JP3644347B2 - Semiconductor device manufacturing method and semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor device having a silicon nitride film subjected to ion implantation, and a semiconductor device such as a pressure sensor and an infrared sensor using the silicon nitride film as a functional structure.
[0002]
[Prior art]
The conventional technology related to the semiconductor device as described above is disclosed in “Mechanical properties control of silicon nitride thin film for pressure sensor by ion implantation” (T.IEE Japan, Vol.110-C, No.4, '90). There is something that has been. In this conventional semiconductor device, after a silicon nitride (SiN) film is formed on both the front and back surfaces of the Si substrate (referred to as a main plane and a sub-plane respectively), the SiN film is formed on the SiN film for the purpose of reducing the internal stress of the SiN film. Phosphorus ions (P ⁺ ), boron ions (B ⁺ ), etc. are ion-implanted. Then, after ion implantation, heat treatment such as activation annealing is performed. After that, an opening for etching is formed in the SiN film on the sub-plane (or the main plane), an etching solution is injected from this opening to etch the Si substrate by anisotropic etching, and the diaphragm structure of the SiN film is formed. Forming.
[0003]
As described above, when P ⁺ ions or B ⁺ ions are implanted into the SiN film, the internal stress of the SiN film is reduced as compared with that before the ion implantation. It is known that the internal stress of tension decreases as the dose amount (ion implantation amount) is increased when both of P ⁺ ions and B ⁺ ions are implanted.
[0004]
[Problems to be solved by the invention]
However, the present inventor has found that the internal stress of the SiN film increases due to the influence of heat treatment such as activation annealing performed after ion implantation.
[0005]
An object of the present invention is to provide a semiconductor device manufacturing method and a semiconductor device capable of suppressing the stress reduction effect caused by ion implantation from being reduced by heat treatment.
[0006]
[Means for Solving the Problems]
The embodiment of the invention will be described in association with FIG.
(1) A method of manufacturing a semiconductor device according to the invention of claim 1 includes a film forming process for forming a silicon nitride film 2 on a semiconductor substrate 1, an ion implantation process for implanting silicon ions into the silicon nitride film 2, and a silicon ion The element forming step of forming the functional element 5 constituting a part of the functional structure in the silicon nitride film 2 into which the silicon nitride is implanted, and the semiconductor substrate on which the silicon nitride film 2 and the functional element 5 are formed are heat-treated. It has a heat treatment process and a functional structure forming process for forming a functional structure including the silicon nitride film 2 and the functional element 5 by forming the silicon nitride film 2 into a diaphragm structure .
(2) The invention of claim 2 is the method of manufacturing a semiconductor device according to claim 1, wherein the functional element is any one of a resistor, a thermopile, and an infrared absorption film.
(3) The invention of claim 3 includes a semiconductor substrate 1 having a recess 1a on the surface, a silicon nitride film 2 having a diaphragm structure laid over the recess 1a, and a functional element formed on the silicon nitride film 2. 5 is applied to a semiconductor device including a functional structure having 5. The silicon nitride film 2 is characterized in that silicon ions are ion-implanted and then heat-treated .
[0007]
In the section of the means for solving the above-described problems for explaining the configuration of the present invention, the drawings of the embodiments of the invention are used for easy understanding of the present invention. The form is not limited.
[0008]
【The invention's effect】
According to the first and second aspects of the invention, by implanting silicon ions into the silicon nitride film, the internal stress of the silicon nitride film can be reduced, and the stress reduction effect of the silicon nitride film by the heat treatment can be reduced. Decline in decline.
According to the invention of claim 3 , even if the semiconductor substrate on which the silicon nitride film is formed is subjected to heat treatment, it is possible to prevent the stress reduction effect of the silicon nitride film due to ion implantation from being reduced, and the internal stress is small. A semiconductor device having a silicon nitride film can be obtained.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS. Semiconductor devices that form a silicon nitride diaphragm structure on a silicon substrate include pressure sensors, infrared sensors, and flow sensors. In the first embodiment described below, a pressure sensor will be described as an example, and in the second embodiment, an infrared sensor will be described as an example.
