to 950°C to 1300°C.
This is achieved by repeating the heat treatment one or more times at a temperature increase rate of 14°C/min or less. In particular, in order to obtain a better gettering effect, it is desirable that the temperature increase rate be 5° C./min or less at least in the first time. Further, for a substrate having an oxygen concentration of 1.5×10 ¹⁸ cm ^-3 or less, heat treatment at 950°C to 1300°C is performed for 10 minutes to 10 hours, the low temperature treatment is performed for 2 hours to 15 hours, and then
This is achieved by repeating the heat treatment one or more times in which the temperature is raised from a low temperature of 500°C to 900°C to 950°C to 1300°C at a temperature increasing rate of 5°C/min or less.

In other words, as mentioned above, the slower the heating rate, the thinner the DZ can be formed, but especially in the case of a substrate with a high oxygen concentration, if the heating rate is too slow, crystals may form near the surface, which is critical for device operation. DZ
In order to further reduce single defects within
Heat treatment is performed at 950° C. to 1300° C. in advance to eliminate defective nuclei near the substrate surface and to out-diffusion oxygen that forms defective nuclei.

Examples of the present invention will be explained below.

FIG. 2 shows the relationship between time and temperature for this example.

In step (a), heat treatment is performed on the silicon substrate at a temperature of, for example, 1100° C. for 60 minutes. This high-temperature treatment eliminates or dissolves defect nuclei near the surface of the substrate. At the same time, oxygen molecules that are present in the vicinity of the surface and cause defect nucleation are out-diffused.

Here, unless the temperature of the heat treatment is 950° C. or higher, it is difficult to sufficiently clean the vicinity of the substrate surface. Further, if the temperature exceeds 1300°C, the influence of heat on the substrate becomes too large, which is undesirable as it may cause warping of the wafer.

Figure 4 shows a substrate with an oxygen concentration of 1.8×10 ¹⁸ cm ^-3.
Processing time when performing high temperature heat treatment at 1100℃
FIG. 3 is a diagram showing the relationship between DZ widths.

As is clear from this figure, the heat treatment time is
The effect can be obtained by applying heat treatment for 10 minutes or more, but approximately 60 minutes is sufficient. The thinner the DZ width, the better the gettering effect, but a width of about 80 μm has also been confirmed to be effective, and a heat treatment time of up to about 10 hours is effective for this purpose.

Furthermore, in order to protect the substrate surface, it is preferable to form a protective film such as silicon dioxide (SiO ₂ ) on the surface before starting the heat treatment of the present invention. It is possible to form a SiO ₂ film on the substrate surface. still,
The SiO ₂ film as the protective film is a normal CVD film.
(Chemical Vapor Deposition) method is also possible, but it is preferable to directly oxidize the substrate itself after surface cleaning.

After the high temperature treatment shown in FIG. 2a is completed, the temperature is once lowered to about 650 DEG C., for example, as shown in FIG. 2b. Since such temperature-lowering treatment does not significantly affect the implementation of the present invention, the substrate may be directly taken out of the furnace and cooled.

Next, heat treatment is performed at approximately 650°C as shown in Figure 2c. A heat treatment time of about 0 to 15 hours is sufficient. The growth of crystal defects according to the present invention is mainly caused by the above-mentioned a.
The low-temperature treatment here is not necessarily necessary because it is performed by the high-temperature treatment and the temperature-raising step performed later. However, depending on the substrate, especially 1.5×10 ¹⁸ cm ^-3
By performing this low-temperature treatment on a substrate having an oxygen concentration below, the density of internal defect nuclei is increased, and excellent characteristics are exhibited.

At a heating rate of 2°C/min. in Fig. 2d, the 650°C
Heat treatment is performed from ℃ to 1100℃.

In the crystal defect growth method according to the present invention, the DZ is almost determined by this first temperature raising step. In the case of a substrate with a relatively high oxygen concentration of 1.5×10 ¹⁸ cm ^-3 or more, a DZ of about 10 to 30 μm can be formed in a well-controlled manner at a heating rate of 5° C./min. or less. Regarding the setting of the DZ width, it is preferable that the DZ width be as thin as possible unless defects are formed in the device operating region as described above, and the temperature increase rate should be as slow as possible.

As described above, when a substrate with a high oxygen concentration of 1.5×10 ¹⁸ cm ^-3 or more is first heat-treated at a heating rate of 5°C/min or less as in the past, crystal defects may occur near the surface where device operation is concerned. Formed, but also 1.5×
Single defects were sometimes formed in the DZ for substrates with low oxygen concentrations of 10 ¹⁸ cm ^-3 or less, but according to the present invention, heat treatment is first performed at 950°C or higher, which eliminates this problem. There is no such thing.

Next, the temperature increased to about 1100° C. in FIG. 2e is maintained for about 30 minutes. In the present invention, holding at such a high temperature is not particularly necessary unless the temperature difference between the low temperature and the high temperature is very small. The same can be said of the holding in the low temperature section shown in FIG. 2g.

