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Furthermore, with this kind of equipment, because the originally established process sequence is followed, cleaning is conducted under completely controlled conditions, and its uniformity and reproducibility are outstanding.
It has become possible to detect organic contaminants existing in extremely small trace amoun... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
[6] S. Yasui, N. Yonekawa, and T. Ohmi: 1994 Semiconductor Pure Water and Chemicals Conference, San Jose, California (March 1994).
[7] M. Kogure, T. Isagawa, T. Futatsuki, N. Yonekawa, and T. Ohmi: 39th Annual Technical Meeting, Institute of Environmental Sciences, 1,282-287, Las Vegas, Nevada (May 1993).
[8] T. Ha... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 36.2 Etching Action Of Sc-1
The etching action in SC-l cleaning has already been touched upon in Kern's paper. However, because the etching rate was less than 1 nm per minute, it was not really discussed quantitatively. The method shown in Fig. 36.1 leaves regions which are partially unetched, and by using optical ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Until then particles had beep. thought to be something that was determined by the cleaning conditions; variations in the number of particles due to the kinds of crystals had never been considered. After detailed examination, the following results became clear:
1) Pits detected by the laser-scanning particle counter oc... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
10) A COP, once generated, will, in the next SC-l cleaning, become larger.
Next, knowledge recently obtained about COP will be summarized. As shown in Fig. 36.5, the COP size distributions for three different crystal pulling speeds are estimated based on the results of repeated cleanings. The COP size and number depe... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 36.4 Relationship Between Sc-L Cleaning And Micro-Roughness
Ra increases according to the chemical composition and cleaning time of SC1, and it is known that if Ra exceeds 0.3 nm it exerts an influence on the dielectric breakdown field [10,11]. The relationship between ammonia water ratio (NH4 0H : H2 0 2 : H2 0 = ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Consequently, the case of wafer manufacturer cleaning does not become like Fig. 36.9. Even if the so-called SC-1 (X = 1) is carried out, it is possible to stabilize the micro-roughness of shipped wafers at a low level. At present, the reason for this difference is unclear.
# 36.5 ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
To clarify the size that influences the haze level, quantities of 0.10 */-lm,*
0.11 /-lm and large particles are brought together and shown in the figure.
According to this figure, when the haze level exceeds a certain point, the quantity of 0.10 */-lm* particles increases dramatically. It is thought that the enlarg... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
The figure shows clearly that, compared with micro-roughness, increases in haze level are larger. Concerning the micro-roughness, up to then, it had been expected that in the extremely easily roughened condition of X = 2, and with a lengthy cleaning time of 180 minutes, there would be great increases in roughness. Howe... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
T. Tanaka, M. Sakurai, S. Kamizuma, and Y. Shimanuki: Extended Abstracts of the 177th Spring Meeting of the Electrochem. Soc., Montreal, Canada, No. 457, 689 (5/1990).
H. Kobayashi, J. Ryuta, T. Shingyouji, and Y. Shimanuki: Jpn. J. Appl. Phys.
32, L45 (1993).
J. Ryuta, E. Morita, T. Tanaka, and Y. Shimanuki: Jpn... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 37.1 Introduction
Cleaning and drying are paired processes. However, compared with the wealth of documentation available on wafer cleaning technology, detailed reports about drying technology are few. In general, cleaning technology is regarded as entailing the crucial processes of wet etching and cleaning the surf... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
| Table 37.1. Technical issues in wafer drying Item Cause | Countermeasure | ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
| 2. Particles | 1. Particle generation from movable parts 2. Si wafer chipping 3. Particle adhesion due to electrostatics | 1. Optimization of air flows in the spin-dryer 2. Prevention of shaking 3. Use of air-ionizers ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
oxygen-free atmosphere [lJ. Of all the countermeasures against adhesion of particles on wafers, those against wafer chipping, particles in the atmosphere during drying, and airborne particles are particularly essential. Also, in order to make it difficult for particles to adhere to the wafer surface, countermeasures ag... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Drying methods include spin-drying, isopropyl alcohol (IPA) vapor drying, gas blow drying, hot air blow drying, vacuum drying, drying by means of pulling up wafers from hot water or IPA, and infrared drying. In general, spin-drying and IPA vapor drying are the most frequently used methods.
