CN102509734A - Method for preparing Ge-based MOS (metal-oxide semiconductor) capacitor by using ALD (atomic layer deposition) - Google Patents

Abstract

The invention belongs to the technical field of semiconductors, and specifically relates to a method for preparing a Ge-based MOS (metal-oxide semiconductor) capacitor by using ALD (atomic layer deposition). The method disclosed by the invention comprises the following steps of: firstly, performing rapid thermal oxidization treatment on a Ge-based substrate to form GeO2; secondly, depositing high-dielectric-constant HfO2 on the GeO2 to serve as a gate dielectric; and finally, manufacturing an electrode to form the Ge-based MOS capacitor. According to the method disclosed by the invention, a layer of high-quality GeO2 is formed on the surface of the Ge-based substrate by adopting a rapid thermal oxidization treatment method, so that Ge can be prevented from diffusing, defect charges and the density of interface state are reduced, and the interface characteristics are improved; and the deposited HfO2 dielectric layer is accurately-controllable in thickness, excellent in conformality, strong in interface controllability and good in uniformity. By adoption of the method disclosed by the invention, the electrical properties of the Ge-based MOS capacitor can be greatly improved, and then the performance of a Ge-based MOS transistor is improved.

Description

one A kind of method utilizing ALD to prepare germanium-based MOS capacitor

technical field

The invention belongs to the technical field of semiconductors, and in particular relates to a method for making germanium-based MOS capacitors by using ALD.

Background technique

Since the 1960s, silicon has been the most important semiconductor material in the modern electronics industry, mainly due to the fact that it forms very high-quality native oxides for surface passivation. After more than 40 years of continuous miniaturization, the scaling of the classic bulk MOSFET is approaching many of its fundamental limits, requiring innovations in new materials and new device structures.

High dielectric constant (k) materials can relax the restriction on the physical thickness of the dielectric by k/3.9 times, and its research in the field of silicon-based integrated circuits has made a lot of progress. Intel has combined high-k gate dielectric materials and metal gates It has been applied to the CPU manufacturing technology of its 45 nm node and has achieved excellent performance. However, it also faces some problems, such as the quality of the oxide and the interface is much worse than that of SiO ₂ , and the channel mobility decreases due to Coulomb scattering and phonon scattering.

Since the mobility of semiconductor germanium (Ge) is much larger than that of silicon (the mobility of electrons is about twice, and the mobility of holes is about 4 times), it can alleviate the problem of MOSFET drain current saturation, and it is different from traditional silicon-based integrated circuits. Technology is compatible, so germanium is considered to be a promising channel replacement material.

Recently, many high-k gate dielectrics have been applied to Ge-based MOS, such as aluminum oxide, hafnium oxide, zirconium oxide, etc. They have great potential in reducing equivalent oxide thickness (EOT), reducing gate leakage current, and increasing hole mobility. However, the mobility of holes is not four times higher than that of silicon materials, and the mobility of electrons is not significantly improved, which may be mainly because the interface formed between the gate dielectric and the Ge semiconductor surface is not perfect or the interface state density is too high.

In addition, the development of thin film preparation technology compatible with modern CMOS technology is also a hot spot in microelectronics research. Among them, atomic layer deposition technology (Atomic Layer Deposition, ALD) is a chemical vapor deposition technology that can control the thickness of the film at the single atomic layer level or Angstrom (Ǻ) level. ALD technology has made great progress since its development in the 1970s, and it has been written into the International Semiconductor Technology Roadmap (ITRS). As a candidate technology compatible with microelectronics technology, it shows broad application prospects in the field of microelectronics.

The reason why ALD technology is favored by the industry is related to its unique growth principle and technical characteristics. Although ALD deposition is a chemical vapor deposition (CVD) technology, it is quite different from the traditional CVD technology. ALD technology is based on the sequential surface saturation chemical self-limiting growth process. The reaction gas is alternately pulsed into the reaction chamber. An ALD reaction cycle consists of four steps: (1) The first reaction precursor enters the reaction chamber in a pulsed manner and is chemically adsorbed on the substrate surface; (2) After the surface adsorption is saturated, the excess reaction precursor is removed with an inert gas. (3) Then the second reaction precursor enters the reaction chamber in a pulsed manner, and reacts with the precursor chemically adsorbed on the surface last time; (4) After the reaction is complete, use an inert The gas flushes excess reaction precursors and their by-products out of the reaction chamber. The whole ALD growth process is realized by repeating multiple cycles of one cycle. The essential feature of all ALD is that the surface reaction reaches saturation, which makes the growth stop automatically. Therefore, the thickness of the film is directly proportional to the number of times the surface reaction has been completed, that is, the number of reaction cycles. This can be achieved by controlling the number of deposition reaction cycles. Precise control of film thickness. In addition, due to its self-limiting surface reaction characteristics, it can form a uniform coverage on the surface with a large aspect ratio. In addition, the content of different substances in the film can also be controlled by controlling the ratio of pulse cycles of different sources.

