A method for forming a dense oxide layer on silicon using static high pressure

Abstract

The present invention discloses a method for forming a dense oxide layer on silicon by using static high pressure, comprising: forming an oxide layer on silicon; and cyclically treating the oxide layer with hydrostatic pressure. The oxide layer is a silicon dioxide film deposited on silicon or a double film of a silicon dioxide film and a silicon nitride film deposited on silicon. Cyclically treating the silicon dioxide film deposited on silicon or the double film of a silicon dioxide film and a silicon nitride film deposited on silicon with hydrostatic pressure greatly reduces the thickness of the transition layer between the oxide layer and silicon, improves the denseness and porosity of the oxide layer, as well as the uniformity of the distribution of these parameters on the surface of the structure, significantly reduces the average mechanical stress between the oxide layer and the silicon structure, and simultaneously increases the yield of components containing such an oxide layer.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor device manufacturing, and particularly to a method for forming a dense oxide layer on silicon using static high pressure. Background Art

[0002] In the manufacturing processes of semiconductor devices, power devices, and large-scale and very large-scale integrated circuits, especially in the manufacturing process of integrated circuit modules, the thickness and density of the gate film and the silicon structure transition layer, as well as the uniformity of the distribution of these parameters on the structure surface, are issues that need continuous improvement.

[0003] Currently, there are mainly two common methods for improving the thickness and density of the gate film and the silicon structure transition layer in semiconductor integrated circuits, and the uniformity of the distribution of these parameters on the structure surface. One is to thermally oxidize a silicon wafer in a dry oxygen stream at a high temperature to produce a silicon-silicon dioxide structure to form an oxide layer, and the other is to continuously oxidize silicon in dry-wet-dry oxygen to obtain a thin film to form an oxide layer.

[0004] Thermally oxidizing a silicon wafer in a dry oxygen stream at a high temperature to produce a silicon-silicon dioxide structure to form an oxide layer; the disadvantage of this method is the low film growth rate. Therefore, in practice, a thin film is obtained by continuously oxidizing silicon in dry-wet-dry oxygen to form an oxide layer. However, such a film is more defective, especially with an increased micropore density. Micropores have a negative impact on the dielectric and masking properties of silicon dioxide and reduce its mechanical strength. As a result, the yield of components containing such a film is reduced.

[0005] Therefore, there is an urgent need to study a method for forming an oxide layer with improved thickness and density on silicon. Summary of the Invention

[0006] Based on the problems existing in the background art, the present invention provides a method for forming a dense oxide layer on silicon using static high pressure.

[0007] Hydrostatic pressure is the pressure exerted by a homogeneous fluid on an object. This is an omnidirectional force and is uniformly applied to all parts of the object surface. When the hydrostatic pressure increases, the volume of the stressed object will shrink, but its shape will not change.

[0008] The object of the present invention is to provide a method for forming a dense oxide layer on silicon using static high pressure, which cyclically processes the silicon dioxide film deposited on silicon or the double film of silicon dioxide film and silicon nitride deposited on silicon with hydrostatic pressure, greatly reducing the thickness of the transition layer between the oxide layer and silicon, improving the density and porosity of the oxide layer, as well as the uniformity of the distribution of these parameters on the structure surface, significantly reducing the average mechanical stress between the oxide layer and the silicon structure, and simultaneously increasing the yield of components containing such an oxide layer.

[0009] The present invention is implemented through the following technical solutions:

[0010] A method for forming a dense oxide layer on silicon by using static high pressure, comprising the following steps:

[0011] S01. Form an oxide layer on silicon;

[0012] S02. Perform cyclic treatment on the oxide layer with hydrostatic pressure.

[0013] Further, the oxide layer is a silicon dioxide film deposited on silicon or a double film of a silicon dioxide film and a silicon nitride film deposited on silicon.

[0014] Further, the hydrostatic pressure treatment time is 3×10 3 -7×10 3 s. When the hydrostatic pressure treatment time is less than 3×10 3 s, there is not enough time for the relaxation process in the film to occur; when the hydrostatic pressure treatment time exceeds 7×10 3 s, the film has obtained the best effect and the characteristics hardly change. An excessive time will cause unproductive losses of time and energy.