## 37.2 Spin-Drying
There ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 37.3 Ipa Vapor Drying
When a wafer is placed in IPA vapor, condensed IPA replaces the water on the wafer or the reduction of surface tension causes a natural drop of mixed water, and the moisture concentration decreases. Then the water is dried with the natural evaporation of IPA. A schematic of the equipment is sh... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
The characteristics of temperature rises after the wafer has been immersed in IPA vapor are shown in Fig. 37.3. In this case twenty-five 5 inch wafers were stored in a cassette. Although the wafer temperature rose to near the boiling
point of IPA during the first two minutes after... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 37.4 Other Drying Techniques
Vacuum drying is a method which is intended to prevent contamination in the atmosphere created during transport from rinse to drying. It hastens the evaporation of pure water from the sample at a reduced pressure.... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 37.5 Evaluation Of Dry Wafers
In order to evaluate adsorbed contaminants on the wafer after drying, atmospheric pressure ionization mass spectrometer-thermal desorption mass spectrometry (APIMS-TDS) was used for analysis. An outline of the APIMS-
influence of the back side to which particles have adhered. The precision of the separation is regulated by the noise level at the time of analysis, so it cannot be decided exactly. However, at its worst it is less than 1%. Heating the plumbing prevents readhesion in the pipes from ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
After spin-drying After IPA drying
Proposed technological issues include how to prevent the occurrence of watermarks and solve particle generation problems. So, although it is believed that in semiconductor ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
[1] M. Watanabe, M. Hamano, and M. Harazono: Materials Science and Engineering B 4, 401 (1989).
[2] Mitsui, Irie, and Mizukami: Ultraclean Technology 2, 183 (1990).
[3] T. Hattori: Cleaning Technology in Semiconductor Device Manufacturing V,
Electrochem. Soc. Proc. PV97-35, 3-14 (1997).
[4] T. Hattori *et al.:* ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Cause 1 depends on the various conditions under which the native oxide layer is created, in other words, the amount of oxygen dissolved in the water and the amounts of oxygen and moisture in the atmosphere. However, the formation of local native oxide is thought to have a strong connection with the drying method. In pa... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Accompanying the formation of oxides in step b), the contact angle of the water droplet on the silicon wafer (Fig. 38.2) becomes smaller with the passage of time.
As shown in Fig. 38.3, the changes in contact angle with the passage of time vary depending on whether they are in air or nitrogen atmosphere; the existenc... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
between oxygen and the Si surface within the droplet. However, it might also be that they occur due to the dissolving of oxide layer in diluted fluoric acid clean or to the elution of the Si surface in ultrapurified water. It is thought that sili... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
However, even when drying in air which contains oxygen, watermark creation can be suppressed by evaporating the droplet in the short time before oxygen dissolves into the droplet, or by replacing the droplets with organic solvents. In particular, with vapor drying, which replaces droplets with vaporized organic solvent... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
In the actual process, slight changes in the conditions of cleaning and drying and the conditions of the process before cleaning greatly influence whether or not watermarks occur. At present, there are things which cannot be easily explained using the qualitative watermark creation mechanism outlined at the beginning o... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
[2] T. Ohsako *et al.:* Proc. of the 41st Spring Meeting of Applied Physical Society, Japan, No.2, 706 (29-ZQ-1), (1994) (in Japanese).
[3] K. Wolke *et al.:* Marangoni wafer drying avoids disadvantages, Solid State Technology, August, 87 (1996).
## 39. Physical Cleaning
Kenji Sugimoto, Nobuyasu Himoka, and Masahi... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Until recently brush scrubbing utilized a drum-type brush. However, the large surface area of the brush disturbs the flow of water on the wafer, and the removed particles subsequently readhere; also, because it is difficult to maintain the cleanliness of the brush itself, self-revolving-type brushes have become the mai... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
On the other hand, for particles that are adhered to the back surface of the wafer, whose diameters are comparatively large, and those strongly adhered from transport mechanisms, a harder brush such as nylon is effective.
