JPH06252154A - Silicon wafer - Google Patents

Abstract

PURPOSE:To provide a silicon wafer which allows the sufficient elimination of the influence of metal contamination and the manufacture of reliable semiconductor devices. CONSTITUTION:The title silicon wafer is one that is sliced from a single crystal of silicon pulled up by the Czochralski method. The interstitial oxygen concentration of the outermost section of its mirror surface is 2X10<17> atoms/cm<3> (IOC-88) or below. The wafer has a non-defect layer 10mum or more in depth under the mirror surface level, and the density of minute defects, such as preciptiation of oxygen, of the non-defect layer is 10<5> defects/cm<3> or less. There is an internal gettering layer, containing 10<8> minute defects/cm<3>, at the level deeper than the non-defect layer, and there is no external gettering layer on the opposite side to the mirror surface.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to silicon wafers used in the manufacture of semiconductor devices.

[0002]

2. Description of the Related Art In a semiconductor device manufacturing line, metal contamination of silicon wafers poses a problem. In order to getter such contaminant metals and reduce their effects,
Various gettering techniques have been developed.

As a method generally adopted, backside damage (BSD) for gettering a contaminated metal on the backside of a wafer or extrinsic gettering (E) for forming backside polysilicon is used.
G) The method is known.

Further, by heat-treating the wafer at a high temperature, a defect-free layer (defected zone) having no defect in the surface layer portion which becomes a device active region and a minute defect (B) grown from oxygen precipitation nuclei as a getter site in the bulk portion are formed.
Intrinsic gettering (I
G) The method is known. It is also reported that the defect-free layer is formed in a reducing atmosphere such as hydrogen. Further, an epitaxial wafer having an epitaxial layer formed on the wafer surface may be used.

[0005]

In the EG method, especially backside damage, the wafer is likely to be contaminated because it is honed after etching, and there is a risk of dust particles from the back surface of the wafer due to improper honing. is there. Similarly, backside polysilicon also poses a problem of dust generation. Further, in these silicon wafers, the interstitial oxygen concentration is the same in both the surface layer portion and the bulk portion, and since minute defects depending on crystal growth exist in the surface layer portion, it is inconvenient to obtain a device with good characteristics. Is.

In the IG method, high temperature heat treatment is performed to outwardly diffuse oxygen in the surface layer portion, but a sufficient amount of BMD is applied to the bulk portion.
It is extremely difficult to simultaneously satisfy the demand for forming getter sites such as the above and the demand for sufficiently reducing the interstitial oxygen concentration in the surface layer portion. Normally, the atmosphere for outward diffusion of solid solution oxygen at high temperature is N ₂ , but at high temperatures, surface roughness easily occurs on the mirror surface of the wafer, and in order to prevent this, high temperature annealing is performed in an atmosphere containing a small amount of O _2. Therefore, the solid solution oxygen concentration on the surface cannot be lowered sufficiently. Further, annealing in an Ar gas atmosphere, which is an inert gas, makes it difficult to purify the Ar gas, and impurities may enter the wafer. Therefore, BMD and the like are formed in the surface layer portion, and a problem arises that the contaminated metal is gettered in the device active region. Further, a technique of performing heat treatment in a reducing atmosphere such as hydrogen has been proposed in order to reduce the oxygen concentration on the outermost surface. However, although the conventionally reported heat treatment in a reducing atmosphere can certainly reduce the oxygen concentration in the surface region, on the contrary, another heat treatment or the like must be performed in order to have a sufficient gettering function inside. No
In such a heat treatment step, new microdefects may be generated in the defect-free layer on the surface, or impurities may be contaminated. Furthermore, the heat treatment in such a reducing atmosphere is intended to reduce the defect-free layer on the surface, and in order to improve the throughput in the process, temperature control is performed only to the extent that defects such as slips do not occur on the wafer. There wasn't. Moreover, the IG method proposed so far has poor reproducibility and has not been put to practical use.

In the epitaxial wafer, since the epitaxial layer has to be formed, the manufacturing cost inevitably rises. Moreover, various crystal defects peculiar to the epitaxial growth layer remain.

As described above, the conventional silicon wafer is
The effect on metal contamination cannot be completely eliminated in the device active region. 64Mbit DRAM
Or E ² In a highly integrated and fine next-generation semiconductor device typified by a flash memory such as a PROM, as a result of contamination metal being taken into a thin insulating film formed on the wafer surface, there arises a problem that reliability is significantly lowered.

The present invention has been made to solve the above problems, and a silicon wafer capable of sufficiently removing the influence of metal contamination and manufacturing a highly reliable semiconductor device is provided. The purpose is to provide.