That is, in the present invention, the temperature in the low temperature section is 500 to 900°C.
Preferably 550-850℃, 950-850℃ in high temperature section
The effect can be obtained by repeating a temperature cycle of 1300℃, preferably 1000 to 1300℃, but
If the temperature is 600° C. or higher and 1000° C. or lower in the high-temperature section, a step to maintain the temperature constant as described above is required.

Then, the temperature is lowered again from 1100°C to 650°C in FIG. 2f. Although crystal defects grow in such a temperature-lowering step, the effect as great as that in the temperature-raising step is not obtained, so there is no need to particularly limit the temperature-lowering rate.

Next, as shown in FIG. 2g, the temperature of 650° C. is maintained for about 30 minutes, but as mentioned above, such a step is not particularly necessary in the present invention.

Next, temperature increase is started in FIG. 2h.

In the present invention, the heating step is carried out approximately twice when the heating rate is 1 to 3°C/min, approximately three times when the heating rate is 3 to 5°C/min, or approximately 3 times when the heating rate is 5°C/min to 14°C/min. Regarding the temperature rate, it is possible to achieve sufficient defect growth by repeating the temperature increase, but the number of times is not constant depending on the substrate.

In addition, as mentioned above, the temperature increase rate in the first temperature increase process is largely related to the setting of the DZ width, and the temperature increase rate or temperature decrease rate from the second time onwards is influenced by the shortening of the process.
It is possible to set the temperature sufficiently within the range of 14°C/min.

As has been made clear from the examples above, in the heat treatment according to the present invention, the heat treatment in the vicinity of the surface of a silicon substrate containing a high concentration of oxygen of 1.5×10 ¹⁸ cm ^-3 or more is performed at a rate of 5°C/min. or less. It is possible to form a DZ in a temperature raising process. In addition, in the present invention, especially at 5°C/
It is not only applicable to heating rates below min.
If the heating rate is 14° C./min. or less, defect nuclei will not be formed near the substrate surface, and crystal defects with sufficient gettering function can be grown inside in a much shorter time than conventional methods.

Furthermore, DZ is difficult to form on a substrate with an oxygen concentration lower than 1.5 × 10 ¹⁸ cm ^-3 , but for the original purpose of cleaning the silicon surface, a high oxygen concentration of 1.5 × 10 ¹⁸ cm ^-3 or higher is required. As with the case of the substrate, a certain effect can be obtained.

Furthermore, when forming a DZ in a well-controlled manner on a low-concentration substrate, it is effective to lengthen the low-temperature treatment time shown in FIG.

Therefore, the present invention does not particularly limit the oxygen concentration, but taking practicality into consideration, it is possible to process in a short time at 1.5×10 ¹⁸ cm ^-3
It is preferable to use a substrate having an oxygen concentration higher than or equal to the above.

In addition, it is known that in heat treatment related to the growth of normal crystal defects, superior results can be obtained when carried out in a non-oxidizing atmosphere such as nitrogen, rather than in an oxidizing atmosphere. Also, after forming the SiO ₂ film as a protective film, it is preferable that the atmosphere in the furnace be non-oxidizing.

[Brief explanation of the drawing]

Figures 1a to 1c are cross-sectional views of the substrate during crystal defect growth by conventional heat treatment, Figure 2 is a diagram showing the relationship between temperature and time of heat treatment in the present invention, and Figure 3 is a diagram showing the temperature increase rate and temperature of the present invention. FIG. 4 is a diagram showing the relationship between the processing time and the DZ width when the substrate of the present invention is subjected to high temperature heat treatment at 1100°C.

Claims (1)

[Claims] 1. In the pretreatment process for manufacturing a semiconductor device using a silicon semiconductor substrate, the oxygen concentration is 1.5×10 ¹⁸ cm ^-3
The substrate having the above is subjected to heat treatment at 950℃ to 1300℃ for 10 minutes to 10 hours, then heat treated at a low temperature of 550℃ to 850℃ for 0 to 15 hours, and then at a low temperature of 550℃ to 850℃. From 950℃ to
1. A method of manufacturing a semiconductor device, comprising the step of forming crystal defects inside the substrate by performing heat treatment one or more times to raise the temperature to a high temperature of 1300° C. at a temperature increasing rate of 14° C./min or less. 2 The temperature increase rate in the heat treatment by temperature increase,
2. The method of manufacturing a semiconductor device according to claim 1, wherein at least the first heat treatment is performed at a temperature of 5° C./min or less. 3. In the pretreatment process for manufacturing semiconductor devices using silicon semiconductor substrates, the oxygen concentration is 1.5×10 ¹⁸ cm ^-3
A substrate having the following is subjected to heat treatment at 950℃ to 1300℃ for 10 minutes to 10 hours, followed by heat treatment at a low temperature of 550℃ to 850℃ for 2 hours to 15 hours, and then at a low temperature of 550℃ to 850℃. From 950℃ to
A method of manufacturing a semiconductor device, comprising performing heat treatment at least once to a high temperature of 1300°C at a temperature increasing rate of 5°C/min or less.