JPH02228032A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To reduce deterioration due to a tungsten film among deteriorations of characteristics because of heat that is applied during the manufacturing of a semiconductor device by controlling the internal stress of the tungsten film for forming a gate film after the formation of the film under the specified conditions. CONSTITUTION:A field oxide film 23 for element isolation is formed on a silicon substrate 21. A gate silicon oxide film 25 for a gate insulating film is further formed. Then, a tungsten film 27 is formed on the silicon oxide film 25. The inner stress of the tungsten film 27 for forming a gate electrode 27a after the film formation is controlled so that the stress becomes tensile stress or compression stress of 3X10<9>dyne/cm<2> or less by heat treatment Thus deterioration due to the tungsten film 27 can be reduced.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing a semiconductor device in which a gate electrode is made of a tungsten film, and particularly relates to a method for manufacturing a semiconductor device in which a gate electrode is formed of a tungsten film. Among the deterioration of characteristics of the device, the method of manufacturing a semiconductor device that can reduce the deterioration of characteristics caused by the tungsten film is hindered.

(Prior Art) As a semiconductor device having a gate electrode, for example, MOS (Met) is known as an important device for constructing LSI such as semiconductor memory and microprocessor.
al Oxide Sem1 conductor) type F
ET (Field Effect Transistor)
There is r).

As for the gate electrode material of such a lock O8 type FET,
Generally, polycrystalline silicon (hereinafter referred to as polysilicon) has been used. The reason for this is that polysilicon has good etchability, good oxidation properties, chemical stability, and excellent step coverage (the ability to coat with a uniform film thickness regardless of the level difference between the substrates). Met.

However, as Llls become more highly integrated and faster, an increase in signal delay time due to resistance of wiring including gate electrodes has become a problem. Therefore, recently, alloys of high melting point metals and silicon (silicide) and polysilicon have been used instead of polysilicon as gate electrode materials, and the structure of gate electrodes has been changed to two types: silicide/polysilicon.
It has a layered structure. However, as LSIs become more highly integrated in the future, the above-described configuration will no longer be able to satisfy the requirements, and a gate electrode material with lower resistance will be needed.

Tungsten is considered as a gate electrode material that satisfies these requirements. FIGS. 6(A) to 6(C) are process diagrams schematically showing, with cross-sectional views, the gate electrode forming process of a MOS type FET using tungsten for the gate electrode.

First, a field oxide 1113 for element isolation is formed on the silicon substrate 11 by a known method, and then a silicon oxide film for a gate insulating film having a thickness of about 150 nm is formed on this silicon substrate 11 by, for example, a thermal oxidation method. 15
(hereinafter referred to as gate silicon oxide film 15) is formed (FIG. 6(A)).

Next, a W (tungsten) film 17 having a thickness of about 3000λ, for example, is formed on the gate silicon oxide film 15 by a suitable method such as a sputtering method, a CvD method, or an EB (electron beam) evaporation method. Figure 6 (B)).

Next, a resist batten (not shown) is formed on this tungsten film 17 to serve as a mask for patterning this tungsten film into the shape of a gate electrode, and using this resist batten as a mask, unnecessary portions of the tungsten film 17 are etched. The gate electrode 17a is formed (sixth
After that, a source region, a train region, etc. are formed to form a MOS type FET (FIG. (C)). However, a description of the steps for forming the source region and the like will be omitted here.

By the way, when a tungsten film is formed by the sputtering method, the literature (IEE Transactions
On Electron Devices (IEEE TRA
NSACTTONS ON ELECTRON
DEVICES) 1 Sword (3) (1987, 3) pp
, 607-613), the internal stress of the tungsten film after deposition changes depending on the Ar (argon) gas pressure during sputtering. FIG. 7 is a diagram showing this situation, and is a diagram cited from the above-mentioned literature. The dependence of the internal stress of the tungsten film on the argon gas pressure'l'
It is a characteristic curve diagram shown in FIG.