Although in brush scrubbing the brush is rotated, with nylon brushes the alternative method of s... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 39.2.2 Problems With Brushes
Because in brush scrubbing there is generally contact between the brush and wafer, efficiently discharging the removed particles from the interior to the exterior of the brush is very important. In order to achieve high cleaning efficiency, the choice of brush material is the most impor... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 39.3.1 Problems With High-Pressure Jets
There have not been any major changes in high-pressure jet techniques for many years, so the development taking place is concentrated on improving the performance of the equipment itself, such as making it clean and highly reliable.
## 3... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 39.4.2 Process Factors
The process factors which determine cleaning efficiency in ultrasonic scrubbing are oscillation frequency, output current, flow rate of water, and distance between the wafer and the nozzle. In our ultrasonic system, D-SONIC, though at present the frequency is fixed at 1.5 MHz, there are recip... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
In the spin scrubber of the future, the most important issue to be faced is the reduction of damage inflicted on the semiconductor device. Obviously, as metallization patterns become more miniaturized, the level of permissible damage becomes lower. Because both brush scrubbing and ultrasonic scrubbing operate on the cl... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
# 40. Dry Cleaning
Takashi Ito, Fujitsu Labs
## 40.1 Dry Cleaning
In ULSI manufacturing, reaction products of CVD and dry etching, as well as contact abrasions from wafer transport, are sources of particulate contamination on the wafer. Metals come from similar processes, or from organic material sediments such as ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
2) By utilizing reactions in a continuous flow of gas, the creation of reaction products and the chemical readhesion of contaminants which occur in cleaning chemicals can be reduced.
3) Treatment can be performed using a comparatively small amount of chemicals, so the burden of treating reaction products is reduced. ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
4) Wafer drying processes can be omitted.
5) It has good adaptability to CVD and some other processes, and is easy to integrate into in-line processes and automation.
6) It is possible to shorten treatment time and reduce the number of process steps required for cleaning, so cost reduction as a whole can be expecte... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Dry cleaning methods developed up to now are listed in Table 40.1. Methods which employ plasma or ions have long histories, but unfortunately lack controllability; also, due to problems with wafer damage and secondary contamination, satisfactory efficiency has never been achieved. Recently, methods have appeared which,... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 40.2 Removal Of Metallic Contaminants 40.2.1 Ultraviolet Excitation Cleaning
Because UV-excitation dry cleaning technology (UV dry cleaning) is not accompanied by mechanical action, in order to remove inorganic particles emitted from the quartz jigs and wafer polishing agents, such as Al20 3 and Si0 2 powders, it i... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
The model for removing trace amounts of metal from the Si surface by using the ultraviolet excited chlorine radicals is shown in Fig. 40.l.
Al and Fe chlorides possess comparatively large vapor pressures, and when supplementary heat is applied to the substrate they evaporate. This reaction proceeds as chlorine radica... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Metal removal by dry cleaning, with the addition of the distinguishing characteristics mentioned above, makes it possible to raise the level of cleanliness higher than previous wet cleaning methods. It can also be effective in removing particles, although it has not yet reached the level of current wet cleaning methods... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
In the case of Si native oxide film which has been contaminated by alkali metals, after a compound with high reactivity is made using plasma excitation or UV excitation it can be made to react with HMDS (hexamethyldisilazane).