[0015] Further, the cyclic treatment with hydrostatic pressure is that the hydrostatic pressure acting on the oxide layer is raised from atmospheric pressure to a given pressure at a certain rising rate, and then the hydrostatic pressure is released from the given pressure to atmospheric pressure at a certain pressure release rate. Thus, one cycle of restoring and releasing the hydrostatic pressure is completed.

[0016] In the present invention, due to the influence of the periodic change of the hydrostatic pressure outside the oxide layer, pore dissolution of the film with vacancy diffusion occurs in the oxide layer. The hydrostatic pressure slowly rises from atmospheric pressure to a given level, and the pressure rising rate remains constant throughout the process, which can suppress discontinuous processes and avoid film rupture caused by the increase of tensile stress.

[0017] Further, the rising rate is 1 - 5 MPa / s.

[0018] Further, the given pressure is 700 - 900 MPa.

[0019] Further, the pressure release rate V is determined by the following formula:

[0020] V = V0 - (n - 1)CΔV + V1

[0021] where V0 is 170 - 300 MPa / s, which is the pressure release rate after the first loading cycle;

[0022] C is the pressure coefficient, which is related to the type of pressure medium;

[0023] ΔV is 1 - 5 MPa / s, which is the change in the pressure release rate after each loading cycle;

[0024] n is 1, 2, 3..., which is the serial number of the next loading cycle;

[0025] V1 is the additional rate related to the number of film layers. When the film is a silicon dioxide film, V1 = 0. When the film is a double film of silicon dioxide and silicon nitride, the range of V1 is related to the characteristics of the multi - layer film. In the present invention, a low - pressure plasma - enhanced chemical vapor deposition film is selected, and V1 is 50 - 150 Mpa / s.

[0026] The sharp drop in hydrostatic pressure in the first cycle allows maintaining an unbalanced concentration of intrinsic point defects in the film, which is the reason for the densification of the oxide film. As the film becomes denser and its resistance to external mechanical loads increases, that is, its resistance to changes in hydrostatic pressure increases, the discontinuity during structural unloading may increase. To avoid this, the unloading rate is gradually reduced cycle by cycle, so that during the process of reducing the pressure from a given pressure to the atmospheric pressure level, a relaxation process occurs in the film. As the number of cycles increases, the reduction in the pressure release rate also contributes to a more complete restoration of balance in the point defect subsystem in the film. For this reason, since the defects dissolve in the film, their total concentration in the film decreases, resulting in an increase in their diffusion path to the drain.

[0027] Furthermore, the hydrostatic pressure is controlled by a pressure control system.

[0028] Furthermore, the pressure control system performs the following operations:

[0029] A. Obtain the flow curve of the hydrostatic pressure intensity, divide the flow curve of each cycle into 6 - 9 segments, calculate the peak value of the flow rate of the hydrostatic pressure applied in each segment. The flow peak value of each segment of the flow curve is the maximum value of the flow peak values of each flow rate in this segment of the flow curve, and then calculate the flow reference value of each flow curve;

[0030] B. Determine the feed - forward coefficient of the control system, calculate the feed - forward output value of the flow curve of each cycle, and its calculation formula is as follows:

[0031] The feed - forward coefficient is:

[0032]

[0033] The feed - forward output value is:

[0034] R i = T i × M i

[0035] Substitute the feed - forward coefficient to obtain:

[0036]

[0037] Among them, R i is the feedforward output value of the flow rate in the i-th segment; T i is the feedforward coefficient; i is the i-th curve segment, n is the total number of segments of the flow rate curve in each cycle; B is the benchmark of the control output proportional coefficient, taking 66%, Q is the real-time control flow rate output, M i is the flow rate benchmark value of the i-th segment of the flow rate curve;

[0038] C. Calculate the control output values of each segment of the flow rate curve in each pressure cycle, and its calculation formula is as follows:

[0039] R out-i =(αR PID +βR i )×2

[0040] Among them, R out-i is the actual control output amount of the flow rate in the i-th segment, R PID is the control output amount of the controller, α and β are coefficients respectively, taking α as 0.5c, then β is 1 - 0.5c, where c is the delay coefficient of the PID controller, and among them, 0.9 ≤ c ≤ 1;

[0041] D. Conduct a hydrostatic pressure test according to the control output values of each segment of the flow rate curve.