Roughly speaking, according to the above-mentioned literature, when the gate electrode of a MOS FET is made of a tungsten film, the magnitude of the internal stress of this tungsten film is related to the formation of interface states;
It is said that this is related to the deterioration of 91 due to hot carriers.

Therefore, in order to avoid this, the above-mentioned literature describes MOS
In manufacturing a type FET, after forming a tungsten film (the state shown in Figure (8)), this tungsten film is subjected to heat treatment (hereinafter sometimes referred to as annealing) at a temperature of 900 to 1100°C. A method has been proposed.

It has been shown that this annealing reduces the internal stress of the tungsten film, resulting in a tensile stress of approximately 4 x IQ' dyne/cm2. In addition, in a MOS type FET in which the gate electrode is formed by buttering tungsten S that has undergone such annealing, 9. It is said that no deterioration occurs.

Furthermore, according to this document, the internal stress of the tungsten film after its formation and before annealing is 1.5x10" d
It is said that a material exhibiting a compressive stress of about yne/cm2 is sufficient. The reason for this is that in order to form a tungsten film with low stress from the beginning, a relatively high argon gas pressure is required, and the tungsten film formed under these conditions will have a large amount of oxygen mixed in and the etched shape will deteriorate. This is to avoid the disadvantage of doing so. Even if the tungsten film has high internal stress (high compressive stress) after being formed, it does not pose a problem because the internal stress can be reduced by annealing according to the method of the above-mentioned document.

(Problem to be Solved by the Invention) However, according to detailed experiments by the inventor of this application 1, the tungsten film formed by the sputtering method 1 has high compressive stress after film formation and before annealing. In the case of a tungsten film, if this is used as a gate electrode to form a capacitor with a locked O3 structure, and this capacitor is annealed at a temperature of about v + ooo degrees Celsius, the problem is that the fixed charge density and interface state density will increase in the affected area. , i.e. MO5
There was a problem that the characteristics deteriorated (the experimental results will be explained later using Figures 2, 4, and 5). Therefore, in the actual manufacture of MOS type FETs, Since the MOS characteristics deteriorate (fluctuate) due to various annealing processes during the manufacturing process, M
This poses a problem when manufacturing OS type FETs.

The present invention has been made in view of the above points, and therefore, an object of the present invention is to solve the above-mentioned problems and to solve the problem of deterioration caused by the tungsten film constituting the gate electrode, which is one of the deterioration of characteristics of the semiconductor device. An object of the present invention is to provide a method for manufacturing a semiconductor device that can reduce the amount of damage.

(Means for Solving the Problem) In order to achieve this objective, the inventor of this application has conducted various studies. As a result, it was found that the above objective can be achieved by controlling the internal stress after the formation of the tungsten film for forming the gate electrode.

Therefore, according to the present invention, when manufacturing a semiconductor device using a tungsten film for a gate electrode, the tungsten film is deposited after the tungsten film is deposited to form the gate electrode. The internal stress of the tungsten film before undergoing heat treatment in the post-process during manufacturing is tensile stress or 3 x 10
It is characterized in that it is carried out under conditions that result in a compressive stress of 9 dyne/cm2 or less.

(Function) According to the method of manufacturing a semiconductor device of the present invention, as is clear from the experimental results described later, MO84R is formed using a tungsten film as a gate electrode and includes this gate electrode.
Even if the structure is annealed at a temperature of about 1,000° C., no substantial deterioration of the MOS characteristics will occur.

Therefore, even if there is a heat treatment step of about 1000°C during the manufacturing process of a MOS type FET, for example, the MOS characteristics of the MOS type FET will not deteriorate due to this heat treatment, so the MOS type as designed FET is obtained.

(Example) Hereinafter, an example of the method for manufacturing a semiconductor device of the present invention will be described with reference to the drawings. Note that this example is an MO using a tungsten film as one electrode (assumed to be a gate electrode).
S-structure capacitors were fabricated using the steps described below under various conditions for forming the tungsten film, and after annealing under the conditions described later, the fixed charge density and interface state density were measured. The results show the effects of the manufacturing method of the present invention.