[0010]

The silicon wafer of the present invention is a silicon wafer cut out from a silicon single crystal pulled by the Czochralski method, and the interstitial oxygen concentration of the surface layer portion of the mirror surface is 2 x 10 ¹⁷
atoms / cm ³ (IOC-88) or less, a defect-free layer having a thickness of 10 μm or more is formed from the mirror surface, and the density of fine defects such as oxygen precipitates in the defect-free layer is 10 ⁵ Pieces / cm ³ The number of micro defects is 10 ^{8 in the} region deeper than the defect-free layer. Pieces / cm ³ It is characterized in that it has the internal gettering layer formed as described above, and does not have the external gettering layer on the back surface side of the mirror surface. The oxygen concentrations in this specification are all obtained by the coefficient of IOC-88.

In the silicon wafer of the present invention, the interstitial oxygen concentration in the surface layer portion serving as the device active region is less than the solid solution limit of oxygen in silicon, and the cause of device failure even when subjected to various heat treatments in the device manufacturing process. Does not cause micro defects. Further, since the wafer surface layer portion is a defect-free layer with few fine defects, it is preferable as a device manufacturing area. The number of microdefects in the defect-free layer is 10 ³ Pieces / cm ³ It is more preferable that it is below, and it is further preferable that it is substantially 0 (below the detection limit). Further, an internal gettering layer (IG layer) in which minute defects are formed is formed under the defect-free layer, and serves as a getter layer against metal contamination in the device manufacturing process. The BMD density in this IG layer is 10 ⁹ Pieces / cm ³ The above is more effective. The silicon wafer of the present invention can be manufactured by the following method.

A silicon single crystal is pulled by a usual CZ method, and a sliced and polished silicon wafer is cut at 1150 ° C.
As described above, the heat treatment is preferably performed in the range of 1200 to 1300 ° C. in a reducing atmosphere in which hydrogen or hydrogen and an inert gas are mixed. At this time, the wafer is allowed to stay in the temperature region of 1100 ° C. or higher for 30 minutes or longer. In order to obtain the wafer of the present invention, it is indispensable to keep the temperature rising rate low in a temperature range of at least 1000 ° C or higher.
The rate of temperature increase is preferably 3.5 ° C./min, more preferably 3 ° C./min or less.

By slowing the rate of temperature rise in the specific region in this manner, a sufficient amount of precipitation nuclei are generated inside the wafer uniformly in the depth direction and in the plane parallel to the surface, which is larger than that of conventional wafers. To do. Furthermore, the growth of the nuclei enables uniform and sufficient deposition of BMD. After that, when the interstitial oxygen around the BMD in the surface layer portion became a low concentration by the heat treatment in a reducing atmosphere at 1150 ° C. or higher, it became clear that the BMD was easily redissolved and disappeared. This is because the oxygen concentration in the surface layer portion is lowered by outward diffusion of oxygen due to the high temperature H ₂ annealing, so that oxygen forming BMD is redissolved.
The oxygen concentration in the surface layer portion of the wafer obtained by redissolving BMD in the surface layer portion and further outward diffusion of interstitial oxygen generated by the dissolution is 2 × 10 ¹⁷ atoms / cm ^3. The following very low concentration forms a defect-free layer of sufficient thickness, and 10 ⁸ is formed in the deep part inside the wafer. Pieces / cm ³ The above-mentioned sufficient amount of BMD is formed.

As described above, since the BMD is formed in the wafer in an amount sufficient to getter the metal impurities, the BSD process and the EG process for forming the backside polysilicon or the like on the back surface of the wafer are unnecessary.

[0015]

EXAMPLES Examples of the present invention will be described below. Example 1

6-inch diameter, n-type (about 1.5Ω · c
m) and a CZ wafer with a plane orientation (100) of 1200
Heat treatment was performed in a high-purity H ₂ gas atmosphere at 1 ° C. for 1 hour. The heat treatment sequence is shown in FIG.

FIG. 2 shows the S of this silicon wafer.
IMS (Secondary Ion Mass Sp)
distribution of the interstitial oxygen concentration [Oi] in the depth direction (depth).
The result of having measured profile) is shown.

As is clear from FIG. 2, [Oi] of the bulk portion deeper than about 50 μm from the surface of the wafer is about 1.2.
× 10 ¹⁸ atoms / cm ³ However, [Oi] on the surface
Is about 1 × 10 ¹⁷ atoms / cm ³ Is. Since a natural oxide film and an adsorbed substance exist on the outermost surface, highly reliable measurement cannot be performed unless these are sputtered. Also in the measurement result of FIG. 2, a reliable profile can be obtained from a depth of about 1 μm. When this profile is extrapolated to a depth of 0 μm, the [Oi] of the outermost surface is 1 × 10 ¹⁷ atoms.
/ Cm ³ It can be seen that

As described above, the high temperature annealing in the reducing H ₂ gas atmosphere reduces the ultra-thin film such as the natural oxide film on the wafer surface to expose the silicon, which is ideal for the outward diffusion of solid solution oxygen. In addition, the surface layer [Oi] can be lowered to a very low level.