[0042] Advantages of the present invention:

[0043] (1) The method for forming a dense oxide layer on silicon by the static high pressure of the present invention can improve the density and porosity of the oxide layer on silicon, as well as the uniformity of the distribution of these parameters on the re-structured surface, and reduce the average mechanical stress between the oxide layer and the silicon structure, thereby improving the reliability and product performance of semiconductor devices.

[0044] (2) The method for forming a dense oxide layer on silicon by the static high pressure of the present invention can not only be used to improve the density of the insulating film of silicon-based semiconductor devices and integrated circuits, but also can be extended and applied to improve the density and adhesion of the insulating film of compound semiconductor power devices and integrated circuits, and improve the reliability of components. Description of the drawings

[0045] Figure 1 is the relationship between the rate of change of the reduction rate per cycle and the rate of pressure release after each loading cycle for the process of releasing from a given pressure to atmospheric pressure (C = 1, V1 = 0, V0 are 200 Mpa / Sec and 300 Mpa / Sec respectively);

[0046] Figure 2For each cycle of the process of releasing from a given pressure to atmospheric pressure, the relationship between the rate of decrease and the change in the pressure release rate after each loading cycle (C = 1, V0 = 300 Mpa / Sec, V1 is 0 and 100 Mpa / Sec respectively);

[0047] Figure 3 For the relationship between the thickness of the transition layer at the junction of silicon dioxide (SiO2) and silicon (Si) and the hydrostatic pressure. Detailed implementation mode

[0048] The technical solution of the present invention will be further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the following embodiments.

[0049] A method for forming an oxide layer on silicon, including depositing a silicon dioxide film on a silicon wafer and performing cyclic treatment with hydrostatic pressure, including performing hydrostatic pressure cyclic treatment with a silicon dioxide film plus a silicon nitride film, characterized in that a pressure treatment of (3-7)×10 3 sec is applied, the pressure is increased regularly, from atmospheric pressure to a pressure of 700-900 MPa at a rate of 1-5 MPa / s, and then decreased to atmospheric pressure. The pressure release rate V of each cycle is determined by the following formula:

[0050] V = Vo - (n - 1)CΔV + V1 EQ (1)

[0051] In the formula

[0052] Vo is 170-300 MPa / s, which is the pressure release rate after the first cycle;

[0053] C is the pressure coefficient, related to the pressure medium;

[0054] ΔV = 1-5 MPa / s, which is the change in the discharge rate after each loading cycle;

[0055] n is 1, 2, 3, which is the serial number of the next loading cycle.

[0056] V1 is the additional rate related to the number of film layers;

[0057] When the film is a silicon dioxide film, V1 = 0;

[0058] When the film is a double film of silicon dioxide and silicon nitride, the range of V1 is related to the characteristics of the multi-layer film. For example, for a low-pressure plasma-enhanced chemical vapor deposition (LP-PECVD) film, it is in the range of 50-150 Mpa / Sec.

[0059] This improves the structure (its continuity) of the silicon oxide film and increases its yield. For details, see Figure 3 .

[0060] It can be seen from Figure 1 that when the fluid medium is pure water (H2O), C = 1, and V1 = 0 (when there is only a silicon dioxide film), the rate of decrease per cycle of the pressure release from a given pressure to atmospheric pressure is strongly correlated with the pressure release rate V0 after the first cycle, and weakly correlated with the change in the pressure release rate after each loading cycle. Slowly releasing the pressure after applying high pressure is very important for ensuring the quality of the film.

[0061] Figure 2 The relationship between the rate of decrease per cycle of the pressure release process from a given pressure to atmospheric pressure and the change in the pressure release rate after each loading cycle is given. From Figure 2 it can be seen that there is a strong corresponding relationship between the rate of decrease per cycle of the pressure release process from a given pressure to atmospheric pressure and the additional rate V1 related to the number of film layers. When a double-layer structure of silicon dioxide and silicon nitride films is used, since the silicon nitride film grown by the low-pressure plasma-enhanced chemical vapor deposition (LP-PECVD) process has a compressive tensor value, when adjusting the thickness and process parameters of the silicon nitride film grown by the (LP-PECVD) process to make V1 = 100, the rate of pressure decrease per cycle will be reduced by more than 30%. This will further reduce the pressure difference during pressure reduction of the silicon dioxide film and reduce the stress at the interface between the silicon dioxide film and silicon, thereby improving the film quality.