First, we will explain the manufacturing procedure of the MOS type capacitor used in the experiment. A large number of MOS capacitors are fabricated on a single silicon substrate. Figures 1 (A) to (E) are manufacturing process diagrams for explaining the process, and show the state of the capacitor in the main steps in the manufacturing process, with two of the many MO3 type capacitors in the silicon substrate. This is shown with a sectional view. However, these figures are only schematic illustrations to the extent that this invention can be understood, and therefore, the dimensions and shapes of each component and the dimensional ratios between each component are also schematic, and the present invention is illustrated only schematically. It is to be understood that the examples are not limited to illustrations only.

First, in this example, 12 silicon substrates were prepared.

Then, each silicon substrate 2 is
A field oxide film 23 for element isolation is formed on 1,
A silicon oxide film 25 for a gate insulating film (hereinafter abbreviated as gate silicon oxide film) having a film thickness of about 800λ and a thickness of 18° was formed by a rough thermal oxidation method (FIG. 1(A)).

Next, in order to be able to determine the fixed charge density, the silicon substrate 21 on which the gate silicon oxide film 25 was formed was immersed in hydrofluoric acid, and the thickness of the film was reduced within one silicon substrate. Gate silicon oxide film 2 with different
5a and 25b were formed (Fig. 1(A)).

Next, these 12 silicon substrates are divided into three groups of four each. Then, on the gate silicon oxide film of each silicon substrate, a tungsten film 27 with a thickness of 3,000 mm was formed by sputtering, and the power was set to 2 W for each group.
(RF power 4W/cm2 at nitrogen temperature) was the same, and the argon gas pressure was 5°12 and 20mmTorr for each group, respectively, forming the film under different conditions (Fig. 1 (C)).
.

Next, in order to prevent the tungsten film from oxidizing during the high-temperature heat treatment that will be performed later, a film thickness of 2,000 cm was deposited on the tungsten film 27 of the 12 silicon substrates using a low-temperature (400°C) atmospheric pressure CVD method. A silicon oxide film 29 of approximately 100 mL was formed (FIG. 1(D)).

Next, the argon gas pressure during sputtering was set to 5 mmTorr.
group, 72 mm Torr group, 20 mm Torr
One sample is extracted from each group designated as r and reorganized into four new groups (hereinafter referred to as groups a, b, c, and d).

Next, the three samples of group a were heated to 800
A heat treatment was performed for 30 cycles in a N2 atmosphere at a temperature of .degree. In addition, three samples from group 5 were heat-treated using an annealing furnace at a temperature of 900"C for 30 minutes in a N2 atmosphere. Three samples from group 0 were also heat-treated using an annealing furnace. Heat treatment was performed for 30 minutes in an N24# atmosphere at a temperature of 1000°C.In addition, the three samples of group d were left as they were formed by sputtering without being heat treated (hereinafter referred to as AS). - sometimes referred to as depo.)

Next, resist batting (
Then, using this resist baton as a mask, unnecessary portions of the silicon oxide film 29 and the tungsten film 27 are removed for each sample, and a gate electrode 27a% composed of the tungsten film is formed.
A type 3 capacitor 31 was formed (FIG. 1(E)). In addition, in FIG. 1(E), 29a is the old gate electrode after patterning.・μ ・1 Next, using each sample including the MO5 type capacitor produced as described above, the fixed charge density N+ was determined by the procedure described below.

First, the remaining portion 29a of the silicon oxide film on the gate electrode 27a made of a tungsten film is removed.

Next, for each sample, a large number of MO3 formed on each sample
of a plurality of predetermined position capacitors of type capacitors,
The film thickness of the gate silicon oxide film (the gate silicon oxide film of each capacitor is different from each other as illustrated in the two capacitors in FIG. 1(B)) t and the flat band voltage VF of that capacitor. [1] was measured by a known method, and the vertical axis was '1/pa, the horizontal axis was t, and the fixed charge density N was determined from the slope of each @moblotted straight line (not shown).