'" '5 7
.;: 6
§ 5
_{3}]_{2}\longrightarrow NaH[Si(CH_{3})_{3}]_{2}+NH_{3}}$$
## 40.3 Native Oxide Film Removal 40.3.1 Hf Gas Etching
The silicon surface is extremely activ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Figure 40.10 shows that by controlling the HF concentration the native oxide film can be selectively removed, without etching the thermal oxide film. However, fluoric acid compounds remain on the surface from which the native oxide film has been removed, and it is necessary to remove the fluorides without damaging the ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
To remove adherents which result from organic compounds, reaction with ozone or ultraviolet excited oxygen is effective. Because oxygen molecules decompose into atomic oxygen in light of wavelength of 242 nm and below, a light source of a low-pressure mercury lamp bright line (184.9... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Also, if ozone is used, it decomposes at a wavelength of 300 nm and under, and has good efficiency. The strong bright line of the low-pressure mercury lamp (253.7 nm) and KrF excimer laser (249 nm) can also be used:
$$\mathrm{O_{3}\ \longrightarrow\ \ O\left(^{1}D\right)+O_{2}\,,\,\lambda<300\ n m}$$
$$\left(7\right)... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Figure 40.15 shows an ultraviolet irradiation ozone treatment system. As shown in Fig. 40.16, the film thickness reduction ratio, in other words the speed of the dissociation reaction, possesses the characteristics of being very fast at the beginning, decreasing with time, and depen... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Fig. 40.17. Dependency of resist ashing on temperature
particles, such as open air dust, many remain even if oxidized, and in general with a cleaning method that uses only oxygen or ozone cleanliness at the atomic level cannot be accomplished. ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
dimers, from (1 x 1) to (1 x 2), and these reconfigured unions have symmetrical and asymmetrical oscillation. A model of cross-section structures is given in Fig. 40.21. It is confirmed that this surface struc... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
[1] R. Sugino, Y. Okui, M. Shigeno, S. Ohkubo, K. Takasaki, and T . Ito: J . Electrochem. Soc. 144, 3984 (1997).
[2] T . Ito, R. Sugino, Y. Sato, M. Okuno, A. Osawa, T . Aoyama, T . Yamazaki, and Y. Arimoto: MRS Symp. Proc. 259, 195 (1993).
[3] S. E. Beck, D. A. Bohling, A. G. Gilicinski, M. A. George, J . C. Ivank... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
[8] K. Kitahara and O. Ueda: Jpn. J . Appl. Phys. 33, L1571 (1994).
[9] S. Verhaverbeke, H. Bender, O. Vatel, M. Caymax, J. Alay, F. Chollet, B. Vermeire, P. Mertens, E. Andre, W. Vandervorst, and M. M. Heyns: Proc. 4th International Symposium on Control of Semiconductor for Interfaces, 9-12
(11/1993).
Part VIn Wa... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
More attention needs to be paid to successive single-wafer processing with regard to cleaning. Though in the future wet cleaning will not lose any importance, the requirements of processes which need in-line and/or *in situ* cleaning will be fulfilled by dry cleaning methods. Vapor cleaning is a simple dry cleaning met... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 41.2.1 The Role Of Hf Vapor Cleaning
Though it had once been thought that wet cleaning would gradually be replaced by dry cleaning, this shift has not yet occurred. And, although there may be further changes in equipment, wet cleaning will continue to occupy an important position in device processing through future... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
In HF vapor cleaning, cleaning reactants and by-products can have easy access to and from the sides and bottom of the hole, so it is easier to clean inside these holes.
2) Reaction products can be exhausted with high efficiency. Because gasified reaction products are exhausted, readhesion, which occurs in the batch c... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
1) The particle lift-off action with wet cleaning cannot be expected during HF vapor cleaning. While the number of particles generated is much smaller than with wet cleaning, those that adhere to the wafer show a variety of compositions. In many cases dissolution by evaporation of particles is difficult, so it is neces... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Of these, the main purpose of HF vapor cleaning is to remove native oxides
(including thermal oxides). It is difficult to remove metallic contamination with HF vapor cleaning only. For this purpose, with dry cleaning, other gases and excitation sources are used. Organic particle removal by UV /03 as a pretreatment for... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Therefore, it is necessary for the process step before HF vapor cleaning to be a step which removes organic contaminants. Combining UV 103 before HF
vapor cleaning for the removal of organic contaminants is probably the most suitable.
## 41.2.5 The Necessity **Of Organic Contaminant Removal** In Hf Vapor Cleaning
A... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 41.2.6 Native Oxide Removal In Hf Vapor Cleaning
HF vapor cleaning methods for the removal of oxide films could be used in the following device processes:
1) pre-treatment of silicide formation 2) pre-treatment of gate oxide film formation 3) pre-treatment of dielectric film formation 4) pre-treatment of polysilic... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
2) The amount of native oxide film and carbon contamination remaining on the Si surface after treatment is reduced in comparison with HF /H20 vapor and DHF immersion treatments.