[0062] Method 1: Growing a silicon dioxide film on silicon and then performing hydrostatic pressure treatment:

[0063] Treating the film structure under hydrostatic pressure in the range of 700 - 900 MPa for (3 - 7)×10 3 seconds (sec). During the treatment, the pressure in the working chamber is periodically increased (for example, in a hydraulic device where a 50% mixture of deionized water and ethanol or isopropanol is used as the pressure transfer fluid) and decreased. According to the linear law EQ(1), the pressure is increased at a rate of 5 - 10 MPa / s in each cycle, and released at a decreasing rate of cycle ratio cycle. After treating the structure by pressure, it is transferred to the subsequent technical process to form a semiconductor device.

[0064] The densification of the silicon dioxide film plays a positive role in this method. In this film, the fine pores where vacancy diffusion occurs under the influence of externally periodically changing pressure dissolve. Slowly increasing the pressure from atmospheric pressure to a given level (the pressure increase rate remains constant throughout the treatment) can suppress discontinuous processes and avoid film rupture caused by the increase in tensile stress. The rupture in the film is caused by the different compression moduli of silicon (100 GPa) and silicon dioxide (38 GPa).

[0065] On the other hand, the sharp drop in pressure during the first processing cycle allows maintaining an unbalanced concentration of intrinsic point defects in the film, which is the cause of densification. As the film becomes denser and its resistance to external mechanical loads increases, i.e., its resistance to changes in hydrostatic pressure increases, the possibility of discontinuity during structural unloading increases. To avoid this, the unloading rate is gradually reduced cycle by cycle, such that during the process of reducing the pressure from the working pressure to the atmospheric pressure level, a relaxation process occurs in the thin film. As the number of cycles increases, the reduction in the pressure release rate also contributes to a more complete restoration of equilibrium in the point defect subsystem of the thin film. For this purpose, over time, due to the dissolution of defects in the thin film, their total concentration in the thin film decreases, resulting in an increase in their diffusion path to the drain.

[0066] Method 2: Grow a silicon dioxide thin film on silicon and then deposit a silicon nitride thin film on the silicon dioxide film, and then perform hydrostatic pressure treatment:

[0067] The treatment of the thin film structure according to this method is to first obtain a silicon dioxide thin film by thermal oxidation at a temperature of 1120 - 1200 °C using the dry oxygen and wet oxygen methods on a (I00) or (111) crystal orientation silicon wafer with a thickness of 600 - 650 micrometers (μm), and then grow a silicon nitride thin film with a thickness of 300 to 1000 angstroms by the method of low-pressure plasma-enhanced chemical vapor deposition (LP-PECVD). By controlling the composition of the LP-PECVD process gas, such as the hydrogen content, and the thickness of the silicon nitride thin film, the additional pressure generated by the silicon nitride thin film on the silicon dioxide thin film and the interface between silicon dioxide and silicon is controlled, and the range of this pressure is between 500 and 1000 megapascals (Mpa).

[0068] The thickness of the silicon dioxide film is 100 angstroms to 0.1 micrometers (μm), and the influence of the growth mode on the film quality can be evaluated by the refractive index measured on an automatic ellipsometer and the concentration of pores recorded by electron photography. Half of the untreated wafers are used as calibration samples. For each treatment method, more than 5 of the above-mentioned samples are subject to hydrostatic pressure reduction. The average values of the batch structure parameters before the pressure treatment are:

[0069] - The concentration of pores in the silicon dioxide thermal film is 97 ± 9 pores / cm 2 ;

[0070] - The refractive indices of the silicon dioxide thermal film are 1.42 ± 0.05 respectively.

