JPH07114207B2 - Semiconductor substrate and manufacturing method thereof - 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 substrate and a method for manufacturing the same, and more particularly to a semiconductor substrate (hereinafter referred to as a device) which has little mechanical damage on the back surface of a Si single crystal wafer and is extrinsic. The present invention relates to a semiconductor substrate having a lasting gettering (EG) effect and a manufacturing method thereof.

[0002]

2. Description of the Related Art In a device manufacturing process, a Si single crystal wafer (hereinafter referred to as a wafer) is subjected to various heat treatments, in which various crystal defects are induced by oxygen, carbon, heavy metal impurities and the like in the crystal. These defects also occur on the surface of the wafer and in the vicinity of the surface, leading to an increase in leak current, which leads to deterioration of device characteristics and a decrease in yield.

However, fine crystal defects and strains formed on the back surface of the wafer opposite to the mirror surface or inside the wafer trap impurities that adversely affect the device characteristics,
It has a function of removing the point defects or the like that are fixed or are involved in the generation of defects. This action is called gettering, and the former is extrinsic gettering (hereinafter EG
Say. ), The latter is intrinsic gettering (I
G).

As one means for imparting this EG, fine particles are blown onto the back surface of the wafer to introduce a strained layer, and dislocations and stacking faults caused by this back strained layer are generated in the heat treatment process of the device. A method used as a gettering source is known as a sandblast method (Japanese Patent Laid-Open Nos. 53-128272 and 54-14).
No. 8474, etc.).

However, in the case of this sandblasting method, the strained layer formed on the back surface of the wafer tends to disappear during high temperature heat treatment during device manufacturing, and the EG effect tends to be lost in the middle of the device manufacturing process. There is also a method to improve the sandblast pressure to form a deeper strained layer, but in this case, the introduction causes new mechanical damage different from the desired strained layer, and this damage occurs in the device manufacturing process. This causes dust generation and slip dislocation generation, which causes deterioration of device characteristics and manufacturing yield.

[0006]

The present invention, when introducing a strained layer on the back surface of a wafer by dry or wet sandblasting, has little mechanical damage on the back surface of the wafer, and in high temperature heat treatment in the device manufacturing process, An object of the present invention is to provide a semiconductor substrate into which a back strain layer having a persistent EG effect is introduced and a method for manufacturing the same.

[0007]

In order to solve the above-mentioned problems, in the semiconductor substrate and the manufacturing method thereof according to the present invention,
Do not use Si oxide film or Si nitride film on the backside of the wafer.
A single-layer protective film is provided, and then a strained layer is introduced into the back surface of the wafer by a sandblast method.

The protective film is a Si oxide film or Si formed by a direct thermal oxidation or thermal nitriding reaction of the wafer.
A nitride film, a film of Si alone or an oxide or nitride thereof formed by the CVD method, and an oxide film based on a metal element different from that of Si are used.

Especially when a Si oxide film is used as the protective film, annealing heat treatment of the wafer is performed in the preceding step of sandblasting, and the inert gas atmosphere at the time of this heat treatment is set to an oxidizing atmosphere containing oxygen. The advantage that the formed thermal oxide film of Si can be directly utilized is obtained.

When the protective film is unnecessary after sandblasting, it can be easily removed by mechanical polishing or, in the case of a Si-based film, a normal etching solution mainly containing hydrofluoric acid.

[0011]

According to the method of the present invention, the Si oxide film is formed on the back surface of the wafer.
In addition, by performing a sandblasting process with a single protective film of Si nitride film interposed, the conventional machine of the wafer has a problem when performing the sandblasting process of directly spraying fine particles (sand) on the back surface of the wafer. It effectively prevents physical damage.

Particularly in the dry sandblast method, when the fine particles to be used are crushed hard materials, the tips of the fine particles collide with the wafer surface at a high speed, and the kinetic energy of the fine particles becomes a destructive force to the wafer surface. Often, there were local fractures on the wafer surface or fine cracks on the surface. Wet sandblasting has been proposed to alleviate this phenomenon, but satisfactory results have not been obtained.

That is, the presence of the protective film of the present invention has an advantage that the destructive force is absorbed in the film by the appropriate film thickness and does not reach the wafer. Therefore, the conditions required for the protective film include a certain degree of hardness, adhesion of the film itself to the wafer, durability against destructive force, and adjustment of the film thickness depending on the film quality. If these requirements are combined, the Si thermal oxide film or the Si oxide film by CVD is
It can be said that it is a suitable material in the present invention.

Furthermore, the present invention achieves the following operational effects in addition to the main operational effects described above.

(A) A semiconductor substrate having a persistent EG effect can be obtained during device manufacturing.