Contents of the invention

The object of the present invention is to provide a Ge-based MOS capacitor capable of improving the electrical performance of the Ge-based MOS capacitor and a preparation method thereof.

The Ge-based MOS capacitor proposed by the invention is composed of a Ge-based substrate (101), _GeO2 (103) formed by rapid thermal oxidation, an _HfO2 gate dielectric layer (104) and an electrode (105).

Ge-based MOS capacitance preparation method of the present invention comprises the following steps:

1) Cleaning the Ge-based substrate;

2) Perform rapid thermal oxidation (RTO) on the cleaned substrate to form GeO ₂ ;

3) Put the rapidly thermally oxidized substrate into the ALD chamber, the temperature of the reaction chamber is 150-300 ^o C, and sequentially pass Hf[N(C ₂ H ₅ )(CH ₃ )] ₄ and deionized water to complete One ALD cycle to generate the HfO ₂ gate dielectric layer; the number of ALD cycles is determined by the thickness requirements of the HfO ₂ gate dielectric layer;

4) Make electrodes on the HfO ₂ gate dielectric layer.

The cleaning process of the above step 1) is: first soak the Ge-based substrate in ethanol for 5-10 min, then ultrasonically clean it in acetone for 5-10 min, and then use ethanol ultrasonic cleaning for 5-10 min to remove the surface For impurities such as oil stains, rinse with deionized water for several times, then use 1:50 volume of hydrofluoric acid and deionized water to cycle several times for ultrasonic oscillation and rinse to remove the natural GeO _x on the surface, each step is 15-20 s, and finally use high-purity nitrogen Blow dry and set aside.

The above step 2) rapid thermal oxidation process is: place the cleaned Ge-based substrate in an ALD reaction chamber at 400 ^o C for oxidation for 3-10 min, the O ₂ flow rate is 400-800 sccm, and directly grow high-k dielectric in ALD The GeO ₂ interface control layer is grown in the reaction cavity of the thin film. This method can avoid chemical reaction after its surface is in contact with air, so that the interface characteristics can be improved.

Step 3 above) The steps of one cycle of ALD deposition process are: first pass Hf[N(C ₂ H ₅ )(CH ₃ )] ₄ pulse time 1-5 s, then pass N ₂ pulse time 1-5 s , the pulse time of H ₂ O is 0.3-1.0 s again, and the pulse time of N ₂ is 0.5-2.0 s at last.

The present invention adopts a rapid thermal oxidation treatment method to form a layer of high-quality GeO ₂ on the surface of a Ge-based substrate, which can prevent the diffusion of Ge, reduce defect charges and interface state density, and improve interface characteristics; the deposited HfO ₂ dielectric layer , The thickness can be precisely controlled, the shape retention performance is excellent, the interface control ability is strong, and the uniformity is good. The invention can greatly improve the electrical characteristics of the Ge-based MOS capacitor, thereby improving the performance of the Ge-based MOS transistor.

Description of drawings

Figure 1 is a flow chart of the fabrication of the entire Ge-based MOS capacitor.

Figure 2 shows the Ge substrate structure before cleaning.

Figure 3 shows the Ge substrate structure after cleaning.

Figure 4 shows the structure after rapid thermal oxidation on a Ge substrate.

Fig. 5 is the structure after depositing _HfO2 gate dielectric on the substrate after rapid thermal oxidation treatment.

FIG. 6 is a structure after depositing a metal electrode on the gate dielectric.

Detailed ways

The present invention will be further described in detail below in conjunction with the manufacturing flow chart 1 of the entire Ge-based MOS capacitor and specific implementation methods. In the figure, for the convenience of description, the thickness of the layers and regions is enlarged or reduced, and the size shown does not represent the actual size. . Although these figures do not fully reflect the actual size of the device, they still fully reflect the interrelationships between the regions and the constituent structures.