[0010]
-First embodiment-
1A and 1B are diagrams showing a first embodiment of a semiconductor device according to the present invention, in which FIG. 1A is a plan view of a pressure sensor, and FIG. 1B is a cross-sectional view taken along line AA ′ of FIG. The Si substrate 1 is formed so that the substrate surface has a plane orientation (100), and a SiN film 2 having a film thickness of about 100 nm to 500 nm is formed on the substrate surface. The SiN film 2 is ion-implanted with silicon ions (Si ⁺ ) in order to reduce the internal stress of the film, and a region indicated by reference numeral 3 in the SiN film 2 represents an ion implantation region.
[0011]
A recess 1a is formed in the Si substrate 1 at the center of the sensor by anisotropic etching, and the SiN film 2 has a diaphragm structure at the center of the sensor. A cross-shaped resistor 5 (see FIG. 1A) is formed on the diaphragm portion of the SiN film 2. A protective film 6 such as PSG (phosphorus glass) is formed on the surfaces of the resistor 5 and the SiN film 2. The resistor 5 is a piezoresistor obtained by doping polysilicon (B) or phosphorus (P). In FIG. 1A, the protective film 6 is omitted. Further, as shown in FIG. 1A, an etching hole 7 is formed in the SiN film 2, and an etching solution is injected from the etching hole 7 when the Si substrate 1 is anisotropically etched. The etching hole 7 is closed by forming the protective film 6, and the recess 1a is sealed in a predetermined pressure state (vacuum state).
[0012]
In the pressure sensor shown in FIG. 1, the SiN film 2 having a diaphragm structure and the resistor 5 form a functional structure. In FIG. 1B, the diaphragm portion of the SiN film 2 is deformed by a differential pressure between the pressure in the sensor upper space and the pressure in the recess 1a. As a result, the resistor 5 on the SiN film 2 is also distorted and its resistance value changes, and a change in pressure is detected by detecting this change in resistance value.
[0013]
Next, the manufacturing process of the pressure sensor shown in FIG. 1 will be described with reference to FIG. First, as shown in FIG. 2A, the SiN film 2 is formed on the main plane (upper surface in the drawing) of the Si substrate 1 with the plane orientation (100) by LPCVD (Low Pressuer Chemical Vapor Deposition) method or the like. As described above, the film thickness of the SiN film 2 is about 100 nm to 500 nm, and the film formation temperature at this time is 780 ° C. Next, as shown in FIG. 2B, Si ⁺ ions are implanted into the entire surface of the SiN film 2. The dose amount at this time is 1 × 10 ¹⁴ (cm ⁻² ) to 1 × 10 ¹⁵ (cm ⁻² ), and the RP (projection range) of Si ⁺ ions is inside the SiN film 2 (region indicated by reference numeral 3). Set the acceleration voltage so that it exists.
[0014]
Thereafter, polysilicon serving as the resistor 5 is formed on the SiN film 2 at a film forming temperature of 620 ° C. by LPCVD, and the formed polysilicon is etched into a cross shape as shown in FIG. (See (c)). Thereafter, a dopant (B or P) for controlling the conductivity of the polysilicon 5 is ion-implanted. Further, after forming a protective film (PSG (phosphorous glass) or the like) 6 ′ as shown in FIG. 2D by the CVD method, the dopant in the polysilicon 5 is activated and the protective film at the end of the polysilicon 5 is formed. In order to improve the 6 ′ step coverage, a heat treatment is performed in N ₂ at 950 ° C. for 20 minutes.