I asked for

FIG. 2 is a characteristic curve diagram showing the dependence of the fixed charge density N, determined in this manner, on the heat treatment temperature, where the horizontal axis represents the heat treatment temperature and the vertical axis represents the fixed charge density N p (X 10"
cm-2) @, argon gas pressure is 5mmTorr
Data for a sample with a tungsten film formed at an argon gas pressure of 12 mmTorr is marked O, data for a sample with a tungsten film formed at an argon gas pressure of 12 mmTorr is marked Δ, and a tungsten film formed at an argon gas pressure of 20 mmTorr is indicated. FIG. 3 is a characteristic curve diagram plotting data of a sample having a temperature of 0 and a case where no heat treatment was performed (as-depo) for each heat treatment temperature. As is clear from Figure 2,
For each level (samples with different argon gas pressures), 90
Until the heat treatment at a temperature of 0°C, the fixed charge density N+ does not increase due to the heat treatment. However, when the heat treatment temperature reaches 1000°C, the argon gas pressure is increased to 12 m
It can be seen that there is a large increase in the fixed charge density Nf at the mTorr level and the 5 mm Torr level.

In addition to the scene description, although the explanation was omitted in the section on the preparation procedure for the MOS type capacitor samples mentioned above, when preparing these capacitor samples, at the same time, the internal stress of the tungsten film formed by the sppack method was A sample for measurement was prepared according to the procedure described below.

First, nine substrates similar to those used in the production of MOS type capacitor samples were prepared, and a gate silicon oxide film was formed on these silicon substrates in the same manner as in the production of the capacitor samples.

Next, these nine samples were divided into three groups of three samples each.
Next, the three silicon substrates of the first group of the three groups were set in the Subaru Nta equipment along with the sample group in which the argon gas pressure during sputtering was set at 5 mmTorr during the capacitor sample preparation described above. Then, a tungsten film with a thickness of 3,000 wafers was formed on the gate silicon oxide layer. Regarding the three silicon substrates of the second group,
The argon gas pressure used in preparing the capacitor sample described above was set in a sputtering apparatus together with the sample group, and a tungsten film with a thickness of 3000 mm was formed on the gate silicon oxide film. In addition, the three silicon substrates of the third group were set in a sputtering apparatus together with the sample group in which the argon gas pressure was set to 20 mmTorr during the above-mentioned cano/shita sample preparation, and a film of 3,000 people was placed on the gate silicon oxide. A thick tungsten film was formed.

Next, in order to determine the internal stress of the tungsten film of each sample before heat treatment after the tungsten film was formed, that is, the as-dopO tungsten film, the warpage of each sample was measured using a flatness tester, and the internal stress was measured using a flatness tester. The stress was calculated. Then, the argon gas pressure t5. 12.20mmT
The average value, maximum value, and minimum value of the internal stress of each group were determined as orr.

Next, a silicon oxide film was formed on the tungsten film of each sample by low-temperature (approximately 400° C.) atmospheric pressure CVD method in order to prevent the tungsten film from being oxidized by heat treatment to be performed later.

Next, increase the argon gas pressure to 5. 12.20mm Torr
One silicon substrate was extracted from each group and reorganized into three groups (referred to as α, β, and 7 groups). after that,
Group α was heat-treated together with group a of the capacitor samples described above using an annealing furnace at a temperature of 800° C. in a N2 atmosphere for 30 minutes. In addition, for the β group, we used an annealing furnace with the capacitor sample B group at 900°C.
A heat treatment was performed for 30 minutes in a N2 atmosphere at a temperature of . Furthermore, the first group was heat-treated together with the capacitor sample No. 0 using an annealing furnace at a temperature of ObO 0 C in a N 2 atmosphere for 30 minutes.

Next, the silicon oxide film on the tungsten film of each sample after the heat treatment was removed using hydrofluoric acid, and then the internal stress of each tungsten film was determined using the same method used to determine the internal stress of the tungsten film of aS-dopo. I asked for it.