Further, a spike-like profile is observed when approaching the bulk part from the surface part, which is due to BMD.
It is a small defect such as. That is, when the temperature rising rate is slow as in the present embodiment, the growth rate of BMD and the like is faster than the increase rate of the critical nucleus radius, so that minute defects such as BMD grow.

Further, based on the outward diffusion theory of oxygen,
Results of simulating a process in which oxygen precipitates (BMD) grow and dissolve by H ₂ annealing are shown in FIGS. 3 and 4.
Shown in. The vertical axis represents the size of BMD, and the horizontal axis represents time. Heat treatment condition is 3 ℃ / min from 900 ℃ to 1200 ℃
At 100 ° C for 100 minutes and then at 1200 ° C for 1 hour or 2
Hold for a time, from 1200 ℃ to 900 ℃, 3 ℃ / min
The condition is that the temperature is decreased over 100 minutes.

The oxygen concentration in the crystal is 8.75 × 10 ¹⁷ atoms / cm ^{3 in} the case of FIG. In the case of FIG. 4, 1.06 × 10 ¹⁸ atoms / cm ³ Is. Further, for each plot in FIGS. 3 and 4, the depth from the surface of the BMD (indicated by numerical values in FIG. 3) and 1
The retention times at 200 ° C. are shown in Table 1 (corresponding to FIG. 3) and Table 2 (corresponding to FIG. 4), respectively.

[0023]

[Table 1]

[0024]

[Table 2]

From the results shown in FIGS. 3 and 4, the following can be understood. First, in the temperature rising process, BMD grows because the temperature rising rate is slow. Further, in the high temperature annealing at 1200 ° C., the behavior is different between the surface layer portion of the wafer and the inside (bulk portion) of the wafer. That is, in the surface layer portion of the wafer, interstitial oxygen around the BMD is diffused outward and the concentration [O
It is considered that BMD re-dissolves and becomes smaller and disappears due to the decrease in [i]. On the other hand, in the bulk portion, interstitial oxygen does not diffuse outward, so that the oxygen concentration around the BMD does not decrease, and it is considered that the BMD remains without being redissolved.

These phenomena are schematically shown in FIGS. 5 (a) to 5 (d). In FIGS. 5A to 5D, the horizontal axis of the graph is the depth from the wafer surface, and the vertical axis is the total oxygen concentration contained in the wafer (interstitial oxygen and oxygen in the precipitate are not considered).
Indicates. FIG. 5A shows the initial state, and the oxygen concentration is uniform in the depth direction. FIG. 5B shows a state in which BMDs are formed at points A and B at a certain depth during the temperature rise. Since BMD is a precipitate, oxygen is concentrated to a high concentration.

FIG. 5C shows a state immediately before the start of annealing at 1200 ° C. In this state, outward diffusion of interstitial oxygen occurs to some extent, and the oxygen concentration decreases toward the wafer surface layer, but there is almost no change in oxygen concentration at points A and B where BMD is formed. BMD
Is not dissolved.

FIG. 5D shows the state after the annealing at 1200 ° C. is completed. The BMD formed at point A in (c) is redissolved and disappears because the oxygen concentration around it is low.
On the other hand, since the depth of the point B is deep, the oxygen concentration around the BMD is not diffused outward and is maintained at a high concentration, so that the BMD remains as it is.

Further, in the present invention, since annealing is performed in a hydrogen atmosphere which is a reducing gas, BM, which is an oxygen precipitate, etc.
The nucleus of D is reduced, and the disappearance of the BMD nucleus in the surface layer portion is further accelerated. As a result, the surface layer portion just below the surface has a solid solution oxygen concentration of 1 × 10 ¹⁷ atoms / cm ^{3 on the surface.} Down to
An ideal defect-free layer is formed in which minute nuclei that become nuclei for generation of BMD and the like are extremely small as compared with a normal wafer. Example 2 A wafer having a reduced oxygen concentration was obtained by performing heat treatment in the same manner as in Example 1 except that the holding time at 1200 ° C. was 4 hours (d).

For comparison, pulled up by the CZ method
It is cut from a single crystal and subjected to normal donor killer heat treatment.
The oxygen concentration [Oi] is 1.04 × 10¹⁸atoms
/ Cm³ Wafer (a) and [Oi] is 0.91
× 10¹⁸atoms / cm³ Wafer (b) was obtained.
Also, the same [Oi] is 0.91 × 10¹⁸atoms /
cm³ Temperature rise rate of 10 ~ 15 ℃ / min
In a hydrogen atmosphere at 1200 ° C for 1 hour
A heat-treated wafer (c) was obtained.