3) Pure water rinse after etching is not required, and the growth of natural oxide film is suppressed.
4) After treatment, the micro-rough... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
| HF concentration (N) | 0.5 | 0.24 | 0.115 | 0.055 | 0.013 |
|------------------------|-------|--------|---------|---------|---------|
| H2 0 | 121 | 153 | 183 | 210 | 242 |
| CH30H | 139 | 164 | 200 | 225 | 251 |
 |
| Method HAVC HF/H2 0... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 41.3.4 Contact Resistance Evaluation
Figure 41.10 shows the relationship between contact resistance and storage time in clean air of a sample after cleaning and before film growth. After cleaning, 100 nm of polysilicon is deposited by LPCVD, and creates a contact of 0.5 */-Lm* d... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
[3] J. R. Vig: UV jOzone Cleaning of Surfaces, J. Vac. Sci. Tech. A3(3), 1027
(1985).
[4] F. A. Cotton and G. Willkinson: Advanced Inorganic Chemistry, 4th edition, Ch. 12,393, Wiley, New York (1980).
[5] J. H. Simons: Fluorine Chemistry, Vol. 1, Ch. 6, 240, Academic Press (1950).
[6] J. Staffa, S. Fakhouri, M. ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
[12] B. Froeschle, F. Glowacki, A. J. Bauer, I. Kasko, R. Oechsner, and C. Schneider: In-Line X-Ray Photoelectron Spectroscopy for Anhydrons Hydrogen Fluoride Cleaning Optimization, Proc. 5th International Symposium on Cleaning Technology in Semiconductor Device Manufacturing, 415 (1997).
# 42. Native Oxide Films And... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 42.2 Types Of Native Oxide
Native oxides can be categorized according to the growth temperature and atmosphere, as listed below [6-16].
Room temperature: in open air, in deionized (DI) water, in chemicals Elevated temperatures (in process equipment): in vacuum, in gases.
Oxides form in DI water or in chemicals ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 42.3 Measurement Of Ultrathin Film Thicknesses
In the past, measurement of native oxide film thickness was mainly conducted by ellipsometry. With ellipsometry, when the film is thin the refractive index loses its precision, so a refractive index regarded as fixed (for example, in the case of a thermal oxide film (S... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
3) Calibrate the XPS spectrum peak area ratio (Isiox/1si) with a film thickness measured by an ellipsometer (see Fig. 42.1).
4) Measure the XPS spectrum of the native oxide film, then determine the film thickness from the peak area ratio and calibration data.
The domain in which the thickness of thermal oxide films... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
The native oxide film thickness obtained by the above-mentioned film thickness determination methods with XPS and ellipsometry are only correct in the case that the atomic density and the photoelectron escape depth of the native film are equal to those of thermal oxide, respectively. Therefore, if the atomic density or... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Analysis results of the Si surface by thermal desorption spectroscopy
(TDS) show, with an Si(100) surface immediately after dilute HF treatment,
that most of the surface is covered by hydrogen, and parts by water or hydroxyl groups [30]. Furthermore, the results indicate that the... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Therefore, it can be seen that peak b' originates in the combination of Si=H2 and Si-H bonds on the Si surface. From these results it can be concluded that most of the Si atoms on the Si surface just after HF cleaning are terminated by hydrogen.
## 42.5 Native Oxide Growth Processes 42.5.1 Growth In Air
Figure 42.3 ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Fig. 42.3. Relationship between time and amount of H20 absorbed on etched Si and 100 200 300 thermal oxide film sur- TIME (min) face
oxide film on the Si surface progresses, because the amount of water adhered to the Si surface is influenced more and more by the native oxide film a... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
In Fig. 42.5, the domains of rapid oxidation and slow oxidation have a reciprocal relationship, and as a result suggest that oxide film grows one layer at a time. The 0.54 nm oxide film thickness on n-Si is two molecular layers of native oxide film, and it can be assumed that a film thickness from 0.54 nm to 0.76 nm co... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 42.5.2 Growth In Ultrapure Water
Figure 42.6 shows the time dependence of an oxide film formed on a P-doped n-Si wafer in ultrapure DI water with different concentrations of dissolved oxygen and on a P-doped n+ -Si wafer in DI water, with 9 ppm dissolved oxygen.