[0015]
Next, an etching hole 7 for anisotropic etching is formed in the protective film 6 ′ and the SiN film 2 by plasma etching or the like. Then, it is immersed in hydrazine (anisotropic etching solution) at 80 ° C. for several hours, and a recess 1a is formed in the silicon substrate 1 by anisotropic etching (FIG. 2E). The surface 1b of the recess 1a formed by this anisotropic etching is a (111) plane of silicon single crystal. Thereafter, after removing the protective film 6 ', the protective film 6 is formed again on the entire surface of the SiN film 2, and the etching hole 7 formed in the SiN film 2 is closed by the protective film 6 (FIG. 2 (f)). . When the protective film 6 is formed, the film forming pressure is adjusted so that the inside of the recess 1a is sealed with a predetermined pressure.
[0016]
FIG. 3 is a diagram showing the internal stress of the SiN film 2 when silicon ions (Si ⁺ ) are ion-implanted in comparison with the conventional case (when P ⁺ and B ⁺ are implanted). In FIG. 3, (a) shows the internal stress before the heat treatment of the protective film 6 ′, (b) shows the internal stress after the heat treatment, the vertical axis shows the internal stress, and the horizontal axis shows the dose of ions. Represents. The internal stress before ion implantation into the SiN film 2 was 1.3 GPa. However, as shown in FIG. 3A, in any case of Si ⁺ ions, P ⁺ ions and B ⁺ ions, Internal stress is reduced. It was also found that for any ion, the amount of decrease in internal stress increases as the dose increases. Hereinafter, the internal stress will be described by focusing on data with a dose amount of 1 × 10 ¹⁵ (cm ⁻² ).
[0017]
When Si ⁺ ions are implanted at a dose of 1 × 10 ¹⁵ (cm ⁻² ), the internal stress of the SiN film 2 decreases from 1.3 GPa to 0.09 GPa, and an almost stress-free SiN film 2 is obtained. It is done. On the other hand, in the case of conventional B ⁺ ions, the pressure is 0.1 GPa, which can be reduced to almost the same level as Si ⁺ ions. Further, in the case of P ⁺ ions, the internal stress becomes a negative value and changes from tensile stress to compressive stress.
[0018]
When the SiN film 2 subjected to the ion implantation is subjected to a heat treatment at 950 ° C. for 20 minutes in an N ₂ atmosphere, the internal stress changes as shown in FIG. That is, it can be seen that the internal stress reduced by the ion implantation is increased by the heat treatment. When the internal stress after the heat treatment is described in the order of Si ⁺ ions, P ⁺ ions, and B ⁺ ions, they are 0.67, 0.73, and 0.97 GPa. In particular, although the change of P ⁺ ions that showed compressive stress before the heat treatment was severe, it was found that the Si ⁺ ion of the present embodiment has a small change of internal stress due to the heat treatment and a stable SiN film can be obtained.
[0019]
-Second Embodiment-
Next, a case where the present invention is applied to an infrared sensor will be described. FIG. 4 is a plan view of the infrared sensor, and FIG. 5 shows a cross section taken along line EE ′ of FIG. In the case of the infrared sensor, a substantially cross-shaped diaphragm structure is formed by the SiN film 2 as shown in FIG. 4, and the components of the infrared sensor which is a functional structure (thermopile and infrared absorption described later) are formed on the diaphragm. A film 104) is formed.
[0020]
The procedure for forming the diaphragm structure is substantially the same as that of the first embodiment described above. That is, as shown in FIG. 5, after forming the SiN film 2 on the Si substrate 1, the etching hole 100 (FIG. 4) is formed in the SiN film 2. Then, the Si substrate 1 is anisotropically etched by injecting an anisotropic etchant from the etching hole 100 to form a recess 1a as shown in FIG.