Each of the obtained wafers was subjected to a heat treatment corresponding to the manufacture of CMOS. That is, first, N ₂ + trace O
₂ at 1200 ° C. for 3 hours, then in N ₂ at 800 ° C. for 3 hours
Heat treatment was then performed for 10 hours at 1000 ° C. in O ₂ .

The depth from the surface of these wafers is 15
FIG. 6 shows the result of measurement of the BMD density distribution in a plane parallel to the surface in μm by the infrared tomography method. Further, FIG. 7 shows the results of measuring the BMD density distribution in the depth direction from the surface of these wafers to a depth of 30 μm by the infrared tomography method.

From FIG. 6, it can be seen that the in-plane distribution of BMD within the plane having a depth of 15 μm from the surface is as follows. That is, BMD was not detected and a good defect-free layer was formed in the wafer (d, Example 2) which was heat-treated in a hydrogen atmosphere for 4 hours and the wafer (c) which was heat-treated in a hydrogen atmosphere for 1 hour. On the other hand, comparative examples (a,
The wafer in b) is 10 ⁵ From 10 ⁶ Pieces / cm ³ B of degree
It can be seen that the MD exists, and the BMD density increases toward the peripheral portion of the wafer even at the same depth.

Further, it can be seen from FIG. 7 that the BMD depth direction distribution is as follows. That is, in the wafer of Example 2, a good defect-free layer without BMD was formed in a region from the surface to a depth of about 15 μm, and conversely, at a depth of more than that, the BMD density sharply increased, A BMD having a higher density than that of the comparative wafer is formed. This BMD acts as a good intrinsic gettering layer.

On the other hand, the wafers (a) and (b) have BMDs formed on their surfaces. Further, the wafer of (c) is BM during the heat treatment process.
Since it is not treated by a gentle temperature increase / decrease such that D is formed and grows, BMD is possible even at a depth of 30 μm from the surface.
Is not formed. Further, even at a depth greater than that, BMD growth was insufficient, and a sufficient amount of BMD for trapping impurities was not formed in the device manufacturing process.

[0036]

As described in detail above, according to the present invention, it is possible to provide a silicon wafer capable of sufficiently removing the influence of metal contamination and manufacturing a highly reliable semiconductor device. .

[Brief description of drawings]

FIG. 1 is a diagram showing a heat treatment sequence in Embodiment 1 of the present invention.

FIG. 2 is a characteristic diagram showing a profile in the depth direction of interstitial oxygen concentration of a silicon wafer in Example 1 of the present invention.

FIG. 3 shows that in Example 1 of the present invention, the initial oxygen concentration in the crystal was 8.75 × 10 ¹⁷ atoms / cm ^3. Figure oxygen precipitates wafer is (BMD) shows a result of simulating the process of growth and dissolution with H ₂ annealing.

FIG. 4 shows that in Example 1 of the present invention, the initial oxygen concentration in the crystal was 1.06 × 10 ¹⁸ atoms / cm ^3. Figure oxygen precipitates wafer is (BMD) shows a result of simulating the process of growth and dissolution with H ₂ annealing.

5A to 5D are schematic views showing the growth and dissolution of BMD.

FIG. 6 is a diagram showing a BMD density distribution in a plane parallel to the surface having a depth of 15 μm from the surface of the wafer in Example 2 of the present invention.

FIG. 7 is a diagram showing a BMD density distribution in the depth direction from the surface of the wafer to a depth of 30 μm in Example 2 of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Seiji Kurihara, 30 Soya, Hadano City, Kanagawa Prefecture Central Research Laboratory, Toshiba Ceramics Co., Ltd. Central Research Laboratory (72) Inventor Koji Izumisuma 30 Soya, Hadano, Kanagawa Prefecture Central Research Laboratory, Toshiba Ceramics Co., Ltd.

Claims (1)

[Claims] 1. A silicon wafer cut out from a silicon single crystal pulled by the Czochralski method, wherein the interstitial oxygen concentration in the surface layer portion of the mirror surface is 2 × 10.
¹⁷ atoms / cm ³ The defect-free layer having a thickness of 10 μm or more from the mirror surface is formed, and the density of fine defects such as oxygen precipitates in the defect-free layer is 10 ⁵ or less. Individual/
cm ³ The number of micro defects is 10 ^{8 in the} region deeper than the defect-free layer. Pieces / cm ³ A silicon wafer having the internal gettering layer formed as described above, and having no external gettering layer on the back surface side of the mirror surface.