The thickness ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Figure 42.8 shows the time dependence of oxide film thickness formed on n+-Si that has been etched with dilute HF and given a DI water (concentration of dissolved oxygen: 0.6 ppm) overflow rinse [16,20]. With a 1 minute DI
water rinse after dilute HF etching, a 0.25 nm native oxide film was formed.
In other words, t... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
oxide growth in DI water can be controlled by reducing the concentration of dissolved oxygen.
Table 42.2 shows the oxide film thickness formed on n- and n+ -Si surfaces which have been etched with HF and given a 10 minute DI water rinse at varied concentrations of dissolved oxygen, followed by drying under certain co... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 42.6 Structure Of Native Oxides And Chemical Oxides
Figure 42.11 shows the Si2p XPS spectra of native oxides formed in Dr water and in air. From this result we see the following:
1) The binding energy of SiOx *(x>* 1) peak for Dr water oxide... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
peroxide. This result suggests that, compared with the oxide formed by sulfuric acid-hydrogen peroxide, the oxidejSi interface formed by ammoniahydrogen peroxide or hydrochloric acid-hydrogen peroxide is not as flat at the atomic level.
Table 4... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
| Table 42.3. Characteristics of native oxide film Sample* Oxide thick- l':.E** Contact | Dissolved Si*** | | | |
|------------------------------------------------------------------------------------------|-------------------|-----------|-------------------|-------------... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
## 42.7 Mechanisms Of Native Oxide Growth 42.7.1 Growth In Air
The oxide film thickness extrapolated at room temperature from the temperature dependence *(800-1050* ° C) of Si thermal oxidation rate is *10-14* nm at 10 hours (600 minutes) [7]. Therefore, the oxidation mechanism at room temperature is completely differ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Using the above knowledge as a base, we can construct an oxidation model in Fig. 42.13.
## 42.7.2 Growth In Ultrapure Water
It can be said that oxidation in ultrapure DI water is the same as oxidation in air in terms of (1) and (4) described in Sect. 42.7.1. Furthermore, the foll... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
2) The native oxide which forms in DI water contains Si compounds easily etched by ions in the DI water or dissolved oxygen.
" , " , " , " , Fig. 42.14. Model of native oxide film growth in DI water
## 42.8 Issues For The Future
Native oxides which form in air or in DI water, a... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Concerning the wafer surface conditions when the temperature rises, it can be seen from the thermal desorption spectra of hydrogen, oxygen, and water from the Si surface cleaned with dilute HF that the temperature rise desorption of hydrogen from the HF-cleaned Si surface happens from about 300 DC,
and when the Si sur... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
[1] [2]
[3]
[4]
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(1975).
H. R. Philip and E. A. Taft: J. App!. Phys. 53, 5224 (1982)... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
[17] M. Morita, T. Ohmi, E. Hasegawa, M. Kawakami, and K. Suma: Tech. Dig.
1989 Symp. VLSI Technology, p. 86 (1989).
[18] R. Williams and A. M. Goodman: Appl. Phys. Lett. 25, 531 (1974).
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[20] M. Morita and T. Ohmi: Mat. Res. Soc. Symp. Proc. 259,... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
[34] N. Awaji, Y. Sugita, S. Ohkubo, T. Nakanishi, K. Takasaki, and S. Komiya:
Jpn. J. Appl. Phys. 34, L1013 (1995).
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(1990).
[37] H. Suzuki, Y. Maeda, K. Morita, M... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Phys. Lett. 60, 2126 (1992).
[43] K. Makihara, A. Teramoto, K. Nakamura, M. Y. Kwon, M. Morita, and T. Ohmi: Jpn. J. Appl. Phys. 32, 294 (1993).