[0021]
Also in this embodiment, Si ⁺ ions are implanted into the entire surface of the SiN film 2, and reference numeral 3 in FIG. 5 indicates an ion implantation region. Hereinafter, in this SiN film 2, the central portion (rectangular portion) of the substantially cross-shaped diaphragm on which the infrared absorption film 104 is formed is referred to as the diaphragm portion D, and the SiN film 2 around the diaphragm portion D is referred to as the peripheral portion C. The four bridging portions connecting the diaphragm portion D and the peripheral portion C are referred to as beams B.
[0022]
On each beam B, n-type polysilicon 106 and p-type polysilicon 107 are alternately formed. Each polysilicon 106, 107 has one end on the diaphragm portion D and the other end on the peripheral portion C. It is formed as follows. The polysilicons 106 and 107 are connected in series by Al wiring 108 so that the n-type polysilicon 106 and the p-type polysilicon 107 are alternately connected. A thermocouple is formed by the pair of polysilicons 106 and 107 connected in this way, and a thermopile is formed by a plurality of thermocouples connected in series.
[0023]
The n-type polysilicon 106 is formed by ion implantation of phosphorus (P) or arsenic (As) into a polysilicon film, and the p-type polysilicon 107 is formed by ion implantation of boron (B) into the polysilicon film. . After that, as shown in FIG. 5, an interlayer insulating film 105 such as PSG (phosphorus glass) is formed by CVD or the like, and then annealing for impurity activation is performed.
[0024]
In the infrared sensor shown in FIG. 4, the thermopile is composed of a plurality of pairs of thermocouples, the hot junction of each thermocouple is arranged in the diaphragm portion D, and the cold junction is arranged in the peripheral portion S. The Al wiring 109 is a thermopile output terminal. Al wirings 108 and 109 formed on the insulating film 105 connect the n-type polysilicon 106 and the p-type polysilicon 107 through contact holes 105 a formed in the insulating film 105.
[0025]
After forming the protective film 110 on the insulating film 105, a protective film 111 is formed for further planarization, and an infrared absorption film (for example, a film made of gold black or the like) 104 is formed. As shown in FIG. 4, the infrared absorption film 104 is formed in a rectangular shape on the diaphragm portion D. In FIG. 4, the infrared absorption film 104 is indicated by an imaginary line (two-dot chain line) and the protective films 110 and 111 are omitted from the insulating film 105 so that the patterns of the Al wirings 108 and 109 are easily understood. .
[0026]
Next, the operation of the infrared sensor shown in FIGS. Infrared rays incident on the infrared absorption film 104 are absorbed by the infrared absorption film 104 and converted into thermal energy. The diaphragm portion D on which the infrared absorption film 104 is formed is only connected to the peripheral portion C of the SiN film 2 by four beams B having a small cross-sectional area, and is separated from the Si substrate 1 by the recess 1b. Therefore, the diaphragm part D is thermally separated from its peripheral part (peripheral part C or Si substrate 1).
[0027]
The thermal energy absorbed by the infrared absorption film 104 is transmitted to the Si substrate 1 as a heat sink via the diaphragm portion D and the beam B of the SiN film 2. Since the cross-sectional area of the SiN film 2 in the beam B is small, the thermal resistance is large, and the temperature of the infrared absorption film 104 is higher than that in the peripheral part C. As shown in FIG. 4, since both ends of the n-type polysilicon 106 and the p-type polysilicon 107 are installed in the diaphragm portion D and the peripheral portion C where the temperature difference occurs, the thermopile is heated by the Seebeck effect. Electric power is generated. This electromotive force is taken out as an infrared detection signal from the Al wiring 109 which is an output terminal.
[0028]
In general, the thermoelectromotive force of the entire thermopile is the sum of the electromotive forces of the thermocouples, and the sensitivity R of the thermopile is expressed by the following equation (1).
[Expression 1]
R = n × (αp + αn) × Rth (1)
In equation (1), n is the number of thermocouple pairs, αn is the Seebeck coefficient of the n-type polysilicon 106, αp is the Seebeck coefficient of the p-type polysilicon 107, and Rth is the combined heat of the diaphragm portion D and the beam B. Resistance.