[0071] From the test results of the hydrostatic pressure experiments on the above-mentioned samples, the following calculation formula can be summarized:

[0072] 1 Relationship between relative change rate of pore concentration of silica thin film and liquid pressure increase rate

[0073] P = -0.0086×V 2 +0.1338×V + 0.1801 EQ (1)

[0074] Where:

[0075] P: Relative change rate of pore concentration of silica thin film;

[0076] V: Liquid pressure increase rate, megapascal per second (Mpa / Sec);

[0077] It can be seen from formula (1) that as the liquid pressure increase rate increases, the relative change rate of pore concentration of silica thin film shows a linear upward trend and then levels off.

[0078] 2 Relationship between relative change rate of pore concentration of silica thin film and liquid pressure release rate after each loading cycle

[0079] P = -0.0952×T 2 +0.4352×T + 0.0314 EQ (2)

[0080] Where:

[0081] P: Relative change rate of pore concentration of silica thin film;

[0082] T: Liquid pressure release rate after each loading cycle, megapascal per second (Mpa / Sec);

[0083] It can be seen from formula (2) that as the liquid pressure increase rate increases, the relative change rate of pore concentration of silica thin film shows a linear upward trend and then levels off.

[0084] The thin film structure is processed under hydrostatic pressure in the range of 700 - 900 MPa for (3 - 7)×10 3 seconds (sec).

[0085] The experimental results show that at a treatment duration of 7×10 3 seconds (Second), the relative change in pore concentration caused by the pressure increase rate from atmospheric pressure to 800 MPa linearly increases from 0.2 to 0.65 and then levels off in the range of 3 - 7 Mpa / Sec. Therefore, the best effect can be obtained at a lifting rate of 3 - 5 MPa / s. The pressure release rate after the first loading cycle is 300 MPa / sec, and the pressure release rate in subsequent cycles is determined by formula EQ(2).

[0086] The experimental results show that the pressure release rate after the first loading cycle from 700MPa to atmospheric level causes the refractive index of the silica film to change. As the pressure release rate increases, the refractive index increases and approaches the level of 1.44, and reaches a maximum value when the pressure release rate is 300MPa / s.

[0087] The experimental results show that in each subsequent pressure treatment cycle, the pore concentration is relatively reduced in dependence on various increments of the pressure release rate, and the optimal range of the increase rate is 1-5MPa / s. The hydrostatic pressure duration is (3-7)×10 3 Seconds, the specific conditions are determined by the following situations: when the exposure time is less than 3×10 3 Seconds, the relaxation process in the film does not have enough time to occur; when the exposure time exceeds 7×10 3 When the time is shorter than 1 second, the film properties hardly change (optimal effect is achieved), while a longer time will result in non-productive loss of time and energy.

[0088] The efficiency of the processing mode of the silicon-silicon dioxide structure discovered according to the above method has been confirmed by the results of actual tests.

[0089] Implementation examples

[0090] Five batches of (I00) oriented films were obtained at 1180°C with a thickness of 1000-1100 angstroms by thermal oxidation in dry and wet oxygen. The structure of single crystal silicon of silica film was treated with hydrostatic pressure (pressure of 700MPa, pressure rise rate of 25MPa / s, duration of 7200s). The experimental results show that when the hydrostatic pressure is in the range of 700 to 900 MPa / sec and the treatment time is 3000 to 7000 seconds, the pore concentration of silica film changes very little, in the range of 25 to 35 pores per cubic centimeter. However, when the hydrostatic pressure is lower than 700 MPa / sec, or the hydrostatic pressure treatment time is less than 3000 seconds, the pore concentration of silica film will gradually increase.

[0091] On the structure processed in the best mode, the thickness of the transition layer between the substrate and the film of stoichiometric composition of silicon dioxide was measured by ellipsometry (the thickness of the transition layer will cause an increase in the surface state density, which directly affects the device performance), and the value of the residual mechanical stress in the sample film was determined using a three-crystal X-ray spectrometer. Together with all the parameters, the average value of the parameters was measured by performing parameter measurements at 12 points on each sample surface, and the distribution of the parameters in the structure was determined at the same time. The measurement results are shown in Figure 3 .