As described above, in the conventional sandblasting process, there are many cases in which the desired strained layer cannot be formed in order to avoid the problem of mechanical damage on the back surface of the wafer due to fine particles. By providing a protective film on the back surface, it is possible to apply strong mechanical energy to the back surface by sandblasting, and as a result, the EG effect can be exerted above the level of the conventional method. After that, the removal of the protective film does not decrease.

After the sandblasting, when a device is manufactured using a semiconductor substrate in which the protective film is left on the back surface of the wafer, despite the various heat treatment steps, the protective film and the wafer are not separated. The strained layer formed near the interface is in a state of being difficult to repair due to the influence of the protective film. Therefore, it is estimated that the stronger the bond strength between the protective film and the wafer, the longer the EG effect is maintained. To be done.

(B) When the protective film is formed of a Si oxide film, it is only necessary to perform it in an oxidizing atmosphere, for example, an oxygen-containing atmosphere, in an inert gas used in the conventional annealing treatment of a semiconductor wafer. It is not necessary to add a new process, and the manufacturing can be performed in the same process as the conventional one.

(C) When the protective film is formed by a method other than the thermal oxidation method or the thermal nitriding method, for example, when the CVD method is adopted, the number of steps is increased only by adding the step of forming the protective film. There is no.

(D) The protective film is removed if necessary, but even in this case, the number of steps for removing the protective film is increased, and no major changes in the steps are required.

(E) The protective film does not necessarily have to be removed. If not removed, there are the following advantages in addition to the above effects.

When the semiconductor substrate is mirror-polished by, for example, a waxless method, the presence of the protective film facilitates the fixing of the substrate and the holding surface of the polishing apparatus.

When a semiconductor substrate is processed, contamination of the substrate surface due to a cassette or the like between steps or during storage can be prevented.

Generation of particles due to the semiconductor substrate is prevented.

[0025]

EXAMPLES Examples of the present invention will be described below.

Examples 1 and 2 and Comparative Example 1 (a) Wafer used for test CZ method pulling axial direction <100>, p-type resistivity 10
Fifteen Si single crystal wafers prepared by cutting (slicing) a Si single crystal rod having a diameter of ˜20 Ω · cm and a diameter of 125 mm into a disk shape, and then chamfering, lapping, and etching were prepared.

(B) Description of Process As for wafer processing conditions, only the atmosphere during annealing is changed,
The following two steps were compared. This annealing heat treatment is a commonly used method for the purpose of erasing oxygen donors. For 5 wafers, the conventional method (Comparative Example 1), 10
The sheets were treated by the method of the present invention (Examples 1 and 2), and five of them were subjected to sandblasting and then the oxide film was removed by etching with dilute hydrofluoric acid (Example 2).

Process of Comparative Example 1 (conventional method): wafer → anneal heat treatment (650 ° C., 30 minutes, nitrogen gas atmosphere) →
Wet sand blast (sand injection pressure 0.9kg / c
m ² ) → Inspection

Process of Examples 1 and 2 (invention method): wafer → annealing heat treatment (650 ° C., 30 minutes, oxygen gas atmosphere) → wet sandblasting (sand injection pressure 0.9 kg)
/ cm ² ) → Inspection

After the annealing heat treatment in the steps of Examples 1 and 2, the thickness of the oxide film formed on the wafer surface was measured by an ellipsometer and found to be in the range of 35 to 80 Å.

Quartz fine powder having an average particle diameter of about 5 μm was used as the sand, and various conditions other than the injection pressure were unified and tested.

(C) Inspection Method The following inspection was performed on each wafer after the sandblasting was completed by the above steps.

Measurement of OSF (oxidation-induced stacking fault) on the back surface of the wafer After thermal oxidation of the wafer at about 1100 ° C./60 minutes in an oxygen atmosphere, the oxide film is removed with a Secco etching solution, and the number of OSFs deposited on the back surface of the wafer is optically measured. Measured with a microscope.

Number of Mechanical Damages The number of scratches observed was measured by scanning the surface of the wafer with a cruciform having a length of 100 mm in one direction at a magnification of 1500 times using a scanning electron microscope.

Depth of mechanical damage The depth of the damaged portion was measured by the angle polish method.

(D) Test results Table 1 shows the results.

[0037]

[Table 1]

From the results shown in Table 1, there is no substantial difference in OSF density between the conventional method (Comparative Example 1) and the method of the present invention (Examples 1 and 2), but the number of mechanical damages and the depth thereof are small. It can be seen that it has been significantly improved.

Further, in the comparison between Examples 1 and 2, there is no difference in the OSF measurement value depending on the presence or absence of the oxide film after sandblasting, and therefore the influence of the presence or absence of the oxide film during the OSF measurement is not recognized.

In the conventional method (Comparative Example 1), the OS
If an F density of 1 million pieces / cm ² or more is attempted, mechanical damage will be severe, and the scratched portion may become a dust source during device manufacturing. It is treated.