Step 1: Select a commercial single crystal Ge wafer, n-type Sb doped, crystal orientation (100), resistivity 0.21-0.26 Ω cm as the substrate, that is, the 101 layer in Figure 2, but the Ge substrate that has not been cleaned There will be a layer of naturally oxidized GeO _x on the surface, which is the 102 layer in Figure 2;

Step 2: Soak the substrate in ethanol for 10 min;

Step 3: put the substrate into acetone and ultrasonically clean it for 10 min;

Step 4: put the substrate into ethanol and ultrasonically clean it for 10 min;

Step 5: Rinse several times with deionized water;

Step 6: put the substrate into a 1:50 hydrofluoric acid solution and ultrasonically vibrate for 15 s;

Step 7: Take out the substrate and rinse it with deionized water for 15 s;

Step 8: Repeat steps 6 and 7 several times to remove the natural GeO _x layer;

Step 9: Blow dry the substrate with _N to obtain the Ge-based substrate shown in Figure 3;

Step 10: Put the substrate into the ALD reaction chamber, pass in O ₂ , perform rapid thermal oxidation for 5 minutes, the temperature is 400 ^o C, and the oxygen flow rate is 600 sccm to form the structure shown in Figure 4. The 103 layer is a high-quality material formed by rapid thermal oxidation. GeO ₂ ;

Step 11: After forming high-quality GeO ₂ , the ALD reaction chamber begins to cool down until its temperature drops to the reaction temperature (250 ^o C) for growing high-k gate dielectric, and immediately starts ALD to grow the HfO ₂ dielectric layer, and sequentially pass through Hf source and deionized water, reach the required number of cycles to obtain the required gate dielectric film, wherein during growth, the reaction chamber pressure is 2-5 torr, and the time for feeding gas in one cycle is Hf[N(C ₂ H ₅ )(CH ₃ )] ₄ : N ₂ : H ₂ O: N ₂ =1.0 s: 3.0 s: 0.3 s: 1.0 s, forming a structure as shown in Figure 5, and layer 104 is HfO ₂ deposited by ALD.

Step 12: Take out the Ge sheet in the reaction chamber, and deposit electrodes. The electrode material can be selected from various materials such as aluminum, gold, platinum, titanium nitride, etc., and the production method can be various processes such as evaporation and sputtering to form the structure shown in Figure 6, and 105 represents the formed electrode.

Claims (5)

1. A germanium-based MOS capacitor is characterized in that it consists of a Ge-based substrate, _GeO2 formed by rapid thermal oxidation of the Ge-based substrate, _HfO2 gate dielectric layer and electrodes formed by atomic layer deposition on _GeO2 . 2. a kind of preparation method of germanium base MOS electric capacity is characterized in that concrete steps are: 1) Cleaning the Ge-based substrate; 2) Perform rapid thermal oxidation on the cleaned substrate to form GeO ₂ ; 3) Put the rapidly thermally oxidized substrate into the ALD reaction chamber, the temperature of the reaction chamber is 150-300 ^o C, and the working pressure of the reaction chamber is kept at 2-5 torr; the Hf[N(C ₂ H ₅ )(CH ₃ )] ₄ and deionized water to complete an ALD cycle to generate HfO ₂ gate dielectric layer; the number of ALD cycles is determined by the thickness requirements of HfO ₂ gate dielectric layer; 4) Make electrodes on the HfO ₂ gate dielectric layer. 3. The preparation method according to claim 1, characterized in that step 1) the cleaning process is: first soak the Ge-based substrate in ethanol for 5-10 min, then ultrasonically clean it in acetone for 5-10 min; then use Ultrasonic cleaning with ethanol for 5-10 min to remove oily impurities on the surface, rinse with deionized water, and cycle ultrasonic vibration and rinse with 1:50 volume of hydrofluoric acid and deionized water to remove natural GeO _x on the surface, 15-20 s per step , and finally blow dry with high-purity nitrogen for use. 4. The preparation method according to claim 2, characterized in that step 2) the rapid thermal oxidation process is: put the cleaned Ge-based substrate into an ALD reaction chamber at 400 ^o C for 3-10 min, O ₂ The flow rate is 400-800 sccm. 5. The preparation method according to claim 2, characterized in that in step 3), the step of an ALD cycle is: first pass Hf[N(C ₂ H ₅ )(CH ₃ )] ₄ pulse time 1-5 s , and then pass N ₂ pulse time 1-5 s; then pass H ₂ O pulse time 0.3-1.0 s, and finally pass N ₂ pulse time 0.5-2.0 s.

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