Figure 3 is a characteristic curve diagram showing the dependence of internal stress on heat treatment temperature determined in this way, with heat treatment temperature on the horizontal axis and internal stress on the vertical axis.
The data for the sample with a tungsten film formed at an argon gas pressure of 12 mmTorr is marked Q, and the data for the sample with a tungsten film formed at an argon gas pressure of 12 mmTorr is marked Δ.The tungsten film formed at an argon gas pressure of 20 mmTorr is FIG. 1 is a characteristic curve diagram in which the data of a sample having 0 is plotted for each heat treatment temperature from the case where no heat treatment was performed (as-depo). In addition, in the as-depo sample, the values indicated by ◯, △, and squares are the average values of each level, and - and L are the maximum and minimum values at each level.

As can be understood from FIG. 3, by varying the argon gas pressure during sputtering, the internal stress of the as-deoo tungsten film becomes different at each level. If the data shows 4, the argon gas pressure is 5. 12.20mm
In the order of Torr, the average value of the internal stress of the tungsten film is -14, 3, -10°5, -3, 2 (X 1o9
dyne/cm2. However, after 30 minutes of heat treatment at a temperature of 1000°C, the internal stress of the tungsten film at any level is equal to the stress determined by the difference in the thermal expansion coefficients of tungsten and silicon. Become. Roughly speaking, the absolute value of the internal stress at that time is smaller than that in the as-deoo phase.

This phenomenon is also described in the literature explained in the prior art section.
! This is what is being done.

1 History Next, the data shown in FIGS. 2 and 3 were organized and considered as described below.

First, as shown in Figure 4, the internal stress (compressive stress) is plotted on the horizontal axis and the fixed charge density N is plotted on the vertical axis. The average value of the internal stress of each sample for stress measurement at the time of aS-depo (as-depo-level - in Figure 3)
14,5, -10,5, -3,2 values), argon gas pressure! 5. Plot the fixed charge density after heat treatment at 900'C and the fixed charge density after heat treatment at 1000°C of each capacitor sample at 12.20mmTorr, and calculate a of the variation due to the heat treatment of fixed charge twice.
The dependence on internal stress during s-depo was considered.

As is clear from Figure 4, the smaller the internal stress during as-depo, the smaller the fixed charge density after heat treatment at 900°C and the fixed charge density after heat treatment at 1000°C. I understand.

In particular, if the internal stress of the tungsten film during as-depo is a compressive stress of approximately 3 x IOgdyne/am2 or less, the fixed charge density will not substantially change even after heat treatment at a temperature of 1000°C for 30 minutes. I understand.

In addition, the MOS type capacitor (Fig. 1 (E
)) The gate silicon oxide film thickness of each sample is 2.
The interface state density Dot of the as-depo sample was determined by the well-known OuasiStatic CV method using a capacitor of 0.00%.
The interface state density D1t of each sample heat-treated at each temperature was determined. Then, using this data as shown in Figure 4, we plot the interface state density D+t (XIOth eV cm-) on the vertical axis as shown in Figure 5.
2), plot the internal stress during as-depo on the horizontal axis, and calculate the as-
We considered the dependence of depo stress on internal stress.

As is clear from Fig. 5, the smaller the as-depo internal stress, the smaller the interface state density after heat treatment at 900'C and the interface state density after heat treatment at 1000°C. It can be seen that this shows that

In particular, if the internal stress of the tungsten film during as-depo is a compressive stress of about 3 x 109 dyne/cm2 or less, the interface state density will substantially change even after heat treatment at 1000"C for 30 minutes. I found out that it doesn't.

Therefore, when forming a tungsten film for forming a gate electrode when forming a semiconductor device M using a tungsten film for the gate electrode, the internal stress after the film is formed and before heat treatment is tensile stress or 3X. IO'dyne/c
If a tungsten film is formed under film formation conditions that result in a compressive stress of m2 or less, an increase in fixed charge density and interface state density will not substantially occur even if heat treatment is performed at a high temperature of 1000°C. I know that it is possible.