In order to eliminate this damage, the kinetic energy applied to the sand must be lowered, so that the sand jet pressure must be lowered to a level of 0.2 to 0.3 kg / cm ² or so. The EG effect of the semiconductor substrate is reduced to the extent of 300,000 to 700,000 / cm ² .

Examples 3 and 4 and Comparative Example 2 (a) Description of Process 5 out of 15 wafers same as those used in Example 1
A Si nitride protective film was formed by the CVD method, using 10 sheets for the conventional method test (Comparative Example 2) and 10 sheets for the present invention method test (Examples 3 and 4). Five of the ten wafers were sandblasted and then the nitride film was removed by etching with dilute hydrofluoric acid (Example 4).

Si nitride on the back surface of the wafer by the CVD method
The formation of the oxide film uses SiH as the source gas. _FourAnd NH₃use
And the atmospheric pressure method with a generation temperature of 800 ° C.
A protective film of 0 to 120Å was formed.

Process of Comparative Example 2 (conventional method): Wafer → annealing heat treatment (650 ° C., 30 minutes, nitrogen gas atmosphere) →
Dry sand blast (sand injection pressure 0.8kg / c
m ² ) → Inspection

Process of Examples 3 and 4 (invention method): wafer → annealing heat treatment (650 ° C., 30 minutes, nitrogen gas atmosphere) → CVD film formation → dry sandblasting (sand injection pressure 0.8 kg / cm ² ) → Inspection

(B) Test Results Table 2 shows the results.

[0047]

[Table 2]

The test conditions of this example were that the OSF density on the back surface of the wafer by sandblasting was 1 million pieces / c.
The condition was set in advance so that it was in the vicinity of m ^2, and results showing the same tendency as in Examples 1 and 2 were obtained. That is, the same effect is obtained by increasing the thickness of the Si nitride film formed by the CVD method of this embodiment as compared with the case of the Si oxide film formed by the thermal oxidation method of Embodiments 1 and 2.

The reason is that, in addition to the difference in the physical property values specific to Si oxide and Si nitride, the difference in the film thickness structure due to the difference in the method of forming the film, and the difference in the interface state between the film and the wafer. Is presumed to be involved, but it is unclear which of them is the main one.

When a Si nitride film is desired to be formed as the protective film, the thermal nitriding method is convenient because the nitrogen atmosphere of the annealing heat treatment in the conventional method can be used as it is. However, there is a problem that a high temperature of at least 1000 ° C. is required to perform the nitriding reaction of Si,
In this case, it can be said that the CVD method, which can form a film at a relatively low temperature, is more advantageous.

Experimental Example 1 In each of Examples 1 and 2 and Comparative Example 1, each wafer whose back surface OSF density was measured was subjected to the heat treatment adopted in the oxygen precipitation test, and then the wafer back surface O
SF was measured.

The heat treatment conditions are 800 ℃ / N _2/4 hours + 1100 ℃ / O _2/12 hours. The results are shown in Table 3.

[0053]

[Table 3]

Judging from the fact that the stability of the EG effect is better as the OSF reduction rate is lower, the effect of the oxide film of Example 1 remaining is clearer than that of the conventional method.

[0055]

As described above, according to the present invention, when a strained layer is introduced into the back surface of a wafer by dry or wet sandblasting, mechanical damage on the back surface of the wafer is small, and high temperature in the device manufacturing process is used. It is possible to manufacture a semiconductor substrate into which a back strain layer having a persistent EG effect is introduced by heat treatment.

Claims (6)

[Claims] 1. A semiconductor characterized in that after a single-layer protective film made of a Si oxide film or a Si nitride film is provided on the back surface of a Si single crystal wafer, a strained layer is introduced on the back surface of the wafer by a sandblast method. substrate. 2. The protective film is removed after introducing a strained layer into the back surface of the Si single crystal wafer.
The semiconductor substrate according to. 3. A semiconductor substrate characterized in that a single-layer protective film made of a Si oxide film or a Si nitride film is provided on the back surface of a Si single crystal wafer, and then a strained layer is introduced on the back surface of the wafer by a sandblast method. Manufacturing method. 4. A method of manufacturing a semiconductor substrate, comprising the steps of annealing a Si single crystal wafer and then introducing a strained layer on the back surface of the wafer by sandblasting, wherein the annealing is performed in an oxygen gas simple substance atmosphere. A method for manufacturing a semiconductor substrate, comprising forming a single-layer Si oxide film on the back surface of, and then introducing a strained layer on the back surface of the wafer by a sandblast method. 5. The method of manufacturing a semiconductor substrate according to claim 3, wherein the protective film is formed by a CVD method. 6. The protective film is removed after introducing a strained layer into the back surface of the Si single crystal wafer.
6. The method for manufacturing a semiconductor substrate according to any one of items 5 to 5.