[0029]
As can be seen from equation (1), in order to improve the sensitivity R of the infrared sensor, it is necessary to increase the combined thermal resistance Rth of the diaphragm portion D and the beam B. That is, it is necessary to make the cross-sectional area of the beam B as small as possible and to make the length of the beam B longer. Since the internal stress of the SiN film 2 constituting the diaphragm portion D and the beam B is one of the factors that cause the beam B to be broken, it is very important to reduce the stress of the SiN film 2 for increasing the sensitivity of the infrared sensor. Yes.
[0030]
As described above, in the infrared sensor of the present embodiment, silicon ions (Si ⁺ ) are implanted into the SiN film 2 so as to reduce the internal stress. Therefore, even if heat treatment is performed after the ion implantation, the internal stress is reduced. The reduction effect is not impaired. As a result, the cross-sectional area of the beam B can be made smaller or longer than the conventional infrared sensor, so that a more sensitive infrared sensor can be produced.
[0031]
In the above-described embodiment, the semiconductor device using the Si substrate having the plane orientation (100) as the substrate has been described as an example. However, any material that can form silicon nitride (SiN) is not limited to the Si substrate described above. Such a material may be used. Moreover, even when the silicon nitride film 2 does not have a diaphragm structure as in the above-described embodiment, the reduction in the internal stress reduction effect of the silicon nitride film 2 after the heat treatment can be suppressed, and the mechanical characteristics are excellent. A silicon nitride film can be formed. As a method for forming silicon nitride, in addition to the above-described LPCVD method, a thermal decomposition type CVD method or a non-thermal decomposition method represented by a plasma CVD method may be used.
[Brief description of the drawings]
1A and 1B are diagrams showing a first embodiment of a semiconductor device according to the present invention, in which FIG. 1A is a plan view of a pressure sensor, and FIG. 1B is a cross-sectional view taken along line AA ′ of FIG.
2 is a diagram illustrating a manufacturing process of the pressure sensor shown in FIG. 1, and the process proceeds in the order of (a) to (f).
FIGS. 3A and 3B are diagrams for explaining internal stress of the SiN film, wherein FIG. 3A shows the relationship between the dose before heat treatment and the internal stress, and FIG. 3B shows the relationship between the dose after heat treatment and the internal stress; Is shown.
FIG. 4 is a diagram showing a second embodiment of a semiconductor device according to the present invention, and is a plan view of an infrared sensor.
FIG. 5 is a diagram showing a cross section taken along line EE ′ of FIG. 4;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Silicon (Si) substrate 1a Recess 2 Silicon nitride (SiN) film 3 Ion implantation region 5 Resistor 7,100 Etching hole 104 Infrared absorption film 106 n-type polysilicon 107 p-type polysilicon 108, 109 Aluminum (Al) wiring

Claims (3)

A film forming step of forming a silicon nitride film on the semiconductor substrate;
An ion implantation step of implanting silicon ions into the silicon nitride film;
An element forming step of forming a functional element constituting a part of the functional structure in the silicon nitride film implanted with the silicon ions;
A heat treatment step of heat treating the semiconductor substrate on which the silicon nitride film and the functional element are formed;
A method of manufacturing a semiconductor device, comprising: forming a functional structure including the silicon nitride film and the functional element by forming the silicon nitride film into a diaphragm structure . In the manufacturing method of the semiconductor device according to claim 1,
  The method of manufacturing a semiconductor device, wherein the functional element is any one of a resistor, a thermopile, and an infrared absorption film. In a semiconductor device comprising a semiconductor substrate having a concave portion on the surface, and a silicon nitride film having a diaphragm structure laid over the concave portion and a functional structure having a functional element formed on the silicon nitride film,
A semiconductor device, wherein silicon ions are ion-implanted into the silicon nitride film, and thereafter heat treatment is performed .

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