[0092] In summary, from the data of the embodiments, it can be observed that the method of the present invention can determine the optimal pressure increase rate according to the relationship between the relative change rate of the pore concentration and the liquid pressure increase rate, and can determine the optimal pressure release rate according to the relationship between the relative change rate of the pore concentration and the liquid pressure release rate during the cyclic loading period. The method of forming a dense oxide layer on silicon by cyclic static high pressure adopted in the present invention can not only be used to improve the compactness of the insulating film of silicon-based semiconductor devices and integrated circuits, but also be extended to improve the compactness and adhesion of the insulating film of compound semiconductor power devices and integrated circuits, thereby improving the reliability of the devices. It can significantly reduce the average mechanical stress of the silicon dioxide film, the thickness of the transition layer (the sensitivity limit of the measurement method) and the porosity, as well as the distribution of these parameters on the surface of the structure, so as to improve the reliability and product performance of semiconductor devices.

[0093] Finally, it should be noted that the above embodiments only represent several implementation manners of the present invention, and are not intended to limit the present invention. For those of ordinary skill in the art, any modifications, equivalent replacements, improvements, etc. made without departing from the concept of the present invention shall be included in the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for forming a dense oxide layer on silicon by using static high pressure, characterized in that, It includes the following steps: S01. Form an oxide layer on silicon; S02. Cyclically process the oxide layer with hydrostatic pressure; The oxide layer is a double film of silicon dioxide film and silicon nitride deposited on silicon; The cyclic processing with hydrostatic pressure means that the hydrostatic pressure acting on the oxide layer is increased from atmospheric pressure to a given pressure at a certain rising rate, and then the hydrostatic pressure is released from the given pressure to atmospheric pressure at a certain pressure release rate. Thus, one cycle of restoring and releasing the hydrostatic pressure is a cycle period; The pressure release rate V is determined by the following formula: V = V0 - (n - 1)CΔV + V1 where V0 is 170 - 300 MPa / s, which is the pressure release rate after the first loading cycle; C is the pressure coefficient, which is related to the type of pressure medium; the pressure medium is water and C takes a value of 1; ΔV is 1 - 5 MPa / s, which is the change in the pressure release rate after each loading cycle; n is 1, 2, 3... which is the serial number of the next loading cycle; V1 is the additional rate related to the number of film layers. When the film is a double film of silicon dioxide and silicon nitride, the range of V1 is related to the characteristics of the multi-layer film, and V1 is 50 - 150 Mpa / s.

2. The method according to claim 1, wherein The hydrostatic pressure treatment time is 3×10 3 -7×10 3 s.

3. The method according to claim 1 or 2, wherein The given pressure is 700 - 900 MPa.

4. The method according to claim 1 or 2, characterized in that The rising rate is 1 - 5 MPa / s.

5. The method according to claim 1 or 2, characterized in that The hydrostatic pressure is controlled by a pressure control system.

6. The method according to claim 5, wherein The pressure control system performs the following operations: A. Obtain the flow curve of the hydrostatic pressure intensity, divide the flow curve of each cycle into 6 - 9 segments, calculate the peak value of the flow rate of the hydrostatic pressure applied in each segment. The flow peak value of each segment of the flow curve is the maximum value of the flow peak values of the flow curve of this segment, and then calculate the flow reference value of each flow curve; B. Determine the feed-forward coefficient of the control system and calculate the feed-forward output value of the flow curve of each cycle; Its calculation formula is as follows: The feed-forward coefficient is: The feed-forward output value is: Substitute the feed-forward coefficient to obtain: Among them, is the feedforward output value of the flow rate in the th segment; is the feedforward coefficient; is the th segment curve, n is the total number of segments of the flow rate curve for each cycle; B is the reference for the control output proportionality coefficient, taking 66%, Q is the real-time control flow rate output, is the flow rate reference value of the th segment flow rate curve; C. Calculate the control output value of each segment of the flow curve in each pressure cycle; its calculation formula is as follows: Among them, is the actual control output of the section flow rate, is the control output of the controller, , are coefficients respectively, taking as 0.5c, then is 1 - 0.5c, where c is the delay coefficient of the PID controller, and among them, 0.9 ≤ c ≤ 1; D. Conduct a hydrostatic pressure test according to the control output values of each segment of the flow curve.

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