Although the embodiments of this invention have been described above, this invention is not limited to the above-mentioned embodiments.

In the embodiments described above, a case has been described in which a tungsten film for forming a gate electrode is formed by sputtering. However, even when a tungsten film is formed by CVD or EB evaporation, the internal stress of the film after film formation and before heat treatment during semiconductor device manufacturing is tensile stress or compressive stress of 3 x 109 dyne/cm2 or less. It is considered that it is better to form the film under film formation conditions that cause stress.

(Effects of the Invention) As is clear from the above description, according to the method for manufacturing a semiconductor device of the present invention, in manufacturing a semiconductor device using tungsten for the gate electrode, the method is performed after forming a tungsten film. The internal stress of the tungsten film before undergoing heat treatment in the post-process during the manufacture of the semiconductor device is tensile stress or 3 x 10 gdyne/
The tungsten film is formed under conditions that result in a compressive stress of cm2 or less. In this way, even if an MO3 structure including this tungsten film is used as a gate electrode is annealed at a temperature of about 1000°C, the fixed charge density will increase and the interface state density will decrease. Changes in MO3 characteristics such as increase do not occur.

Therefore, it is desirable to provide a method for manufacturing a semiconductor device that can reduce the deterioration caused by the tungsten film constituting the gate electrode among the deterioration of characteristics due to heat of a semiconductor device having a MOS FET using tungsten for the gate electrode, for example. I can do it.

[Brief explanation of the drawing]

Figures 1 (A) to (E) are diagrams used to explain the present invention, and are diagrams showing the manufacturing procedure of the MOS type capacitor used in the experiment. Figure 2 is a diagram showing the dependence of fixed charge density on heat treatment temperature. Figure 3 is a diagram showing the dependence of internal stress on heat treatment temperature. Figure 4 is a diagram showing the as-d variation of fixed charge density due to heat treatment.
FIG. 5 is a diagram showing the internal stress dependence during epo, and FIG. 5 is a diagram showing the dependence of the variation of interface state density due to heat treatment on internal stress during as-depo, and FIGS. 6 (A) to (C) are: 7 is a diagram illustrating the argon gas pressure dependence of the internal stress of the sputtered tungsten film; FIG. It is. 21...Silicon substrate, 23...Field oxide film 25...Gate silicon oxide films 25a, 25b...Gate silicon oxide film 27...Tungsten film 27a...Tungsten film with different film thicknesses gate electrode 29
...Silicon oxide film, 29a...Remaining portion of silicon oxide film 31...MOS type capacitor. Patent applicant Oki Electric Industry Co., Ltd. 29: Silicon oxide films 25a, 25b, gate silicon oxide film 27 with different film thicknesses: Tungsten film Figure 1 for explaining this invention Figure 1 for explaining this invention ( (No heat treatment) Heat treatment temperature (℃) Shows the heat treatment temperature dependence of fixed charge and degree.7 Shows the heat treatment temperature dependence of internal stress. dyne/cm2) Fixed voltage? tf
As-depo internal stress dependence of variation due to heat treatment in fi degree 1 Fig. 4 Internal stress (compressive stress) of as-depo tungsten film (XIO” dyne/cm2) - Dependency on internal stress during deposition Figure 5 Diagram used to explain the prior art Argon gas pressure (Pa) Figure 7 showing the dependence of internal stress on sputtered tungsten film on argon gas pressure

Claims (1)

[Claims] (1) When manufacturing a semiconductor device that uses a tungsten film for the gate electrode, the tungsten film is formed after the tungsten film is formed to form the gate electrode and during the manufacturing of the semiconductor device. The internal stress of the tungsten film before undergoing heat treatment in the post-process is tensile stress or 3×10^9
A method for manufacturing a semiconductor device, characterized in that the manufacturing method is carried out under conditions that result in a compressive stress of dyne/cm^2 or less.