[44] M. Morita and T. Ohmi: The Physics and Chemistry of Si02 and the Si-Si02 Interface 2, eds. C. R. Helms and B. E. Deal, 199 Plenum (1993).
# 43. Hydrogen Termination... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Recently there has been much research concerning the structure of the Si surface on which DHF cleaning has been carried out. It has been reported that most of the dangling bonds on the Si surface are terminated by hydrogen
[4-6], and that native oxide film does not grow for 100 minutes in air, or for approximately 1 w... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Higashi *et ai.* conducted oxidation removal and planarization on a (111)
using buffered hydrogen fluoride with pH controlled at 9-10, and obtained a surface which was entirely Si-H [13].
Ito *et ai.* investigated the influence of DI water rinse after oxide film removal by DHF solution, and confirmed the occurrence ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
in the (100) step as D and *Mil.* Furthermore, Fig. 43.2 shows the absorption spectrum after a 600 second treatment of boiling DI water. In the case of P polarized light in Fig. 43.2, because sharp absorption at 2085.5 cm-1 can be seen, and no ab... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Yabumoto *et al.* measured the amount of water adhered to the Si surface using thermal desorption spectroscopy [17]. Although a water separation spectrum from an Si surface on which native oxide film was deliberately attached was confirmed, water separation from an Si surface after HF cleaning was not observed. It is s... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Ito *et al.* observed with FT-IR the hydrogen termination conditions of an Si(100) surface on which the hydrogen annealing temperature had been changed. In Si(100) which had been hydrogen terminated with dilute HF solution, SiH, SiH2 , and SiH3 were observed, but it was confirmed that when the wafer temperature is rais... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
It is thought that the hydrogen-terminated surface is destroyed at the same time as surface oxidation. When oxygen and water do not coexist, the growth of native oxide film can be controlled [7], so in order to maintain Si
10°'--__ .L...-_--''--_--'-__ ---'-__ -'-__ ..l----' Fig. ... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
These organics can be removed easily by wet cleaning [24]. Changes in the structure of the Si surface are also influenced by the materials of transport.
Figure 43.6 shows the results of FT-IR measurements of hydrogen termination conditions of S... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
64, 3516 (1988).
M. Niwano, T. Miura, R. Tajima, and N. Miyamoto: J. Appl. Phys. 79, 3708.
O. Chyan, J. Wu, and J. Chen: Appl. Spectrosc. 51, 1905 (1997).
M. Morita, T. Ohmi, E. Hasegawa, K. Kawasaki, and M. Ohwada: J. Appl.
Phys. 68, 1272 (1990).
T. Kosugi, H. Ishii, and Y. Arita: J. Vac. Sci. Technol. A 15,... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
M. Sakuraba, J. Murota, and S. Ono: J. Appl. Phys. 75, 3701 (1994).
H. Aomi, H. F. Derouin, and T. Ohmi: Materials Research Soc. Symp. Proc.,
Vol. 315, pp. 333-337 (1993).
T. Yabune, T. Futasuki, K. Yamada, and T. Ohmi, 1994 Proceedings, 40th Annual Technical Meeting, Institute of Environmental Science, Vol. 1, Ch... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Therefore, in order to prevent the adsorption of organic contaminants onto silicon surfaces before gate oxidation or before CVD to eliminate film thickness variations due to variable incubation times in thin film deposition, it is necessary to determine the origin of the contaminants by identifying organic compounds ad... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
In this chapter, the identification and removal of organic contaminants adsorbed on the surface of silicon wafers stored in plastic boxes and the adsorption behavior of the organic volatiles on silicon surfaces are investigated [14].
## 44.2 Analytical Methods Of Organic Contamination Adsorbing On Silicon Surfaces
I... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers | ||
Figure 44.1 is a schematic diagram of the TD-GC /MS system for analyzing the organic contaminants adsorbing on the surface of the silicon wafers.
The system consists of a thermo desorption unit, a condensation unit, and
a gas chromatography mass spectrometer unit. The system can... | text_only | 14_Ultraclean Surface Processing of Silicon Wafers |
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